Thermoelectric energy harvester comprising inorganic-based alkali-activated materials

Abstract

The present disclosure relates a thermoelectric energy harvester comprising at least one thermoelectric module comprising a plurality of inorganic-based alkali-activated materials connected in series, each of the inorganic-based alkali-activated materials comprises two conductive mesh electrodes, wherein each of the inorganic-based alkali-activated material is configured to generate a Seebeck voltage in response to a temperature gradient established between opposing ends of each inorganic-based alkali-activated material, and wherein the plurality of inorganic-based alkali-activated materials are ionic thermoelectric materials configured to exhibit a capacitance sufficient to store electrical energy generated by the Seebeck voltage. (FIG. 2)

Description

THERMOELECTRIC ENERGY HARVESTER COMPRISING INORGANIC-BASED ALKALI-ACTIVATED MATERIALSRELATED APPLICATION

[0001] This patent application claims the benefit of priority to Singapore patent application no. 10202500814T, filed on 27 March 2025, the contents of which are hereby incorporated by reference in their entirety for all purposes.TECHNICAL FIELD

[0002] The present disclosure generally relates to a thermoelectric energy harvester. In particular, the present disclosure relates to a thermoelectric energy harvester comprising a plurality of inorganic-based alkali-activated materials for harvesting and converting harvested energy into electrical energy.BACKGROUND

[0003] Energy underpins the majority of modern human activities, yet global energy supply remains heavily dependent on fossil fuels. It has been reported that fossil fuels account for approximately 80% of global energy consumption, and the combustion of these fuels is a major contributor to greenhouse gas emissions, including carbon dioxide. Such emissions are widely recognised as a key driver of climate change, global warming, and the imposition of carbon taxation regimes. In addition, the finite nature of fossil fuel resources presents a long-term sustainability challenge.

[0004] Renewable energy technologies such as solar and wind power provide important pathways toward decarbonisation However, there remains significant untapped potential in harvesting energy from ambient and waste sources. Thermoelectric technology offers a direct means of converting heat, including waste heat from industrial processes, geothermal sources, and solar radiation, into electrical energy.

[0005] Conventional thermoelectric devices have primarily relied on semiconductor materials such as bismuth telluride, lead telluride, and silicon-germanium alloys. Such materials are reported to exhibit relatively high thermoelectric performance under certain conditions. However, some conventional thermoelectric materials incorporate elements, such as lead, that may raise environmental and health concerns. In addition, many conventional thermoelectric materials are mechanically brittle, which may limit their suitability for use in structural or harsh environments. Some conventional thermoelectric materials may also be susceptible to corrosion when exposed to moisture or acidic conditions. Furthermore, fabrication of thermoelectric devices based on such materials may involve complex manufacturing processes and the use of scarce or relatively expensive elements, such as tellurium, which can affect scalability and deployment of thermoelectric energy harvesting technologies in large-scale applications.

[0006] In recent years, attention has turned toward alternative materials and architectures that are more abundant, cost-effective, and environmentally benign. Cement-based and construction-material-based systems have attracted interest as multifunctional platforms capable of combining structural performance with energy harvesting function lity. The thermoelectric response of a material is commonly characterised by its Seebeck coefficient, defined as the open-circuit voltage generated per unit temperature difference across the material. Ordinary Portland cement exhibits a relatively low Seebeck coefficient, indicating limited intrinsic thermoelectric capability. Furthermore, ordinary Portland cement is also itself associated with substantial carbon dioxide emissions during production. This has prompted growing interest in looking for other alternatives, as the field lacks a low-carbon, constructionready material that simultaneously delivers high thermopower, structural-grade strength, and straightforward module integration without relying on scarce or toxic semiconductors.

[0007] It is therefore desirable to provide a thermoelectric system that seeks to address at least one of the problems described hereinabove, or at least to provide an alternative solutionSUMMARY

[0008] In accordance with a first aspect of the present disclosure, a thermoelectric energy harvester is provided. The thermoelectric energy harvester comprises at least one thermoelectric module comprising a plurality of inorganic-based alkali-activated materials connected in series, each of the inorganic-based alkali -activated materials comprises two conductive mesh electrodes, wherein each of the inorganic-based alkali-activated material is configured to generate a Seebeck voltage in response to a temperature gradient established between opposing ends of each inorganic-based alkali-activated material, and wherein the plurality of inorganicbased alkali-activated materials are ionic thermoelectric materials configured to exhibit a capacitance sufficient to store electrical energy generated by the Seebeck voltage.

[0009] In some embodiments, the thermoelectric energy harvester comprises two or more of the thermoelectric modules connected in parallel.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various embodiments of the present disclosure are described hereinbelow in the detailed description with reference to the following drawings:FIG. 1 shows a schematic representation of an inorganic-based thermoelectric material with a temperature gradient established between a hot side and an opposing side for the purpose of illustrating the Seebeck effect. Mobile charge carriers migrate within the material in response to the temperature gradient, as indicated by the arrows, thereby contributing to the generation of a Seebeck voltage.FIG. 2 shows a schematic representation of a thermoelectric energy harvester comprising a thermoelectric module comprising a plurality of inorganic-based alkali-activated materials (AAMs) connected in series in accordance with some embodiments of the present disclosure. FIG. 3A shows a schematic representation of two thermoelectric modules arranged in parallel, with each thermoelectric module comprising nine inorganic-based AAMs arranged in series, in accordance with an exemplary embodiment of the present disclosure.FTG. 3B shows a schematic representation of three thermoelectric modules arranged in parallel, with each thermoelectric module comprising nine inorganic-based AAMs arranged in series, in accordance with an exemplary embodiment of the present disclosure.FIG. 4 shows a schematic representation of an experimental setup for measuring Seebeck coefficient of an inorganic-based AAM.FTG. 5A shows a schematic representation of an experimental setup for thermoelectric energy harvesting. The figure illustrates a thermoelectric energy harvester comprising a thermoelectric module comprising nine inorganic-based AAMs connected in series, with each inorganic-based AAM comprising a p-type material. The electrodes of the thermoelectric energy harvester are connected to a multimeter and an external electrical load for measuring electrical output of the thermoelectric moduleFIG. 5B shows an image of a plurality of the inorganic-based AAMs assembled for the experimental setup illustrated in FIG. 5A.FIG. 6 shows a comparison of Seebeck voltage and temperature differences between employing (a) one inorganic-based AAM; and (b) two inorganic-based AAMs connected in series.FIG. 7 illustrates a graph showing illumination of an LED for a duration of 4 seconds after a switch is turned on, using the voltage generated by a thermoelectric module comprising nine cylindrical metakaolin-based AAMs comprising a metakaolin-based geopolymer.FIGs. 8A to 8D illustrate results obtained from thermoelectric energy harvesting by a thermoelectric module comprising nine metakaolin-based AAMs, each containing 0.01 wt.% carbon fiber. FTG. 8A shows a graph of Seebeck voltage as a function of time. FTG. 8B shows Seebeck voltage at an LED illumination start time. FIG. 8C shows Seebeck voltage at an LED illumination mid-time. FIG. 8D shows Seebeck voltage at an LED illumination end time. FIG. 9 is an image illustrating the cracked areas at the bottoms of the cylindrical inorganicbased AAMs.FTG. 10 shows a schematic representation of an experimental setup for estimating capacitance of the inorganic-based AAM.FIG. 11 illustrates a graph showing the Seebeck voltage as a function of time of a thermoelectric energy harvester comprising three thermoelectric modules connected in parallel, with each thermoelectric module comprising nine metakaolin-based AAMs connected in series, after a switch is turned on to illuminate the LED.FIG. 12 is an image illustrating an inorganic-based AAM comprising iron-rich sand for Seebeck coefficient testing.FIG. 13 illustrates a graph showing the Seebeck voltage difference (AV) against the temperature difference (AT) for a single thermoelectric inorganic-based AAMs specimen, each comprising a sodium hydroxide-activated ground granulated blast-furnace slag (GGBS) matrix with iron-rich sand.FIG. 14 illustrates a graph showing Seebeck voltage as a function of time of a thermoelectric module comprising nine GGBS-based AAMs connected in series, after an LED is switched on. FIG. 15 illustrates a graph showing the temperature difference as a function of time of a thermoelectric module comprising nine GGBS-based AAMs connected in series.FIG. 16 illustrates a graph showing the Seebeck voltage as a function of temperature of a thermoelectric module comprising nine GGBS-based AAMs connected in series.FIG. 17 illustrates a graph showing the Seebeck voltage difference as a function of temperature difference of a thermoelectric module comprising nine GGBS-based AAMs connected in series when exposed to high temperature.DESCRIPTION

[0011] The following description sets forth exemplary methods, parameters, and the like. The embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and structural and logical changes may be made without departing from the scope of the invention. The various embodiments are notnecessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0012] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0013] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0014] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e.g. within 10% of the specified value.

[0015] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0016] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0017] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0018] The present disclosure relates to a thermoelectric energy harvester comprising one or more thermoelectric modules, with each thermoelectric modules comprising a plurality of inorganic-based alkali-activated materials (AAMs) for harvesting thermal energy and converting the harvested thermal energy into electrical energy.

[0019] Thermoelectricity refers to the generation of electrical energy when a temperature difference is established between opposing surfaces of a material. The thermoelectric behavior of a material is characterized by three thermoelectric properties, namely the Seebeck coefficient, electrical conductivity, and thermal conductivity. The Seebeck coefficient is defined as the ratio of a voltage difference generated across the material to a temperature difference between two ends of the material, as expressed in the following equation:

[0020] where a is the Seebeck coefficient, Lis the electrical potential (voltage) difference and T is the temperature gradient from hot to cold end of the materaial (J. Li, et al., Construction and Building Materials, 272, 121615, 2021).

[0021] The Seebeck coefficient of a material is a measure of the magnitude of an induced electric voltage in response to a temperature difference across that material, i.e., positive charges (holes, cations) or negative charges (electrons, anions) diffuse inside the thermoelectric material due to temperature difference between the two sides as shown in FIG. 1. For an n-type thermoelectric material 101, electrons or anions are the predominant mobile charges. For a p-type thermoelectric material 102, holes or cations are the predominant mobile charges. As a result, in n-type thermoelectric material 101, a voltage is generated when negative mobile charges 103 accumulate at a colder region 104 relative to a hotter region 105 of the n-type thermoelectric material. In constrast, in p-type thermoelectric material 102, a voltage is generated when positive mobile charges 106 are accumulated at a colder region 107 relative to a hotter region 108 of the p-type thermoelectric material.

[0022] According to a first aspect of the present disclosure, a thermoelectric energy harvester is provided. Referring to FIG. 2, the thermoelectric energy harvester comprises at least one thermoelectric module 201 comprising a plurality of inorganic-based alkali-activated materials 202 connected in series, each of the inorganic-based al kali -activated materialscomprises two conductive mesh electrodes (203(a), 203(b)), wherein each of the inorganicbased alkali-activated material is configured to generate a Seebeck voltage in response to a temperature gradient established between opposing ends of each inorganic-based alkali-activated material, and wherein the plurality of inorganic-based alkali-activated materials are ionic thermoelectric materials configured to exhibit a capacitance sufficient to store electrical energy generated by the Seebeck voltage.

[0023] In some embodiments, the thermoelectric energy harvester comprises two or more of the thermoelectric modules connected in parallel. FIG. 3A illustrates an exemplary embodiment comprising two thermoelectric modules 301 connected in parallel, with each thermoelectric module comprising nine inorganic-based alkali-activated materials 302 connected in series. FIG. 3B illustrates another exemplary embodiment comprising three thermoelectric modules 301 connected in parallel, with each thermoelectric module comprising nine inorganic-based alkali-activated materials 302 connected in series. The arrangements illustrated in FIG. 3A and FIG. 3B are provided for illustrative purposes only and are not intended to be limiting. The thermoelectric module may comprise any suitable number of inorganic-based al kali -activated materials connected in any appropriate configuration but in series arrangement. The number of inorganic-based alkali-activated materials within the thennoelectric module may be selected according to the desired voltage, current, power output, or application requirements, without departing from the scope of the present disclosure.

[0024] In various embodiments, the inorganic-based alkali-activated materials connected in series generate a higher Seebeck voltage than inorganic-based al kali -activated materials connected in parallel. In such configurations, the Seebeck voltage generated may be sufficient to power an electrical load, such as a light-emitting diode (LED) In various embodiments, the thermoelectric modules connected in parallel exhibit a higher capacitance than thermoelectric modules connected in series. The increased capacitance enables the thermoelectric modules tostore a greater amount of energy generated by the Seebeck effect, which may allow operation of a connected electrical load over a longer duration.

[0025] As used herein, the term “inorganic-based alkali-activated material”, referred herein as “inorganic-based AAM”, is an inorganic, amorphous to semi-crystalline material and the structure consists of three-dimensional (3D) polymeric Si-O-Al-O linkages. In some embodiments, in order to form 3D polymeric structures, alkali metal salt and hydroxide are required as activators for the dissolution of Si and Al to proceed.

[0026] In various embodiments, the inorganic-based al kali -activated material is derived from one or more aluminosilicate precursor materials selected from metakaolin, fly ash, and ground granulated blast-furnace slag (GGBS). Upon alkali activation, each of these precursor materials gives rise to aluminosilicate structures containing Si-O-Al-O linkages In nonlimiting examples, the inorganic-based alkali-activated materials derived therefrom include a metakaolin-based geopolymer, a fly ash-based geopolymer, and an alkali-activated GGBS matrix, such as a sodium hydroxide activated GGBS matrix.

[0027] In various embodiments, the inorganic-based alkali-activated material is formed from one or more aluminosilicate precursor materials and an alkali activator.

[0028] In various embodiments, the alkali activator comprises an alkali metal salt and a hydroxide or a sodium-based alkali solution. In some embodiments, the alkali activator comprises sodium silicate and sodium hydroxide. The alkali activator may be prepared by mixing sodium hydroxide with a solution containing sodium silicate to form an alkaline sodium silicate solution. In other embodiments, the alkali activator may comprise only sodium hydroxide. The sodium hydroxide may be mixed with other precursor materials for alkali activation.

[0029] The metakaolin used for the preparation of the metakaolin-based geopolymer is a thermally activated, amorphous aluminosilicate derived from kaolin. The metakaolin comprises silicon- and aluminium-containing phases, primarily in the form of disordered silicate (Si-O)and aluminate (Al-O) structural units. In oxide notation, metakaolin typically comprises silica (Si O2) and alumina (AI2O3) as its major constituents. Depending on the source of the kaolin and the thermally activated conditions, the metakaolin may further comprise minor amounts of oxides such as iron oxide (Fe20s), titanium dioxide (TiCh), calcium oxide (CaO), magnesium oxide (MgO), and alkali metal oxides. The relative proportions of these components may vary between different grades of metakaolin without departing from the scope of the present disclosure.

[0030] Fly ash is a fine particulate by-product generated from the combustion of coal, comprising mainly silica (Si O2) and alumina (AI2O3), with lesser amounts of iron oxide (Fe20s) and calcium oxide (CaO) (varies depending on the class of CaO), and with minor amounts of other oxides such as magnesium oxide (MgO), titanium dioxide (TiO2), and alkali metal oxides. The relative proportions of these components may vary between different grades and classes of fly ash without departing from the scope of the present disclosure.

[0031] In some embodiments, the inorganic-based alkali-activated material is selected from a metakaolin-based geopolymer and a fly ash-based geopolymer. In an exemplary embodiment comprising a metakaolin-based geopolymer, the inorganic-based alkali-activated material is prepared by mixing metakaolin with an alkali activator such as an alkaline sodium silicate solution, followed by curing the mixture to induce geopolymerisation, thereby forming the inorganic-based alkali-activated material.

[0032] Ground granulated blast-furnace slag (GGBS) is a cementitious by-product of the iron-making process It comprises mainly calcium oxide (CaO), silica (SiO2) and alumina (AI2O3), with minor amounts of other oxides such as magnesium oxide (MgO), iron oxide (Fe2O3), titanium dioxide (TiO2), sulfur trioxide (SO3), manganese (II) oxide (MnO), and alkali metal oxides. The relative proportions of these components may vary between different grades of GGBS without departing from the scope of the present disclosure.

[0033] n some embodiments, the inorganic-based alkali-activated material comprises a sodium hydroxide-activated GGBS matrix. The sodium hydroxide-activated GGBS matrix comprises a copper slag sand (CSS) as a sole aggregate, a GGBS, and an alkali activator comprising sodium hydroxide. In an exemplary embodiment, the inorganic-based alkali-activated material is prepared by mixing GGBS with the copper slag sand and sodium hydroxide solution, followed by curing the mixture to form the inorganic-based al kali -activated material.

[0034] In some embodiments, the inorganic-based alkali-activated material further comprises carbon fiber. The carbon fiber is present in an amount of up to 0.01 wt.% based on the total weight of the inorganic-based alkali activated material. In some embodiments, the inorganic-based alkali-activated material comprising the carbon fiber has a Seebeck coefficient of about 167% higher than the Seebeck coefficient of an inorganic-based alkali-activated material that does not contain any carbon fiber.

[0035] The inorganic-based alkali-activated material described herein may be formed, shaped, or processed into a variety of physical forms depending on the intended application. By way of non-limiting example, the material may be cast, molded, extruded, pressed, or otherwise shaped into bulk bodies such as cylindrical bodies, blocks, plates, tiles, pellets, or rods, etc. The material may also be formed as a monolithic body or as an assembly comprising a plurality of elements arranged in series. The shape, size, and configuration of the material are not particularly limited and may be selected according to functional, structural, or performance requirements. When assembled into a thermoelectric module, the plurality of inorganic-based al kali -activated materials may be the same or different, and their size, shape and orientation may be varied as appropriate.

[0036] The forming, shaping, or processing steps described above may be carried out prior to curing, after curing, or at least partly during curing of the inorganic-based alkali-activated material, depending on the intended form and application.

[0037] Tn some embodiments, the inorganic-based al kali -activated material is cylindrical in shape as shown in FIG. 4. The cylindrical inorganic-based alkali-activated material 400 may have any suitable height and diameter. In some embodiments, the cylindrical inorganic-based alkali-activated material has a height in the range from 40 to 50 mm, and in some embodiments, a height of about 45 mm. In some embodiments, the cylindrical inorganic-based alkali-activated material has a diameter in the range from 24 to 26 mm, and in some embodiments, a diameter of about 25.4 mm.

[0038] In various embodiments, the inorganic-based alkali-activated material comprises a monolithic body. The two conductive mesh electrodes may be embedded within the monolithic body, disposed on a surface of the monolithic body, partially embedded within the monolithic body, or arranged at an interface between the monolithic body and another component The positions of the two conductive mesh electrodes within the monolithic body are not particularly limited, as long as they are located at opposing regions, or at any other suitable locations to allow a temperature gradient to be established to generate a Seebeck voltage. In some embodiments, the two conductive mesh electrodes extend partially or fully through the monolithic body of the inorganic-based al kali -activated material

[0039] FIG. 4 illustrates an experimental setup for Seebeck coefficient measurement. The figure also illustrates an exemplary configuration of the two conductive mesh electrodes. In FIG. 4, the inorganic-based alkali-activated material 400 comprises a monolithic body 401, a first electrode 402 and a second electrode 403. The first electrode 402 is embedded at a top end 404 of the monolithic body 401, whereas the second electrode 403 is embedded at a bottom end 405 of the monolithic body 401. In some embodiments, the two conductive mesh electrodes are embedded in the respective locations by placing the two conductive mesh electrodes in a mould and cured together with the mixture forming the inorganic-based alkali-activated material. The two embedded conductive mesh electrodes are configured to be connected to a multimeter 406 to determine voltage generated by the inorganic-based alkali-activated material. The twoconductive mesh electrodes may each comprise a conductive mesh formed from steel, copper, carbon or other electrically conductive materials.

[0040] In some embodiments, the inorganic-based alkali-activated material further comprises two K-type thermocouples (406(a), 406(b)) configured to measure temperatures of the inorganic-based alkali-activated material. A first K-type thermocouple 406(a) of the two K-type thermocouples is embedded at the top end 404 of the monolithic body 401, and a second K-type thermocouple 406(b) of the two K-type thermocouples is embedded at the bottom end 405 of the monolithic body 401. The two K-type thermocouples are configured to be connected to a thermocouple input module 407.

[0041] In various embodiments, the inorganic-based alkali-activated material comprises p-type materials. As described above, in p-type materials, temperature gradient causes positively charged mobile carriers to accumulate at the colder region and generates a voltage.

[0042] FIG. 5A illustrates an exemplary embodiment of a thermoelectric module 500 comprising nine inorganic-based alkali-activated materials 400 connected in series, with each inorganic-based alkali-activated material comprising a p-type material. In various embodiments, the inorganic-based alkali-activated materials are heated and as the heating progresses, a temperature difference or temperature gradient is created between the top end 404 and the bottom end 405 of the monolithic body 401 of the inorganic-based alkali-activated material 400, causing positively charged mobile carriers 501 to accumulate at colder region at the top end 404 of the inorganic-based alkali-activated material 400 to generate a voltage. The voltage generated by the thermoelectric module 500 is measured using a multimeter 406, connected to the thermoelectric module via the first electrode 402 and the second electrode 403. An electrical load 502, such as an LED, may also be connected to the thermoelectric module, as illustrated in FIG. 5A.

[0043] In some embodiments, when the temperature gradient reaches a specified temperature, for example, 15 °C, heating stops. As the inorganic-based alkali-activated materialcools down naturally, positively charged mobile carriers 501 move to and accumulate at the colder region at the top end 404 of the inorganic-based alkali-activated material 400, thereby generating a Seebeck voltage.

[0044] In various embodiments, the plurality of inorganic-based alkali-activated materials connected in series are capable of generating a Seebeck voltage in the range from 1.8 V to 2.3 V In some embodiments, the plurality of inorganic-based alkali-activated materials connected in series is configured such that the Seebeck voltage of the thermoelectric module increases with the number of inorganic-based alkali-activated materials employed in the thermoelectric module. The number of inorganic-based alkali-activated materials employed in a thermoelectric module may vary depending on the intended application. In some embodiments, 9 or more inorganic-based alkali-activated materials are employed per thermoelectric module

[0045] In various embodiments, the plurality of inorganic-based alkali-activated materials are p-type materials, each having a Seebeck coefficient of 1600 pV / °C, or in the range from 1600 uV / °C to 3013 pV / °C, or about 3013 pV / °C. In some embodiments, the plurality of inorganic-based alkali-activated materials comprise metakaolin-based alkali-activated materials, each having a Seebeck coefficient of 1600 pV / °C. In other embodiments, the plurality of inorganic-based alkali-activated materials comprise iron-rich sand alkali-activated materials, each having a Seebeck coefficient of 3013 pV / °C. In some embodiments, the thermoelectric module may comprise a plurality of inorganic-based alkali-activated materials comprising one or more p-type materials and one or more n-type materials.

[0046] In various embodiments, the two or more thermoelectric modules connected in parallel, comprising the plurality of inorganic-based alkali-activated materials connected in series, are configured to act as a capacitor for storing harvested energy. When connected in parallel, the capcitance of the thermoelectric modules increases and the thermoelectric modules are able to store more energy and have a longer operating time. The stored energy converts toelectrical energy and is able to light up an electrical load, such as an LED. The LED becomes brighter when more thermoelectric modules are connected in parallel.

[0047] The thermoelectric energy harvester of the present disclosure may be used in applications where energy harvesting and direct conversion of the harvested energy are desired. The configurations described herein provide a thermoelectric energy harvester configured to harvest thermal energy and convert the thermal energy into electrical energy through a thermoelectric module comprising a plurality of inorganic-based alkali-activated materials. The thermoelectric module operates based on the Seebeck effect. The arrangement of the plurality of inorganic-based alkali-activated materials in series increases the Seebeck voltage of the thermoelectric energy harvester, allowing the thermoelectric energy harvester to have sufficient Seebeck voltage to light up an electrical load, such as an LED. The arrangement of two or more thermoelectric modules in parallel increases the capacitance of the thermoelectric energy harvester. The increased capacitance may be sufficient to store electrical energy generated via the Seebeck effect and may enable operation of a connected electrical load over a longer duration.

[0048] Target applications of the thermoelectric energy harvester of the present disclosure may include self-powered sensing in bridges and pipelines, industrial waste-heat recovery on ducts and process lines, LTV AC loops in buildings, and distributed loT nodes. Products may include, but not limited to, precast tiles or pucks with embedded electrodes and inorganic-based AAMs connected in series packaged with power conditioning and supercapacitor storage.

[0049] The present disclosure enables low material cost, cementitious thermoelectric elements and modules for harvesting low-grade heat while serving as structural components, compatibility with conventional concrete production, durability in harsh environments, scalable as the voltage can be increased by cell count and by thermal management rather than extreme temperatures, and sustainable as sustainable aggregate such as copper slag is used, which fully replaces natural sand, reducing landfilling and easing sand scarcity.

[0050] Other advantages compared to commonly used metal-based thermoelectric materials include: Firstly, the raw materials and inorganic-based alkali-activated materials itself are harmless to the environment. Secondly, the raw materials are widely available than metal -based thermoelectric materials. Additionally, the inorganic-based alkali-activated materials are simple to fabricate, use standard concrete equipment and sealed ambient curing, and enable large-scale production possibilities. Also, the the inorganic-based al kali -activated materials are environmentally friendly as they use less cement, thus support significant CO2 reduction relative to Ordinary Portland cement binders. The inorganic-based alkali-activated materials of the present disclosure serves as potential alternatives to OPC. In addition, the thermoelectric module is easy to assemble as the embedded conductive mesh electrodes enable direct series or parallel connection into modules. In addition, the present disclosure provides operational insights in that it identifies polarity inversion window (about 30 °C to 44 °C), which is useful for thermal sensing and control.

[0051] To facilitate a better understanding of the present disclosure, the following examples of specific embodiments are given. In no way should the following examples be read to limit or define the entire scope of the disclosure. One skilled in the art will recognize that the examples set out below are not an exhaustive list of the embodiments of this disclosure.EXAMPLESExample 1

[0052] Preparation of an inorganic-based alkali-activated material comprising a metakaolinbased geopolymer

[0053] An inorganic-based alkali -activated material (AAM) comprising a metakaolin-based geopolymer was prepared in this example.

[0054] Metakaolin was commercially available and used as received. The chemical composition of the metakaolin is shown in Table 1.

[0055] Table 1: Chemical composition of Metakaolin (by wt. %).ChemicalS1O2 A12O3TiO2Fe2O3Na20 K,0 MgO P2O5SO3CaO Lol compositionPercent (%) 53.0 43.8 1.70 0.43 0.23 0.19 0.03 0.03 0.03 0.02 0.46

[0056] As can be seen, silicon dioxide (SiO2), aluminum oxide (AI2O3) and titanium dioxide (TiO2) account for the largest proportions of metakaolin, at 53.0 wt.%, 43.8 wt.% and 1.7 wt.%, respectively. Sodium silicate (NaSiCL) solution and sodium hydroxide (NaOH) pellets were obtained from a commercial source. The composition of the metakaolin-based geopolymer by mass ratio and molar ratio of the elements are shown in Table 2.

[0057] Table 2: Composition of metakaolin-based geopolymer and molar ratio of the elements.

[0058] The inorganic-based AAM comprising a metakaolin-based geopolymer was prepared by first dissolving sodium hydroxide pellets in ultrapure water before mixing with a sodium silicate solution to form an alkali activator. Metakaolin and the alkali activator were then mixed to form a metakaolin-based geopolymer material. The metakaolin-based geopolymer material was mixed in a mixer (KMM040) for about 10 mins. The mixture was then poured into a cylindrical mould (25.4 mm (D) x 45mm (H)) with two conductive meshes formed from steel and two K-type thermocouples. One conductive mesh and one K-type thermocouple were placed at a top end of the cylindrical mould, while the other conductive mesh and the other K- type thermocouple were placed at a bottom end of the cylindrical mould, as shown in FIG. 4.The mixture in the cylindrical mould was cured in a lab environment (at a temperature of 23 ± 2 °C, and RH at 64 ± 3%) for 7 days after casting, before further tests and examinations were carried out. A cylindrical inorganic-based AAM was formed, with conductive mesh electrodes embedded therein.

[0059] Tn some samples, carbon fiber (L: 12 mm, D: 7 pm) of about 0.01 wt.% was added to the metakaolin-based geopolymer material to form an inorganic-based AAM containing carbon fiber.Example 2

[0060] Seebeck Coefficient of the inorganic-based alkali-activated material comprising a metakaolin-based geopolymer

[0061] FIG. 4 illustrates the test setup used to measure the Seebeck coefficient of the cylindrical inorganic-based AAM prepared in Example 1.

[0062] Each inorganic-based AAM was placed on a hot plate and heated at a bottom end (the hot side) at a rate of 0.02 °C / s, while a top end (the cold side) was exposed to room temperature at 24 ± 1 °C. When a temperature difference of approximately 15 °C was established between the hot side and the cold side, heating was stopped and the inorganic-based AAM was allowed to cool naturally. The two embedded conductive mesh electrodes formed from steel were connected to a digital multimeter, such as Keithley, DMM6500 to determine the voltage generated. The electrode at the top end (the cold side) was electrically connected to a positive terminal of the multimeter, and the electrode at the bottom end (the hot side) was electrically connected to a negative terminal of the multimeter. The temperatures at the top end and the bottom end were measured by connecting the two embedded K-type thermocouples to a thermocouple input module (National Instruments-9212) to establish a temperature gradient between the opposing ends.

[0063] The Seebeck coefficient of a single p-type inorganic-based AAM was measured to be around 1600 pV / °C. When two inorganic-based AAMs were connected in series, the Seebeck coefficient of the two inorganic-based AAMs was around 2200 pV / °C, as shown in Table 3.

[0064] Table 3: The Seebeck coefficients of a single inorganic-based AAM and two inorganic-based AAMs connected in series.

[0065] FIG. 6 illustrates a comparison of Seebeck voltage and temperature difference for configurations employing (a) one inorganic-based AAM; and (b) two inorganic-based AAMs connected in series. The results show that when the temperature difference for a single inorganic-based AAM was at 22.2 °C, the Seebeck voltage of the inorganic-based AAM was around 0.034 V. For two inorganic-based AAMs connected in series, the Seebeck voltage was around 0.056 V when the temperature difference was at 21.5 °C.Example 3

[0066] Electrical load illumination using a thermoelectric module

[0067] FIG. 5A illustrates a test setup for measuring the Seebeck coefficient of a thermoelectric module comprising nine cylindrical inorganic-based AAMs prepared in accordance with Example 1. FIG. 5B shows an image of a plurality of the inorganic-based AAMs assembled for the experimental setup illustrated in FIG. 5A.

[0068] For this lab setup, crocodile clips were used to connect the cylindrical inorganicbased AAMs from one cylindrical inorganic-based AAM to another, connecting them in series. Thereafter, all the nine cylindrical inorganic-based AAMs were placed on a hot plate and were heated at the bottom ends (the hot side) of the cylindrical inorganic-based AAMs, at a rate of 0.06 °C / s. The top ends (the cold sides) of all the nine cylindrical inorganic-based AAMs were exposed to room temperature at 24 ± 1 °C. The Seebeck voltage generated from the module was monitored until it exceeded 2 V.

[0069] The Seebeck voltage generated by the thermoelectric module comprising the nine cylindrical inorganic-based AAMs was determined using a digital multimeter. This was performed by connecting a top (cold side) electrode of the first cylindrical inorganic-basedAAM to the positive terminal of the multimeter and connecting a bottom (hot side) electrode of the last (or the 9th) cylindrical inorganic-based AAM to the negative terminal of the multimeter An LED was electrically connected acorss the electrical pathway of the thermoelectric module via its terminals, and a switch was provided in series to selectively complete the circuit. The switch was actuated, and upon generation of a sufficient Seebeck voltage by the thermoelectric module, the LED was illuminated.

[0070] Heating by the hot plate established a temperature difference between the top end and the bottom end of the cylindrical inorganic-based AAMs, resulting in generation of a Seebeck voltage. The Seebeck voltage generated by the cylindrical inorganic-based AAMs comprising the metakaolin-based geopolymer materials was measured to be approximately 2.3 V As more heat was applied to the cylindrical inorganic-based AAMs by the hot plate, an increase in the Seebeck voltage was observed. When a 3 mm red LED was emplopyed, the input voltage and input current were 1.8 to 2.2 V and 20 mA, respectively. FIG. 7 shows that the LED illuminated for 4 seconds by the Seebeck voltage generated by the cylindrical inorganic-based AAMs after the switch was actuated.

[0071] In another experiment, carbon fiber was added to the metakaolin-based geopolymer materials. About 0.01 wt.% of carbon fiber was added and the Seebeck voltage generated by nine cylindrical inorganic-based AAMs comprising metakaolin-based geopolymer materials and connected in series was measured. A Seebeck voltage of approximately 2.2 V was measured, and illumination of an LED was observed for a duration of about 5 minutes.

[0072] When the LED illuminated, the voltage remained constant at 1.5 V, as shown in FIG.8B. During continuous LED operation, the voltage fluctuated slightly, as seen in FIG. 8C. When the voltage dropped to 1.3 V, illumination of the LED ceased, as shown in FIG 8D. The heat from the hot plate caused cracks at the bottom end of the cylindrical inorganic-based AAMs, as shown in FIG. 9, leading to voltage fluctuations.

[0073] The intermittent illumination of the LED when used with the inorganic-based AAMs is attributable to the ionic thermoelectric behaviour of the materials. Ionic thermoelectric materials exhibit capacitive characteristics associated with charge accumulation and release. As a result, the energy harvested by the thermoelectric module may be temporarily stored and subsequently discharged. When the thermoelectric module is electrically connected to the LED and a switch is actuated, stored energy in the thermoelectric module is released to power the LED, resulting in illumination. Upon depletion of the stored energy, illumination of the LED ceases.

[0074] The relationship between a high Seebeck coefficient and low electrical conductivity in ionic thermoelectric systems has been discussed inMassetti (Massetti, M., etal., Chem. Rev.121 (20): 12465-12547, 2021) and Wu (Wu, X , etal., Chem. Asian J, 16(2): 129-141, 2021). A comparison between the inorganic-based AAMs with a high Seebeck coefficient and low electrical conductivity, and an electronic-based thermoelectricity was conducted.Example 4

[0075] Capacitance of the inorganic-based alkali-activated material comprising a metakaolin-based geopolymer

[0076] Capacitance can be identified through the relation between time constant (T) and resistance, r = RC In the ionic thermoelectric system of the present disclosure, the capacitance was determined from the measured time constant, which was obtained by connecting the inorganic-based AAMs in series with an external resistor.

[0077] FIG. 10 is a schematic representation showing an example of an experimental setup for measuring capacitance of the inorganic-based AAMs. The setup comprises a hot plate 1001, a multimeter 1002 and a resistor at 470 1003. A single unit of a thermoelectric module 1004 comprising metakaolin-based geopolymer as the inorganic-based AAMs was placed on the hot plate 1001 and connected to the resistor at 470 Q 1003 and the multimeter 1002 for measuring the Seebeck voltage when the hot plate increased its heat at a rate of 0.02 °C / s. When theSeebeck voltage reached around 0.1 V, discharging of the Seebeck voltage through the resistor at 470 was monitored, and the capacitance of the thermoelectric module was determined based on the voltage-time response. The capacitances of thermoelectric energy harvesters comprising two and three thermoelectric modules connected in series and in parallel were determined in a similar manner. The results are as shown in Table 4.

[0078] Table 4: Capacitances of thermoelectric energy harvesters comprising one, two and three thermoelectric modules connected in series and in parallel.Sample Capacitance (pF)1 sample 232±572 samples 111±1Senes3 samples 77±162 samples 466±11Parallel3 samples 710±9

[0079] In Table 4, the capacitance of one thermoelectric module was 232 pF but when two or three thermoelectric modules were connected in series, the capacitance decreased to 111 pF and 77 pF, respectively. This is because the depth is higher when the thermoelectric modules were connected in series. In the capacitance equation, depth is also inversely proportional, C oc A / d. However, when the thermoelectric modules were connected in parallel, the capacitance increased to 466 pF and 710 pF, respectively. This is because the area is higher when the thermoelectric modules were connected in parallel and in the capacitance equation, area is also directly proportional, C oc A / d.

[0080] The results in Table 4 demonstrate that when two or three thermoelectric modules, comprising nine inorganic-based AAMs connected in series, were connected in parallel, capacitance of the thermoelectric energy harvester increases. The Seebeck voltage of the inorganic-based AAMs connected in parallel with two modules and three modules was 2.11 V and 2.12 V, respectively.Example 5

[0081] Electrical load illumination using two or three parallel thermoelectric modules on inorganic-based AAMs comprising a metakaolin-based geopolymer

[0082] Tests were conducted to evaluate the ability of the thermoelectric module to illuminate an electrical load, such as an LED.

[0083] An LED and a switch were electrically connected to the setup of FIG. 3A and 3B.The switch was actuated, and the duration for which the LED remained illuminated was monitored. The results indicate that the LED exhibited increased brightness when two thennoelectric modules were connected in parallel, although the overall brightness remained limited. The results further indicate that the LED exhibited increased brightness when three thermoelectric modules were connected in parallel, as compared to two thermoelectric modules connected in parallel. Additionally, the LED remained bright for a longer duration compared to two thermoelectric modules connected in parallel. Although it was less bright, it stayed illuminated for more than 4 minutes and 20 seconds. The voltage remained constant at approximately 1.5 V during the period in which the LED was illuminated, as shown in FIG. 11.

[0084] Further tests were conducted to evaluate the ability of three thermoelectric modules connected in parallel to illuminate a plurality of LEDs, including configurations comprising two LEDs, three LEDs, and four LEDs. The results show that the three thermoelectric modules connected in parallel, comprising nine metakaolin-based AAMs connected in series, are able to illuminate two LEDs, three LEDs, as well as four LEDs. However, as more LEDs were added, the brightness of the LEDs decreased, and the duration in which the LEDs remained illuminated became shorter. The two LEDs, three LEDs, and four LEDs were illuminated for 4, 2, and 1 seconds, respectively.

[0085] The tests as described herein demonstrate that the inorganic-based AAMs of the present disclosure can harvest energy using LEDs and the feasibility and efficacy were proven in the above examples. From Table 3 and FIGs. 6A, 6B, connecting a plurality of inorganicbased AAMs in series resulted in a higher Seebeck voltage of the thermoelectric module, whichraised the Seebeck voltage of the thermoelectric module above the input voltage of the LED (1.8 to 2.2 V), illuminating the LED. The tests also demonstrate that inorganic-based AAMs can store energy with a capacitance equal to A / d. When the thermoelectric modules are connected in parallel, the inorganic-based AAMs connected in series will store more energy and have a longer operating time.Example 6

[0086] Preparation of an inorganic-based alkali-activated material comprising a ground granulated blast-furnace slag (0068)

[0087] A ground granulated blast-furnace slag (GGBS) was used as the sole binder in this experiment and was obtained from a commercial source. Bulk oxide composition contained in the GGBS was determined by X-ray fluorescence using a Bruker S8 TIGER spectrometer and the results are as shown in Table 5. Particle size distribution of the GGBS, measured by laser diffraction with an Anton Paar PSA 1190 in liquid dispersion mode, yielded a median particle size (D50) of 10.86 pm and a 90tll-percentile size (D90) of 26.81 pm.

[0088] A copper slag sand (CSS) was used as the aggregate, with a maximum particle size of below 0.6 mm. The CSS was obtained from a commercial source Its oxide composition is summarized in Table 5. The CSS has an iron oxide (Fe Os) content of 93.95 wt.%.

[0089] Table 5: Oxide composition of GGBS and CSS

[0090] Table 6 shows the mixture proportion of the inorganic-based AAM. The activating solution was sodium hydroxide in solution form (50 wt.% NaOH and 50 wt.% H2O), obtained from a commercial source. Copper slag is capable of alkali activation; however, due to its low reactivity in unground form, it was treated as sand (filler) in this example.

[0091] Table 6: Mixture proportion of an inorganic-based AAM comprising the ground granulated blast-furnace slag (GGBS)

[0092] The inorganic-based AAM comprising the ground granulated blast-furnace slag (GGBS) was prepared by mixing GGBS, CSS, sodium hydroxide solution and water in a planetary mixer (Kenwood KMM040) for 5 minutes at a low speed, followed by 3 minutes at medium speed to achieve casting workability. The sodium hydroxide solution was prepared one day in advance by mixing NaOH with water. The fresh mixture was cast into cylindrical moulds (25.4 mm diameter 45 mm height), with two conductive mesh electrodes formed from steel and two K-type thermocouples embedded at the top end and the bottom end (FIG. 12) of the inorganic-based AAMs for thermoelectric characterization of the Seebeck coefficient. For mechanical testing, 50 mm cube samples were cast for compressive strength. All the samples were sealed in bags to prevent moisture loss and cured at 24 ± 2 °C until testing at 28 days.

[0093] Compressive strength was tested using a Recherches & Realisations REMY testing machine in load-controlled mode at a rate of 90 kN / min. The reported values are the average of three specimens.

[0094] The Seebeck coefficient of the cylindrical GGBS-based AAM was measured using a procedure similar to that described in Example 2. Firstly, the cylindrical GGBS-based AAM was placed on a hot plate and heated from the bottom end (hot side) at a rate of 0.02 °C / s, while the top end (cold side) was exposed to ambient condition at 24 ± 1 °C. Once the end-to-end temperature difference (AT) reached about 15 °C, heating was stopped and the mixture was allowed to cool naturally; during the ensuing transient, AT increased to approximately 20 °C before decaying. The two embedded conductive mesh electrodes were connected to a multimeter to record the Seebeck voltage, with the top (cold-side) electrode connected to the positive terminal and the bottom (hot-side) electrode connected to the negative terminal.T emperatures at both ends were measured using embedded K-type thermocouples interfaced to a National Instruments NI-9212 thermocouple input module. The cylindrical GGBS-based AAMs were tested three times and average value was reported.

[0095] Results

[0096] FIG. 13 illustrates a graph showing the voltage difference (AV) against the temperature difference (AT) for the GGBS-based AAM sample. The Seebeck coefficient was obtained from the slope of the AV-AT relation (AV / AT). The mean Seebeck coefficient was 3013 pV / °C with a standard deviation of 451 pV / °C (equivalently, piV / K . This value is substantially higher than those reported for most cementitious systems. The elevated Seebeck coefficient response is attributed to coupled ionic and electronic transport within the GGBS-based AAM The alkaline pore solution provides mobile cations like Na+and anions like OI 1 that develop concentration gradients under AT with the pore network of GGBS-based AAM, contributing an ionic Seebeck component. In parallel, the iron-oxide-rich copper slag aggregate supplies electronic carriers through the matrix.

[0097] The compressive strength was observed to be 36.5 MPa with a standard deviation of 1.7 MPa, which indicates adequate mechanical integrity.

[0098] A test was conducted to evaluate the ability of the GGBS-based AAMs in illuminating a 3 mm red LED. Firstly, nine cylindrical GGBS-based AAMs were wired in series using crocodile clips, forming a thermoelectric module. Polarity was kept consistent such that the Seebeck voltages generated by the thermoelectric module added up, with the top electrode at the cold side connected to the positive terminal and the bottom electrode at the hot side connected to the negative terminal. The thermoelectric module comprising the GGBS-based AAMs connected in series was placed on a digital hot plate and was heated from the bottom end at a rate of 0.04 °C / s, while the top end remained at 24 ± 1 °C. The Seebeck voltage generated was monitored using a digital multimeter, such as a Keithley DMM6500, and a switch connected in series with an LED was actuated when the open-circuit voltage reached a sufficientlevel. As the temperature gradient developed, the thermoelectric module produced a voltage of about 2.2 V, which was sufficient to illuminate the LED (forward voltage 1.8 to 2.2 V; rated current at 20 mA), and the LED remained illuminated for approximately 16 minutes after switching on (FIG. 14).

[0099] The series module demonstration illustrates the feasibility and scalability for thermoelectric energy harvesting: nine cylindrical GGBS-based AAMs connected in series produced approximately 2.2 V, but only at an end-to-end AT of more than 166 °C (FIG. 15), with hot-side temperatures of more than 230 °C, causing surface cracking on hot side (FIG. 16).FIG. 16 shows the variation of Seebeck voltage with temperature difference of series module demonstration. During the initial increase in Seebeck voltage, the Seebeck coefficient was determined to be 33.9 mV / °C. As the voltage decreased, the coefficient changed to -50.8 mV / °C, and in the subsequent decreasing stage, it further reached -68.7 mV / °C. High-temperature characterization of the single cylindrical GGBS-based AAM showed a polarity inversion, with p-type behavior at low gradients (AT less than about 30 °C) transitioning to n-type beyond a turning point of 30 to 40 °C (FIG. 17), and average Seebeck coefficients of +2544 ± 285 Mv / °C, -12056 ± 9 pV / °C, and -2924 ± 41 pV / °C across the respective AT segments (Table 7). Together, these findings establish functional viability, define a practical operating window, and indicate clear paths to deployment: scale voltage by increasing cell count rather than temperature, adopt thermal management to utilize lower heat.

[0100] Table 7: Average Seebeck coefficient for GGBS-based AAM after exposure to high temperature.

[0101] The thermoelectric module of the present disclosure achieves millivolt-per-kelvin Seebeck performance (approximately 3.0 mV / K) alongside structural integrity (approximately 36.5 MPa at 28 days), does so without graphene / CNTs or exotic semiconductors, identifies a carrier-type inversion window (approximately 30 °C to 44 °C) useful for sensing and control, and demonstrates a series-connected cementitious module that powers an LED, thereby establishing a validated and scalable pathway for thermoelectric energy harvesting.

[0102] Although embodiments of the invention have been shown and described, the invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that various modifications and variations can be made to the embodiments of the invention without departing from the scope of the invention, the scoop of which is set forth in the following claims.

Claims

Claims:

1. A thermoelectric energy harvester comprising:at least one thermoelectric module comprising a plurality of inorganic-based alkali-activated materials connected in series, each of the inorganic-based alkali -activated materials comprises two conductive mesh electrodes,wherein each of the inorganic-based alkali-activated material is configured to generate a Seebeck voltage in response to a temperature gradient established between opposing ends of each inorganic-based alkali-activated material, andwherein the plurality of inorganic-based alkali-activated materials are ionic thermoelectric materials configured to exhibit a capacitance sufficient to store electrical energy generated by the Seebeck voltage.

2. The thermoelectric energy harvester of claim 1, wherein the thermoelectric energy harvester comprises two or more of the thermoelectric modules connected in parallel.

3. The thermoelectric energy harvester of claim 1 or 2, wherein each of the inorganicbased alkali-activated materials is selected from the group consisting of metakaolin-based geopolymer and a fly ash-based geopolymer.

4. The thermoelectric energy harvester of claim 3, wherein the metakaolin-based geopolymer comprises a metakaolin and an alkali activator, wherein the alkali activator comprises an alkaline sodium silicate solution.

5. The thermoelectric energy harvester of claim 1, wherein each of the inorganic-based alkali-activated materials comprises a sodium hydroxide-activated ground granulated blastfurnace slag matrix6. The thermoelectric energy harvester of claim 5, wherein the sodium hydroxide-activated ground granulated blast-furnace slag matrix comprises a copper slag sand as a sole aggregate, a ground granulated blast-furnace slag and an alkali activator comprising sodium hydroxide.

7. The thermoelectric energy harvester of claim 3, wherein each of the inorganic-based alkali-activated materials further comprises carbon fiber.

8. The thermoelectric energy harvester of claim 7, wherein the carbon fiber is present in an amount of up to 0.01 wt.% based on a total weight of the inorganic-based alkali activated material.

9. The thermoelectric energy harvester of any one of the preceding claims, wherein each of the inorganic-based alkali-activated materials comprises a monolithic body, wherein the two conductive mesh electrodes are embedded within the monolithic body.

10. The thermoelectric energy harvester of claim 9, wherein a first electrode of the two conductive mesh electrodes is embedded at a top end of the monolithic body, and a second electrode of the two conductive mesh electrodes is embedded at a bottom end of the monolithic body.

11. The thermoelectric energy harvester of claim 1 or 2, wherein the plurality of inorganicbased alkali-activated materials comprise p-type materials12. The thermoelectric energy harvester of claim 11, wherein the plurality of inorganicbased alkali-activated materials connected in series are capable of generating a Seebeck voltage in the range of from 1.8 V to 2.3 V.

13. The thermoelectric energy harvester of claim 1 , wherein the plurality of inorganic-based al kali -activated materials comprise p-type materials, each having a Seebeck coefficient of 1600 pV / °C.

14. The thermoelectric energy harvester of claim 1 or 11, wherein the thermoelectric module comprising the plurality of inorganic-based alkali-activated materials connected in series is configured such that a Seebeck voltage of the thermoelectric module increases with the number of inorganic-based alkali-activated materials.

15. The thermoelectric energy harvester of claim 2, wherein the two or more thermoelectric modules connected in parallel are configured to act as a capacitor for storing harvested energy.

16. The thermoelectric energy harvester of claim 10, wherein each of the inorganic-based alkali-activated materials further comprises two K-type thermocouples configured to measure a temperature of the inorganic-based alkali-activated material.

17. The thermoelectric energy harvester of claim 16, wherein a first K-type thermocouple of the two K-type thermocouples is embedded at the top end of the monolithic body, and a second K-type thermocouple of the two K-type thermocouples is embedded at the bottom end of the monolithic body.

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