Composite material for thermochemical energy storage and integration into heating systems

Abstract

A composite material for thermochemical energy storage and systems incorporating the composite material are described. The composite material comprises a porous adsorbent, a binder, and optionally one or more hygroscopic salts capable of reversible thermochemical cycles comprising an endothermic reaction and an exothermic reaction. In some examples, a magnesium oxide-based binder forms a cementitious phase that binds the adsorbent to provide improved mechanical strength and stability. Also described are thermochemical energy storage systems comprising a reactor containing the composite material and a fluid flow system configured to pass a gas through the reactor. The systems may operate in charging and discharging modes to store and release thermal energy, and may be integrated with heating devices to provide efficient and flexible thermal energy delivery.

Description

COMPOSITE MATERIAL FOR THERMOCHEMICAL ENERGY STORAGE AND INTEGRATION INTO HEATING SYSTEMS TECHNICAL FIELD

[0001] The present invention is directed to a composite material design and manufacturing for a thermochemical energy storage system and the system is designed for integration with existing heating systems.BACKGROUND OF THE INVENTION

[0002] Thermochemical energy storage (TCES) systems offer advantages over sensible heat storage and phase change materials, such as higher energy density and minimal heat loss during prolonged storage. Conventional sorbent materials like zeolite have been employed; however, these materials are often limited by their relatively low energy density, necessitating large volumes. Hygroscopic salts offer increased energy density but suffer from durability issues and require high temperatures for regeneration. Prior attempts using porous mediums (such as zeolite, activated carbon etc) and cementitious materials (based on Portland cement) to host these salts have shown promise but are hindered by limited energy density and thermal conductivity.

[0003] Magnesium-based cements, notably Magnesium Oxychloride Cement (MOC) and Magnesium Oxysulphate Cement (MOS), represent alternatives to Portland cement, utilizing magnesium oxide (MgO) as a primary binder. MOC, also known as Sorel cement, is formed by the reaction of MgO with magnesium chloride solution, forming strong, rapidly setting cementitious phases, as first patented by Sorel in 1866. MOS cement is produced similarly, but using magnesium sulphate solution instead. Despite their benefits, including rapid strength development and fire resistance, these binders are susceptible to water degradation via leaching. While magnesium-based binder exhibits limitations as a direct substitute for Portland cement in construction, its inherent cementitious characteristics provide a unique opportunity for the incorporation of hygroscopic magnesium salts for energy storage applications.

[0004] Integrating thermal energy storage (TES) units with existing heating infrastructure, such as fan heaters and heat pumps, offers a pathway to improve energy efficiency and manage energy demand. Prior art focuses on storing excess heat utilizing sensible heat (e.g., water tanks) or phase change materials (PCMs). This enables load shifting, reducing peak electricity demand and potentially lowering energy costs. However, traditional TES systems face limitations: Sensible heat storage requires large volumes due to their relatively low energy density. PCM systems, while more compact, have narrow operating temperature ranges dictated by their phase change temperature, and can suffer from subcooling, phase segregation, and limited cycle stability. Critically, both sensible and PCM systems are passive, releasing heat based solely on temperature differences, thus offering limited control over the timing and rate of energy release and restricting the overall flexibility and responsiveness of the heating system.

[0005] Thus, the invention seeks to provide an active thermal energy storage system using a composite material that combines the high energy density of hygroscopic salts with the structural stability and tailored porosity of a cementitious matrix, allowing for enhanced control, flexibility, and responsiveness. In one example there is provided a thermochemical energy storage (TCES) system and its integration with heating appliances. It is one object of these systems to overcome the limitations of prior art sensible heat and phase change material (PCM) based thermal energy storage systems, or at least to provide the public with a useful choice.

[0006] In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.SUMMARY OF THE INVENTION

[0007] In some examples, there are provided three interconnected aspects: a composite material, a TCES reactor utilizing this material, and the integration of this reactor with heating systems, specifically fan heaters and heat pumps.

[0008] In one example there is provided a composite material for thermochemical energy storage comprising a binder and a porous adsorbent. The composite material is configured to undergo a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction. The endothermic reaction comprises release of a working fluid from the composite material, optionally by dehydration and / or desorption; and the exothermic reaction comprises uptake of the working fluid by the composite material, optionally by hydration and / or sorption. These reversible reactions enable storage and release of thermal energy.

[0009] In one example the composite material further comprises one or more hygroscopic salts capable of undergoing a reversible endothermic reaction and a reversible exothermic reaction, for example reversible hydration and dehydration, optionally wherein the hygroscopic salt is distributed within pores or interparticle regions of the porous adsorbent.

[0010] In one example the binder comprises magnesium oxide and one or more inorganic salts, optionally forming a magnesium oxychloride cement, magnesium oxysulphate cement, or a combination thereof, thereby forming a stabilising matrix that binds the porous adsorbent and hygroscopic salt.

[0011] In one example there is provided a method of producing a composite material for thermochemical energy storage, the method comprising:a. providing a porous adsorbent;b. combining the porous adsorbent with a binder comprising magnesium oxide and one or more salts to form a mixture;c. adding a liquid to form a slurry;d. shaping the slurry into a formed body;e. curing the formed body to form a magnesium oxide-based composite material;andf. drying the composite material to produce a thermochemical energy storage material.

[0012] In one example the method further comprises pre-treating the porous adsorbent by contacting it with a solution comprising one or more hygroscopic salts prior to forming the composite material.

[0013] In one example the formed body comprises pellets, beads, granules, or extrudates, optionally spherical beads having a diameter of approximately 1 mm to 10 mm.

[0014] In one example the method further comprises impregnating the formed body with a hygroscopic salt solution after curing.

[0015] A thermochemical energy storage system comprising:a. a reactor containing a composite material as described herein; and b. a fluid flow system configured to pass air through the reactor;wherein the system is configured to operate in:i. a charging mode in which heated air capable of inducing dehydration is passed through the composite material to induce dehydration; and ii. a discharging mode in which humid air is passed through the composite material to induce hydration and release heat.

[0016] In one example the charging mode is carried out at a charging temperature of approximately 60°C to approximately 350°C, wherein temperatures below approximately 60°C result in insufficient dehydration kinetics and temperatures above approximately 350°C result in degradation or instability of the binder and / or hygroscopic salt phases.

[0017] In one example the system comprises a plurality of airflow pathways configured to selectively direct air through a heating element, through the reactor, or to bypass the reactor.

[0018] In one example there is provided a method of operating a thermochemical energy storage system comprising:a. operating the system in a charging mode by passing heated air through a composite material as described herein to induce dehydration and store thermal energy; andb. operating the system in a discharging mode by passing air comprising water vapour through the composite material to induce hydration and release stored thermal energy.

[0019] In one example, there is provided a composite material comprising:a. a hosting matrix formed from a magnesium oxide-based binder, wherein the binder is formed by the reaction of light-burned magnesium oxide (MgO) and magnesium salts (magnesium chloride (MgCh) and magnesium sulphate (MgSO4)), optionally wherein the matrix provides structural stability and tailored porosity.b. Zeolite 13X, optionally serving as a porous sorbent to enhance water uptake and improve the kinetics of the thermochemical reactions,c. hygroscopic magnesium salts, specifically magnesium chloride (MgCh) andd. magnesium sulphate (MgSC ), as the primary active thermochemical material, providing high energy storage density; and thermal additives to enhance heat transfer.

[0020] In one example the binder comprises a magnesium oxide-based binder. In one example, the binder is formed by the reaction of light-burned magnesium oxide (MgO) and magnesium salts (magnesium chloride (MgCh) and magnesium sulphate (MgS04)) .

[0021] In one example the porous adsorbent comprises a hydrophilic adsorbent material. In one example the porous adsorbent is selected from the group consisting of zeolites, MOFs, porous silicas, salt-based composites, or combinations thereof. In one example the zeolite comprises at least one of Zeolite 13X, Zeolite 4A / 5A, Zeolite Y, Beta, ZSM-5. These materials serve as a porous sorbent to enhance water uptake and improve the kinetics of the thermochemical reactions.

[0022] In one example the hygroscopic salt comprises a magnesium salt. In one example the hygroscopic salt comprises at least one of magnesium chloride (MgCh) and magnesium sulphate (MgSC ).

[0023] In another example, there is provided a method of manufacturing a composite material through a multi-stage process designed to achieve a homogeneous distribution of active components within a porous, stable matrix. In one particular example, the method comprises:a) pre-treating a porous zeolite with a concentrated magnesium salt(s) solution;b) dry-mixing the pre-treated zeolite with magnesium oxide and thermal additives; c) preparing a magnesium salt(s) solution;d) combining the magnesium salt solution with the dry ingredients to form a slurry; e) generating a stable foam separately using a foaming agent and a foam generator; f) incorporating the foam into the slurry;g) casting the foamed mixture;h) curing the cast material under controlled conditions; andi) oven-drying the material to activate its thermochemical properties by partially dehydrating the composite.

[0024] In one example, this process provides a foamed, extruded composite with controlled porosity, high energy density (120 ~450 Wh / kg), and cyclic stability (at least 10 cycles).

[0025] In a further example, there is provided a thermochemical energy storage (TCES) reactor specifically designed to utilize the aforementioned composite material. In one example the reactor comprises an open fixed-bed reactor, configured to allow for controlled airflow through a bed of the composite material. In some examples the reactor is configured to operate in two modes:a) a charging mode (energy storage) andb) a discharging mode (energy release).

[0026] During charging, hot, dry air may be passed through the reactor, driving the endothermic dehydration of the composite hydrates (and potentially water desorption from the zeolite) within the composite. During discharging, cool, humid air may be passed through the reactor, initiating the exothermic hydration of the composite (and water adsorption by the zeolite), releasing stored heat. The reactor design facilitates efficient heat and mass transfer, and its construction utilizes materials resistant to the corrosive effects of magnesium salt(s).

[0027] In one example there is further provided the integration of the TCES reactor with heating appliances. In one example the TCES reactor is integrated with a fan heater, creating a combined thermal storage and delivery system. In one configuration the fan forces air through the reactor, where it is heated during the discharging phase. An electric resistance heating element may be included for supplementary heating or for providing the heat source during the charging phase. This integrated system functions as a "thermal battery," providing on-demand heating with active control over the timing and rate of heat release.

[0028] In a further example, the TCES reactor is integrated with a heat pump system, enabling enhanced efficiency and operational flexibility. The TCES system can be connected to either the air ductwork or the water circuit of the heat pump. A system of control valves allows for three primary modes of operation: (a) direct heat pump heating, bypassing the TCES system; (b) heat pump charging of the TCES system; and (c) TCES system discharging for heating. This integration allows the heat pump to operate at optimal conditions, storing excess heat in the TCES system during periods of low demand or high renewable energy availability, and releasing the stored heat when needed.

[0029] Aspects of the invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of this application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein that have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0030] Further aspects of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 illustrates an example particle size distribution of magnesium oxide (MgO) suitable for use in formation of the magnesium oxide-based binder of the composite material. In the illustrated example, the median particle size is approximately 10.03 pm and the mean particle size is approximately 17.18 pm.Figure 2 presents thermogravimetric analysis (TGA) data obtained for the composite material after hydration, showing water uptake behaviour of the composite material and demonstrating enhanced water uptake relative to conventional zeolite 13X.Figure 3 illustrates an example thermochemical reactor and operating modes of the reactor. Figure 3a illustrates a charging mode in which heated air is introduced into the reactor to induce dehydration of the composite material.Figure 3b illustrates a discharging mode in which humid air is introduced into the reactor to induce hydration of the composite material and release heat.Figure 4 illustrates dimensions of a filter mesh contained within the thermochemical reactor. Figure 5 depicts an example temperature profile observed within the reactor during an exothermic reaction, demonstrating an increase in temperature suitable for space heating. Figure 6 illustrates integration of the thermochemical reactor system with a fan heater.Figure 7 illustrates integration of the thermochemical reactor system with a heat pump.Figure 8 illustrates a schematic representation of the composite material structure and functional interactions between the components of the thermochemical energy storage material.Figure 8a illustrates a representative composite material structure comprising a porous adsorbent, a binder matrix, and a hygroscopic salt phase distributed within the structure. Figure 8b schematically illustrates interfacial interactions between the porous adsorbent particles, the hygroscopic salt phase, and the binder matrix.Figure 8c illustrates interactions at a smaller structural scale within the composite material, including vapour diffusion pathways, adsorption sites, and hydration / dehydration domains. Figure 9 presents scanning electron microscopy (SEM) images of representative composite materials.Figure 9a shows a material comprising porous adsorbent and hygroscopic salt in the absence of a binder phase.Figure 9b shows a material comprising porous adsorbent, hygroscopic salt, magnesium oxidebased binder, and graphite additive, illustrating whisker-like binder-derived structures interconnecting the composite.Figure 10 presents thermochemical analysis of composite materials. Figures 10A-10D show heat flow over time for selected samples, as measured by differential scanning calorimetry (DSC). Figures 10E-10H show mass percentage change over time for selected samples, as measured by thermogravimetric analysis (TGA).Figure 11 presents scanning electron microscopy images of ion-exchanged porous adsorbent materials. Figure 11A shows a lithium-ion exchanged zeolite material. Figure 11C shows a magnesium-ion exchanged zeolite material.Figure 12 shows power output over time for untreated zeolite, lithium-ion exchanged zeolite, and magnesium-ion exchanged zeolite during reactor testing, illustrating improved thermochemical performance of ion-exchanged materials relative to untreated zeolite.Figure 13A and B illustrate compressive strength behaviour of composite beads formed with varying binder contents and / or salt compositions, showing the relationship between formulation and mechanical strength.Figure 14 illustrates variation in volumetric energy density of a composite material over repeated hydration-dehydration cycles, demonstrating stability of energy storage performance over at least 64 cycles.Figure 15 shows representative power profiles for selected hydration-dehydration cycles, illustrating consistency of power output and hydration behaviour over repeated cycling.DETAILED DESCRIPTION

[0032] The present invention relates to composite materials suitable for thermochemical energy storage and to systems and methods that utilise such materials. In one example, the composite material comprises a porous host material, a binder configured to consolidate the composite into a mechanically stable structure, and optionally a hygroscopic salt capable of undergoing a reversible endothermic reaction and a reversible exothermic reaction, optionally reversible hydration and dehydration reactions.

[0033] In some examples, the invention provides a composite material for thermochemical energy storage designed to overcome conventional limitations through improved energy density, thermal conductivity, and durability, and is suitable for integration into existing heating systems.Definitions

[0034] As used herein the term "comprising" means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise", include", "including" and "comprises" are to be interpreted in the same manner.

[0035] As used herein, "a" or "an" does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims. Any reference signs in the claims shall not be construed so as to limit their scope.

[0036] The term "about" as used herein in relation to numerical terms means permissible variation of the term such that the end result is not significantly changed. For example, when applied to a value, the term should be construed as including a deviation of + / - 5% of the value.

[0037] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0038] Whenever a range is given in the specification, for example, a dimensional range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. In the disclosure and the claims, "and / or" means additionally or alternatively. Moreover, any use of a term in the singular also encompasses plural forms.

[0039] As used herein, the term "magnesium oxide-based binder" refers to a cementitious material formed by reaction of magnesium oxide with one or more inorganic salts in the presence of water.

[0040] "Crush Strength" refers to the force required to cause fracture of an individual pellet under a uniaxial compressive load. For the purposes of the present disclosure, crush strength is measured on substantially spherical pellets having a diameter of 3 mm (±0.2 mm), using a compressive force testing instrument configured to apply load along a single axis at a constant displacement rate until failure. The pellet is positioned between two substantially flat, parallel platens, and the maximum force recorded at the point of fracture is taken as the crush strength. The measurement is conducted on a plurality of pellets (n > 5), and the reported crush strength value corresponds to the mean force required to fracture the pellets. The measured value is reported in kilogram-force (kgf).

[0041] Unless the context requires otherwise, the term "capable of undergoing a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction" is intended to mean that the endothermic reaction comprises release of a gaseous reactant species from the composite material, the release occurring by one or more of dehydration, desorption, decomposition, or a combination thereof; and the exothermic reaction comprises uptake of the gaseous reactant species by the composite material, gaseous reactant species. These reversible reactions enable storage and release of thermal energy. In some examples the gaseous reactant species comprises water vapour; however, the gaseous reactant species is not limited thereto. The gaseous reactant species may comprise one or more of water vapour, ammonia, alcohol vapours, carbon dioxide, or other gas-phase species capable of participating in a reversible thermochemical, chemisorption, or physisorption reaction with the composite material.

[0042] "Charging temperature" refers to a temperature at which the composite material undergoes endothermic dehydration and / or desorption to remove at least a portion ofreversibly bound gaseous reactant species sufficient to place the material in a charged state capable of subsequent heat release upon rehydration and / or resorption, while remaining below a temperature at which decomposition or irreversible degradation of one or more components of the composite material occurs.Composite Material Composition

[0043] In one example there is provided a composite material for thermochemical energy storage comprising a binder, a porous adsorbent, and optionally a hygroscopic salt.

[0044] In one example, there is provided a composite material comprising:a. a hosting matrix formed from a magnesium oxide-based binder, wherein the binder is formed by the reaction of light-burned magnesium oxide (MgO) and magnesium salts (magnesium chloride (MgCh) and magnesium sulphate (MgSC )), optionally wherein the matrix provides structural stability and tailored porosity.b. Zeolite 13X, optionally serving as a porous sorbent to enhance water uptake and improve the kinetics of the thermochemical reactions,c. hygroscopic magnesium salts, specifically magnesium chloride (MgCh) andd. magnesium sulphate (MgSC ), as the primary active thermochemical material, providing high energy storage density; and thermal additives to enhance heat transfer.

[0045] In contrast to prior thermochemical storage systems in which salts are supported only by porous matrices or encapsulation materials, in some examples the present composite material comprises a cementitious binder that consolidates the composite structure while preserving vapour transport pathways necessary for thermochemical reactions. The binder forms a structural host matrix that binds the porous adsorbent and optional hygroscopic salt phases together while maintaining sufficient internal porosity for mass and heat transfer during operation. In this way the binder may function not merely as a structural component but as a stabilising matrix that supports the thermochemical composite material.

[0046] In some examples the binder performs one or more of the following functions within the composite material. The binder binds the porous adsorbent and optional hygroscopic salt phases together to form a mechanically stable structure. Further, the binder may immobilise the optional hygroscopic salt within the composite to reduce salt migration or leakage during repeated hydration-dehydration cycles. In addition, the binder maintains interconnected pore pathways that enable the transport of water vapour and heat during thermochemical reactions. These functions enable the composite material to undergo repeated charging and discharging cycles while maintaining structural integrity and thermochemical performance.

[0047] The binder may be formed from a binder material capable of consolidating the composite components while retaining internal porosity. In some examples the binder is an inorganic binder. Such binders may exhibit improved thermal stability relative to organicpolymeric binders which may soften, degrade, or volatilise at elevated temperatures. In one example the binder comprises a magnesium oxide-based binder. Magnesium oxide-based binders are advantageous because they can react with magnesium salt solutions to form cementitious phases that provide crush strength while maintaining permeability for vapour transport.

[0048] In some examples the cementitious binder forms crystalline phases within the composite material. These phases may develop as interparticle bridges or whisker-like structures that interconnect particles of the porous adsorbent and hygroscopic salt, thereby reinforcing the composite structure while maintaining void spaces between particles.

[0049] In some examples the binder comprises a magnesium oxide-based binder, optionally formed by reaction of magnesium oxide with one or more inorganic salts and / or metal salts in the presence of water. The one or more inorganic salts may comprise one or more acids, phosphate salts, chloride salts, sulphate salts, aluminate salts, double salts, or combinations thereof. In some examples the inorganic salts may include phosphoric acid, citric acid, tartaric acid, glycolic acid, potassium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, sodium pyrophosphate, potassium chloride, iron chloride, zinc chloride, calcium chloride, iron sulphate, zinc sulphate, sodium sulphate, copper sulphate, manganese sulphate, magnesium sulphate, potassium aluminate, sodium aluminate, aluminium alkoxides, potassium fluoroaluminate, sodium hexafluorosilicate, sodium bicarbonate, potassium aluminium sulphate, ammonium aluminium sulphate, or combinations thereof.

[0050] In the descriptions herein, the magnesium oxide referred to may be a light-burned magnesium oxide as described herein. Magnesium oxide-based binders may form cementitious phases that consolidate the composite material while maintaining sufficient internal porosity to permit vapour transport during thermochemical reactions.

[0051] Magnesium oxide-based binders can be particularly suitable for thermochemical energy storage composites. These binders enable formation of a mechanically stable host matrix that binds the porous adsorbent and optional hygroscopic salt phases together while maintaining permeability for water vapour and heat transfer during hydration-dehydration reactions. In some examples the magnesium oxide-based binder is chemically compatible with hygroscopic salts when used in the composite material, which may assist in stabilising the salt phase within the composite structure during repeated thermochemical cycling.

[0052] In some examples the magnesium oxide-based binder forms a host matrix to support the other components of the composite material. Such binders may comprise magnesium oxychloride cement, magnesium oxysulphate cement, or other magnesium-based cementitious systems that provide binding phases capable of consolidating the composite structure while maintaining internal porosity for vapour transport. The magnesium oxide component in these systems primarily can function as both a structural binder and an activethermochemical storage material. In examples comprising a hygroscopic salt, this hygroscopic salt phase provides the primary thermochemical energy storage functionality.

[0053] In the systems described herein, the magnesium oxide participates forms a binder phase that stabilises the composite structure. Examples comprising hygroscopic salts provide enhanced thermochemical energy storage through reversible hydration and dehydration reactions. Unlike latent heat storage systems incorporating phase change materials, the present composite materials store energy through reversible hydration-dehydration reactions of hygroscopic salts. In some examples, the composite material may operate as an adsorption-based thermochemical storage material in the absence of hygroscopic salts, wherein the porous adsorbent provides reversible endothermic and exothermic reactions comprising release or uptake of a gaseous reactant species from the composite material contributing to thermal energy storage.

[0054] In some examples the magnesium oxide-based binder comprises a cementitious system formed from magnesium oxide and one or more inorganic salts and / or metal salts. The one or more inorganic salts may comprise one or more acids, phosphate salts, chloride salts, sulphate salts, aluminate salts, double salts, or combinations thereof. Suitable salts may include, for example, phosphoric acid, citric acid, tartaric acid, glycolic acid, potassium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, sodium pyrophosphate, potassium chloride, iron chloride, zinc chloride, calcium chloride, iron sulphate, zinc sulphate, sodium sulphate, copper sulphate, manganese sulphate, magnesium sulphate, potassium aluminate, sodium aluminate, aluminium alkoxides, potassium fluoroaluminate, sodium hexafluorosilicate, sodium bicarbonate, potassium aluminium sulphate, ammonium aluminium sulphate, or combinations thereof.

[0055] In some examples the salt may comprise an alkaline earth metal salt such as magnesium chloride or magnesium sulphate, or an alkali metal salt such as potassium dihydrogen phosphate. In use, magnesium oxide may react with the one or more salts in the presence of water to form hydrated cementitious phases, including oxychloride, oxysulphate, or phosphate-based phases, which provide structural strength within the host matrix while maintaining porosity for vapour transport.

[0056] In some examples the magnesium oxide-based binder comprises magnesium oxychloride cement formed from magnesium oxide (optionally light-burned magnesium oxide) and magnesium chloride. Magnesium oxychloride cement, sometimes referred to as Sorel cement, forms when magnesium oxide reacts with magnesium chloride in the presence of water to produce hydrated magnesium oxychloride phases that provide structural strength within the host matrix. In contrast to Portland cement-based matrices, magnesium oxychloride cement systems are chemically compatible with chloride-containing salt hydrates. Portland cement matrices may undergo degradation or undesirable chemical reactions in the presence of chloride salts, which can compromise mechanical integrity or alter salt chemistry.By contrast, magnesium oxychloride systems share common Mg2+and Cl“ chemical components with many thermochemical salts which may be used in the present composite materials. This chemical affinity can reduce adverse reactions between the binder and salt phases and assist in stabilising the salt within the composite structure.

[0057] Where used, the chemical compatibility between the hygroscopic salts (such as magnesium chloride salts) as thermochemical storage materials and the magnesium oxychloride binder matrix can assist in retaining the salt within the composite structure. In some examples this compatibility allows the binder matrix to function as a chemically compatible host structure for the hygroscopic salt phase, thereby reducing salt migration during repeated hydration-dehydration cycles and contributing to improved structural stability of the composite.

[0058] In some examples the magnesium oxychloride binder forms whisker-like crystalline phases. These phases have been shown by the inventors to interconnect particles within the composite structure.

[0059] In other examples the magnesium oxide-based binder comprises magnesium oxysulphate cement formed from magnesium oxide (optionally light-burned magnesium oxide) and magnesium sulphate. Magnesium oxysulphate cement forms when magnesium oxide reacts with magnesium sulphate in the presence of water to produce hydrated magnesium oxysulphate phases that act as a binding matrix.

[0060] Magnesium oxysulphate binders can provide similar structural consolidation functions while utilising sulphate-based chemistry. In some examples the resulting matrix binds the composite components together while maintaining internal porosity that enables vapour transport during thermochemical operation.

[0061] In some examples the binder may comprise both magnesium oxychloride and magnesium oxysulphate phases. These mixed-salt binders may be formed by using a composition of magnesium salts during binder formation.

[0062] In some examples the magnesium oxide-based binder may further comprise supplementary cementitious materials (SCMs) incorporated into the binder system. Such materials may include additional oxides, mineral components, or other inorganic additives that modify the properties of the binder matrix. For example, calcium oxide (CaO), silicate materials, aluminates, or combinations thereof may be incorporated into the binder composition together with magnesium oxide. Incorporation of such supplementary materials may modify crush strength, setting behaviour, or microstructure of the binder matrix while maintaining the magnesium oxide-based cementitious framework that consolidates the composite material.

[0063] In one example the binder comprises a magnesium oxide-based binder formed by reaction of light-burned magnesium oxide (MgO) with one or more inorganic salts and / or metal salts. The one or more salts may comprise acids, phosphate salts, chloride salts, sulphate salts, aluminate salts, double salts, or combinations thereof. Suitable salts mayinclude, for example, magnesium chloride (MgCH), magnesium sulphate (MgSCM), potassium dihydrogen phosphate (KH2PO4), phosphoric acid, calcium chloride, sodium sulphate, sodium dihydrogen phosphate, potassium aluminium sulphate, ammonium aluminium sulphate, or combinations thereof. One or more salts may be used in combination to produce the binder.

[0064] In some examples, reaction of magnesium oxide with the one or more salts in the presence of water forms hydrated cementitious phases, including magnesium oxychloride, magnesium oxysulphate, or magnesium phosphate-based phases, which provide structural integrity to the composite material.

[0065] In some examples the magnesium oxide-based binder is formed using a controlled molar ratio of magnesium oxide (MgO) to the one or more inorganic salts. The molar ratio of MgO to salt may be selected to promote formation of desired cementitious phases and to control mechanical strength, porosity, and stability of the composite material.

[0066] In conventional cementitious systems formed by casting methods, MgO:MgCl2 molar ratios of approximately 5:1 to 7:1 may be used to provide high crush strengths.However, in the present composite systems incorporating a porous adsorbent phase, it has been found that substantially lower MgO:MgCl2 ratios may result in improved mechanical performance, indicating that the optimal binder chemistry is dependent on the presence and proportion of the porous adsorbent. Accordingly, in examples comprising porous adsorbent, the molar ratio of MgO to magnesium chloride may be selected within a range from about 0.5:1 to about 12:1. In another example, where the salt comprises magnesium chloride (MgCh), the molar ratio of MgO:MgCl2 may be selected within a range of from about 0.7:1 to about 8:1. Without wishing to be bound by theory, it is believed that composite materials comprising a porous adsorbent and an MgO-based binder, molar ratios within this lower range may provide improved crush strength in formed bodies such as pellets In alternative examples, the MgCI2 may be substituted with other suitable salts as described herein, for example magnesium sulphate (MgSCM), phosphate salts, or other inorganic salts, and in these examples the molar ratio of MgO to the salt may be selected within a range from about 0.1:1 to about 12:1.

[0067] Magnesium oxide suitable for use in the binder may be produced by calcination of magnesium-containing minerals. For example, magnesite (MgCOs) or magnesium hydroxide (Mg(OH)2) may be calcined at temperatures between approximately 700 °C and 1000 °C to produce light-burned magnesium oxide. Light-burned magnesium oxide typically exhibits relatively high surface area and chemical reactivity compared with more highly calcined forms of magnesium oxide, which can facilitate formation of cementitious binder phases when the magnesium oxide is combined with magnesium salt solutions.

[0068] The calcined magnesium oxide may be ground to further increase surface area and reactivity. The particle size and surface area of the magnesium oxide may influence the rate and extent of binder phase formation during production of the composite material. During production of the composite material, magnesium oxide may react with a salt-containingsolution to form hydrated magnesium cement phases that bind the composite components together. Formation of these binder phases may stabilise the distribution of hygroscopic salts within the composite structure and may reduce migration or redistribution of salts during repeated hydration-dehydration cycles.

[0069] In one example there is provided a composite material for thermochemical energy storage comprising:a. a binder, optionally a magnesium oxide-based binder; andb. a porous adsorbent material.

[0070] In another example there is provided a composite material for thermochemical energy storage comprising:a. a binder, optionally a magnesium oxide-based binder;b. at least one hygroscopic salt capable of capable of undergoing a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction; andc. a porous adsorbent material.

[0071] In some examples the hygroscopic salt is present in addition to magnesium oxide forming the binder. The magnesium oxide therefore primarily functions as a structural binder, while the hygroscopic salt, when present, provides additional thermochemical energy storage, primarily through reversible hydration and dehydration reactions. In some examples the composite material comprises a magnesium oxide-based binder phase and a hygroscopic salt phase distributed within the composite structure. The binder phase consolidates the composite material and retains the hygroscopic salt within the matrix. In some examples the hygroscopic salt is incorporated within the host matrix such that the salt is distributed throughout the binder structure together with the porous adsorbent material. Distribution of the salt within the matrix may facilitate contact between the salt and water vapour during thermochemical operation. In some examples the magnesium oxide-based binder stabilises the hygroscopic salt within the composite structure and may reduce migration or leakage of the salt during repeated hydration-dehydration cycles.

[0072] In some examples the composite material comprises components in proportions selected to provide a balance between mechanical integrity, vapour transport, and thermochemical energy storage capacity. The relative amounts of binder, porous adsorbent, and hygroscopic salt are selected such that the combined composition forms a mechanically stable composite material having sufficient internal porosity and thermochemical activity for the intended application. In one example the binder may be present in an amount of approximately 2.5 wt% to approximately 50 wt% of the composite material. Amounts within this range may provide sufficient cementitious material to consolidate the composite structure while maintaining a useful proportion of porous adsorbent and hygroscopic salt for thermochemical performance. At binder contents below approximately 2.5 wt%, the binder may be insufficient to provide adequate crush strength or structural cohesion of thecomposite material. At binder contents above approximately 50 wt%, the proportion of active thermochemical components may become reduced, which may diminish thermochemical energy storage performance. In some examples the binder may be present in an amount of approximately 5 wt% to approximately 35 wt% of the composite material. Amounts within this range may provide an effective balance between structural binding, retention of internal porosity, and thermochemical activity of the hygroscopic salt and porous adsorbent phases.

[0073] The composite material may therefore comprise a multi-phase structure including a binder phase, a porous adsorbent phase, and optionally a hygroscopic salt phase. Figure 1 illustrates an example particle size distribution for magnesium oxide suitable for use in formation of the binder of the composite material. The magnesium oxide may comprise a fine particulate material having a particle size distribution centred in the micrometre range. In one example the magnesium oxide has a median particle size of approximately 10 pm and a mean particle size of approximately 17 pm. In some examples the magnesium oxide has a particle size distribution within a range of approximately 5 pm to approximately 200 pm, optionally from approximately 5 pm to approximately 100 pm, or from approximately 5 pm to approximately 50 pm, wherein the upper bound of 200 pm represents an outer particle size limit and the majority of particles fall within the narrower ranges described herein.

[0074] The particle size and surface characteristics of the magnesium oxide may influence its reactivity and the formation of cementitious binder phases. In some examples the magnesium oxide is a light-burned magnesium oxide exhibiting a relatively high surface area and chemical reactivity. Reactivity of the magnesium oxide may be characterised by one or more measures including acid neutralisation rate, hydration rate, temperature rise during hydration, or specific surface area (for example BET surface area). In one example, reactivity may be assessed by measuring the rate of temperature increase upon mixing the magnesium oxide with water or an aqueous salt solution under controlled conditions.

[0075] In some examples the magnesium oxide is selected to have a reactivity sufficient to enable formation of cementitious phases under ambient or low-temperature curing conditions (for example below approximately 50°C). Magnesium oxide materials exhibiting excessively low reactivity may result in slow or incomplete binder formation, while excessively high reactivity may lead to rapid setting and reduced processability of the composite mixture.

[0076] In some examples the magnesium oxide particle size distribution comprises a primary particle population having a median particle size in a range of 5-20 pm. Such particle sizes can provide relatively high surface area and reactivity, which may facilitate formation of cementitious binder phases when the magnesium oxide is combined with magnesium salt solutions during formation of the composite material.

[0077] In some examples the magnesium oxide particle size distribution may further include a secondary population of coarser particles. For example, the magnesium oxide particle size distribution may comprise a second particle population having a median particle size between 20 pm and 80 pm. The presence of a broader particle size distribution mayimprove particle packing and may contribute to formation of a consolidated binder matrix while maintaining internal porosity suitable for vapour transport during thermochemical operation.

[0078] In some examples the magnesium oxide particle size distribution exhibits multiple volume density peaks. For example, the particle size distribution may exhibit a first volume density peak for particles having diameters between 8 pm and 15 pm, and a second volume density peak for particles having diameters between 20 pm and 60 pm.

[0079] In some examples the cumulative particle size distribution of the magnesium oxide may be characterised by one or more threshold particle sizes. For example, the particle size distribution may be such that:a. 15-55% of particles have diameters less than 15 pm;b. 50-80% of particles have diameters less than 40 pm; andc. 70-100% of particles have diameters less than 90 pm.

[0080] In some examples the particle size distribution of the magnesium oxide may be characterised using percentile particle size parameters. Such parameters may include D10, D50 and D90 particle sizes, where D10 represents the particle diameter below which 10% of the particle volume is present, D50 represents the median particle diameter below which 50% of the particle volume is present, and D90 represents the particle diameter below which 90% of the particle volume is present. In some examples the magnesium oxide has a D50 particle size in a range of approximately 5-20 pm, and optionally approximately 10 pm. In some examples the magnesium oxide particle size distribution may further be characterised by a D10 particle size between approximately 2 pm and 8 pm, and a D90 particle size between approximately 60 pm and 100 pm. Control of the particle size distribution of the magnesium oxide may influence the reactivity of the magnesium oxide and the formation of binder phases within the composite material. In some examples the particle size distribution may also influence packing behaviour within the composite structure and may contribute to formation of a consolidated matrix that retains internal porosity suitable for transport of water vapour during thermochemical charging and discharging.

[0081] Table 1 shows an example chemical composition of magnesium oxide suitable for forming the host matrix of the composite material. In the illustrated example the material comprises a magnesium oxide-rich composition containing approximately 65.8 wt% MgO, together with minor amounts of other oxides including SiC>2, AI2O3, Fe2Os, CaO, Na2O and K2O. The presence of minor oxide components may arise from the natural mineral source used to produce the magnesium oxide, such as magnesite or other magnesium-containing minerals. In some examples such minor oxide components may be present as naturally occurring impurities in the calcined magnesium oxide. The composition illustrated in Table 1 further includes a loss on ignition (LOI) value of approximately 19.65 wt%, which may correspond to residual volatile components or partially calcined magnesium compounds remaining after calcination. Such compositions can be characteristic of reactive or light-burned magnesium oxide materials suitable for formation of cementitious binder phases. In some examples magnesium oxide suitable for use in the binder may comprise a magnesium oxide-rich material having an MgO content of greater than approximately 50 wt%, optionally greater than approximately 60 wt%. Minor oxide components may be present in amounts sufficient to arise from mineral impurities without substantially affecting formation of the binder matrix.

[0082] The binder, when combined with other components of the composite material, provides a scaffold that supports the porous adsorbent and optional hygroscopic salt phases while maintaining interconnected pore pathways that enable diffusion of water vapour and heat during thermochemical charging and discharging. In this manner the composite material comprising a host matrix that enables thermochemical reactions to occur within the composite structure while maintaining mechanical integrity of the material.

[0083] In one example the composite material comprises one or more hygroscopic salts. In some examples the hygroscopic salt is selected from salts capable of undergoing a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction.Suitable salts may include chloride salts, sulphate salts, phosphate salts, carbonate salts, or combinations thereof. In some examples the hygroscopic salt comprises a salt hydrate or a salt capable of forming hydrated phases during operation. Suitable salts include magnesium chloride (MgCh), magnesium sulphate (MgSCM), calcium chloride (CaCh), potassium carbonate (K2CO3), sodium phosphate (e.g., NasPCM), strontium chloride (SrCH), strontium bromide (SrBr2), lanthanum chloride (LaCIs), lithium chloride (LiCI), or combinations thereof. In some examples the hygroscopic salt may be present in hydrated form, for example MgCl2-6H2O, MgSO4-7H2O, CaCl2-6H2O, SrCl2-6H2O, SrBr2-6H2O, LaCls-7H2O,Na3PO4-12H2O, LiCI-l-hO, or related hydrated salts capable of reversible dehydration.

[0084] In one example the hygroscopic salt comprises a magnesium salt. In one example the hygroscopic salt comprises at least one of magnesium chloride (MgCH) and magnesium sulphate (MgSCM), optionally in hydrated form such as MgCl2-6H2O or MgSO4-7H2O. One or more hygroscopic salts may be incorporated into the composite material as the primary thermochemical storage component. These salts are hygroscopic materials that readily absorb water vapour to form hydrated phases and release water vapour upon heating. The reversible hydration-dehydration reactions of these salts enable the storage of thermal energy in chemical form and the subsequent release of heat during rehydration. In some examples the thermochemical reaction can be represented generically as:Salt-xl-hO (s) + Heat Salt-yHsO (s) + (x-y)H2O (g)where x represents a higher hydration state and y represents a lower hydration state.

[0085] In some examples the hygroscopic salts are selected based on their hydration enthalpy, vapour pressure characteristics, stability of hydration phases, and compatibility with the composite matrix. Chloride salts such as MgCh, CaCl2, SrCl2, SrBr2, LaCIs, and LiCI can exhibit strong hygroscopic behaviour and high water uptake capacity, enabling highenergy density storage. Sulphate salts such as MgSCM and phosphate salts such as NasPCM may provide stable hydration cycles at moderate temperatures and humidity conditions. Hydrated forms of these salts may be used directly or may form during thermochemical operation through reversible hydration reactions.

[0086] In some examples the hygroscopic salt may comprise a salt capable of forming one or more hydrated phases that undergo reversible dehydration and rehydration reactions under thermochemical energy storage operating conditions.

[0087] In some examples the one or more hygroscopic salts comprises a mixture of two or more hygroscopic salts. Mixed salt systems may be used to tune hydration equilibrium conditions, including relative humidity and operating temperature ranges, or to reduce deliquescence during hydration cycles.

[0088] In some examples the hygroscopic salts may be incorporated within the composite material in amounts sufficient to provide thermochemical energy storage capacity. For example, the hygroscopic salts may be present in amounts ranging from 0 wt% to approximately 50 wt% of the composite material. Amounts within this broader range may allow the composite material to include formulations in which the porous adsorbent and binder provide the principal structural and adsorption functions, together with formulations in which the hygroscopic salt makes a substantial contribution to thermochemical energy storage. At salt contents above approximately 50 wt%, pore blockage of the porous adsorbent may occur, which may reduce vapour accessibility and impair thermochemical performance. In some examples the hygroscopic salts may be present in an amount of approximately 20 wt% to approximately 50 wt% of the composite material. Amounts within this range may provide substantial thermochemical storage capacity while maintaining sufficient porous adsorbent and binder to preserve vapour transport pathways and structural stability.

[0089] In some examples the hygroscopic salts are distributed within the porous adsorbent. Incorporation of the hygroscopic salts within the host matrix can improve durability by reducing salt migration or leakage during repeated hydration-dehydration cycles. The magnesium oxide-based binder, once set, provides a stabilising host matrix that retains the hygroscopic salts while maintaining vapour transport pathways necessary for thermochemical reactions.

[0090] In some examples the hygroscopic salt may be present within interparticle voids between adsorbent particles, on external surfaces of the porous adsorbent, or within accessible pore regions of the adsorbent structure. The spatial distribution of the salt phase may influence vapour transport, hydration kinetics, and thermochemical energy storage performance.

[0091] In some examples the hygroscopic salt is present as a distributed phase within the composite material, for example as discrete salt domains confined within pores or interparticle regions of the porous adsorbent and immobilised by the magnesium oxide-basedbinder matrix. Such confinement can reduce or suppress deliquescence of the salt during hydration cycles by limiting the formation of bulk liquid brine phases and restricting migration of dissolved salt within the composite structure. In some examples a synergistic interaction arises between the porous adsorbent and the magnesium oxide-based binder. The porous adsorbent distributes and supports the hygroscopic salt while maintaining vapour transport pathways required for thermochemical reactions, and the binder matrix immobilises the salt domains and provides structural integrity to the composite material. This synergy between salt confinement within the porous adsorbent and immobilisation by the binder matrix can stabilise the salt phase during repeated hydration-dehydration cycles and improve cyclability of the composite material compared with systems in which the hygroscopic salt is present as an unconstrained bulk phase.

[0092] In some examples, the selection of hygroscopic salts allows the composite material to operate at charging temperatures in the range of approximately 60 °C to approximately 350 °C. Temperatures above approximately 60 °C provide sufficient thermal driving force to promote dehydration of the hydrated salt phases, while temperatures above approximately 350 °C may lead to degradation or instability of one or more components of the composite material, including the binder and / or salt phases. In some examples, operation at temperatures below approximately 200 °C enables integration with low-grade heat sources such as heat pumps, fan heaters, solar thermal systems, and industrial waste heat streams.

[0093] In some examples the binder comprises at least one reactant in common with at least one of the hygroscopic salts. In this way, the binder chemistry may be selected to be chemically compatible with the hygroscopic salt phase. For example, magnesium oxide-based binders may use a magnesium chloride reactant to a form magnesium oxychloride phase that when combined with a magnesium chloride hygroscopic salt solution can reduce the likelihood of undesirable chemical reactions between the binder and the hygroscopic salt. Using the same material for the binder as the hygroscopic salt also results in more efficient manufacturing and resource use. In one example, the binder salt is combined with the binder oxide to form a binder, then the hygroscopic salt is combined with the porous adsorbent, potentially in a pre-impregnation step, before being mixed with the binder and cured.

[0094] In one example the composite material further comprises a porous adsorbent. The porous adsorbent may comprise a material capable of adsorbing water vapour under thermochemical energy storage operating conditions. In some examples the porous adsorbent comprises a hydrophilic adsorbent capable of reversibly adsorbing water vapour during thermochemical hydration-dehydration cycles. In one example the porous adsorbent is selected from the group consisting of zeolites, metal-organic frameworks (MOFs), porous silicas, porous aluminosilicates, carbonaceous porous materials, salt-loaded porous materials, or combinations thereof. Carbonaceous porous materials may include activated carbon, expanded graphite, porous graphite materials, or combinations thereof.

[0095] In one example, the porous adsorbent comprises a specific surface area of at least approximately 50 m2 / g, optionally at least 100 m2 / g, and in some examples in the range of approximately 50 m2 / g to 1,500 m2 / g, as measured by gas adsorption techniques such as BET analysis. Porous adsorbents as used in the composite materials described herein comprise a pore structure that enables rapid transport of water vapour into and through the material. In some examples the porous adsorbents are capable of adsorbing at least approximately 0.05 g of water per gram of adsorbent. In further examples, the adsorption capacity may be at least approximately 0.05 g / g, optionally at least 0.1 g / g. In some examples it may be in the range of approximately 0.1 g / g to 0.8 g / g, depending on material composition, pore structure, and relative humidity.

[0096] In one example the porous adsorbent comprises a zeolite material. In one example the zeolite comprises a gravimetric water adsorption capacity of at least approximately 0.05 kg H2O per kg of dry adsorbent at 25°C and >90% relative humidity, and a hydrophilicity corresponding to a Si / AI ratio <2.5. Suitable zeolites may include Zeolite 13X, Zeolite 4A, Zeolite 5A, Zeolite Y, Zeolite Beta, ZSM-5, or combinations thereof. These materials possess well-defined microporous structures that provide high surface area and strong affinity for water vapour.

[0097] In one example the porous adsorbent comprises Zeolite 13X. Zeolite 13X can provide a high density of adsorption sites and a pore structure capable of facilitating rapid water vapour uptake, thereby enhancing the kinetics of thermochemical hydration and dehydration reactions within the composite material.

[0098] In some examples, the porous adsorbent may be provided in particulate form, such as powders, granules, beads, or pellets. The porous adsorbent particles may be obtained or prepared using conventional size reduction or classification techniques, including milling and / or screening, to achieve a desired particle size distribution. In some examples, the porous adsorbent comprises fine particles having a characteristic diameter in the sub-micron to approximately 100 pm range. In certain embodiments, the particle size is less than approximately 50 pm, such as less than approximately 44 pm, or less than approximately 10 pm. Without wishing to be bound by theory, smaller particle sizes may provide increased surface area and therefore increased reactivity and adsorption capacity, as well as improved interfacial contact with the binder phase. In one example, the porous adsorbent comprises a zeolite powder having a mesh size of 325 or finer, corresponding to particles capable of passing through a 325 mesh sieve (i.e. particles smaller than approximately 44 pm), such as a zeolite 13X powder. In other examples, the porous adsorbent may comprise larger particles, such as granules, beads, or pellets having a characteristic diameter in the range of approximately 0.1 mm to approximately 5 mm, or more broadly approximately 0.1 mm to approximately 10 mm. Such larger particle sizes may provide improved mechanical robustness and structural integrity in formed composite bodies, particularly in packed bed or pelletised configurations. The particle size of the porous adsorbent may also influence thepelletisation or forming process. For example, very small particle sizes may require increased liquid (e.g. water) addition during mixing to achieve suitable workability, whereas larger particle sizes may result in less effective packing and reduced surface area available for adsorption and hydration reactions. Accordingly, the particle size may be selected to balance surface area, reactivity, vapour transport, packing density, and crush strength of the composite material.

[0099] In some examples the porous adsorbent may comprise a carbonaceous porous material. Carbon-based porous materials such as activated carbon or expanded graphite can provide high surface area and a network of micro- and mesopores capable of facilitating vapour transport and adsorption. These materials may also enhance thermal conductivity within the composite material, which can improve heat transfer during thermochemical charging and discharging cycles.

[0100] In some examples the porous adsorbent may comprise a salt-loaded porous material in which one or more hygroscopic salts are incorporated into the pore structure or surface regions of a porous host material. Salt loading may be achieved by impregnation, solution infiltration, precipitation, or other deposition techniques that distribute the hygroscopic salt within the porous framework. Salt-loaded porous materials can provide a high surface area support for the hygroscopic salt phase and may improve dispersion of the salt within the composite structure.

[0101] In some examples the porous adsorbent may be prepared as a salt-loaded porous material prior to incorporation into the composite material. In such examples a porous host material, such as a zeolite, porous silica, or metal-organic framework, may be contacted with a solution comprising one or more hygroscopic salts. The salt solution may infiltrate the pore structure or surface regions of the porous host material, after which the material may be dried to deposit the hygroscopic salt within the porous structure. The resulting salt-loaded porous material may then be incorporated into the composite material together with the binder matrix.

[0102] Pre-loading the porous host material with hygroscopic salt may promote uniform distribution of the salt phase and may provide enhanced thermochemical performance compared with systems in which the salt and porous material are combined only during composite formation. Pre-preparation of salt-loaded porous adsorbents may also assist in controlling the microstructural distribution of the hygroscopic salt within the composite material. For example, the porous host may act as a scaffold that retains the salt within pore regions or near-surface adsorption sites prior to incorporation into the binder matrix. When incorporated into the composite material, these pre-loaded adsorbent particles can provide distributed salt domains that enhance vapour accessibility and reduce migration or agglomeration of the salt during hydration-dehydration cycles.

[0103] In some examples the hygroscopic salt may therefore be present at least partially within the porous adsorbent phase. Unless otherwise indicated, references herein to acomposite material comprising a hygroscopic salt and a porous adsorbent are intended to encompass both arrangements in which the hygroscopic salt is present as a separate phase within the composite material, as well as arrangements in which the hygroscopic salt is incorporated within or supported by the porous adsorbent. In such cases the salt-loaded porous material may function both as a porous adsorbent and as a carrier for the hygroscopic salt phase within the composite structure.

[0104] In some examples the porous adsorbent may be provided in the form of beads, pellets, powders, agglomerates, or structured forms such as monoliths, extrudates, or honeycomb structures. The geometry and packing of the adsorbent material may influence vapour transport, pressure drop, and heat transfer characteristics within the composite material.

[0105] In some examples the porous adsorbent may be modified by ion exchange to alter its adsorption behaviour. Ion exchange may partially replace framework cations within the zeolite structure with alternative cations such as lithium ions (Li+), magnesium ions (Mg2+), strontium ions (Sr2+), sodium ions (Na+), potassium ions (K+), or combinations thereof.

[0106] In some examples the porous adsorbent may be pre-processed by subjecting it to an ion-exchange process prior to incorporation into the composite material. Ion exchange may be performed by contacting the porous adsorbent with an aqueous solution containing a desired cation, optionally followed by washing and drying of the adsorbent material. For example, a zeolite may be contacted with a solution containing lithium salts, magnesium salts, sodium salts, potassium salts, or strontium salts in order to partially replace native framework cations within the zeolite structure. The degree of ion exchange may be controlled by the concentration of the ion-exchange solution, contact time, temperature, and the number of exchange cycles.

[0107] Ion exchange of the porous adsorbent may modify the adsorption thermodynamics and water affinity of the adsorbent material. For example, incorporation of lithium ions may increase the strength of water adsorption within the zeolite pore structure, which can enhance water uptake at lower vapour pressures and improve the energy storage characteristics of the composite material. Similarly, exchange with divalent cations such as magnesium or strontium may modify the electrostatic environment within the pores and influence hydration behaviour. In some examples the ion-exchanged porous adsorbent can therefore be selected to tailor the interaction between the adsorbent and the hygroscopic salt phase within the composite structure.

[0108] In some examples the use of ion-exchanged porous adsorbents may further influence the distribution and stability of hygroscopic salts within the composite material. Modified cation sites within the adsorbent framework may promote interaction between the adsorbent surface and dissolved salt species during composite formation. This interaction may assist in retaining the hygroscopic salt within pore regions or near-surface domains ofthe porous adsorbent, thereby improving salt dispersion and reducing migration or agglomeration during hydration-dehydration cycling.

[0109] In some examples lithium-ion exchanged zeolites may be used as the porous adsorbent. Lithium exchange may increase the affinity of the zeolite for water vapour and may enhance hydration energy density while maintaining the structural integrity of the porous framework.

[0110] In some examples the porous adsorbent provides a porous host structure capable of retaining hygroscopic salts within its pore network or near-surface regions. The porous structure of the adsorbent can facilitate distribution of the salt phase throughout the composite material while maintaining pathways for vapour transport during thermochemical operation. In some examples the porous adsorbent may be present in the composite material in an amount of approximately 20 wt% to approximately 75 wt%. Amounts within this range may provide sufficient porous structure to facilitate vapour transport and adsorption while also contributing to the thermochemical energy storage behaviour of the composite material. At approximately 20 wt%, the porous adsorbent supplements the thermochemical energy contribution of the hygroscopic salt while maintaining a useful porous host structure. At higher levels, for example up to approximately 75 wt%, the porous adsorbent and optional hygroscopic salt may act synergistically to enhance thermochemical performance while maintaining structural integration with the binder matrix. In some examples the porous adsorbent may be present in an amount of approximately 25 wt% to approximately 60 wt% of the composite material. Amounts within this range may provide an effective balance between adsorption capacity, vapour transport, and retention of sufficient binder and hygroscopic salt within the composite structure.

[0111] In some examples a synergistic interaction may arise between the porous adsorbent, the hygroscopic salt, and the magnesium oxide-based binder matrix. The porous adsorbent can distribute and support the hygroscopic salt within the composite structure, while maintaining accessible pore pathways for water vapour transport. The binder matrix may immobilise the adsorbent particles and salt domains within a mechanically stable host matrix. This synergistic combination can enhance thermochemical performance and cycling stability compared with systems in which the hygroscopic salt is present without a structured porous host and binder matrix.

[0112] In some examples the thermal additive comprises a thermally conductive material. Suitable thermal additives may include graphite. Improved heat transfer within the composite material may increase the rate at which thermochemical reactions occur during both charging (dehydration) and discharging (hydration) processes. In particular, improved thermal conductivity may reduce temperature gradients within pellets, particles, or packed beds comprising the composite material, thereby improving reaction kinetics and enabling more efficient thermal energy storage and release. In some examples the thermal additive may also influence the microstructure of the composite material. For example, particulate or flake-like thermal additives may occupy interparticle regions between porous adsorbent particles and binder phases. Such materials may contribute to maintaining interconnected pore pathways within the composite structure, thereby assisting in the transport of water vapour during thermochemical operation. In some examples the thermal additive may therefore contribute both to improved heat transfer and to maintaining vapour transport pathways within the composite material.

[0113] In some examples the thermal additive may be present in an amount of approximately 0.5 wt% to approximately 10 wt% of the composite material. Amounts within this range may improve the effective thermal conductivity of the composite material while maintaining sufficient quantities of porous adsorbent and hygroscopic salt for thermochemical energy storage.

[0114] FIG. 8 illustrates a schematic representation of the composite material structure and functional interactions between the components of the thermochemical energy storage material described herein.

[0115] In particular, FIG. 8(a) illustrates a representative composite material structure comprising a porous adsorbent. The composite comprises a binder that consolidates the composite material and retains a hygroscopic salt phase distributed throughout the structure. The hygroscopic salt may be present as discrete domains located within interparticle regions of the porous adsorbent and within pores of the host matrix. FIG. 8(b) schematically illustrates interfacial interactions between the porous adsorbent particles, the hygroscopic salt phase, and the binder matrix. In this arrangement the binder matrix provides mechanical consolidation and structural stability while maintaining interparticle pathways that enable vapour transport. The binder matrix may further immobilise the hygroscopic salt within the composite structure and reduce migration of dissolved salt during hydration-dehydration cycling. FIG. 8(c) illustrates interactions at a smaller structural scale within the composite material. Water vapour entering the composite structure can diffuse through interconnected pores of the binder and porous adsorbent. The porous adsorbent provides adsorption sites that facilitate rapid water uptake and vapour transport, while the hygroscopic salt undergoes reversible hydration and dehydration reactions that store and release thermal energy. The binder matrix primarily provides structural support while maintaining permeability for vapour diffusion.

[0116] The schematic representation in FIG. 8 therefore illustrates the synergistic interaction between the porous adsorbent, the hygroscopic salt phase, and the magnesium oxide-based binder matrix. The porous adsorbent facilitates vapour transport and adsorption kinetics, the hygroscopic salt provides thermochemical energy storage through reversible hydration reactions, and the binder matrix stabilises the composite structure while retaining internal porosity. This synergistic combination of structural confinement, vapour transport pathways, and distributed salt phases can improve cycling stability and reduce salt migrationor deliquescence compared with systems in which hygroscopic salts are present as unconstrained bulk materials.

[0117] In one example the composite material comprises a magnesium oxide-based binder. The binder assists in the development of a hosting matrix comprising: Magnesite (MgCOs) or magnesium hydroxide (Mg(OH)2) which can be calcined at temperatures between 700°C and 1000°C to produce light burned MgO. The calcined MgO powder may then be further ground to increase its surface area and reactivity. An exemplary particle size distribution is shown in Figure 1. In this example the median size of the MgO is 10.03 pm, while the mean size is 17.18 pm. This approach ensures high reactivity and improved binding with hygroscopic salts compared to conventional Portland cement.Table 1. Exemplary chemical composition of Magnesium Oxide (MgO) used to produce binderSiO2AI2O3Fe2O3CaO MgO Na2O K2O LOI Total 9 0.52 0.25 3.47 65.8 0.19 0.11 19.65 99.07

[0118] In one example the porous adsorbent (porous additive) comprises Zeolite 13x. Its three-dimensional structure is composed of silicon dioxide (SiO2) and aluminium oxide (AI2O3), and has the chemical formula Na86[(AIO2)86(SiO2)i06]»H2O. In one example the diameter of the zeolite bead used is 0.5-5.0 mm. In one example Zeolite 13X is incorporated as the porous adsorbent to provide high moisture adsorption capacity. It may be present in the composite material in an amount of about 5-30% by weight.Table 2. Exemplary physical properties of a porous adsorbent zeolite in this inventionStatic Static CO2 Bulk Crush Loss on Water Water Adsorption Density Strength Attrition Content Adsorption (%wt) (g / mL) (N) (g / mL) (%wt) (%wt)Zeolite >22.50 >18.50 >0.64 >85.00 <0.10 <1.50

[0119] In one example the hygroscopic salt comprises a magnesium-based salt. Hydrated magnesium salts may act as the primary active thermochemical material within the composite material by undergoing reversible hydration and dehydration reactions that enable thermal energy storage and release. In one example the magnesium-based salt comprises magnesium chloride hexahydrate (MgCl2-6H2O, CAS No. 7791-18-6). Magnesium chloride hydrates may exhibit strong hygroscopic behaviour and high water uptake capacity, which can contribute to increased thermochemical energy density within the composite material. In another example the magnesium-based salt comprises magnesium sulphate heptahydrate (MgSO4-7H2O, CAS No. 10034-99-8). Magnesium sulphate hydrates may provide favourable hydration thermodynamics and stability during repeated thermochemical hydrationdehydration cycles.

[0120] In some examples the hygroscopic magnesium salt may be present in the composite material in an amount of 0 wt% to approximately 50 wt%. Amounts within this range may provide sufficient thermochemical reactant to contribute to energy storage while allowing incorporation of porous adsorbents and binder materials that stabilise the composite structure and maintain vapour transport pathways. In one example the hygroscopic salt is incorporated as the primary thermochemical reactant within the composite material and may provide the principal contribution to thermal energy storage and energy density of the composite.

[0121] In one example the composite material further comprises a thermal additive. The thermal additive may improve heat transfer within the composite material during thermochemical charging and discharging cycles and may also contribute to mechanical reinforcement of the composite structure. In one example the thermal additive comprises graphite. Graphite may be incorporated in an amount of approximately 1 wt% to approximately 5 wt% of the composite material to improve thermal conductivity and facilitate more uniform heat transfer during thermochemical hydration and dehydration reactions.

[0122] In some examples the composite materials described herein are configured to provide a combination of thermochemical energy storage performance and crush strength suitable for use in packed-bed or fixed-bed reactor systems. In particular, the composite material may be configured to exhibit both a high volumetric energy density and sufficient crush strength to maintain structural integrity during handling and thermochemical cycling. In some examples, the composite material may exhibit a volumetric energy density of greater than approximately 150 kWh / m3while also exhibiting a crush strength of at least approximately 1.5 kg-force when measured on individual pellets. In further examples, the composite material may exhibit a volumetric energy density of greater than approximately 170 kWh / m3and a crush strength of at least approximately 1.7 kg-force. In still further examples, the composite material may exhibit a volumetric energy density of greater than approximately 200 kWh / m3while maintaining a crush strength of at least approximately 1.7 kg-force. These combined performance characteristics may arise from the interaction between the porous adsorbent, the binder, and optionally the hygroscopic salt phase. The binder provides a mechanically stable host matrix, while the porous adsorbent and hygroscopic salt contribute to thermochemical energy storage through adsorption and / or hydration processes. In some examples where durability is the defining functional requirements, the composite material may exhibit an energy density of greater than ~60kWh / m3. Below this threshold, a material may adsorb moisture but does not function as a useful thermochemical energy carrier.

[0123] In one example, as illustrated in Example 4, composite materials comprising approximately 60 wt% porous adsorbent, approximately 20 wt% binder, and approximately 20 wt% hygroscopic salt exhibited volumetric energy densities in the range of approximately115 kWh / m3to approximately 243 kWh / m3, depending on the identity of the hygroscopic salt. In these examples, the composite materials exhibited crush strengths in a range of approximately 1.7 kg-force to approximately 4.9 kg-force. In particular, a composite material comprising magnesium sulphate as the hygroscopic salt exhibited a crush strength of approximately 4.87 kg-force while maintaining a volumetric energy density of approximately 194 kWh / m3, demonstrating that the composite material can achieve both high thermochemical performance and improved mechanical robustness.

[0124] In another example, as illustrated in Example 3, composite materials comprising a binder and a porous adsorbent in the absence of hygroscopic salt were capable of achieving volumetric energy densities of greater than approximately 150 kWh / m3, for example approximately 168 kWh / m3, while maintaining structural integrity. These results demonstrate that the composite material may provide useful thermochemical energy storage performance even in two-component systems, with the porous adsorbent contributing to adsorption-driven energy storage and the binder providing mechanical stability. Accordingly, in some examples the composite material is characterised by a combination of thermochemical energy density and crush strength, wherein the composite material exhibits a volumetric energy density of at least approximately 150 kWh / m3and a crush strength of at least approximately 1.5 kg-force. In further examples, the composite material exhibits a volumetric energy density of at least approximately 200 kWh / m3and a crush strength of at least approximately 1.7 kg-force. This combination of properties may enable the composite material to be used in practical thermochemical energy storage systems, including packed-bed reactors, without significant degradation, attrition, or structural failure during repeated hydration-dehydration cycles.Method of production of a composite material

[0125] In some examples the composite material described herein may be produced using a method that combines a porous adsorbent, one or more hygroscopic salts, and a magnesium oxide-based binder to form a thermochemical energy storage material. The method may include one or more processing steps including porous adsorbent pre-treatment, salt solution preparation, mixing of composite components, formation of a slurry, optional incorporation of a foaming agent, casting or shaping of the composite material, curing, and drying or activation. These steps may be performed in various sequences or combinations depending on the desired properties of the composite material.

[0126] In some examples the porous adsorbent may be subjected to an impregnation pretreatment prior to incorporation into the composite material. The impregnation pre-treatment may comprise contacting the porous adsorbent with a solution containing one or more hygroscopic salts. For example, the porous adsorbent may be combined with an aqueous solution of one or more hydrated hygroscopic salts for an impregnation pre-treatment period. In one example the period is approximately 1 hour to approximately 4 hours. This allows infiltration of the salt solution into the pore structure of the porous adsorbent. Suitable1porous adsorbents are described above and may include zeolites, metal-organic frameworks (MOFs), porous silicas, porous aluminosilicates, carbonaceous porous materials, salt-loaded porous materials, or combinations thereof. Carbonaceous porous materials may include activated carbon, expanded graphite, porous graphite materials, or combinations thereof. Suitable zeolites may include Zeolite 13X, Zeolite 4A, Zeolite 5A, Zeolite Y, Zeolite Beta, ZSM-5, or combinations thereof. Following impregnation, the solid material may be separated from the solution by filtration, decanting, or other suitable separation techniques. The impregnated porous material may then be dried to remove excess moisture while retaining the hygroscopic salt within the pore structure. This impregnated pre-treatment step may improve the uniform distribution of hygroscopic salts within the composite material and enhance interaction between the salt phase and the porous adsorbent.

[0127] In some examples the hygroscopic salt may be prepared as an aqueous solution prior to mixing with other composite components. Hydrated hygroscopic salts may be dissolved in water to form a concentrated or saturated hygroscopic salt solution. Suitable salts include magnesium chloride (MgCH), magnesium sulphate (MgSCM), calcium chloride (CaCh), potassium carbonate (K2CO3), sodium phosphate (e.g., NasPCM), strontium chloride (SrCH), strontium bromide (SrBr2), lanthanum chloride (LaCIs), lithium chloride (LiCI), or combinations thereof. In some examples the hygroscopic salt may be present in hydrated form, for example MgCl2-6H2O, MgSO4-7H2O, CaCl2-6H2O, SrCl2-6H2O, SrBr2-6H2O, LaCl3-7H2O, Na3PO4-12H2O, LiCI-H2O, or related hydrated salts capable of reversible dehydration. Hydrated salts may be used directly to prepare the hygroscopic salt solution. Preparation of a salt solution may facilitate uniform distribution of the hygroscopic salt within the composite material during subsequent mixing steps.

[0128] In some examples the porous adsorbent, binder precursor, and optional additives may be combined in a dry mixing step to form a binder-adsorbent mix. For example, the porous adsorbent, binder precursor magnesium oxide powder (for example light-burned MgO), and optional thermal additives such as graphite or reinforcing fibres may be combined using a mechanical mixer to form the binder-adsorbent mix. Suitable mixers may include paddle mixers, planetary mixers, or industrial mixers such as a Hobart mixer. In some examples the dry mixing process may be conducted at a rotational speed of approximately 135 rpm to approximately 145 rpm for a duration of approximately 30 seconds to approximately 120 seconds to produce a homogeneous dry mixture. This mixing step may promote uniform distribution of the composite components prior to introduction of the salt solution.

[0129] In some examples a composite slurry may be formed by introducing the hygroscopic salt solution into the binder-adsorbent mix. The slurry may be mixed to promote dispersion of the binder precursor and hygroscopic salt within the composite mixture. In one example, the slurry may be mixed at a rotational speed of approximately 135 rpm to approximately 145 rpm for approximately 60 seconds, followed by mixing at a higher speedof approximately 275 rpm to approximately 295 rpm for approximately 60 seconds to approximately 120 seconds. These mixing conditions may assist in producing a uniform composite slurry suitable for casting or shaping.

[0130] In some examples the composite material may be prepared as a foamed composite material in order to increase porosity and reduce bulk density. In such examples a foaming agent may be used to introduce air bubbles into the composite slurry. The foaming agent may comprise a protein-based foaming agent (for example hydrolysed protein foaming agents) or a synthetic foaming agent such as alkyl sulphates or alkyl ether sulphates. The foaming agent may be diluted with water and passed through a foam generator that introduces compressed air into the solution to produce a stable foam containing a large number of air bubbles. The generated foam may then be incorporated into the composite slurry using a low-shear mixing process such as folding or paddle mixing. This step may produce a foamed composite mixture with increased internal porosity. In some examples the foaming step may be omitted.

[0131] Following preparation of the composite slurry or foamed mixture, the composite material may be transferred into moulds or formed into a desired shape. The composite mixture may be cast into moulds, trays, pellets, or other shaped forms suitable for thermochemical energy storage applications. In some examples the composite material may also be formed into pellets, blocks, extrudates, or structured reactor components.

[0132] After casting or shaping, the composite material may undergo a curing process to allow the binder system to form a host matrix that stabilises the porous adsorbent and hygroscopic salt phases. In some examples curing may be performed under controlled environmental conditions including temperature and humidity. In one example the composite material may be cured at a temperature of less than approximately 50°C, or from about 15 to about 50°C. In one example the composite material may be cured at a relative humidity of approximately 30% to approximately 70%. In one example the composite material may be cured for a curing period of approximately 1 day to approximately 7 days.

[0133] During this curing period the binder may react with dissolved salts to form cementitious magnesium oxychloride or related oxy-salt phases that interconnect the porous adsorbent particles and hygroscopic salt domains to form a stabilising host matrix. These cementitious phases may develop at ambient or moderately elevated temperatures, enabling consolidation of the composite material without the need for high-temperature sintering or thermal processing. In some examples the curing process may therefore be performed using low-temperature processing conditions relative to thermochemical storage materials that require ceramic sintering or high-temperature consolidation. For example, certain prior art thermochemical materials based on ceramic matrices or high-temperature binders may require processing temperatures of several hundred degrees Celsius in order to form a consolidated structure. In contrast, the binder system described herein forms a structurally stable composite matrix at temperatures close to ambient conditions. Low-temperaturecuring, for example the range of 15-50°C, provides several advantages. For example, lower processing temperatures may reduce manufacturing energy requirements, simplify fabrication processes, and allow production using conventional mixing and casting techniques. In addition, curing at relatively low temperatures may preserve the porous microstructure of the adsorbent material and prevent premature dehydration or degradation of the hygroscopic salt phase, thereby maintaining the adsorption capacity and thermochemical performance of the composite material. In one example the curing temperature of the composite material is at ambient temperature and humidity, for example less than about 35°C, or between about 15-30°C

[0134] Following curing, the composite material may be subjected to a drying or activation process. The composite may be dried in an oven or drying chamber at a temperature of approximately 60°C to approximately 200°C. This drying step may remove residual water and may partially dehydrate the hygroscopic salt phases, thereby activating the thermochemical energy storage properties of the composite material.

[0135] In one particular example, there is provided a method of production of a composite material comprising:a) pre-treatment of porous adsorbent - the porous material is initially combined with a saturated solution of hydrated hygroscopic salts for a duration of one to four hours to ensure complete impregnation. Subsequently, the impregnated solid is filtered and dried, which improves homogeneity and salt integration.b) salt solution preparation - hydrated hygroscopic salts are dissolved in water to form a solution, thereby ensuring maximum salt incorporation.c) dry mixing - the pre-treated porous adsorbent, magnesium oxide, and any additional additives, optionally graphite and fibres, are combined using a Hobart mixer.d) slurry preparation - the prepared salt solution is introduced into the dry mix within the mixer.e) optional foaming generation - an aqueous dilution of a foaming agent, which may be either protein-based (e.g., hydrolysed proteins) or synthetic (e.g., alkyl sulphates, alkyl ether sulphates), is prepared. Subsequently, this diluted solution is conveyed through a foam generator. The foam generator employs compressed air to induce agitation within the solution, resulting in the generation of a substantial volume of stable and consistent air bubbles.f) foam incorporation - the pre-generated foam is incorporated into the slurry through a folding or blending process. A paddle mixer is employed to ensure minimal shear, thereby preserving the foam structure and achieving a consistent, homogeneous mixture.g) casting and curing - the foamed concrete mixture is dispensed into moulds or positioned at its final emplacement. The composite undergoes a curing process within a controlled environment, specifically regarding temperature(20-50°C) and humidity(30-70% Relative Humidity), for a defined duration (ranging from 1 to 7 days) to attain the required mechanical strength.h) curing and oven-drying - following curing, the composite material undergoes ovendrying at a specified temperature range of 60-200 °C. This process serves to eliminate residual water, chemically bound water, and activate the thermochemical energy storage properties.In this specific example, the composite material demonstrates a thermal energy density between 120 ~ 450 Wh / kg, with sustained stability observed across a minimum of 10 cycles.

[0136] The composite materials described herein exhibit favourable thermochemical energy storage properties. In some examples the composite material may exhibit a gravimetric thermal energy density determined from thermochemical hydration and dehydration reactions of the hygroscopic salt phase. Energy density may be determined experimentally using calorimetric techniques such as differential scanning calorimetry (DSC) in combination with thermogravimetric analysis (TGA), for example as described in Example 1. In such measurements, TGA may be used to determine the mass change associated with water adsorption and desorption of the composite material, thereby allowing determination of the water uptake capacity. DSC may be used to measure the heat flow associated with the hydration and dehydration reactions of the composite material. The thermochemical energy density may then be determined from the measured enthalpy change associated with the hydration / dehydration reaction together with the amount of water adsorbed by the material. For example, the energy density may be calculated by multiplying the enthalpy change per unit mass of adsorbed water by the measured water uptake of the composite material, and normalising the resulting energy value to the total mass of the composite material.

[0137] In some examples the composite material may exhibit a gravimetric thermochemical energy density of greater than approximately 400 kJ / kg. Energy densities above this threshold may indicate that the composite material contains sufficient quantities of hygroscopic salt capable of undergoing reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction, while still maintaining a stabilising host structure formed by the porous adsorbent and magnesium oxide-based binder.

[0138] In some examples the composite material may exhibit an energy density of approximately 400 kJ / kg to approximately 1200 kJ / kg. Energy densities within this range may arise from composite formulations containing different relative proportions of hygroscopic salt, porous adsorbent, and binder phases. Lower values within the range may correspond to formulations containing higher fractions of porous adsorbent or binder material, which can improve structural stability and vapour transport pathways. Higher values within the range may correspond to formulations containing larger fractions of hygroscopic salt capable of undergoing reversible hydration reactions, thereby increasing the thermochemical energy storage capacity of the composite material. In some examples thecomposite material may exhibit an energy density of approximately 500 kJ / kg to approximately 1000 kJ / kg. Energy densities within this range may represent composite formulations in which the hygroscopic salt provides substantial thermochemical storage capacity while the porous adsorbent and binder phases maintain a stable porous structure that permits vapour transport during thermochemical cycling. In some examples the composite material may exhibit an energy density of approximately 500 kJ / kg to approximately 950 kJ / kg.

[0139] In some examples the composite material may exhibit a gravimetric energy density of approximately 120 Wh / kg to approximately 450 Wh / kg (approximately 430 kJ / kg to approximately 1620 kJ / kg). Energy densities within this range may arise from composite formulations containing different relative proportions of hygroscopic salt, porous adsorbent, and binder components. Lower values within this range may correspond to formulations containing larger fractions of porous adsorbent or binder phases, which can improve structural stability and vapour transport pathways but may reduce the fraction of active thermochemical reactant. Higher values within the range may correspond to formulations containing greater quantities of hygroscopic salt capable of undergoing reversible hydration reactions, thereby increasing the thermochemical energy storage capacity of the composite material. In some examples the composite material may exhibit a gravimetric energy density of approximately 150 Wh / kg to approximately 350 Wh / kg (approximately 540 kJ / kg to approximately 1260 kJ / kg). Energy densities within this intermediate range may represent composite formulations in which the hygroscopic salt provides substantial thermochemical storage capacity while the porous adsorbent and binder phases maintain a stable porous structure capable of supporting vapour transport during thermochemical cycling. In some examples the composite material may exhibit a gravimetric energy density of approximately 180 Wh / kg to approximately 300 Wh / kg (approximately 650 kJ / kg to approximately 1080 kJ / kg).

[0140] In some examples the thermochemical performance of the composite material may be characterised by the heat of hydration (AH) associated with the composite material. The heat of hydration may include contributions from hygroscopic salts (where present) and / or adsorption-desorption processes of the porous adsorbent. The heat of hydration may be determined using differential scanning calorimetry (DSC) by integrating the heat flow curve associated with hydration reactions, as described in Example 1.

[0141] In some examples the heat of hydration may be approximately 2000 kJ / kgwater to approximately 4000 kJ / kgwater, optionally from approximately 2500 kJ / kgwater to approximately 3800 kJ / kgwater. In some examples the heat of hydration is greater than approximately 3000 kJ / kgwater.

[0142] Values within this range may arise from composite materials in which the porous adsorbent and binder matrix contribute to adsorption-driven thermochemical storage, as well as from systems incorporating hygroscopic salts capable of undergoing exothermic hydrationreactions. Lower values within this range may correspond to composite formulations in which binder or structural components reduce the proportion of active adsorption or hydration material. Higher values within this range may correspond to composite materials in which adsorption processes and / or salt hydration reactions are enhanced by the microstructure of the binder matrix.

[0143] In some examples, incorporation of a magnesium oxide-based binder into a porous adsorbent structure may increase the effective heat of hydration compared to the porous adsorbent alone. For example, a commercial zeolite material may exhibit a heat of hydration of approximately 2900 kJ / kgwater, while a composite comprising the same zeolite and approximately 25 wt% binder may exhibit a heat of hydration of greater than approximately 3300 kJ / kgwater. In further examples, modified porous adsorbents such as ion-exchanged zeolites, carbonaceous materials, or graphite-based materials combined with a binder matrix may exhibit heat of hydration values of greater than approximately 3500 kJ / kgwater, or greater than approximately 3700 kJ / kgwater. Accordingly, the composite materials described herein may exhibit enhanced thermochemical performance relative to conventional porous adsorbents, with heat of hydration values exceeding those of commercial zeolite materials.

[0144] In some examples the composite materials may exhibit a water adsorption capacity determined from thermogravimetric analysis (TGA). Water adsorption capacity may be measured as the percentage mass increase of the material during hydration under controlled humidity conditions. In some examples the composite material may exhibit a water adsorption capacity of approximately 10 wt% to approximately 45 wt%, optionally from approximately 15 wt% to approximately 40 wt%, and in some examples from approximately 20 wt% to approximately 35 wt%.

[0145] Adsorption capacities within this range may arise from composite formulations containing different relative proportions of hygroscopic salt, porous adsorbent, and binder phases. Lower values within this range may correspond to formulations containing larger fractions of binder or structural components that provide mechanical stability while reducing the proportion of active adsorption material. Higher values within this range may correspond to formulations containing larger proportions of hygroscopic salt and / or porous adsorbent capable of adsorbing and retaining water vapour during thermochemical operation.

[0146] In some examples, water adsorption capacities below approximately 10 wt% may result in insufficient thermochemical energy release to provide practical energy storage performance. Conversely, water adsorption capacities above approximately 45 wt% may be associated with excessive expansion, swelling, or structural degradation of the composite material during hydration-dehydration cycling, which may adversely affect mechanical integrity and long-term durability.

[0147] In some examples the composite materials described herein may exhibit a volumetric energy density (VED) of greater than approximately 50 kWh / m3, optionally greater than approximately 100 kWh / m3, and in some examples greater than approximately150 kWh / m3. Values within this range may arise from composite materials containing different proportions of porous adsorbent, binder, and optionally hygroscopic salt phases.

[0148] Lower values within this range may correspond to composite materials containing higher fractions of binder and / or porous adsorbent phases, which may improve mechanical stability and vapour transport pathways but reduce the proportion of thermochemically active material. In some examples, the composite material comprises a two-component system including a binder and a porous adsorbent in the absence of hygroscopic salt, and may exhibit a VED of greater than approximately 150 kWh / m3, for example greater than approximately 160 kWh / m3or greater than approximately 170 kWh / m3, as illustrated in Example 3.

[0149] Higher values within this range may correspond to composite materials comprising one or more hygroscopic salts capable of undergoing exothermic hydration reactions. In some examples, where the hygroscopic salt is present in an amount of greater than approximately 30 wt% of the composite material, the VED may be greater than approximately 170 kWh / m3, optionally greater than approximately 180 kWh / m3.

[0150] In further examples, where the hygroscopic salt is present in an amount of greater than approximately 45 wt%, optionally greater than approximately 50 wt%, the VED may be greater than approximately 200 kWh / m3, optionally greater than approximately 220 kWh / m3, and in some examples greater than approximately 300 kWh / m3, as demonstrated in Example 3.

[0151] In some examples, composite materials comprising a porous adsorbent content of approximately 20-40 wt%, a binder content of approximately 5-30 wt%, and a hygroscopic salt content of approximately 30-55 wt% may exhibit VED values in a range of approximately 200 kWh / m3to approximately 350 kWh / m3. In one particular example, a composite material comprising approximately 20 wt% porous adsorbent, approximately 30 wt% binder, and approximately 50 wt% hygroscopic salt may exhibit a VED of approximately 300 kWh / m3or greater.

[0152] In further examples, composite materials comprising higher porous adsorbent content (for example greater than approximately 60 wt%) and reduced hygroscopic salt content (for example less than approximately 35 wt%) may exhibit VED values in a range of approximately 150 kWh / m3to approximately 300 kWh / m3, while benefiting from improved vapour transport and adsorption kinetics.

[0153] Accordingly, the composite material may be tailored across a range of compositions, including both two-component systems (binder and porous adsorbent) and three-component systems (binder, porous adsorbent, and hygroscopic salt), to achieve a desired balance between volumetric energy density, structural integrity, and thermochemical performance.

[0154] The relative proportions described above may be independently selected within the ranges described herein.

[0155] In some examples, the composite materials described herein may exhibit stable thermochemical performance over multiple hydration-dehydration cycles. As used herein, substantially stable thermochemical performance refers to the ability of the composite material to retain a significant proportion of its initial thermochemical activity during repeated thermochemical cycling. In some examples substantially stable performance may correspond to the retention of at least approximately 85% of the initial thermochemical performance after repeated hydration-dehydration cycles. Thermochemical performance may be assessed using one or more measurable parameters including energy density, heat of hydration, water adsorption capacity, or temperature rise during hydration reactions.

[0156] Cycling performance may be assessed by subjecting the composite material to repeated hydration and dehydration steps under controlled conditions. In one example, hydration may be carried out using a humidified gas stream having a relative humidity of approximately 80% at a temperature of approximately 20°C, while dehydration (charging) may be carried out at an elevated temperature, for example approximately 150°C.

[0157] In some examples, the composite material retains a substantial proportion of its initial volumetric energy density over multiple cycles. For example, the composite material may retain at least approximately 85% of its initial energy density (optionally volumetric energy density) after at least 50 cycles. In some examples, the composite material may exhibit stable performance over at least approximately 70 cycles. According to example 8 the present composite material retains at least 85% of its initial energy density after at least 120 cycles.

[0158] Without wishing to be bound by theory, the observed cycling stability may be attributed to the interaction between the porous adsorbent phase and the magnesium oxidebased binder. The binder may provide structural integrity that resists degradation, fragmentation, or pore collapse during repeated hydration-dehydration cycles, while maintaining accessibility of adsorption and hydration sites within the composite material. In some examples, composite materials comprising a zeolitic adsorbent and a magnesium oxidebased binder, optionally further comprising a hygroscopic salt.

[0159] In one example, as described in Example 8, a composite material comprising approximately 75 wt% lithium-exchanged Zeolite 13X and approximately 25 wt% magnesium oxide-based binder exhibited stable thermochemical performance over at least 64 hydrationdehydration cycles.

[0160] In some examples the composite material may maintain substantially stable thermochemical performance over greater than approximately 100 hydration-dehydration cycles. This range may correspond to composite formulations having different relative proportions of hygroscopic salt, porous adsorbent, and binder phases, where the interaction between these components maintains structural integrity and thermochemical functionality during repeated cycling. In some examples the composite material may maintain substantially stable thermochemical performance over at least approximately 20 cycles.Stability over this number of cycles may indicate that the composite structure effectively immobilises the hygroscopic salt phase and reduces salt migration or agglomeration during hydration-dehydration operation.

[0161] The thermochemical performance characteristics described above are believed to arise from the structural interaction between the hygroscopic salt phase, the porous adsorbent, and the magnesium oxide-based binder matrix. In particular, the magnesium oxide-based binder may form cementitious phases that interconnect particles of the porous adsorbent and hygroscopic salt while maintaining internal porosity within the composite material. As observed in Example 1, the binder may form whisker-like crystalline structures that create a scaffold within the composite material while preserving vapour transport pathways.

[0162] This host matrix structure may stabilise the distribution of hygroscopic salts within the composite material and reduce salt migration or agglomeration during hydrationdehydration cycling. As a result, the composite materials described herein may retain favourable thermochemical performance while maintaining mechanical integrity. The thermochemical performance ranges described above, including the gravimetric energy density, hydration enthalpy, and water adsorption capacity, are therefore consistent with composite materials in which the hygroscopic salt phase is stabilised within a porous adsorbent and binder matrix as described in the present disclosure.

[0163] In some examples the composite materials described herein may be incorporated into a thermochemical reactor configured to store and release thermal energy through a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction. The reactor may contain a bed or volume of the composite material and may be configured to allow a gaseous working fluid to pass through or over the composite material in order to facilitate heat and mass transfer during thermochemical operation. In some examples the reactor may be configured to operate in at least two operational modes including a charging mode, in which the composite material undergoes dehydration through the application of heat, and a discharging mode, in which the composite material undergoes hydration and releases stored thermal energy. The reactor may be configured to allow control of one or more process variables including temperature, humidity, gas flow rate, pressure, or airflow direction in order to regulate the thermochemical reactions occurring within the composite material.

[0164] The composite material described herein may be provided in any suitable thermochemical reactor. In some examples the thermochemical reactor may comprise a fixed-bed reactor in which the composite material is arranged as a stationary packed bed of particles or pellets through which a gaseous working fluid flows. In some examples the reactor may comprise a packed-bed reactor, in which discrete particles of the composite material are arranged within a containment vessel and the working fluid passes through interparticle voids to facilitate heat and mass transfer. In some examples the reactor maycomprise a fluidised-bed reactor, in which the composite material is present as particulate solids suspended by an upward flow of gas. In some examples the reactor may comprise a moving-bed reactor in which the composite material gradually moves through the reactor while undergoing hydration or dehydration reactions. In some examples the reactor may comprise a rotating drum reactor or rotary reactor in which the composite material is slowly agitated or transported through a rotating chamber while exposed to the gaseous working fluid. In some examples the reactor may comprise a structured reactor in which the composite material is incorporated into structured elements such as monoliths, honeycomb structures, plates, foams, or porous matrices.

[0165] In some examples the composite material may be introduced into the reactor in the form of particles, pellets, granules, beads, or agglomerates. The particle size and geometry may be selected to optimise gas flow distribution, heat transfer, and pressure drop within the reactor. In some examples the composite material may be formed into monolithic structures, blocks, porous panels, or extruded shapes prior to incorporation into the reactor. In some examples the composite material may be cast directly into the reactor vessel or into removable cartridges that are inserted into the reactor.

[0166] In some examples, the composite material may be formed into shaped bodies, including pellets, beads, granules, extrudates, or other structured forms suitable for use in thermochemical energy storage systems. The formation of such bodies may be achieved via a pelletisation process involving shaping of a composite mixture comprising the porous adsorbent, optional hygroscopic salt component, and binder. In one example, the composite mixture is prepared as a paste or slurry through combination of the porous adsorbent, binder precursor, and liquid phase (for example water and / or a salt solution). The resulting mixture may be shaped into discrete bodies using methods including extrusion, granulation, moulding, or bead formation. In one example, the mixture is formed into substantially spherical beads having a diameter in the range of approximately 1 mm to 10 mm, for example approximately 2 mm to 5 mm. In a specific example, the composite material is formed into beads of approximately 3 mm diameter, as described in the Examples. Following shaping, the formed bodies may be subjected to a curing process under ambient or moderately elevated temperature conditions, for example at temperatures of approximately 15 °C to 50 °C and ambient humidity. During curing, the magnesium oxide-based binder reacts with the hygroscopic salt component to form cementitious magnesium oxychloride and / or related oxy-salt phases. These phases act to bind the porous adsorbent particles together and generate mechanically robust composite bodies without requiring high-temperature sintering.

[0167] The pelletisation method described herein differs from conventional pelletisation techniques for porous adsorbents, which typically rely on inert binders such as clays, silica, or alumina and often require high-temperature calcination or sintering steps. In contrast, the present method enables formation of mechanically stable bodies at relatively lowtemperatures, thereby preserving the pore structure of the porous adsorbent and reducing degradation or premature dehydration of hygroscopic salt components.

[0168] In some examples, a magnesium oxide-based binder, such as light burned magnesium oxide, is used to bind a porous adsorbent, for example zeolite powder, to form a composite material in the form of pellets or other shaped bodies.

[0169] In some examples, the method further comprises a post-formation impregnation step, in which the shaped composite bodies are contacted with a saturated solution of one or more hygroscopic salts. For example, the formed and cured bodies may be dried and subsequently soaked in a saturated salt-hydrate solution (for example unary, binary, or ternary salt systems) for a period of time sufficient to allow infiltration of the salt into the pore structure. A unary salt system comprises a single salt as an active thermochemical component of the system (for example, magnesium chloride), capable of undergoing reversible hydration and dehydration. A binary salt system comprises two different salts as active thermochemical components within the same system, enabling interactions between the salts that can influence hydration behaviour, reaction kinetics, or stability. A ternary salt system comprises three different salts as active thermochemical components within the same system, providing increased flexibility in tuning thermochemical properties, including energy density, reaction temperature, and cycling stability. This approach enables decoupling of structural formation and salt loading, thereby improving control over salt distribution and loading within the composite material. In some examples, the mechanical properties of the shaped bodies may be controlled through adjustment of the binder content relative to the porous adsorbent. As demonstrated in the Examples, increasing the binder loading in increments of approximately 5 wt% relative to the porous adsorbent results in a substantial increase in crush strength of the formed bodies, including formation of beads that do not fail under applied loads of at least approximately 16 kg. This enables tuning of crush strength while maintaining functional adsorption properties.

[0170] In some examples, the internal structure of the shaped bodies may be modified through inclusion of a foaming agent during formation, thereby introducing macroporosity and improving vapour transport within the composite material. Foaming agents may include protein-based foaming agents and / or synthetic foaming agents. Additionally, the particle size of the porous adsorbent used in the pelletisation process may influence packing density, surface area availability, and water demand during processing, thereby affecting both mechanical and thermochemical performance of the resulting bodies.

[0171] In some examples the reactor may comprise a vessel or chamber constructed from materials capable of withstanding the temperature and humidity conditions associated with thermochemical operation. The reactor may have various geometries including cylindrical, rectangular, cuboidal, conical, or annular configurations. In some examples the reactor may comprise multiple reactor modules arranged in series or parallel in order to increase storage capacity. The reactor may further include gas distribution structures such as perforatedplates, gas distributors, manifolds, or flow baffles to ensure uniform distribution of the working fluid through the composite material. The reactor may also include retaining structures, including mesh screens, porous plates, or perforated supports, that retain the composite material while allowing passage of the working fluid. In some examples the reactor may further comprise one or more heat exchange elements configured to transfer heat between the composite material and a heat transfer fluid. The heat exchange elements may comprise heat exchange tubes, plates, fins, or other thermally conductive structures positioned within or adjacent to the bed of composite material. The heat transfer fluid may comprise air, water, steam, oil, refrigerant, or other heat transfer media.

[0172] In one example of the invention, a thermochemical energy storage system comprises an open fixed-bed reactor, an example of which is illustrated schematically in Figure 3. As shown in Figure 3, the reactor comprises a generally cylindrical reactor vessel containing a packed bed of composite material. The composite material is retained within the reactor by filter mesh structures positioned at the upper and lower ends of the packed bed. The mesh structures allow passage of the working fluid while preventing entrainment of composite material particles in the air stream. The reactor may operate in two distinct modes: a charging mode, illustrated in Figure 3(a), and a discharging mode, illustrated in Figure 3(b). In the charging mode the composite material is dehydrated using a heated gas stream to store thermal energy. In the discharging mode humidified gas is introduced to the reactor to hydrate the composite material and release stored thermal energy.

[0173] Although Figure 3 illustrates one example of a thermochemical reactor configuration, it will be understood that various modifications and alternative designs may be employed without departing from the scope of the invention. For example, the reactor may operate with different airflow directions, alternative reactor geometries, different gas humidification systems, or alternative gas circulation arrangements. Similarly, the reactor may incorporate multiple beds of composite material, integrated heat exchangers, modular reactor cartridges, or distributed reactor systems depending on the desired application and energy storage capacity.

[0174] Charging Mode (Energy Storage - Dehydration) - In the charging mode, a stream of heated, dehumidified gas (for example air) is introduced to the reactor to induce dehydration of the composite material. In some examples, the temperature of the heated gas is greater than approximately 60°C. Temperatures below approximately 60°C may result in insufficient driving force for dehydration and correspondingly low energy storage efficiency. In some examples, the charging temperature of the heated gas is in the range of approximately 60°C to approximately 350°C. In one example, the temperature is in the range of approximately 80°C to approximately 200°C. In further examples, the temperature may be in the range of approximately 100°C to approximately 180°C.

[0175] Temperatures above approximately 350°C may be undesirable, as thermal degradation or instability of one or more components of the composite material may occur.For example, at elevated temperatures the magnesium oxide-based binder and / or hydrated salt phases may undergo decomposition, phase transformation, or loss of structural integrity, which may reduce the crush strength and / or thermochemical performance of the composite material. In one example, the air inlet during charging is located at a lower portion of the reactor (for example corresponding to the element designated "Hot air inlet" in Figure 3a). The temperature of the inlet gas is maintained above a threshold sufficient to induce an endothermic dehydration reaction of the composite material. This threshold temperature depends on the specific hydrate chemistry and the partial pressure of water vapour in the gas stream, and may typically fall within the range of approximately 80°C to approximately 200°C. In some examples, the heated gas is dehumidified to reduce the partial pressure of water vapour, thereby increasing the thermodynamic driving force for dehydration at a given temperature.

[0176] In some examples, the heat used during the charging mode may be supplied from a low-temperature heat source. Suitable heat sources may include solar thermal collectors, industrial waste heat streams, electrical heaters, heat pumps, geothermal heat sources, or combinations thereof.This reaction can be represented generically as:Composite-xH2O(s) + Heat - Composite-yH2O(s) + (x-y)H20(g)wherein x represents the initial hydration state of the composite, y represents the hydration state after the dehydration process, and x is greater than y. The specific values of x and y are dependent on the initial composition of the composite material and the operating conditions. The water vapor liberated during the dehydration process is entrained in the air stream and exits the reactor at an upper portion thereof (corresponding to the element designated "Cold air outlet" in Figure 3a). The humidified air stream may then be exhausted to the atmosphere or, in an alternative example, directed to a condenser for water recovery and closed-loop operation. An air saturator, present in the system, is bypassed during the charging operation.

[0177] Discharging Mode (Energy Release - Hydration) - In the discharging mode, the direction of airflow through the reactor is reversed: a stream of air, having a temperature below that of the charging mode and a relative humidity above a predetermined threshold, is introduced to the reactor. In one example, the air inlet during discharging is located at the upper portion of the reactor (corresponding to the "Cold air inlet" in Figure 3b). This humid air may be generated by passing ambient air through an air saturator, thereby increasing its water vapor content. As the humid air flows through the fixed bed of composite material, an exothermic hydration reaction is initiated:Composite -yH20(s) + (x-y)H20(g) - Composite -xH20(s) + Heatwherein x and y have the same meanings as described above. The heat released by this exothermic reaction is transferred to the air stream. The heated, and now dehumidified, airstream exits the reactor at a lower portion thereof (corresponding to the "Hot air Outlet" in Figure 3b) and is available for use in various thermal applications, including, but not limited to, space heating and domestic hot water generation. As an example, the temperature profile within the reactor during the exothermic reaction in discharging mode is shown in Figure 5. The controlled temperature increase, from ambient temperature (22°C) to approximately 35°C, demonstrates the reactor's capacity for space heating.

[0178] In one example the reactor comprises a vessel containing a bed of the composite material described herein. In one example the reactor vessel is substantially cylindrical and contains a fixed bed of the composite material. The composite material may be present as particulate forms as described above and arranged as a bed within the reactor. The size and geometry of the composite material particles may be selected to optimise gas flow distribution and heat and mass transfer characteristics within the reactor while reducing pressure drop across the bed. In one example the composite material is retained within the reactor by one or more porous retaining structures positioned at the upper and lower ends of the bed. Such retaining structures may comprise filter mesh, perforated plates, porous screens, or other gas-permeable support structures that permit passage of the working fluid while preventing entrainment of composite material particles in the gas stream.

[0179] In one example the retaining structure comprises a filter mesh having an aperture size smaller than the minimum particle size of the composite material. In one example the mesh aperture size may be approximately 1 mm to 3 mm, as illustrated schematically in Figure 4. In one example the reactor dimensions may be selected depending on the desired storage capacity and operating conditions of the system. In one example the reactor may have a height (H) of approximately 250 mm to approximately 500 mm and a diameter of approximately 25 mm to approximately 200 mm. These dimensions are provided as illustrative examples and may be varied depending on the scale of the thermochemical energy storage system.

[0180] In some examples the reactor system further comprises a gas humidification unit, such as an air saturator, configured to increase the relative humidity of the gas stream entering the reactor during the discharging mode. The air saturator may operate by contacting the incoming gas stream with liquid water in order to increase its water vapour content. The specific design of the air saturator is not critical and may include various conventional gas humidification devices including packed-bed humidifiers, spray towers, bubble columns, evaporative humidifiers, or wetted membrane systems.

[0181] In some examples the thermochemical reactor may form part of a thermal energy storage system configured to store heat during periods of energy availability and release heat during periods of demand. The system may be integrated with building heating systems, domestic hot water systems, district heating networks, industrial process heating systems, or other thermal energy utilisation systems.Integration of the Thermochemical Energy Storage System with a Fan Heater

[0182] Figure 6 illustrates an example of the present invention in which a thermochemical energy storage system is integrated with a fan heater to provide a combined thermal energy storage and heat delivery apparatus. In the example shown in Figure 6, the system comprises a fan (1) configured to draw ambient air (0) into the apparatus and drive airflow through the system. The airflow generated by the fan may be adjusted by controlling the fan speed in order to regulate the heat output delivered by the system. In one example the system further comprises an electric resistance heating element (2) positioned downstream of the fan. The heating element may be configured to heat the incoming air stream. In some examples the heating element may operate in multiple functions. For example, the heating element may provide conventional resistive heating comparable to a standard fan heater. The heating element may also provide supplementary heat during operation of the thermochemical reactor if the heat released from the reactor is insufficient to meet heating demand. In addition, the heating element may provide a heat source for charging the thermochemical reactor by supplying thermal energy required to induce dehydration of the composite material. The system further comprises a thermochemical reactor (3) containing the composite thermochemical energy storage material described herein. The reactor is configured to allow airflow through or over the composite material in order to facilitate heat and mass transfer between the air stream and the composite material.

[0183] In some examples the system may further include ductwork (4) configured to direct airflow through the components of the system. The ductwork may guide the airflow between the fan, the heating element, the thermochemical reactor, and the air outlet. In some examples the system further comprises a control unit (5) configured to regulate operation of the system. The control unit may comprise sensors, actuators, and a control algorithm. The control unit may monitor parameters such as air temperature, humidity, airflow rate, and operational state of the thermochemical reactor. The control unit may control one or more of the fan speed, the power supplied to the electric resistance heating element, and the airflow pathways used during charging or discharging operation of the reactor.Operational Modes

[0184] In one example there is provided a thermochemical energy storage system operable in multiple modes including a charging mode, a discharging mode, and a standard fan heater mode.

[0185] Charging Mode (Energy Storage) - During the charging mode the system stores thermal energy in the composite thermochemical material contained within the reactor.Ambient air (0) is drawn into the system by the electric fan (1). The air then passes through the electric resistance heating element (2), where the air temperature is increased to a level sufficient to induce dehydration of the composite material. The heated air stream flows (3) through the thermochemical reactor containing the composite material. Heat from the airstream drives an endothermic dehydration reaction within the composite material as previously described. During this process water vapour is released from the composite material and carried away in the air stream. The resulting humid air exits the system as exhaust air (5). In some examples this air may be vented to the atmosphere. In other examples the humid air may be directed to a condenser for water recovery in a closed-loop configuration.

[0186] B. Discharging Mode (Energy Release) - During the discharging mode the thermochemical reactor releases stored thermal energy. Ambient air (0) is drawn into the system by the electric fan (1). In some examples the incoming air may optionally be preheated by the electric resistance heating element (2), although this may not be necessary because the hydration reaction occurring within the composite material is exothermic. The air stream flows through the thermochemical reactor (3). If the incoming air is not sufficiently humid, a humidification stage may be provided upstream of the reactor to increase the water vapour content of the air. The humidification stage may comprise, for example, a water spray, evaporative humidifier, or air saturator. Within the reactor the composite material adsorbs water vapour from the air stream, undergoing an exothermic hydration reaction that releases heat. The heat generated by this reaction is transferred to the air stream flowing through the reactor. The resulting heated air stream (5) exits the system and may be supplied to an indoor environment for space heating.

[0187] C. Standard Fan Heater Mode - In some examples the system may also operate as a conventional fan heater without using the thermochemical reactor. In this mode ambient air (0) is drawn into the system by the electric fan (1) and passed through the electric resistance heating element (2), where the air is heated. The heated air may bypass the thermochemical reactor and be delivered directly as a warm air stream (5) for space heating.

[0188] Integration of the thermochemical reactor with a fan heater as described herein enables thermal energy to be stored and subsequently released within a compact heating appliance. Such a system may allow heat to be stored during periods when energy is available or inexpensive and later released when heating demand arises.

[0189] In one example there is provided a thermochemical energy storage system comprising a reactor containing a composite material as described herein (for example as described herein or in relation to claims 1 to 18), and a fluid flow system configured to pass a gas, such as air, through the reactor. The reactor may comprise a vessel or housing containing the composite material, wherein the composite material is disposed within a flow path such that a fluid passing through the reactor is brought into contact with the composite material to facilitate heat and mass transfer. The fluid flow system may be configured to pass air through or over the composite material within the reactor. In some examples the composite material may be arranged as a packed bed, fixed bed, or a plurality of pellets or granules disposed within the reactor such that interstitial voids define flow channels for the air stream. In this configuration, air passing through the reactor is in direct contact with thecomposite material, enabling adsorption and desorption of water vapour and associated thermochemical heat exchange. In some examples the system is configured to operate in a charging mode in which thermal energy is stored in the composite material. In the charging mode, air passing through the reactor is heated and has a reduced relative humidity, such that the air is capable of inducing dehydration of the composite material. The heated, dehumidified air may be generated by passing ambient air through a heating element, such as an electric resistance heating element, or by heat exchange with a heat pump or other thermal energy source. In some examples the charging mode may operate at temperatures in the range of approximately 60°C to approximately 350°C, depending on the composition of the composite material and the desired level of dehydration. In some examples the system is configured to operate in a discharging mode in which stored thermal energy is released from the composite material. In the discharging mode, air passing through the reactor comprises water vapour, such that the air induces hydration of the composite material. The hydration reaction is exothermic, and heat released from the composite material is transferred to the air stream passing through the reactor. The resulting heated air may be used to supply a heating load, such as a space heating system or other thermal application. In some examples the system may further comprise at least one of a fan heater and a heat pump. For example, as described in relation to Figures 6 and 7, a fan heater may be used to draw ambient air into the system and to provide a heating element for raising the temperature of the air during charging operation. Alternatively or additionally, a heat pump may be used to supply thermal energy to the reactor during charging operation and / or to transfer heat to a heating load during discharging operation. The integration of the thermochemical reactor with a fan heater and / or heat pump may enable flexible operation of the system across different energy availability and demand conditions.

[0190] In some examples the reactor comprises a housing defining a flow path through the reactor, wherein the composite material is disposed within the flow path such that air passing through the reactor is in contact with the composite material. The fluid flow system may comprise one or more airflow pathways extending between an air inlet and an air outlet of the system. In one example the fluid flow system comprises a first airflow pathway extending from the air inlet, through a heating element, and through the reactor to the air outlet, and a second airflow pathway extending from the air inlet, through the reactor to the air outlet. In this configuration, the first airflow pathway enables a charging configuration in which heated air is brought into contact with the composite material within the reactor, and the second airflow pathway enables a discharging configuration in which air is brought into contact with the composite material within the reactor. In some examples the fluid flow system may further comprise a third airflow pathway extending from the air inlet to the air outlet and bypassing the reactor. The third airflow pathway may enable a direct heating configuration in which air is heated, for example by a heating element, and delivered to a heating load without passing through the reactor. In some examples the system further comprises acontrol system configured to selectively enable one or more of the airflow pathways. The control system may comprise one or more actuators, such as valves, dampers, or flow control elements, configured to regulate airflow through the system. By selectively enabling different airflow pathways, the system may be configured to operate in the charging mode, the discharging mode, and optionally a direct heating mode, as described herein. It will be appreciated that the configurations described above enable the thermochemical energy storage system to be operated in a flexible manner, allowing thermal energy to be stored during periods of energy availability and released during periods of heating demand, while optionally providing direct heating functionality.

[0191] Accordingly, in one example there is provided a thermal energy storage and heating system comprising:a. a fan configured to draw ambient air into the apparatus;b. a heating element positioned downstream of the fan and configured to heat the air stream;c. a thermochemical reactor containing a thermochemical energy storage composite material (as described herein) comprising a porous adsorbent, a hygroscopic salt, and a binder, optionally a magnesium oxide-based binder; andd. a control unit configured to regulate airflow through the apparatus,wherein the apparatus is configured to operate in:i. a charging mode in which heated air from the heating element passes through the thermochemical reactor to induce dehydration of the composite material thereby storing thermal energy, andii. a discharging mode in which air containing water vapour passes through the thermochemical reactor to induce hydration of the composite material thereby releasing stored thermal energy to the air stream.

[0192] In a further example, there is provided a method of operating a thermal energy storage and heating system comprising a fan, a heating element, and a thermochemical reactor containing a thermochemical energy storage composite material as described herein, comprising:a. a porous adsorbent,b. a hygroscopic salt, andc. a binder,the method comprisingi. drawing ambient air into the apparatus using the fan,ii. heating the air using the heating element and directing the heated air through the thermochemical reactor to dehydrate the composite material and store thermal energy, andiii. subsequently directing air containing water vapour through the thermochemical reactor to hydrate the composite material and release stored thermal energy, thereby producing a heated air stream.Integration of the Thermochemical Energy Storage System with a Heat Pump

[0193] Figure 7 illustrates an example in which the thermochemical energy storage system described herein is integrated with a heat pump to form a combined thermal energy storage and heating system. In this example the thermochemical energy storage system functions as a thermal battery, storing thermal energy during periods when operation of the heat pump is favourable and releasing stored thermal energy when heating demand arises. In one example the integrated system comprises a heat pump, which may be an air-source heat pump, a water-source heat pump, a ground-source heat pump, or another heat pump system capable of providing heating and optionally cooling by transferring thermal energy between a heat source and a heating load.

[0194] The system further comprises a thermochemical reactor containing the thermochemical energy storage composite material described herein. The reactor is configured to store thermal energy through dehydration of the composite material and release stored thermal energy through hydration of the composite material.

[0195] In some examples the system further comprises one or more heat transfer fluid circuits, which may comprise an air-based or liquid-based heat transfer circuit, configured to transfer thermal energy between the heat pump, the thermochemical reactor, and a heating load. The heat transfer fluid may comprise, for example, air, water, steam, oil, refrigerant, or a water-glycol mixture. In the example illustrated in Figure 7, the thick solid lines represent the flow of heated heat transfer fluid and the thick dotted lines represent the flow of cooled heat transfer fluid.

[0196] In some examples the system further comprises a plurality of control valves, indicated as valves VI to V6 in Figure 7, configured to regulate the flow of the heat transfer fluid through the system. The control valves may be electronically actuated and may be controlled by a control unit in order to enable different operational modes of the system. In one example the different operational modes are achieved through selective opening and closing of the control valves. In some examples the system further comprises a heating load configured to receive thermal energy from the system. The heating load may comprise any suitable heating load including a space heating system, a building heating system, a domestic hot water system, a radiant heating system, or an industrial process heating system. Thermal energy may be delivered to the heating load through one or more heat exchangers, radiant panels, air handling units, or other heat distribution devices. In some examples the system further comprises a control unit configured to regulate operation of the system.Operational Modes

[0197] In one example the integrated heat pump and thermochemical energy storage system may operate in multiple operational modes including a charging mode, a thermochemical discharging mode, and a direct heat pump heating mode.

[0198] A. Heat Pump Charging Mode - In a first operational mode the thermochemical energy storage system is charged using thermal energy supplied by the heat pump. In this mode the control valves are configured such that valves V3 and V5 are closed, and valves VI, V2, V4, and V6 are open. In this configuration heated heat transfer fluid generated by the heat pump is directed through the thermochemical reactor containing the composite material. Heat supplied by the heat transfer fluid drives an endothermic dehydration reaction within the composite material, thereby storing thermal energy in the thermochemical energy storage system. The heat transfer fluid exiting the thermochemical reactor is cooled relative to the inlet temperature and is returned to the heat pump for reheating. This charging mode may be used when the heat pump is operating efficiently, when electricity prices are low, or when renewable energy sources are available.

[0199] B. Thermochemical Discharging Mode - In a second operational mode the thermochemical energy storage system releases stored thermal energy to supply heat to the heating load. In this mode the control valves are configured such that valves V2 and V6 are closed, and valves VI, V3, V4, and V5 are open. In this configuration the heat pump may be turned off or operated at reduced capacity. Heat transfer fluid is circulated through the thermochemical reactor. Humidified air or another humidifying medium is introduced to the thermochemical reactor, for example using a humidification system as described previously in relation to the thermochemical reactor. The composite material absorbs water vapour and undergoes an exothermic hydration reaction, releasing stored thermal energy. The released heat is transferred to the heat transfer fluid circulating through the reactor. The heated heat transfer fluid is then directed to the heating load in order to provide space heating or other thermal energy services. This mode may be used when operation of the heat pump is inefficient, for example in extremely cold environments, during peak electricity demand periods, or when utilisation of stored thermal energy is economically advantageous.

[0200] C. Direct Heat Pump Heating Mode - In a third operational mode the system operates in a direct heat pump heating mode. In this mode the control valves are configured such that valves VI and V4 are closed, and valves V2, V3, V5, and V6 are open. In this configuration the heat pump operates in its normal heating mode and the heated heat transfer fluid produced by the heat pump is directed directly to the heating load, bypassing the thermochemical reactor. This operational mode may be used when the heat pump can efficiently supply the required heating load without the need for thermal energy storage.

[0201] Integration of the thermochemical energy storage system with a heat pump as described herein may enable improved overall system efficiency, increased utilisation of renewable or off-peak energy sources, and enhanced flexibility in meeting heating demand.

[0202] Accordingly, in one example there is provided a thermal energy storage and heating system comprising:a. a heat pump configured to provide thermal energy to a heat transfer fluid; b. a thermochemical reactor containing a thermochemical energy storage composite material (as described herein) comprising a porous adsorbent, a hygroscopic salt, and a binder, optionally a magnesium oxide-based binder; c. one or more heat transfer fluid circuits configured to transfer thermal energy between the heat pump, the thermochemical reactor, and a heating load; d. a plurality of control valves configured to regulate the flow of the heat transfer fluid through the system; ande. a control unit configured to regulate operation of the system,wherein the apparatus is configured to operate in:i. a charging mode in which heated heat transfer fluid from the heat pump passes through the thermochemical reactor to induce dehydration of the composite material thereby storing thermal energy;ii. a thermochemical discharging mode in which hydration of the composite material is induced in the thermochemical reactor and heat released from the hydration reaction is transferred to the heat transfer fluid and supplied to a heating load; andiii. a direct heat pump heating mode in which the heat pump supplies heated heat transfer fluid directly to the heating load while bypassing the thermochemical reactor.

[0203] In a further example, there is provided a method of operating a thermal energy storage and heating system comprising a heat pump and a thermochemical reactor containing a thermochemical energy storage composite material as described herein, comprising:a. a porous adsorbent,b. a hygroscopic salt, andc. a binder, optionally a magnesium oxide-based binder,the method comprisingi. operating the heat pump to heat a heat transfer fluid and directing the heated heat transfer fluid through the thermochemical reactor to induce dehydration of the composite material and thereby store thermal energy;ii. subsequently introducing a humidifying medium to the thermochemical reactor to initiate hydration of the composite material and transferring heat released from the hydration reaction to the heat transfer fluid; andiii. directing the heated heat transfer fluid to a heating load in order to provide space heating or other thermal energy services.

[0204] The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference. Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world. Whilst it will be appreciated that various features of the examples may be combined, they may also be used independently of each other. The above-mentioned examples illustrate rather than limit the disclosure, and those skilled in the art will be able to design many alternative examples without departing from the scope of the appended claims.EXAMPLESExample 1 - Preparation of a Composite Thermochemical MaterialMethodology

[0205] A series of composite thermochemical energy storage materials were prepared in order to evaluate the effect of a magnesium oxide-based binder on composite materials comprising a porous adsorbent and a hygroscopic salt. The following materials were used:• a porous adsorbent comprising zeolite 13X powder• a hygroscopic salt comprising magnesium chloride (MgCh) in anhydrous powder form • light-burned magnesium oxide (MgO) suitable for formation of a magnesium oxidebased cement binder• graphite powder used as a thermal additive in selected formulations.The porous adsorbent and hygroscopic salt were obtained commercially and used as received. The magnesium oxide was provided as a light-burned magnesium oxide material suitable for formation of a magnesium oxide-based cement binder.

[0206] A binder paste was prepared by combining magnesium oxide and magnesium chloride in proportions corresponding to a molar ratio of MgO : MgCh = 6 : 1, forming a magnesium oxychloride cement system. Water was added to the mixture to form a cementitious binder paste. Composite materials were prepared by combining the porous adsorbent, hygroscopic salt, and binder components according to the formulations listed below. The binder components were first mixed to produce a cement paste. The porous adsorbent and hygroscopic salt powders were mixed separately. Water was then added dropwise to the powder mixture using a syringe while mixing to ensure uniform wetting. The binder paste was subsequently combined with the powder mixture to form a single composite paste. Mixing was carried out for approximately 10 minutes using a motorised mortar and pestle mixing device until a uniform paste was obtained without visible agglomerates. The paste was then pelletised and allowed to cure at room temperature for approximately three days prior to testing. A control sample was tested comprising zeolite bead with kaolin for comparative purposes.

[0207] Multiple formulations were prepared with different proportions of porous adsorbent, hygroscopic salt, and binder components.Chemical compositionZeolite MgCI Kaolin r l e e t2Graphite So e c m nMaterial Name (%) (%) (%) (%)MgO MgCI2(%) (%)MgCI2100Zeolite bead 70 30Zeolite powder 100XVA 65 7.2 2.8 25TXVB 65 3.6 1.4 30XVC 60 10.8 4.2 25XVD 60 7.2 2.8 30XVE 55 14.4 5.6 25XVF 40 14.4 5.6 40XVG 20 21.5 8.5 50XVH 20 43 17 20XVG-Gnew 35 10.8 4.2 45 5

[0208] Two representative samples were examined using SEM a) a material comprising porous adsorbent and hygroscopic salt (zeolite 13X+sorel cement : MgCh = 50 : 50 wt%); and b) a material comprising porous adsorbent, hygroscopic salt, magnesium oxide-based binder, and graphite additive (XVG-Gnew formulation = Zeolite: Sorel Cement: MgClz:Graphite 35: 15: 45: 5). Pelletised samples were sectioned using a razor blade and examined under SEM.

[0209] Thermochemical performance was evaluated using simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). TGA was used to determine water adsorption capacity. DSC was used to measure heat flow associated with hydration and dehydration reactions. The heat of hydration (AHkgwater) was calculated from the area under the DSC heat flow curves. Energy density values were calculated from the measured heat flow data.Results

[0210] Microstructure - Figure 9(a) shows a scanning electron microscopy (SEM) image of a composite material comprising a porous adsorbent and a hygroscopic salt in the absence of a binder phase. The image shows aggregated particles of the porous adsorbent and salt material forming an irregular particulate structure. The microstructure exhibits visible voids and pores between particles, but the particles appear largely unconstrained and loosely associated. No continuous binding phase is evident between the particles. Figure 9(b) shows a scanning electron microscopy (SEM) image of a composite material comprising a porous adsorbent, a hygroscopic salt, and a magnesium oxide-based binder. In contrast to Figure 9(a), the image shows a fibrous or whisker-like microstructure distributed throughout the material. These whisker-like structures appear to interconnect the porous adsorbent particlesand hygroscopic salt domains, forming a scaffold-like network within the composite. The porous structure of the adsorbent particles remains visible, indicating that pore accessibility is retained. The binder-derived whisker structures appear to provide mechanical interconnection between particles while maintaining void spaces that may permit transport of water vapour during thermochemical operation. The SEM images indicated that the porous microstructure of the material was retained, providing pathways that may permit mass transport of water vapour during thermochemical operation.

[0211] Thermochemical Performance - The thermochemical properties of the materials are summarised below.AH kg water Water Energy Density Material Name(kJ / Kg water) adsorption (%) (kJ / kg)MgCI22089 47.7 997 Zeolite bead 2488 12.3 306 Zeolite powder 2118 28.3 599XVA 3413 16.7 570XVB 3278 22.7 744XVC 2930 21.5 630XVD 2510 29.4 738XVE 2804 21.4 600XVF 2694 24.5 660XVG 2116 43.1 912XVH 2516 31 780XVG-Gnew 3507 20.7 726

[0212] The data show that composite formulations containing the magnesium oxide-based binder exhibited thermochemical performance comparable to or improved relative to materials comprising porous adsorbent alone. Heat flow is shown in Figures 10A-D for the samples over time. Mass % change over time is shown in figures 10E-H.Conclusions

[0213] The experimental results demonstrate that a magnesium oxide-based binder system can be used to form consolidated thermochemical composite materials comprising porous adsorbents and hygroscopic salts. The microstructural analysis indicated that the binder formed whisker-like cement phases that interconnect particles within the composite and act as a structural scaffold. These binder structures appeared to stabilise the porous adsorbent and hygroscopic salt phases while maintaining a porous network capable ofpermitting water vapour transport. The thermochemical analysis showed that incorporation of the magnesium oxide-based binder did not prevent thermochemical hydration and dehydration reactions and allowed the composite materials to retain favourable thermochemical performance.

[0214] In the experimental formulation containing graphite, the composite material retained a porous microstructure and exhibited thermochemical activity, indicating that incorporation of graphite as a thermal additive was compatible with formation and operation of the composite material. The results are consistent with graphite functioning as a thermal additive without substantially impairing porosity or thermochemical performance of the composite material.

[0215] These observations show that binder systems can be used to stabilise thermochemical storage materials while preserving vapour transport pathways and thermochemical functionality. In particular, the results indicate that incorporation of a magnesium oxide-based binder can provide mechanical consolidation of porous adsorbent and hygroscopic salt particles, maintain porous pathways for vapour transport, enable thermochemical hydration and dehydration reactions to occur within the composite material, and support stable composite microstructures suitable for thermochemical energy storage applications. Accordingly, the experimental results demonstrate the feasibility and advantages of composite materials comprising a porous adsorbent, hygroscopic salt, and binder, as described in the present disclosure.Example 2 - Ion-Exchanged Porous Adsorbents for Thermochemical Energy Storage Methodology

[0216] Ion-exchanged porous adsorbent materials were prepared and evaluated in order to investigate the effect of cation exchange on the adsorption behaviour and thermochemical performance of porous adsorbents suitable for use in thermochemical energy storage materials. In this example the porous adsorbent comprised a zeolite material.

[0217] Commercial zeolite 13X beads were obtained from a commercial supplier and comprised ~30% kaolin. Hygroscopic salts and other materials used in this study were the same as those described in Example 1. The zeolite beads were used as a porous host material for ion-exchange modification. Prior to ion exchange, the zeolite beads were dried at approximately 150 °C to remove residual moisture. Approximately 10 g of dried zeolite beads were then placed in a 250 mL vessel containing approximately 50 mL of a 1 M aqueous salt solution comprising either lithium chloride (LiCI) or magnesium chloride (MgCH). The zeolite beads were allowed to soak in the ion-exchange solution for approximately 67 hours.Following this soaking step the solution was decanted and replaced with a fresh 50 mL portion of the corresponding salt solution. The vessel containing the zeolite beads and solution was then placed in an oven at approximately 65 °C for two hours.

[0218] After the ion-exchange step the zeolite beads were washed three times with water to remove residual solution from the external surfaces of the beads. The washed beads were subsequently dried at approximately 150 °C for two hours, followed by vacuum drying overnight. The ion-exchanged samples were then stored in a desiccator prior to further characterisation. Using this procedure two types of ion-exchanged porous adsorbent materials were prepared:• lithium-ion exchanged zeolite (sample 1)• magnesium-ion exchanged zeolite (sample 2)The ion-exchanged porous adsorbent materials were subsequently evaluated in a reactor to assess their thermochemical performance during hydration reactions. Experiments were conducted in a glass reactor operating at a gas flow rate of approximately 3.5 L / min with an inlet gas temperature of approximately 22-24 °C and a relative humidity of approximately 85-90%. The thermochemical performance of the materials was assessed by measuring the temperature rise (AT) associated with the hydration process and calculating the corresponding volumetric energy density.Results

[0219] The ion-exchanged porous adsorbent samples were characterised using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) in order to determine the elemental composition of the materials and assess the extent of ion exchange within the zeolite structure. SEM images of the ion-exchanged materials are shown in Figure 11 A and B. The images indicate that the overall bead morphology and porous structure of the zeolite material were retained following the ion-exchange treatment. EDS spectra obtained from multiple measurement locations on the beads were used to determine the elemental composition of the samples and are shown below:Sample 1 Sample 2Elements Wt% a Elements Wt% aO 50.4 0.3 O 44.7 0.3Si 25.3 0.2 Si 24.9 0.2Al 16.9 0.2 Al 17.4 0.2Na 4.8 0.1 Na 5.9 0.1Mg 1.4 0.1 Mg 4.9 0.1Cl 0.9 0.1 Cl 1.2 0.1Ca 0.4 0.1 Fe 0.6 0.2Ca 0.3 0.1

[0220] Lithium ions are not directly detected using EDS; however, the reduction in sodium content relative to untreated zeolite provides an indication of ion exchange within the zeolite structure. A summary of the EDS analysis is provided below.Observed Stoic. Mg Mg (%) Sample Bead # Site # Na (%) Li (%) (%) by EDS Neatzeolite 1 1 10.4Li-zeolite 1 1 4.3 6.12 5.1 5.32 1 5.3 5.12 5.5 4.93 5.4 53 1 5.1 5.32 5.2 5.2Mg-zeolite 1 Overall 5.5 2.45 4.71 5.85 2.28 4.85 2 5.85 2.28 4.72 Overall 5.5 2.45 4.71 5.65 2.38 4.83 Overall 5.3 2.55 4.61 4.45 2.92 4.65

[0221] The lithium-ion exchanged samples showed a reduction in sodium content from approximately 10.4% in the untreated zeolite to approximately 5.1%, indicating that a substantial fraction of sodium ions within the zeolite framework had been replaced by lithium ions. In the magnesium-ion exchanged samples the sodium content decreased from approximately 10.4% to approximately 5.4%. The observed magnesium content was approximately 4.7%, which was higher than the stoichiometric level expected from complete ion exchange. This difference is believed to be associated with the presence of residual magnesium chloride on the external surfaces of the beads.

[0222] A summary of the thermochemical performance during hydration reactions is provided below:Energy Density Material AT (°C) Run Time (min)(kWh / m3) Lithium-ion28 170 161exchanged zeoliteMagnesium-ion25 113 136exchanged zeoliteUntreated zeolite 25 75 64Figure 12 shows power output from the three treatments over time, clearly illustrating the superiority of Mg and Li ion exchanged zeolite materials over neat zeolite. After completion of the reactor experiments the magnesium-ion exchanged zeolite beads did not show visible liquid water on the bead surfaces, suggesting that the materials maintained their structural integrity during operation.Conclusions

[0223] The experimental results indicate that ion-exchange modification of porous adsorbent materials can influence the adsorption behaviour and thermochemical performance of the materials. In particular, lithium-ion exchanged zeolite materials exhibited an increased temperature rise and increased volumetric energy density relative to untreated zeolite under the tested operating conditions. These observations are consistent with ion exchange modifying the adsorption properties of the porous adsorbent material. Replacement of native cations within the zeolite framework can alter the electrostatic environment within the pore structure and influence the interaction between the adsorbent and water molecules.Accordingly, ion-exchanged porous adsorbents may be used to tailor adsorption characteristics and thermochemical behaviour of porous materials used in thermochemical energy storage systems. Such ion-exchanged porous adsorbents may be incorporated into composite thermochemical materials comprising a porous adsorbent, a hygroscopic salt, and a binder as described in the present disclosure.Example 3 - Effect of Composite Composition on Volumetric Energy Density

[0224] In order to evaluate the influence of component ratios on thermochemical performance, a series of composite materials were prepared having varying proportions of porous adsorbent (PA), binder, and hygroscopic salt.MethodologyThe binder in each case comprised a magnesium oxide-based binder as described in example 1, and the porous adsorbent comprised a zeolite material (zeolite 13X). Where present, the hygroscopic salt comprised a magnesium salt.

[0225] The composite materials were prepared using a method consistent with that described in example 1, including mixing of the porous adsorbent, magnesium oxide, and optional additives, followed by addition of a salt solution (where applicable), casting, curing, and drying to form the composite material. The compositions tested were powders and are expressed as weight ratios of porous adsorbent (PA), binder, and hygroscopic salt, respectively.

[0226] Thermochemical energy density was determined using either differential scanning calorimetry (DSC) or reactor-based testing. DSC measurements were used to determine the enthalpy associated with hydration and dehydration reactions, while reactor testing measured heat output under dynamic operating conditions.Results

[0227] The results are summarised in the table below.Material composition (PA: Binder: Salt) Energy Density (kWh / m3) and measurement method20: 30: 50 324 (DSC)40 :5: 55 230 (DSC)65: 5: 30 178 (DSC)75: 25: 0 168 (reactor)Conclusion

[0228] The results demonstrate that composite materials comprising higher proportions of hygroscopic salt generally exhibit higher volumetric energy density, consistent with the role of the salt phase in providing thermochemical storage capacity through reversible endo- and exo-thermic reactions such as hydration and dehydration reactions. However, compositions comprising reduced or zero hygroscopic salt content (for example 75:25:0) are still capable of exhibiting measurable energy storage performance, which is attributed to adsorption and desorption processes occurring within the porous adsorbent phase.

[0229] These results further demonstrate that the relative proportions of porous adsorbent, binder, and hygroscopic salt may be selected to achieve a balance between thermochemical energy density, structural integrity, and material stability. Accordingly, the composite materials described herein may be tailored across a range of compositions, including both two-component systems (binder and porous adsorbent) and three-component systems (binder, porous adsorbent, and hygroscopic salt), depending on the desired performance characteristics and application.Example 4. Composite Materials with Hygroscopic Salt Loading

[0230] A series of composite materials were prepared in order to evaluate thermochemical performance and crush strength for compositions comprising moderate amounts of hygroscopic salt. In this example, the composite material comprised a porous adsorbent, a magnesium oxide-based binder, and a hygroscopic salt. The binder phase comprised a magnesium oxychloride cement (Sorel cement) formed from light-burned magnesium oxide (MgO) and magnesium chloride (MgCH), providing mechanical stability while maintaining internal porosity within the composite structure. The porous adsorbent comprised a zeolite material, specifically Zeolite 13X, selected for its microporous framework and high affinity for water vapour.

[0231] Moderate amounts of hygroscopic salts were incorporated into the composite material to enhance water uptake and thermochemical energy storage capacity. The hygroscopic salts evaluated included calcium chloride (CaCh), magnesium sulphate (MgSCM), strontium chloride (SrCh), and potassium carbonate (K2CO3). These salts contribute to thermochemical storage through reversible hydration reactions, while the porous adsorbent primarily facilitates vapour transport and dispersion of the salt within the composite structure.Methodology

[0232] The hygroscopic salt was weighed into a 100 mL beaker. Distilled water was measured using a volumetric flask and added to the beaker to prepare a solution having a concentration of approximately 20 wt%. A magnetic stirrer bar was introduced into the solution, and the mixture was stirred for approximately 30 minutes to ensure complete dissolution of the salt. The porous adsorbent (Zeolite 13X) was weighed into a ceramiccrucible. Magnesium oxide powder was added in an amount corresponding to the desired binder-to-porous adsorbent ratio. Magnesium chloride was then added to the powder mixture to form the precursor components for the magnesium oxychloride binder. The resulting powder mixture comprising porous adsorbent, magnesium oxide, and magnesium chloride was thoroughly mixed using a mortar and pestle for approximately 5 minutes to achieve a homogeneous mixture.

[0233] The prepared salt solution was transferred into a syringe (10 mL capacity) and added dropwise to the powder mixture while continuously mixing using the mortar and pestle. Mixing was continued until the mixture formed a cohesive paste. Once the desired paste consistency was achieved, mixing was stopped. The paste was formed into substantially spherical pellets and allowed to cure under ambient conditions for approximately 3 days prior to testing.

[0234] The cured pellets were loaded into a glass tube reactor. The reactor was operated under inlet gas conditions of approximately 80% relative humidity and a temperature of approximately 20°C. Outlet relative humidity and temperature data were recorded and analysed to determine volumetric energy density. The pellets tested were substantially spherical and had a characteristic diameter in the range of approximately 3 mm to approximately 6 mm. Crush strength (kgf) was measured as the force required to cause fracture of an individual pellet using a compressive force testing instrument, with load applied along a single axis until failure.Results

[0235] The compositions tested are expressed as weight ratios of porous adsorbent (PA), binder, and hygroscopic salt.PA: Binder: Salt Hygroscopic Energy Density Crush strengthratio salt (kWh / m3) (kg. Force)60: 20: 20 CaCI2207 1.9360: 20: 20 MgS04194 4.8760: 20: 20 SrCI3243 1.7660: 20: 20 K2CO3115 1.7260: 15: 25 MgCI2 159 -Conclusions

[0236] The results demonstrate that composite materials comprising a porous adsorbentbinder-salt ratio of approximately 60:20:20 can provide favourable thermochemical energy storage performance while maintaining measurable crush strength. The composite containing calcium chloride exhibited a volumetric energy density of approximately 207 kWh / m3, indicating strong water sorption and hydration capacity within the composite structure. The formulation containing magnesium sulphate exhibited a slightly lower energy density of approximately 194 kWh / m3but demonstrated a higher crush strength of approximately 4.87 kg-force, indicating improved mechanical robustness and a balance between thermochemical performance and structural integrity. The composite comprising strontium chloride exhibiteda relatively high energy density of approximately 243 kWh / m3, indicating strong thermochemical activity, although with comparatively lower crush strength. The potassium carbonate-based composite exhibited a lower energy density of approximately 115 kWh / m3, suggesting that the thermochemical performance may depend on the specific hydration characteristics and equilibrium behaviour of the selected hygroscopic salt.

[0237] These results demonstrate that incorporation of moderate amounts of hygroscopic salts into a porous adsorbent-binder composite can provide a balance between thermochemical energy density and mechanical stability. In particular, compositions comprising approximately 20 wt% hygroscopic salt can achieve volumetric energy densities exceeding approximately 150 kWh / m3, and in some cases exceeding approximately 200 kWh / m3, while maintaining sufficient structural integrity for practical application.

[0238] The results further indicate that the selection of hygroscopic salt influences both thermochemical performance and mechanical properties of the composite material, and that optimisation of salt type and composition may be used to tailor the composite material for specific energy storage and durability requirements.Example 5. High hygroscopic salt loading compositionMethodology

[0239] A series of composite materials were prepared in order to evaluate the effect of high hygroscopic salt loading on thermochemical performance. In this example, composite materials were prepared comprising a porous adsorbent, a magnesium oxide-based binder, and a hygroscopic salt. The porous adsorbent comprised Zeolite 13X, and the binder comprised a magnesium oxychloride cement (Sorel cement) formed from magnesium oxide (MgO) and magnesium chloride (MgCh). The composite materials were formulated to include elevated concentrations of hygroscopic salt, in a range of approximately 40 wt% to approximately 55 wt% of the composite material. Composite materials were prepared using a method consistent with that described in Example 1. In particular, the porous adsorbent, magnesium oxide, and magnesium chloride were combined and mixed to form a homogeneous powder mixture. A salt solution was prepared and added to the powder mixture to form a paste, which was subsequently shaped into pellets and cured under ambient conditions prior to testing. The composite materials were evaluated in a reactor under inlet gas conditions of approximately 80% relative humidity and a temperature of approximately 20°C. Reactor outlet temperature and humidity were recorded and analysed to determine thermochemical performance, including temperature lift and volumetric energy density.Results

[0240] The composition tested and corresponding performance are summarised in the table below.Sample Name PA: Binder: Salt Energy Densityratio (kWh / m3)XVK 20: 25: 45 54The composite material exhibited a maximum temperature lift of approximately 6°C during the hydration process. The measured volumetric energy density was approximately 54 kWh / m3, indicating relatively low thermochemical performance compared to compositions containing moderate salt loading.Conclusions

[0241] The results demonstrate that increasing the hygroscopic salt content to levels of approximately 45 wt% does not necessarily lead to improved thermochemical energy storage performance. Without wishing to be bound by theory, it is believed that at higher salt concentrations the hygroscopic salt may accumulate within the microporous and mesoporous structure of the porous adsorbent, leading to partial pore blockage and reduced accessibility of adsorption sites. In addition, repeated hydration-dehydration cycling may promote salt aggregation, crystallisation, and caking within the composite matrix. These effects can increase mass transfer resistance and restrict diffusion of water vapour through the composite structure. As a result, the effective utilisation of both the hygroscopic salt phase and the porous adsorbent may be reduced. Consequently, the expected increase in energy density associated with higher salt loading may be offset by transport limitations and structural changes within the composite material.

[0242] This example demonstrates that composite materials comprising high hygroscopic salt loadings (for example approximately 45 wt% or greater) may exhibit reduced thermochemical performance, including lower volumetric energy density and limited temperature lift, despite the increased proportion of thermochemically active material.Accordingly, there exists an upper practical limit for hygroscopic salt content within the composite material, above which thermochemical performance and material stability may be adversely affected. These results support the selection of moderate salt loading compositions, as described in Example 4, to achieve an optimal balance between energy storage capacity, vapour transport, and structural integrity.Example 6 - Foamed Composite Materials

[0243] A series of composite materials were prepared in order to evaluate the effect of incorporating a foaming agent during manufacture on thermochemical performance and mechanical properties. In this example, a foaming-assisted manufacturing approach was applied to composite materials comprising a porous adsorbent and a magnesium oxide-based binder. The porous adsorbent comprised Zeolite 13X, and the binder comprised a magnesium oxychloride cement (Sorel cement) formed from magnesium oxide (MgO) and magnesium chloride (MgCh). A foaming agent was introduced during preparation to generate additional macroporosity within the composite structure. The incorporation of a foaming agent isexpected to produce an interconnected pore network, increase overall porosity, and enhance vapour transport within the composite material. Such structural modifications may facilitate improved accessibility of adsorption and hydration sites within the porous adsorbent, potentially reducing mass transfer limitations and improving thermochemical performance. The composite materials were prepared using the following procedure.1. Preparation of Foam Solution - A foaming agent was added to distilled water to form a solution containing approximately 1 wt% foaming agent. The solution was subjected to vigorous mechanical mixing using a hand-held beating device or an automated mixing device to generate a stable foam.2. Powder Mixing - The porous adsorbent (Zeolite 13X) was weighed into a ceramic crucible. Light-burned magnesium oxide powder was added in an amount corresponding to the desired binder-to-porous adsorbent ratio. Magnesium chloride was then added to the powder mixture to form the precursor components of the magnesium oxychloride binder. The resulting mixture was thoroughly mixed using a mortar and pestle for approximately 5 minutes to achieve a homogeneous powder mixture.3. Formation of Foamed Slurry - Water was introduced dropwise into the powder mixture using a syringe while mixing with a mortar and pestle until a viscous slurry was formed. The prepared foam was then added to the slurry and mixed to achieve a substantially uniform distribution of the foam within the slurry.4. The foamed slurry was then placed in an oven at approximately 40°C for approximately 30-60 minutes to allow partial evaporation of water and development of a porous structure.5. Pellet Formation - Once the slurry reached a paste-like consistency, it was formed into substantially spherical pellets.6. Curing - The formed pellets were cured in an oven at approximately 40°C for approximately 24 hours, followed by a further curing period of approximately 48 hours under ambient conditions prior to testing.

[0244] The foamed composite pellets were loaded into a reactor and subjected to an inlet gas stream having a relative humidity of approximately 80% and a temperature of approximately 20°C. Outlet temperature and relative humidity were recorded and analysed to determine thermochemical performance, including energy density measured using DSC. The heat of hydration (AH) was determined using calorimetric analysis, and crush strength was measured as described in example 4.Results

[0245] The table below shows performance of a foamed composite material.AH / kg of Energy Density Crush strength Material water (kWh / m3) (kg. Force)Foamed sphericalpellets 3491 114 0.34Conclusion

[0246] The results indicate that the introduction of a foaming agent leads to the formation of a highly porous structure within the composite material. While increased porosity is expected to enhance vapour transport and accessibility of adsorption and hydration sites, the experimental results demonstrate that these advantages are dependent on the degree and uniformity of the generated pore structure. Without wishing to be bound by theory, it is believed that the highly porous structure generated during foaming may reduce the structural integrity of the composite matrix, leading to lower crush strength than non-foamed materials. In addition, excessive or non-uniform macroporosity may result in reduced packing density and incomplete utilisation of the active material, thereby lowering the measured volumetric energy density.

[0247] However, the foamed composite materials exhibited a relatively high heat of hydration, indicating that the intrinsic thermochemical activity of the material remains high. This suggests that the reduced performance observed in terms of volumetric energy density may be associated with transport limitations, pore structure heterogeneity, or reduced material density, rather than a loss of fundamental adsorption or hydration capability.Accordingly, in some examples the introduction of controlled levels of macroporosity may be advantageous in applications where enhanced vapour transport, reduced pressure drop, or rapid adsorption-desorption kinetics are desirable. For example, foamed composite materials may be suitable for use in low-density packed beds, monolithic structures, or supported configurations in which crush strength requirements are reduced. These results indicate that the level and structure of porosity within the composite material should be carefully controlled in order to achieve an optimal balance between vapour transport, thermochemical activity, and mechanical stability.Example 7 - Composite Materials Comprising a Magnesium Oxide-Based Binder and Porous Adsorbents

[0248] A series of composite materials were prepared in order to evaluate the use of a magnesium oxide-based binder (Sorel cement) to consolidate porous adsorbents into mechanically stable structures, in the absence of separately added hygroscopic salts. Binders play a critical role in the fabrication of structured adsorbent materials for thermochemical energy storage, as they provide the mechanical stability required for shaping powders into pellets, monoliths, or other structured forms suitable for reactor applications. In this example, a magnesium oxychloride cement (Sorel cement), formed from light-burned magnesium oxide (MgO) and magnesium chloride (MgCh), was used as the binder.Commercial zeolites was formed using kaolin as the binder and was used as received without any changes to the composition.

[0249] In this example, the binder was used to consolidate zeolitic adsorbents, including Zeolite 13X, Zeolite 4A, and Zeolite 5A, as well as non-zeolitic materials including activatedcarbon, expanded natural graphite, and a metal-organic framework (CALF-20), while maintaining a significant fraction of the original pore structure required for vapour adsorption. Although no additional hygroscopic salt was incorporated into the composite materials, the binder itself contains magnesium chloride, which is capable of undergoing reversible hydration-dehydration reactions.

[0250] Composite pellets were prepared using the following procedure:1. The porous adsorbent material was weighed into a ceramic crucible. Magnesium oxide powder was added in an amount corresponding to a binder content of approximately 25 wt% relative to the total composite. Magnesium chloride was then added to the powder mixture to form the precursor components for the magnesium oxychloride binder.2. The resulting mixture comprising porous adsorbent, magnesium oxide, and magnesium chloride was thoroughly mixed using a mortar and pestle for approximately 5 minutes to achieve a homogeneous mixture.3. Water was introduced dropwise into the powder mixture while mixing until a viscous paste was formed. The paste was manually shaped into substantially spherical pellets 4. The formed pellets were allowed to cure under ambient conditions for approximately 3 days prior to testing.

[0251] The composite pellets were evaluated for thermochemical performance using reactor-based testing under inlet gas conditions of approximately 80% relative humidity and a temperature of approximately 20°C. Energy density values were calculated based on measured temperature and humidity changes during hydration. Crush strength was assessed using a hand-held compressive force testing instrument as described in example 4.ResultsThe table below shows performance of binder-adsorbent composite materials:Material Energy Density Crush strength (kWh / m3) (kg-force) Commercial zeolite 13x (<30% 135 3.10kaolin bound) beadsZeolite 13x with 25% binder (Sorel 173 2.27cement) beadLi-Zeolite 13x with 25% binder 166 2.36(Sorel cement) beadZeolite 4A with 25% binder (Sorel 147 2.36cement) beadZeolite 5A with 25% binder (Sorel 84 4.85cement) beadCALF-20 (Metal Organic Framework) 101 2.34with 25% binder (Sorel cement)Expanded Natural Graphite (ENG) 74 0.1with 25% binder (Sorel cement)beadActivated Carbon (AC) with 25% 145.3 0.1binder (Sorel cement) beadConclusions

[0252] The results demonstrate that magnesium oxychloride cement can be used as a binder to successfully form structured composite materials from a wide range of porous adsorbents while maintaining measurable thermochemical performance. Zeolite-based composites generally exhibited the highest energy densities and moderate to high crush strength, while carbonaceous materials exhibited lower crush strength despite reasonable thermochemical performance. The results further indicate that the binder itself may contribute to thermochemical energy storage through the presence of magnesium chloride, even in the absence of separately added hygroscopic salts. Accordingly, composite materials comprising a porous adsorbent and a magnesium oxide-based binder may provide a two-component thermochemical energy storage system that combines structural integrity with measurable thermochemical performance.Example 8 - Cycling Performance of Binder-Adsorbent Composite Materials

[0253] The cyclic stability of composite materials is an important parameter for thermochemical energy storage applications, as practical systems require repeated hydration-dehydration cycles without significant degradation in performance. In this example, the cyclic performance of a composite material comprising a porous adsorbent and a magnesium oxide-based binder was evaluated over multiple hydration-dehydration cycles.

[0254] A composite material was prepared comprising lithium-exchanged Zeolite 13X as the porous adsorbent phase and a Sorel cement binder formed from magnesium oxide and magnesium chloride. The composition of the composite material was approximately 75 wt% lithium-exchanged Zeolite 13X and approximately 25 wt% binder. Pellets of the composite material were prepared using the hand-pelletisation method described in previous examples. The pellets were allowed to cure under ambient conditions prior to testing.

[0255] Cyclic performance testing was carried out using a glass tube reactor. During each hydration cycle, the composite pellets were exposed to an inlet gas stream having a relative humidity of approximately 80% and a temperature of approximately 20°C. The outlet relative humidity and temperature were continuously monitored throughout the hydration process in order to determine thermochemical performance and energy density. Following hydration, the composite material was subjected to a dehydration (charging) step using a moisture analyser. Dehydration was carried out at a temperature of approximately 150°C for approximately 30 minutes to regenerate the material prior to the next cycle. This hydrationdehydration process was repeated for multiple cycles, and the energy density was determined for each cycle.Results

[0256] The composite material was subjected to repeated cycling for up to 64 cycles and retained 85% of its initial energy density after 64 cycles.Energy DensityMaterial (kWh / m3) Power (W / g) Outlet temp (°C) Li-exchanged zeolitewith Sorel cement 165.6 + / -19.1 337.2 + / -39.3 46.3 + / -3.6

[0257] Figure 14 illustrates the variation in volumetric energy density of the composite material over 64 hydration-dehydration cycles, demonstrating that the energy density remains substantially stable over repeated cycling. Figure 15 shows representative power (W / g) profiles for cycle 1, cycle 30, and cycle 50, with the similarity of the profiles indicating that the hydration behaviour and heat release characteristics are maintained over repeated use. Together, these results demonstrate that the composite material exhibits stable thermochemical performance over multiple cycles, with no substantial degradation in energy density or power output observed over at least 64 cycles, indicating retention of a substantial proportion of its thermochemical storage capacity.Conclusion

[0258] This example demonstrates that composite materials comprising a porous adsorbent and a magnesium oxide-based binder can exhibit stable thermochemical performance over multiple hydration-dehydration cycles. In particular, the composite material comprising approximately 75 wt% lithium-exchanged Zeolite 13X and approximately 25 wt% Sorel cement binder maintained its energy storage capability over at least 64 cycles, indicating suitability for repeated use in thermochemical energy storage systems.Without wishing to be bound by theory, the stability of the composite material may be attributed to the interaction between the porous adsorbent phase and the magnesium oxidebased binder. The binder may provide mechanical support that limits structural degradation, particle fragmentation, or loss of material during cycling. In addition, the distribution of active sites within the composite matrix may remain accessible over repeated cycles, enabling consistent adsorption and hydration behaviour. The use of lithium-exchanged Zeolite 13X may also contribute to improved cycling stability due to its high affinity for water vapour and stability under repeated hydration-dehydration conditions.Example 9 - Effect of Binder Content on Crush StrengthMethodology

[0259] A composite material was prepared using a porous adsorbent and a magnesium oxide-based binder system. In each case, Zeolite 13X powder was used as the porous adsorbent, and polyvinyl alcohol (PVA, Mw 30k-70k) was added at approximately 4.0 wt% relative to the mass of the zeolite.• Composition 1. Magnesium chloride hexahydrate (MgCl2-6H2O) was added at approximately 38.1 wt% relative to the mass of the zeolite.• Composition 2. Magnesium chloride hexahydrate (MgCl2-6H2O) was added at approximately 43.1 wt% relative to the mass of the zeolite.• Composition 3. Magnesium chloride hexahydrate (MgCl2-6H2O) was added at approximately 48.1 wt% relative to the mass of the zeolite.• Composition 4. Magnesium chloride hexahydrate (MgCl2-6H2O) was added at approximately 38.1 wt% relative to the mass of the zeolite, with approximately 5 mol% of the MgCh replaced by magnesium sulphate heptahydrate (MgSO4-7H2O). The components were finely ground and water was added to achieve a mass ratio of H2O:zeolite of approximately 0.85:1. The resulting mixture was allowed to stand for approximately 18 hours to form a base composition. Magnesium oxide (MgO) was then added at varying loadings (10 wt%, 15 wt%, and 20 wt% relative to zeolite mass), and the mixture was formed into approximately 3 mm diameter beads. The beads were cured under ambient conditions (approximately 22°C and ambient humidity) for approximately 7-10 days.

[0260] The cured beads were subjected to an impregnation process. The beads were dried at approximately 130°C for at least 4 hours, and then soaked in a saturated salt-hydrate solution for approximately 18 hours. Following soaking, the beads were removed, washed with distilled water, and dried again at approximately 130°C. Zeolite-MgO composite beads were impregnated with MgCI2 salt solutions of 45 wt%, 60 wt% and 75 wt%.Results

[0261] The crush strength of the resulting beads was measured after approximately 7 days. Figure 13 shows crush strength and delta.Binder loading (wt%Composition Salt system Crush strength (kgf) cf. PA)1 MgCI2(38.1 wt%) 10 wt% 11.35 kg15 wt% >16 kg (no failure) 20 wt% >16 kg (no failure) 2 MgCh (43.1 wt%) 10 wt% 10.3 kg15 wt% >16 kg (no failure) 20 wt% >16 kg (no failure) 3 MgCl2 (48.1 wt%) 10 wt% 2.71 kg15 wt% 5.75 kg20 wt% 7.92 kgMgCl2 + MgSCM (54 10 wt% 6.69 kgmol% substitution)15 wt% 9.57 kg20 wt% >16 kg (no failure)Material AH / kg- Energy Densityof-water (kWh / m3)(kJ)Composition B (15wt% MgO) 3712 114 (DSC)impregnated with a 60 wt%MgCI2-6H2O solutionComposition C (20wt% MgO) 3260 123 (DSC)impregnated with a 45 wt%MgCI2-6H2O solution.Composition A (10wt% MgO) 3356 133 (DSC)impregnated with a 75 wt%MgCI2-6H2O solutionConclusions

[0262] The results demonstrate that crush strength of the composite material increases with binder content across a range of salt loadings and salt compositions. In particular, increasing the binder content by increments of approximately 5 wt% resulted in a substantial increase in strength, with higher loadings producing pellets that did not fail under the maximum applied load (~16 kg).

[0263] At moderate MgCh loadings (Treatments 1 and 2), high crush strengths were achieved, particularly at binder contents of 15 wt% and above. In contrast, at higher MgCh loading (Treatment 3), crush strength was significantly reduced, indicating that excessive salt content adversely affects structural integrity of the composite material. The inclusion of a secondary salt (MgSCM) resulted in intermediate strength values, indicating that mixed salt systems can be used to tune mechanical properties.ClausesClause 1. A composite material for thermochemical energy storage, comprising: a light burned magnesium oxide, and mixtures thereof; a hygroscopic salt selected from the group consisting of magnesium chloride, magnesium sulphate, and mixtures thereof; and a zeolite. Clause 2. The composite material of clause 1, wherein the zeolite is zeolite 13X.Clause 3. The composite material of clause 1 or 2, wherein the hygroscopic salt comprises magnesium chloride.Clause 4. The composite material of clause 1 to 3, wherein the hygroscopic salt comprises magnesium sulphate.Clause 5. The composite material of clause 1 to 4, wherein the hygroscopic salt is present in an amount of 20% to 80% by weight.Clause 6. The composite material of clause 1 to 5, wherein the zeolite is present in an amount of 5% to 30% by weight.Clause 7. The composite material of clause 1 to 6, wherein the composite material has a foamed structure.Clause 8. The composite material of clause 7, wherein the foamed structure has a porosity of 30% to 50%.Clause 9. The composite material of clause 1 to 8, wherein the composite material has an energy density between 120-450 Wh / kg.Clause 10. A method of manufacturing a composite material for thermochemical energy storage, comprising:• pre-treating zeolite 13X with a solution comprising a magnesium salt selected from the group consisting of magnesium chloride, magnesium sulphate, and mixtures thereof;• mixing magnesium oxide powder with the pre-treated zeolite 13X;• adding a solution comprising a magnesium salt selected from the group consisting of magnesium chloride, magnesium sulphate, and mixtures thereof to the mixture of magnesium oxide and pre-treated zeolite, to form a slurry;• incorporating a foam into the slurry; and• curing and drying the foamed slurry to form a solid composite.Clause 11. The method of clause 10, wherein the foam is generated using a foaming agent selected from the group consisting of protein-based foaming agents and synthetic foaming agents.Clause 12. The method of clause 10 or 11, wherein the composite material is cured in a controlled environment (20-50°C, 30-70% Relative Humidity) for a certain period of time (1~7 days).Clause 13. The method of clause 10 to 12, wherein the drying step comprises drying the material at a temperature between 60°C and 200°C.Clause 14. A thermochemical energy storage reactor comprising a vessel containing a composite material according to any one of clauses 1 to 9.Clause 15. The reactor of clause 14, wherein the reactor is an open fixed-bed reactor configured for airflow through the composite material.Clause 16. The reactor of clause 14 or 15, wherein the reactor has a filter mesh to constrain the composite material, wherein the mesh size is 1-3 mm.Clause 17. A heating system comprising:• a heating element;• a thermochemical energy storage reactor according to clause 14;• a fan configured to direct a flow of air through the reactor; and• a control system configured to control fan speed, the power supplied to the electric resistance heating element, and also the valves to direct airflow.Clause 18. The integrated heating system of clause 17, wherein the control system is configured to operate the system in at least the following modes:a) a direct heating mode, wherein the fan heater provides heat directly to the heating load, bypassing the reactor;b) a charging mode, wherein the fan heater provides heat to the reactor to dehydrate the composite material; andc) a discharging mode, wherein the reactor releases heat to the heating load by hydrating the composite material.Clause 19. An integrated heating system, comprising:• a heat pump;• a thermochemical energy storage reactor according to clause 14;• a heat transfer fluid circuit connecting the heat pump and the reactor; and• a control system configured to control the flow of a heat transfer fluid between the heat pump, the reactor, and a heating load.Clause 20. The integrated heating system of clause 19, further comprising a plurality of control valves within the heat transfer fluid circuit, wherein the control system is configured to operate the valves to selectively direct the flow of heat transfer fluid.Clause 21. The integrated heating system of clause 19 or 20, wherein the control system is configured to operate the system in at least the following modes:a) a direct heating mode, wherein the heat pump provides heat directly to the heating load, bypassing the reactor;b) a charging mode, wherein the heat pump provides heat to the reactor to dehydrate the composite material; andc) a discharging mode, wherein the reactor releases heat to the heating load by hydrating the composite material.

Claims

CLAIMS1. A composite material for thermochemical energy storage comprisinga. a magnesium oxide-based binder; andb. a porous adsorbent.

2. The composite material of claim 1, further comprising one or more hygroscopic salts capable of undergoing a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction.

3. The composite material of any preceding claim, wherein the hygroscopic salt is distributed within pores or interparticle regions of the porous adsorbent.

4. The composite material of claim 2 or 3, wherein the hygroscopic salt comprises a chloride, sulphate, phosphate, carbonate salt, or combinations thereof.

5. The composite material of any of claims 2 to 4, wherein the hygroscopic salt comprises at least one of magnesium chloride, magnesium sulphate, calcium chloride, strontium chloride, strontium bromide, lithium chloride, lanthanum chloride, sodium phosphate, potassium carbonate.

6. The composite material of any preceding claim, wherein the binder comprises magnesium oxide and one or more inorganic salts, optionally selected from the group consisting of magnesium salts, magnesium chloride, magnesium sulphate, acids, phosphate salts, chloride salts, sulphate salts, aluminate salts, double salts, phosphoric acid, citric acid, tartaric acid, glycolic acid, potassium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, sodium pyrophosphate, potassium chloride, iron chloride, zinc chloride, calcium chloride, iron sulphate, zinc sulphate, sodium sulphate, copper sulphate, manganese sulphate, magnesium sulphate, potassium aluminate, sodium aluminate, aluminium alkoxides, potassium fluoroaluminate, sodium hexafluorosilicate, sodium bicarbonate, potassium aluminium sulphate, ammonium aluminium sulphatechloride salts, sulphate salts, aluminate salts, double salts, potassium dihydrogen phosphate (KH2PO4), phosphoric acid, calcium chloride, sodium sulphate, sodium dihydrogen phosphate, potassium aluminium sulphate, ammonium aluminium sulphate, or combinations thereof,wherein the magnesium oxide optionally comprises light-burned magnesium oxide.

7. The composite material of any preceding claim, wherein the binder comprises magnesium oxychloride cement, magnesium oxysulphate cement, or a combination thereof.

8. The composite material of claim 6 or 7 wherein the molar ratio of magnesium oxide:inorganic salt is approximately 0.5:1 to approximately 12:1.

9. The composite material of claim 6 or 7, wherein the molar ratio of magnesium oxide:salt is approximately 0.7:1 to approximately 8:1.

10. The composite material of any preceding claim, wherein the porous adsorbent is selected from the group consisting of zeolites, metal-organic frameworks (MOFs), poroussilicas, porous aluminosilicates, carbonaceous porous materials, or combinations thereof.

11. The composite material of claim 10, wherein the porous adsorbent comprises a zeolite comprising a gravimetric water adsorption capacity of at least approximately 0.05 kg H2O per kg of dry adsorbent at 25°C and >90% relative humidity, and a hydrophilicity corresponding to a Si / AI ratio <2.5.

12. The composite material of claim 10 or 11 wherein the zeolite is selected from the group consisting of Zeolite 13X, Zeolite 4A, Zeolite 5A, Zeolite Y, Zeolite Beta, and ZSM-5.

13. The composite material of any preceding claim, further comprising a hygroscopic salt selected from the group consisting of magnesium chloride and magnesium sulphate, wherein the binder comprises magnesium oxide and a magnesium salt, and wherein the porous adsorbent comprises a zeolite.

14. The composite material of any preceding claim, wherein the porous adsorbent has a specific surface area of at least approximately 50 m2 / g.

15. The composite material of any preceding claim, wherein the binder is present in an amount of approximately 2.5 wt% to approximately 50 wt% of the composite.

16. The composite material of any of claims 2 to 15, wherein the hygroscopic salt is present in an amount of greater than 0 wt% and up to approximately 50 wt%.

17. The composite material of any preceding claim, wherein the porous adsorbent is present in an amount of approximately 20 wt% to approximately 75 wt%.

18. The composite material of any preceding claim, wherein the composite material is in the form of pellets, beads, granules, or extrudates.

19. The composite material of any preceding claim, wherein the composite material exhibits a volumetric energy density of at least approximately 150 kWh / m3, optionally 150- 350 kWh / m3.

20. The composite material of any preceding claim, wherein the composite material exhibits a crush strength of at least approximately 1.5 kgf.

21. The composite material of any preceding claim, wherein the composite material comprises a foamed structure.

22. The composite material of any preceding claim, wherein the composite material is comprises a charging temperature of less than approximately 350°C, optionally between about 60 and 350°C.

23. The composite material of any preceding claim, wherein the composite material retains at least approximately 85% of its initial volumetric energy density after 50 hydration / dehydration cycles.

24. The composite material of any preceding claim comprisinga. a porous adsorbent;b. a hygroscopic salt; andc. a magnesium oxide-based binder,wherein the binder forms a matrix stabilising the hygroscopic salt and porous adsorbent for reversible thermochemical reactions.

25. A method of producing a composite material for thermochemical energy storage, the method comprising:a. providing a porous adsorbent;b. combining the porous adsorbent with a binder comprising magnesium oxide and one or more salts to form a mixture;c. adding a liquid to form a slurry;d. shaping the slurry into a formed body;e. curing the formed body to form a magnesium oxide-based composite material;andf. drying the composite material to produce a thermochemical energy storage material.

26. The method of claim 25 wherein the composite material comprises a composite material as claimed in any of claims 1 to 24.

27. The method of claim 25 or 26, further comprising pre-treating the porous adsorbent by contacting it with a solution comprising one or more hygroscopic salts for an impregnation pre-treatment period, wherein the one or more hygroscopic salts is capable of undergoing a reversible thermochemical cycle comprising an endothermic reaction and an exothermic reaction.

28. The method of any of claims 25 to 27, wherein the liquid to form a slurry comprises a saturated salt solution.

29. The method of any of claims 25 to 28, wherein the formed body comprises pellets or beads, optionally comprising pellets of approximately 1 mm to 10 mm diameter.

30. The method of any of claims 25 to 29, wherein curing is performed at a curing temperature of approximately 15°C to approximately 50°C.

31. The method of any of claims 25 to 30, further comprising impregnating the formed body with a hygroscopic salt solution after curing, optionally wherein the hygroscopic salt comprises at least one of a chloride, sulphate, phosphate, carbonate salt, magnesium chloride and magnesium sulphate,wherein the one or more hygroscopic salts capable of reversible hydration and dehydration.

32. The method of any of claims 25 to 31, further comprising incorporating a foaming agent into the composite material, optionally into the slurry.

33. A thermochemical energy storage system comprising:a. a reactor containing a composite material according to any of claims 1 to 24;andb. a fluid flow system configured to pass air through the reactor;wherein the system is configured to operate in:i. a charging mode in which heated air capable of inducing dehydration is passed through the composite material to induce dehydration; andii. a discharging mode in which humid air is passed through the composite material to induce hydration and release heat.

34. The system of claim 33, wherein the charging mode operates at a charging temperature of approximately 60°C to approximately 350°C.

35. The system of claim 33 or 34, wherein the system further comprises at least one of a fan heater and a heat pump.

36. The system of any of claims 33 to 35 wherein the reactor comprises an open fixed-bed reactor configured to enable airflow through the composite material.

37. The system of any of claims 33 to 36, further comprising a gas humidification unit disposed in the fluid flow system and configured to increase the humidity of an incoming air flow upstream of the reactor during the discharging mode.

38. The system of any of claims 33 to 37, further comprising a condenser disposed in the fluid flow system and configured to remove water vapour from an incoming air flow upstream of the reactor during the charging mode.

39. The system of any of claims 33 to 38, wherein:a. the reactor comprises a housing defining a flow path through the reactor, the composite material being disposed within the flow path such that air passing through the reactor is in contact with the composite material;b. the fluid flow system comprises:i. a first airflow pathway extending from an air inlet, through a heating element, and through the reactor to an air outlet;ii. a second airflow pathway extending from the air inlet, through the reactor to the air outlet; andiii. optionally, a third airflow pathway extending from the air inlet to the air outlet and bypassing the reactor; andc. a control system configured to selectively enable one or more of the airflow pathways, wherein:i. the first airflow pathway corresponds to a charging configuration in which heated air contacts the composite material within the reactor; ii. the second airflow pathway corresponds to a discharging configuration in which air contacts the composite material within the reactor; and iii. the optional third airflow pathway corresponds to a direct heating configuration in which air bypasses the reactor.

40. The system of claim 39, further comprising a plurality of control valves within the fluid flow system, wherein the control system is configured to operate the control valves to selectively enable one or more of the airflow pathways.

41. A method of operating a thermochemical energy storage system comprising:a. passing heated air through a composite material according to any of claims 1 to 24 disposed within a reactor to induce dehydration of the composite material and store thermal energy; andb. passing air comprising water vapour through the composite material to induce hydration of the composite material and release stored thermal energy to the air.

42. The method of claim 41 wherein the system is as claimed in any of claims 33 to 40.

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