Methods and assemblies for ion separation and uses thereof

Abstract

Described herein are assemblies, devices and methods relating to effecting selective migration of an ion species across a potential gradient, utilising a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto, and an untethered counterion species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

Description

[0001] METHODS AND ASSEMBLIES FOR ION SEPARATION AND USES THEREOF

[0002] Technical Field

[0003]

[0001] The disclosure herein relates to methods and assemblies for ion separation. More particularly, the disclosure herein relates to methods of modifying, and assemblies that modify, ion mobility to create ion separation and a potential gradient and which are useful for generating electricity, among other uses.

[0004] Background of Invention

[0005]

[0002] Global warming caused by greenhouse gas emissions, primarily carbon dioxide (CO2) emissions from human activities, is one of the key challenges of our time. Carbon capture, utilisation, and storage (CCUS) strategies are expected to play crucial roles in mitigating this challenge. However, current CCUS technologies remain energy intensive and costly, compromising their environmental and economic sustainability. At present, chemical-based CO2 adsorption, where CO2 is adsorbed by aquatic adsorbents like alkanolamines or amines, is the most commercially available option. The negative enthalpy change (AH) of the chemical adsorption process, as indicated by its spontaneous and exothermic nature, offers the potential for serving as an energy harvesting target to enhance its energy efficiency.

[0006]

[0003] Choosing a feasible approach for realising energy harvesting from CO2 can be guided by nature-based ‘ionics’ processes. Biological processes of energy conversion or signal propagation are fundamentally reliant on regulated ion transport in bio-channels. This has encouraged emerging advances in pursuing selective ion transport in synthetic nanofluidic channels for harvesting electricity from unconventional resources. Devices based on this technique involve directional ion separation across artificial channels in response to external environmental gradients exemplified by thermal, pressure, salinity, moisture, light, etc. The external environment drives charged ions to diffuse across the ion channels presented in the generators. The ion channels are pre-designed to transport oppositely charged ions at distinguishable speeds, leading to the generation of net diffusion current and electric potential difference across the generator.

[0007]

[0004] In commercially available CO2 chemical adsorption, amine solutions can generate oppositely charged ions upon CO2 absorption as follows: CO2 + R-NH2 + H2O R-NHs++ HCOs- (Equation 1 ). The positively charged amine ions and negatively charged bicarbonate ions generated in these CO2 adsorption processes have a similar size and are well mixed, making their efficient separation challenging. One solution has been to use a positively charged separation membrane, which yields a mobility selectivity of 2.5 between HCOs" and R-NHs+ions, which is a significantly lower magnitude compared to what is achievable using osmotic energy generation processes based on concentration gradients.

[0008]

[0005] Accordingly, improved methods of separating ions, such as of separating HCOs- and R-NHs+ions used in commercial CO2 capture systems, that address one or more of the above problems or at least provide a useful alternative, are desirable.

[0006] In one aspect, the invention described herein uses size modification of one ion in an ion pair to create a potential gradient and generate electricity. The present invention is based on the discovery that efficient ion separation may be achieved by impairing mobility of one unevenly distributed ion in an ion pair by tethering it to an anchor species, such that only its free or untethered counterion can move across the potential gradient created by the uneven ion distribution. This potential gradient can then be exploited to, for example, generate electricity.

[0009]

[0007] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0010] Summary of the Invention

[0011]

[0008] Unless the context indicates otherwise, where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims), they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0012]

[0009] According to a first aspect of the present invention, there is provided an assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto, and an untethered counterion species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0013]

[0010] In one embodiment, there is provided an assembly for effecting selective migration of an ion species across an electrochemical potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species, optionally a portion of the anchor species confined to one surface region of the matrix, comprises an ionised species tethered thereto, and an untethered counterion species, wherein the matrix comprises a mixture of a conductive and non-conductive nanosheet material, optionally in a mass ratio of from 95:5 to 50:50 conductivemon-conductive, wherein the conductive and non-conductive nanosheet materials are each independently selected from: hexagonal boron nitride, graphitic carbon nitride, graphene, silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework, optionally with a binder, and wherein the conductive, non-conductive, or both nanosheet material(s) is / are the anchor species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0014]

[0011] In one embodiment, there is provided an assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto, wherein the precursor species is adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, optionally wherein the precursor species comprises a functional group that chemically reacts with the trigger species on contact to form the tethered ionised species and the untethered counterion species, optionally wherein the trigger species contacts the precursor species at one surface region of the matrix, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0015]

[0012] In one embodiment, there is provided an assembly for effecting selective migration of an ion species across an electrochemical potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto, wherein the precursor species is an amine or polyamine adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, wherein the trigger species is carbon dioxide, and wherein reaction between the amine group(s) and carbon dioxide produces tethered ionised species comprising ammonium cation(s) and untethered counterion species comprising carbonate anions, optionally wherein the trigger species contacts the precursor species at one surface region of the matrix, wherein the matrix comprises a mixture of a conductive and non-conductive nanosheet material, optionally in a mass ratio of from 95:5 to 50:50 conductivemon-conductive, wherein the conductive and non-conductive nanosheet materials are each independently selected from: hexagonal boron nitride, graphitic carbon nitride, graphene, silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework, optionally with a binder, and wherein the conductive, non-conductive, or both nanosheet material(s) is / are the anchor species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0016]

[0013] According to a second aspect of the present invention, there is provided a device for generating electricity from a potential gradient, the device comprising: an assembly according to the first aspect above connected into an external circuit. In one embodiment, the external circuit comprises current collectors in electrical contact with different, optionally opposing, portions or faces of the matrix such that the potential gradient is defined therebetween.

[0017]

[0014] In one embodiment, there is provided a flexible electricity generating device comprising an assembly according to the first aspect above connected into an external circuit.

[0018]

[0015] In one embodiment, there is provided a device for generating electricity from a potential gradient, optionally wherein the device is a flexible electricity generating device, the device comprising: a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto, wherein the precursor species is an amine or polyamine adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, wherein the trigger species is carbon dioxide, and wherein reaction between the amine group(s) and carbon dioxide produces tethered ionised species comprising ammonium cation(s) and untethered counterion species comprising carbonate anions, optionally wherein the trigger species contacts the precursor species at one surface region of the matrix, wherein the matrix comprises a mixture of a conductive and non-conductive nanosheet material, optionally in a mass ratio of from 95:5 to 50:50 conductivemon-conductive, wherein the conductive and non-conductive nanosheet materials are each independently selected from: hexagonal boron nitride, graphitic carbon nitride, graphene, silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework, optionally with a binder, and wherein the conductive, non-conductive, or both nanosheet material(s) is / are the anchor species, and wherein the matrix is mounted on a substrate comprising a conductive layer and an insulating layer such that a first face of the matrix is in contact with the conductive layer, wherein the matrix is connected to an external circuit through a first conductive wire connected to the conductive layer of the substrate, and a second conductive wire in electrical contact with a second face of the matrix opposing the first face, optionally wherein the one surface region of the matrix where the trigger species contacts the precursor species is the second face of the matrix, optionally wherein the matrix and substrate are in the form of flexible sheets, such as sheets that can be bent at least 90°, at least 120 °, or at least 180 °, with a less than 10% impact, less than 5% impact, less than 2% impact, or 0% impact, on electricity generating performance, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix and causes electric current to flow through the external circuit.

[0019]

[0016] According to a third aspect of the present invention, there is provided a method of separating one ion of an ion pair across a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient whereby the untethered counterion species is separated from the tethered ionised species across the potential gradient.

[0020]

[0017] According to a fourth aspect of the present invention, there is provided a method of generating electricity from a potential gradient, the method comprising: providing an assembly according to the first aspect above, wherein the assembly comprises a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto that is adapted to react with a trigger species, and, contacting a portion of the matrix with the trigger species, wherein the precursor species and trigger species react to form a tethered ionised species and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity when the assembly is connected to an external circuit.

[0021]

[0018] In one embodiment, there is provided a method of generating electricity from a potential gradient, the method comprising providing an assembly according to the first aspect above or the device according to the second aspect above, and optionally exposing a portion of the anchor species in the matrix having precursor species tethered thereto to a trigger species.

[0022]

[0019] In one embodiment, there is provided a method of generating electricity from a potential gradient, the method comprising: providing an assembly comprising: a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto, optionally wherein the trigger species contacts the precursor species at one surface region of the matrix, wherein the precursor species is an amine or polyamine adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, wherein the trigger species is carbon dioxide, and wherein reaction between the amine group(s) and carbon dioxide produces tethered ionised species comprising ammonium cation(s) and untethered counterion species comprising carbonate anions, wherein the matrix comprises a mixture of a conductive and non-conductive nanosheet material, optionally in a mass ratio of from 95:5 to 50:50 conductivemon-conductive, wherein the conductive and non-conductive nanosheet materials are each independently selected from: hexagonal boron nitride, graphitic carbon nitride, graphene, silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework, optionally with a binder, and wherein the conductive, non-conductive, or both nanosheet material(s) is / are the anchor species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix and when the matrix is connected to an external circuit, causes electric current to flow.

[0023] Brief Description of Drawings

[0024]

[0020] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0025]

[0021] Figure 1 shows the an electricity generator from CO2 adsorption according to one embodiment of the invention described herein : (a) schematic illustration of an electricity generator with a symmetric structure between two electrical collectors to ensure a balanced chemical potential across the generator at the initial stage; (b) process of ion separation induced electricity generation from CO2 adsorption starts, in one embodiment, from (i) grafting / tethering PEI onto boron nitride nanosheets to get h-BN-NHs adsorbents, (ii) CO2 adsorption induces ion formation, releasing cations (h-BN-NHs+) and anions (HCO3 ); (iii) the hundred nanometre cations are spatially confined while the anions can freely transverse within the hydrogel channels, leading to precise ion separation; (c) TEM image of the as-exfoliated and functionalised h-BN-NH2 nanosheets, (d) SEM image of the cross-section structure of the h-BN-NH2 composite showing trapped h-BN-NH2 nanosheets in hydrogel network in white circles; (e) photograph of an agarose gel-based electricity generator according to one embodiment;

[0026]

[0022] Figure 2 demonstrates CC>2-induced electricity generation: (a) Cyclic CO2 adsorption-induced open circuit voltage of one embodiment of an electricity generator using agarose gel as a matrix; (b) cyclic CO2 adsorption-induced short circuit current of the electricity generator, where a pH-swing was applied to recover the power generation after the 5th cycle. CO2 was fed into the testing box at a rate of 2.5 L / min for 3 min in each cycle for both Voc and Isc tests; (c) electricity generation in terms of the peak Voc and half value time (t1 / 2) of the induced open circuit potential as a function of the concentration of the h-BN-NH2 nanosheets in agarose hydrogel; (d) electricity generation in terms of the peak Voc and half value time (t1 / a) of the induced open circuit potential as a function of the weight ratio of PEI functionalities on h-BN nanosheets. Error bars are standard deviations from three tests; (e) electricity generation using carbon and platinum electrodes for electrical signal collection (top panel), and electricity generation using PEI functionalised graphene (Graphene-PEI) and PEI functionalised graphic carbon nitride (g-CsN^PEI) (bottom panel); (f) electricity generation in different control experiments: using N2 to substitute CO2 as the feed gas for the testing (top panel), replacing the h-BN nanosheets in the generator with graphene oxide nanosheets (middle panel) and pure PEI molecules (bottom panel);

[0027]

[0023] Figure 3 shows the mechanism of the electricity generation from CO2 adsorption: (a) comparison of the adsorption isotherms (293.15K) of CO2 by h-BN-NH2 nanosheets and bulk h-BN measured by Brunauer-Emmett-Teller (BET) analysis; (b) the pH value of h-BN-NH2 water solution as a function of CO2 adsorption time, which drops gradually because of the generation of HCOs- ions. Total solution: 100 mL water solution of h-BN-NH2 nanosheets at 1 mg / mL. CO2 feeding rate was 10 mL / min; (c) l-V curves of h-BN-NH2 nanosheet water solution bubbled with CC^and N2 respectively in an H-cell. The other side was fed with DI water; (d) MD simulation model of agarose channel for selective transport of h-BN-NHs+and bicarbonate ions. The channel size was set to be wide enough to eliminate size effects. The relative positions of h-BN-NHs+and HCOs" were investigated at t = 0 and t=25 ns respectively, which shows that h-BN-NHs+gets anchored while HCOs" freely move within and across the channel; (e) the electrostatic and van der Waals interaction energies between agarose and HCOs' compared with those of between agarose and h-BN-NHs+nanosheet; (f) ion permeation rate comparison of negative ions (HCO3 ) and positive ions (h-BN-NHs+) under concentration gradient. A homemade diffusion setup was applied to confirm the simulation results with a hydrogel bridge in between two reservoirs containing h-BN-NH2 and DI water;

[0024] Figure 4 shows scaling up of one embodiment of a CO2 adsorption electricity generator; (a) CO2 adsorption induced electricity was stored by charging a commercial capacitor (0.5 pF); (b) energy harvested from the generator in a one-adsorption cycle when connected with different external resistors. The total electricity was calculated according to the current curve as a function of time monitored by the source meter. Error bars are standard deviations from three tests; (c) photographs of a large size of NAH composite fabricated by casting method depicting scalability; (d) schematic of a vertically stacked generator and power generation from devices with different thicknesses (h indicates the total thickness of the devices). By using the vertically stacked generator, the accelerated ion transport leads to a prompt response to the CO2. The induced Voc of the generators reached their peaks in several seconds after feeding CO2 into the testing box. In addition, the thicker the generator, the higher the peak Voc and the longer the electrical signals last; (e) electricity generation by five parallel connections of vertically stacked generator groups comprising ten generators in series (5 x 10). Inset is the photograph of the output voltage measured by the source meter; (f) generators in parallel and series (5 x 10) were used to power a light-emitting diode. Fluctuations on the voltage ascending curve likely indicate that the charging speed is influenced by the characteristics of the external circuit;

[0028]

[0025] Figure 5 shows a schematic of another embodiment of a membrane CC>2-electricity generator with a non-gel, nanosheet-based matrix;

[0029]

[0026] Figure 6 shows a photograph of a membrane CO2 electricity generator constructed according to Fig 5 and described in Example 2 herein;

[0030]

[0027] Figure 7 shows the electricity generating performance of the membrane CO2 electricity generator depicted in Fig 5, having a peak and stable voltage of 0.65 V; and

[0031]

[0028] Figure 8 shows, diagrammatically, (a) the exploded layers of an ion separation assembly according to one embodiment of the invention described herein from a side-on perspective, and its connections to an external circuit; and (b) a layered matrix according to one embodiment described herein having sublayers.

[0032] Detailed Description

[0033]

[0029] Described herein are methods and assemblies for effecting selective migration of ion species across a potential gradient. The methods and assemblies utilise a matrix comprising an anchor species dispersed therein, where a portion of the anchor species in the matrix comprises an ionised species tethered thereto and an untethered counterion species. Due to the structure and / or composition of the anchor species, mobility of the tethered ionised species is impaired by the matrix. This allows the untethered counterion species to selectively migrate across a potential gradient created by uneven dispersion of the tethered ionised species in just a portion of the matrix. These assemblies and methods have application in electricity generating devices and methods, where the potential gradient and charge separation of the ions are exploited to create electrical energy.

[0034]

[0030] The present inventors have thus devised and constructed assemblies and methods that can realise precise ion separation across a matrix, even in cases where the free ions might be of similar molecular size. To overcome the size similarity of ions generated by traditional adsorbents, the present inventors have tethered one ion in an ion pair to an anchor molecule having structure and / or composition that substantially inhibits its mobility within the matrix. This has been realised in certain embodiments by synthesis of nanocomposite anchors with abundant reactive groups onto two- dimensional (2D) nanosheets to form functionalised nanosheets. Upon reacting with a trigger molecule, the nanocomposite reactive groups transform into positively charged ions tethered to the sheets and possessing a size on the scale of hundreds of nanometres, and into negatively charged, Angstrom-scale free (untethered) counter-anions. The size disparity between the ions in the ion pair is thus, in some embodiments, over two orders of magnitude. The extended skeleton of the positive ions then becomes trapped by the matrix while the negative ions are free to move around, and so these oppositely charged ions diffuse across the matrix at a remarkable rate difference. Such a diffusion rate gap can then be translated into electricity and further amplified to power external electronic devices.

[0035]

[0031] This work by the present inventors is the first to demonstrate ion tethering to an anchor molecule as a means to effect selective ion migration, and the first time such mobility inhibition-based ion separation has been used to produce electricity. As this work can utilise, but does not require, aqueous or hydrogel-based media or rigid or thick membranes to effect selective ion migration, the present invention allows ion separation within, and electricity to be produced from, previously inaccessible dry, flexible, and / or flat assemblies and devices. Furthermore, the present ion separation assemblies and methods achieve superior ion separation efficiencies, even being capable of near perfect ion separation in certain embodiments, in contrast to other methods used in the art that rely on charged membranes and the like.

[0036]

[0032] The ion separation methods described herein have applications in ion-separation related energy resource and environmental applications, including harvesting green energy from natural sources like light, heat, salt gradients, and moisture, and / or in water treatment. The assemblies are also demonstrably useful for generating electricity directly from adsorbing CO2 (Fig. 1 (a)). Other applications for this technology will be apparent from the disclosure herein.

[0037]

[0033] Described herein is an assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto, and an untethered counterion species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0038]

[0034] It should be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "from x to " or “between x and y” is intended to include all sub-ranges between x and y and also range end points x and y.

[0039]

[0035] As used herein, the singular forms “a,” “an,” and “the” may refer to plural articles unless specifically stated otherwise.

[0036] As used herein, the term “tethered” in relation to an ionised species refers to the ionised species being adsorbed onto, or chemically bonded to, or a combination of adsorbed onto and chemically bonded to, an anchor species. In certain embodiments, the ionised species tethered to the anchor species is such that the ionised species are not and cannot be separated from the anchor species under the conditions used during the ion separation processes described herein. In certain embodiments, the ionised species is non-separably associated with the anchor species, such as non- separably associated with the anchor species under the conditions used during the ion separation processes described herein.

[0040]

[0037] As used herein, the term “untethered” in relation to a counterion species refers to the counterion species being free to move, and most critically free to move separately from the anchor species, under a potential gradient. It will be understood that the counterion species will still experience intermolecular forces, including ionic interactions with its oppositely charged ion in an ion pair, but the fact that the counterion is untethered refers to there being no or substantially no physical or molecular bond barrier to movement of the counterion species away from the anchor species across a suitable potential gradient. In certain embodiments, the untethered counterion species has a molecular radius in the order of about < 25 A, or about < 10 A, or about < 7 A, or about < 5 A.

[0041]

[0038] As used herein, the term “potential gradient” refers to an electric potential gradient, a chemical potential gradient, or a combination of the two in the form of an electrochemical potential gradient. The potential gradient will be understood to provide a driving force for migration of chemical species from regions of high potential to regions of low potential. The potential gradient in the methods and assemblies / devices described herein is created by uneven dispersion, that is, uneven distribution, of the tethered ionised species and its accompanying anchor species within the matrix. In some embodiments, the uneven dispersion and subsequent potential gradient is created by selective exposure of only a portion of the matrix / precursor species tethered to the anchor species to a trigger molecule. In other embodiments, the uneven dispersion may be created by other means, such as by introducing the anchor species and tethered ionised species into a layer or section of the matrix mechanically (e.g., by sequential drop casting).

[0042]

[0039] As used herein, the term “impaired” in relation to mobility of the ionised species tethered to the anchor species refers to physical movement of the anchor species and tethered ionised species being at least partially, predominantly, substantially completely, or completely prevented within and / or through the matrix, and most critically across the potential gradient, by one or more of molecular size, molecular shape, and / or intermolecular interactions between the ionised species and / or the anchor species and / or components of the matrix. The skilled person will appreciate that molecular size may impact mobility such that species having sizes in the order of hundreds of nanometres may be less mobile than species having sizes in the order of Angstroms, that molecular shape may impact mobility such that 2D extended flat layer species may be less mobile than 0D condensed particle species, and that intermolecular interactions may impact mobility such that species that form hydrogen bonds with surrounding species may be less mobile than species that interact with surrounding species through van der Waals forces only. In some embodiments, the impaired mobility is a result of the structure and / or composition of the anchor species, such as that it has a size and / or shape and / or composition that reduces mobility in any matrix. In other embodiments, the impaired mobility is a result of the structure and / or composition of the anchor species in combination with the structure and / or composition of components of the matrix, such as that both the anchor species and components of the matrix have a size and / or shape and / or composition that reduces mobility of the anchor species in the matrix.

[0043] Matrix and substrate

[0044]

[0040] The assemblies, devices and methods herein comprise or utilise a matrix. The matrix comprises the anchor species and provides the assemblies, devices and methods herein with a physical structure that enables creation of a potential gradient to drive ion separation. The matrix may be any suitable matrix. The matrix may comprise any suitable components.

[0045]

[0041] In one embodiment, the matrix is a self-supporting structure, such as comprises a hydrogel, or a three-dimensionally interconnected hydrogel. The hydrogel may comprise pores and channels, which advantageously provide physical and chemical means for inhibiting anchor species mobility. In one embodiment, the hydrogel has an average pore size of from 50 to 350 nm. In one embodiment, the matrix comprises agarose gel, but other gels such as agar, polyacrylamide, corn starch or the like may be suitable. In some embodiments, a self-supporting matrix structure may be mounted on a substrate, e.g., for strength or containment.

[0046]

[0042] In other embodiments, the matrix need not be self-supporting and can instead be mounted on a substrate, e.g., for strength or containment. In such embodiments, the matrix may comprise, consist essentially of, or consist of, anchor species or a mixture of two or more different anchor species, optionally wherein the or each anchor species comprise(s) tethered precursor species. In one embodiment, the matrix comprises anchor species, such as a mixture of two or more anchor species, optionally with a binder. In one embodiment, the matrix consists, or consists essentially of, anchor species, such as a mixture of two or more anchor species, optionally with a binder. Accordingly, the matrix may comprise or consist of any one or more of the species described in the following section entitled “Anchor species”. In one embodiment, the matrix is selected from hexagonal boron nitride (h- BN), graphene, graphitic carbon nitride (g-CN), and mixtures thereof. In one embodiment, the matrix consists of nanosheet species, such as nanosheets having thicknesses of less than 5 nm, optionally with a binder. In one embodiment, the matrix consists essentially of nanosheet species, such as nanosheets having thicknesses of less than 5 nm, optionally with a binder. The nanosheets may be one type of nanosheet or may be a mixture of different types of nanosheets.

[0047]

[0043] In one embodiment, the matrix comprises a mixture of graphene and a 2D network-forming material selected from hexagonal boron nitride (h-BN), graphitic carbon nitride (g-CN), silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework, such as a 5 / 95, 10 / 90, 20 / 80, 30 / 70, 40 / 60, 50 / 50, 60 / 40, 70 / 30, 80 / 20, 90 / 10 or 95 / 5 by weight mixture of graphene / hexagonal boron nitride (h-BN), graphitic carbon nitride (g-CN), silicene, germanene, stanene, phosphorene, a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework and a 2D covalent organic framework. In one embodiment, the graphene and hexagonal boron nitride (h- BN), graphitic carbon nitride (g-CN), silicene, germanene, stanene, phosphorene, transition metal dichalcogenide, transition metal halide, metal carbide / nitride (MXene), 2D oxide / hydroxide, 2D metalorganic framework and 2D covalent organic framework comprise tethered precursor species, such as where the tether load is from 1 -50 wt% or 1 to 20 wt% of the anchor species. In one embodiment, the matrix comprises a mixture of from 5 to 50 wt% hexagonal boron nitride (h-BN), graphitic carbon nitride (g-CN), silicene, germanene, stanene, phosphorene, transition metal dichalcogenide, transition metal halide, metal carbide / nitride (MXene), 2D oxide / hydroxide, 2D metal-organic framework or 2D covalent organic framework, and from 95 to 50 wt% graphene. In one embodiment, the matrix consists of a mixture of from 5 to 50 wt% hexagonal boron nitride (h-BN), graphitic carbon nitride (g-CN), silicene, germanene, stanene, phosphorene, transition metal dichalcogenide, transition metal halide, metal carbide / nitride (MXene), 2D oxide / hydroxide, 2D metal-organic framework, or 2D covalent organic framework, and from 95 to 50 wt% graphene optionally with a binder, such as in an amount of < 5 wt%.

[0048]

[0044] In another embodiment, the matrix comprises a mixture of conductive graphene and non- conductive hexagonal boron nitride (h-BN) or graphitic carbon nitride (g-CN), such as a 5 / 95, 10 / 90, 20 / 80, 30 / 70, 40 / 60, 50 / 50, 60 / 40, 70 / 30, 80 / 20, 90 / 10 or 95 / 5 by weight mixture of conductive graphene / non-conductive hexagonal boron nitride (h-BN) or graphitic carbon nitride (g-CN), such as graphene with tethered precursor species / hexagonal boron nitride (h-BN) with tethered precursor species or graphitic carbon nitride (g-CN) with tethered precursor species, where the tether load is from 1 -50 wt% or 1 to 20 wt% of the anchor species (graphene, h-BN or g-CN). In one embodiment, the matrix comprises a mixture of from 5 to 50 wt% hexagonal boron nitride (h-BN) or graphitic carbon nitride (g-CN) and from 95 to 50 wt% graphene, optionally wherein the anchor species comprise tethered precursor species, such as at a loading of 1 to 50 wt% or 1 to 20 wt%. In one embodiment, the matrix consists of a mixture of from 5 to 50 wt% hexagonal boron nitride (h-BN) or graphitic carbon nitride (g-CN) comprising from 1 to 50 wt% of precursor species tethered thereto and from 95 to 50 wt% graphene comprising from 1 to 50 wt% of precursor species tethered thereto, optionally with a binder, such as in an amount of < 5 wt%.

[0049]

[0045] In some embodiments, the matrix comprises a binder to assist in immobilising the matrix components. In embodiments where the matrix comprises a binder, any suitable binder may be used, such as a binder with a suitable electrochemical window and adhesive properties, and optionally conductivity. In some embodiments, the binder may comprise poly(vinylidene difluoride) (PVDF), polytetrafluoroethylene (PTFE), poly(acrylic acid) (PAA), styrene-butadiene rubber (SBR), polyethylene oxide (PEG), sodium carboxymethylcellulose (CMC), or alginate, but other binders may also be suitable.

[0050]

[0046] In one embodiment, the matrix comprising the anchor species is at least partially electrically conductive, as this advantageously allows the matrix to complete an external circuit and thereby generate electricity. The matrix may have any suitable conductivity, such that efficient electrical signal transmission to the external circuit is not excessively impeded, leading to significant energy loss, and that self-discharging and internal short circuits are minimised. In one embodiment, the matrix has a sheet resistance of from 0.1 MQ / square to 10 MQ / square, or of from 0.1 MQ / square to 1 MQ / square, or of from 0.5 MQ / square to 1 .5 MQ / square, or of from 0.25 MQ / square to 0.75 MQ / square, or of from 0.9 MQ / square to 1 .2 MQ / square, or of from 1 MQ / square to 5 MQ / square, or of from 4 MQ / square to 10 MQ / square. Suitably, a sheet resistance of a matrix comprising a mixture of graphene and hexagonal boron nitride may be in the order of about 106Q, such as of from about 105Q to about 107Q. Conductivity of the matrix may be adjusted by including conductive materials in the matrix, such as conductive anchor species like graphene and the like, or by adding other conductive materials such as graphene, graphite or conductive carbon to the matrix to assist with conductivity, or by using a conductive hydrogel, in addition to any non-conductive or insulating components such as non- conductive anchor species like boron nitride nanosheets. In one embodiment, conductive materials may have a bulk resistivity of about 10-2to 10-8Q.m, semi-conductive materials may have a bulk resistivity of about 10-6to 106Q.m, and non-conductive / insulating materials may have a bulk resistivity of about 1011to 1019Q.m. In one embodiment, the matrix comprises an electrically conductive material in combination with the anchor species. In another embodiment, the matrix comprises a mixture of two or more anchor species, at least one of which is electrically conductive, such as a combination of a conductive anchor species, a non-conductive anchor species and / or a semiconductive anchor species. Conductive and non-conductive materials will be known to those of skill in the art, as will methods of measuring sheet resistance. It will be understood that the term “conductive” herein and related terms such as “semi-conductive” and “non-conductive” refer to electrical conductivity.

[0051]

[0047] In one embodiment, the matrix is flexible, such as can be bent at least 90 ° or more preferably 180 ° on itself without cracking or breaking. In one embodiment, the matrix is flexible, such as can be bent at least 90°, or at least 120°, at least 180° on itself without losing ion separation and / or electricity generating function, or can be bent at least 90°, or at least 120°, at least 180° on itself with a less than 10% impact, less than 5% impact, less than 2% impact, or 0% impact, on electricity generating performance. In one embodiment, the matrix is thin, such as of the order of micrometres or millimetres in thickness, and flexible. In one embodiment, the matrix has a thickness of from about 1 pm to about 5 cm, or of from about 1 pm to about 999 pm, or of from about 1 mm to about 0.5 cm, or of from about 1 cm to about 5 cm, or of from about 0.5 cm to about 1 .5 cm, or of from about 10 pm to about 100 pm, or of from about 50 pm to about 250 pm, or of from about 250 pm to about 750 pm, or of from about 500 pm to about 999 pm.

[0052]

[0048] In embodiments where the matrix is mounted on a substrate, the substrate may provide mechanical strength to the assemblies and devices herein, permitting use of a broader range of nonself-supporting matrix materials. In one embodiment, the substrate is a non-permeable substrate having a conductive surface, such as a non-woven substrate with a conductive surface. In one embodiment, the substrate is a non-permeable insulating substrate having a conductive surface. The conductive surface is designed for contact with the matrix and connection to an external circuit where required, and the non-conductive surface or insulating surface of the substrate is designed to be facing externally from the assembly or device such that it safe to touch without transferring electricity. The matrix may be fixed to the substrate by any suitable means, such as by using an adhesive or other binder to fix a pre-formed matrix to the substrate, or by forming the substrate layer in situ on the substrate layer, such as by drop casting, such that intermolecular forces ensure adequate adhesion. In one embodiment, the non-permeable preferably insulating substrate is thin, such as of the order of micrometres or millimetres in thickness, and flexible, such as can be bent at least 90 ° or more preferably 180 ° on itself with cracking or breaking. In one embodiment, a flexible substrate is paired with a flexible matrix to provide a flexible assembly. In one embodiment, the substrate has a thickness of from about 1 pm to about 5 cm, or of from about 1 pm to about 999 pm, or of from about 1 mm to about 0.5 cm, or of from about 1 cm to about 5 cm, or of from about 0.5 cm to about 1 .5 cm, or of from about 10 pm to about 100 pm, or of from about 50 pm to about 250 pm, or of from about 250 pm to about 750 pm, or of from about 500 pm to about 999 pm. In one embodiment, the substrate and matrix forms a flexible composite layer, such as can be bent at least 90°, or at least 120°, at least 180° on itslef without losing ion separation and / or electricity generating function, or can be bent at least 90°, or at least 120°, at least 180° on itself with a less than 10% impact, less than 5% impact, less than 2% impact, or 0% impact, on electricity generating performance.

[0053]

[0049] In one embodiment, the substrate comprises a polymer, such as polyethylene terephthalate (PET) or polyester, or polyethylene, polypropylene, nylon or the like. The substrate material such as polymer is not particularly limited provided that it is non-permeable, such as non-permeable to the matrix, and the skilled person will appreciate a range of materials including plastics and polymers may be utilised. In one embodiment, the non-permeable substrate has a conductive surface that is selected from a metal foil or a metal cloth, and such foil or cloth may be in intimate contact with an insulative backing such as a polymer sheet, such as glued or otherwise affixed to the backing to provide structural integrity. In other embodiments, the substrate may be a composite metallised polymer such as met-PET, where the metal is coated on the polymer by chemical deposition means such as vapour deposition or the like. The substrate surface may comprise part or all of one surface of the substrate, but preferably all of the surface of the substrate exposed to the matrix is covered to maximise electrical contact and / or to cover what would otherwise be an exposed face of the matrix, such as a face of the matrix that may otherwise be in contact with trigger species. The metal is not particularly limited, but is particularly suitably electrically conductive and inert, such as is selected from copper, silver, gold and aluminium. Other metals may be utilised. In some embodiments, the conductive layer may comprise non-metal, such comprise graphite or graphene or conductive carbon black or the like, optionally bound to an insulative layer in a binder.

[0054]

[0050] In some embodiments, the matrix is monolithic in the sense that it is provided in a single piece or section. However, in other embodiments, the matrix may comprise two or more sections in electrical contact with each other. The term “section” here refers to separately laid and / or set layers or parts of the matrix. Provided that the sections are in electrical contact with each other, such as through an appropriate binder, conductive glue, aqueous / fluid contact, or physical contact, the number of sections comprising the matrix is not particularly limited. In one embodiment, the matrix comprises two sections in electrical contact with each other. In this embodiment, a first section may be an ionised species formation matrix and the second section may be an untethered counterion species receiving section. In another embodiment, the matrix comprises three sections in electrical contact with each other, a first section being an ionised species formation matrix, a second section being an untethered counterion species receiving section, and a third section being sandwiched between the first and second sections and being a travel pathway for untethered counterion species. Formation of a matrix in sections may allow for tuning of the ion separation pathway and distance, as well as distribution of anchor species in portions of the matrix proximal to trigger species exposure.

[0055]

[0051] Where the matrix comprises two or more sections, the first and second sections, and third section if present, may be mounted in a side-by-side configuration or in a vertically stacked configuration. Construction of the matrix sections as flat layers may aid these stacking arrangements by shortening the ion pathway and increasing the surface area of the matrix exposed to the trigger species. Accordingly, in some embodiments, the matrix, and sections thereof if present, and substrate if present, may each independently or all be in the form of a flat or substantially flat layer or sheet. In sheet form, the length and width dimensions of the matrix or sections or substrate may be at least 10x greater, or at least 100x to 1000x greater, than their height dimension.

[0056]

[0052] In one embodiment, the matrix is aqueous. In other embodiments, the matrix is non-aqueous. In non-aqueous embodiments, a quantity of water may be present, such as part of or associated with the anchor species and / or precursor species and / or ionised species and / or other component, in the matrix in an amount of <10% w / v, or <8% w / v, <6% w / v, <4% w / v, or <2% w / v. In some embodiments, a quantity of water may be present, such as part of or associated with the anchor species and / or precursor species and / or ionised species and / or other component, in a region of the matrix where trigger species will be contacted, in an amount of <10% w / v, or <8% w / v, <6% w / v, <4% w / v, or <2% w / v.

[0057] Anchor species

[0058]

[0053] The assemblies, devices and methods herein comprise or utilise anchor species. The anchor species may be any suitable species, such as any suitable species whose structure and / or composition inhibits movement of a tethered ionised species through a matrix, and whose structure permits tethering of an ionised species thereto. It will be appreciated that the ion immobilisation function of the anchor species may be achieved through use of any suitably sized and shaped material, and that the structure and composition of the anchor species herein is not particularly fixed provided that it can perform this function and have an ionised species tethered thereto. However, nanosheets have been found to be a particularly suitable size and shape for anchor species, such as due to their hundred-nanometre to micrometre size scale, flat shape, and physicochemical functionalisability. Nanosheets can be formed from network forming materials, and particularly two-dimensional (2D) network-forming materials.

[0059]

[0054] In one embodiment, the anchor species thus comprises a 2D network-forming material. Any suitable 2D network-forming material may be used, but in some embodiments, the 2D network-forming material is hexagonal boron nitride (h-BN), graphene, graphitic carbon nitride (g-CN), silicene, germanene, stanene, and phosphorene. In other embodiments, the 2D network-forming material is a transition metal dichalcogenide, a transition metal halide, a metal carbide / nitride (MXene), a 2D oxide / hydroxide, a 2D metal-organic framework, a 2D covalent organic framework, or another 2D nanomaterial. 2D network-forming materials are known in the art and may be synthesised following published methods and / or may be sourced from commercial suppliers such Sigma Aldrich® / Merck®, Alfa Aesar®, and the like. In one embodiment, the anchor species comprises hexagonal boron nitride (h-BN), graphene or graphitic carbon nitride (g-CN), or a mixture of two or more of these.

[0060]

[0055] In one embodiment, the anchor species comprises nanosheets of a two-dimensional (2D) network-forming material. Nanosheets are generally single or multi-layer 2D arrays of atoms or molecules, such as of about 1 nm to 10 nm in thickness, and flat faces having dimensions generally in the range of 0.1 to about 10 pm. In one embodiment, the nanosheets are naturally occurring or form on synthesis. In other embodiments, the nanosheets comprising the anchor species are exfoliated. Exfoliation, such as through use of ball or rod milling or manual grinding or the like, advantageously separates agglomerated or stacked nanosheets to expose more nanosheet surfaces and increase the total nanosheet surface area. In one embodiment, an exfoliation process for the anchor species may be as described in WO 2024 / 059892 A1 , the contents of which are incorporated herein in their entirety by cross-reference. In one embodiment, the anchor species comprises hexagonal boron nitride (h-BN) nanosheets, graphene nanosheets, or graphitic carbon nitride (g-CN) nanosheets, or a mixture of two or more of these.

[0061]

[0056] In yet other embodiments, the anchor species comprises another network-forming material, such as in the form of an 0D quantum dot, a 1 D nanotube, or a 3D nanoparticle. Again, such materials are known in the art and may be synthesised following published methods and / or may be sourced from commercial suppliers.

[0062]

[0057] The anchor species herein may have any suitable dimensions. In one embodiment, the anchor species herein has dimensions that assist in physically hindering movement of the anchor species through the matrix, and therefore may have dimensions influenced by the specific matrix being used. Accordingly, the exact dimensions of the anchor species herein are not particularly limited. In one embodiment, the anchor species are in the form of sheets. In one embodiment, the anchor species has dimensions of from about 1 nm to 10 nm in thickness, or of from about 1 nm to 5 nm, or of from about 3 nm to 7 nm, or of from about 5 nm to 10 nm, or of less than about 10 nm, or of less than about 5 nm, and flat or substantially flat faces having dimensions in the range of from about 50 nm to about 10 pm, or of from about 50 nm to about 250 nm, or of from about 75 nm to about 500 nm, or of from about 250 nm to about 999 nm, or of from about 1 pm to about 5 pm, or of from about 2 pm to about 7 pm, or of from about 5 pm to about 10 pm, or of from about 750 nm to about 2 pm. In one embodiment, these dimensions may be the dimensions of nanosheets. In one embodiment, the anchor species has a maximum dimension of about 80-500 nm and a minimum dimension of <10 nm, such as < 5nm, and in other embodiments the anchor species comprise nanosheets having these dimensions.

[0058] In one embodiment, the anchor species is present in the matrix at a concentration of from about 1 wt% to about 100 wt%, or of from about 25 wt% to 100 wt%, or of from about 10 wt% to 75 wt%, or of from about 50 wt% to 95 wt%, or of from about 75 wt% to 100 wt%. In one embodiment, the anchor species is present in the matrix at a concentration of from about 1 %w / v to about 100 %w / v, or of from about 25 %w / v to 100 %w / v, or of from about 10 %w / v to 75 %w / v, or of from about 50 %w / v to 95 %w / v, or of from about 75 %w / v to 100 %w / v.

[0063]

[0059] In one embodiment, only a portion of the matrix comprises anchor species and the anchor species is confined to a particular region of the matrix. In one embodiment, the portion of the matrix comprising anchor species is confined to a surface region of the matrix. In such embodiments, the matrix may have more than one section and comprise a surface section comprising the anchor species dispersed therein. In other embodiments, the anchor species is dispersed throughout the matrix, but only a portion of the anchor species is exposed to a trigger species such that ionised species only form in a portion of the matrix.

[0064] Ionised and counterion species

[0065]

[0060] The present disclosure describes selective ion migration processes, and thus the methods and assemblies / devices herein comprise ions to be separated. Accordingly, a portion of the anchor species herein comprise ionised species tethered thereto. The term “portion” is not particularly limited, but indicates that not all of the anchor species in the matrix can comprise ionised species tethered thereto. In one embodiment, the term “portion” refers to about from about 0.5 wt% to about 60 wt%, or of from about 1 wt% to 50 wt%, or of from about 5 wt% to 25 wt%, or of from about 15 wt% to 40 wt%, or of from about 1 to 20 wt%, or of from about 30 wt% to 60 wt% of the anchor species comprising ionised species tethered thereto, wherein the weight percent is based on the weight of the entire matrix. In one embodiment, a region of the matrix comprises a local concentration of anchor species comprising ionised species tethered thereto of from about 1 wt% to about 100 wt%, or of from about 25 wt% to 100 wt%, or of from about 10 wt% to 75 wt%, or of from about 50 wt% to 95 wt%, or of from about 75 wt% to 100 wt%, but in other portions of the matrix, the local concentration of anchor species comprising ionised species tethered thereto is approaching 0 wt%, such as is from 0 to 5 wt%, or less than 4 wt%, or less than 3 wt%, or less than 2 wt%, or less than 1 wt%. The skilled person will recognise that this uneven distribution of ionised species within a region of the matrix, such as in a confined region, is responsible for creating the potential gradient. In one embodiment, the ionised species is confined to a particular region of the matrix, such as a surface region of the matrix. In such embodiments, the matrix may have more than one section and comprise a surface section comprising the ionised species dispersed therein as described below. In other embodiments, the anchor species is dispersed throughout the matrix, but only a portion of the anchor species is exposed to a trigger species such that ionised species only form in a particular region of the matrix, and that particular region in one embodiment is one surface of a sheet of matrix.

[0066]

[0061] In one embodiment, the ionised species may be tethered to the anchor species as is, such as in the form of a tetherable ion / free counterion salt. In such embodiments, the anchor species comprising ionised species tethered thereto may be unevenly distributed in the matrix, such as where the matrix has more than one section and one section comprises anchor species comprising ionised species therein. In one embodiment, the section comprising the anchor species comprising ionised species is a surface region, such as one face of a matrix sheet, such as achieved by laying an upper layer of a matrix comprising ionised species on a lower layer of matrix not comprising ionises species. In such embodiments, tethering of the ionised species to the anchor species may be achieved by milling, grinding or otherwise mixing the ionised species and its counterion with the anchor species. Such a process may also achieve exfoliation as well as tethering. In such embodiments, the tetherable ion / free counterion salt may be a liquid, such as an ionic liquid. In one embodiment, the ionic liquid may have a viscosity of from 20,000 to 150,000 cps at 25 °C. This high viscosity of the liquid salt may assist in exfoliation of anchor species nanosheets, when used, and may also assist in tethering the ionised species to the anchor species during mixing or milling.

[0067]

[0062] In another embodiment, the ionised species may be tethered to the anchor species via an intermediate or precursor species that is tethered to the anchor species and reacts to form the ionised species in situ. In such embodiments, the anchor species comprising the precursor species tethered thereto may be evenly or unevenly distributed in the matrix such that ionised species are formed in a portion of the matrix. In such embodiments, tethering of the precursor species to the anchor species may be achieved by milling, grinding or otherwise mixing the precursor species with the anchor species, and the precursor species may form a tethered ionised species and free counterion in situ on reaction with a trigger molecule. Such a process may also achieve exfoliation as well as tethering. Accordingly, in one embodiment, the tethered ionised species is formed from a precursor species adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species. In one embodiment, the precursor species comprises a functional group that chemically reacts with the trigger species on contact to form the tethered ionised species and the untethered counterion species. In one embodiment, the ionised species forms in a portion of the matrix through contact of a precursor species with a trigger species, wherein the precursor species comprises a functional group that chemically reacts with the trigger species.

[0068]

[0063] In one embodiment, the ionised species and untethered counterion species are formed on reaction of a trigger species with a precursor species comprising one or more amine functional group(s). In one embodiment, the amine functional group is of formula -NR2, where each R is independently H or optionally substituted C1-C10 alkyl, in one embodiment -NH2. In one embodiment, the ionised species thus comprise one or more ammonium cations. In one embodiment, the ammonium cation is of formula -NHR2+, where each R is independently H or optionally substituted C1- C10 alkyl, or in one embodiment is -NH3+.

[0069]

[0064] In one embodiment, the ionised species and untethered counterion species are formed on reaction of carbon dioxide with the amine functional group. In such embodiments, the untethered counterion may comprise a carbonate. In one embodiment, the untethered counterion may be hydrogen carbonate, HCOs- or a carbonate, COs2-anion. In one embodiment, the untethered counterion may comprise or be a carbamate, NH2C(=O)O_. In other embodiments, with different trigger species, a variety of other ions may form, including but not limited to, HSC , NOs", NH2S(=O)O_, etc.

[0070]

[0065] The untethered counterion species may be any suitable species that has a size, shape and / or composition that enables it to move freely within the matrix, such as responsive to a potential gradient, such as a chemical potential gradient and / or an electrical potential gradient. The nature of the counterion species is not particularly limited, but in some embodiments, the counterion species has a maximum dimension that is a factor of at least 50x smaller than a maximum dimension of the anchor species, or that is at least 100x smaller, or at least 200x smaller, or at least 300x smaller, or at least 400x smaller, or at least 500x smaller, or at least 750x smaller, or at least 1000x smaller, or at least 2500x smaller, or at least 5000x smaller, or of from 100x to 1000x smaller, or of from 500x to 5000x, or that is of from 50x to 5000x smaller than a maximum dimension of the anchor species. In one embodiment, the untethered counterion species has a maximum dimension or molecular radius in the order of about < 25 A, or about < 10 A, or about < 7 A, or about < 5 A, or of from 50 A to 5 A, or of from 75 A to 40 A, or of from 25 A to 5 A, or of from 10 A to 3 A. In one embodiment, the untethered counterion species has a size in the order of Angstroms, whereas the anchor species has a size in the order of hundreds of nanometres to micrometres.

[0071]

[0066] In one embodiment, the ionised species and untethered counterion species are formed from a precursor species and a trigger species in the presence of water molecules. The water may assist with solubilisation of the trigger species to enable reaction with the precursor species, and / or may assist with formation of the ionised species and counterion species through donating or accepting a proton or electron pair. In such embodiments, provided that some water is present to enable ionised species formation and / or trigger species dissolution in the matrix, the amount of water is not particularly limited. Where the matrix is aqueous or otherwise comprises water, such as where the matrix comprises a hydrogel, the water may be available from the matrix for ion formation and / or trigger species dissolution. In other embodiments, such as those where a non-aqueous matrix is used, the water may be introduced to the matrix by any suitable means. In one embodiment, the water is introduced through the trigger species stream, such as the trigger species stream is humidified, or the trigger species stream is passed through water, before being contacted with the matrix and precursor species. In one embodiment, the trigger species is provided in a humidified gas stream. In such embodiments, a relative humidity in the gas stream of from 5 to 80% may be used, or of from 10 to 50%, or of from 20 to 70%, or of from 40 to 80%. In one embodiment, a gas stream such as a stream of carbon dioxide is bubbled through water prior to being contacted with the matrix and precursor species. In other embodiments, the water may be introduced as part of the precursor species tethering process, such as may be water associated with the precursor species during or after synthesis, or may be water added to the precursor species during the tethering process. In yet other embodiments, the water may be associated with, on the surface of, and / or part of a crystal lattice of, the anchor species. In some embodiments, a combination of these strategies may be used to provide water molecules.

[0072]

[0067] In one embodiment, the ionised species or precursor species are tethered to the anchor species via an exfoliation process, such as by physico-chemical milling of the anchor species with the ionised species or precursor species, or by roll-milling or ball-milling. However, it will be appreciated that the tethering may be achieved through any suitable tethering means, such as by post-synthetic grafting of the ionised species or precursor species on the anchor species, or by chemical reaction, such as “click” type chemical reaction, with one or more functional groups or defects or the like in or on the surface of the anchor species. In yet other embodiments, other suitable synthetic routes may be used, such as tethering the ionised species or precursor species to the anchor species through a functional intermediate created by reaction of a reactive group with the anchor species and then reaction of the ionised species or precursor species with the reactive group, or by immersion or the like of the anchor species or pre-exfoliated anchor species in the ionised species or precursor species or solution thereof. Other suitable ways for effecting tethering ionised species or precursor species to anchor species will be known to those of skill in the art.

[0073] Precursor species

[0074]

[0068] Any suitable precursor species may be used. In preferred embodiments, the precursor species is selected such that it is adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species. In one embodiment, the precursor species is adapted for this purpose by comprising a functional group that chemically reacts with the trigger species on contact to form the tethered ionised species and the untethered counterion species. In one embodiment, the precursor species is an uncharged precursor species. This advantageously avoids additional ions in the matrix and that may interfere with the potential gradient.

[0075]

[0069] The precursor species is advantageously in liquid phase for ease of processing and to enable control over purity of the species tethered to the anchor species. Accordingly, in one embodiment, the precursor species is a liquid having a viscosity of from 20,000 to 150,000 cps at 25 °C. This high viscosity of the precursor species may assist in exfoliation of anchor species nanosheets, when used, and may also assist in tethering the precursor species to the anchor species during mixing or milling. In other embodiments, other phase precursor species, such as gas phase species, may be used if provided to the anchor species in a suitable liquid vehicle species. Such embodiments are less preferred due to potentially lower loadings of precursor species on the anchor species and / or interfering vehicle species in the matrix.

[0076]

[0070] In one embodiment, the precursor species is tethered to the anchor species by adsorption, that is, the precursor species is adsorbed to the anchor species, or by chemical bonding of the precursor species to the anchor species, or by a combination of these. In one embodiment, the precursor species is adsorbed onto the anchor species during a process of exfoliation. The exfoliation process may comprise milling, such as ball- or rod-milling, but other manual methods of exfoliation may also be utilised. In one embodiment, an exfoliation process for tethering the precursor species to the anchor species may be as described in WO2024 / 059892 A1 . Other methods for tethering a precursor species to the anchor species are described in the previous section.

[0077]

[0071] In one embodiment, the precursor species is a Lewis base. Such species may be designed to react with a Lewis acid to form an ion pair. Any suitable Lewis base may be used. In one embodiment, the Lewis base comprises an amine group. Amine groups are able to donate an electron pair from the nitrogen in the amine to form a bond, and a cation, on reaction with certain trigger species. In one embodiment, the precursor species is capable of accepting a proton to form a cation. In one embodiment, the precursor species comprises one or more amine functional groups. The precursor species may therefore be an amine, or may be a polyamine species. In one embodiment, the precursor species is a natural or synthetic linear or branched alkyl amine or alkyl polyamine, such as a C2-C20 amine or polyamine. In one embodiment, the precursor species is selected from putrescine, spermidine, cadaverine, spermine, and branched or linear polyethyleneimine. In one embodiment, the precursor is branched or linear polyethyleneimine having an average Mnof -10,000. In one embodiment, the precursor is branched or linear polyethyleneimine having an average Mw of -25,000 g / mol. Amines, polyamines, and branched or linear polyethyleneimine suitable for use in the assemblies, devices and methods herein can be made by synthetic methods known in the art, or may be purchased commercially. Although alkyl amines or polyethyleneimine may be utilised in some embodiments, in other embodiments, the precursor species may contain other functional groups also, such as an alcohol (ethanolamine and the like), aromatic ring (histamine, tyramine, tryptamine, and the like), acid (arginine, lysine, alanine, serine, glycine and polymers thereof, and the like), etc., and such compounds can be made by synthetic methods known in the art, or may be purchased commercially. The precursor species may be selected to have particular affinity for forming an ionised species and counterion pair on reaction with a particular trigger species.

[0078]

[0072] In other embodiments, the precursor species is a Lewis acid. In still further embodiments, the precursor species is a Bronsted-Lowry acid capable of donating a proton to form a cation. Any suitable Lewis or Bronsted acid may be used. In one embodiment, the precursor species comprises a carboxylic acid or sulfonic acid group. Such groups are able to donate a proton, and form an anion, on reaction with certain trigger species. In one embodiment, the precursor species comprises one or more carboxylic or sulfonic acid functional groups. Suitable acids for use in the assemblies, devices and methods herein can be made by synthetic methods known in the art, or may be purchased commercially.

[0079]

[0073] It will be appreciated that the charge of the ionised species on the anchor species and the charge of the untethered counterion are not fixed, and that tethered cation / free anion or tethered anion / free cation pairings are both within the scope of the disclosure herein depending on the trigger molecule / precursor combination being used / ion pair being separated.

[0080]

[0074] The precursor species may be loaded on the anchor species at any suitable concentration. Adjustment of the concentration may be made by a person of skill in the art by adjusting the ratio of precursor species mixed in with anchor species, such as during milling, and / or by adjusting time allowed for tethering of the precursor species to the anchor species. In one embodiment, the precursor species may be loaded on the anchor species at a concentration of from about 1 wt% to about 80 wt%, or of from about 1 wt% to 50 wt%, or of from about 1 wt% to 20 wt%, or of from about 5 wt% to 30 wt%, or of from about 10 wt% to 60 wt%. In this embodiment, the wt% may be the mass of anchor species comprising tethered precursor species divided by the total mass of the precursor-comprising anchor species and non-precursor comprising anchor species mixture added to the matrix. In one embodiment, the concentration of from about 1 wt% to about 80 wt%, or of from about 1 wt% to 50 wt%, or of from about 1 wt% to 20 wt%, or of from about 5 wt% to 30 wt%, or of from about 10 wt% to 60 wt%, represents an indicative loading concentration of polyethyleneimine, such that these loadings may be adjusted for other precursor species to achieve an equivalent concentration of functional groups, such as equivalent concentration of amine groups, on the anchor species.

[0081] Trigger species

[0082]

[0075] Any suitable trigger species may be used in the assemblies, devices and methods herein. In one embodiment, the trigger species is a Lewis acid, such as is designed to react with a precursor Lewis base to form an anion / cation pair. In one embodiment, the trigger species is selected from carbon dioxide, sulphur dioxide and nitrogen dioxide. In one embodiment, the trigger species is carbon dioxide, such as carbon dioxide gas.

[0083]

[0076] In other embodiments, the trigger species is a Lewis base, such as is designed to react with a precursor Lewis acid to form an anion / cation pair, or is a Bronsted acid, such as designed to donate a proton to a trigger species. In one embodiment, the trigger species is ammonia gas or an alkylamine.

[0077] In one embodiment, the trigger species is in the gas phase, and as such is advantageously able to be directed towards a surface of the matrix containing anchor species with tethered precursor species for reaction to form ion pairs. In one embodiment, the trigger species is provided to the matrix and tethered precursor species therein in pure form, that is, in undiluted form. In other embodiments, the trigger species is provided in an otherwise inert carrier gas or similar, that is, in diluted form. In one embodiment, as previously described, the trigger species may be provided in a humidified gas stream to provide water to the assembly, such as to facilitate dissolution of the trigger species in the matrix and / or formation of ionised and counterion species. Otherwise, other embodiments where the trigger species is provided in a liquid or solution form (diluted or undiluted) are also envisaged, in some embodiment where the liquid or solution comprises water.

[0084]

[0078] Trigger species such as those contemplated herein may be synthesised according to known literature methods and / or may be purchased commercially.

[0085] Assembly

[0086]

[0079] Disclosed herein is an assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises an uncharged precursor species tethered thereto; wherein a portion of the uncharged precursor species exposed to a trigger species is adapted to form a tethered ionised species and an untethered counterion species on contact / reaction with the trigger species, whereby mobility of the anchor species / tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the anchor species / tethered ionised species within the matrix.

[0087]

[0080] Also described herein is a method of producing an assembly for effecting selective migration of one ion of an ion pair across a potential gradient, the method comprising: providing an anchor species; and, mixing the anchor species with a precursor species such that the precursor species become tethered to the anchor species. In such embodiments, the mixture of the anchor species with the precursor species may comprise or be the matrix. The method optionally further comprises a step of forming the anchor species comprising precursor species tethered thereto into a matrix. In such embodiments, the mixture of the anchor species with the precursor species may comprise the matrix, but a binder or similar may be required to formulate the matrix for use in the assembly or device, or the anchor species comprising precursor species tethered thereto may be formed into a matrix by being dispersed into or otherwise mixed with other components, such as other anchor species, or other anchor species comprising precursor species tethered thereto, or a combination thereof.

[0088]

[0081] In one embodiment, there is provided a method of producing an assembly for effecting selective migration of one ion of an ion pair across a potential gradient, the method comprising: providing an anchor species comprising nanosheets; exfoliating the anchor species in mixture with a precursor species, optionally by milling, such that the nanosheets are separated from each other and their surface areas exposed for adsorption and reaction with the precursor species and the precursor species becomes tethered to the anchor species. In one embodiment, the method further comprises forming the anchor species comprising precursor species tethered thereto into a matrix.

[0089]

[0082] As shown in Figure 8(a), in one embodiment, an assembly 20 herein may comprise a substrate layer 21 comprising a metallised coating or other conductive layer 21a in contact with a lower face of the matrix layer 22 comprising the anchor species and ionised species, and an insulative outer layer 21b. The current collector layer 21a in contact with a surface of the matrix may be connected to an external circuit via a wire 25, and a second current collector wire 24 may be connected directly to another opposing surface of the matrix, 22a, at 23 using, e.g., conductive glue. Outer surface of assembly and upper face of the matrix, 22a, is exposed to a trigger species, such as CO2 gas, to trigger production of ionised species, such as ammonium ion groups, tethered to the anchor species distributed in and on the outer surface layer / upper face 22a of the matrix 22, and whose uneven distribution within the matrix layer 22 creates a potential gradient between current collected at point 23 and layer 21a that results in external current generation. In an alternative embodiment shown in Figure 8(b), matrix layer 22 may comprise two or more sub-layers (221a and 221 b) in vertical stacked arrangement, where sublayer 221a does not comprise any tethered ionised species but sublayer 221 b does comprise tethered ionised species.

[0090] Device for electricity generation

[0091]

[0083] The assemblies described herein may be used to construct a device for generating electricity. In one embodiment, the disclosure provides a device for generating electricity from a potential gradient, the device comprising, an assembly as described herein connected into an external circuit. In one embodiment, the device herein is an electricity generating device, or is an electricity generator, comprising an assembly as described herein connected into an external circuit.

[0092]

[0084] Although the format of the external circuit is not particularly limited, in one embodiment, a device is provided that comprises a first current collector in electrical contact with a first portion of the matrix, which may in some embodiments be a conductive layer on a substrate and in contact with the first portion of the matrix as described elsewhere herein, and a second current collector in electrical contact with a second portion of the matrix, which may in some embodiments be a conductive wire in contact with the second portion of the matrix and fixed using a conductive adhesive or glue, and wherein an ion gradient region is defined between the current collectors. Electrical connection of the first and second current collectors, such as with wires, to a load, such as capacitor or battery or the like, forms the completed external circuit. In other embodiments, the first and second current collectors can both be in the form of conductive layers or sheets / foil, provided that, if needed, there is some means for trigger species to react with a portion of the precursor species in the matrix. Such means may include enclosure of the matrix in a sealed environment, or exposure to a sealed source of trigger species. In such embodiments, as further described below, it is exposure to the trigger species that generates ions to be separated and that creates the potential difference and electrical signal.

[0093]

[0085] In one embodiment, the first and second portions of the matrix are first and second surfaces of the matrix, respectively, such as where the first surface opposes the second surface. In a flat sheetlike matrix, the first portion may be an upper surface facing away from the substrate, and the second portion may be the opposing bottom face facing the conductive layer on the substrate. It will be appreciated that the current collectors or conductive materials must be positioned such that a potential gradient can form between them. Advantageously, positioning the current collectors on opposing faces of a thin, sheet-like matrix reduces the ion path distance for separation of ions, and therefore detection of electrical signal as the potential gradient quickly establishes. However, there may be other circumstances under which an alternative placement of the current collectors is desired.

[0094]

[0086] As shown in Figure 5, in one embodiment, a device herein may comprise a current collector 14 in contact with matrix layer 16 comprising the anchor species 11 and ionised species 12. A current collector wire may be connected directly to a surface of the matrix, 16, at 15 using, e.g., conductive glue. Outer surface of matrix 16 is exposed to a trigger species, CO2 gas at 10, to trigger production of ionised species, -NHs+groups 12 tethered to the anchor species distributed in and on the outer surface layer of the matrix 16, and whose uneven distribution within the matrix layer 16 creates a potential gradient that drives movement of HCOs" as shown in the direction 13 between current collected at point 15 and layer 14. Anchor species comprising tethered ionised species are inhibited from moving through the matrix 16 following the HCOs- ions due at least in part to their size and structure, and the ion separation of the ion pairs results in external current generation.

[0095] Uses and methods

[0096]

[0087] The assemblies and devices herein may be used to generate electricity. Accordingly, described herein is use of an assembly or device as defined herein to generate electricity. More broadly, there is also described herein use of size modification of one ion in an ion pair to create a potential gradient and generate electricity. These uses may be realised through the methods described below.

[0097]

[0088] In one embodiment, the present disclosure provides a method of separating one ion of an ion pair across a potential gradient. The method may comprise providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient whereby the untethered counterion species is separated from the tethered ionised species across the potential gradient. The matrix, anchor species, ionised species, and counterion species are as described elsewhere herein.

[0098]

[0089] In one embodiment, the disclosure herein provides a method of generating electricity from a potential gradient, the method comprising providing an assembly or device as described herein. Such embodiments may be appropriate where the assembly or device comprises a matrix loaded with anchor species, wherein a portion of the anchor species comprise tethered ionised species and untethered counterion species.

[0099]

[0090] In another embodiment, the present disclosure provides a method of generating electricity from a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity. The matrix, anchor species, ionised species, and counterion species are as described elsewhere herein.

[0100]

[0091] In another embodiment, the present disclosure provides a method of generating electricity from a potential gradient, such as a potential gradient established by separation of one ion of an ion pair, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto that is adapted to react with a trigger species, and, contacting a portion of the matrix with the trigger species, wherein the precursor species and trigger species react to form a tethered ionised species and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity. The matrix, anchor species, ionised species, counterion species, precursor species, and trigger species are as described elsewhere herein.

[0101]

[0092] In another embodiment, the disclosure herein provides a method of generating electricity from a potential gradient, the method comprising providing an assembly or device as described herein and exposing a portion of the anchor species in the matrix having precursor species tethered thereto to a trigger species. Such embodiments may be appropriate where the assembly or device comprises a matrix loaded with anchor species, wherein at least a portion, if not all, the anchor species comprise tethered precursor species, wherein a portion of the precursor species react with a trigger species to form tethered ionised species and untethered counterion species.

[0102]

[0093] In another embodiment, the present disclosure provides a method of generating electricity from a potential gradient as described above using an assembly or device as described herein.

[0103] Embodiments Embodiment 1. An assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto, and an untethered counterion species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

[0104] Embodiment 2. The assembly of Embodiment 1 , wherein the tethered ionised species is formed from a precursor species adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, optionally in the presence of water.

[0105] Embodiment 3. The assembly of Embodiment 2, wherein the precursor species is an uncharged precursor species.

[0106] Embodiment 4. The assembly of Embodiment 2 or Embodiment 3, wherein the precursor species comprises a functional group that chemically reacts with the trigger species on contact to form the tethered ionised species and the untethered counterion species.

[0107] Embodiment 5. The assembly of any one of Embodiments 2 to 4, wherein the precursor species has a viscosity of from 20,000 to 150,000 cps at 25 °C.

[0108] Embodiment 6. The assembly of any one of Embodiments 2 to 5, wherein the precursor species is tethered to the anchor species by adsorption, that is, the precursor species is adsorbed to the anchor species, or by chemical bonding of the precursor species to the anchor species, optionally wherein the precursor species is loaded onto the anchor species at a concentration of from 1 to 50 wt%, such as from 1 to 20 wt%.

[0109] Embodiment 7. The assembly of any one of Embodiments 2 to 6, wherein the precursor species is adsorbed onto the anchor species during a process of exfoliation, optionally milling. Embodiment 8. The assembly of any one of Embodiments 2 to 7, wherein the precursor species is a Lewis base.

[0110] Embodiment 9. The assembly of any one of Embodiments 2 to 8, wherein the precursor species comprises one or more amine functional groups.

[0111] Embodiment 10. The assembly of any one of Embodiments 2 to 9, wherein the precursor species is selected from a natural or synthetic linear or branched alkyl amine or polyamine, such as a C2-C20 amine or polyamine.

[0112] Embodiment 11. The assembly of any one of Embodiments 2 to 10, wherein the precursor species is selected from putrescine, cadaverine, spermidine, spermine, and branched or linear polyethyleneimine, optionally wherein the polyethyleneimine has an average Mn of 5,000-20,000 and average MW of 10,000-40,000.

[0113] Embodiment 12. The assembly of any one of Embodiments 2 to 11 , wherein the trigger species is selected from carbon dioxide sulphur dioxide and nitrogen dioxide, such as is carbon dioxide, optionally provided in the form of a humified gas stream. Embodiment 13. The assembly of any one of the preceding Embodiments, wherein the portion of the anchor species comprising the ionised species is a confined portion, such as a portion confined to a region of the matrix, such as confined to a surface region of the matrix.

[0114] Embodiment 14. The assembly of any one of the preceding Embodiments, wherein the anchor species comprises nanosheets of a two-dimensional network-forming material.

[0115] Embodiment 15. The assembly of any one of the preceding Embodiments, wherein the anchor species comprises exfoliated nanosheets of a two-dimensional (2D) network-forming material.

[0116] Embodiment 16. The assembly of any one of the preceding Embodiments, wherein the anchor species comprises nanosheets of a two-dimensional network-forming material, optionally a 2D network-forming material, selected from: hexagonal boron nitride (h-BN), graphene, graphitic carbon nitride (g-CN), silicene, germanene, stanene, and phosphorene, or from a transition metal dichalcogenide (TMDC), a transition metal halide, a metal carbide / nitride (Mxene), a 2D oxide / hydroxide, a 2D metal-organic framework, a 2D covalent organic framework, and a 2D nanomaterial, or an OD quantum dot, a 1 D nanotube, or a 3D nanoparticle, optionally selected from: hexagonal boron nitride (h-BN), graphene, graphitic carbon nitride (g-CN), a transition metal dichalcogenide (TMDC), a transition metal halide, a metal carbide / nitride (Mxene), a 2D oxide / hydroxide, a 2D metal-organic framework, and a 2D covalent organic framework, optionally selected from: hexagonal boron nitride (h-BN), graphene, and graphitic carbon nitride (g-CN).

[0117] Embodiment 17. The assembly of any one of the preceding Embodiments, wherein the anchor species has a maximum dimension of from about 50 nm to about 10 pm and a minimum dimension of <10 nm, optionally wherein the anchor species comprises nanosheets having a length and width of about 80-500 nm and a height of <5 nm, optionally wherein the anchor species has a maximum dimension that is at least 10Ox, or at least 500x, or at least 10OOx, or at least 5000x the size of a maximum dimension of the untethered counterion species.

[0118] Embodiment 18. The assembly of any one of the preceding Embodiments, wherein the ionised species is tethered to the anchor species by adsorption, optionally through exfoliating the anchor species with a precursor species, optionally wherein the untethered counterion species has a molecular radius in the order of about < 25 A, or about < 10 A, or about < 7 A, or about < 5 A. Embodiment 19. The assembly of any one of the preceding Embodiments, wherein the ionised species and untethered counterion species are formed on reaction of carbon dioxide with an amine functional group, thereby forming tethered ionised species comprising ammonium cations and hydrogen carbonate anion untethered counterion species.

[0119] Embodiment 20. The assembly of any one of the preceding Embodiments, wherein the ionised species is loaded onto the anchor species at a concentration of from 1 to 50 wt%, such as from 1 to 20 wt%.

[0120] Embodiment 21. The assembly of any one of the preceding Embodiments, wherein the matrix is a self-supporting structure or is mounted on a substrate. Embodiment 22. The assembly of any one of the preceding Embodiments, wherein the matrix is a self-supporting structure comprising a hydrogel, optionally a three-dimensionally interconnected hydrogel comprising pores and channels.

[0121] Embodiment 23. The assembly of any one of the preceding Embodiments, wherein the matrix comprises agarose gel.

[0122] Embodiment 24. The assembly of any one of the preceding Embodiments, wherein the matrix comprises a hydrogel having an average pore size of from 50 to 350 nm.

[0123] Embodiment 25. The assembly of any one of the preceding Embodiments, wherein the matrix comprises two or more sections in electrical contact with each other.

[0124] Embodiment 26. The assembly of Embodiment 25, wherein the matrix comprises two sections in electrical and fluid contact with each other, the first section being an ionised species formation matrix and the second section being an untethered counterion species receiving section.

[0125] Embodiment 27. The assembly of Embodiment 25, wherein the matrix comprises three sections in electrical contact with each other, the first section being an ionised species formation matrix, the second section being an untethered counterion species receiving section, and the third section being sandwiched between the first and second sections and being a travel pathway for untethered counterion species.

[0126] Embodiment 28. The assembly of Embodiment 25 or Embodiment 26, wherein the ionised species forms in the first section through contact of a precursor species with a trigger species, wherein the precursor species comprises a functional group that chemically reacts with the trigger species.

[0127] Embodiment 29. The assembly of any one of Embodiments 25 to 27, wherein the first and second sections, and third section if present, are mounted in a side-by-side configuration.

[0128] Embodiment 30. The assembly of any one of Embodiments 25 to 27, wherein the first and second sections, and third section if present, are mounted in a vertically stacked configuration. Embodiment 31. The assembly of any one of the preceding Embodiments, wherein the matrix is mounted on a non-permeable substrate having a conductive surface, optionally a flexible non- permeable substrate having a conductive surface, wherein the matrix is mounted on the conductive surface thereof.

[0129] Embodiment 32. The assembly of Embodiment 31 , wherein the non-permeable substrate having a conductive surface is selected from a metal foil, a metal cloth, or a metallised polymer, wherein the metal is optionally selected from copper, silver, gold and aluminium, optionally wherein the substrate further comprises a polymer selected from polyethylene terephthalate (PET) or polyester, polyethylene, polypropylene, and nylon.

[0130] Embodiment 33. The assembly of any one of the preceding Embodiments, wherein the matrix is at least partially electrically conductive.

[0131] Embodiment 34. The assembly of any one of the preceding Embodiments, wherein the matrix has a sheet resistance of from 0.1 MQ / square to 10 MQ / square, such as of about 1 MQ / square. Embodiment 35. The assembly of any one of the preceding Embodiments, wherein the matrix consists, or consists essentially of, nanosheet species, such as nanosheets having thicknesses of < 10 nm, optionally with a binder.

[0132] Embodiment 36. The assembly of any one of the preceding Embodiments, wherein the matrix consists, or consists essentially of, anchor species, such as a mixture of two or more anchor species, optionally with a binder.

[0133] Embodiment 37. The assembly of any one of the preceding Embodiments, wherein the anchor species is present in the matrix at a concentration of from about 1 wt% to about 100 wt%, such as of from about 25 wt% to 100 wt%.

[0134] Embodiment 38. The assembly of any one of the preceding Embodiments, wherein the matrix comprises an electrically conductive material in combination with the anchor species or wherein the matrix comprises a mixture of two or more anchor species, at least one of which is electrically conductive or at least partially electrically conductive.

[0135] Embodiment 39. The assembly of Embodiment 35, wherein the matrix comprises a mixture of graphene with hexagonal boron nitride (h-BN), graphitic carbon nitride (g-CN), silicene, germanene, 28tanine, phosphorene, a transition metal dichalcogenide (TMDC), a transition metal halide, a metal carbide / nitride (Mxene), a 2D oxide / hydroxide, a 2D metal-organic framework, a 2D covalent organic framework, a 2D nanomaterial, an 0D quantum dot, a 1 D nanotube, and / or a 3D nanoparticle, preferably is a mixture of graphene with hexagonal boron nitride (h-BN) and / or graphitic carbon nitride (g-CN).

[0136] Embodiment 40. The assembly of any one of the preceding Embodiments, wherein the matrix further comprises a binder, such as poly(vinylidene difluoride) (PVDF), polytetrafluoroethylene (PTFE), poly(acrylic acid) (PAA), styrene-butadiene rubber (SBR), polyethylene oxide (PEG), sodium carboxymethylcellulose (CMC), or alginate.

[0137] Embodiment 41. The assembly of any one of the preceding Embodiments, wherein the untethered counterion species comprises a carbonate and / or carbamate, such as is hydrogen carbonate (HCO3 ).

[0138] Embodiment 42. The assembly of any one of the preceding Embodiments, wherein the matrix, and substrate if present, are in the form of a flat or substantially flat layer, or have length and width dimensions at least 10x greater, optionally 10Ox to 10OOx greater, than their height dimension, optionally wherein the height (thickness) dimension is of from about 1 pm to about 5 cm.

[0139] Embodiment 43. The assembly of any one of the preceding Embodiments, wherein the anchor species and tethered ionised species are impaired by one or more of: molecular size, molecular shape, and / or intermolecular interactions, such as hydrogen bonding interactions.

[0140] Embodiment 44. The assembly of any one of the preceding Embodiments, wherein matrix, and substrate if present, are flexible, such as can be bent at least 90° or at least 180° without damage or loss of function. Embodiment 45. The assembly of any one of the preceding Embodiments, wherein the potential gradient is an electric potential gradient, a chemical potential gradient, or a combination of the two.

[0141] Embodiment 46. Use of an assembly as defined in any one of Embodiments 1 to 45 to generate electricity.

[0142] Embodiment 47. Use of size modification of one ion in an ion pair to create a potential gradient and generate electricity.

[0143] Embodiment 48. A device for generating electricity from a potential gradient, the device comprising: an assembly according to any one of Embodiments 1 to 45 connected into an external circuit.

[0144] Embodiment 49. The device of Embodiment 48, wherein the device comprises: a first current collector in electrical contact with a first portion of the matrix, and a second current collector in electrical contact with a second portion of the matrix, wherein an ion gradient region is defined between the current collectors, wherein the first and second current collectors are electrically connected to form the external circuit.

[0145] Embodiment 50. The device of Embodiment 49, wherein the first and second portions of the matrix are first and second surfaces of the matrix, respectively, optionally wherein the first surface opposes the second surface.

[0146] Embodiment 51. A method of separating one ion of an ion pair across a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient whereby the untethered counterion species is separated from the tethered ionised species across the potential gradient.

[0147] Embodiment 52. A method of generating electricity from a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity.

[0148] Embodiment 53. A method of generating electricity from a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto that is adapted to react with a trigger species, and, contacting a portion of the matrix with the trigger species, wherein the precursor species and trigger species react to form a tethered ionised species and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity. Embodiment 54. A method of generating electricity from a potential gradient according to Embodiment 52 or Embodiment 53 using the assembly according to any one of Embodiments 1 to 45 or the device according to any one of Embodiments 48 to 50.

[0149] Embodiment 55. A method of producing an assembly for effecting selective migration of one ion of an ion pair across a potential gradient, the method comprising: providing an anchor species; and, mixing the anchor species with a precursor species such that the precursor species become tethered to the anchor species, and, optionally, forming the anchor species comprising precursor species tethered thereto into a matrix, optionally wherein the assembly is according to any one of Embodiments 1 to 45.

[0150] Examples

[0151] Example 1 - Gel composite generator

[0152] Materials and methods

[0153]

[0094] The PEI-functionalised nanosheets were synthesised using a sticky exfoliation process. Briefly, 0.5 g pristine bulk layered material such as hexagonal boron nitride (powder, -1 pm, 98%, Sigma-Aldrich), graphite (Flakes, 99% Carbon, Sigma-Aldrich), carbon nitride and 2 g PEI (Mnat -10,000 by GPC, average Mw at -25,000 by LS, Sigma-Aldrich, 408727) were charged into a 250 mL ZrO2 milling jar. Three types of ZrOs balls with different weights and diameters (100 g d=10 mm, 200 g d = 5 mm, and 20 g d = 0.1 mm) were used as grinding balls. The milling jar was loaded into a planetary ball mill (ZQM-P2, Changsha Mitr Instrument Equipment Co., Ltd, Revolution radius: 10 cm, Rotation radius: 39 mm), and the rotation speed was set at 250 rpm for revolution and 500 rpm for rotation. After milling for a set duration (10 h unless stated otherwise), 100 g of DI water was added to the milling jar to wash out the nanosheets and PEI mixture. The resulting water solution containing the mixture was filtered onto nylon membranes (pore size: 0.45 m, diameter 47 mm, Sterlitech, USA) and rinsed with water repeatedly until the pH value of the outlet water reached 8. The nylon membranes with the nanosheets atop were then subjected to ultrasonication for 30 min (Unisonics FXP12M, 40 kHz, 100 W) to re-disperse the nanosheets in water. Finally, the dispersion was centrifuged at RCF of 236 G (Rotor 12181 , Sigma 2-16 P) for 20 min to remove thick flakes. The supernatant was decanted as the final water dispersion product of PE-functionalised nanosheets.

[0154]

[0095] Ultrahigh-viscosity liquid polyethyleneimine (PEI) achieved simultaneous exfoliation and functionalisation, where the high viscosity of PEI efficiently broke and delaminated layered bulk h-BN particles, whilst grafting / tethering reactive-ready amine groups onto the freshly exfoliated h-BN nanosheets. The resulting product was named “h-BN-NHs”. Transmission electron microscopy (TEM) images show that the resultant h-BN nanosheets had a lateral size in the range of from -100 to 300 nm (Fig. 1 (c)). The thermogravimetric and elemental analysis also reveal that the PEI molecules bonded to h-BN nanosheets accounted for 7.92 wt% of the final product. The crystalline structure of BN lattices was preserved even after exfoliation and PEI grafting / tethering via chemical bonding, as shown by the characteristic X-ray diffraction peaks at 26.2° and 42.8°, corresponding to (002) and (100) planes of hexagonal boron nitride. Moreover, the X-ray diffraction (XRD) peaks of exfoliated h- BN show a significantly reduced intensity and broadened width, indicating successful exfoliation in terms of lateral size and layer number of h-BN.

[0155]

[0096] Agarose powder (Sigma-Aldrich, BioReagent, gel point 36 °C ± 1 .5 °C) was dissolved in water at 80 °C to obtain the hydrogel precursor solutions at concentrations of 2 wt% and 4 wt%, respectively, and were stored at 70 °C oven for generator fabrication. A PDMS (Sylgard 184, Dow Corning) rubber cell measuring 6 mm 2 mm x 0.4 mm was cut and used as the generator mould. Current collectors were created by coating silver paint at the bottom of the two ends of the PDMS cell. Carbon tape and platinised titanium mesh (Fuel cell store, 592770) were also adopted as current collectors. After embedding electric collectors, pure agarose solution (2 wt%) at 70 °C was firstly drop cast into the PDMS mould and left in the atmosphere for 30 min to undergo the sol-gel transition to form a hydrogel film. Two ends of the pure hydrogel film (2 mm x 2 mm x 0.4 mm) were then graved with only the middle part left in the mould. Second, the nanosheets solution with a concentration of 2 mg / mL (unless stated otherwise) was heated to 70 °C and mixed with equal volume of agarose precursor solution at the concentration of 4 wt%. The obtained mix solution was drop casted into the two ends of the PDMS mould and left for another 30 min to finally obtain the 3-module NAH generator. For the whole piece of NAH generator, the agarose and nanosheet mix solution was directly drop casted into the corresponding mould without the procedure of casting pure agarose solution. The device was subsequently connected to an external circuit equipped with a source meter (Keithley 2450) to monitor the generator's electrical signals during testing.

[0156]

[0097] Agarose hydrogel was selected as the matrix due to its highly porous structure with suitable pore size which is large enough to transport bicarbonate ions but too small for h-BN-NHs+nanosheets to penetrate through freely. The mixture solution of h-BN-NHs nanosheets and agarose was drop- casted into a polydimethylsiloxane (PDMS) mould and underwent a thermo-responsive sol-gel transition to produce a flexible hydrogel film (Fig. 1 (d),(e)). The ionic PEI molecules grafted on / tethered to h-BN nanosheets improved the dispersibility of nanosheets in agarose solution in comparison to neat hydrophobic h-BN (Fig. 1 (d), €). The agarose molecules formed a three-dimensional interconnected reticular matrix with an average diameter of 102 nm resulting from the extended hydrophilic polymer chains (Fig. 1 (d)). Inter / intra-chain crosslinking was established by weaving the functional groups of (-OH) of agarose molecules into a coordinated hydrogen bonding network. The properties of the hydrogel matrix provide strong mechanical strength and high flexibility in shape. As shown in Fig. 1 (a), to construct the prototype NAH electricity generator, two NAH hydrogels, serving as ion releasing and receiving reservoirs, respectively, were connected with a pure agarose hydrogel which acted as high-speed ion-selective channels.

[0157]

[0098] The open circuit voltage and short circuit current of the NAH composite generator were measured using a source meter (Keithley 2450) under ambient conditions. The current output test was set to 0 nA and the voltage was set to 0 V for the open circuit and short circuit measurements, respectively. The generator was placed in a testing box (50 cm by 25 cm) with a CO2 inlet at its bottom and outlet at the top, and the two collectors on the left / right sides were short connected via an external circuit to discharge the device until the Isc dropped below 5 nA. This pre-discharging process helped to reduce the influence of slight chemical potential differences within the hydrogel composite caused by artificially introduced asymmetric structure. CO2 was then fed into the box at a flow rate of 2.5 L / min 1 for 3 min, after which the device was covered for further testing. To evaluate the power density, the generator was connected with external resistors of varying resistances, and the external current was monitored for density calculation. The l-V curves of the nanosheet water solution were obtained using a pair of Ag / AgCI electrodes with applied voltages ranging from -0.2 V to 0.2 V.

[0158]

[0099] The regeneration of the generator was explored by choosing a pH swing strategy to study its multiple utilisation potential. Following 5 cycles of electricity generation, the generator was removed and immersed in a calcium hydroxide (Ca(OH)s, > 95%, Sigma-Aldrich) solution with a pH value of 10 for 1 h. This was followed by washing the generator in excessive DI water 3 times. Subsequently, the generator was placed back in the testing box and subjected to the same testing procedures.

[0159] Electricity generation

[0160]

[0100] To evaluate the electricity generation capacity of NAH electricity generator, it was placed into a testing box (50 by 25 cm) with a CO2 inlet. The ion receiving reservoir side was covered while the ion-releasing reservoir side was exposed to CO2 gas. To start the testing, CO2 was fed into the testing box at a rate of 2.5 L / min for 3 min. Upon CO2 feeding, the open-circuit voltage (Voc) of the NAH electricity generator peaked at approximately 80 ± 10 mV within 1 to 2 h (Fig. 2(a)), and then gradually decreased to an undetectable level in about 15 h, confirming that electricity was generated upon CO2 adsorption. Gas CO2 was then fed into the box again to start another test cycle. The electricity generation was found to be robust, with the peak Voc maintained at a level of 80 ± 10 mV in five consecutive tests spanning 60 h. The short-circuit current (Isc) behaved similarly to Voc, peaking at approximately 150 ± 20 nA for 1 to 2 h before it slowly faded to 0 in the following 5 to 10 h (Fig. 2(b)). However, unlike Voc, the peak Isc decayed after each CO2 adsorption cycle, and the peak Isc of the 5thcycle was only half that of the 1stcycle. For Voc testing, the total current was set as 0, which equals to an infinite external load resistance (R to «) while the total resistance of the Isc testing is only contributed by the intrinsic resistance of the generator. Thereby, the lower total resistance during Isc testing led to higher discharging current and thus an apparent performance decay relative to that of Voc testing.

[0161]

[0101] The observed ISE decay necessitates a proper regeneration method to ensure the reusability of NAH electricity generator. Referring to the Bjerrum plot, the adsorbed CO2 presents mainly as HCOs" ions in the pH range from 6.0 to 9.0. Considering the aqueous environment of the NAH electricity generator, the commonly adopted pH swing strategy should be able to remove CO2 and regenerate NAH electricity generator. During the pH swing desorption process, HCOs" ions can transition into CO2 ions if the pH value is increased above 10.0, allowing sequestration by reacting with Ca2+to form CaCOs precipitates. Alternatively, lowering the pH value below 4.0 converts HCOs" ions into CO2 gas, which can be harvested for utilisation. The regeneration was conducted by immersing the generator in an alkaline buffer solution (pH=10). The outcomes demonstrate that the Isc and Voc signals can be fully restored to their initial levels via pH swing after five adsorption-and- discharging cycles (refer to the last regeneration cycle in Fig. 2(b)).

[0162]

[0102] Electricity generation of NAH electricity generator was boosted by increasing the density of CO2 adsorption sites in NAH generator through increasing nanosheet concentration or raising PEI grafting / tether ratios of h-BN-NHs+. Increasing the concentration of h-BN-NHs nanosheets in NAH hydrogel from 1 mg / mL 1 to 5 mg / mL resulted in an increase of Voc from 90.4 mV to 145.7 mV with an extended half-value period of VOE from 3.5 h to 5.4 h (Fig. 2(c)). No further significant enhancement was achieved by increasing the concentration to 10 mg / mL. Raising the PEI grafting / tether ratios of h-BN-NHs nanosheets from 1 .46 wt% to 8.95 wt% boosted Voc by five times, and the half-value period was also extended by over two times (Fig. 2(d)).

[0163]

[0103] To gain a better understanding of the origin of electricity generation, NAH electricity generator was tested under various conditions. First, the silver electrodes of the electricity generator were replaced by inert carbon and platinised titanium electrodes, respectively. The devices using inert electrodes still generated electricity with a peak V of -90mV (Fig. 2e). These data rule out the possibility that electricity comes from the chemical reactions on the electrodes. Second, when we replaced CO2 with N2 as the feed gas, no obvious electricity signals were detected (Fig. 2(f)), indicating that electricity was generated from CO2 adsorption.

[0164]

[0104] To investigate the importance of the 2D skeletons of h-BN-NH2 nanosheets in the hydrogel matrix, we tailored the components of NAH hydrogel. When PEI-functionalised graphene and graphitic carbon nitride (g-CN), which have similar structures to h-BN-NH2 nanosheets, were applied as nanofillers in hydrogel, the as-constructed generators had similar performance to the h-BN-NH generator (Fig. 2(e)). However, when graphene oxide (GO) nanosheets with -OH / -COOH groups were used, no electricity was generated under identical operation conditions, highlighting the critical role of -NH / -NH2 groups (Fig. 2(f)). In addition, when pure liquid PEI was used to replace 2D h-BN-NH2 nanosheets, the generator failed to generate electricity also (Fig. 2(f)). These results reveal that large physical size of nanosheets (hundreds of nanometres) and abundant amino groups are essential for the electricity generation in NAH electricity generator.

[0165]

[0105] The CO2 adsorption capacity of h-BN-NH2 nanosheets was measured as shown in Fig. 3(a). The results reveal that h-BN-NH2 nanosheets grafted / tethered with 7.92 wt.% of PEI functionalities exhibit a CO2 adsorption capacity of 0.238 mmol / g at standard temperature and pressure, while bulk h-BN exhibits no measurable CO2 adsorption capacity. To confirm the production of equimolar amine and bicarbonate ions, the pH change of h-BN-NH2 water solution during CO2 adsorption process was monitored, showing a rapid decrease from 8 to 4.5 in minutes (Fig. 3(b)). The release of ions from adsorption is further substantiated by a threefold higher ion conductivity observed in the nanosheet solution bubbled with CO2 compared to N2 (Fig. 3(c)).

[0166]

[0106] Selective directional ion transport is required following the release of ions to achieve diffusion current. The pore size of the hydrogel matrix is 102 nm on average, which is much larger than the physical size and the hydrated radius (A~4A) of HCOs". The size difference significantly reduces the physical and charge effects and lowers the energy barrier for HCOs- movements in the ion channel. Notably, the hydrogel channels greatly limit the h-BN-NHs+ ion diffusion due to two main reasons. First, the lateral size of the h-BN-NHs+nanosheets (100-300 nm) is comparable to the hydrogel pore size. As a result, these nanosheets are physically trapped within the network of hydrogel chains. Second, the -OH groups on agarose chains can form strong interactions with h-BN-NHs+nanosheets through Van der Waals force and electrostatic interaction. Computational calculation indicates that the interaction energy of agarose chains with h-BN-NHs+nanosheets is up to ~80 KJ / mol, while that of bicarbonate ions only peaks at ~2.2 KJ / mol (Fig. 3(d), (e)). These results show that the confined size exclusion effect, combined with intensive molecular interactions of the interlocked 3D hydrogen bond in hydrogel, anchors the nanosheet ions and severely limits their movement within the matrix.

[0167]

[0107] To gain further insight into selective ion transport within the hydrogel, an ion-diffusion experiment was conducted. Two cells of a custom-made diffusion device, acting as ion- releasing / receiving compartments, were separated by a hydrogel bridge serving as the selective ion channel. A h-BN-NHs nanosheet water solution and a sodium bicarbonate salt solution, representing positive and negative ions, respectively, were separately filled into the feeding cell while the receiving cell was filled with deionised (DI) water. The concentration gradient between the two cells drove the h-BN-NHs nanosheets or sodium bicarbonate ions to diffuse from their respective cells to the Dl-water cell through the hydrogel bridge. Quantitative analysis revealed a high diffusion rate of sodium bicarbonate ions in the hydrogel at 0.16 mol / m2 / h which is roughly 1 .8x106times faster than that of h- BN-NH2 nanosheets in a testing span of four days (D- / D+ Fig. 3(f)). We also monitored the / -I / curves of h-BN-NH2 water solutions after CO2 adsorption in an H-cell, with a 3-fold concentration gradient separated by pure hydrogel. From this, a transference number of anion (t-) nearing 1 was derived. This outcome further indicates the near-perfect anion / cation selectivity achieved by the hydrogel channels. Therefore, the distinguishable ion diffusion rate in artificial channels between oppositely charged ions is the underlying principle for the ion-transport-induced electricity generation process in our NAH electricity generator.

[0168]

[0108] Experimental verification was also conducted by controlling the length of the ion diffusion path, specifically by adjusting the width of the pure hydrogel in the middle. Reducing the width from 3 cm to 1 cm increased the peak lSc, escalating from 140 nA to 169.7 nA, indicating a higher peak ion diffusion flux. Moreover, it achieved the peak Isc in only 11.4 min compared to the 20.4 min required by the prototype of 3 cm. Additionally, the time taken to decay to half its peak Isc decreased to 24.6 min from 40.2 min. This expedited charging and discharging process, achieved through the reduction of the diffusion path, agrees well with the characteristics of ion-diffusion-induced power generation. Practical demonstration of NAH electricity generator

[0169]

[0109] The practicality of NAH electricity generator was evaluated in terms of energy storage, conversion efficiency, scalability, response time, and modular integration. The generated electricity can be stored by charging a commercial capacitor (0.5 pF) (Fig. 4a). When connected to an external circuit with a 0.5 MQ resistor during an adsorption cycle, the generator reaches its peak total energy generation of 24 pW-h / mol with a volumetric density of 0.0027 pW / cm3(Fig. 4b), corresponding to an energy conversion efficiency of approximately 0.6% relative to the total input energy. Although the energy conversion efficiency aligns with those of recently reported moisture electricity generators, the present peak density falls short of the required threshold. Given that near perfect selectivity has been achieved, the bottleneck issue affecting the current low power density appears to be the insufficient ion flux in the system. Therefore, to improve the power density of the NAH power generator, we pursued two distinct strategies: optimising the device configuration for improved ion transport efficiency and enhancing CO2 adsorption capacity for a higher concentration gradient. These two approaches achieved an overall 10-fold improvement in the power density.

[0170]

[0110] To demonstrate the scalability of NAH electricity generator, a 180 mm x 180 mm x 4 mm NAH composite hydrogel was fabricated. The hydrogel composite film was then cut into small generators (60 mm x 20 mm x 4 mm). Connecting four of them in either series or parallel, led to a linear increase in output Voc of approximately 280 mV or lscof approximately 400 nA (Fig. 4c). As the electricity generation process of NAH electricity generator is primarily determined by selective ion transport within NAH hydrogel matrix, the speed of electricity generation can be theoretically maximised by rational design of the ion-diffusion path length and the effective ion diffusion area. To prove this hypothesis, we designed another type of the NAH electricity generator, in which two NAH hydrogels (20 mm x 20 mm x 4 mm) sandwiched a pure hydrogel of the same size but were vertically stacked (Fig. 4d). This configuration reduces the length of the ion channel while expanding its effective area. A prompt rather than time-lagged electricity generation process was observed in the vertical configuration, reducing the response time of NAH electricity generator from minutes to seconds (Fig. 4d).

[0171]

[0111] When 50 generators (10 in series as a group. 5 groups in parallel) were integrated with the vertical configuration, a stable output voltage of 5 V was generated (Fig. 4e). The generated electricity was sufficient to power a light-emitting diode (Fig. 4(g)) with an operating voltage of 1 .6 V and forward current of 1 mA. Upon lighting the diode, the induced voltage dropped below the operating voltage but was rapidly recovered once the external circuit was disconnected. Only a minor reduction in the voltage was observed after four cycles of charge and discharge (Fig. 4(f)). This discharge and selfcharge behaviour further confirm that the electricity generated by the device results from selective ion transport.

[0172] Example 2 - Membrane generator

[0173] Methods and materials

[0174]

[0112] A flexible membrane comprising amine-functionalised nanosheets was made through highspeed mixing or ball milling. Polyamines such as putrescine, spermidine, and spermine, alongside branched or linear polyethyleneimine (PEI), were blended with layered materials in a high-speed mixer or ball mill. This method facilitated the grafting / tethering of amines onto the nanosheets and exfoliated the layered materials into monolayer to few-layer nanosheets similarly to as described in Example 1 above. In one generator, a conductive PEI functionalised graphene was made with a 1 -20 wt% PEI loading, and was mixed with 5 to 50 wt% of insulator PEI functionalised boron nitride (also with 1 -20 wt% PEI loading). This was formed into a layer of from 1 pm to 500 pm thickness by adjusting the deposition density on a current collector. A 50 pm layer made by mixing an equal amount of PEI functionalised graphene and PEI functionalised boron nitride had a suitable sheet resistance for electricity generation of 105Q.

[0175]

[0113] Amine / nanosheet mixtures were directly utilised as the membrane starting material. The membrane product was obtained by coating the starting material (amines / polymer) onto the substrate, typically, a polymeric non-woven fabric like PET was chosen with one face completely coated with a conductive metal, such as copper, using the sputter deposition method. Spray coating or doctor blade coating was used to apply the amine / polymer mixture to a thickness controlled by loading amount, such as to a thickness of to 50 pm to 100 pm. The generator was connected to an external circuit through a wire connected directly to the top face of the starting material on the substrate and fixed with conductive glue.

[0176]

[0114] Only the top face of the starting material on the substrate was exposed to CO2.

[0177] Internal Resistance

[0178]

[0115] To manage the intrinsic electrical sheet resistance of the nanosheets placed atop the substrate, which function both as CO2 adsorbers and electrical collectors, the sheet resistance was optimised by selecting two types of nanosheet materials: conductive materials like graphene and insulators such as carbon nitride or boron nitride. Adjusting the weight ratio of these materials allowed for the sheet resistance of the top layer to be tuned to a level that supported effective signal transmission without risking internal short circuits.

[0179] Performance and mechanism

[0180]

[0116] When adsorbing CO2, the top surface of the generator released positively charged amine ions and negative bicarbonate ions. The bottom surface, however, could not access CO2 and thus no ions were generated. The positively charged ions were fixed on the nanosheets or amine molecules, while the negative ions freely diffused to the bottom driven by the concentration difference between the top and bottom surface. This ion flow then translated into electrical signals by the top layers and bottom conductive substrates and that could be stored or utilised in an external circuit. Since the concentration gradient between the top layer and the bottom layer was maintained throughout the testing period, the electrical signal was maintained at a constant level of 0.65 V (Figure 7), instead of pulse signals obtained by the generator of Example 1 .

[0181]

[0117] The present invention is described with reference to the above examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

[0182]

[0118] It will be apparent to the person skilled in the art that while the invention has been described in some detail for the purposes of clarity and understanding, various modifications and alterations to the embodiments and methods described herein may be made without departing from the scope of the inventive concept disclosed in this specification.

Claims

Claims1 . An assembly for effecting selective migration of an ion species across a potential gradient, the assembly comprising: a matrix comprising an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto, and an untethered counterion species, wherein mobility of the tethered ionised species is impaired by the matrix such that the untethered counterion species selectively migrates across a potential gradient created by uneven dispersion of the tethered ionised species within the matrix.

2. The assembly of claim 1 , wherein the tethered ionised species is formed from an uncharged precursor species adapted to form the tethered ionised species and the untethered counterion species on contact with a trigger species, optionally in the presence of water.

3. The assembly of claim 2, wherein the precursor species comprises a functional group that chemically reacts with the trigger species on contact to form the tethered ionised species and the untethered counterion species.

4. The assembly of claim 2 or claim 3, wherein the precursor species is adsorbed onto and / or chemically bonded to the anchor species during a process of exfoliation.

5. The assembly of any one of claims 2 to 4, wherein the precursor species comprises one or more amine functional groups, optionally selected from a natural or synthetic linear or branched alkyl amine or polyamine, such as polyethyleneimine or a C2-C20 amine or polyamine.

6. The assembly of any one of claims 2 to 5, wherein the trigger species is selected from carbon dioxide, sulphur dioxide and nitrogen dioxide, such as is carbon dioxide, optionally wherein the trigger species is provided in a humidified gas stream.

7. The assembly of any one of the preceding claims, wherein the portion of the anchor species comprising the ionised species is a confined portion, such as a portion confined to a region of the matrix, such as confined to a surface region of the matrix.

8. The assembly of any one of the preceding claims, wherein the anchor species comprises nanosheets of a two-dimensional network-forming material, optionally a 2D network-forming material selected from: hexagonal boron nitride (h-BN), graphene, graphitic carbon nitride (g-CN), silicene, germanene, stanene, and phosphorene, or from a transition metal dichalcogenide (TMDC), a transition metal halide, a metal carbide / nitride (Mxene), a 2D oxide / hydroxide, a 2D metal-organic framework, a 2D covalent organic framework, and a 2D nanomaterial, or an OD quantum dot, a 1 D nanotube, or a 3D nanoparticle.

9. The assembly of any one of the preceding claims, wherein the anchor species has a maximum dimension of about 50-10 pm and a minimum dimension of <10 nm, optionally wherein the anchor species comprises nanosheets having a length and width of about 80-500 nm and a height of <5 nm.

10. The assembly of any one of the preceding claims, wherein the ionised species, or precursor species if present, is loaded onto the anchor species at a concentration of from 1 to 50 wt%, such as at a concentration of from 1 to 20 wt%.11 . The assembly of any one of the preceding claims, wherein the matrix is mounted on a non- permeable substrate having a conductive surface, wherein the matrix is mounted on the conductive surface thereof.

12. The assembly of any one of the preceding claims, wherein the matrix is electrically conductive, optionally having a sheet resistance of from 0.1 MQ / square to 10 MQ / square, such as about 1 MQ / square.

13. The assembly of any one of the preceding claims, wherein the anchor species is present in the matrix at a concentration of from about 1 wt% to about 100 wt%, such as about 5 wt% to 70 wt%.

14. The assembly of any one of the preceding claims, wherein the matrix comprises an electrically conductive material in combination with the anchor species or wherein the matrix comprises a mixture of two or more anchor species, at least one of which is electrically conductive, optionally wherein the matrix comprises from 50 to 95 wt% conductive anchor species and from 5 to 50 wt% non-conductive anchor species, optionally wherein the conductive and non- conductive anchor species have precursor species tethered thereto.

15. The assembly of any one of the preceding claims, wherein the matrix, and substrate if present, are in the form of a flat or substantially flat layer, optionally wherein the matrix, and substrate if present, are flexible.

16. The assembly of any one of the preceding claims, wherein the anchor species and ionised species tethered thereto are impaired by one or more of: molecular size, molecular shape, and / or intermolecular interactions, such as hydrogen bonding interactions.

17. The assembly of any one of the preceding claims, wherein the potential gradient is an electric potential gradient, a chemical potential gradient, or a combination of the two.

18. A device for generating electricity from a potential gradient, the device comprising: an assembly according to any one of claims 1 to 17 connected into an external circuit.

19. A method of separating one ion of an ion pair across a potential gradient, the method comprising: providing an assembly comprising a matrix, wherein the matrix comprises an anchor species dispersed therein, wherein a portion of the anchor species comprises an ionised species tethered thereto and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient whereby the untethered counterion species is separated from the tethered ionised species across the potential gradient, optionally wherein the assembly is according to any one of claims 1 to 17.

20. A method of generating electricity from a potential gradient, the method comprising: providing an assembly according to any one of claims 2 to 17, wherein the assembly comprises a matrix comprising an anchor species dispersed therein, wherein the anchor species comprises a precursor species tethered thereto that is adapted to react with a trigger species, and, contacting a portion of the matrix with the trigger species, wherein the precursor species and trigger species react to form a tethered ionised species and an untethered counterion species, wherein uneven distribution of the tethered ionised species and the untethered counterion species within the matrix creates a potential gradient, and movement of the untethered counterion species across the potential gradient generates electricity when the assembly is connected to an external circuit.

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