Method and apparatus for ion separation and uses thereof

Abstract

The disclosure herein relates to an apparatus for effecting selective migration of an ion species, comprising: a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species; a receiving solution; and a membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution, as well as methods of using same to generate electricity.

Description

[0001] METHOD AND APPARATUS FOR ION SEPARATION AND USES THEREOF

[0002] Cross-Reference

[0003]

[0001] This application claims priority from Australian Application No. 2025900955 filed on 24 March 2025, the contents of which are incorporated herein cross-reference in their entirety.

[0004] Technical Field

[0005]

[0002] The disclosure herein relates to a method and apparatus for ion separation. More particularly, the disclosure herein relates to a method and apparatus that separates ions in an ion pair and creates a potential gradient and which is useful for generating electricity, among other uses.

[0006] Background of Invention

[0007]

[0003] 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 (A / - / ) 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. However, the energy required for adsorbent regeneration limits its sustainability and cost-effectiveness. To address these challenges, research has long emphasised designing more efficient CO2 adsorbents that facilitate rapid and reversible adsorption-desorption cycles. By improving the energy efficiency of these systems, such strategies aim to reduce operational costs and enhance overall performance. While these advancements are promising, they do not fully address the inherent energy-intensive nature of the CO2 capture process.

[0008]

[0004] 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.

[0009]

[0005] In commercially available CO2 chemical adsorption, amine solutions can generate oppositely charged ions upon CO2 absorption as follows: CO2+ R-NH2 + H2O «-> R-NHs++ HCCh' (Equation 1). The positively charged amine ions and negatively charged bicarbonate ions generated in these CO2adsorption 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. Other processes, such as in Wang et al., Nature Communications, 2024:15:2672 rely on spatial confinement of ions without a membrane to effect separation.

[0010]

[0006] 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.

[0011]

[0007] In one aspect, the invention described herein relates to apparatus for ion separation that utilise an enhanced size difference between ions in an ion pair in combination with a membrane 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 ion in an ion pair across a membrane, such that only its free counterion can move across, and this effect may be exploited to, for example, generate electricity.

[0012]

[0008] 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.

[0013] Summary of the Invention

[0014]

[0009] 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.

[0015]

[0010] According to a first aspect of the present invention, there is provided an apparatus for effecting selective migration of an ion species, the apparatus comprising: a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species; a receiving solution; and a membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution at least in part on the basis of their different molecular weights. In one embodiment, there is provided an apparatus for generating electricity via selective passive migration of ions, the apparatus comprising, the apparatus comprising: a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species; a receiving solution; and a membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the freecounterion species, but not the ionised reactant species, from the receiving solution to the reactant solution at least in part on the basis of their different molecular weights.

[0016]

[0011] The reactant species may have a formula mass of at least 1 ,000 g / mol. In one embodiment, the reactant species has a formula mass of at least 20,000 g / mol. The reactant species may be a polymer comprising one or more amine functional groups. In one embodiment, the reactant species may be a polymer comprising one or more monomers each comprising one or more amine functional groups. In another embodiment, the reactant species may comprise polyethyleneimine (PEI), polyallylamine, tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAM AM). The reactant species may be water soluble. In one embodiment, the reactant species may have a solubility of more than 10 mg / L in water at 40 °C. The ionised reactant species may have a molecular weight that is at least 10x larger than a molecular weight of the free counterion species.

[0017]

[0012] The trigger species may be selected from carbon dioxide, sulphur dioxide and nitrogen dioxide. In one embodiment, the trigger species is solubilised in the reactant solution and reacts with the reactant species in a solubilised or ionised form. The ionised reactant species may be present in the reactant solution at a concentration of from 1 to 75 wt%. The ionised reactant species may be present in the reactant solution at a concentration of from 5 mM to 500 mM.

[0018]

[0013] The membrane may be a nanofiltration membrane or may be an anion exchange membrane. In one embodiment, the membrane is a nanofiltration membrane. The membrane may have a molecular weight cutoff (MWCO) that is smaller than the molecular weight of the ionised reactant species but larger than the molecular weight of free counterion species.

[0019]

[0014] The receiving solution may comprise a concentration of free counterion species that is lower than a concentration of free counterion species in the reactant solution so as to create a potential gradient across the membrane. In one embodiment, wherein the receiving solution may be initially devoid of free counterion species, so as to create a maximum potential gradient across the membrane. The reactant solution and the receiving solution may both be aqueous. The receiving solution may comprise an osmotic pressure adjusting agent. In one embodiment, the osmotic pressure adjusting agent is present in an amount to balance the osmotic pressure between the reactant solution and the receiving solution.

[0020]

[0015] According to a second aspect of the present invention, there is provided a device for generating electricity, the device comprising: an apparatus according to the first aspect above connected into an external circuit. In one embodiment, the external circuit comprises current collectors in electrical contact with the reactant solution and the receiving solution. The external circuit may comprise a load. In one embodiment, the device comprises a stack of two or more apparatus connected in series or in parallel.

[0021]

[0016] According to a third aspect of the present invention, there is provided a method of generating electricity, the method comprising: providing an apparatus according to the first aspect above or a device according to the second aspect above, contacting a trigger species with the reactant solution, wherein the reactant species and trigger species react to form an ionised reactant species and a freecounterion species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species, wherein a concentration of the free counterion species in the reactant solution is higher than a concentration of the free counterion species in the receiving solution such that a potential gradient is created that drives selective movement of the free counterion species, but not the ionised reactant species, across the membrane and into the receiving solution on the basis of its smaller molecular weight, thereby generating a potential difference and electric current when the apparatus is connected to an external circuit. In one embodiment, there is provided a method of generating electricity, the method comprising: providing an apparatus according to the first aspect above or a device according to the second aspect above, contacting a trigger species with the reactant solution, wherein the reactant species and trigger species react to form an ionised reactant species and a free counterion species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species, wherein a concentration of the free counterion species in the reactant solution is higher than a concentration of the free counterion species in the receiving solution such that a concentration gradient is created across the membrane that drives selective passive migration of the free counterion species, but not the ionised reactant species, across the membrane and into the receiving solution on the basis of its smaller molecular weight, thereby generating a potential difference and electric current when the apparatus is connected to an external circuit.

[0022]

[0017] According to a fourth aspect of the present invention, there is provided use of the apparatus according to the first aspect above or the device according to the second aspect above to generate electricity,

[0023] Brief Description of Drawings

[0024]

[0018] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0025]

[0019] Figure 1 shows (a) a schematic of current industrial CO2 adsorption process; (b) a schematic of an industrial CO2 adsorption process integrated with an apparatus as described herein; and (c) a schematic of an apparatus as described herein according to one embodiment;

[0026]

[0020] Figure 2 shows (a) voltage-time test results PEI MW = 25,000, concentration = 10 wt%; (b) current-time test results, PEI MW= 25,000, concentration = 10 wt%;

[0027]

[0021] Figure 3 shows (a) voltage-time test, PEI MW = 25,000, concentration = 30 wt% (b) voltagetime test, PEI MW = 25,000, concentration = 10 wt%;

[0028]

[0022] Figure 4 shows (a) voltage-time test, PEI MW = 800, concentration =10 wt%; (b) voltage-time test, PEI MW = 2,000, concentration = 10 wt%;

[0029]

[0023] Figure 5 shows (a),(c) voltage-time test and current-time test with nanofiltration membrane (NF270); (b),(d) voltage-time test and current-time test with anion exchange membrane (Sustainion X37-50);

[0030]

[0024] Figure 6 shows (a) voltage-time test for 10% PEI solution (MW = 10,000) where CO2 was kept open for 2 h (high flow speed) and then closed; and (b) voltage-time test for 10% PEI solution (MW =10,000) where solution was pre-washed with CO2 until saturation point and CO2 was closed during testing;

[0031]

[0025] Figure 7 shows (a) voltage-time test for 10% PEI solution (MW = 10,000) where CO2 was kept open (low speed) throughout testing, showing that voltage can be maintained at around 400 mV with the CO2 on; comparative gel-based data without a membrane shown for comparison; and (b) currenttime test for 10% PEI solution (MW = 10,000) where CO2 was kept open (low speed) throughout testing; and

[0032]

[0026] Figure 8 shows (a) an expanded perspective view of a diagram of a stack comprising component parts of more than two apparatus according to one embodiment herein connected in series; (b) an expanded perspective view of a current collector / membrane configuration according to one embodiment herein; and (c) a perspective illustration of a device comprising a stack according to an embodiment described herein prior to connection to an external circuit.

[0033] Detailed Description

[0034]

[0027] Described herein is an apparatus for effecting selective migration of an ion species. The apparatus comprises a reactant solution, a receiving solution, and a membrane separating the reactant solution from the receiving solution. The reactant solution comprises a reactant species comprising one or more ionisable groups and is adapted to form an ionised reactant species and free counterion species on contact with a trigger species. The membrane is adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution.

[0035]

[0028] The membrane-based ion separation apparatus and process described herein may be suitable for large-scale efficient energy harvesting during CO2 capture. This approach leverages advanced nanofiltration membranes with size selected adsorbents to overcome low ion flux and selectivity challenges with existing apparatus. In certain embodiments, high molecular weight polyamines are used as adsorbents for carbon dioxide, which release distinctively sized ions upon CO2 adsorption: specifically, large amine-based cations and small bicarbonate anions. Using the apparatus and methods described herein, efficient ion separation is enabled based on size exclusion through a nanofiltration membrane and a concentration gradient of one ion across the membrane, without requiring the use of an external energy supply. By integrating membrane technology with strategic control over adsorbent molecular size, the apparatus and methods described herein combine the scalability of membrane processes with the precise ion separation capabilities of more sophisticated mobility- and channel- based hydrogel systems. The resulting platform achieves higher power densities, sustained energy output, and improved scalability compared to previous systems. Accordingly, the apparatus and methods described herein have application in electricity generation, where the potential gradient and charge separation of the ions can be exploited to create electrical energy.

[0036]

[0029] To overcome the size similarity of ions generated by traditional adsorbents, the present inventors have size altered one ion in an ion pair to inhibit its mobility across a membrane. Uponreacting with a trigger molecule, the reactant species are transformed into high-molecular-weight positively charged ions (molecular weight > 500) and low-molecular-weight counterions (molecular weight < 100). The molecular weight disparity of at least 5 times enables effective separation by a membrane, as the high-molecular-weight ions are rejected while the low-molecular-weight counterions pass through the membrane with ease driven by a concentration gradient across the membrane, i.e. , by passive migration, without the application of an external electric field, such as application of voltage. The diffusion rate gap can then be used to generate electricity and be amplified to power external electronic devices. The apparatus and 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 / or in water treatment. The apparatus is also useful for generating electricity directly from adsorbing CO2 (Fig. 1). Other applications for this technology will be apparent from the disclosure herein.

[0037]

[0030] 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 y" or “between x and is intended to include all sub-ranges between x and y and also range end points x and y.

[0038]

[0031] As used herein, the singular forms “a,” “an,” and “the” may refer to plural articles unless specifically stated otherwise.

[0039]

[0032] As used herein, the term “free” in relation to a counterion species refers to the counterion species being free to move, and most critically free to move separately from the ionised reactant 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 free refers to there being no or substantially no physical or molecular bond barrier to movement of the counterion species away from the ionised reactant species across a suitable potential gradient. In certain embodiments, the free 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.

[0040]

[0033] 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 apparatus / devices described herein is created by uneven distribution of ionised reactant species and counterion species across the membrane.

[0041]

[0034] As used herein, the term “passive” in the context of migration refers to free counterion species moving across the membrane driven by a difference in free counterion species concentration across the membrane, e.g., diffusion-driven transport, rather than by application of energy, i.e., voltage. Reactant Solution and Species

[0042]

[0035] The apparatus, devices and methods herein comprise or utilise solutions. The reactant solution comprises the reactant species. In certain embodiments, the reactant species are fully dissolved in the reactant solution, such as fully dissolved in the reactant solution under the conditions of use of the apparatus, device and / or method.

[0036] In one embodiment, the reactant solution comprises only reactant species and solvent. This advantageously reduces possible ion or redox interference. In other embodiments, the reactant solution may comprise one or more other components. In one embodiment, the reactant solution may comprise an osmotic pressure adjusting agent to balance the osmotic pressure of the reactant solution with that of the receiving solution. In one embodiment, any suitable osmotic pressure adjusting agent may be used. In one embodiment, the osmotic pressure adjusting agent may be a non-charged, pH neutral, non-chemically reactive and non-redox active compound. In one embodiment, PEG may be used as the osmotic pressure adjusting agent.

[0043]

[0037] In one embodiment, the reactant solution is aqueous. In one embodiment, water is the preferred solvent because the water may assist with solubilisation of the trigger species to enable reaction with the reactant species, and / or may assist with formation of the ionised reactant species and counterion species through donating or accepting a proton or electron pair. Provided that sufficient water is present to enable ionised reactant species formation and / or trigger species dissolution in the reactant solution, the amount of water is not particularly limited.

[0044]

[0038] In one embodiment, the reactant solution is at least partially electrically conductive, as this advantageously allows the solution to form part of a complete circuit and thereby generate electricity. The reactant solution may have any suitable conductivity, such that efficient electrical signal transmission to the external circuit is facilitated. In one embodiment, the reactant solution has a conductivity during operation of greater than least 50 S.cnrr1. Conductivity of the reactant solution is preferably adjusted by addition of reactant species and trigger molecules, that together form ions capable of conducting charge.

[0045]

[0039] The reactant species may be any suitable species, such as any suitable species whose structure and / or composition inhibits movement of ionised reactant species through the membrane, and whose structure comprises one or more ionisable groups. In one embodiment, the reactant species has a molecular weight of at least 300 g / mol, or of at least 400 g / mol, or of at least 500 g / mol, or of at least 1 ,000 g / mol, or of at least 2,500 g / mol, or of at least 5,000 g / mol, or of at least 10,000 g / mol, or of at least 50,000 g / mol, or of at least 100,000 g / mol, or of from 300 g / nmol to 100,000 g / mol, or of from 500 g / mol to 250,000 g / mol, or of from 500 g / mol to 100,000 g / mol, or of from 1 ,000 g / mol to 10,000 g / mol, or of from 5,000 g / mol to 50,000 g / mol, or of from 10,000 g / mol to 100,000 g / mol.

[0046]

[0040] The reactant solution may comprise reactant species in any suitable concentration. In some embodiments, the reactant solution may comprise at least 50 wt%, or at least 40 wt%, or at least 30 wt%, or at least 20 wt%, or at least 10wt%, or at least 5 wt%, or at least 1 wt% of the reactant species, or up to 50 wt%, or up to 40 wt%, or up to 30 wt%, or up to 20 wt%, or up to 10 wt%, or up to 5 wt%, or up to 1 wt% of the reactant species, or of from 1 wt% to 75 wt%, or of from 1 wt% to 20 wt%, or of from 5 wt% to 50 wt%, or of from 10 wt% to 40 wt%, or of from 20 wt% to 60 wt%, or of from 25 wt% to 35 wt%, or of from 30 wt% to 70 wt%, or of from 40 wt% to 65 wt%, or of from 50 wt% to 75 wt% of the reactant species. In some embodiments, the reactant solution may comprise at least 0.01 mM, or at least 0.1 mM, or at least 1 mM, or at least 10 mM, or at least 5 mM, or at least 7.5 mM, or at least 10 mM, or at least 12.5 mM, or at least 15 mM, or at least 25 mM, or at least 50 mM, or at least 100mM, or at least 150 mM, or at least 200 mM, or at least 250 mM, or at least 300 mM, or at least 350 mM, or at least 400 mM, or at least 450 mM, or at least 500 mM of the reactant species, or up to 5 mM, or up to 7.5 mM, or up to 10 mM, or up to 12.5 mM, or up to 15 mM, or up to 25 mM, or up to 50 mM, or up to 100 mM, or up to 150 mM, or up to 200 mM, or up to 250 mM, or up to 300 mM, or up to 350 mM, or up to 400 mM, or up to 450 mM, or up to 500 mM of the reactant species, or of from 5 mM to 500 mM, or of from 5 mM to 50 mM, or of from 50 mM to 150 mM, or of from 5 mM to 20 mM, or of from 50 mM to 250 mM, or of from 100 mM to 300 mM, or of from 250 mM to 400 mM of the reactant species.

[0047]

[0041] In some embodiments, the reactant solution may comprise at least 0.01 mM, or at least 0.1 mM, or at least 1 mM, or at least 10 mM, or at least 50 mM, or at least 75 mM, or at least 100 mM, or at least 150 mM, or at least 250 mM, or at least 500 mM, or at least 1 M, or at least 5 M, or at least 10 M, or at least 20 M, or at least 30 M, or at least 40 M, or at least 50 M, or at least 60 M, or at least 80 M, or at least 100 M, or at least 250 M, or at least 500 M of ionisable groups, or up to 50 mM, or up to 75 mM, or up to 100 mM, or up to 150 mM, or up to 250 mM, or up to 500 mM, or up to 1 M, or up to 5 M, or up to 10 M, or up to 20 M, or up to 30 M, or up to 40 M, or up to 50 M, or up to 60 M, or up to 80 M, or up to 100 M, or up to 250 M, or up to 500 M of ionisable groups, or of from 50 mM to 500 M, of from 50 mM to 500 mM, of from 250 mM to 1 M, of from 750 mM to 20 M, of from 1 M to 250 M, of from 10 M to 300 M, of from 100 M to 500 M of ionisable groups.

[0048]

[0042] The reactant solution may have any suitable pH. In one embodiment, the pH is from 10 to 12.

[0049]

[0043] Any suitable reactant species may be used. In preferred embodiments, the reactant species is selected such that it is adapted to form the ionised reactant species and the free counterion species on contact with a trigger species. In one embodiment, the reactant species is adapted for this purpose by comprising a functional group that chemically reacts with the trigger species on contact to form the ionised reactant species and the free counterion species. In one embodiment, the reactant species is an uncharged reactant species. This advantageously avoids additional ions in the reactant solution and that may interfere with the potential gradient.

[0050]

[0044] In one embodiment, the reactant 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 reactant species is capable of accepting a proton to form a cation.

[0051]

[0045] In one embodiment, the polymer is synthetic. In one embodiment, the polymer is linear. In another embodiment, the polymer is branched. The reactant species may be soluble in the reactant solution, such as have a solubility of at least 10 mg / L or more at 40 °C. The reactant species may be soluble in water, such as have a solubility of at least 10 mg / L or more at 40 °C. In one embodiment, the reactant species is a polymer having a molecular mass of at least 500 g / mol, at least 800 g / mol, at least 1 ,000 g / mol, at least 2,500 g / mol, at least 5,000 g / mol, at least 7,500 g / mol, at least 10,000 g / mol, at least 12,500 g / mol, at least 15,000 g / mol, at least 20,000 g / mol, at least 25,000 g / mol, or at least 30,000 g / mol, or of up to 500 g / mol, up to 800 g / mol, up to 1 ,000 g / mol, up to 2,500 g / mol, up to5,000 g / mol, up to 7,500 g / mol, up to 10,000 g / mol, up to 12,500 g / mol, up to 15,000 g / mol, up to 20,000 g / mol, up to 25,000 g / mol, or up to 30,000 g / mol, or of from 500 to 30,000 g / mol, or of from 800 to 1 ,000 g / mol, or of from 1 ,000 to 5,000 g / mol, or of from 500 to 7,500 g / mol, or of from 5,000 to 12,500 g / mol, or of from 9,500 to 10,500 g / mol or of from 20,000 to 40,000 g / mol, or of from 20,000 to 30,000 g / mol, or of from 10,000 to 25,000 g / mol.

[0052]

[0046] In one embodiment, the reactant species comprises one or more amine functional groups. In one embodiment, the reactant species is an amine. In another embodiment, the reactant species is a polyamine. In one embodiment, the reactant species is a polymer comprising one or more monomeric units comprising one or more amine groups per monomer. In one embodiment, the reactant species is a polymer made of monomers comprising one or more amine groups per monomer.

[0053]

[0047] In one embodiment, the reactant species comprises or is a polymer comprising one or more alkylamine monomer(s). In one embodiment, the alkylamine is a C2-C10 linear or branched alkylamine. In one embodiment, the alkylamine is a cyclic alkylamine. In one embodiment, the alkylamine is a C2-C10 cyclic alkylamine. In one embodiment, the cyclic alkylamine is aziridine. In another embodiment, the reactant species comprises polyethyleneimine (PEI), polyallylamine, tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAMAM). In one embodiment, the reactant species comprises polyethyleneimine (PEI) or a copolymer thereof. In one embodiment, the reactant species comprises a copolymer of one or more of polyethyleneimine (PEI), tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and polyamidoamine (PAMAM), such as a block copolymer. In one embodiment, the reactant species comprises a copolymer of polyethyleneimine (PEI), tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAMAM) and a non-amine functionalised water soluble polymer, in one embodiment a polyethylene glycol) or the like. In one embodiment, a reactant species comprising a block copolymer such as polyethyleneimine-block-poly(ethylene glycol) or polyethylene glycol)-block-polyethyleneimine may be suitable. In another embodiment, the reactant species is polyethyleneimine (PEI), polyallylamine, tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAMAM). In one embodiment, the reactant species is polyethyleneimine (PEI) or a copolymer thereof. In one embodiment, the reactant species is a copolymer of one or more of polyethyleneimine (PEI), tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and polyamidoamine (PAMAM), such as a block copolymer. In one embodiment, the reactant species is a copolymer of polyethyleneimine (PEI), tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAMAM) and a non-amine functionalised water soluble polymer, in one embodiment a polyethylene glycol) or the like. In one embodiment, a block copolymer such as polyethyleneimine-block-poly(ethylene glycol) or polyethylene glycol)-block-polyethyleneimine may be suitable.

[0054]

[0048] In other embodiments, the reactant species comprises or is a polymer comprising one or more arylamine monomer(s). Examples of arylamine-based polymers include polyanilines,poly(phenylenediamine), poly (amino styrene), polypyrrole, and the like. In one embodiment, the reactant species comprises a copolymer of an arylamine polymer and a non-amine functionalised water soluble polymer, in one embodiment a polyethylene glycol) or the like. In one embodiment, the reactant species is a copolymer of an arylamine polymer and a non-amine functionalised water soluble polymer, in one embodiment a polyethylene glycol) or the like. In one embodiment, the reactant species comprises or is a copolymer of an arylamine polymer and an alkylamine polymer as described above.

[0055]

[0049] In one embodiment, the reactant species comprises or is an amine-modified polymer, such as comprises or is a polyethylene glycol) bis(amine) or methoxypolyethylene glycol amine. In one embodiment, the reactant species comprises or is a post-synthetically modified polymer, which is post-synthetically modified to comprise amine groups.

[0056]

[0050] In one embodiment, the reactant comprises a branched or linear polyethyleneimine having an average Mw of ~800 g / mol. In one embodiment, the reactant comprises a branched or linear polyethyleneimine having an average Mw of ~1 ,000 g / mol. In one embodiment, the reactant species comprises a branched or linear polyethyleneimine having an average Mnof ~10,000. In one embodiment, the reactant comprises a branched or linear polyethyleneimine having an average Mw of ~25,000 g / mol. In one embodiment, the reactant is a branched or linear polyethyleneimine having an average Mw of ~800 g / mol. In one embodiment, the reactant is a branched or linear polyethyleneimine having an average Mw of ~1 ,000 g / mol. In one embodiment, the reactant species is a branched or linear polyethyleneimine having an average Mnof ~10,000. In one embodiment, the reactant is a branched or linear polyethyleneimine having an average Mwof ~25,000 g / mol.

[0057]

[0051] In one embodiment, the reactant species is dissolved in the reacting solution. The reactant species may be fully dissolved, or may be partially dissolved and, for example, have its solubility driven by formation of ionised reactant species.

[0058]

[0052] Although alkylamines or polyethyleneimine may be utilised in some embodiments, in other embodiments, the reactant 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. Amines, polyamines, and branched or linear polyethyleneimine suitable for use in the apparatus, devices and methods herein can be made by synthetic methods known in the art, or may be purchased commercially. The reactant species may be selected to have particular affinity for forming an ionised species and counterion pair on reaction with a particular trigger species.

[0059]

[0053] In one embodiment, when the reactant species comprises one or more amine functional group(s), the ionised reactant species may comprise one or more ammonium cations. In one embodiment, the ammonium cation is of formula -N+(R)-, where R is H or C1-C5 alkyl, or in one embodiment is part of a polymer backbone in the form -N+(H)-.

[0060]

[0054] It will be appreciated that the charge of the ionised reactant species and the charge of the free counterion are not fixed, and that cation / free anion or anion / free cation pairings are both within thescope of the disclosure herein depending on the trigger molecule / reactant combination being used / ion pair being separated. Accordingly, in some embodiments, the reactant species may be a Lewis acid. In still further embodiments, the reactant 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 reactant 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 reactant species comprises one or more carboxylic or sulfonic acid functional groups. Suitable acids for use in the apparatus, devices and methods herein can be made by synthetic methods known in the art, or may be purchased commercially.

[0061]

[0055] In one embodiment, the ionised reactant species and free counterion species are formed on reaction of carbon dioxide with the amine functional group. In such embodiments, the free counterion may comprise a carbonate. In one embodiment, the free counterion may be hydrogen carbonate, HCOs' or a carbonate, COs2' anion. In one embodiment, the free 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, HSOs', NC , NH2S(=O)O_, etc.

[0062]

[0056] The free counterion species that forms on reaction with a trigger species may be any suitable species that has a size, shape and / or composition that enables it to move freely across the membrane, such as responsive to a concentration gradient. The nature of the counterion species is not particularly limited, but in some embodiments, the counterion species has a molecular weight that is at least 5 x smaller than a molecular weight of the reactant species, or that is at least 6x smaller, or at least 7x smaller, or at least 8x smaller, or at least 9x smaller, or at least 10x smaller, or at least 50x smaller, or at least 100x smaller, or at least 1 ,000x smaller, or of from 5x to 20x smaller, or of from 5x to 10x smaller, or of from 5x to 15x smaller, or of from 5x to 10Ox smaller, or of from 5x to 1 ,000x smaller, or of from 10xto 100x smaller, or of from 100xto 1,000x smaller, than a molecular weight of the reactant species. In one embodiment, the free counterion species has a molecular weight of less than 250 g / mol, less than 200 g / mol, less than 150 g / mol, less than 100 g / mol, less than 75 g / mol, or less than 50 g / mol, or of from 250 to 50 g / mol, or of from 150 to 50 g / mol, or of from 100 to 50 g / mol. In one embodiment, the free 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 5 A to 50 A, or of from 40 A to 75 A, or of from 5 A to 25 A, or of from 3 A to 10 A. In one embodiment, the free counterion species has a size in the order of Angstroms, whereas the reactant species may in some embodiments have a size in the order of nanometres.

[0063]

[0057] The ionised reactant species that forms on reaction of the reactant species with a trigger species may be any suitable ionised reactant species. In one embodiment, the ionised reactant species has a molecular weight of at least 300 g / mol, or of at least 400 g / mol, or of at least 500 g / mol, or of at least 1 ,000 g / mol, or of at least 2,500 g / mol, or of at least 5,000 g / mol, or of at least 10,000 g / mol, or of at least 50,000 g / mol, or of at least 100,000 g / mol, or of from 300 g / nmol to 100,000 g / mol, or of from 500 g / mol to 250,000 g / mol, or of from 500 g / mol to 100,000 g / mol, or of from 1 ,000 g / mol to 10,000 g / mol, or of from 5,000 g / mol to 50,000 g / mol, or of from 10,000 g / mol to 100,000 g / mol. Insome embodiments, the ionised reactant species has a molecular weight that is at least 5 x greater than a molecular weight of the free counterion species, or that is at least 6x greater, or at least 7x greater, or at least 8x greater, or at least 9x greater, or at least 10x greater, or at least 50x greater, or at least 100x greater, or at least 1 ,000x greater, or of from 5x to 20x greater, or of from 5x to 10x greater, or of from 5x to 15x greater, or of from 5x to 10Ox greater, or of from 5x to 1 ,000x greater, or of from 10x to 100x greater, or of from 100x to 1 ,000x greater, than a molecular weight of the free counterion species.

[0064] Receiving Solution

[0065]

[0058] The receiving solution is for receiving the free counterion species. The receiving solution may have any suitable composition.

[0066]

[0059] In one embodiment, the receiving solution is aqueous. In one embodiment, water is the preferred solvent because the water may assist with maintaining the solubilisation of the free counterion species as it moves through the membrane into the receiving solution. The amount of water is not particularly limited.

[0067]

[0060] In one embodiment, the receiving solution is at least partially electrically conductive, as this advantageously allows the solution to form part of a complete circuit and thereby generate electricity. The receiving solution may have any suitable conductivity, such that efficient electrical signal transmission to the external circuit is facilitated. In one embodiment, the receiving solution has a conductivity during operation of at least 1 pS / cm. Conductivity of the receiving solution may be adjusted by addition of a lower concentration of reactant species into the receiving solution than is present in the reactant solution. In other embodiments, a salt or other conductivity enhancing agent may be initially added to solution, preferably wherein the conductivity enhancing agent does not participate in any redox reactions. In some embodiments, the receiving solution initially comprises no or a negligible quantity of dissolved ions, and free counterions crossing from the reactant solution during operation provide adequate conductivity to the receiving solution.

[0068]

[0061] As the presence of a higher concentration of ions in the reactant solution may cause solvent, such as water, to move from the receiving solution into the reactant solution, in preferred embodiments, neutral species that will not react with reactants and / or counter ions may be added to the receiving solution to balance osmotic pressure. Accordingly, in one embodiment, the receiving solution may comprise an osmotic pressure adjusting agent to balance the osmotic pressure of the receiving solution with that of the reactant solution. This advantageously reduces the tendency of water to move through the membrane from reactant solution (where solute (reactant) species are relatively concentrated) to receiving solution (where solute species are relatively dilute). In such embodiments, the osmotic pressure adjusting agent may be any suitable compound. In one embodiment, the osmotic pressure adjusting agent is a non-ionic water soluble species. In one embodiment, the osmotic pressure adjusting agent may be a non-charged, pH neutral, non-chemically reactive and non-redox active compound. In one embodiment, the osmotic pressure adjusting agent is polyethylene glycol) (PEG), but other agents may be useful. The osmotic pressure equalising agent may be added at any suitable concentration, and will preferably be added such that the osmoticpressure of the receiving solution is approximately equal to the osmotic pressure of the reactant solution. The amount of osmotic pressure equalising agent required can be calculated by the following:

[0069] n = i - C R T ... Equation (1)

[0070]

[0071] ... Equation (2) where: n : Osmotic pressure (Pa), i : Van’t Hoff factor (for non-dissociating polymers, i =1), C : Solute molar concentration (mol / L), R : Ideal gas constant =8.314 J-K-1-mol-1, T : Absolute temperature (K), m: mass of reactant species (g), M: molecular weight of reactant species (g / mol), and V volume of solution (L).ln one embodiment, the concentration of reactant species in the reactant solution is higher than the concentration of reactant species in the receiving solution before the trigger species is introduced. In one embodiment, the concentration ratio of reactant species in the reactant solution vs. reactant species in the receiving solution before the trigger species is introduced is at least 10:1, at least 25:1 , at least 50:1 , at least 100:1 , at least 250:1 , at least 500:1 , at least 1000:1 , at least 1500:1 , at least 2000:1 , at least 3000:1 , at least 4000:1 , or at least 5000:1 , or is from 500:1 to 5000:1 , or is of from 750:1 to 1250:1, or of from 1000:1 to 5000:1, or of from 10:1 to 5000:1, or of from 10:1 to 100:1, or of from 250:1 to 500:1, or is of about 25:1, 50:1, 100:1, 250:1, 500:1, 1000:1, 1500:1, 2000:1, 3000:1, 4000:1, or 5000:1.

[0072]

[0062] In order to generate electricity, the receiving solution should comprise a concentration of free counterion species that is lower than a concentration of free counterion species in the reactant solution whilst operating, including when trigger species are reacting with the reactant species to generate free counterions that are crossing the membrane into the receiving solution. In one embodiment, the receiving solution is initially (i.e., before the trigger species is introduced to the reactant solution) devoid of free counterion species, so as to create a maximum concentration gradient across the membrane to drive diffusion.

[0073]

[0063] The receiving solution may have any suitable pH. In one embodiment, the pH is of from 6 to 10.

[0074] Trigger species

[0075]

[0064] Any suitable trigger species may be used in the apparatus, devices and methods herein. In one embodiment, the trigger species is a Lewis acid, such as is designed to react with a reactant Lewis base to form an anion / cation pair. In one embodiment, the trigger species is selected from carbon dioxide, sulfur dioxide and nitrogen dioxide. In one embodiment, the trigger species is carbon dioxide. The carbon dioxide may be delivered to the reactant solution and reactant species in any suitable form, such as in the form of carbon dioxide gas. The trigger species may be required to undergo solubilisation in the reactant solution prior to reacting with the reactant species. In the case of carbon dioxide, the trigger species may initially be in the form of carbon dioxide gas and then dissolve in water to form aqueous carbonic acid. Similarly, sulfur dioxide and nitrogen dioxide may also solubilise in water into aqueous acidic forms prior to reacting with the reactant species.

[0076]

[0065] In other embodiments, the trigger species is a Lewis base, such as is designed to react with a reactant Lewis acid to form an anion / cation pair, or is a Bronsted acid, such as designed to donate aproton to a trigger species. In one embodiment, the trigger species is ammonia gas or an alkylamine. As above, the trigger species may be required to undergo solubilisation in the reactant solution prior to reacting with the reactant species. In the case of ammonia, the trigger species may initially be in the form of ammonia gas and then dissolve in water to form aqueous ammonium hydroxide.

[0077]

[0066] In one embodiment, the trigger species is initially in the gas phase, and as such is advantageously able to be directed into a solution containing reactant species for reaction to form ion pairs. In one embodiment, the trigger species is provided to the reactant solution and reactant 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.

[0078]

[0067] Trigger species such as those contemplated herein may be synthesised according to known literature methods and / or may be purchased commercially, or may be the product of industrial waste, such as may be combustion by-products.

[0079]

[0068] The trigger species is contacted with the reactant solution and reactant species in the apparatus and methods described herein. In other words, the trigger species is not provided to the receiving solution. By providing the trigger species to the reactant solution only, the reactant species reacts with the trigger species only in the reactant solution side of the cell (or the reactant solution side of the membrane) to produce ionised reactant species and free counterion species. It is this concentration gradient that causes free counterions to diffuse across the membrane into the receiving solution, and this potential difference caused by movement of ions that generates electrical current. Accordingly, it will be understood that the trigger species may be provided to the reactant solution in a sealed environment, or that the reactant solution is exposed to a sealed source of trigger species. In some embodiments, where the trigger species is a gas, the trigger species gas may be bubbled through the reactant solution, such as to solubilise or dissolve it. In other embodiments, the trigger species is pre-solubilised and / or preconcentrated in a separate solution to the reactant solution and added to the reactant solution in a liquid-liquid phase reaction. Gas-liquid or liquid-liquid reactors suitable for contacting the trigger species with the reactant solution are known in the art.

[0080] Membrane

[0081]

[0069] The apparatus and methods herein utilise a membrane between the reactant solution and the receiving solution. The membrane may be any suitable membrane, provided it separates the ionised reactant species and the free counterion species at least in part on the basis of their difference in molecular weight. It will be understood that in addition to molecular weight, the shape / size and / or charge difference between the ionised reactant species and the free counterion species may also contribute to their separation by the membrane. In one embodiment, the membrane is an ion exchange membrane (IX). In one embodiment, the membrane is a nanofiltration membrane.

[0082]

[0070] The membrane may have any suitable molecular weight cutoff (MWCO). In some embodiments, the membrane may have a molecular weight cutoff (MWCO) of from 200 to 10,000 Da, or of from 200 to 5,000 Da, or of from 500 to 10,000 Da, or of from 250 to 5,000 Da, or of from 300 to 7,500 Da. In certain embodiments, the MWCO of the membrane is smaller than the molecular weight of the ionised reactant species but larger than the molecular weight of free counterion species.

[0071] The membrane may comprise pores having any suitable average size. In some embodiments, the membrane comprises pores having an average size of at least 1 nm, at least 5 nm, at least 10 nm, at least 25 nm, at least 50 nm, or at least 75 nm, or of 80 nm or smaller, 70 nm or smaller, 60 nm or smaller, 50 nm or smaller, 40 nm or smaller, 30 nm or smaller, 20 nm or smaller, of 15 nm or smaller, of 10 nm or smaller, or 7 nm or smaller, or 5 nm or smaller, or of from 1 nm to 100 nm, or of from 5 nm to 60 nm, or of from 25 nm to 50 nm, or of from 40 nm to 80 nm. In one embodiment, the membrane comprises pores having a minimum size of 1-2 nm, such that size-based exclusion is enabled.

[0083]

[0072] The membrane may have any suitable thickness. In some embodiments, the membrane may have a thickness of less than 100 pm, or less than 75 pm, or less than 50 pm, or less than 25 pm, or of from 25 to 75 pm, or of from 40 to 100 pm, or of from 40 to 60 pm, or of from 75 to 100 pm. It may be possible in other embodiments for membranes thicker than 100 pm to be used, but such membranes may reduce the rate of ion migration relative to thinner membranes.

[0084]

[0073] In one embodiment, the membrane may be charged or carry charged surface groups. In one embodiment, the membrane is positively charged and functions as an anion exchange membrane. Suitable anion exchange and nanofiltration membranes are known in the art and may be purchased commercially from, e.g., Dow® FilmTec, ASTOM Corporation®, DuPont®, Dioxide Materials® Ltd., Co., and the like.

[0085]

[0074] The membrane is not particularly limited, provided that it is able to selectively allow free counterions to cross from the reactant solution to the receiving solution, whilst blocking the ionised reactant species, at least in part on the basis of their difference in molecular weight. In some embodiments, it will be appreciated that molecular shape of the ionised reactant species and / or intermolecular interactions between the ionised reactant species and the membrane, such as ionic interactions, may also occur (in addition to the ionised reactant species being of a certain molecular weight / size) and some combination of these interactions or characteristics may impact the separation efficiency and / or selectivity of the membrane.

[0086]

[0075] The reactant solution, receiving solution, and membrane may be constructed in any suitable orientation and positioning to facilitate flow of ions across the membrane on application of trigger species. In one embodiment, the reactant and receiving solutions are provided in separate reaction vessels separated by a membrane wall. In another embodiment, the solutions are provided concentrically in a tubular reactor, such as where the membrane forms to wall between the inner and outer tubes. Other constructions may be suitable depending on the source and state of the trigger species. It will be appreciated that no applied electric field is required across the membrane in the apparatus herein, as ion separation is driven by concentration differences of free counterion species on different sides of the size exclusion membrane (i.e., passive migration) rather than by electrochemical separation methods (i.e., active migration). Accordingly, the apparatus herein may be adapted to allow selective passive migration of free counterion species, and not ionised reactant species, across the membrane at least in part by being devoid of an applied energy source, such as an applied electric field. Indeed, isolation of the ionised reactant species on one side of the membranein the apparatus and method herein generates an electric potential difference across the membrane as a result of the generated net diffusion current.

[0087] Electricity generation

[0088]

[0076] The apparatus described herein may be used to construct a device for generating a potential difference and electric current / electricity. In one embodiment, the disclosure herein provides a device for generating electricity, the device comprising, an apparatus 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 apparatus as described herein connected into an external circuit. In one embodiment, the device herein may comprise a stack comprising two or more apparatus stacked in series or in parallel to generate electric current. The two or more apparatus may be stacked in series. The two or more apparatus may be stacked in parallel. Methods of stacking two or more apparatus as described herein will be known to those of skill in the art, but in one embodiment, may comprise stacking two or more apparatus each comprising a current collector, a membrane, a reactant solution cavity, and a receiving solution cavity, and which are separated from each other by a separator ora bipolar plate.

[0089]

[0077] 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 the reactant solution, and a second current collector in electrical contact with the receiving solution. 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. The reactant solution and the receiving solution are connected via a membrane. The external circuit may be devoid of a power source for applying a voltage across the membrane.

[0090]

[0078] Where two or more apparatus herein may be stacked in series, each apparatus may be separated from its neighbour by a bipolar plate. Although any suitable bipolar plate may be used, in one embodiment, the bipolar plates may comprise graphite. Each bipolar plate herein may be in electrical communication with an adjacent current collector. Each bipolar plate herein may comprise one or more fluid channels in a face thereof fortransporting reactant solution to, or receiving solution from, the membrane. In some cases, a bipolar plate herein may comprise one or more fluid channels in each of its two opposing faces for transporting reactant solution to the membrane on one side, and transporting receiving solution from the membrane on another side.

[0091]

[0079] The current collectors are not particularly limited in their size, shape and / or composition in the methods and apparatus described herein. In one embodiment, the current collectors comprise an inert material. In one embodiment, the current collectors are inert. Suitable current collectors may comprise one or more inert metals, such as platinum, gold, palladium, or the like. In other embodiments, the current collectors may comprise inert conductive materials such as graphite or carbon felt. In one embodiment, the inert current collectors may comprise a porous conductive material. In one embodiment, the porous conductive material is carbon felt. Accordingly, the inert current collectors herein may comprise carbon felt. A current collector comprising a porous conductive material, such as carbon felt, may be particularly useful for an internal current collector ineach of the two or more apparatus in a stack, such as because the fabric construction is conductive to help facilitate the conversion of ion movement into electron flow in the external circuit and / or because the current collector is porous, thus providing a larger interfacial region for ion migration relative to a non-porous current collector. In one embodiment, a porous conductive material current collector, such as comprising carbon felt, may be positioned directly adjacent to the membrane. This may advantageously shorten the ion transport path for reactant solution through the membrane to the receiving solution to improve ion transport efficiency and, in certain embodiments, enhance power generation performance. In one embodiment, a current collector may comprise gold. Such embodiments may be particularly useful at the terminal ends of the stack for collecting current produced by the stack. Other suitable combinations of current collectors may be used.

[0092]

[0080] In one embodiment, as noted above, the current collectors may be positioned one on either side of the membrane. In one embodiment, two current collectors may sandwich the membrane. In such embodiments, the current collectors may comprise a porous current collector material, such as carbon felt, and thus additionally function to ensure reactant and receiving solution are in contact with and readily accessible to the membrane.

[0093]

[0081] The receiving solution and reactant solution may be provided to the device in any suitable manner, but in one embodiment, are provided in cavities or fluid paths in a surface of a bipolar plate, where the bipolar plate is in electrical communication with a current collector and in fluid communication with the membrane. In some embodiments, the device may utilise a gasket or other watertight seal to retain the reactant and / or receiving solutions. Other configurations may also be used, such as configurations analogous to a fuel cell or flow battery, for providing and circulating liquid phase reactant and receiving solutions to and from the membrane.

[0094]

[0082] Referring to Figure 1 (c), in one embodiment, a device herein may comprise a current collector 3 in contact with reactant solution 1 comprising the reactant species (-NH2) and ionised reactant species (-NHs+), and a current collector 6 in contact with the receiving solution 5. On exposure of the reactant solution 1 to a trigger species, CO2 gas via inlet 2, ionised reactant species comprising -NHs+groups, and free HCOs' counterions are formed. The free HCOs' ions are able to move across the membrane 4 driven by osmotic concentration differences between the reactant solution 1 and the receiving solution 5, whereas the ionised reactant species are not. This uneven distribution creates a potential gradient that results in external current generation.

[0095]

[0083] Referring to Figure 8(a), in one embodiment, a device 81 herein may comprise a stack comprising two or more apparatus as described herein in series. Figure 8(a) shows three apparatus in series, comprising end plate 86, terminal current collectors 82, bipolar plates 84 comprising fluid channels 84a, and a current collector / membrane / current collector assembly 83 for receiving reactant solution or receiving solution 85. The device may be sealed by use of gaskets (not shown). Figure 8(b) shows an expanded perspective view of the current collector / membrane / current collector assembly 83 showing current collectors 83a sandwiching a membrane 83b. Referring to Figure 8(c), in another embodiment, a device herein may comprise a stack comprising two or more apparatus as described herein in series, comprising end plate 86, terminal current collectors 82, and alternatingcurrent collectors sandwiching a membrane and conductive bipolar plates 83,84 for supplying reactant solution or receiving solution (not shown). Figure 8(c) shows one possible configuration for external device screws and fluid inlets / outlets.

[0096]

[0084] The apparatus and devices herein may be used to generate electricity. Accordingly, described herein is use of an apparatus or device as defined herein to generate electricity.

[0097]

[0085] The present disclosure also provides a method of generating electricity, the method comprising: providing an apparatus comprising: a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species; a receiving solution; and a membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution, contacting a trigger species with the reactant solution, wherein the reactant species and trigger species react to form an ionised reactant species and a free counterion species, wherein a concentration of the free counterion species in the reactant solution is higher than a concentration of the free counterion species in the receiving solution such that a potential gradient is created that causes selective movement of the free counterion species across the membrane and generates electricity when the apparatus is connected to an external circuit.

[0098]

[0086] Once the reacting solution is no longer required for reaction with the trigger species, and / or the receiving solution contains an equilibrium concentration of free counterions, the reacting solution and the receiving solution may be regenerated. The method of regeneration is not particularly limited, and may utilise thermal swing and pH swing methods known in the art. In summary, the pH swing method uses pH changes to liberate or precipitate carbon dioxide from solution, such as in the form of a gas ora solid, e.g., a solid salt. The thermal swing method utilises heat to desorb or liberate gas from solution. In some embodiments, the method of regeneration may comprise coupling electrolytic water splitting with reactant species regeneration. In such cases, electrolysis of water produces H+and OH- ions, and generated H+may react with free counterion species comprising a solubilised form of the trigger species in order to reform and release the trigger species. In one embodiment, where the trigger species is CO2, the solubilised form and free counterion species may be HCOs , and reaction with H+generated by electrolysis of water may leading to release of high-purity CO2 gas. Simultaneously, OH' ions generated by electrolysis of water may interact with the ionised reactant species such, thus regenerating the reactant species. In one embodiment, where the ionised reactant species comprises a protonated ammonium cation, the OH' ions may combine with the proton of the cation to produce water and regenerate the amine reactant species. In some embodiments, this process may not only regenerate the trigger species and the reactant species, but also H2 and O2 gas byproducts, which may in some embodiments be used as fuel.

[0099]

[0087] The present disclosure also provides a method of generating electricity from a potential gradient as described above using an apparatus or device as described herein.Embodiments

[0100] Embodiment 1.An apparatus for effecting selective migration of an ion species, the apparatus comprising: a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species; a receiving solution; and a membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution at least in part on the basis of their different molecular weights.

[0101] Embodiment 2. The apparatus of Embodiment 1 , wherein the reactant species has a formula mass of at least 1 ,000 g / mol, optionally of at least 20,000 g / mol.

[0102] Embodiment 3. The apparatus of Embodiment 1 or Embodiment 2, wherein the reactant species is a polymer comprising one or more amine functional groups, optionally wherein the reactant species is a polymer comprising one or more monomers each comprising one or more amine functional groups. Embodiment 4. The apparatus of any one of Embodiments 1 to 3, wherein the reactant species comprises polyethyleneimine (PEI), polyallylamine, tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAM AM). Embodiment 5. The apparatus of any one of the preceding Embodiments, wherein the reactant species is water soluble, such as has a solubility of more than 10 mg / L at 40 °C.

[0103] Embodiment 6. The apparatus of any one of the preceding Embodiments, wherein the ionised reactant species has a molecular weight that is at least 10x larger than a molecular weight of the free counterion species.

[0104] Embodiment 7. The apparatus of any one of the preceding Embodiments, wherein the trigger species is selected from carbon dioxide, sulphur dioxide and nitrogen dioxide.

[0105] Embodiment 8. The apparatus of any one of the preceding Embodiments, wherein the ionised reactant species is present in the reactant solution at a concentration of from 1 to 75 wt%, or of from 5 mM to 500 mM.

[0106] Embodiment 9. The apparatus of any one of the preceding Embodiments, wherein the membrane is a nanofiltration membrane or an anion exchange membrane.

[0107] Embodiment 10. The apparatus of any one of the preceding Embodiments, wherein the membrane has a molecular weight cutoff (MWCO) that is smallerthan the molecularweight of the ionised reactant species but larger than the molecular weight of free counterion species.

[0108] Embodiment 11. The apparatus of any one of the preceding Embodiments, wherein the receiving solution comprises a concentration of free counterion species that is lower than a concentration of free counterion species in the reactant solution, optionally wherein the receiving solution is initially devoid of free counterion species, so as to create a potential gradient across the membrane.

[0109] Embodiment 12. The apparatus of any one of the preceding Embodiments, wherein the reactant solution and receiving solution are both aqueous.Embodiment 13. The apparatus of any one of the preceding Embodiments, wherein the receiving solution comprises an osmotic pressure adjusting agent.

[0110] Embodiment 14. A device for generating electricity, the device comprising: an apparatus according to any one of Embodiments 1 to 13 connected into an external circuit.

[0111] Embodiment 15. The device of Embodiment 14, wherein the external circuit comprises a first current collector in electrical contact with the reactant solution and a second current collector in electrical contact with the receiving solution.

[0112] Embodiment 16. A method of generating electricity, the method comprising: providing an apparatus according to any one of Embodiments 1 to 13 or the device according to Embodiment 14 or Embodiment 15; contacting a trigger species with the reactant solution, wherein the reactant species and trigger species react to form an ionised reactant species and a free counterion species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species, wherein a concentration of the free counterion species in the reactant solution is higher than a concentration of the free counterion species in the receiving solution such that a potential gradient is created that drives selective movement of the free counterion species, but not the ionised reactant species, across the membrane and into the receiving solution on the basis of its smaller molecular weight, thereby generating a potential difference and electric current when the apparatus is connected to an external circuit.

[0113] Embodiment 17. Use of the apparatus according to any one of Embodiments 1 to 13 or the device according to Embodiment 14 or Embodiment 15 to generate electricity.

[0114] Examples

[0115] Example 1 - Apparatus and electricity generation

[0116]

[0088] Polyethylenimine, branched (PEI, average Mw~25,000 by LS), polyethylenimine, branched (average Mw~800 by LS), polyethylenimine, branched (average Mw~2000 by LS), polyethylene glycol (PEG, Mw~6000) and polyethylene glycol (Mw~600) were purchased from Sigma-Aldrich. Nanofiltration membrane, NF270 was purchase from Guochu technology Ltd., Co. Anion exchange membrane, Sustainion X37-50 was purchased from Dioxide Materials Ltd., Co.

[0117]

[0089] A nanofiltration membrane (NF270) with a side length of 3 cm was positioned between two polytetrafluoroethylene (PTFE) cells each with a volume of 60 mL, ensuring a tight seal between the cells and the membrane. Each PTFE cell contained a single circular opening to the membrane with a diameter of 2.2 cm to ensure ions could pass through the nanofiltration membrane.

[0118]

[0090] A long tube connected the carbon dioxide (CO2) outlet valve to a flow rate controller. CO2 exiting the flow rate controller was directed into a bubbler filled with deionised water to ensure the gas was humidified. The outlet of the bubbler was then connected to the PTFE cell and sealed securely.

[0119]

[0091] An aqueous solution of polyethyleneimine (PEI) at a defined concentration (10 wt%, 30 wt%) was prepared and thoroughly mixed to ensure uniformity. Concentrated PEI solution (30 wt%) was placed into one side of the PTFE cell and diluted PEI (10 wt%) solution was placed into the other side each of the PTFE cell. The concentration ratio between the two solutions was 1 :1000.

[0092] Due to the solute concentration difference between the solutions on both sides of the nanofiltration membrane, water will tend to flow toward the concentrated solution. Accordingly, to balance the osmotic pressure, a certain amount of PEG solution was added into the dilute PEI solution side of the cell. The amount of PEG required can be calculated using Equations (1) and (2) above, where the reactant species is PEI.

[0120]

[0093] To make an assumption, PEI on the dilute side can be ignored, such that the osmosis pressure is only related to the molar concentration as follows:

[0121] m(PEG required') = C(PEI concentrated side) * M PEG) * V ... Equation (3)

[0094] The open-circuit voltage and short-circuit current of a membrane generator were measured under ambient conditions using a Keithley 2450 source meter. For the open-circuit measurement, the current output was set to 0 A, while for the short-circuit measurement, the voltage was set to 0 V. A platinum electrode was inserted into each PTFE cell and connected to Keithley 2450 source meter in series. Before the start of the test, CO2 gas was then fed into the cell (PEI concentrated side) at a flow rate of 20 cm3 / min. The results are shown in Figures 2 to 7.

[0122]

[0095] A 10 wt% PEI solution was firstly used to evaluate the electricity generation capacity. To start the test, CO2 gas was fed into the PEI concentrated side at speed of 20 cm3 / min. When CO2 was introduced, the open-circuit voltage (Voc) of the device reached a peakof approximately 310 mV within 10-15 hours (Figure 2a). Subsequently, the voltage gradually declined, still maintained above 250 mV over 60 h, confirming that electricity generation occurred as a result of CO2 adsorption. As shown in Figure 2b, the current reached a peakataround 23 nA when the generatorwas connected to a 10 MQ resistor in series. Similar to the voltage-time (VT) test results, the current was relatively stable (excluding the external disturbance signals).

[0123]

[0096] To assess the impact of varying concentrations, a 30 wt% PEI solution was utilised as the concentrated agent. As demonstrated in Figure 3a, the open circuit voltage reached above 400 mV (around 425 mV). Compared with Figure 3b, the peak voltage only went below 320 mV when the PEI concentration was 10 wt%. The data indicate that as the concentration of the PEI increased, the peak voltage also increased. Furthermore, the voltage can remain above 320 mV for over 70 hours of operation when the concentration was increased to 30 wt%.

[0124]

[0097] To explore the effect of different molecular weight of PEI on electricity generation during the adsorption process, two additional tests were conducted using PEI with molecular weights of 800 and 2000 g / mol. From the results in Figure 4a, it can be observed that, with a molecular weight of 800, the peak voltage exceeded 400 mV within two hours but then rapidly declined to 300 mV. Subsequently, the voltage stabilised at approximately 300 mV, maintaining this level for over 20 hours. In contrast, using PEI with a molecular weight of 2,000 yielded a voltage significantly lower than that of the PEI with a molecular weight of 800. Although the voltage initially increased to approximately 280 mV within the first two hours, it subsequently declined to around 225 mV and remained at this lower level for over 60 hours.

[0125]

[0098] Data in Figure 6 shows voltage-time tests for 10% PEI solution (MW = 10,000) where CO2 was either kept open for 2 h (high flow speed) and then closed, the peak voltage achieved being around350 mV; and when the same solution was pre-washed with CO2 until saturation point and CO2 was closed during testing, which had a lower peak voltage of approximately 220 mV. Figure 7 shows voltage-time and current-time data for a 10% PEI solution (MW = 10,000) where CO2 was kept open (low speed) throughout testing, showing that the voltage could be maintained at around 400 mV with the CO2 on.

[0126]

[0099] To evaluate the impact of different membrane types, under identical conditions and with a consistent CO2flow rate, we replaced the NF270 membrane with the Sustainion X37-50 and measured the open-circuit voltage and short-circuit current for PEI (MW = 25,000). The comparative results (see Figure 5) demonstrated that the NF270 membrane exhibited superior voltage and current performance. For the NF270 nanofiltration membrane, the maximum power density can reach 959 uW / m2, whereas when using the Sustainion X37-50 membrane, the maximum power density was 776 uW / m2. This may be due to the thinner functional layer and higher ion flux of the NF270.

[0127] Example 2 - Device stack

[0128]

[0100] A device comprising a stack was constructed containing multiple cells as described in Example 1 above using a reactant solution pre-saturated with dissolved CO2 in series, each having a 50 cm2current collector area. Each cell comprised two carbon felt current collectors each in fluid communication with opposing sides of a membrane, and having an active area of 12.25 cm2. Each current collector was then in electrical communication with a graphite bipolar plate (1.7 mm thickness) comprising a series of fluid channels to supply reactant and receiving solutions to the current collector and membrane, and the current collector / bipolar plate join was fluid sealed using two 3.5 mm thick rubber gaskets. The stack was flanked by gold-plated current collector plates and end plates. One end plate comprised a flow channel inlet and outlet to provide reactant and receiving solutions to the stack. A 3 cell stack produced 0.45 V of electricity, well aligned with expectations (single cell ~0.15 V).

[0129]

[0101] 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.

[0130]

[0102] 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 apparatus for selective passive migration of ions, the apparatus comprising:a reactant solution comprising a reactant species comprising one or more ionisable groups and adapted to form an ionised reactant species and free counterion species on contact with a trigger species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species;a receiving solution; anda membrane separating the reactant solution from the receiving solution and adapted to allow selective migration of the free counterion species, but not the ionised reactant species, from the receiving solution to the reactant solution at least in part on the basis of their different molecular weights.

2. The apparatus of claim 1 , wherein the reactant species has a formula mass of at least 1 ,000 g / mol, optionally of at least 20,000 g / mol.

3. The apparatus of claim 1 or claim 2, wherein the reactant species is a polymer comprising one or more amine functional groups, optionally wherein the reactant species is a polymer comprising one or more monomers each comprising one or more amine functional groups.

4. The apparatus of any one of claims 1 to 3, wherein the reactant species comprises polyethyleneimine (PEI), polyallylamine, tris(2-aminoethyl)amine (TREN), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyamidoamine (PAM AM).

5. The apparatus of any one of the preceding claims, wherein the reactant species is water soluble, such as has a solubility of more than 10 mg / L at 40 °C.

6. The apparatus of any one of the preceding claims, wherein the ionised reactant species has a molecular weight that is at least 10x larger than a molecular weight of the free counterion species.

7. The apparatus of any one of the preceding claims, wherein the trigger species is selected from carbon dioxide, sulphur dioxide and nitrogen dioxide.

8. The apparatus of any one of the preceding claims, wherein the ionised reactant species is present in the reactant solution at a concentration of from 1 to 75 wt%, or of from 5 mM to 500 mM.

9. The apparatus of any one of the preceding claims, wherein the membrane is a nanofiltration membrane or an anion exchange membrane.

10. The apparatus of any one of the preceding claims, wherein the membrane has a molecular weight cutoff (MWCO) that is smaller than the molecular weight of the ionised reactant species but larger than the molecular weight of free counterion species.

11. The apparatus of any one of the preceding claims, wherein the receiving solution comprises a concentration of free counterion species that is lower than a concentration of free counterion species in the reactant solution, optionally wherein the receiving solution is initially devoid of free counterion species, so as to create a free counterion species concentration gradient across the membrane that drives passive migration of the free counterion species.

12. The apparatus of any one of the preceding claims, wherein the reactant solution and receiving solution are both aqueous.

13. The apparatus of any one of the preceding claims, wherein the receiving solution comprises an osmotic pressure adjusting agent.

14. The apparatus of any one of the preceding claims, wherein the apparatus is devoid of an applied electric field, optionally wherein the apparatus is for generating electricity via selective passive migration of ions.

15. A device for generating electricity, the device comprising:an apparatus according to any one of claims 1 to 14 connected into an external circuit.

16. The device of claim 15, wherein the external circuit comprises a first current collector in electrical contact with the reactant solution and a second current collector in electrical contact with the receiving solution.

17. The device of claim 15 or claim 16, wherein the external circuit comprises a load.

18. The device of any one of claims 15 to 17, comprising a stack of two or more apparatus connected in series or in parallel.

19. A method of generating electricity, the method comprising:providing an apparatus according to any one of claims 1 to 14 or the device according to any one of claims 15 to 18;contacting a trigger species with the reactant solution, wherein the reactant species and trigger species react to form an ionised reactant species and a free counterion species, wherein the ionised reactant species has a molecular weight at least 5x greater than a molecular weight of the free counterion species,wherein a concentration of the free counterion species in the reactant solution is higher than a concentration of the free counterion species in the receiving solution such that a concentration gradient is created across the membrane that drives selective passive migration of the free counterion species, but not the ionised reactant species, across the membrane and into the receiving solution on the basis of its smaller molecular weight,thereby generating a potential difference and electric current when the apparatus is connected to an external circuit.

20. Use of the apparatus according to any one of claims 1 to 14 or the device according to any one of claims 15 to 18 to generate electricity.

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