US20210180196A1 - Anion exchanger fillings through which flow can occur for electrolyte splitting in co2 electrolysis for better spatial distribution of gassing - Google Patents

Anion exchanger fillings through which flow can occur for electrolyte splitting in co2 electrolysis for better spatial distribution of gassing Download PDF

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US20210180196A1
US20210180196A1 US16/771,065 US201816771065A US2021180196A1 US 20210180196 A1 US20210180196 A1 US 20210180196A1 US 201816771065 A US201816771065 A US 201816771065A US 2021180196 A1 US2021180196 A1 US 2021180196A1
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compartment
salt bridge
cathode
exchange membrane
ion exchange
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Bernhard Schmid
Günter Schmid
Christian Reller
Dan Taroata
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Siemens AG
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Siemens AG
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Assigned to SIEMENS AKTIENGESELLSCHAFT reassignment SIEMENS AKTIENGESELLSCHAFT ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: Schmid, Günter , RELLER, CHRISTIAN, TAROATA, DAN, SCHMID, BERNHARD
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B13/00—Diaphragms; Spacing elements
    • C25B13/02—Diaphragms; Spacing elements characterised by shape or form
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C25B3/26—Reduction of carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

  • the present invention relates to an electrolysis cell with a multi-compartment structure, wherein a first ion exchange membrane comprising an anion exchanger is adjacent to a cathode compartment, wherein a salt bridge compartment which comprises a solid anion exchanger is adjacent to this first ion exchange membrane; an electrolysis system with such an electrolysis cell; and a method for the electrolysis of CO 2 using such an electrolysis cell or electrolysis system.
  • CO 2 is converted by photosynthesis to carbohydrates. This process, which is divided into many partial steps both temporally, and on a molecular level, spatially, can be reproduced on an industrial scale only with great difficulty.
  • the method that is currently more efficient compared to pure photocatalysis is the electrochemical reduction of CO 2 .
  • a mixed form is light-assisted electrolysis or electrically assisted photocatalysis. The two terms are to be used as synonyms, depending of the viewpoint of the observer.
  • CO 2 is converted to an energetically higher value product (such as CO, CH 4 , C 2 H 4 , etc.) under supply of electrical energy (optionally photo-assisted), which can be obtained from renewable energy sources such as wind or sun.
  • electrical energy optionally photo-assisted
  • the amount of energy required in this reduction ideally corresponds to the combustion energy of the fuel and should only be derived from renewable sources.
  • surplus production of renewable energy is not continually available, but at the moment only during times of strong solar radiation and heavy wind. However, this will be further increased in the near future with further development of renewable energy.
  • Electrolysis methods have undergone considerable further development over the past few decades. For example, it has been possible to optimize PEM water electrolysis with respect to high current densities. Large-scale electrolyzers showing performance in the megawatt range are being introduced onto the market.
  • HCO 3 ⁇ produced as a byproduct can be further transported in the direction of the anode and decomposed into CO 2 at a site depending on the cell design, for example by protons formed on the anode side. It has been shown that it can be advantageous to use three-compartment cells in which the CO 2 is generated separately from the product of the electrodes, as this makes recycling easier. Corresponding cell designs can be found for example in US 2017037522 A1, DE 102017208610.6, and DE 102017211930.6.
  • the cathode compartment is ordinarily delimited by an AEM.
  • This allows cathodically produced anions such as HCO 3 ⁇ , CO 3 2 ⁇ , and OH ⁇ to be transported away in the direction of the anode.
  • these sources vary to a great degree.
  • they have in common an area between the AEM, which delimits the cathode compartment, and the anode, said area containing a strongly acidic medium or producing protons, in which the HCO 3 ⁇ and CO 3 2 ⁇ are decomposed by protonation into CO 2 .
  • the charge transport in all of these cells can be carried in sections by various charge carriers. In contrast to other electrochemical arrangements, in this case the charge carriers are ordinarily not exchanged between the half cells, but are destroyed in the additional gap between them.
  • the central gap exclusively contains strongly acidic media.
  • the generation of CO 2 therefore ordinarily takes place directly on the surface of the AEM, wherein in US 2017037522 A1, the medium of the gap is solid, while it is liquid in DE 102017211930.6.
  • the surface of the AEM can be strongly impacted with gas bubbles, which can lead to a partial insulation of the membrane and thus to greater electrical losses in the cell.
  • direct contact between strongly acidic solid media and the AEM should be avoided, as the solid media cannot avoid the CO 2 generated at this pH limit.
  • the gap contains a neutral to weakly basic electrolyte, which as a rule contains carbonates. Therefore, the CO 2 generation ordinarily takes place on the surface of the second separator membrane, which can be just as problematic.
  • the use of salts, in particular with metal cations, in electrolyte gaps can be disadvantageous.
  • this component is preferably integrated such that in the resulting cell as a whole, neither salt encrustation of the electrodes nor CO 2 generation in the anode compartment are possible.
  • the present invention thus constitutes a significant improvement over previously disclosed cell designs.
  • a salt bridge compartment in an electrolysis cell is filled with a solid anion exchanger that comprises, at least in the vicinity of the cathode/AEM, e.g. a hydrogencarbonate-, carbonate- and/or hydroxide-conductive, for example strongly basic anion exchanger.
  • the anion exchanger makes it possible for gassing, for example the release of CO 2 in CO 2 electrolysis, to be distributed into the volume of the salt bridge compartment rather than taking place only at the AEM-salt bridge compartment interface.
  • anion exchanger and anion transporter are used as synonyms.
  • the transport function is characterized in that the anion exchange/anion transport material provides cations that compensate for the charge of the anions.
  • the anion itself is bound only so lightly that dynamic exchange is possible, thus providing a transport path for the anion in the electrolyte.
  • the cation is immobilized on the polymer backbone of the anion exchange material so that it cannot participate in charge transport processes.
  • the present invention relates to an electrolysis cell, comprising —a cathode compartment comprising a cathode; —a first ion exchange membrane, which contains an anion exchanger and which is adjacent to the cathode compartment, wherein the cathode comes into contact with the first ion exchange membrane; —an anode compartment comprising an anode; and —a first separator, which is adjacent to the anode compartment; further comprising a salt bridge compartment, wherein the salt bridge compartment is arranged between the first ion exchange membrane and the first separator, wherein the salt bridge compartment comprises a solid anion exchanger, which is at least partially in contact with the first ion exchange membrane.
  • an electrolysis system comprising an electrolysis cell according to the invention.
  • the present invention relates to a method for the electrolysis of CO 2 , wherein an electrolysis cell according to the invention or an electrolysis system according to the invention is used, wherein CO 2 is reduced at the cathode and hydrogencarbonate and/or carbonate generated at the cathode migrates through the first ion exchange membrane to an electrolyte in the salt bridge compartment, wherein the hydrogencarbonate and/or carbonate is also transported through the solid anion exchanger in the salt bridge compartment away from the first ion exchange membrane.
  • Yet a further aspect of the present invention relates to the use of an electrolysis cell according to the invention or an electrolysis system according to the invention for the electrolysis of CO 2 and/or CO.
  • FIGS. 1 to 9 are schematic diagrams of possible configurations of an electrolysis cell according to the invention.
  • FIG. 10 a schematic diagram of an electrolysis system according to the invention is shown by way of example.
  • hydrophobic is understood to mean water-repellent. According to the invention, therefore, hydrophobic pores and/or channels are those which repel water. In particular, hydrophobic properties according to the invention are associated with substances or molecules having nonpolar groups.
  • hydrophilic is understood to refer to the capacity to interact with water and other polar substances.
  • gas diffusion electrodes are electrodes in which liquid, solid and gaseous phases are present, and where in particular a conductive catalyst catalyzes an electrochemical reaction between the liquid and the gaseous phase.
  • the configuration can be of various types, for example a porous “solid material catalyst,” optionally with auxiliary layers for adjusting the hydrophobicity, wherein for example a membrane-GDE composite, e.g. an AEM-GDE composite, can then be produced; a conductive porous carrier to which a catalyst can be applied in a thin layer, wherein again a membrane-GDE composite, e.g. an AEM-GDE composite, can then likewise be produced; or a porous composite in the catalyst that can optionally be applied with an additive directly to a membrane, e.g. an AEM, and can then form in the composite a membrane coated with a catalyst (CCM; catalyst coated membrane).
  • a membrane-GDE composite e.g. an AEM-GDE composite
  • Electro-osmosis is understood to refer to an electrodynamic phenomenon in which a force is exerted toward the cathode on particles in solution with a positive zeta potential, and a force is exerted toward the anode on all particles having a negative zeta potential. If conversion occurs on the electrode, i.e. if a galvanic current flows, a material flow of the particles with a positive zeta potential to the cathode also takes place, regardless of whether the species is involved in the conversion or not. The same applies for a negative zeta potential and the anode. If the cathode is porous, the medium is also pumped through the electrode. This is also referred to as an electro-osmotic pump.
  • the material flows caused by electro-osmosis can also flow against the concentration gradients. In this manner, flows caused by diffusion that can offset the concentration gradients can be overcompensated for.
  • the present invention relates to an electrolysis cell, comprising —a cathode compartment comprising a cathode; —a first ion exchange membrane, which contains an anion exchanger and which is adjacent to the cathode compartment, wherein the cathode comes into contact with the first ion exchange membrane; —an anode compartment comprising an anode; and —a first separator, which is adjacent to the anode compartment; further comprising a salt bridge compartment, wherein the salt bridge compartment is arranged between the first ion exchange membrane and the first separator, wherein the salt bridge compartment comprises a solid anion exchanger, which is at least partially in contact with the first ion exchange membrane.
  • the salt bridge compartment is not particularly limited, provided that it is correspondingly connected to the first ion exchange membrane at least partially, in particular mechanically or ionically, so that the solid anion exchanger can be at least partially in contact with the first ion exchange membrane therein.
  • the solid anion exchanger is in contact with the first ion exchange membrane at least essentially in an area in which the cathode is in contact with the first ion exchange membrane on an opposite side of this membrane, or in an area that is larger. This allows a favorable transfer of anions to be ensured that are generated in the cathode and fed through the first ion exchange membrane.
  • the term “in contact with the first ion exchange membrane” does not exclude the possibility that the contact does not take place over the entire surface, but is such, according to certain embodiments, that a material flow of fluids, i.e. liquids and/or gases, through the solid anion exchanger is also possible.
  • salt bridge compartment is used with respect to its function of acting as a “bridge” between the anode arrangement and cathode arrangement and comprising cations and anions which, however, in the present case do not have to form salts.
  • ion exchanger is present in the salt bridge compartment
  • the compartment according to the invention will be referred to as a salt bridge compartment, even though it is not necessary for any salt to be present therein in the classical sense.
  • the dimensions of the salt bridge compartment are also not particularly limited, and it can be configured for example as a compartment or gap, e.g. between the first ion exchange membrane and the first separator, which for example are arranged parallel to each other.
  • the salt bridge compartment need not necessarily be in contact with the first separator that is adjacent to the anode compartment, i.e., more than three compartments may also be present in an electrolysis cell according to the present invention.
  • the expression “arranged between the first ion exchange membrane and the first separator” thus means that the salt bridge compartment can be located at any desired position between the first ion exchange membrane and the first separator, provided that it comprises a solid anion exchanger that is at least partially in contact with the first ion exchange membrane.
  • the salt bridge compartment is thus adjacent to the first ion exchange membrane, which however does not rule out the possibility that even a second separator or even further separators and/or further cell compartments are present and oriented toward the first separator.
  • the salt bridge compartment is in contact with the first separator. Therefore, the electrolysis cell according to the invention can be configured for example as a multi-compartment cell, e.g. a three-compartment cell, as described in US 2017037522 A1, DE 102017208610.6, and DE 102017211930.6, and reference is made thereto with respect to such cells. For example, therefore, a three-compartment cell may be present having three compartments (I, II, III). With the salt bridge compartment, electrolytic contact between the cathode compartment and the anode compartment can thus be achieved and/or facilitated.
  • a multi-compartment cell e.g. a three-compartment cell, as described in US 2017037522 A1, DE 102017208610.6, and DE 102017211930.6, and reference is made thereto with respect to such cells.
  • a three-compartment cell may be present having three compartments (I, II, III).
  • the cathode compartment, anode compartment and salt bridge compartment are not particularly limited in the electrolysis cell according to the invention with respect to form, material, dimensions, etc., provided that they can accommodate the cathode, the anode and the first ion exchange membrane and the first separator.
  • the three compartments are formed in the electrolysis cell according to the invention, wherein they can then be correspondingly separated, for example by the first ion exchange membrane and the first separator, for example with the first separator arranged between the salt bridge compartment and the anode compartment.
  • inlet and outlet devices for reactants and products for example in the form of a liquid, gas, solution, suspension, etc.
  • flow can occur through the individual compartments in parallel flows or in counterflow.
  • electrolysis of CO 2 which can further comprise CO, i.e. for example containing at least 20 vol. % CO 2 —the CO 2 can be supplied to the cathode in solution, as a gas, etc.—there can for example be a counterflow to an electrolyte flow in the salt bridge compartment with a three-compartment configuration.
  • electrolysis of CO 2 which can further comprise CO, i.e. for example containing at least 20 vol. % CO 2
  • the CO 2 can be supplied to the cathode in solution, as a gas, etc.
  • a counterflow to an electrolyte flow in the salt bridge compartment with a three-compartment configuration there is no limitation in this respect.
  • the respective inlet can be configured either continuously or discontinuously, for example in a pulsed configuration, etc. for which purpose corresponding pumps, valves, etc. can be provided in an electrolysis system according to the invention—which will also be further discussed below—as well as cooling and/or heating devices in order to allow corresponding catalysis of desired reactions at the anode and/or cathode.
  • each electrolysis cell of course also comprises at least one power source.
  • Further device components that occur in electrolysis cells or electrolysis systems can also be provided in the electrolysis system or electrolysis cell according to the invention. According to certain embodiments, these individual cells are combined into a stack that comprises 2-1000, preferably 2-200 cells, and the operating voltage of which is preferably in the range of 3-1500 V, particularly preferably 200-600 V.
  • a gas formed in the salt bridge compartment which e.g. corresponds to the reactant gas, e.g. CO 2 , which may also optionally contain trace amounts of H 2 and/or CO, may be recycled back in the direction of the cathode compartment, where a corresponding return device may be provided in an electrolysis system according to the invention.
  • the reactant gas e.g. CO 2
  • a corresponding return device may be provided in an electrolysis system according to the invention.
  • the cathode is not particularly limited according to the invention and can be adapted to a desired half reaction, for example with respect to the reaction products, provided that it is in direct contact with the first ion exchange membrane, i.e. is directly in contact with the first ion exchange membrane at at least one site, preferably wherein the cathode is essentially in direct planar contact with the first ion exchange membrane.
  • the cathode is thus directly adjacent, at least in one area, to the first ion exchange membrane.
  • a cathode for the reduction of CO 2 and optionally CO can for example comprise a metal such as Cu, Ag, Au, Zn, Pb, Sn, Bi, Pt, Pd, Ir, Os, Fe, Ni, Co, W, Mo, etc., or mixtures and/or alloys thereof, preferably Cu, Ag, Au, Zn, Pb, Sn, or mixtures and/or alloys thereof, and/or a salt thereof, wherein suitable materials can be adapted to a desired product.
  • the catalyst can thus be selected according to the desired product.
  • the catalyst is preferably based on Ag, Au, Zn and/or compounds thereof such as Ag 2 O, AgO, Au 2 O, AU 2 O 3 , ZnO.
  • Ag, Au, Zn and/or compounds thereof such as Ag 2 O, AgO, Au 2 O, AU 2 O 3 , ZnO.
  • Cu or Cu-containing compounds such as CU 2 O, CuO and/or copper-containing mixed oxides with other metals, etc.
  • catalysts based on Pb, Sn and/or Cu, in particular Pb, Sn may be used.
  • hydrogen formation at high current densities may be completely inhibited by anion transport, catalysts for CO 2 reduction that do not possess high overvoltage with respect to hydrogen can be used, e.g.
  • the cathode is the electrode on which the reductive half reaction takes place. It can have a single or multiple component(s) and can be configured for example as a gas diffusion electrode, a porous electrode or directly with the AEM in the composite, etc.
  • a gas diffusion electrode or porous bound catalyst structure which according to certain embodiments can e.g. be ion-conductively and/or mechanically bonded by means of a suitable ionomer, for example a anionic ionomer, to the first ion exchange membrane, for example an anion exchange membrane (AEM);
  • a gas diffusion electrode or porous bound catalyst structure which according to certain embodiments can be partially pressed onto the first ion exchange membrane, for example an AEM;
  • a porous, conductive, catalytically inactive structure e.g.
  • a carbon-paper GDL gas diffusion layer
  • a carbon-cloth GDL and/or a polymer-bound film of granular vitreous carbon, which is impregnated with the catalyst of the cathode and optionally an ionomer that allows the binding to the first ion exchange membrane, for example an AEM
  • the electrode can then be mechanically pressed onto the first ion exchange membrane, for example an AEM, or can be pre-pressed together with the first ion exchange membrane, for example an AEM, in order to form a composite
  • a particulate catalyst which is applied by means of a suitable ionomer to a suitable carrier, for example a porous conductive carrier, and according to certain embodiments can be adjacent to the first ion exchange membrane, for example an AEM
  • a particulate catalyst which is pressed into the first ion exchange membrane, for example an AEM, or is coated thereon and for example is correspondingly conductively bound, wherein this structure can then be pressed for example
  • a mesh or a metal mesh which for example consists of or comprises a catalyst or is coated therewith and according to certain embodiments is adjacent to the first ion exchange membrane, for example an AEM
  • a polymer-bound solid catalyst structure of a particulate catalyst which comprises an ionomer that allows binding to the first ion exchange membrane, for example an AEM, or has been subsequently impregnated therewith, wherein the electrode is then mechanically pressed onto the first ion exchange membrane, for example an AEM, or can be pre-pressed together with the first ion exchange membrane, for example an AEM, in order to form a composite
  • a non-ion-conductive gas diffusion electrode which has subsequently been impregnated with a suitable Ionomer, for example an anion-conductive Ionomer,
  • the corresponding cathodes can also contain materials commonly used in cathodes, such as binders, ionomers, for example anion-conductive ionomers, fillers, hydrophilic additives, etc., which are not particularly limited.
  • the cathode can also, according to certain embodiments, comprise at least one ionomer, for example an anion-conductive or anion-transporting ionomer (e.g. an anion exchange resin, an anion transport resin) which e.g. can comprise various functional groups for ion exchange that can be the same or different, for example tertiary amine groups, alkylammonium groups and/or phosphonium groups), an e.g. conductive carrier material (e.g.
  • a metal such as titanium
  • at least one non-metal such as carbon, Si, boron nitride (BN), boron-doped diamond, etc.
  • at least one conductive oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated tin oxide (FTO)—for example as is used for the production of photoelectrodes, and/or at least one polymer based on polyacetylene, polyethoxythiophene, polyaniline or polypyrrole, such as for example in polymer-based electrodes; non-conductive carriers such as e.g. polymer networks are possible for example if the catalyst layer has sufficient conductivity), binders (e.g.
  • hydrophilic and/or hydrophobic polymers e.g. organic binders, e.g. selected from PTFE (polytetrafluorethylene), PVDF (polyvinylidene difluoride), PFA (perfluoroalkoxy polymers), FEP (fluorinated ethylene-propylene copolymers), PFSA (perfluorosulfonic acid polymers), and mixtures thereof, in particular PTFE), conductive fillers (e.g. carbon), non-conductive fillers (e.g. glass) and/or hydrophilic additives (e.g. Al 2 O 3 , MgO 2 , hydrophilic materials such as polysulfone, e.g.
  • organic binders e.g. selected from PTFE (polytetrafluorethylene), PVDF (polyvinylidene difluoride), PFA (perfluoroalkoxy polymers), FEP (fluorinated ethylene-propylene copolymers), PFSA (
  • polyphenylsulfone polyimide, polybenzoxazole or polyether ketone or polymers that are generally electrochemically stable in the electrolyte, polymerized “ionic liquids,” and/or organic conductors such as PEDOT:PSS or PANI (camphor sulfonic acid doped polyaniline), which are not particularly limited.
  • the cathode in particular in the form of a gas diffusion electrode, e.g. connected to the first ion exchange membrane, or contained in the form of a CCM, comprises according to certain embodiments ion-conductive components, in particular an anion-conductive component.
  • cathode forms are also possible, for example cathode structures such as those described in US 20160251755 A1 and U.S. Pat. No. 9,481,939.
  • the anode is also not particularly limited according to the invention and can be adapted to a desired half reaction, for example with respect to the reaction products.
  • the oxidation of a substance takes place in the anode compartment on the anode, which is electrically connected to the cathode by means of a power source for supplying the voltage for the electrolysis.
  • the material of the anode is not particularly limited and depends primarily on the desired reaction. Examples of anode materials include platinum or platinum alloys, palladium or palladium alloys and vitreous carbon, iron, nickel, etc.
  • anode materials are also conductive oxides such as doped or undoped TiO 2 , indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), iridium oxide, etc.
  • these catalytically active compounds can also be superficially applied only in thin-film technology, for example to a titanium and/or carbon carrier.
  • the anode catalyst is not particularly limited. For example, as a catalyst for O 2 or Cl 2 production, one also uses IrO x (1.5 ⁇ x ⁇ 2) or RuO 2 . These can also be present as mixed oxides with other metals, e.g.
  • TiO 2 and/or be supported on a conductive material such as C (in the form of conductive carbon black, activated carbon, graphite, etc.).
  • a conductive material such as C (in the form of conductive carbon black, activated carbon, graphite, etc.).
  • catalysts based on Fe—Ni or Co—Ni can also be used for O 2 generation.
  • the structure described below with a bipolar membrane or a bipolar membrane is suitable for this purpose.
  • the anode is the electrode on which the oxidative half reaction takes place. It can also be configured as a gas diffusion electrode, a porous electrode, or a full electrode or solid electrode, etc.
  • a gas diffusion electrode or porous bound catalyst structure which according to certain embodiments can be e.g. ion-conductively and/or mechanically bonded by means of a suitable ionomer, for example a cationic ionomer, to the first separator, for example a cation exchange membrane (CEM) or a diaphragm;
  • a gas diffusion electrode or porous bound catalyst structure which according to certain embodiments can be partially pressed into the first separator, for example a CEM or a diaphragm;
  • a particulate catalyst which is applied by means of a suitable ionomer onto a suitable carrier, for example a porous conductive carrier, and according to certain embodiments can be adjacent to the first separator, for example a CEM or a diaphragm;
  • a particulate catalyst which is pressed into the first separator, for example a CEM or a diaphragm, and for example is correspondingly conductively
  • a mesh or a metal mesh which for example consists of or comprises a catalyst or is coated therewith and according to certain embodiments is adjacent to the first separator, for example a CEM or a diaphragm;
  • a solid electrode wherein in this case there can also be a gap between the first separator, for example a CEM or a diaphragm, and the anode;
  • a porous, conductive carrier which is impregnated with a suitable catalyst and optionally an ionomer and according to certain embodiments is adjacent to the first separator, for example a CEM or a diaphragm;
  • a non-ion-conductive gas diffusion electrode which has been subsequently impregnated with a suitable Ionomer, for example a cation-conductive ionomer, and according to certain embodiments is adjacent to the first separator, for example a CEM or a diaphragm; —any desired variants of the discussed embodiments, wherein the electrode e.g. contains
  • the corresponding anodes can also contain materials commonly used in anodes, such as binders, ionomers, e.g. also cation-conductive ionomers, for example containing sulfonic acid and/or phosphonic acid groups, fillers, hydrophilic additives, etc., which are not particularly limited, and which for example are also described above with respect to the cathode.
  • binders ionomers, e.g. also cation-conductive ionomers, for example containing sulfonic acid and/or phosphonic acid groups, fillers, hydrophilic additives, etc., which are not particularly limited, and which for example are also described above with respect to the cathode.
  • the cathode and/or the anode is/are configured as a gas diffusion electrode, as a porous bound catalyst structure, as a particulate catalyst on a carrier, as a coating of a particulate catalyst on the first and/or second ion exchange membrane, as a porous conductive carrier in which a catalyst is impregnated, and/or as a non-closed flat structure.
  • the cathode is configured as a gas diffusion electrode, as a porous bound catalyst structure, as a particulate catalyst on a carrier, as a coating of a particulate catalyst on the first and/or second ion exchange membrane, as a porous conductive carrier in which a catalyst is impregnated, and/or as a non-closed flat structure, which contain(s) an anion exchange material and/or an anion transport material.
  • the anode is configured as a gas diffusion electrode, as a porous bound catalyst structure, as a particulate catalyst on a carrier, as a coating of a particulate catalyst on the first and/or second ion exchange membrane, as a porous conductive carrier in which a catalyst is impregnated, and/or as a non-closed flat structure, which contain(s) a cation exchange material and/or is/are coupled and/or bound to a bipolar membrane.
  • the anode and/or the cathode is/are brought into contact on the side opposite the salt bridge compartment with a conductive structure.
  • the conductive structure is not particularly limited here.
  • the anode and/or the cathode are thus brought into contact with side facing away from the salt bridge with conductive structures.
  • These are not particularly limited.
  • these can be carbon flows, metal foams, metal knit fabrics, metal meshes, graphite structures, or metal structures.
  • electrolytes can also be present in the anode compartment and/or cathode compartment, and these are also referred to as the anolyte or catholyte, but it is not excluded according to the invention for no electrolytes to be present in the two compartments, and correspondingly, for example, for only gases to be fed to said compartments for conversion, for example only CO 2 , optionally also as a mixture with e.g. CO and/or H 2 O, which can optionally also be a fluid, e.g. an aerosol, but preferably gaseous H 2 O to the cathode and/or water or HCl to the anode.
  • an anolyte is present, which can be different from an electrolyte of the salt bridge compartment or can correspond thereto, for example with respect to solvents, acids etc. contained therein.
  • a catholyte is the electrolyte flow around the cathode or on the cathode and serves according to certain embodiments to provide the cathode with substrate or reactant.
  • the catholyte can be present e.g. as a solution of substrate (CO 2 ) in a liquid carrier phase (e.g. water) and/or as a mixture of the substrate with other gases (e.g. CO+CO 2 ; water vapor+CO 2 , N 2 and/or also certain proportions of O 2 , SO 2 , SO 3 ; etc.). Gases recycled through a return line, such as CO and/or H 2 , can also be present.
  • the substrate can also be in the form of a pure phase, e.g. CO 2 . If uncharged liquid products are generated in the reaction, they can be washed out by the catholyte and can then optionally also be correspondingly separated out.
  • An anolyte is an electrolyte flow around the anode or at the anode and serves according to certain embodiments to provide the anode with substrate or reactant, and optionally to transport anode products away.
  • the anolyte is an aqueous electrolyte, wherein corresponding reactants, which are converted at the anode, can optionally be added to the anolyte.
  • Addition of the reactant in this case is not particularly limited.
  • reactant addition at the inlet to the cathode compartment is also not limited.
  • CO 2 can thus be added outside the cathode compartment to water, or can also be added via a gas diffusion electrode, or can also be supplied only as a gas to the cathode compartment.
  • corresponding configurations are possible for the anode compartment, depending on the reactant used, e.g. water, HCl, NaCl, KCl, etc. and the desired product.
  • the first ion exchange membrane which contains an anion exchanger and/or anion transporter or an anion transport material and which is adjacent to the cathode compartment, is not particularly limited according to the invention.
  • it separates the cathode from the salt bridge compartment, such that the sequence from the direction of the cathode compartment in the direction of the electrolyte is cathode/first ion exchange membrane/salt bridge compartment.
  • the first ion exchange membrane is an anion exchange membrane and/or an anion transport membrane.
  • the first ion exchange membrane can comprise a hydrophobic layer, for example on the cathode side, for better gas contact.
  • the ion exchange membrane and/or anion transport membrane also functions as a cation blocker (even if only in trace amounts, for example), in particular a proton blocker.
  • an anion exchanger and/or anion transporter with solidly bound cations can constitute a blockade here for mobile cations through Coulomb repulsion, which can additionally counteract salt precipitation, in particular within the cathode.
  • the accumulation of the electrolyte cations in the area of the interface is ordinarily attributable to electro-osmosis.
  • a concentration gradient on the electrode side as a catalyst-based cathode that is configured as discussed above, e.g. a gas diffusion electrode or a CCM, may show only extremely poor anion conductivity depending on the anion and a selected electrolyte.
  • the anion conductivity can be significantly improved by the integration of anion-conductive components.
  • anion transporters in particular anion transport resins, can be used as a binding material or an additive in the electrode itself and/or in an anion exchange layer adjacent to the cathode, in order for example to quickly dissipate or partially buffer any Off ions generated, such that the reaction with CO 2 and the accompanying formation of hydrogencarbonates and/or carbonates can be reduced or the anion transport resins themselves conduct HCO 2 or CO 3 2 ⁇ .
  • anion transport can take place by means of anion exchangers.
  • an integrated anion exchanger in particular also constitutes a blockade for cations, e.g. metal cation traces as well, which can additionally counteract salt precipitation and contamination of the electrode. In the case of protons, for example, hydrogen formation can also be inhibited.
  • the first ion exchange membrane can thus for example contain an anion exchanger and/or an anion transporter in the form of an anion exchange and/or transport layer, wherein further layers can then be included, such as hydrophobicity-imparting layers in order to improve the contact with a gas such as CO 2 .
  • the first ion exchange membrane is an anion exchange membrane and/or anion transport membrane, e.g. for example an ion-conductive membrane (or also in the broader sense a membrane with an anion exchange layer and/or an anion transport layer) with positively charged functional groups, with this not being particularly limited.
  • a preferred charge transport takes place in the anion exchange layer and/or the anion transport layer or an ion exchange membrane and/or an anion transport membrane by means of anions.
  • the first ion exchange membrane and/or in particular an anion exchange layer and/or an anion transport layer or an anion exchange membrane and/or an anion transport membrane therein serve(s) to provide an anion transport along stationary fixed positive charges.
  • penetration of an e.g. proton-containing electrolyte into the cathode due to electro-osmotic forces can be reduced or completely prevented.
  • the ion exchanger contained in the membrane can be converted in operation to the carbonate/hydrogencarbonate form and the passage of protons through the membrane to the cathode can thus be prevented.
  • a suitable first ion exchange membrane for example an anion exchange membrane and/or an anion transport membrane, shows favorable wettability by water and/or acids, in particular aqueous acids, high ion conductivity, and/or a tolerance of the functional groups contained therein with respect to high pH values, and in particular shows no Hoffmann elimination.
  • An exemplary AEM according to the invention is the A201-CE membrane produced by Tokuyama used in the example, the “Sustainion” produced by Dioxide Materials, or an anion exchange membrane produced by Fumatech such as e.g. the Fumasep FAS-PET or the Fumasep FAD-PET.
  • the first separator is not particularly limited.
  • the first separator which for example according to certain embodiments is adjacent to the salt bridge compartment seen from the anode side, is selected from an ion exchange membrane containing a cation exchanger, a bipolar membrane, wherein preferably, in said bipolar membrane, the cation-conductive layer is oriented toward the cathode and the anion-conductive layer is oriented toward the anode, and a diaphragm.
  • the first separator is a cation exchange membrane, a bipolar membrane or a diaphragm.
  • a suitable first separator for example a cation exchange membrane or a bipolar membrane, contains for example a cation exchanger, which can be in contact with the salt bridge compartment.
  • a cation exchanger in the form of a cation exchange layer, wherein further layers such as hydrophobicity-imparting layers can then be included.
  • It can also be configured as a bipolar membrane or as a cation exchange membrane (CEM).
  • the cation exchange membrane or cation exchange layer is e.g. an ion-conductive membrane or ion-conductive layer with negatively charged functional groups.
  • An exemplary charge transport into the salt bridge compartment takes place in such a first separator by means of cations.
  • Nafion® membranes are suitable as a CEM, or also the Fumapem-F membranes produced by Fumatech, Aciplex produced by Asahi Kasei, or the Flemion membranes produced by AGCs.
  • other modified polymer membranes with strongly acidic groups groups such as sulfonic acid or phosphonic acid
  • the first separator prevents the movement of anions, in particular HCO 3 ⁇ , into the anode compartment.
  • the first separator can be configured as a diaphragm, which allows the cell to be configured in a less complex and expensive manner.
  • the diaphragm essentially separates the anode compartment and the salt bridge compartment, for example to more than 70%, 80%, or 90%, based on the interface between the anode compartment and the salt bridge compartment, or separates the anode compartment and the salt bridge compartment, i.e. to 100%, based on the interface between the anode compartment and the salt bridge compartment.
  • Particularly preferred are embodiments that produce gas separation, e.g. of the CO 2 in the salt bridge compartment and the O 2 in the anode compartment.
  • the diaphragm is not particularly limited and can for example be based on a ceramic (e.g. ZrO 2 or Zr 3 (PO 4 ) 3 ) and/or a swellable functionalized polymer, e.g. PTFE.
  • Binders e.g. hydrophilic and/or hydrophobic polymers, e.g. organic binders, e.g.
  • PTFE polytetrafluorethylene
  • PVDF polyvinylidene difluoride
  • PFA perfluoroalkoxy polymers
  • FEP fluorinated ethylene-propylene copolymers
  • PFSA perfluorosulfonic acid polymers
  • conductive fillers e.g. carbon
  • non-conductive fillers e.g. glass
  • hydrophilic additives e.g. Al 2 O 3 , MgO 2
  • hydrophilic materials such as polysulfone, e.g. polyphenylsulfone (PPSU), polyimide, polybenzoxazole or polyether ketone or polymers that are generally electrochemically stable in the electrolyte can also be present.
  • the diaphragm is porous and/or hydrophilic. As it is not ion-conductive per se, it should preferably be capable of swelling in an electrolyte, for example an acid. Moreover, it constitutes a physical barrier for gases and cannot be penetrated by gas bubbles.
  • it is a porous polymer structure, wherein the base polymer is hydrophilic (e.g. PPSU). In contrast to the CEM or bipolar membrane, the polymer does not comprise any charged functional groups.
  • the diaphragm can contain hydrophilic structuring components such as metal oxides (e.g. ZrO 2 and/or other materials such as particles over the surface thereof) or ceramics, as mentioned above.
  • a suitable first separator for example a cation exchange membrane, a bipolar membrane and/or a diaphragm, shows favorable wettability by water and/or acids, a high ion conductivity, stability with respect to reactive species that can be generated at the anode (given for example for perfluorinated polymers), and/or stability in the required pH range, for example with respect to an acid in the salt bridge compartment.
  • the first ion exchange membrane and/or the first separator are hydrophobic, in particular such that they form a CCM with the electrodes, at least on the side facing the electrodes, so that the reactants of the electrodes are in gaseous form.
  • the anode and/or cathode are at least partially hydrophilic.
  • the first ion exchange membrane and/or the first separator are wettable with water. In order to ensure favorable ion conductivity of ionomers, swelling with water is preferred. In the experiment, it was found that poorly wettable membranes or separators can cause significant deterioration in the ionic binding of the electrodes.
  • the anode and/or cathode also show sufficient hydrophilicity.
  • this can be adjusted by means of hydrophilic additives such as TiO 2 , Al 2 O 3 , or other electrochemically inert metal oxides, etc.
  • At least one of the following first separators is used:
  • a bipolar membrane can for example be configured as a sandwich of a CEM and an AEM.
  • the membrane ordinarily comprises at least two layers rather than two membranes placed atop one another. These membranes are virtually impenetrable to both anions and cations. Accordingly, the conductivity of a bipolar membrane is not based on the transport capacity for ions. Instead, the ion transport ordinarily takes place by means of acid-base dissociation of water in the middle of the membrane. In this manner, two oppositely charged charge carriers are generated and transported away by the E field.
  • a bipolar membrane as a first separator membrane
  • bases e.g. a hydroxide base
  • an acid is also possible if an acid is used in the salt bridge.
  • the anode comes into contact with the first separator, as described above by way of example. This makes favorable binding to the salt bridge compartment possible. In this case, moreover, no charge transport by the anolyte is needed, and the charge transport path is shortened. Electric shading effects due to supporting structures between the anode and the first separator can therefore also be avoided.
  • the solid anion exchanger which is at least partially in contact with the first ion exchange membrane and is contained in the salt bridge compartment, is not particularly limited according to the invention, provided that it is present in the form of a solid—i.e. not in solution—, can exchange anions, and is at least partially in contact with the first ion exchange membrane.
  • the solid anion exchanger is hydrophilic.
  • the solid anion exchanger at least in the area of the cathode on the opposite side of the first ion exchange membrane, to be substantially in contact therewith—that is, touching it—, i.e. for example for contact with the solid anion exchanger to be more than 50% of the area of the first ion exchange membrane, preferably more than 60%, further preferably more than 70%, in particular more than 80% based on the area of the first ion exchange membrane which is in contact with the cathode.
  • the solid anion exchanger is not in contact with the first ion exchange membrane over its entire surface, in particular not in the area in which the cathode on the opposite side of the first ion exchange membrane comes into contact therewith, in order to allow fluid transport between the first anion exchange membrane and the solid anion exchanger to be ensured.
  • the solid anion exchanger at least in the area of the cathode on the opposite side of the first ion exchange membrane, to be in contact therewith, such that contact with the solid anion exchanger is 99% or less of the area of the first ion exchange membrane, preferably 97% or less, further preferably 95% or less, in particular 92% or less, based on the area of the first ion exchange membrane which is in contact with the cathode.
  • the further mechanical configuration of the solid anion exchanger which can also be understood as a filling medium, is not particularly limited, and it can be configured for example as a bed of solid anion exchange particles, which are not particularly limited, as a porous structure, for example a spongelike structure, and/or as an e.g. regular porous self-supporting structure.
  • the particles should preferably have a particle size of between 5 ⁇ m and 2 mm, further preferably between 100 ⁇ m and 1 mm, wherein the particle size can be determined for example by sieve analysis.
  • the particles are adapted to the size of the cell and/or to the corresponding flow regime.
  • the solid anion exchanger is present as a bed and/or a porous structure. According to certain embodiments, the solid anion exchanger, optionally with further solid components, e.g. neutral particles or cation exchangers, forms a filling in the salt bridge compartment.
  • Examples of the mechanical configuration of the solid anion exchanger include: —a compressed bed of e.g. pelletized anion exchange particles; —a spongelike porous structure; —a regular porous self-supporting structure such as can be obtained for example by overmolding of polymer-beads with a solution of the anion exchange material of the solid anion exchanger and subsequent dissolution of the template beads.
  • the structure should be at least partially open or completely open in order to allow an electrolyte and gas flow to be ensured.
  • porous carrier beads can also be impregnated with an anion exchange ionomer and thus function as ion exchange particles.
  • an anion exchange ionomer e.g., the bonding of a particle bed of any desired e.g. neutral and/or uncharged particles, such as polymeric particles, to an anion exchange ionomer is preferred.
  • the advantage of this method lies in a greater number of available exchange groups for the transport of anions.
  • the solid anion exchanger serves as an open extension of the first ion exchange membrane, for example an AEM, into the volume of the salt bridge compartment (e.g. referred to as a gap volume if the salt bridge compartment is configured as a gap).
  • a gas such as e.g. the CO 2 released by protons from the anode, thus covers a smaller portion of the surface area of the first ion exchange membrane and thus does not cause ionic insulation.
  • the solid anion exchanger possesses intrinsic ion conductivity, which can result in the production of an additional conduction path through the salt bridge compartment exclusively by means of solid electrolytes.
  • the first separator for example not only HCO 3 ⁇ and/or CO 3 2 ⁇ , but additionally or solely one anion of the electrolyte used in the salt bridge compartment, for example an acid used, can serve as a mobile charge carrier in the solid ion exchanger.
  • the solid anion exchanger should preferably be selected such that in addition to favorable HCO 3 ⁇ and/or CO 3 2 ⁇ conductivity, it also shows favorable SO 4 2 ⁇ conductivity.
  • the material of the solid anion exchanger can be adapted not only to an anion such as HCO 3 ⁇ and/or CO 3 2 ⁇ that is cathodically produced, but also to further anions, e.g. in the salt bridge compartment.
  • the material of the solid anion exchanger is not limited, provided that it is correspondingly adapted to the first ion exchange membrane and/or an electrolyte in the salt bridge compartment, except for the fact that it must be capable of anion exchange and/or anion transport.
  • the solid anion exchanger can comprise an anion exchange resin in which cations are immobilized, preferably alkali metal or alkaline earth metal cations, e.g. by means of complexation, and/or ammonium ions and/or derivatized ammonium ions such as quaternary ammonium ions, further preferably alkali metal cations and/or ammonium ions and/or derivatized ammonium ions such as quaternary ammonium ions.
  • phosphonium, pyridinium, piperidinium, guanidinium, imidazolium, pyrazolium and/or sulfonium ions can be bound to a carrier of the solid anion exchanger.
  • the solid anion exchanger comprises in the salt bridge compartment cations, which are immobilized in a polymeric backbone, wherein the cations in particular can exchange hydrogencarbonate ions and/or carbonate ions, wherein these hydrogencarbonate ions and/or carbonate ions should preferably be transportable by the solid anion exchanger in order to provide suitable conductivity in the salt bridge compartment.
  • Anion exchangers are ordinarily available in solid acidic (e.g. in HSO 4 ⁇ form, where they can also be present as solid acids), neutral (e.g. as a TFO or Cl salt) or basic form (e.g. HCO 3 ⁇ form, weakly basic, or OH ⁇ form, strongly basic).
  • various such anion exchangers can be present next to one another in a cell according to the invention, wherein a basic anion exchange is preferably used near to and/or on the first ion exchange membrane.
  • the solid anion exchanger is basic, preferably strongly basic.
  • the immobilized cations of the anion exchanger are configured such that an ion pair formed by them is always present in completely dissociated form, which can be controlled for example by means of pH.
  • the solid anion exchanger comprises hydrogencarbonate, carbonate and/or OH ions and/or anions of the electrolyte used in the electrolyte of the salt bridge compartment, e.g. an acid, as counterions. This allows the transport of hydrogencarbonate and/or carbonate of the first ion exchange membrane to be improved by means of ion hopping (in contrast to the “tunneling” in the Grotthuss mechanism).
  • a solid e.g. acidic ion exchanger and a basic liquid electrolyte in the salt bridge compartment.
  • CO 2 electrolysis In the special case of CO 2 electrolysis, however, this is not possible because basic solutions are converted by the CO 2 present into neutral carbonate solutions.
  • basic media are also considered to be anion conductors, and acidic media are considered to be proton conductors.
  • cation transport predominates in neutral (e.g. alkaline) carbonates, a corresponding carbonate solution produced does not correspond to an extension of the first ion exchange membrane into the salt bridge compartment.
  • the solid anion exchanger is hydrophilic. This means that it is lightly wettable with an aqueous medium, with the result that an aqueous medium such as an aqueous acid can be used in the salt bridge compartment.
  • an aqueous medium such as an aqueous acid can be used in the salt bridge compartment.
  • the water can also serve as an additional reactant in carbon dioxide reduction, as discussed above, thus allowing favorable conductivity.
  • the first anion exchanger and/or a filling comprising the solid anion exchanger, optionally with further solid components, e.g. neutral particles or cation exchangers, also serves to support the separators and/or membranes, e.g. the first ion exchange membrane and the first separator, against one another in the salt bridge compartment.
  • this filling possesses its own ion conductivity, this type of support does not lead to insulation of electrode areas.
  • the bed can also be used for force transfer (non-positive locking) via the entire stack.
  • the filling contains, at least in the area of the cathode/AEM, a solid e.g. strongly basic anion exchanger.
  • the filling can also consist entirely of a solid e.g. strongly basic anion exchanger.
  • the chemical nature of the solid anion exchanger is as similar as possible to that of the first ion exchange membrane, e.g. an AEM.
  • Both components can also, for example, be constructed based on the same polymer, wherein, however, e.g. the chain length and/or the degree of crosslinking can be different.
  • FIGS. 1 to 3 Examples of embodiments in which the salt bridge compartment comprises only a solid anion exchanger are shown schematically in FIGS. 1 to 3 .
  • the first separator is shown such that it is in contact with the anode.
  • the separator can also be separate from the anode, such that an anode compartment can also be formed for example between the separator and the anode, and the anode can optionally also comprise on an opposite side of such an anode compartment a compartment for the supply of a substrate, e.g. a gas.
  • the solid anion exchanger 4 for example a strongly basic anion exchanger, is arranged in the salt bridge compartment II, which is located between an anion exchange membrane AEM as a first ion exchange membrane based on an e.g. strongly basic anion exchange material 1 and a cation exchange membrane CEM as a first separator based on an e.g. strongly acidic cation exchange material 3 .
  • the cathode K and the cathode compartment I are adjacent to the AEM, and the anode A and the anode compartment III are adjacent to the CEM.
  • the solid anion exchanger 4 can be penetrated by fluids such as gases and/or electrolytes.
  • An inlet and an outlet are provided for each of the three compartments I, II, and III.
  • FIG. 2 An alternative embodiment is shown in FIG. 2 , wherein the electrolysis cell largely corresponds to that of FIG. 1 , except that the CEM has been replaced by a diaphragm D, for example in the form of a hydrophilic gas separator 5 .
  • FIG. 3 A further alternative embodiment is found in FIG. 3 , which also largely corresponds to the embodiment of FIG. 1 , wherein the CEM has been replaced by a bipolar membrane BPM in which a cation exchange layer based on an e.g. strongly acidic cation exchange material 3 is oriented toward the salt bridge compartment II, while an anion exchange layer based on an e.g. strongly basic anion exchange material 1 is oriented toward the anode.
  • the filling can thus comprise, e.g. in addition to an e.g. strongly basic and/or weakly basic anion exchanger, nonionic ion exchangers, e.g. polyalcohols, and/or cation exchangers, e.g. weakly and/or strongly acidic cation exchangers, which are not particularly limited.
  • an e.g. strongly basic and/or weakly basic anion exchanger nonionic ion exchangers, e.g. polyalcohols
  • cation exchangers e.g. weakly and/or strongly acidic cation exchangers
  • Acidic additives in the solid anion exchanger can be used for example for converting CO 3 2 ⁇ to HCO 3 ⁇ .
  • monovalent ions are mobile in ion exchange media, while polyvalent ions are mobile in solution.
  • an optimum highly conductive conduction path is produced for each type of ion.
  • FIG. 4 shows a schematic view of an exemplary embodiment in which such a filling is provided in the salt bridge compartment II with a mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material, which for example can be homogeneously mixed.
  • a mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material, which for example can be homogeneously mixed.
  • the further configuration of the cell in FIG. 4 corresponds to that of FIG. 1 .
  • FIGS. 5 and 6 A comparison of these two cell designs, with an e.g. strongly basic anion exchange material 4 ( FIG. 5 ) and a mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material ( FIG. 6 ), is also shown in FIGS. 5 and 6 with a generic separator S composed of a generic material 6 , which can have a single or multi-layer structure. The further structure corresponds to that shown in FIG. 1 .
  • the solid salt bridge compartment further comprises non-ion-conductive and/or unfunctionalized particulate matter or particles, nonionic ion exchangers and/or cation exchangers, wherein preferably the non-ion-conductive and/or unfunctionalized particles, nonionic ion exchangers and/or cation exchangers, further preferably the non-ion-conductive and/or unfunctionalized particles and/or nonionic ion exchangers, are contained in an area not adjacent to the first ion exchange membrane in an amount of up to 20 vol. %, preferably up to 17 vol. %, further preferably up to 14 vol. %, even further preferably up to 10 vol. % or up to 5 vol.
  • the mixture of the solid anion exchangers with the uncharged particles, the nonionic ion exchangers and/or the cation exchangers is not particularly limited, and can be homogeneous or heterogeneous, e.g. in the form of layers, etc.
  • the uncharged particles, nonionic ion exchangers and/or cation exchangers are not particularly limited.
  • these layers are preferably parallel to the first ion exchange membrane and/or the first separator, wherein the layer adjacent to the first ion exchange membrane comprises the uncharged particles, nonionic ion exchangers and/or cation exchangers in an amount of up to 20 vol. %, preferably up to 17 vol. %, further preferably up to 14 vol. %, even further preferably up to 10 vol. % or up to 5 vol. %, based on the layer, or comprises or contains only the solid anion exchanger.
  • a layer adjacent to the first separator can for example comprise the solid anion exchanger in an amount of up to 20 vol. %, preferably up to 17 vol. %, further preferably up to 14 vol. %, even further preferably up to 10 vol. % or up to 5 vol. %, based on the layer, wherein according to certain embodiments, the remainder can be a solid cation exchanger.
  • a layer adjacent to the first separator can also comprise or contain only the solid cation exchanger.
  • the salt bridge compartment further comprises a solid cation exchanger, which is at least partially in contact with the first separator.
  • the solid cation exchanger at least in the area of the anode on the opposite side of the first separator, to be substantially in contact therewith, i.e. for example in contact with, i.e. touching, more than 50% of the area of the first separator, preferably more than 60%, further preferably more than 70%, and in particular more than 80% based on the area of the first separator, which is in contact with the anode.
  • the solid cation exchanger is not in contact with the first separator over its entire area, in particular not in the area in which the anode on the opposite side of the first separator is in contact therewith, in order to allow fluid transport between the first separator and the solid cation exchanger to be ensured. It is therefore also preferable according to certain embodiments for the solid cation exchanger, at least in the area of the anode on the opposite side of the first separator, to be in contact with 99% or less of the area of the first separator, preferably 97% or less, further preferably 95% or less, in particular 92% or less, based on the area of the first separator, which is in contact with the anode.
  • solid ion exchangers which contain no e.g. strongly basic anion exchanger materials and/or are not solid anion exchangers, preferably are not in contact with the first ion exchange membrane, e.g. an AEM, in order to prevent gas release at the contact point.
  • first ion exchange membrane e.g. an AEM
  • the composition of the filling in particular e.g. along the cathode-anode connection line, need not be homogenous.
  • the filling can thus also be coated, for example with an e.g. strongly basic solid anion exchanger or a mixture comprising the solid anion exchanger in the area of the cathode and the first ion exchange membrane, e.g. an AEM, and an e.g. strongly acidic solid cation exchanger or a mixture comprising the solid cation exchanger in the area of the anode and the first separator.
  • an e.g. strongly basic solid anion exchanger or a mixture comprising the solid anion exchanger in the area of the cathode and the first ion exchange membrane e.g. an AEM
  • an e.g. strongly acidic solid cation exchanger or a mixture comprising the solid cation exchanger in the area of the anode and the first separator e.g. strongly basic solid anion exchanger or a mixture compris
  • the number of different layers that can be used is not specified, nor is the order thereof, provided that they meet the requirement that the material adjacent to the first ion exchange membrane, e.g. an AEM, contains an e.g. strongly basic anion exchanger.
  • two or more layers of the filling may be present, as shown by way of example in FIGS. 7 to 9 for two layers.
  • the cell structure with cathode K, anode A, AEM and separator S as well as the cathode compartment I and anode compartment III corresponds to that shown in FIG. 5 , and only the structure of the filling in the salt bridge compartment II differs.
  • adjacent to the AEM is a layer with an e.g. strongly basic anion exchange material 4
  • adjacent to the separator S is a layer with a mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material.
  • this mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material of FIG. 7 has been replaced by an e.g. acidic or strongly acidic cation exchange material 3 .
  • FIG. 9 however, in comparison to FIG. 8 , the material adjacent to the AEM has been replaced by a mixed ion exchange material 2 containing an e.g. strongly basic anion exchange material.
  • the filling even when composed only of the solid anion exchanger, is not closed, such that an amount of an electrolyte and/or a liquid-gas bubble gas can flow through it, i.e. the filling does not comprise any pores or structured free compartments.
  • a further aspect of the present invention relates to an electrolysis system comprising an electrolysis cell according to the invention.
  • the corresponding embodiments of the electrolysis cell as well as further exemplary components of an electrolysis system according to the invention have already been discussed above and are thus also applicable to the electrolysis system according to the invention.
  • an electrolysis system according to the invention comprises multiple electrolysis cells according to the invention, wherein it is not excluded for other additional electrolysis cells also to be present.
  • the electrolysis system according to the invention further comprises a return device, which is connected to an outlet of the salt bridge compartment and an inlet of the cathode compartment, which is configured to recycle a reactant of the cathode reaction which can be formed in the salt bridge compartment, back into the cathode compartment.
  • FIG. 10 An electrolysis cell according to the invention is shown by way of example in FIG. 10 , wherein the electrolysis cell can be configured with the cathode compartment I, the salt bridge compartment II and the anode compartment III, the anode A, the separator S, the cathode K and the first ion exchange membrane as an AEM, for example according to the structure shown in FIG. 5 or FIG. 6 .
  • CO 2 is supplied to the cathode compartment, and the remaining CO 2 , product P and optionally water are discharged from the cathode compartment, wherein the water is separated off.
  • CO 2 generated in the salt bridge compartment that may have migrated into the salt bridge compartment can be recycled via a return line to the inlet of the cathode compartment after electrolyte j has been separated from the salt bridge compartment, which can also be recycled.
  • an anolyte A is recycled to the anode compartment III, wherein anodic conversion of H 2 O and/or HCl to O 2 and/or Cl 2 is shown here by way of example, wherein the half cell reaction does not limit the invention.
  • the further symbols in FIG. 10 are common fluidic circuit symbols.
  • the electrolysis system according to the invention further comprises an external device for electrolyte treatment, in particular a device for the removal of dissolved gases from an acid, with the anolyte and/or the electrolyte in particular being treated in the salt bridge compartment, in order for example to remove gases such as CO 2 or O 2 and thus allow recycling of the anolyte and/or the electrolyte to the salt bridge compartment.
  • an external device for electrolyte treatment in particular a device for the removal of dissolved gases from an acid, with the anolyte and/or the electrolyte in particular being treated in the salt bridge compartment, in order for example to remove gases such as CO 2 or O 2 and thus allow recycling of the anolyte and/or the electrolyte to the salt bridge compartment.
  • the electrolysis system comprises two separate circuits for the anolyte and electrolyte in the salt bridge compartment, which can optionally comprise separate devices for electrolyte treatment, in particular devices for the removal of dissolved gases from an acid, or wherein only the circuit for the electrolyte in the salt bridge compartment comprises a corresponding device.
  • the present invention relates to the use of an electrolysis cell according to the invention or an electrolysis system according to the invention, which can also comprise multiple electrolysis cells according to the invention, for the electrolysis of CO 2 and/or
  • a method for the electrolysis of CO 2 wherein an electrolysis cell according to the invention or an electrolysis system according to the invention is used, wherein CO 2 is reduced at the cathode and hydrogencarbonate and/or carbonate generated at the cathode by the first ion exchange membrane migrates to an electrolyte in the salt bridge, wherein the hydrogencarbonate and/or carbonate is also transported through the solid anion exchanger in the salt bridge compartment away from the first ion exchange membrane.
  • the cathode compartment, the cathode, the first ion exchange membrane, the anode compartment, the anode, the separator, the salt bridge compartment and the solid anion exchanger, as well as further components, have already been discussed with respect to the electrolysis cell according to the invention and the electrolysis system according to the invention. Therefore, the corresponding features can thus be implemented correspondingly in the method according to the invention.
  • the method according to the invention can also be implemented with the electrolysis cell according to the invention or the electrolysis system according to the invention, so that comments or aspects with respect to the method for the electrolysis of CO 2 according to the invention can also be applied thereto, for example with respect to an electrolyte in the salt bridge compartment and accompanying configurations of the components of the electrolysis cell, such as e.g. the first separator.
  • CO 2 is electrolyzed, wherein, however, it is not excluded, in addition to CO 2 , for a further reactant such as CO to also be present on the cathode side, which can also be electrolyzed, i.e. for a mixture to be present that comprises CO 2 , as well as e.g. CO.
  • a reactant on the cathode side comprises at least 20 vol. % of CO 2 , e.g. at least 50 or at least 70 vol. % of CO 2 , and in particular, the reactant on the cathode side can comprise up to 100 vol. % of CO 2 .
  • the electrolysis cell according to the invention can also convert pure CO, wherein in this case, of course, no CO 2 is then released in the salt bridge compartment.
  • an electrolyte i.e. a liquid medium
  • the electrolyte is not particularly limited, but according to certain embodiments may also be aqueous.
  • the salt bridge compartment thus comprises an aqueous electrolyte. It may correspond to the anolyte and/or catholyte, as appropriate, or may be different therefrom.
  • the electrolyte of the salt bridge compartment comprises an acid, preferably a water-soluble or water-miscible acid.
  • the electrolyte contains at least 10 ⁇ 6 mol/l of H + and/or hydrated variants thereof, preferably at least 10 ⁇ 4 mol/l, further preferably at least 10 ⁇ 3 mol/l, and even further preferably at least 10 ⁇ 2 mol/l.
  • the electrolyte of the salt bridge compartment comprises essentially no mobile cations other than H + and/or hydrated variants thereof.
  • the electrolyte comprises no mobile cations other than protons, with the exception of mobile cations in a number of common contaminants. The electrolyte serves to discharge the CO 2 and keep the filling moist.
  • the at least one acid in the electrolyte in the salt bridge compartment is not particularly limited, but is preferably a water-soluble and/or water-miscible acid, such as for example HCl, HBr, HI, H 2 SO 4 , H 3 PO 4 , HTfO (trifluoromethane sulfonic acid), etc.
  • the use of at least one acid in the electrolyte promotes the CO 2 release from hydrogencarbonate and/or carbonate in the solid anion exchanger, for example a basic or strongly basic ion exchanger.
  • the release of the CO 2 preferably takes place in the volume of the salt bridge compartment and not at the contact surface between the filling comprising the solid anion exchanger or the solid anion exchanger and the separator, as this would also lead to considerable voltage losses.
  • an improvement in gas release in the salt bridge compartment can be achieved using multi-layer fillings, as described above.
  • separators such as the first ion exchange membrane, the first separator and optionally further contained separators and/or ion exchange membranes, for example with multiple electrolyte inlets to the salt bridge compartment or layers of fillings, wherein in this case laminar flows are also optionally possible in order to produce such electrolyte gradients.
  • the filling comprising the solid anion exchanger or composed of the solid anion exchanger is preferably ion-conductive in order to improve charge transport by the electrolyte.
  • the first separator is preferably configured as an ion exchange membrane comprising a cation exchanger, for example as a cation exchange membrane (CEM), or as a bipolar membrane (BPM).
  • a cation exchanger for example as a cation exchange membrane (CEM), or as a bipolar membrane (BPM).
  • the solid filling also contains acidic components, e.g. cation exchangers. Because of the conductivity, however, the use of an acidic solution is preferred.
  • the electrolyte comprises in the salt bridge compartment at least one acid, as the diaphragm is not intrinsically ion-conductive.
  • the electrolyte of the salt bridge compartment can for example correspond to the anolyte, but can also be different therefrom.
  • a particularly preferred embodiment of the method according to the invention lies in the use of the solid anion exchanger, optionally in a mixture with further components in the filling of the salt bridge compartment, in combination with an acidic electrolyte.
  • the contact surface between the anion exchanger of the first ion exchange membrane and the acidic media can be sharply increased.
  • the surface area of the first ion exchange membrane is also the transition to the acidic medium in all cases. According to the invention, this transition is moved into the volume of the salt bridge compartment, thus massively increasing the surface area.
  • the insulating action of the gas bubbles generated in CO 2 electrolysis less adversely affects the cell voltage.
  • the action of the anion exchanger/transporter contained in the first ion exchange membrane as a transporter for anions can be continued by the filling in the salt bridge compartment.
  • the anode compartment comprises an anolyte, which comprises a liquid and/or a dissolved acid, preferably wherein the anolyte and/or the acid in the salt bridge compartment or the electrolyte in the salt bridge compartment comprise no mobile cations other than protons and/or deuterons, in particular no metal cations.
  • an acid in the salt bridge compartment comprises no mobile cations other than protons and/or deuterons, in particular no metal cations.
  • the anolyte comprises no mobile cations other than protons and/or deuterons, in particular no metal cations.
  • Mobile cations are cations that are not bound by a chemical bond to a carrier and/or in particular have an ion mobility of more than 1.10 ⁇ 8 m 2 /(s ⁇ V), in particular more than 1.10 ⁇ 1 ° m 2 /(s ⁇ V).
  • no mobile cations other than “D + ” and H + ′′, in particular no metal cations are released or produced.
  • water in particular in the case of a CCM anode
  • acids with non-oxidizable anions may be used as an anolyte or reagent.
  • the halogen-hydrogen acids HCl, HBr and/or HI are suitable, wherein for example halide salts are not suitable in use of a diaphragm as a first separator membrane, but can be used in use of a bipolar membrane as a first separator membrane.
  • SO 2 in the anolyte for the production of sulfuric acid or H 2 O for the production of H 2 O 2 , etc. is also.
  • the cathode compartment I of the salt bridge compartment II is separated by a composite of a CO 2 reducing cathode K and an AEM.
  • CO 2 for example moistened CO 2
  • the moistened CO 2 flow constitutes the substrate supply to the cathode. It then constitutes the catholyte within the meaning of a classical three-compartment cell.
  • the salt bridge compartment II is separated from the anode compartment III by the first separator S (e.g. a diaphragm, a bipolar membrane, a cation-conductive membrane) in conjunction with the anode A, wherein—as discussed above—it is also possible for the anode compartment III to be directly adjacent to the first separator.
  • the salt bridge compartment II is packed with a solid filling through which substances can flow that contains an e.g. strongly basic anion exchanger, and is flowed through by an electrolyte flow, which in addition to water can also comprise an acid.
  • the first separator can be freely selected e.g. from a cation exchange membrane (CEM), a not intrinsically ion-conductive hydrophilic gas separator (diaphragm), or a bipolar membrane (BPM), in which the anion-conductive layer is preferably oriented toward the anode.
  • CEM cation exchange membrane
  • diaphragm not intrinsically ion-conductive hydrophilic gas separator
  • BPM bipolar membrane
  • the anion-conductive layer is preferably oriented toward the anode.
  • the electrolyte in anode compartment III and the liquid electrolyte in the salt bridge compartment II are preferably identical and conductive.
  • the anolyte e.g. aqueous HCl, aqueous H 2 SO 4 , H 2 O, etc.
  • flows through the anode compartment III which can provide the anode A with substrate.
  • the selected electrolyte of the salt bridge compartment and the anolyte are identical, they can also be obtained from a common reservoir, wherein in particular, however, suitable devices are present in order to prevent the discharge of dissolved gases (degassing), e.g. in a return line of the electrolyte.
  • the anode compartment III can also be located between the anode A and the first separator S. In such a case, however, the anolyte must be conductive.
  • the cathode compartment I and the anode compartment III can additionally comprise e.g. electrically conductive, e.g. non-closed, structures, which are used for contacting of the electrodes. If the anode is not adjacent to the first separator, the requirement of conductivity can be dispensed with. Preferably, the anolyte contains only salts and thus mobile “non-H + ” cations if the first separator is a bipolar membrane.
  • the electrochemical conversion at the anode is not further limited, wherein it preferably leads to the transition of H + from (bipolar membrane) or through (diaphragm or CEM) the first separator into the electrolyte of the salt bridge compartment.

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DE102017223521.7A DE102017223521A1 (de) 2017-12-21 2017-12-21 Durchströmbare Anionentauscher-Füllungen für Elektrolytspalte in der CO2-Elektrolyse zur besseren räumlichen Verteilung der Gasentwicklung
PCT/EP2018/081741 WO2019120812A1 (de) 2017-12-21 2018-11-19 Durchströmbare anionentauscher-füllungen für elektrolytspalte in der co2-elektrolyse zur besseren räumlichen verteilung der gasentwicklung

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