PHOTOELECTROCHEMICAL DEVICE FOR THE CAPTURE, CONCENTRATION AND COLLECTION OF ATMOSPHERIC CARBON DIOXIDE

Abstract

The present disclosure relates to a carbon dioxide capture device comprising a first reactor and a second reactor both of which show a (photo)anode containing or connected to oxygen evolution and/or carbon dioxide evolution catalyst(s) and a (photo)cathode containing or connected to an oxygen reduction catalyst, wherein the first reactor comprises an anion exchange membrane placed between the porous (photo)anode and porous (photo)cathode, and the second reactor comprises a proton exchange membrane placed between the porous (photo)anode and porous (photo)cathode. On the porous (photo)cathode side of the first reactor there is a fluid inlet able to carry carbon dioxide, air and water, and on the side of the porous (photo)cathode of the second reactor there is a fluid outlet able to carry carbon dioxide and water.

Claims

1. Carbon dioxide capture device comprising : (A) a first reactor comprising an anion exchange membrane placed between a porous (photo)anode and porous (photo)cathode, wherein the (photo)anode contains or is connected physically or electrically to oxygen evolution and/or carbon dioxide evolution catalyst(s), and the (photo)cathode contains or is connected physically or electrically to an oxygen reduction catalyst; (B) a second reactor comprising a proton exchange membrane placed between a porous (photo)anode and porous (photo)cathode, wherein the (photo)anode contains or is connected physically or electrically to an oxygen evolution catalyst, and the (photo)cathode contains or is connected physically or electrically to an oxygen reduction catalyst; wherein the porous (photo)cathode of the first reactor has at least a fluid inlet able to carry carbon dioxide, air and water, and the porous (photo)anode of the first reactor has at least a fluid inlet able to carry water and oxygen, the porous (photo)cathode of the second reactor has at least a fluid outlet able to carry carbon dioxide and water, and the porous (photo)anode of the second reactor has at least a fluid outlet able to carry water and oxygen, wherein the carbon dioxide capture device is configured to transfer fluid exiting the porous (photo)cathode of the first reactor to the porous (photo)anode of the second reactor, and to transfer fluid exiting the porous (photo)anode of the first reactor to the porous (photo)cathode of the second reactor.

2. Carbon dioxide capture device according to claim 1, wherein: the porous (photo)cathode of the first reactor has a fluid inlet and a fluid outlet both able to carry carbon dioxide in air and water, and the porous (photo)anode of the first reactor has a fluid inlet and a fluid outlet both able to carry water and oxygen; the porous (photo)cathode of the second reactor has a fluid inlet and a fluid outlet able both to carry carbon dioxide, oxygen and water, and the porous (photo)anode of the second reactor has a fluid inlet and a fluid outlet both able to carry water and oxygen, wherein the fluid outlet of the porous (photo)cathode of the first reactor is fluidically connected to the fluid inlet of the porous (photo)anode of the second reactor, and the fluid outlet of the porous (photo)anode of the first reactor is fluidically connected to the fluid inlet of the porous (photo)cathode of the second reactor.

3. Carbon dioxide capture device according to claim 1, wherein the first and second reactor are placed in a consolidated block separated by a separator such that the porous (photo)cathode of the first reactor is situated opposite the porous (photo)anode of the second reactor and separated therefrom by the separator, and the porous (photo)anode of the first reactor is opposite the porous (photo)cathode of the second reactor and separated therefrom by the separator, and a single fluid line including the fluid inlet of the porous (photo)cathode of the first reactor and the fluid outlet of the porous (photo)anode of the second reactor runs along one wall of the consolidated block, and a further single fluid line including the fluid inlet of the porous (photo)anode of the first reactor and the fluid outlet of the porous (photo)cathode of the second reactor runs along another wall of the consolidated block, the two walls facing one another and both being in contact with the separator.

4. Carbon dioxide capture device according to claim 1, wherein the porous (photo)anode of the first reactor comprises: BiVO.sub.4, TaO.sub.xN.sub.y, LaTiO.sub.2N, BaTaO.sub.2N, SrTaO.sub.2N, WO.sub.3, CuWO.sub.4, Fe.sub.2O.sub.3, ZnFe.sub.2O.sub.4, and/or TiO.sub.2, and may further include (co)catalyst materials based on one or more of: Ni, Ni Raney, NiCo, NiFe, NiP, CoP, CoPi, SrCoO.sub.3, Ru, Mg, Ag, Au, Fe-OOH, Ni-00H, IrOx, CoOH, FeOx, Pt, Rh, RhOx, RuOx, and PtOx.

5. Carbon dioxide capture device according to claim 1, wherein the porous (photo)anode of the second reactor comprises: BiVO.sub.4, TaO.sub.xN.sub.y, LaTiO.sub.2N, BaTaO.sub.2N, CuWO.sub.4, WO.sub.3, and/or TiO.sub.2, and may further include (co)catalyst materials based on one or more of: Ir, IrOx, Rh, RhOx, Pt, PtOx, Ni, Co, CoOx, NiOx, MnOx, Co phosphate, Mg, Ru, Au, Pt.sub.3M where M =Ni or Co or Y, PtRu, NiP, CoP, FeP, NiCo, NiMo, and NiW.

6. Carbon dioxide capture device according to claim 1, wherein the porous (photo)cathode of the first reactor comprises one or more of: MoS.sub.2, MoSe.sub.2, WS.sub.2, GaP, CdS, CdSe, ZnSe, CuNbO.sub.4, PMPDI, InP, WSe.sub.2, ZnFe.sub.2O.sub.4, CuNbO.sub.3, PMPDI, Cu.sub.2O, g-C.sub.3N.sub.4, CIGS, CIGSe, CaFeO.sub.2, CuFeO.sub.2, and may further include (co)catalyst materials based on one or more of: Ni, Ni Raney, LaNiO.sub.3, LaMnO.sub.3, Ag, Ru, Au, Pt, Pt.sub.3M where M=Ni or Co or Y, PtRu, Co, NiP, CoP, FeP, NiCo, NiMo, NiW, Ir, Mg, Ru, Pt, Rh, and RhOx.

7. Carbon dioxide capture device according to claim 1, wherein the porous (photo)cathode of the second reactor comprises one or more of: MoS.sub.2, MoSe.sub.2, WS.sub.2, GaP, CdS, CdSe, ZnSe, CuNbO.sub.4, PMPDI, InP, WSe.sub.2, ZnFe.sub.2O.sub.4, CuNbO.sub.3, PMPDI, Cu.sub.2O, g-C.sub.3N.sub.4, CIGS, CIGSe, CaFeO.sub.2, and CuFeO.sub.2, and may further include (co)catalyst materials based on: Ru, Au, Pt, Pt.sub.3M where M=Ni, Co, Y, PtRu, NiP, CoP, FeP, NiCo, NiMo, and/or NiW.

8. Carbon dioxide capture device according to claim 1, wherein the porous (photo)anode of the first reactor and/or the porous (photo)anode of second reactor and/or the porous (photo)cathode of the first reactor and/or the porous (photo)cathode of second reactor, comprise(s) porous substrates, such as those in mesh, felt or foam form, the porous substrates comprising a material selected from the group consisting of: carbon; titanium; tungsten; stainless steel; nickel; and conducting oxides.

9. Carbon dioxide capture device according to claim 1, wherein the anion exchange membrane of the first reactor comprises a material selected from the group consisting of: materials containing quaternary ammonium groups; low density polyurethane with quaternary ammonium groups; materials containing imidazolium or polybenzimidazole groups; and tri-or di-amine cross-linked quaternized polysulfones.

10. Carbon dioxide capture device according to claim 9, wherein the anion exchange membrane of the first reactor comprises a material with vinylbenzyl chloride and imidazolium groups.

11. Carbon dioxide capture device according to claim 1, wherein the proton exchange membrane for the second reactor comprises a material selected from the group consisting of: perfluorocarbonsulfonic acid polymers; polysulfonic acid polymers; polybenzimidazoles; polyacrylic acids; and hydrocarbon membrane materials.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0024] FIG. 1 shows a schematic diagram of carbon dioxide (CO.sub.2) concentration by the first reactor of the carbon dioxide capture device of the present disclosure, comprising a (photo)cathode able to carry out the oxygen reduction reaction (ORR) and a photoanode able to carry out the oxygen evolution reaction (OER)/carbon dioxide evolution reaction (CO.sub.2ER). The symbol “h.sup.+” here refers to a positive hole, absorbing electrons.

[0025] FIG. 2 shows the band-gap of various semiconductors with potential for oxygen evolution and reduction indicated with dotted, long lines, based on the reference Nanoscale Horiz., 2016, 1, 243-267.

[0026] FIG. 3 shows a schematic diagram of carbon dioxide (CO.sub.2) separation by the second reactor of the carbon dioxide capture device of the present disclosure, comprising a (photo)cathode able to carry out the oxygen reduction reaction (ORR) and a photoanode able to carry out the oxygen evolution reaction (OER).

[0027] FIG. 4A shows combined device configurations wherein capture and separation functions are combined into one device, shown here in exemplary configuration as FIG. 4A.

[0028] FIG. 4B shows combined device configurations wherein capture and separation functions are combined into one device, shown here in exemplary configuration as FIG. 4B.

[0029] FIG. 5 shows carbon dioxide (CO.sub.2) capture through absorption in the anion exchange membrane. In FIG. 5, the light is shining from the (photo)anode side. In the case that there would only be a photocathode (with anode), it would preferable to shine the light from the opposite side.

[0030] FIG. 6A shows the gases collected on the opposite side of the device, the part of the device concerned being shown in FIG. 6A.

[0031] FIG. 6B shows the gases collected on the opposite side of the device, the results in FIG. 6B.

[0032] FIG. 7A shows experimental data of CO.sub.2 separation using the concept of the disclosure, the part of the device concerned being shown in FIG. 7A.

[0033] FIG. 7B shows experimental data of CO.sub.2 separation using the concept of the disclosure, the results in FIG. 7B.

[0034] FIG. 8 shows possible device structure elements that can be used within the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0035] The present disclosure relates to a device that comprises two membrane reactors connected with each other. The reactors can be placed in various configurations, for example but not restricted to, side-by-side or one on top of the other, if the first reactor is sufficiently transparent.

[0036] Among advantages one or more of which may be observed with respect to known carbon dioxide capture devices, the present disclosure may be seen as providing;

[0037] 1) an easy-to-implement, stand-alone device; and/or

[0038] 2) a new method for separation of O.sub.2 and CO.sub.2 by converting O.sub.2 to H.sub.2O (gas to liquid).

[0039] The present disclosure provides a new mechanism to transfer the CO.sub.2 from the sorbent to the collector via continuous oxygen reduction/oxidation cycles. (Photo)electrochemical CO.sub.2 sorption has been so far restricted to ionic liquids and redox mediators are generally expensive, exotic materials. The present disclosure provides a mechanism for a simple, solid-state device design which captures CO.sub.2 and produces electricity simultaneously—incentivizing its use. Additionally, a photoelectrochemical method to separate O.sub.2 /CO.sub.2 by converting the O.sub.2 to H.sub.2O is proposed. The present disclosure envisages: [0040] i. Utilisation of oxygen reduction and oxygen evolution reaction cycles to create a bias free current as a way to drive HCO.sub.3.sup.− ions through the anion exchange membrane. [0041] ii. Utilisation of water to push H.sup.+ ions through the proton exchange membrane. [0042] iii. The use of solar energy to power the reaction with parallel production of electricity in the same device (but the disclosure could also be powered or supported by an external power source).

[0043] The function of the first reactor is to remove the CO.sub.2 from the atmosphere—this can be ideally directly from the ambient air or alternatively from a concentrated solution such as KHCO.sub.3. In effect, in this alternative embodiment, efforts to capture CO.sub.2 in liquid solutions e.g. via KOH.fwdarw.KHCO.sub.3 conversion, may be combined with the system integrated in the present disclosure in order to subtract CO.sub.2 from KHCO.sub.3 and concentrate in particular at the side of the fluid outlet of the photoanode of the first reactor (117).

[0044] The first reactor comprises an anion exchange membrane placed between a porous (photo)anode and porous (photo)cathode. The (photo)anode contains or is connected (physically or electrically) to oxygen evolution and/or carbon dioxide evolution catalyst(s), whilst the (photo)cathode contains or is connected to an oxygen reduction catalyst. This may create a bias free current, where a photocurrent is generated only by light irradiation and applied potential bias is not needed. In order to generate a photocurrent efficiently from a photoelectrode, both solar light as well as an applied potential bias may be required across the photoelectrode. The main function of this is to improve charge separation between e.sup.− and h.sup.+. However, applying a potential adds an additional degree of complexity. In an advantageous embodiment of the present disclosure, the photocurrent may be generated only under light irradiation i.e. applied potential bias is not needed. The anion exchange membrane absorbs CO.sub.2 from the atmosphere through natural or forced convection to form HCO.sub.3.sup.− ions. Forced convection may for example be carried out by using fans or a pump to force/circulate air through the device. The device can operate without the forced convection, but this is a possible embodiment to speed up the CO.sub.2 sorption inside the anion exchange membrane. Under solar irradiation, the HCO.sub.3.sup.− ions are forced to the other side of the device, i.e. the OER and CO.sub.2ER fluid outlet of the photoanode of the first reactor (117), under the bias free current. The collection step may appropriately be carried out primarily during the night, but collection is also possible in parallel with the transfer step under sunlight irradiation (FIG. 1). The mixture gathered on the opposite side is a mixture of CO.sub.2 and O.sub.2, but preferably a higher concentration of CO.sub.2. The total overpotential losses for performing oxygen evolution and oxygen reduction are around 0.7 V, giving a wide variety of materials with a suitable band-gap to be potential photoelectrodes (FIG. 2).

[0045] In the present disclosure, appropriate materials for the porous (photo)anode (113, 213, 313, 413) of the first reactor (1) containing an anion exchange membrane (AEM) (112, 212, 312, 412) are n-type or p-type (photo)electrode materials compatible with AEM with a suitable band-gap (according to FIG. 2). Examples include BiVO.sub.4, TiO.sub.2, WO.sub.3, which can be combined with a (photo)cathode to reach both OER/CO.sub.2ER and ORR potentials. TiO.sub.2 is a practical example for device preparation, but the bandgap of TiO.sub.2 is large, essentially restricting absorption to that of UV light. Materials with a smaller band-gap where the conduction band (CB) and valence band (VB) are on either side of the OER/CO.sub.2ER and ORR reaction potentials are advantageous. A smaller bandgap would enable higher absorption of visible light which allows considerably more energy to be used in practical applications. Materials with the band gap of around 1.0 to 2.0 eV and a conduction band edge lower than around 0.7 eV vs. NHE and valence band at higher than around 1.7 eV vs. NHE are appropriate, NHE (=Normal Hydrogen Electrode) here being a reference electrode and the potential of platinum in a 1 M acid solution (pH =0). Preferred materials for the porous (photo)anode of the first reactor (1) may be selected from the group consisting of: BiVO.sub.4, TaO.sub.xN.sub.y, LaTiO.sub.2N, BaTaO.sub.2N, SrTaO.sub.2N, WO.sub.3, CuWO.sub.4, Fe.sub.2O.sub.3, ZnFe.sub.2O.sub.4, TiO.sub.2. A particularly preferred list consists of: BiVO.sub.4, TiO.sub.2, WO.sub.3. Protective layers or cocatalysts (catalysts on photoelectrodes, the materials may be the same) may enhance performance and/or provide chemical compatibility to the alkaline environment. OER/CO.sub.2ER (co)catalyst materials for the porous (photo)anode (113, 213, 313, 413) of the first reactor (1) may appropriately include catalysts based on one or more of: (A) OER: Ni, Ni Raney, NiCo, NiFe, NiP, CoP, CoPi, SrCoO.sub.3, Ru, Mg, Ag, Au; (B) CO.sub.2ER: Ni, Ni Raney, LaNiO.sub.3, LaMnO.sub.3, Ag, Ru, Au, Pt, Pt.sub.3M where M=Ni, Co, Y, PtRu, Co, NiP, CoP, FeP, NiCo, NiMo, NiW (and their oxides for all metals in the list). For the CO.sub.2ER, these materials can either be alone or supported, for example on carbon. Protection can be provided by overcoatings e.g. of TiO.sub.2. Furthermore, in the case of the use of TiO.sub.2 as materials for the porous photoanode, a co-catalyst is not necessary—the TiO.sub.2 is self-catalysing.

[0046] In the present disclosure, appropriate materials for the porous (photo)anode (123, 223, 333, 423) of the second reactor (2) containing a proton exchange membrane (PEM) (122, 222, 322, 422) are similar, although not identical, to the materials described above for the porous (photo)anode of the first reactor. In effect, the different environment of the two reactors creates different potential stability issues, with the membrane of reactor 1 being alkaline, and the membrane of reactor 2 being acidic.

[0047] Preferred materials for the porous (photo)anode of the second reactor (2) may thus be selected from the group consisting of: BiVO.sub.4, TaO.sub.xN.sub.y, LaTiO.sub.2N, BaTaO.sub.2N, CuWO.sub.4, WO.sub.3, TiO.sub.2. Protective layers or cocatalysts may enhance performance and/or provide chemical compatibility to the alkaline environment. OER catalysts may advantageously include: Ir, Mg, Ru, Rh and their oxides (such as IrOx, RhOx), Pt, Pd, Au. ORR catalysts may advantageously include: Ru, Au, Pt, Pt.sub.3M where M=Ni or Co or Y, PtRu, NiP, CoP, FeP, NiCo, NiMo, NiW. These may be used alone or supported, for example on carbon. OER (co)catalyst materials for the porous (photo)anode (123, 223, 323, 423) of the second reactor (2) may preferably include catalysts based on: Ir, Mg, and/or Ru. Protection can be provided by overcoatings e.g. of TiO.sub.2. Furthermore, in the case of the use of TiO.sub.2, a co-catalyst is not necessary—the TiO.sub.2 is self-catalysing.

[0048] In the present disclosure, appropriate materials for the porous (photo)cathode (111, 211, 311, 411) of the first reactor (1) containing an anion exchange membrane (AEM) (112, 212, 312, 412) are generally speaking p-type (photo)electrode materials compatible with alkaline exchange membranes with a suitable band-gap and edges (according to FIG. 2). Examples of cathode materials include: Pt/C, Pt-Ru/C, Au/C, Ni/C and Ni-felt, preferred among these being: Pt, Pt-Ru/C. Materials with the band gap of around 1.0 to 2.0 eV and a conduction band edge lower than around 0.7 eV vs. NHE and valence band at higher than around 1.7 eV vs. NHE are appropriate. Preferred materials for the porous (photo)cathode of the first reactor (1) may be selected from the group consisting of: Si, MoS.sub.2, MoSe.sub.2, W5.sub.2, GaP, CdS, CdSe, ZnSe, CuNbO.sub.4, PMPDI, InP, WSe.sub.2, ZnFe.sub.2O.sub.4, CuNbO.sub.3, PMPDI, Cu.sub.2O, g-C.sub.3N.sub.4, CIGS, CIGSe, CaFeO.sub.2, and/or CuFeO.sub.2. Protective layers or cocatalysts may enhance performance. ORR (co)catalyst materials for the porous (photo)cathode (111, 211, 311, 411) of the first reactor (1) may appropriately include catalysts based on: Ni, Ni Raney, LaNiO.sub.3, LaMnO.sub.3, Ag, Ru, Au, Pt, Pt.sub.3M where M=Ni, Co, Y, PtRu, Co, NiP, CoP, FeP, NiCo, NiMo, NiW, Ir, Mg, Ru, Pt, Rh, and/or RhOx. Protection and or providing chemical compatibility with the alkaline environment can be provided by overcoatings e.g. of TiO.sub.2. Carbon is also a suitable cathode but requires the use of a catalyst such as platinum, Pt/C cathodes being typically 60:40 Pt:C by weight.

[0049] In the present disclosure, appropriate materials for the porous (photo)cathode (121, 221, 321, 421) of the second reactor (2) containing a proton exchange membrane (PEM) (122, 222, 322, 422) are similar, although not identical, to the materials described above for the porous (photo)cathode of the first reactor (1). Preferred materials for the porous (photo)cathode of the second reactor (2) may thus be selected from the group consisting of: Si, MoS.sub.2, MoSe.sub.2, WS.sub.2, GaP, CdS, CdSe, ZnSe, CuNbO.sub.4, PMPDI, InP, WSe.sub.2, ZnFe.sub.2O.sub.4, CuNbO.sub.3, PMPDI, Cu.sub.2O, g-C.sub.3N.sub.4, CIGS, CIGSe, CaFeO.sub.2, and CuFeO.sub.2. Protective layers or cocatalysts may enhance performance. ORR (co)catalyst materials for the porous (photo)cathode (121, 221, 321, 421) of the second reactor (2) may appropriately include catalysts based on: Ru, Au, Pt, Pt.sub.3M where M=Ni, Co, Y, PtRu, NiP, CoP, FeP, NiCo, NiMo, and/or NiW. Protection can be ensured by overcoatings e.g. of TiO.sub.2. Carbon is also a suitable cathode but requires the use of a catalyst such as platinum, Pt/C cathodes being typically 60:40 Pt:C by weight.

[0050] In the present disclosure, the anion exchange membrane (AEM) (112, 212, 312, 412) for the first reactor can appropriately be: anion exchange membrane materials containing quaternary ammonium groups (such as those sold under the commercial names: Fumasep® FAA, A201, Orion® TM1, Durion®, Selemion®) or low density polyurethane with quaternary ammonium groups; anion exchange membrane materials containing imidazolium or polybenzimidazole groups (such as those sold under the commercial names: Aemion®, Sustainion®), or tri-or di-amine cross-linked quaternized polysulfones. Preferred anion exchange membrane materials are ones containing quaternary ammonium groups, low density polyurethane with quaternary ammonium groups, or anion exchange membrane containing imidazolium or polybenzimidazole groups. A particularly preferred choice is the use of anion exchange membranes based on materials with vinylbenzyl chloride and imidazolium groups (such as those sold under the commercial name: Sustainion®). Low-density polyethylene (LDPE) including grafted LDPE is another preferred embodiment of the anion exchange membrane (AEM) in the present disclosure.

[0051] The proton exchange membrane (PEM) (122, 222, 322, 422) for the second reactor is for example appropriately based on a polysulfonic acid material such as those sold commercially under the names Aquivion® and Nafion®. Other proton exchange membranes may be used. Generally speaking, materials for the proton exchange membrane that can be used to carry out the present disclosure may be perfluorocarbonsulfonic acid or polysulfonic acid polymers (such as those sold commercially under the names: Nafion®, Aquivion®, Fumapem®-F, Fumapem® SX Pemion®), polybenzimidazole membranes (notably for possible high temperature use) such as those sold commercially under the names: Celtec®, Fumapem® AM, Fumapem® ST, polyacrylic acids, and hydrocarbon membranes (such as those sold commercially under the names commercial names: Fumatech® ST, Fumatech® P, E). Preferred materials for the proton exchange membrane are: perfluorocarbonsulfonic acid or polysulfonic acid polymers, or polyacrylic acids, most preferred being perfluorocarbonsulfonic acid or polysulfonic acid polymers.

[0052] In the present disclosure, the porous (photo)anode and/or porous (photo)cathode of either the first or second reactor may be ionomer coated, which may help to increase CO.sub.2 sorption capacity. The ionomers used for such a coating may notably include ionomer materials mentioned above for use as anion exchange membrane (AEM) or proton exchange membrane (PEM). In the first reactor, with AEM, the loading of ionomer coating is preferably at most 50 mg/cm.sup.2, more preferably 0.5 to 10 mg/cm.sup.2. In the second reactor, with PEM, the loading of ionomer coating is preferably at most 50 mg/cm.sup.2, more preferably 0.5 to 10 mg/cm.sup.2, still more preferably 1.0 to 5.0 mg/cm.sup.2, for example about 3.0 mg/cm.sup.2. The ionomer coating is not necessary to carry out the present disclosure, and an ionomer coating of the porous (photo)anode and/or porous (photo)cathode of, for example, the second reactor does not necessitate an ionomer coating of the porous (photo)anode and/or porous (photo)cathode of the other, for example the first reactor. Further, the ionomers do not need to be the same on the (photo)anode and (photo)cathode side of either the first or second reactor, but this option is envisaged for the practice of the disclosure.

[0053] The present disclosure provides what may be a fully solid-state device. Thus the hydrogen carbonate HCO.sub.3.sup.− anion as shown in FIG. 1 may be generated in the absence of any liquid, with the cathode and anode inlets all gaseous. It may be noted here, that for most ion exchange membrane materials, like polysulfonic acid materials including those sold under the name Nafion®, the membrane itself is hygroscopic. Therefore there is in practice H.sub.2O inside of the membrane which allows the flow of HCO.sub.3.sup.−. However, there may be no fully “liquid” water, and the membrane still retains a plastic-like/polymer structure when it is hydrated. In appropriate field use of the device of the disclosure, the water for the hydration may come from ambient humidity. Additional liquid water may however be needed in very dry conditions (low relative humidity, deserts).

[0054] The function of the second reactor is to convert any remaining O.sub.2 in the CO.sub.2/O.sub.2 mixture, which can be transferred to the second reactor via piping, into water to facilitate the purification of the CO.sub.2 (separation of liquid and gas). The second reactor comprises a proton exchange membrane placed between a porous (photo)anode and porous (photo)cathode. The (photo)anode is connected (physically or electrically) to an oxygen evolution catalyst, whilst the (photo)cathode is connected to an oxygen reduction catalyst (FIG. 3). The CO.sub.2/water mixture can be easily separated and can be stored/used for other applications.

[0055] There is potential for the capture and separation functions to be combined into one device, for example, the two configurations shown in FIG. 4.

[0056] Thus in a device for which an exemplary embodiment is illustrated in FIG. 4a, the present disclosure provides a carbon dioxide capture device wherein:

[0057] the porous (photo)cathode of the first reactor has a fluid inlet and a fluid outlet both able to carry carbon dioxide in air and water, and the porous (photo)anode of the first reactor has a fluid inlet and a fluid outlet both able to carry water and oxygen;

[0058] the porous (photo)cathode of the second reactor has a fluid inlet and a fluid outlet able both to carry carbon dioxide, oxygen and water, and the porous (photo)anode of the second reactor has a fluid inlet and a fluid outlet both able to carry water and oxygen,

[0059] wherein the fluid outlet of the porous (photo)cathode of the first reactor is fluidically connected to the fluid inlet of the porous (photo)anode of the second reactor, and the fluid outlet of the porous (photo)anode of the first reactor is fluidically connected to the fluid inlet of the porous (photo)cathode of the second reactor.

[0060] Thus in a device for which an exemplary embodiment is illustrated in FIG. 4b, the present disclosure provides a carbon dioxide capture device wherein:

[0061] the first and second reactor are placed in a consolidated block separated by a separator such that the porous (photo)cathode of the first reactor is situated opposite the porous (photo)anode of the second reactor and separated therefrom by the separator, and the porous (photo)anode of the first reactor is opposite the porous (photo)cathode of the second reactor and separated therefrom by the separator, and a single fluid line including the fluid inlet of the porous(photo)cathode of the first reactor and the fluid outlet of the porous photoanode of the second reactor runs along one wall of the consolidated block, and a further single fluid line including the fluid inlet of the porous (photo)anode of the first reactor and the fluid outlet of the porous (photo)cathode of the second reactor runs along another wall of the consolidated block, the two walls facing one another and both being in contact with the separator.

[0062] The hashed border region in the middle of FIG. 4b is a frame/space to separate reactor 1 and 2 (first and second reactors). The essential function of the hashed border region is to avoid contact between the two reactors.

[0063] Example of operation

[0064] In an appropriate method for using the carbon dioxide capture device of the present disclosure, firstly, during the night, the anion exchange membrane is allowed to absorb CO.sub.2. This type of membrane absorbs around 95% of its CO.sub.2 capacity after 15 hours (FIG. 5), making it ideal for day—night cycling with the solar light.

[0065] The light irradiation is then begun to concentrate the CO.sub.2. This generates charge (photocurrent—I (mA)—FIG. 6) which pushes the ions across the anion exchange membrane (FIG. 1). The gases collected on the opposite side of the first reactor (FIG. 6) are at a ratio of approx. 4:1 0.sub.2:CO.sub.2 (in comparison, ambient air is 2000:1 0.sub.2:CO.sub.2). As the gases collected, CO.sub.2 is obtained in the fluid output, as shown at the bottom right of FIG. 1 as part of the gaseous mixture H.sub.2O, O.sub.2, and CO.sub.2.

TABLE-US-00001 TABLE 1 I OER CO.sub.2ER Selectivity (mA) (ppm) (ppm) to CO.sub.2 Experiment 3 630 170 27% Theory 3 560 1120 (35%)

[0066] OER here is a reference to a type of reaction (oxygen evolution reaction) CO.sub.2ER refers to the CO.sub.2 evolution reaction. OER (ppm) refers to the levels of oxygen in the fluid outlet (117, 217) of the first reactor and CO.sub.2ER (ppm) to the levels of CO.sub.2 in in the fluid outlet (117, 217) side of the first reactor.

[0067] The carbon dioxide capture and separation in a (OH.sup.−)-PEC cell was carried out here with:

[0068] Inlet-Cathode: 400 ppm CO.sub.2+3% H.sub.2O in He;

[0069] Inlet-Anode: >3% H.sub.2O in He;

[0070] Electrolyte: Grafted LDPE anion exchange membrane. Here, LDPE is low-density polyethylene, and the “electrolyte” is the anion exchange membrane (AEM)

[0071] Photoanode: TiO.sub.2/Ti-felt (substrate)

[0072] Cathode: Pt/C

[0073] UV lamp: 7 mW cm.sup.−2 intensity

[0074] Pre-treatment in CO.sub.2: overnight

[0075] Here “(AEM)-PEC cell” refers to the first reactor, containing a anion exchange membrane. The PEC stands for “photoelectrochemical”. The second reactor is the (PEM)-PEC cell, also containing an anion exchange membrane.

[0076] Different cathodes have been tested for the oxygen reduction reaction/CO.sub.2ER. Pt/Ru, Au and Ni. Pt/Ru and Pt have given promising results and are considered among the preferred choices.

[0077] The next step is the conversion from O.sub.2 to H.sub.2O through the proton exchange membrane, again through oxygen reduction and oxygen evolution cycling (FIG. 3). Again the reaction starts when light is shone on the device to generate charge carriers, which push the 1-1.sup.+ions through the membrane. A clear drop in O.sub.2 concentration can be seen when the light is on.

[0078] The oxygen purification in a PEM(H.sup.+)-PEC cell was carried out here with:

[0079] Inlet-Anode: 500 ppm CO.sub.2+500 ppm O.sub.2+3% H.sub.2O in He;

[0080] Inlet-Cathode: 2% H.sub.2O;

[0081] Flow rate: 50 sccm (standard cubic centimetres per minute)

[0082] Electrolyte: Nafion® proton exchange membrane (PEM)

[0083] Photoanode: TiO.sub.2/Ti-felt, ionomer coated Nafion®

[0084] Cathode: Pt/C

[0085] UV lamp: 7 mW cm.sup.−2

[0086] The data shows a CO.sub.2 signal which is stable and an O.sub.2 signal decreased by 25 ppm which corresponds to around 65% faradaic efficiency.

SUMMARY OF REFERENCE NUMERALS

[0087] 1: First reactor

[0088] 111, 211, 311, 411: (Photo)cathode of first reactor

[0089] 112, 212, 312, 412: Anion Exchange Membrane (AEM) of first reactor

[0090] 113, 213, 313, 413: Photoanode of first reactor

[0091] 114, 214, 314, 414: Fluid inlet of (photo)cathode of first reactor

[0092] 115, 215, 315, 415: Fluid inlet of photoanode of first reactor

[0093] 116, 216: Fluid outlet of (photo)cathode of first reactor

[0094] 117, 217: Fluid outlet of photoanode of first reactor

[0095] 2: Second reactor

[0096] 121, 221, 321, 421: (Photo)cathode of second reactor

[0097] 122, 222, 322, 422: Proton Exchange Membrane (PEM) of second reactor

[0098] 123, 223, 323, 423: Photoanode of second reactor

[0099] 124, 224: Fluid inlet of (photo)cathode of second reactor

[0100] 125, 225: Fluid inlet of photoanode of second reactor

[0101] 126, 226, 326, 426: Fluid outlet of (photo)cathode of second reactor

[0102] 127, 227, 327, 427: Fluid outlet of photoanode of second reactor

[0103] 330, 430: Separator for consolidated block assembly of first and second reactors