Preparation of a gas diffusion electrode with an ion transport resin for electrochemical reduction of CO2 to chemically useful substances

Abstract

The present invention relates to a gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein an ion transport material is at least partially contained in the pores and / or channels of the gas diffusion electrode and / or an ion transport material is at least partially applied to the surface of the gas diffusion electrode; the present invention also relates to a method for preparing the gas diffusion electrode, the use of the gas diffusion electrode in the reduction of CO2 and / or CO, and an electrolysis cell and an electrolysis system each comprising the gas diffusion electrode.

Description

[0001] The present invention relates to a gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein ion transport materials are at least partially contained in the pores and / or channels of the gas diffusion electrode and / or ion transport materials are at least partially applied to the surface of the gas diffusion electrode; the present invention also relates to a method for preparing the gas diffusion electrode, the use of the gas diffusion electrode in CO2 and / or CO reduction, and an electrolysis cell and an electrolysis system respectively comprising the gas diffusion electrode. Existing technology

[0002] The prior art described here is based on the knowledge of the inventor and does not necessarily constitute the prior art known from the literature. Therefore, in the following description of the prior art, there may also be paragraphs that may not only come from the cited literature, but also be based on further expanded designs of the inventor, and therefore may not necessarily constitute ordinary prior art.

[0003] Today, approximately 80% of global energy needs are met by burning fossil fuels, a process that results in the global emission of approximately 34 billion metric tons of carbon dioxide per year into the atmosphere. A large portion of this carbon dioxide is removed through this release into the atmosphere, which can be up to 50,000 metric tons per day in the case of lignite-fired power plants, for example.

[0004] Carbon dioxide is a so-called greenhouse gas, and its adverse effects on the atmosphere and climate are a matter of considerable concern. Producing useful products from carbon dioxide is a technological challenge. Due to its very low thermodynamic levels, it is difficult to convert it into reusable products, making its practical reuse largely theoretical or academic.

[0005] Natural CO2 degradation occurs, for example, through photosynthesis. This involves the conversion of CO2 into carbohydrates, a process that is divided into many sub-steps at the molecular level, both over time and spatially. Therefore, this process cannot be easily applied on a large scale. To date, attempts to replicate the natural photosynthesis process using large-scale photocatalysis have been inefficient.

[0006] Another approach is the electrochemical reduction of carbon dioxide. Systematic research into the electrochemical reduction of carbon dioxide is still a relatively new area of ​​development. Research activity has increased significantly over the past few years, as the availability of excess electricity from non-fossil sources such as solar or wind power makes the storage and utilization of this energy economically viable.

[0007] Only in recent years have electrochemical systems been developed that are capable of reducing acceptable amounts of carbon dioxide. Laboratory-scale studies have shown that metals are preferred catalysts for the electrolysis of carbon dioxide. Therefore, metals are commonly used as catalysts for the electrolysis of CO2, some of which are shown, for example, in Table 1, taken from Y. Hori, Electrochemical CO2 reduction on metal electrodes, in: C. Vayenas, et al. (eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189.

[0008] Table 1: Faradaic efficiency of CO2 conversion to various products on various metal electrodes

[0009]

[0010] Table 1 lists the Faradaic efficiencies [FE] (%) of the products generated during the reduction of carbon dioxide on various metal electrodes. The values ​​shown are for 0.1 M potassium bicarbonate solution as the electrolyte.

[0011] While carbon dioxide is reduced almost completely to carbon monoxide at silver, gold, zinc, palladium and gallium cathodes, for example, at copper cathodes various hydrocarbons are formed as reaction products.

[0012] However, at the silver cathode, carbon monoxide and a small amount of hydrogen are mainly formed. The reactions at the anode and cathode can be represented by the following reaction equations:

[0013] Cathode: 2CO2+4e - +4H + →2CO+2H2O

[0014] Anode: 2H2O→4H + +4e -

[0015] Of particular economic interest is, for example, the electrochemical production of carbon monoxide, methane or ethylene, among other substances.

[0016] Examples:

[0017] Carbon monoxide: CO2 + 2e - +H2O→CO+2OH -

[0018] Ethylene: 2CO2+12e - +8H2O→C2H4+12OH -

[0019] Methane: CO2 + 8e - +6H2O→CH4+8OH -

[0020] Ethanol: 2CO2+12e - +9H2O→C2H5OH+12OH -

[0021] Monoethylene glycol: 2CO2+10e - +8H2O→HOC2H4OH+10OH -

[0022] Only in recent years has systematic research into the electrochemical reduction of carbon dioxide (CO2) increased. Despite numerous efforts, it has not yet been possible to develop an electrochemical system that can stably and energetically favorably reduce CO2 to a competitive energy carrier at sufficiently high current densities and acceptable yields over the long term. Due to the increasing scarcity of fossil fuel resources and the erratic availability of renewable energy sources, research into CO2 reduction is becoming increasingly interesting. This approach could reduce CO2 emissions and make CO2 a cost-effective carbon source.

[0023] In order to ensure high current density or to try to increase the current density further, what has been considered so far is only the reduction of carbon dioxide on the surface of the catalytically active cathode. An electrolytic cell suitable for the electrochemical reduction of carbon dioxide usually consists of at least a cathode chamber and an anode chamber, in which, for example, a gas chamber or the like may also be present. In order to achieve an effective conversion of the CO2 used, ideally, the cathode is designed as a porous gas diffusion electrode, which usually consists of a mixture of an inorganic metal catalyst (such as Ag, Au, Cu, Pb, etc.) and an organic binder, such as PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PFA (perfluoroalkoxy polymer), FEP (fluorinated ethylene-propylene copolymer), PFSA (perfluorosulfonic acid polymer). In order to adjust the hydrophilicity, polysulfones such as polyphenylsulfone, polyimide, polybenzoic acid, etc. can also be used. The electrodes are made from hydrophilic materials such as azoles or polyetherketones, or polymers that are generally electrochemically stable in electrolytes, including, for example, polymeric "ionic liquids," or organic conductors such as PEDOT:PSS or PANI (camphorsulfonic acid-doped polyaniline). The outstanding features of the prepared electrodes are high pore connectivity and a wide pore radius distribution.

[0024] In the prior art, the current densities of the known methods without gas diffusion electrodes are usually far below the values ​​relevant for economic utilization, i.e. <100 mA / cm 2The use of gas diffusion electrodes allows the realization of technologically relevant current densities, as is known from the prior art, for example, for chlor-alkali electrolysis operated on an industrial scale.

[0025] For example, gas diffusion electrodes based on silver / silver oxide / PTFE have recently been used on an industrial scale to produce sodium hydroxide solutions in existing chlor-alkali electrolysis processes (oxygen-consuming electrodes). The efficiency of these chlor-alkali electrolysis processes can be increased by 30-40% compared to conventional electrodes. Methods for embedding catalysts with PTFE are known from numerous publications and patents. The "dry process" methodology is based on a roller-calendering process using PTFE / catalyst powder. The corresponding technology originates from EP 0 297 377 A2 from 1988, in which an electrode based on Mn 2 O 3 was produced for battery cells. DE 3 710 168 A1 first described the use of a dry process for the production of metal electrocatalyst electrodes. This technology is also used in patents for the production of gas diffusion electrodes (oxygen-consuming electrodes) based on silver (silver(I) oxide or silver(II) oxide). EP 2 444 526 A2 and DE 10 2005 023 615 A1 mention mixtures with a binder content of 0.5-7%. The support used is an Ag or nickel mesh with a wire diameter of 0.1-0.3 mm and a mesh size of 0.2-1.2 mm. The powder is applied directly to the mesh, which is then fed to a roller calender. DE 101 48 599 A1 and EP 0 115 845 B1 describe a similar process, in which the powder mixture is first extruded to obtain a sheet (Fell) or film, which is then pressed onto the mesh in a further step, such as Figure 8 , in which a catalyst material 6 is applied to a web 7 and calendered into a gas diffusion electrode GDE in a two-stage calendering process.

[0026] The latter method is inferior to the one-step method due to its relatively low mechanical stability. EP2410079A2 describes a one-step method for producing silver-based oxygen-consuming electrodes, which is supplemented with metal oxide additives such as TiO2, Fe3O4, Fe2O3, NiO2, Y2O3, Mn2O3, Mn5O8, WO3, CeO2, spinels such as CoAl2O4, Co(AlCr)2O4, inverse spinels such as (Co,Ni,Zn)2(Ti,Al)O4, and perovskites such as LaNiO3 and ZnFe2O4. Also considered suitable additives are silicon nitride, boron nitride, TiN, AlN, SiC, TiC, CrC, WC, Cr3C2, TiCN, or oxides of the ZrO2 and WO3 type. These materials are referred to herein as fillers. Specifically, the goal here is to reduce the hydrophobicity of the electrode.

[0027] DE10335184A1 discloses alternative catalysts for oxygen-consuming electrodes, such as precious metals such as Pt, Rh, Ir, Re, and Pd; precious metal alloys such as Pt-Ru; precious metal-containing compounds such as precious metal sulfides and oxides; and Chevrel phases such as Mo4Ru2Se8 or Mo4Ru2S8, which may also contain Pt, Rh, Re, Pd, etc.

[0028] Known Cu-based gas diffusion electrodes for the production of hydrocarbons based on CO 2 are mentioned, for example, in the work of R. Cook [J. Electrochem. Soc., vol. 137, no. 2, 1990], in which a wet-chemical method based on a PTFE 30B (suspension) / Cu (OAc) 2 / Vulkan XC 72 mixture is mentioned. The method describes how to apply a hydrophobic, conductive gas transport layer by means of three coating cycles and how to apply a catalyst-containing layer by means of three further coating operations. Each application of the layer is followed by a drying phase (325° C.) and then a static pressing process (1000-5000 psi). For the resulting electrode, a Faradaic efficiency of >60% and a current of >400 mA / cm 2 are given. 2 Reproduction experiments showed that the described static pressure method did not lead to a stable electrode. A negative effect of the added Vulkan XC 72 was also observed, so that no hydrocarbons were obtained.

[0029] The described calendering method results in highly porous single-layer electrodes characterized by low flow resistance or a low bubble point of about 5-20 mbar. Due to the high porosity (50-70%) or the large pore radius resulting from this preparation method, the correspondingly prepared electrodes have a very narrow operating window during CO2 electrolysis in aqueous electrolytes. This is generally characterized by the fact that the cations of the electrolyte, such as Li + , K + 、Na + 、Cs + , penetrate into the porous structure due to the electrical attraction of the cathode, and there they can be converted into OH according to the following reaction equation - The absorbed CO2 forms bicarbonates, which usually precipitate at higher current densities due to the high salt content of the electrolyte.

[0030] M + +CO2+OH - →MHCO3↓

[0031] Another undesirable subsequent effect observed is the passive infiltration of water by diffusion along the concentration gradient (osmosis), also known as the "water inlet pressure" effect. As a result of the described salinization, a complete blockage of the pore structure can be achieved, depending on the amount of salt and the water content, by the generation of anions and their diffusion out of the pores more slowly than by the electrostatic attraction of cations into the pores. In addition to complete blockage by salt crystals, it is also possible to be completely flooded (filled, Durchflutung) with electrolyte, so that electrolyte can appear continuously at the back. Both extreme states lead to a breakdown of stable operation and have a direct impact on the desired product Faradaic efficiency or the achievable current density. The latter phenomenon is also known in the field of chlor-alkali electrolysis and has been recognized as critical in DE102010054643A1 and EP2398101A1, because the penetrating liquid can form a continuous film at the back, which can prevent the gas from entering the pore system further.

[0032] However, in the ideal operating state of the gas diffusion electrode, the stable formation of the catalyst / electrolyte / gas three-phase boundary should be ensured. Another criterion is the bubble point of the gas diffusion electrode, which is very low in the range of 5-20 mbar due to the high porosity in the case of calendared electrodes.

[0033] Electrodes with a low bubble point react relatively strongly to pressure fluctuations, so that in industrial applications the control of the differential pressure (the back pressure of CO2 downstream of the electrode) by means of a differential pressure regulator is complicated, as can be seen, for example, in DE102013011298A1, where a more complex control loop with the following control parameters may be required: gas composition, pressure and volume flow.

[0034] From the field of electrochemical CO2 reduction research, there are known research works which use MEAs (membrane electrode assemblies) and which are similar in concept to the electrochemical reduction of CO2 in ion exchange electrolyzers with solid-state electrolytes:

[0035] US 9481939 B2 and US 2016 / 0251766 A1, for example, describe methods for the electrochemical reduction of CO2, which target CO as the target product and use a vinylbenzene ionomer modified with imidazolium groups, poly(1-(p-vinylbenzyl)-3-methylimidazolium). The other functional anion exchange group described is a 1-(2-hydroxyethyl)imidazolium group. The polymer backbone used is primarily a polyvinylbenzyl structure. Also described is a copolymer of chloromethylstyrene (vinylbenzyl chloride) and styrene, poly(4-VBC-co-St). Also mentioned is poly(2,6-dimethyl-1,4-phenylene oxide). In these methods, the anode and cathode are in direct contact with the membrane. The electrodes are prepared on the basis of catalyst-coated carbon paper (GDL) (Sigracet 35BC). These are not all-catalyst gas diffusion electrodes. Reproduction experiments have led to stability issues with the ionomer on the anode side.

[0036] For the electrochemical reduction of CO₂ to methanol, US Pat. No. 7,704,369 B2 also proposes the use of alkylammonium halides as electrolytes in aqueous mixtures. Journal of Power Sources 223 (2013), pp. 68-73, describes a method using a tin-based electrolyte-free cathode. This method is based on a cation exchange membrane with an electrode arrangement known from the field of fuel cells.

[0037] D. Dewolf, Catalysis Letters (1988), (1), pp. 73-83, uses liquid-free electrodes based on copper / perfluorosulfonic acid (Nafion), which are also operated in an electrolyzer with a cation exchange membrane. 2 The target products at very low current densities are methane and ethylene.

[0038] L. Aeshala, Separation and Purification Technology 2012 (94), pp. 131-137 also describes a method for using a copper catalyst in a device with a solid electrolyte, such as Nafion, Speek (polyetheretherketone), or alkali-doped PVA. Another publication of the group (L. Aeshala, Journal of CO2 Utilization, 2013 (3), pp. 49-55) also describes a copper catalyst with solid anion and cation exchange electrolytes as MEA, rather than as components of the electrode itself, i.e., acid-doped CMI 7000 and alkali-doped AMI 7001. Process improvements are described in Phys. Chem. Chem. Phys. 2014, (16), pp. 17588-17594, which include modification of the solid electrolyte with functional groups (alkali-doped PVA / PEI).

[0039] S. Shironita, J. Power Sources, 2013 (228), pp. 68-74, describes a reversible methanol fuel cell for producing methanol by electroreduction of CO 2 , using a Pt-Ru / C catalyst with an MEA configuration.

[0040] The electrodes used in the described methods are based solely on catalyst-coated carbon fiber GDL structures, which originate from the field of fuel cell development and are generally unsuitable for industrial electrolysis processes due to their low mechanical stability. Another disadvantage is usually the carbon black or carbon component, which often contains impurities of transition metals such as Ni and Fe, and thus increases the formation of undesirable hydrogen. The adhesion of the catalyst particles to the GDL structure is also generally insufficient, resulting in significant catalyst losses over hundreds to thousands of operating hours. Similar problems can also be observed during membrane renewal, as a large part of the catalyst can be lost when separating the GDL and the membrane. Gas diffusion electrodes constructed according to the all-catalyst concept have substantial advantages over these methods. The suitability of this type of electrode for ion bonding on membranes is still unknown.

[0041] Anion exchange membranes are known from other fields of application, such as electroosmosis, but these have not yet been modified with catalysts. The use of ion exchange resins in electrolytic cells is known from the field of exchanger regeneration by electrodeionization (EDI). However, these methods differ fundamentally from electrochemical CO reduction.

[0042] During the electroreduction of CO2 in aqueous electrolyte solutions, gas diffusion electrodes can usually be used within a relatively narrow process window for extended periods of >1000 h. In CO2 electrolysers, the anode and cathode compartments are usually kept separate from one another by means of cation / anion selective membranes or diaphragms. This prevents mixing of gaseous useful substances formed at the cathode and anode. Although the membranes used are practically impermeable to gases, they must be permeable to ionic charge carriers. Since the membranes usually used are chemically solid acids, charge transport can usually only be achieved via positively charged species such as protons or electrolyte cations (e.g. Li + ,Na + ;K + ; Rb + ;Cs + ;NRR′R″R″′ + , wherein R, R′, R″, R′″ can be the same or different organic groups and / or D, H).

[0043] As a result, during electrolysis operation, the cation concentrations of the anolyte and catholyte deviate from each other. In the catholyte, the charge of the incoming cations is compensated (balanced) by the hydroxide ions formed at the cathode, which can further react to form bicarbonate ions or carbonate ions. This leads to a continuous increase in the carbonate concentration in the catholyte and, if necessary, an increase in the pH value to HCO3 - During operation, in the worst case, this can lead to the precipitation of insoluble salts in the cathode electrolyte or on or in the electrodes.

[0044] In the anolyte, the missing cations are replaced by protons produced at the anode. This generally results in either the generation of acid in the anolyte, which leads to a drop in the pH value, or, in the case of hydroxide or carbonate electrolytes, in the neutralization of the anions. In the former case, the anolyte can be converted into pure water. Another problem is the migration of salts into the porous electrode itself. If the electrode itself is not ionically conductive, the combination of electrochemically active sites with water and ion transport can only be achieved by partial penetration of the electrode with liquid electrolyte. However, for charge balance at the cathode, two driving forces should generally be taken into account: first, the electrostatic attraction of the electrolyte cations; second, the generation of anionic species at the cathode, usually bicarbonate ions, which require cations for charge balance. This creates a concentration gradient, which also leads to the penetration of cations into the electrode.

[0045] Typically, this charge compensation exceeds the level required for ion binding. Due to electroosmosis, electrolyte can also reach the side of the electrode facing away from the electrolyte compartment. In extreme cases, this can lead to pore blockage, potentially causing an undesirable CO2 undersupply to the catalyst. As a further extreme case, it can be observed that the aqueous medium penetrates the pores extensively, which can lead to overflowing of the pore system and, in turn, contribute to a CO2 undersupply to the catalyst. This problem is often observed in electrolyzer configurations where the cathode is in direct contact with a liquid salty electrolyte. Another potential problem with this variant is pore overflow with electrolyte. A known cause of electrolyte penetration into the electrode pores can be the hydrostatic pressure of the water column in the electrolyte gap, which limits the technical height of the electrolyzer. During operation, it can also be observed that bicarbonate salt crystallization increases in the area facing away from the electrolyte, which, in extreme cases, can lead to pore blockage, resulting in an undesirable CO2 undersupply to the catalyst. As a further extreme case, it can be observed that the aqueous medium penetrates the pores extensively, which can contribute to overflowing of the pore system and, in turn, to a CO2 undersupply to the catalyst. By avoiding these extreme cases, stable operating conditions can be achieved.

[0046] It was therefore found to be technically necessary to broaden the stable operating window for the industrial application of this technology in order to ensure a more efficient conversion of CO 2 in the long-term operation of large cells, avoiding the drawbacks known from the prior art.

[0047] Therefore, one object of the present invention is to prepare a gas diffusion electrode having an elevated bubble point (bubble point) and elevated overflow pressure (wetting pressure) in order to widen the operating window of the gas diffusion electrode and prevent salinization or electrolyte crossover.

[0048] Another object of the present invention is to provide a gas diffusion electrode for carbon dioxide utilization by an alternative or improved method. SUMMARY OF THE INVENTION

[0050] Firstly, the inventors have found that for cell configurations with an electrolyte gap between cathode and membrane / diaphragm, in CO2 operation, salt deposition in the gas diffusion electrode occurs, especially at relatively high operating temperatures, which leads to failure of the GDE.

[0051] Furthermore, the inventors have found that for a cell construction without an electrolyte gap or for an M / DEA (membrane / diaphragm electrode assembly) using a gas diffusion electrode as a cathode, severe salt formation / salt deposition may also occur in the interface area between the gas diffusion electrode (cathode) and the diaphragm / membrane during electrolysis operation, and therefore stable electrolysis operation cannot be ensured.

[0052] Salt formation / salt deposition is also independent of whether the anode is present directly on the membrane or whether a separate electrolyte gap is provided in the cell.

[0053] The reason for this is probably the previously described formation of bicarbonate ions during electrolysis and the resulting formation of bicarbonate salts from the cations transported across the membrane. These or their salts cannot usually be removed without a liquid electrolyte or sufficiently active anion transport.

[0054] In the case of M / DEA in particular, the enrichment of electrolyte cations in the interfacial region can often be attributed to electroosmosis. Here, the concentration gradient cannot simply dissipate on the electrode side, since catalyst-based gas diffusion electrodes generally have only very poor anion conductivity or have not previously offered any anion conductivity at all. In order to improve operational stability, in the context of the present invention, ion transporters, in particular anion transport resins, are used as binder materials or additives, for example, in order to rapidly conduct away or partially buffer the OH groups formed. - ions, thereby reducing the reaction with CO2 and the associated bicarbonate formation, or the anion transport resin itself can conduct HCO3 - In principle, anion transport can be achieved by anion exchangers. Since certain anion exchangers contain cationic functionality, counterions are already present for charge compensation of the bicarbonate ions formed, and it is no longer necessary for the cations to penetrate into the electrode. More precisely, a transport or displacement of anions from the electrode can be achieved. It is important to emphasize here that anion transport resins do not necessarily have anion exchange functionality. When using OH in particular - or HCO3 - It is sufficient if the functionalized resin has a sufficient anion mobility. Thus, the ion exchange resin, in particular the anion exchange resin, also provides a path via which, for example, hydroxide or bicarbonate anions can be transported out of the cathode in the direction of the electric field, thereby eliminating the need to use any other cations from the electrolyte for charge compensation, which in turn would lead to salt crystallization and thus blockage of the GDE.

[0055] Furthermore, the integrated anion exchanger, in particular, forms a barrier to cations, which can additionally counteract salt deposition. It is not important here whether the electrode is completely permeated with anion transporters. What is important is the anion transport function in the direction of the electrolyte or in the active region of the GDE.

[0056] In a first aspect, a gas diffusion electrode is disclosed, comprising a metal M selected from Ag, Au, Cu, Pd, and mixtures, alloys, and / or salts thereof, and at least one binder. The gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein an ion transport material is at least partially contained within the pores and / or channels of the gas diffusion electrode, wherein the ion transport material is an anion transport material. In one embodiment of the present invention, the ion transport material is at least partially applied to the surface of the gas diffusion electrode.

[0057] The invention further relates to an electrolysis cell comprising a gas diffusion electrode according to the invention as cathode, and an electrolysis system comprising a gas diffusion electrode according to the invention or an electrolysis cell according to the invention.

[0058] Also disclosed is a method for electrolyzing CO2 and / or CO, wherein a gas diffusion electrode according to the invention is used as a cathode, or wherein an electrolysis cell according to the invention is used, and also disclosed is the use of a gas diffusion electrode according to the invention or an electrolysis cell according to the invention in the electrolysis of CO2 and / or CO.

[0059] The present invention also relates to a method for producing a gas diffusion electrode, the gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein an ion transport material is at least partially contained in the pores and / or channels of the gas diffusion electrode, the method comprising

[0060] - preparing a first mixture comprising at least a metal M, an ion transport material and at least one binder,

[0061] - applying a first mixture comprising at least a metal M, an ion transport material and at least one binder to a support, preferably in the form of a sheet-like structure, and

[0062] - dry rolling the first mixture onto a support to form a first layer;

[0063] or

[0064] - preparing a first mixture comprising at least a metal M, an ion transport material and optionally at least one binder,

[0065] - preparing a second mixture comprising at least a metal M and at least one binder,

[0066] - applying a second mixture comprising at least a metal M and at least one binder to a support, preferably in the form of a sheet-like structure,

[0067] - applying a first mixture comprising at least a metal M, an ion transport material and optionally at least one binder onto the second mixture,

[0068] - optionally applying a further mixture to the first mixture, and

[0069] - dry rolling the second and first mixtures and optionally further mixtures onto a support to form the second layer and the first layer and optionally further layers;

[0070] or

[0071] - providing a gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, and

[0072] - at least partially introducing the ion transport material into the pores and / or channels of the gas diffusion electrode.

[0073] Here, the ion transport material is an anion transport material.

[0074] Further aspects of the invention can be derived from the dependent claims and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The accompanying drawings are intended to illustrate embodiments of the present invention and to further understand the present invention. Together with the description, they serve to illustrate the concepts and principles of the present invention. Reference to the accompanying drawings enables further embodiments and the numerous advantages enumerated. The elements in the drawings are not necessarily shown to scale relative to one another. Unless otherwise indicated, identical elements, features, and components having the same function and effect are provided with the same reference numerals in the drawings.

[0076] Figure 1 An exemplary illustration showing a possible configuration of an electrolytic cell according to one embodiment of the present invention.

[0077] Figure 2 Another exemplary illustration shows a possible configuration of an electrolytic cell according to one embodiment of the present invention.

[0078] Figure 3 A third exemplary illustration shows a possible configuration of an electrolytic cell according to one embodiment of the present invention.

[0079] Figure 4 A fourth exemplary illustration shows a possible configuration of an electrolytic cell according to one embodiment of the present invention.

[0080] Figure 5 One configuration of an electrolysis system for CO2 reduction is shown.

[0081] Figure 6 Another exemplary configuration of an electrolysis system for CO2 reduction is shown.

[0082] Figure 7 A schematic diagram shows a specific embodiment of a gas diffusion electrode according to the invention.

[0083] Figure 8 A schematic diagram shows a method for producing a gas diffusion electrode using a roller calender.

[0084] Figure 9 A schematic structural diagram of an exemplary gas diffusion electrode according to the present invention is shown, wherein an electrolyte and a gas are provided in operation.

[0085] Figure 10 A schematic diagram showing the treatment of a gas diffusion electrode with ion exchange material by spray coating is shown.

[0086] Figures 11 to 14 An exemplary embodiment of an electrolysis cell according to the invention is shown with a possible gas (here for example CO 2 ) and electrolyte supply.

[0087] Figures 15 to 23 The results achieved using a gas diffusion electrode in an example of the present application are shown.

[0088] Figures 24 to 28 The role of anion transport material in an exemplary gas diffusion electrode according to the invention during operation is schematically illustrated.

[0089] Figure 29 Another exemplary illustration shows a possible configuration of an electrolytic cell according to one embodiment of the present invention.

[0090] Figure 30 and 31 Other exemplary configurations of the electrolysis system of the present invention for CO2 reduction are shown.

[0091] Detailed description of the invention

[0092] definition

[0093] Unless defined otherwise, technical and scientific expressions used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0094] In the context of the present invention, "hydrophobic" is understood to mean repelling water. According to the present invention, hydrophobic pores and / or channels are those that repel water. In particular, the hydrophobic property according to the present invention is associated with substances or molecules having non-polar groups.

[0095] In contrast, "hydrophilicity" is understood to refer to the ability to interact with water and other polar substances.

[0096] In the present application, the statements of quantities are based on weight %, unless otherwise stated or evident from the context. In the gas diffusion electrode according to the invention, the weight percentage contents add up to 100 weight %.

[0097] The standard pressure is 101 325 Pa = 1.01325 bar.

[0098] In a first aspect, the present invention relates to a gas diffusion electrode (GDE) comprising a metal M selected from the group consisting of Ag, Au, Cu, Pd, and mixtures and / or alloys and / or salts thereof, and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein an ion transport material is at least partially contained in the pores and / or channels of the gas diffusion electrode and / or an ion transport material is at least partially applied to the surface of the gas diffusion electrode. According to a specific embodiment, the ion transport material is at least partially contained in the pores and / or channels of the gas diffusion electrode. According to a specific embodiment, an ion exchange material is at least partially contained in the pores and / or channels of the gas diffusion electrode and is at least partially applied to the surface of the gas diffusion electrode.

[0099] The metal M in the present invention can function as both a catalyst and an electron conductor in the gas diffusion electrode of the present invention. According to the present invention, the metal M is selected from Cu, Ag, Au, Pd, and mixtures, alloys, and / or salts thereof. The metal M is preferably selected from Cu, Ag, and mixtures, alloys, and / or salts thereof, particularly Ag and / or alloys and / or salts thereof.

[0100] Here, the salt of metal M is, for example, a charged compound of metal M, wherein the metal M is present in the form of a cation, preferably in the form of M + and / or M 2+ (especially Cu 2+ and / or Pd 2+ ) form, especially in the M+ form, and it helps catalyze the reduction. The counter ions in these salts are not particularly limited.

[0101] The content of the metal M in the gas diffusion electrode of the present invention is not particularly limited and can be 30% by weight to 99.8% by weight, preferably 40% by weight or more and 96% by weight or less, further preferably 50% by weight or more and 92% by weight or less, further preferably 65% ​​by weight or more and 85% by weight or less, based on the weight of the gas diffusion electrode.

[0102] According to a specific embodiment, the metal M in the gas diffusion electrode of the present invention is present both in the form of elemental metal M and in the form of cations, preferably in the form of M +and / or M 2+ (especially Cu and / or Pd), more preferably M + Form exists.

[0103] Furthermore, the at least one binder contained in the gas diffusion electrode of the present invention is also not particularly limited, and two or more different binders can also be used, even in different layers of the electrode. The binder or adhesive of the gas diffusion electrode of the present invention, if present, is not particularly limited and comprises, for example, hydrophilic and / or hydrophobic polymers, such as hydrophobic polymers. According to a particular embodiment, the at least one binder is an organic binder, for example selected from PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PFA (perfluoroalkoxy polymer), FEP (fluorinated ethylene-propylene copolymer), PFSA (perfluorosulfonic acid polymer), and mixtures thereof, in particular PTFE. To adjust the hydrophilicity, hydrophilic materials such as polysulfones, i.e. polyphenylsulfone, polyimide, polybenzoic acid, can also be used. azoles or polyetherketones, or generally electrochemically stable polymers in electrolytes, also including, for example, polymeric "ionic liquids", or organic conductors such as PEDOT:PSS or PANI (camphorsulfonic acid doped polyaniline). In this way, appropriate adjustment of the hydrophobic pores or channels can be achieved. More specifically, PTFE particles having a particle size of 0.01 to 95 μm, preferably 0.05 to 70 μm, further preferably 0.1 to 40 μm, for example 0.3 to 20 μm, for example 0.5 to 20 μm, for example about 0.5 μm can be used to prepare the gas diffusion electrode. Suitable PTFE powders include, for example TF 9205 or Dyneon TF 1750. Suitable binder particles, such as PTFE particles, can be, for example, approximately spherical, for example, and can be produced, for example, by emulsion polymerization. According to a particular embodiment, the binder particles do not contain surfactants. The particle size can be determined, for example, according to ISO 13321 or D4894-98a and can, for example, correspond to the manufacturer's data (e.g., TF 9205: average particle size 8 μm according to ISO 13321; TF 1750: average particle size 25 μm according to ASTM D4894-98a).

[0104] The binder content can be, for example, from 0.1% to 50% by weight, for example when a hydrophilic ion transport material is used, for example from 0.1% to 30% by weight, preferably from 0.1% to 25% by weight, for example from 0.1% to 20% by weight, further preferably from 3% to 20% by weight, further preferably from 3% to 10% by weight, even more preferably from 5% to 10% by weight, based on the gas diffusion electrode. According to certain embodiments, the binder has significant shear-thinning properties so that fiber formation occurs during mixing. Ideally, the fibers formed during the preparation process should wrap around the particles without completely wrapping around the surface. The optimal mixing time can be determined, for example, by direct observation of fiber formation in a scanning electron microscope.

[0105] According to a particular embodiment, the at least one binder is stable at a pH of 7 or higher, preferably in a strongly alkaline environment, such as at a pH of 9 or higher, such as 10 or higher.

[0106] According to a particular embodiment, the metal M, at least one binder and the ion transport material, such as an ion exchange resin, such as an anion transport material, such as an anion exchange resin, are substantially uniformly distributed at least in a part of the GDE, such as the side facing the electrolyte during operation.

[0107] According to the present invention, the ion transport material, such as the ion exchange material, is not particularly limited and can be, for example, an ion transport resin, such as an ion exchange resin, but can also be other ion transport materials, such as ion exchange materials such as zeolites. According to a specific embodiment, the ion transport material is an ion exchange resin. In this regard, there is no particular limitation.

[0108] According to certain embodiments, the ion transport material is an anion transport material, such as an anion exchange resin. According to certain embodiments, the anion transport material or anion transporter is an anion exchange material, such as an anion exchange resin. According to certain embodiments, the ion transport material also functions as a cation blocker, i.e., it prevents or at least reduces the penetration of cations into the gas diffusion electrode.

[0109] In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.In some embodiments, the anion transport material of the present invention can be used as the anion transport material of the present invention.

[0110] The integration (introduction) of cation transport, for example cation exchange functions, can be disadvantageous here, since on the one hand they can promote the formation of hydrogen and on the other hand can provide pathways for the cations of the electrolyte which can lead to salt deposition.

[0111] The advantages of anion transport by means of anion exchange materials, in particular at least partially in the pores and / or channels of the gas diffusion electrode, in particular on the side of the gas diffusion electrode facing the electrolyte, are explained below. However, it should first be noted that anion transport additives are very effective for GDEs (e.g. oxygen-consuming cathodes) up to high current densities, for example above 500 mA / cm 2 The operation is not absolutely necessary.

[0112] Figure 24 The ground state of an exemplary GDE, such as an oxygen-consuming cathode or a GDE for converting CO and / or CO, is depicted when no voltage is applied. Here, the electrolyte 45 can penetrate the porous structure of the catalyst, here an exemplary silver catalyst Ag, wherein PTFE is used as a binder material. All cations (e.g., K + ) by anions (such as HCO3 - or SO4 2- ) equilibrium, wherein mobile cations 51 and mobile anions 52 are shown here as an example. If a voltage is then applied, then in the case of an oxygen-consuming cathode or generally when, for example, O 2 is present in the gas to be converted, the following overall reaction can occur:

[0113] 2e - +H2O+1 / 2O2→2OH -

[0114] The hydroxide ions formed by way of example now diffuse out of the gas diffusion electrode. The inward diffusion of cations should be suppressed, since otherwise salt crystallization would occur.

[0115] The diffusion of cations is typically several orders of magnitude slower than that of hydroxide ions. This is because cations must “migrate,” whereas hydroxide ions can be transported into the bulk electrolyte or electrolyte45 without energy consumption due to Grotthus tunneling or the Grotthus effect53, as shown in Figure 25 As shown by way of example in FIG, a voltage is applied to the GDE.

[0116] As shown above, the same electrode can also be used, for example, to reduce CO2 to CO. Similar to the reduction of oxygen, two hydroxide ions are formed in the reduction of CO2.

[0117] 2e - +CO2+H2O→2OH - +CO

[0118] The CO formed diffuses out of the electrode and can be discharged with the electrolyte and / or gas flow. The generated hydroxide ions can also be transported out of the electrode by the Grotthus mechanism. 2 ) and low temperatures (e.g. <30°C), the reaction is sufficient to ensure stable operation.

[0119] Figure 26 By way of example, the electrochemical reduction of CO 2 to CO with (concomitant) hydroxide (hydroxyl) transport via the Grotthus mechanism is shown when a voltage is applied.

[0120] At higher temperatures, eg 50°C or higher, eg >50°C, bicarbonate formation starts to predominate.

[0121]

[0122] The equilibrium is unfavorably on the side of bicarbonate, which can no longer pass through tunneling processes but must be brought out of the electrode by true transport processes, e.g. Figure 27 As shown, a summary of the chemical equilibrium in an exemplary gas diffusion electrode is shown in the figure. For bicarbonate, the inward migration of cations can lead to salt precipitation in the GDE, or at least to the formation of permeates on the side of the GDE away from the electrolyte.

[0123] Hydroxyl ions can diffuse out of the GDE via the Grotthus tunneling effect in a low-energy manner with the aid of an applied field, whereas bicarbonate ions must actively resist the high electrolyte concentration and be transported out of the GDE. The distance required for this purpose is typically in the range of several hundred micrometers. Anion transport materials can play a supporting role here.

[0124] If the anion transport material is an anion exchanger, the anion exchanger can be introduced into the GDE with any anion. - or HCO3 - exchange, or may occur spontaneously during operation due to concentration differences with the electrolyte.

[0125] Figure 28 An exemplary GDE is shown, which shows an anion transport material 54 and a catalyst, such as catalyst particles, such as Ag, wherein an existing binder (here, for example PTFE) is provided in a uniformly distributed manner. The anion transport material includes a plurality of localized charges 55, which can be transferred by counterions such as OH - or HCO3 - Compensation (balance). This forms anion paths along which anions can move. If additional ions are generated at a location in the GDE by electroreduction that have not yet been compensated at least at the moment of formation (in statu nascendi), these additional ions push out the anions at the phase boundary of the GDE by a hopping mechanism. This means that the generated OH - or HCO3 - With OH who left GDE - or HCO3 - are not the same. Thus, along this path, only the energy for hopping needs to be applied, and the anion itself does not need to be pushed out of the GDE. Thus, in addition to the Grotthus mechanism, an additional "hopping path" is created. Furthermore, the positive charge of anion transport resins, such as anion exchange resins, inhibits the inward diffusion of mobile cations 51 (e.g., potassium). Figure 28 The anion transport in the GDE is exemplarily shown in the electrolytic operation as follows. - Due to the lack of charge compensation, it is first 3 HCO3 - Swap positions, then 3 HCO3 - and 2 HCO3 - Swap positions, finally 2 HCO3 - and 1 HCO3 - Exchange positions. 1 HCO3 - At the electrolyte boundary, it enters the electrolyte, where its charge is compensated. This is how the transport is terminated.

[0126] Therefore, anion transport materials, such as anion exchange materials, such as anion exchange resins, can fulfill multiple functions:

[0127] -In addition to diffusion, it can also - Anions provide a transport pathway.

[0128] - In addition, it can act as a blocker for mobile cations from the electrolyte due to Coulomb blockade, where parts of the GDE can be positively charged by this anion exchange material even when a negative potential is applied.

[0129] - When mobile cations are blocked, the deposition of salts in the GDE or the permeation of substances through the GDE can also be suppressed. Independent of the electrolyte, the permeate can be pure bicarbonate, for example in the case of CO2 electrolysis (charge compensation by cations in the electrolyte).

[0130] According to certain embodiments, the ion transport material, such as an ion exchange material, such as an ion exchange resin, such as an anion exchange material, comprises polar groups, such as ROR, RCOO - ,R-NR3 + ,R-NH2,RPO3 2- ,ROH, where R is any group, such as an organic group. Use an ion exchange resin with polar functionality (group) (ROR, RCOO - ,R-NR3 + ,R-NH2,RPO3 2- ,ROH) increases the proportion of hydrophilic electrode areas, thereby increasing electrolyte transport through the electrode. The resulting dilution effect can also counteract oversaturation or salt crystallization, but complete flooding should be avoided. Therefore, when producing gas diffusion electrodes using such ion-transporting materials, such as ion exchange materials, a multilayer structure, such as a two-layer structure, is advantageous according to certain embodiments, wherein at least one layer substantially does not contain ion exchange material, such as the layer facing the gas during operation, for example, located on a support. Preferably, no chemical reactions should occur in this layer, which can be ensured, for example, by correspondingly adjusting the gas pressure and / or electrolyte supply during operation.

[0131] Furthermore, it is not excluded that the resin used has a functional group that binds CO2 (combines CO2), since OH- can react with CO2 to form bicarbonate.

[0132] According to certain embodiments, the ion exchange material, such as an anion exchange material, is stable at a pH greater than 7. According to certain embodiments, the ion exchange material, such as an anion exchange material, is stable in a strongly alkaline environment, such as at a pH of 9 or higher, such as 10 or higher.

[0133] According to specific embodiment, ion transport material, for example ion exchange material, preferably anion exchange material, with 0.1 to 50 weight %, preferably 0.1 to 40 weight %, preferably 3 to 35 weight %, further preferably 5 to 30 weight %, even more preferably 10 to 25 weight % amount exists, based on gas diffusion electrode meter and / or based on the layer (for example catalyst layer) that wherein exists.The ion transport material of hydrophilicity or main hydrophilicity (for example more hydrophilic than hydrophobic region), for example ion exchange material, for example anion transport material, for example anion exchange material, for example anion exchange resin, preferably with 0.1 to 20 weight %, preferably 1 to 18 weight % amount exists, based on gas diffusion electrode meter and / or based on the layer (for example catalyst layer) that wherein exists.The reason of this " lower " upper limit is that conventional anion exchange resin is prepared for the use in aqueous environment, and is therefore mainly hydrophilic.If these anion exchange resins are now mixed into too much, then GDE becomes so strongly hydrophilic that GDE can be fully permeable by water and and then may lose the function of GDE.

[0134] However, the anion transport material according to the invention also includes hydrophobic variants of "anion exchange resins," which are generally completely unusable in aqueous media. Correspondingly, higher amounts of these are possible in the gas diffusion electrode, as specified above. If the anion transport material is sufficiently hydrophobic, it can also simultaneously serve as a binder, which is preferred. Accordingly, in this case, the binder content can also be reduced.

[0135] In certain embodiments, the amount of the hydrophilic or mainly hydrophilic ion exchange material in the gas diffusion electrode of the present invention is lower than the amount of the hydrophobic binder, and / or there is at least one layer, the amount of the hydrophobic binder that described layer comprises is greater than the amount of the hydrophilic or mainly hydrophilic ion exchange material.When the consumption of hydrophilic or mainly hydrophilic anion exchange resin exceeds the amount of the hydrophobic binder used in whole GDE, can for example obtain undesirable electrolyte penetration.Therefore, for example, the ratio of the hydrophilic or mainly hydrophilic resin and 7 % by weight PTFE that exceeds 20 % by weight is considered to be problematic.Such high-content exchange resin can for example be realized in the catalyst layer in the double-layer GDE with the substantially hydrophobic base layer that comprises for example>10 % by weight PTFE, and can not reach complete overflow.

[0136] According to a particular embodiment, the ion-transporting material, preferably the anion-transporting material, is added in the form of a powder during the preparation process, wherein the powder may, for example, have a particle size of 0.1-100 μm, for example 1 to 50 μm, for example 1 to 20 μm or 1 to 10 μm, wherein the powder may also be macroporous, i.e., formed from aggregates of the aforementioned particles. The particle size can be determined, for example, by microscopy with the aid of image analysis, by laser diffraction, and / or by dynamic light scattering.

[0137] Alternatively, for the impregnation with ion exchange materials, microemulsions can also be used, wherein the ion exchange materials can have a particle size of 0.01 to 10 μm, for example 0.05 to 5 μm, for example 0.1 to 1 μm. The particle size can be determined, for example, by microscopy with the aid of image analysis, by laser diffraction and / or by dynamic light scattering.

[0138] The ion transport material, e.g., ion exchange material, e.g., anion transport material, is preferably an ion transport polymer, and is also, for example, an ion exchange polymer, wherein the polymer backbone of the ion transport material, e.g., ion exchange material, e.g., anion transport material, e.g., anion exchange material may also optionally be partially or fully fluorinated. However, the polymer backbone of the ion transport material, e.g., ion exchange material, e.g., anion transport material, e.g., anion exchange material is not particularly limited and may, for example, be based on a polymer or copolymer, such as styrene. The polymer backbone may, for example, consist of a divinylbenzene-styrene copolymer with functionalized side chains or a directly functionalized one.

[0139] Of course, hydrophobic polymer backbones, such as those based on PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PFA (perfluoroalkoxy polymer), FEP (fluorinated ethylene-propylene copolymer), PFSA (perfluorosulfonic acid polymer), and mixtures thereof, particularly PTFE, are also possible as polymer backbones for ion-transporting materials, such as ion-transporting polymers. In this case, ion transport occurs primarily or even exclusively, since the electrolyte can no longer penetrate into the gas diffusion electrode, and the ion-transporting material is no longer an ion exchange material.

[0140] The polymer backbone of ion transport materials, such as ion exchange materials, such as anion transport materials, such as anion exchange materials can be used to adjust the hydrophilicity / hydrophobicity of the gas diffusion electrode. In order to adjust the hydrophilicity, hydrophilic materials such as polysulfone, polyphenylsulfone, polyimide, polybenzoic acid, etc. can also be used. Azoles or polyetherketones or generally electrochemically stable polymers in electrolytes, such as polymeric "ionic liquids". All of the polymer backbones mentioned can be embedded with functional groups suitable for ion transport, which are also described below by way of example, for example by replacing the functional groups present therein with suitable leaving groups.

[0141] According to a particular embodiment, the ion transport material, for example an anion transport material, for example an anion exchange material, for example an ion exchange polymer, is an ion exchange resin, preferably a non-polar ion exchange resin, and / or at least one non-polar ion exchange resin is used as the ion exchange material in the GDE according to the invention. The use of polar ion exchange resins in the catalyst layer leads to a significant increase in the hydrophilicity of the gas diffusion electrode, thereby enabling an overall adjustment of the hydrophilicity.

[0142] When a polar ion transport material is used as a cathode in a GDE, the cathode is preferably in direct contact with the anion exchange membrane and / or anion exchange diaphragm on the side facing the anode in the electrolyzer of the present invention. A full catalyst electrode having only one ion-conducting layer is preferably used for direct contact with the anion exchange membrane and / or anion exchange diaphragm. However, it is also possible that no contact with the membrane and / or diaphragm, i.e., a gap, is provided.

[0143] Ion transport materials, such as ion exchange materials, such as anion transport materials, such as ion exchange polymers or anion exchange resins, may contain various functional groups for ion exchange, which may be the same or different, such as tertiary amine groups, alkylammonium groups and / or phosphonium groups. According to a specific embodiment, the ion transport material, such as anion exchange material, has alkyl quaternary ammonium groups ( Alkylammonium group). The alkyl group in the alkylammonium group is not particularly limited here and can be, for example, a substituted and / or unsubstituted linear and / or branched alkyl group having 1 to 40 carbon atoms, for example 1 to 20 carbon atoms, such as a substituted or unsubstituted methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl group, etc., especially a methyl group. Suitable substituents are, for example: F and Cl, preferably F; OH, etc., preferably OH and / or F. According to a specific embodiment, the ion exchange material, for example the anion exchange material, has quaternary alkylammonium groups, preferably unsubstituted tetraalkylammonium groups, especially tetramethylammonium groups, and / or dialkylethanolammonium groups, where the alkyl group is unsubstituted, such as dimethylethanolammonium groups. According to a specific embodiment, the ion exchange material, for example the anion exchange material, does not contain any trialkylethanol groups.

[0144] According to certain embodiments, the ion transport material, such as the ion exchange material, does not have imidazolium-, pyridinium- and / or beta-hydrogen-containing groups, as the chemical stability under electrolysis conditions may be insufficient.

[0145] In particular for the electrochemical reduction of CO , examples of suitable ion transport polymers, such as ion exchange polymers, include basic or strongly basic ion exchange resins of type I (with tetraalkylammonium groups) and / or type II (with dimethylethanolammonium groups). Commercially available and suitable anion exchange materials are exemplified in Table 2 below.

[0146] Table 2: Examples of suitable commercially available anion exchange materials

[0147]

[0148]

[0149] In addition to anion exchange resins, ionomers can also be used as anion transport materials, for example, anion exchange materials. These ionomers can be used, for example, in the form of dispersions during the production process. According to certain embodiments, ionomers can also be based on quaternary ammonium functional groups. Known ionomers are available, for example, from Tokuyama under the type AS 4, which is also based on quaternary ammonium functionality. Ionomers, for example, have a lower molecular weight than the resins, but are essentially chemically similar. Due to their lower molecular weight, low-molecular-weight ionomers are generally more soluble than the corresponding resins.

[0150] According to a particular embodiment, the ion transport material, in particular the anion transport material, such as the anion exchange material, such as the anion exchange resin, is at least partially fluorinated. According to a particular embodiment, the ion exchange material, in particular the anion exchange material, has fluorinated, at least partially fluorinated, such as fully fluorinated side chains.

[0151] According to a particular embodiment, the ion transport material, in particular the anion transport material, also has OH groups and / or NH 2 groups. By actively binding the CO 2 to the R—NH 2 or R—OH functional groups, the ion transport material, for example an ion exchange resin, can itself be co-catalytically active.

[0152] According to a particular embodiment, the ion transport material, preferably anion transport material, is chemically unchanged during the preparation process, for example by a mixing process and / or the presence of a metal M, for example as a catalyst. However, it can be mechanically deformed, for example into fibers.

[0153] The electrode according to the present invention is a gas diffusion electrode. There are no particular restrictions on the design of a gas diffusion electrode, provided that, as in the case of a gas diffusion electrode, three physical states (solid, liquid, and gas) can generally be brought into contact with one another, and the solid material of the electrode comprises at least one electron-conducting catalyst capable of catalyzing an electrochemical reaction between the liquid and gas phases. The gas diffusion electrode can be operated in either a flow-through or a through-flow configuration, i.e., with gas flowing through it or through it, but preferably with through-flow. It is also not excluded that the gas diffusion electrode is not completely porous, but rather has structuring, for example, micro- and / or nanostructuring, only at the surface through which the gas can diffuse.

[0154] For example, according to certain embodiments, a gas diffusion electrode (GDE) may include hydrophobic channels and / or pores or regions on the electrolyte side and optionally hydrophilic channels and / or pores or regions, wherein catalyst centers may be present in the hydrophilic regions. On the gas side of the gas diffusion electrode, this may include hydrophobic channels and / or pores. In this regard, the gas diffusion electrode may include at least two side surfaces, one side having a hydrophilic region and optionally a hydrophobic region, and one side having a hydrophobic region.

[0155] In GDEs, the most active catalyst centers reside in the liquid / solid / gas three-phase region. Therefore, an ideal GDE would have maximum penetration of the bulk material containing both hydrophilic and hydrophobic channels and / or pores to maximize the three-phase region available for active catalyst centers.

[0156] According to a particular embodiment, the electrode according to the invention, in particular as a gas diffusion electrode, comprises or consists of a metal M, an ion transport material, such as an anion transport material, and a binder.

[0157] Figure 7 The ratio between the hydrophilic and hydrophobic regions of an exemplary GDE with two layers is illustrated, which allows for a good liquid / solid / gas three-phase relationship. In this case, for example, in the electrode, on the electrolyte side E, there are hydrophobic channels or regions 1 and hydrophilic channels or regions 2, wherein in the hydrophilic region 2, there may be low-activity catalyst centers 3, which may be provided by a compound of the metal M. In addition, on the gas G side, there are inert catalyst centers 5, which are inaccessible to the electrolyte.

[0158] The particularly active catalyst centers 4 are in the liquid / solid / gas three-phase region. Therefore, an ideal GDE would have maximum penetration of the host material containing both hydrophilic and hydrophobic channels in order to obtain as much three-phase region as possible for active catalyst centers.

[0159] However, the present invention also encompasses gas diffusion electrodes having only one layer, provided that the gas diffusion electrode comprises a metal M, at least one binder, and at least one ion transport material, such as an anion transport material. In such a single-layer embodiment, hydrophilic and hydrophobic regions (e.g., pores and / or channels) can also be present in one layer, thereby creating predominantly hydrophilic and predominantly hydrophobic regions within the layer. The explanation of the catalyst centers is similar to that for the exemplary two-layer structure. The ion transport material can be present in both layers. However, the side facing the electrolyte is particularly preferred.

[0160] In the gas diffusion electrode, anions generated preferably in the GDE are advantageously transported away from the gas side and in the direction of the electrolyte via the anion transport material, while the anion transport material also prevents cations of the electrolyte from penetrating into the GDE.

[0161] According to a particular embodiment, the gas diffusion electrode has pores and / or channels with a diameter of 10 nm to 100 μm, preferably 50 nm to 50 μm, further preferably 100 nm to 10 μm, which can be determined, for example, by scanning electron microscopy, optionally after prior cutting of the GDE. + and / or M 2+ (the latter especially for Pd and / or Cu), especially M + The catalyst may also have a dendritic structure with a fine structure, for example the distance between two dendrites, having a size of 1 to 100 nm, preferably 2 to 20 nm, further preferably 3 to 10 nm.

[0162] In addition to the metal M and the ion transport material and the binder, the electrode according to the invention may also comprise further components, such as a substrate or support, to which the metal M, at least one binder, and optionally an ion transport material, such as an anion transport material, may be applied. However, in the case of a multilayer gas diffusion electrode, it is also possible for a first layer, which does not contain an ion transport material, such as an anion transport material, to be applied to the support, wherein the ion transport material, such as an anion transport material, may then be contained in the second layer, the third layer, etc.

[0163] Here, the carrier is not particularly limited and may include, for example, metals such as silver, platinum, nickel, lead, titanium, nickel, iron, manganese, copper or chromium or their alloys such as stainless steel, and / or at least one non-metal, such as carbon, Si, boron nitride (BN), boron-doped diamond, etc., and / or at least one conductive oxide, such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorine tin oxide (FTO) (for example, used for preparing a photoanode), and / or at least one polymer based on polyacetylene, polyethoxythiophene, polyaniline or polypyrrole, such as in a polymer-based electrode. A non-conductive carrier such as a polymer mesh is possible, for example, when the catalyst layer has sufficient conductivity. At a sufficient conductivity greater than 0.01 m / ohm·mm 2 and, for example, the back contact of the electrode is correspondingly solved by a titanium metal plate mesh, a polymer carrier or mesh is also possible.

[0164] However, according to a specific embodiment, the carrier may be substantially formed of a metal M, optionally having at least one binder. According to a specific embodiment, a preferred carrier is a mesh having a mesh size w of 0.3 mm < w < 2.0 mm, preferably 0.5 mm < w < 1.4 mm, and a wire diameter x of 0.05 mm < x < 0.5 mm, preferably 0.1 mm ≤ x ≤ 0.25 mm.

[0165] In addition, the first layer may also contain other promoters that improve the catalytic activity of the GDE when interacting with the metal M. According to a specific embodiment, the first layer contains at least one metal oxide, which preferably has a lower reduction potential than ethylene generation, preferably ZrO2, Al2O3, CeO2, Ce2O3, ZnO2, MgO; and / or at least one metal-rich (based on M), such as copper-rich and / or silver-rich intermetallic phases, such as a Cu-rich phase, which is selected from binary systems Cu-Al, Cu-Zr, Cu-Y, Cu-Hf, Cu-Ce, Cu-Mg and ternary systems Cu-Y-Al, Cu-Hf-Al, Cu-Zr-Al, Cu-Al-Mg, Cu-Al-Ce, where the Cu content > 60 at%, and / or the corresponding Ag-rich phase, such as Ag-Al, Ag-Zr, Ag-Y, Ag-Hf, Ag-Ce, Ag-Mg, Ag-Y-Al, Ag-Hf-Al, Ag-Zr-Al, Ag-Al-Mg, Ag-Al-Ce, where the Ag content < 60 at% (atomic percentage); and / or perovskite and / or defective perovskite and / or perovskite-related compounds containing the metal M such as silver and / or copper, such as YBa2Cu3O 7-δ 、YBa2Ag3O 7-δ where 0 ≤ δ ≤ 1 (corresponding to YBa2Cu3O 7-δ X σ )、CaCu3Ti4O12 、La 1.85 Sr 0.15 CuO 3.930 Cl 0.053 , (La, Sr)2CuO4, AgTaO3 or lithium-modified Ag 1-x Li x NbO3, etc.

[0166] Suitable promoters are also compounds of metals M, the solubility of which in water at 25° C. and standard pressure is less than 0.1 mol / L, preferably less than 0.05 mol / L, more preferably less than 0.01 mol / L, even more preferably less than 0.0001 mol / L, and particularly preferably less than 1×10 -10 mol / L, for example, less than 1×10 -20 mol / L. Such solubility of the compound of the metal M can be obtained, for example, from the product data sheet and / or can be determined in a simple manner by simple experiments and is therefore readily known to the person skilled in the art, for example by placing a fixed amount of the compound of the metal M in a specific volume of water, such as distilled water, double distilled water or triple distilled water, at 25° C. and standard pressure and measuring the concentration of ions released from the compound over time until an approximately constant value is reached.

[0167] The compound of the metal M having a solubility in water of less than 0.1 mol / L at 25° C. and standard pressure may have a metal selected from the group consisting of 1-x X, M 2-y Y, M 2-y Y′ w and M 3-z The chemical formula of Z, wherein 0≤x≤0.5; 0≤y≤1; 0≤z≤1.5; preferably 0≤x≤0.4; 0≤y≤0.8; 0≤z≤1.2; further preferably 0≤x≤0.3; 0≤y≤0.6; 0≤z≤0.9; X is selected from Cl, Br, Br3, I, I3, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example, Cl, Br, Br3, I, I3, P3 and mixtures thereof; Y is selected from S, Se, Te and mixtures thereof; Y′ is selected from S, Se, Te and mixtures thereof, for example S, Se and mixtures thereof, for example, S, Se; w≥2, preferably w≤10, for example, w≤5; and Z is selected from P, As, Sb, Bi, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example, P, As, Sb, Bi and mixtures thereof; and / or is selected from molybdates, tungstates, selenates, arsenates, vanadates, chromates, manganates, niobates of metal M, and thio and / or seleno derivatives of molybdates, tungstates, selenates, arsenates, vanadates, chromates, manganates, niobates of metal M; and / or is of formula M a Xb Y c Z d a compound of, where a ≥ 2, for example a ≥ 3; 0 ≤ b ≤ 4, for example 0 ≤ b ≤ 3, for example 0 ≤ b ≤ 2, for example 0 ≤ b ≤ 1; 0 ≤ c ≤ 8, for example 0 ≤ c ≤ 6, for example 0 ≤ c ≤ 5, for example 0 ≤ c ≤ 4, for example 0 ≤ c ≤ 3, for example 0 ≤ c ≤ 2, for example 0 ≤ c ≤ 1; 0 ≤ d ≤ 4, for example 0 ≤ d ≤ 3, for example 0 ≤ d ≤ 2, for example 0 ≤ d ≤ 1; X is selected from Cl, Br, Br3, I, I3, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example Cl, Br, Br3, I, I3, P3 and mixtures thereof; Y is selected from S, Se, Te and mixtures thereof; and Z is selected from P, As, Sb, Bi, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, where at least two of b and c are not 0 simultaneously.

[0168] Therefore, a compound of metal M with a solubility in water of less than 0.1 mol / L at 25 °C and standard pressure does not need to be stoichiometric here either and can also have a mixed phase. Also included are ternary, quaternary, etc. compounds, such as Ag3SbS3, pyrargyrite or Ag3AsS3, proustite.

[0169] According to a particular embodiment, a compound of metal M with a solubility in water of less than 0.1 mol / L at 25 °C and standard pressure is a compound of formula IaM 1-x X, where 0 ≤ x ≤ 0.5; preferably 0 ≤ x ≤ 0.4; more preferably 0 ≤ x ≤ 0.3, X is selected from Cl, Br, Br3, I, I3, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example Cl, Br, Br3, I, I3, P3 and mixtures thereof, also for example a mixture of Cl, Br, I, for example a compound of formula I'aAg 1-x X, where X = F, Cl, Br, Br3, I, I3, P3, As3, As5, As7, Sb3, Sb5, Sb7 or a mixture thereof, for example X = F, Cl, Br, Br3, I, I3, P3 or a mixture thereof, for example a mixture of Cl, Br and / or I. Some of the latter silver compounds are partially photosensitive. However, this is usually not important for operation because the electrodes in the electrolyzer are not exposed to sunlight. Also suitable are substoichiometric compounds, where 0 < x ≤ 0.5; preferably 0 < x ≤ 0.4; more preferably 0 < x ≤ 0.3; for example 0 < x ≤ 0.2; 0 < x ≤ 0.1. According to a particular embodiment, x = 0. Examples of compound Ia are for example AgCl, AgBr, AgI, AgP3, CuCl, CuBr, CuI, AuCl, AuBr, AuI.

[0170] According to a particular embodiment, a compound of metal M having a solubility in water at 25 °C and standard pressure less than 0.1 mol / L is a chalcogen-based compound having the formula Ib: M 2-y Y, or I*: M 2-y Y′ w , where 0 ≤ y ≤ 1; preferably 0 ≤ y ≤ 0.8; more preferably 0 ≤ y ≤ 0.6; Y is selected from S, Se, Te, and mixtures thereof; Y′ is selected from S, Se, Te, and mixtures thereof, such as S, Se, and mixtures thereof, such as S, Se; and w ≥ 2, preferably w ≤ 10, such as w ≤ 5, such as the formula I'b: Ag 2-y Y or I*′b: Ag 2-y Y′ w of the compound, where Y = S, Se, Te, or a mixture thereof; Y' = S, Se, Te, or a mixture thereof, such as S, Se, or a mixture thereof, such as S, Se; w ≥ 2, preferably w ≤ 10, such as w ≤ 5. Thus, polymeric or oligomeric anions Y′ of sulfur or selenium w 2- are also within the scope of the present invention. These compounds are partly semiconductive, thus ensuring an electrical coupling with the silver catalyst. Also suitable are substoichiometric compounds, where 0 < y ≤ 1; preferably 0 < y ≤ 0.8; more preferably 0 < y ≤ 0.6; such as 0 < x ≤ 0.4; 0 < x ≤ 0.2; 0 < x ≤ 0.1. According to a particular embodiment, y = 0. Examples of the compound of formula Ib are, for example, Ag2S, Ag2Se, Ag2Te, Cu2S, Cu2Se, Cu2Te, Au2S, and examples of the compound of formula I'b are, for example, Ag2(S2), Ag2(Se2), Cu2(S2), Cu2(Se2), etc.

[0171] According to a particular embodiment, a compound of metal M having a solubility in water at 25 °C and standard pressure less than 0.1 mol / L is a compound of formula Ic: M 3-z Z, where 0 ≤ z ≤ 1.5; preferably 0 ≤ z ≤ 1.2; more preferably 0 ≤ z ≤ 0.9; and Z is selected from P, As, Sb, Bi, P3, As3, As5, As7, Sb3, Sb5, Sb7, and mixtures thereof, such as, for example, the formula I′c: Ag 3-zCompounds of Z, where Z = P, As, Sb, Bi, P3, As3, As5, As7, Sb3, Sb5, Sb7 or mixtures thereof. These compounds are partly semi-conductive or metallic-conductive, thus ensuring electrical coupling with the silver catalyst. Also suitable are sub-stoichiometric compounds, where 0 < z ≤ 1.5; preferably 0 < z ≤ 1.2; more preferably 0 < z ≤ 0.9; for example 0 < x ≤ 0.6; 0 < x ≤ 0.4; 0 < x ≤ 0.2; 0 < x ≤ 0.1. According to a particular embodiment, z = 0. Examples of compounds of formula Ic are, for example, Ag3P, Ag3As, Ag3Sb, Ag3Bi, Cu3P, Cu3As, Cu3Sb, Cu3Bi.

[0172] Also included within the scope of the present invention are compounds of the following metals M with a solubility in water at 25 °C and standard pressure of less than 0.1 mol / L, which contain heavy anions such as molybdate, tungstate, arsenate, selenate, vanadate, chromate, manganate in various oxidation states, niobate or their thio- and / or seleno-derivatives. These anions can also exist in polymeric form as polyoxometalates. They are then mainly used in the form of their silver salts. Also included are inorganic compounds of metal M, such as of the formula M a X b Y c Z d , where a ≥ 2, for example a ≥ 3; 0 ≤ b ≤ 4, for example 0 ≤ b ≤ 3, for example 0 ≤ b ≤ 2, for example 0 ≤ b ≤ 1; 0 ≤ c ≤ 8, for example 0 ≤ c ≤ 6, for example 0 ≤ c ≤ 5, for example 0 ≤ c ≤ 4, for example 0 ≤ c ≤ 3, for example 0 ≤ c ≤ 2, for example 0 ≤ c ≤ 1; 0 ≤ d ≤ 4, for example 0 ≤ d ≤ 3, for example 0 ≤ d ≤ 2, for example 0 ≤ d ≤ 1; X is selected from Cl, Br, Br3, I, I3, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example Cl, Br, Br3, I, I3, P3 and mixtures thereof; Y is selected from S, Se, Te and mixtures thereof; Z is selected from P, As, Sb, Bi, P3, As3, As5, As7, Sb3, Sb5, Sb7 and mixtures thereof, for example P, As, Sb, Bi and mixtures thereof, where at least two of b and c are not simultaneously 0, for example, Ag3SbS3, pyrargyrite or Ag3AsS3, proustite.

[0173] The compounds of metal M mentioned within the scope of the present invention with a solubility in water at 25 °C and standard pressure of less than 0.1 mol / L can exist in different crystal forms, which can be distinguished in their crystal structures. In addition to the compounds described, for example, the following ternary compounds are also known: Ag3SbS3, pyrargyrite, Ag3AsS3, proustite, which can be used in the gas diffusion electrodes according to the present invention.

[0174] Preferred promoters here are compounds and / or metal oxides of metal M having a solubility in water of less than 0.1 mol / L at 25° C. and standard pressure.

[0175] According to certain embodiments, the compound and / or metal oxide of the metal M used, which has a solubility in water of less than 0.1 mol / L at 25°C and standard pressure, is water-insoluble. Therefore, aqueous electrolytes can be used in electrolysis using the gas diffusion electrode according to the present invention. Furthermore, the redox potential of the metal oxide is lower than the redox potential for ethylene production, ensuring that ethylene can be produced from CO2 using the GDE according to the present invention. According to certain embodiments, the oxide should also not be reduced during the carbon dioxide reduction. For example, nickel and iron are unsuitable because hydrogen is produced during this process. Furthermore, the metal oxide should preferably not be inert but should form a preferably hydrophilic reaction center that can be used to donate protons.

[0176] In this case, promoters, in particular promoters with a solubility in water of less than 0.1 mol / L at 25° C. and standard pressure, especially compounds and / or metal oxides of metal M, can contribute to the function and production of long-term stable electrocatalysts, since they stabilize the catalytically active metal (M) nanostructures, for example, those of Cu and / or Ag. These structural promoters can reduce the high surface mobility of the nanostructures and thus their tendency to sinter.

[0177] Promoters for the electrochemical reduction of CO2 are, in particular, the following metal oxides that cannot be reduced to metal within the electrochemical window: ZrO2 (E = -2.3V), Al2O3 (E = -2.4V), CeO2 (E = -2.3V), MgO (E = -2.5). It should be noted that the oxides mentioned are not added as additives but are part of the catalyst itself. In addition to their function as promoters, the oxides also satisfy the characteristics of stabilizing the metal M in the first oxidation state, such as Cu and / or Ag, and also intermediates in the carbon dioxide reduction process, such as CO, C2H4 (or OH).

[0178] Particularly preferred in the gas diffusion electrode of the present invention is a metal oxide-metal M catalyst structure produced as follows, wherein a metal oxide of the metal M is used in the production process.

[0179] To prepare the metal oxide of the metal M, according to a particular embodiment, the precipitation can be carried out not at pH=5.5-6.5 as generally described, but in the pH range of 8.0-8.5. Also suitable are metal oxides having the composition [M z+ 1- x M3+ x (OH)2] q+ (X n- ) q / n ·yH2O layered double hydroxides (LDH), where M 1+ =Ag + 、Li + 、Na + , K + ,M 2+ =Ca 2+ Mg 2+ 、Cu 2+ And M 3+ =Al, Y, Ti, Hf, Ga. The corresponding precursors can be precipitated by combining a metal salt solution and an alkaline carbonate solution with controlled pH. A special feature of these materials is the presence of extremely fine metal M crystallites with a size of 4-10 nm, which are structurally stabilized by the presence of metal M oxides.

[0180] The following effects can be achieved: due to the high specific surface area of ​​metal oxides, metal oxides can better distribute the catalyst metal M; metal oxides can stabilize highly dispersed metal centers; the chemical adsorption of gases such as carbon dioxide can be improved by metal oxides; metal oxides of metal M such as Cu and Ag can be stabilized.

[0181] After precipitation, drying can be carried out and then calcination can be carried out in an O2 / Ar gas stream. Depending on the method, the resulting oxide precursor can also be reduced directly in an H2 / Ar gas stream. An electrochemical activation step can also be carried out subsequently. In order to improve the conductivity of the applied layer before electrochemical activation, the oxide precursor and the activated precursor can also be partially mixed.

[0182] The present invention also does not exclude subjecting the pre-calendered electrode to a subsequent calendering / heat treatment and then to electrochemical activation.

[0183] Another possibility for the preparation of suitable electrocatalysts is to generate metal M-rich intermetallic phases such as Cu5Zr, Cu 10 Zr7、Cu 51 Zr 14 、Ag5Zr、Ag 10 Zr7、Ag 51 Zr 14These intermetallic phases can be prepared from the melt by a method of forming an ingot. The corresponding ingot can then be ground, completely or partially calcined in an O2 / Ar flow and converted into the oxide form. Exemplary phases rich in metal M are binary systems Cu-Al, Cu-Zr, Cu-Y, Cu-Hf, Cu-Ce, Cu-Mg and corresponding ternary systems, wherein the content of metal M is >60 at %: CuYAl, CuHfAl, CuZrAl, CuAlMg, CuAlCe and / or corresponding Ag-rich phases such as Ag-Al, Ag-Zr, Ag-Y, Ag-Hf, Ag-Ce, Ag-Mg, Ag-Y-Al, Ag-Hf-Al, Ag-Zr-Al, Ag-Al-Mg, Ag-Al-Ce, wherein the Ag content is <60 at %. Copper-rich phases are known, for example, from E. Kneller, Y. Khan, U. Gorres, The Alloy System Copper-Zirconium, Part I. Phase Diagram and Structural Relations, Zeitschrift für Metallkunde 77(1), pp. 43-48, 1986, Cu-Zr phase; from Braunovic, M.; Konchits, VV; Myshkin, NK: Electrical contacts, fundamentals, applications and technology; CRC Press 2007, Cu-Al phase; from Petzoldt, F.; Bergmann, JP; Schürer, R.; Schneider, 2013, 67 Metall, 504-507, Cu-Al phase; from Landolt- - Cu-Ga phase is known from Group IV Physical Chemistry Volume 5d, 1994, pages 1-8; and Cu-Hf phase is known from PR Subramanian, DELaughlin, Bulletin of Alloy Phase Diagrams, 1988, 9, 1, 51-56, which documents are cited here with respect to these phases and the contents of which are hereby incorporated by reference in this respect at least.

[0184] The proportion of the metal M, such as Cu and Ag, is preferably greater than 40 at %, further preferably greater than 50 at %, and particularly preferably greater than 60 at %.

[0185] However, it is not excluded that the intermetallic phase also contains non-metallic elements such as oxygen, nitrogen, sulfur, selenium and / or phosphorus, that is, for example, oxides, sulfides, selenides, nitrides and / or phosphides, arsenides, antimonides, bismuthides. According to a specific embodiment, the intermetallic phase is partially oxidized.

[0186] In addition, the following copper-containing perovskite structures and / or defective perovskites and / or perovskite-related compounds can be used as electrocatalysts, especially for the generation of CO or hydrocarbons: YBa2Cu3O 7-δ Where 0≤δ≤1, CaCu3Ti4O 12 , La 1.85 Sr 0.15 CuO 3.930 Cl 0.053 , (La, Sr) 2 CuO 4 , AgTaO 3 or lithium-modified Ag 1-x Li x Furthermore, it is not excluded that mixtures of these materials can be used for the electrode preparation, or, if necessary, with a subsequent calcination or activation step.

[0187] With regard to promoters and suitable metals M or metal oxides and their structures, reference is also made here to DE 102015203245.0 or DE 102015215309.6, the contents of which are hereby incorporated by reference at least in this respect.

[0188] The inventors have further discovered that a particularly active and CO- or C2H4-selective gas diffusion electrode for CO2 and / or CO electrolysis should meet multiple parameters that favor selective product formation. Inventive properties of specific embodiments of the inventive electrodes are presented below. Furthermore, the inventors have discovered that specific embodiments of the catalyst are advantageous in order to enable the electrode to selectively form products.

[0189] The specific parameters and requirements that have been found to be important for hydrocarbon-selective gas diffusion electrodes are as follows:

[0190] Accessibility of the catalyst particles to reactant gases such as CO2 and / or CO via predominantly hydrophobic pores,

[0191] predominantly hydrophilic regions that enable contact between electrolyte and catalyst particles,

[0192] Sufficiently high electrical conductivity of the electrode or catalyst and uniform potential distribution over the entire electrode area (potential-dependent product selectivity)

[0193] High chemical and mechanical stability during electrolytic operation (inhibition of cracking and corrosion)

[0194] A certain porosity with a suitable ratio between hydrophilic and hydrophobic channels or pores in direct adjacent relationship (in the presence of H + ions to ensure the availability of CO2)

[0195] Ideally, all particles involved should be part of the three-phase boundary to enable high current densities. Especially for copper, the pore system should have sufficient absorption of the intermediates to ensure further reaction or dimerization / oligomerization.

[0196] In addition, for metal M and its cationic form, especially M + The electrocatalyst has the following properties that are beneficial for electrochemical reduction, especially the electrochemical reduction of CO2 to ethylene:

[0197] Uniform particle size and high specific surface area

[0198] Dendritic morphology, without isolated centers or clusters

[0199] Metal M, such as Ag and Cu, should not exist in a pure face-centered cubic lattice but should have structural defects.

[0200] The presence of a monovalent oxide of the metal M (e.g., Cu2O for Cu, Ag2O for Ag (or PdO for Pd)) favors ethylene selectivity; the formation of higher-valent oxides should be advantageously avoided.

[0201] High purity, free of transition metal impurities and carbon components (carbon black, charcoal)

[0202] To stabilize structural defects, electrochemically stable oxides can be used

[0203] High selectivity and long-term stability

[0204] Low overvoltage relative to gas reduction such as CO2 reduction

[0205] Therefore, for CO or hydrocarbon selective gas diffusion electrodes, more intrinsic properties are required than those provided by known systems in the case of CO2 and / or CO reduction. Therefore, electrocatalyst and electrode interact closely.

[0206] According to a particular embodiment, the gas diffusion electrode of the present invention comprises:

[0207] a carrier, preferably in the form of a sheet-like structure, and

[0208] A layer comprising a metal M, an ion transport material and at least one binder, wherein the layer comprises hydrophilic and hydrophobic pores and / or channels, wherein the weight proportion of the ion transport material in the layer is preferably greater than the weight proportion of the binder.

[0209] According to a particular embodiment, the gas diffusion electrode of the invention comprises a support, preferably in the form of a sheet-like structure,

[0210] a first layer comprising a metal M, an ion exchange material and optionally at least one binder, wherein the first layer comprises hydrophilic and optionally hydrophobic pores and / or channels, and

[0211] It also includes a second layer, which comprises a metal M and at least one binder, wherein the second layer is located on the support, and the first layer is located on the second layer, wherein the binder content in the first layer is preferably less than the binder content in the second layer, wherein the second layer comprises hydrophobic pores and / or channels, further preferably, wherein the second layer comprises 3-30 wt.% binder, preferably 4-28 wt.% binder, further preferably 5-20 wt.%, for example 10-20 wt.% binder, based on the second layer, and the first layer preferably comprises 0-20 wt.% binder, further preferably 0.1-15 wt.% binder, further preferably 1-12 wt.% binder, still more preferably 5-10 wt.% binder (e.g. PTFE), and / or 0.1-40 wt.% ion transport material, preferably 1-35 wt.% ion transport material, more preferably 3-30 wt.% ion transport material, for example 10-25 wt.% ion transport material, based on the first layer. In the first and second layers, for example, according to a particular embodiment, the proportions of metal M, binder, and ion transport material can each add up to 100% by weight. This does not exclude the presence of an ion transport material in the second layer, but the second layer facing the gas side preferably does not contain an ion transport material, such as an anion transport material.

[0212] In a further aspect, the invention relates to an electrolysis cell comprising a gas diffusion electrode according to the invention.

[0213] According to a particular embodiment, the electrolytic cell of the invention further comprises an anode and at least one membrane and / or at least one separator, for example at least one anion exchange membrane, between the cathode and the anode.

[0214] Other components of the electrolytic cell such as the anode, optionally a membrane and / or a diaphragm, an inlet and outlet device (plural inlet and outlet devices), a voltage source, etc., as well as other optional devices such as cooling or heating devices are not particularly restricted according to the present invention, just as there are no restrictions on the anode electrolyte and / or cathode electrolyte used in such an electrolytic cell, wherein the electrolytic cell is used for the reduction of carbon dioxide and / or CO on the cathode side according to a specific embodiment.

[0215] Within the scope of the present invention, the design of the anode and cathode compartments is likewise not particularly restricted.

[0216] exist Figures 1 to 4A first exemplary design for an exemplary structure of a general electrolytic cell and possible anode and cathode compartments is shown in FIG. 29 .

[0217] The electrochemical reduction of, for example, CO2 and / or CO occurs in an electrolytic cell, which typically comprises an anode chamber and a cathode chamber. Figures 1 to 4 Examples of possible cell arrangements (cell arrays or cell configurations) are shown. For each of these cell arrangements, a gas diffusion electrode according to the invention can be used, for example as cathode. Figures 1 to 4 as well as Figure 29 Schematically, membranes M for separating the cathode electrolyte and the anode electrolyte are shown in FIG, but these membranes can also be supplemented or replaced, for example, by diaphragms.

[0218] For example, Figure 1 The cathode chamber II in is constructed to supply a cathode electrolyte from the bottom, wherein the cathode electrolyte leaves the cathode chamber II at the top. Alternatively, the cathode electrolyte can also be supplied from the top, for example in the case of a falling film electrode. For example, CO2 and / or CO can be supplied via a gas diffusion electrode K. At the anode A, which is electrically connected to the cathode K by means of a power supply for providing a voltage for electrolysis, oxidation of a substance supplied from the bottom, for example with an anode electrolyte, occurs in the anode chamber I, and the anode electrolyte then leaves the anode chamber together with the oxidation products. This two-chamber structure is similar to Figure 2 The difference of the three-chamber structure in is that the reaction gas such as carbon dioxide or CO can be transported to the cathode chamber II through a porous gas diffusion electrode as a cathode for reduction. Although not shown, an embodiment with a porous anode is also conceivable. Figure 1 and Figure 2 In both cases, the membrane M separates chambers I and II. Figure 3 In the PEM (proton or ion exchange membrane) structure, the porous cathode K and the porous anode A are directly adjacent to the membrane M, thereby separating the anode chamber I from the cathode chamber II. Figure 4 The structure in corresponds to Figure 2 The structure and Figure 3 A hybrid form of the structure, in which a cathode electrolyte side is provided with Figure 2 The structure shown has a gas diffusion electrode, while on the other hand, anode electrolyte side is provided as shown in FIG. Figure 3The structure shown. Of course, mixed forms or other designs of the electrode chambers shown by way of example are also conceivable. Embodiments without membranes are also conceivable. According to a specific embodiment, the cathode side electrolyte and the anode side electrolyte can therefore be identical, and the electrolytic cell / electrolytic unit can cope even without a membrane. Adequate gas separation can then be achieved, for example, by a corresponding construction of the electrolytic cell. However, it is not excluded that the electrolytic cell has a membrane and / or diaphragm or a plurality of membranes and / or diaphragms in these embodiments, for example 2, 3, 4, 5, 6 or more membranes and / or diaphragms which may be the same or different, but this is necessarily associated with additional expenditure on the membrane and the applied voltage. The cathode electrolyte and the anode electrolyte may also optionally be mixed again outside the electrolytic cell.

[0219] Figures 1 to 4 It is a schematic diagram. Figures 1 to 4 Electrolysis cells can also be combined into hybrid variants. For example, the anode compartment can be designed as Figure 3 The PEM half cell is shown, while the cathode compartment consists of Figure 1 The half-cell composition shown contains a certain volume of electrolyte between the membrane and the electrodes.

[0220] In the electrolysis cell according to the invention, a flow-by operation can also be carried out, wherein the electrolysis cell according to the invention can also have the following Figure 29 The structure shown. Figure 29 Here, CO2 can diffuse through the gas diffusion electrode and reach the cathode electrolyte.

[0221] According to a particular embodiment, when the membrane and / or diaphragm is in a porous form and includes a supply (feed) of electrolyte, the distance between the electrode and the membrane and / or diaphragm is very small or zero. The membrane and / or diaphragm can also be in a multilayer form, so that a separate supply of anolyte and cathode electrolyte can be achieved. In the case of aqueous electrolytes, the separation effect can be achieved, for example, by the hydrophobicity of the intermediate layer and / or a corresponding adjustment of the capillary forces present. When conductive groups are integrated into such a separation layer, conductivity can still be ensured. The membrane and / or diaphragm can be an ion-conducting membrane and / or an ion-conducting diaphragm, or can be a separator that only achieves mechanical separation and is permeable to cations and anions.

[0222] The electrode according to the invention is a gas diffusion electrode which can form a three-phase electrode. For example, gas can be supplied from the back to the electroactive front side of the electrode in order to realize the electrochemical reaction there. According to a specific embodiment, the gas diffusion electrode can also be supplied only from the back. That is, gases such as CO and / or CO are directed through the back side of the gas diffusion electrode relative to the electrolyte, where the gas can then penetrate the pores of the gas diffusion electrode and the products can be discharged at the back side. It has been found that, although gases such as CO do not "bubble" through the electrolyte, a similarly high Faradaic efficiency (FE) for the products is still achieved. For example, in the case of backflow, the gas flow is preferably also directed in the opposite direction to the electrolyte flow so that any liquid that may have been squeezed through can be transported away. The gap between the gas diffusion electrode and the membrane, which serves as an electrolyte reservoir, is also advantageous here.

[0223] In addition, for Figure 3 The gas diffusion electrode shown in FIG can also realize the supply of gas in another way, for example, when supplying CO 2 . By guiding a gas such as CO 2 through the electrode in a targeted manner, the reduction products can be discharged quickly.

[0224] In a particular embodiment, the electrolytic cell has a membrane and / or diaphragm that separates the cathode and anode compartments of the electrolytic cell to prevent mixing of the electrolytes. The membrane and / or diaphragm is not particularly limited herein, as long as it separates the cathode and anode compartments. More specifically, it substantially prevents gases formed at the cathode and / or anode from being transferred to the anode compartment or cathode compartment. Preferred membranes are ion exchange membranes, such as polymer-based ion exchange membranes. Preferred materials for ion exchange membranes are sulfonated tetrafluoroethylene polymers, such as For example Besides polymer membranes, it is also possible to use ceramic membranes, such as those mentioned in EP 1 685 892 A1 and / or polymers loaded with zirconium oxide, such as polysulfone.

[0225] According to a particular embodiment, at least one membrane and / or at least one diaphragm, in particular at least one anion exchange membrane (e.g. Tokuyama A201) and / or anion exchange diaphragm, is not in contact with the anode. According to a particular embodiment, at least one further membrane and / or further diaphragm, e.g. a cation exchange membrane and / or a cation exchange diaphragm, e.g. based on Membrane, wherein here preferably an electrolyte column (Elektrolytspat) is provided in between. According to a specific embodiment, the electrolytic cell of the present invention comprises 2 or more, for example 3, 4, 5, 6 or more membranes and / or diaphragms, wherein an electrolyte chamber can be arranged between the various membranes and / or diaphragms and / or membranes and / or diaphragms and the electrodes. According to a specific embodiment, the electrolytic cell of the present invention comprises at least one anion exchange membrane and / or anion exchange diaphragm and at least one cation exchange membrane and / or cation exchange diaphragm. According to a specific embodiment, the cation exchange membrane and / or cation exchange diaphragm is in direct contact with the anode. According to a specific embodiment, the anion exchange membrane and / or anion exchange diaphragm is in direct contact with the gas diffusion electrode of the present invention, which is connected as a cathode.

[0226] By using anion transport resins or ionomers, it is possible to ensure that the GDE is ionically bound to the anion exchange membrane and / or anion exchange diaphragm in a zero-gap arrangement. This step is advantageous for this mode of operation because otherwise more salt formation can be observed in the boundary layer region between the GDE and the anion exchange membrane, which can ultimately lead to complete insulation of the GDE.

[0227] Furthermore, the anode material is not particularly limited and depends primarily on the desired reaction. Exemplary anode materials include platinum or platinum alloys, palladium or palladium alloys, and glassy carbon. Other anode materials are also conductive oxides, such as doped or undoped TiO2, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), iridium oxide, etc. These catalytically active compounds can optionally also be applied only to the surface using thin film technology, for example, on titanium and / or carbon supports.

[0228] For example, it is also possible to use gas diffusion electrodes made of ion exchange materials, in particular anion exchange resins and / or ionomers. Figures 11 to 14 The operating mode is shown in , wherein, depending on the specific embodiment, a diaphragm can also be provided here instead of a membrane.

[0229] Figures 11 to 14 In principle, two cell variants for electrolysis cells are shown: all cell variants use a fully catalyst GDE having a single-layer structure, for example rolled onto a mesh, which has been prepared or impregnated with an anion exchange resin or ionomer as an anion transport material and is in direct contact with the AEM. In all cases, gaseous CO is supplied from the reverse side of the GDE without passing through it completely, which can also be considered a flow-through variant. In the cells shown, as in general in the reduction method according to the present invention, gases such as CO and / or CO can be humidified before they reach the GDE.

[0230] exist Figure 11 and12 In the variant shown in , there is a gap on the anode side formed with the anode A1 which is filled with electrolyte 45 and is designed as a dimensionally stable anode. Figure 13 and 14 In the variant shown in FIG, the anodes A1, A2 are in direct contact with the membrane M2, wherein Figure 14 The anode catalyst of the middle anode A2 is pressed directly onto the membrane M2, e.g. On a membrane (catalyst coated membrane (CCM)). Figure 13 and 14 A further feature of the variant shown in FIG is that the product gas P formed on the anode side is not contaminated by CO 2 , since bicarbonate penetrates only into the intermediate electrolyte gap and can be replaced there by H 2 . + break down.

[0231] It is advantageous in the design of the anode to avoid direct contact with the anion exchange membrane M1 due to observed stability problems. Figure 14 The CCM design in which the anode catalyst, for example an IrOx catalyst, is pressed directly into the membrane M2 is also suitable for the use of a dimensionally stable anode A1, which can consist, for example, of a titanium metal plate mesh coated with IrOx. In this case, the gap between the anode and the GDE (cathode) should advantageously be as small as possible in order to achieve the highest possible system efficiency. This distance can be ensured, for example, by a thin spacer (for example a plastic mesh, a diaphragm, etc.; not shown), which preferably has no electrical conductivity but has a high ion conductivity. Figure 13 and 14 In the variant shown in , direct bonding of the anode to the membrane is possible because the Nafion polymer of membrane M2 is stable towards IrOx.

[0232] Due to the electrophoretic separation of electrolytes, in the case of using an anion exchange membrane as membrane M1, Figure 11 and 12 In the variant shown, a more vigorous CO2 formation can be detected at the anode A1, since bicarbonate (HCO3) is initially formed at the cathode GDE (e.g. KOH + CO2 = KHCO3) and enters the anode electrolyte through the anion exchange membrane M1. - ) is unloaded here. Due to this structure, a large amount of CO2 can be formed at the anode A1 in addition to oxygen, resulting in an undesirable exhaust gas mixture and ultimately causing CO2 loss. This can be Figure 13 and 14 This is avoided in the variant shown in FIG1 by using two membranes, since the electrolyte gap in the inner portion is filled with HCO3 - The formation of CO2 can proceed according to the following reaction: HCO3- +H + =CO2+H2O. By means of a corresponding arrangement (permutation), gas separation between CO2 and O2 can be achieved, whereby CO2 can be separated and provided again for the reaction. The operating mode shown describes the diffusion operation of a gas diffusion electrode, wherein the gaseous reactant (here CO2) and the product P can be provided via the reverse side of the electrode without passing through the electrode. The gas pressure used should advantageously be selected according to the bubble point of the electrode GDE (for example, in the range of 1-50 mbar) so that no gas passes through. One advantage of this operating mode is that the conversion rate of the CO2 used is higher compared to the flow-through variant. The gas diffusion electrode described according to the present invention is particularly suitable for this cell operation.

[0233] The described fabrication technique could form the basis for larger-scale production of electrodes that, depending on the mode of operation, could achieve >200 mA / cm 2 In particular, all methods known to date for producing ethylene-selective Cu electrodes are not suitable for scalability or are not dimensionally stable, as is the case with other electrolytic cells for the reduction of CO2 and / or CO. The use of ion transport materials such as resins in the gas diffusion electrodes (GDEs) of the present invention enables catalyst-based GDEs to be used in Figures 1 to 4 11 to 14 in a cell arrangement shown in Figures 11 to 14 at high current density in a saline electrolyte for long-term stable electrolysis operation.

[0234] The anode reaction in the electrolytic cell of the present invention is by no means limited to the production of oxygen. Further examples are the formation of peroxodisulfate or the generation of chlorine. In particular, in the case of chlorine production, it is particularly important to avoid salt deposition, since, for example, NaHCO3 is a poorly soluble carbonate and forms an outlet channel for sodium ions, which are exemplary cations of the electrolyte 45. Therefore, concentrated solutions close to the saturation limit (e.g., NaHCO3: 96 g / L at 20°C; 165 g / L at 60°C; 236 g / L at 100°C) are advantageous for electrolyte conductivity and further processing. Anion transport materials, such as anion exchange materials, can prevent the intense diffusion of sodium ions into the gas diffusion electrode. This is particularly important for operation at high current densities and high operating temperatures, so that the generated anions can be more easily transported away and the increased mobility of cations, such as sodium ions, can be offset.

[0235] As Figures 1 to 4 As in the electrolytic cell shown in 29, Figures 11 to 14The electrolytic cells shown in can also be combined into hybrid variants. For example, the anode chamber can be implemented as a PEM half cell, while the cathode chamber can be composed of a half cell containing a certain electrolyte volume between the membrane M, M1, M2 and the electrode. According to a specific embodiment, when the membrane is implemented in a porous form and includes a supply of electrolyte, the distance between the electrode and the membrane M, M1, M2 is very small or zero. The membrane M, M1, M2 can also be implemented in a multilayer form, so that separate supply of the anode electrolyte or the cathode electrolyte can be achieved. The separation effect can be achieved, for example, in the case of aqueous electrolytes, for example by the hydrophobicity of the intermediate layer. When, for example, ion-conducting groups are integrated into such a separation layer, conductivity can still be ensured. The membranes M, M1, M2 can be ion-conducting membranes or separators (diaphragms) that only produce mechanical separation.

[0236] Another aspect of the present invention also relates to an electrolysis system comprising the gas diffusion electrode of the present invention or the electrolysis cell of the present invention.

[0237] Figure 5 An abstract diagram of the apparatus of a general electrolysis system is shown in FIG.

[0238] Figure 5 In the embodiment shown, an electrolysis is shown by way of example, wherein carbon dioxide is reduced on the cathode side and water is oxidized on the anode side A, although other reactions can also take place, for example on the anode side. On the anode side, according to further embodiments, chlorides can react to give chlorine, bromides to give bromine, sulfates to give peroxodisulfate (with or without gas evolution), etc. Suitable anodes A are, for example, iridium oxide or platinum on a titanium support, and suitable cathodes K are, for example, electrodes for reducing CO2, for example based on Cu. The two electrode compartments of the electrolysis cell are composed of a membrane M, for example Separated by membrane. Figure 5 The incorporation of an electrolytic cell into a system having an anolyte loop 10 and a catholyte loop 20 is schematically shown in FIG.

[0239] According to this exemplary embodiment, on the anode side, water with electrolyte additives is supplied to the electrolyte storage container 12 via the inlet 11. However, it is not excluded that water is supplied at another location of the anode electrolyte circuit 10 in addition to or instead of the inlet 11, because according to Figure 5 The electrolyte storage container 12 also serves for gas separation. Water is pumped from the electrolyte storage container 12 into the anode compartment by means of a pump 13, where it is oxidized. The product is then pumped back into the electrolyte storage container 12, where it can be discharged into the product gas container 14. The product gas can be removed from the product gas container 14 via the product gas outlet 15. Of course, the product gas can also be separated at another location, for example, in the anode compartment. This results in an anolyte circuit 10, since the electrolyte is circulated on the anode side.

[0240] On the cathode side, in the cathode electrolyte circuit 20, carbon dioxide is introduced into the electrolyte storage container 21 via the CO2 inlet 22, where the carbon dioxide is physically dissolved, for example. With the help of a pump 23, this solution is introduced into the cathode chamber, where the carbon dioxide is reduced at the cathode K. An optional further pump 24 then pumps the solution obtained at the cathode K further to a container 25 for gas separation, where the product gas can be discharged into a product gas container 26. The product gas can be taken from the product gas container 26 via the product gas outlet 27. The electrolyte is pumped back from the container for gas separation to the electrolyte storage container 21, where carbon dioxide can be added again. Here, only an exemplary arrangement of the cathode electrolyte circuit 20 is given, wherein the individual device components of the cathode electrolyte circuit 20 can also be arranged differently, for example in such a way that gas separation is already achieved in the cathode chamber. Preferably, gas separation and gas saturation are carried out separately, i.e. the electrolyte is saturated with CO2 in one of the containers and then pumped through the cathode chamber as a solution without bubbles. According to a particular embodiment, the gas leaving the cathode chamber may then consist mainly of product gas, since the CO 2 itself may remain dissolved and / or since it has been consumed and is therefore at a slightly lower concentration in the electrolyte.

[0241] The electrolysis Figure 5 This is achieved by adding current via a current source not shown.

[0242] In order to be able to control the flow of water and CO 2 dissolved in the electrolyte, valves 30 may optionally be introduced into the anolyte loop 10 and the catholyte loop 20 .

[0243] The valve 30 is shown upstream of the inlet to the electrolytic cell in the figure, but can also be arranged, for example, downstream of the outlet of the electrolytic cell and / or at other locations in the anolyte circuit or the catholyte circuit. For example, the valve 30 can also be upstream of the inlet to the electrolytic cell in the anolyte circuit, while in the catholyte circuit the valve can be located after the electrolytic cell, or vice versa.

[0244] Figure 6 An abstract diagram of an exemplary arrangement of an electrolysis system is shown in FIG.

[0245] Figure 6 The device in this case corresponds to Figure 5 An arrangement in which the carbon dioxide is not introduced into the electrolyte storage container 21 via the CO2 inlet 22, but directly via the cathode K, which is designed as a gas diffusion electrode according to the present invention. The CO2 supply can be carried out, for example, by backflow or throughflow of the gas diffusion electrode.

[0246] Figure 30 and31 A further exemplary device according to the invention is shown in FIG, which has a gas diffusion electrode with through-flow and counter-flow as the cathode, wherein the carbon dioxide is conducted in counter-flow. Figure 31 In the embodiment, a diaphragm D is also provided instead of a membrane.

[0247] Here, an arrangement with mixed anolyte and catholyte can also be realized by using corresponding electrolysis cells, as also described above by way of example.

[0248] The composition of the liquid or solution, such as the electrolyte solution, supplied to the electrolysis cell is not particularly limited and can include all possible liquids or solvents, such as water, which may optionally contain additional electrolytes such as conductive salts, ionic liquids, substances for electrolytic conversion such as carbon dioxide (which can be dissolved in water, for example), additives for improving solubility and / or wetting properties, defoaming agents, etc. Carbon dioxide can be included in the cathode electrolyte, for example.

[0249] Liquids or solvents, and optionally additional electrolytes such as conductive salts, ionic liquids, substances for electrolytic conversion, additives for improving solubility and / or wetting properties, defoamers, etc., may be present in at least one electrode compartment or in both electrode compartments. In each case, two or more of the substances mentioned or mixtures thereof may also be included. According to the present invention, these are not particularly limited and can be used on the anode side and / or the cathode side.

[0250] replace Figure 6 、 30 The construction of the electrolysis system with an electrolysis cell (comprising an anode chamber with an anode A, a membrane M and a cathode chamber with a gas diffusion electrode K) shown in FIG. 31 can also be used in the electrolysis system according to the invention, for example Figure 1-4 or Figure 11-14 The electrolytic cell shown in .

[0251] The electrolysis cell of the present invention or the electrolysis system of the present invention can be used, for example, for the electrolysis of carbon dioxide and / or CO.

[0252] In a further aspect, the present invention relates to a method for the electrolysis of CO and / or CO, wherein a gas diffusion electrode according to the invention, an electrolysis cell according to the invention, or an electrolysis system according to the invention is used. According to a particular embodiment, the method is carried out at a temperature of 40° C. or higher, for example 50° C. or higher. According to a particular embodiment, an aqueous electrolyte is used.

[0253] The electrochemical reduction of CO2 and / or CO can be carried out in an electrolytic cell, which generally consists of an anode chamber and a cathode chamber. The anode chamber and the cathode chamber are generally kept separated from each other by at least one ion-selective membrane or diaphragm. Figures 1 to 411 to 14 show examples of possible cell arrangements of electrolysis cells for the electrolysis of CO2 and / or CO according to the present invention, which are also described in detail above. Each of these cell arrangements can be used to perform the electrolysis method according to the present invention. According to specific embodiments, the electrochemical reduction of CO2 and / or CO is carried out in flow-through mode.

[0254] The invention also relates to the use of a gas diffusion electrode according to the invention or an electrolysis cell according to the invention for the electrolysis of CO 2 and / or CO.

[0255] Also disclosed is a method for preparing a gas diffusion electrode, the gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd, and mixtures and / or alloys and / or salts thereof, and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein the pores and / or channels of the gas diffusion electrode at least partially contain an ion transport material and / or an ion exchange material is at least partially applied to the surface of the gas diffusion electrode, the method comprising:

[0256] - preparing a mixture comprising at least a metal M, an ion transport material and at least one binder,

[0257] - applying a mixture comprising at least a metal M, an ion-transporting material and at least one binder to a support, preferably in the form of a sheet-like structure, and

[0258] - rolling the mixture onto a support in a dry or wet manner to form a layer; or

[0259] - preparing a first mixture comprising at least a metal M, an ion transport material and optionally at least one binder,

[0260] - preparing a second mixture comprising at least a metal M and at least one binder,

[0261] - applying a second mixture comprising at least a metal M and at least one binder to a support, preferably in the form of a sheetlike structure,

[0262] - applying a first mixture comprising at least a metal M, an ion transport material and optionally at least one binder onto the second mixture,

[0263] - optionally applying further mixtures to the first mixture, and

[0264] - rolling the second and first mixtures and, if necessary, further mixtures onto a support in a dry or wet manner to form the second layer and the first layer and, if necessary, further layers; or

[0265] - providing a gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, and

[0266] The ion transport material is at least partially introduced into the pores and / or channels of the gas diffusion electrode and / or the ion transport material is at least partially applied to the surface of the gas diffusion electrode.

[0267] This production method of the present invention can be used, in particular, to produce the gas diffusion electrode of the present invention. The corresponding features of the gas diffusion electrode of the present invention can also be applied to this production method. In particular, the weight ratios of the components can be appropriately adjusted during production based on the weight ratios in the gas diffusion electrode, and corresponding materials can be used as the metal M, ion transport material, and binder. Depending on specific embodiments, the aforementioned promoters may also be added as appropriate.

[0268] The preparation of the first and second mixtures or the first mixture is not particularly restricted here and can be carried out in a suitable manner, for example by stirring, dispersing or the like.

[0269] If a second mixture is applied, the first mixture may also contain 0% by weight of binder, i.e., be free of binder, since during rolling, binder from the second mixture may be pressed into the first layer formed from the first mixture, and thus the first layer may also have, for example, a binder content of at least 0.1% by weight, such as 0.5% by weight. However, according to certain embodiments, in the case of applying (or applying) two or more mixtures, the first mixture contains a binder.

[0270] According to a particular embodiment, the binder comprises a polymer, such as a hydrophilic and / or hydrophobic polymer, such as a hydrophobic polymer, such as PTFE. Thereby, an appropriate adjustment of the predominantly hydrophobic pores or channels can be achieved.

[0271] According to a specific embodiment, the metal M used to prepare the mixture is present in the form of particles or catalyst particles having a uniform particle size of, for example, 1-80 μm, preferably 10-50 μm, and more preferably 30-50 μm. The particle size can be determined, for example, by microscopy with the aid of image analysis, laser scattering, and / or dynamic light scattering. Furthermore, according to a specific embodiment, the catalyst particles are of high purity and free of metallic impurities. By appropriate structuring, optionally with the aid of promoters, as described above, high selectivity and long-term stability can be achieved.

[0272] By appropriately adjusting the particle size of the metal M, the ion transport material and the binder, and optionally other additives such as promoters, the pores and / or channels of the GDE, i.e., the hydrophobic and hydrophilic pores and / or channels, can be adjusted in a targeted manner to allow gases and / or electrolytes to pass through and thus be used for catalytic reactions.

[0273] The application of the first and further mixture(s) is not particularly limited and may be achieved, for example, by spreading, sieving, doctoring, or the like.

[0274] Rolling is likewise not particularly restricted and can be achieved in any suitable manner. For this purpose, the respective mixture can be moistened, for example, to a moisture content of 20% by weight or less, such as 5%, 4%, 3%, 2%, 1% by weight or less, based on the respective mixture. Depending on the embodiment, it is clearly necessary to roll the mixture or the material (granules) onto a support structure, such as a mesh structure, to ensure high mechanical stability of the electrode. This is not the case in the two-stage process; here, the pre-extruded film rests solely on the mesh.

[0275] Therefore, even when applying multiple layers, it is preferred to apply the mixtures for these layers separately to the support and then roll them together in order to achieve better adhesion between the layers.

[0276] The mechanical stress of the binder, e.g., polymer particles, achieved by the rolling process, causes the powder to crosslink due to the formation of binder channels, e.g., PTFE fibrils. Achieving this state is particularly important for ensuring the appropriate porosity or mechanical stability of the electrode. The hydrophobicity can be adjusted by the corresponding contents of the polymer and the ion transport material, e.g., ion exchange resin, or by the physical properties of the metal M or the catalyst powder, e.g., as discussed above in conjunction with the gas diffusion electrode of the present invention.

[0277] The degree of fibrillation (structural parameter ζ) of binders such as PTFE is directly related to the applied shear rate, as binders, such as polymers, behave as shear-thinning (pseudoplastic) fluids when rolled. After extrusion, the resulting layer acquires elastic properties due to fibrillation. This structural change is irreversible, so the effect cannot be subsequently enhanced by further rolling. Instead, the layer's elastic properties are damaged by further shear forces. Particularly pronounced fibrillation can disadvantageously lead to lateral curling of the electrode layer, so excessive binder content should be avoided.

[0278] Heating of the rollers during rolling may additionally assist the flow process.Preferred temperature ranges for the rollers are between room temperature, eg 20-25°C, and 200°C, eg 20-200°C, preferably 40-100°C.

[0279] According to a particular embodiment, the rolling or calendering is carried out at a roll speed of 0.3 to 3 U / min, preferably 0.5 - 2 U / min. According to a particular embodiment, the flow rate or feed rate (length of the GDE per unit time, e.g., during calendering) Q is in the range of 0.04 to 0.4 m / min, preferably 0.07 to 0.3 m / min.

[0280] For dry rolling, it is preferred that the water content during rolling is, for example, at most equal to the ambient humidity. For example, the content of water and solvent during the rolling process is less than 5 wt%, preferably less than 1 wt%, and can also be, for example, 0 wt%.

[0281] According to a particular embodiment, the carrier is a mesh, for example containing metal M, with a mesh size w of 0.3 mm < w < 2.0 mm, preferably 0.5 mm < w < 1.4 mm, and a wire diameter x of 0.05 mm < x < 0.5 mm, preferably 0.1 mm ≤ x ≤ 0.25 mm.

[0282] According to a particular embodiment, during the application process, the bulk height y of the first mixture on the carrier is in the range of 0.3 mm < y < 3.0 mm, preferably 0.5 mm ≤ y ≤ 2.0 mm. In the case of multiple layers, each layer can have a corresponding bulk height y, but the total bulk height of all layers is preferably not more than 3.0 mm, preferably not more than 2 mm, and further preferably not more than 1.5 mm.

[0283] According to a particular embodiment, the rolling is carried out by a calender. According to a particular embodiment, the method of the present invention can thus be implemented by a calendering process, as Figure 8 schematically shown and described above. The rolling process itself is characterized by the formation of a material reservoir upstream of the roll. According to a particular embodiment, the gap width H0 in rolling is from 40% to 50% of the height of the carrier + the total bulk height Hf of the mixtures of each layer, for example, if only the first mixture is used, it is the bulk height y of the first mixture, or approximately corresponds to the thickness of the mesh + a feed allowance of 0.1 - 0.2 mm. The ratio between the exit thickness H and the gap width H0 should preferably be in the range of 1.2.

[0284] According to a specific embodiment, a dry calendering method is used in the preparation method of the present invention, wherein the principle is to prepare a mixture from a binder, for example a cold-flow polymer, for example preferably PTFE, a corresponding powder of a metal M or a catalyst powder and, if necessary, a powder of an ion transport material, for example, in an intensive mixing device or on a laboratory scale using a cutting mill (IKA). The mixing procedure can, for example, be followed in the following manner: 30 seconds of grinding / mixing and a 15-second pause, for a total of 6 minutes, based on a cutting mill with a total loading of 50 g. After the mixing process, the mixed powder obtains a slightly sticky consistency. Depending on the amount of powder or the selected polymer or chain length or ion exchange material, the mixing duration can also vary until this state is reached. The resulting powder mixture can then be spread or sieved onto a carrier such as a metal mesh with a suitable bulk thickness, the carrier having, for example, a mesh size of >0.5 mm and <1.0 mm and a wire diameter of 0.1-0.25 mm. In order to prevent the powder from flowing through the mesh, the reverse side of the mesh can be sealed with a film. The produced layer can then be compacted by means of a two-roll rolling unit (calender).

[0285] The following examples illustrate specific methods for preparing a gas diffusion electrode including an anion transport material, wherein the gas diffusion electrode has a double-layer and a single-layer structure.

[0286] Preparation of a gas diffusion electrode with a double-layer structure:

[0287] To prevent the gradual overflow of the hydrophobic regions of the GDE required for gas transport, which is further enhanced by the additional mixing of the hydrophilic exchange resin, a double-layer structure can be used for GDEs with solid anion exchange resins. For this purpose, for example, a hydrophobic base layer can be prepared as the second layer on a carrier serving as a current distributor, the base layer comprising, for example, 15% by weight of PTFE and 85% by weight of a metal M such as Cu or Ag powder, to which a second layer with the corresponding exchange resin is applied. The extruded base layer should preferably have a thickness of 100-500 μm, preferably 250-400 μm. The base layer can be characterized by, for example, very high electrical conductivity, such as 7 mohm / cm, and a high porosity and hydrophobic properties, such as 50-70%. The base layer itself can be catalytically active in the region of the overlap with the catalyst layer (first layer). This base layer provides for better planar electrical connection of the electrocatalyst and, due to its high porosity, can improve the availability of gases, such as CO2. With this method, the required amount of catalyst can be reduced by 20-30 times, depending on specific embodiments. The corresponding electrocatalyst or metal M / binder such as PTFE / ion exchanger mixture can be screened onto the base layer in a subsequent step to prepare the first layer and also be calendered. The preparation can also start with the production of the catalyst layer, and then the application of the binder such as PTFE can be carried out on the reverse side of the mesh. The binder used, such as PTFE, can also be pretreated in a cutting mill if necessary to achieve fiber formation. The exemplary preparation of a gas diffusion electrode with a diffusion barrier layer based on a binder such as PTFE is based on multiple layers, which are not considered to be isolated from each other, but have as wide an overlap as possible, for example 1-20 μm, in the boundary area. The total layer thickness of the gas diffusion electrode can be in the range of 200-800 μm, for example 450-600 μm.

[0288] This double-layer structure enables the use of a hydrophilic ion transport resin in the catalyst layer without flooding of the gas transport pores.

[0289] Figure 9 , an exemplary schematic construction of a double-layer GDE is shown, wherein a hydrophobic layer 47 is applied to a carrier 44 as a current distributor, the hydrophobic layer comprising a mixture 43 of a metal M and a binder, for example, Cu and PTFE, and a hydrophilic layer 46 is applied thereon as a first layer, the hydrophilic layer comprising catalyst particles 40 of the metal M, binder particles 41 such as PTFE, and an ion exchange resin 42. An electrolyte 45 reaches the hydrophilic layer 46, while a reaction gas such as CO2 reaches the hydrophobic layer.

[0290] Preparation of gas diffusion electrodes with single-layer structure:

[0291] In the production of single-layer, catalyst-based electrodes, the content of polar ion exchange polymers should be significantly reduced in order not to adversely affect gas transport properties or prevent electrolyte overflow. Therefore, if the polar ion exchanger is a direct component of the powder mixture, it is preferred for this application to reduce the content of polar ion exchanger to a maximum of 1-20% by weight. Otherwise, the production can be carried out similarly to the production of GDEs with a double-layer structure.

[0292] The preparation method of the present invention may further comprise the following steps:

[0293] - providing a gas diffusion electrode comprising a metal M selected from Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, and

[0294] The ion transport material is at least partially introduced into the pores and / or channels of the gas diffusion electrode and / or the ion transport material is at least partially applied to the surface of the gas diffusion electrode.

[0295] Thus, existing GDEs containing a metal M and a binder such as PTFE, i.e., commercially available silver gas diffusion electrodes (oxygen-consuming cathodes or depolarized oxygen cathodes, ODCs), for example, from the field of chlor-alkali electrolysis, can also be post-treated, for example by directly impregnating them with a microemulsion composed of an ion-transport resin or ionomer, for example, in such a way that essentially only the surface or near-surface region of the electrode becomes hydrophilic. Thus, for example, existing GDEs can be modified with a potential-free diffusion barrier. In this preparation method, it is advantageous to prepare a microemulsion or microdispersion of an ion exchange material, such as an anion exchange material, in water or another suitable solvent, such as an alcohol, such as ethanol, in particular water, since this can better prevent penetration into the pore structure and adverse changes in the gas transport properties.

[0296] Figure 10 This is shown schematically, where a hydrophilic coating and / or layer 46 may be formed on a hydrophobic layer 47 by spray coating.

[0297] On a test scale, the production of gas diffusion electrodes can be achieved, for example, based on a GDL structure, such as Freudenberg C2, Sigracet 25BC. To produce the electrodes, for example, a catalyst suspension of nanoparticles and ionomers in alcohol can be used.

[0298] The above-described embodiments, designs, and extensions can be combined with one another in any manner, as long as this makes sense. Other possible designs, extensions, and embodiments of the present invention also include combinations of features of the present invention described above or described below with reference to the exemplary embodiments, which are not explicitly mentioned. More particularly, those skilled in the art will also be able to add individual aspects to the corresponding basic form of the present invention as improvements or supplements.

[0299] The present invention will be described in further detail below with reference to various embodiments thereof. However, the present invention is not limited to these embodiments. Example

[0300] Example 1: Preparation of a Single-Layer Gas Diffusion Electrode (GDE) from Powdered Cation Exchange Resin and Catalyst Powder (Comparative Example)

[0301] 1. 15 g of Amberlite IRA-900 (21.4 wt %) (chloride form; Rohm & Haas) were pulverized in an IKA A10 cutting mill for 3 minutes.

[0302] 2. A further 5 g (7.2 wt. %) of PTFE powder (Dyneon TF 1750) were added with repeated mixing cycles lasting 3 minutes.

[0303] 3. Then add 50 g (71.4% by weight) of copper powder with a particle size of 100-150 μm and mix for another 3 minutes.

[0304] 4. The mixture was sieved onto a copper mesh (L×W=10 cm×4 cm) with the help of a 0.5 mm thick template and excess material was removed with a spatula or scraper to obtain a powder layer of uniform thickness.

[0305] 5. The web with the sieved powder layer is rolled in a double-roll calender to a thickness of 500 μm. The rollers in this step are preferably heated to a temperature of 60-80°C.

[0306] Electrochemical characterization was performed using an experimental setup that essentially corresponds to the experimental setup of the electrolytic cell described above or Figure 12 Experimental setup with corresponding equipment of a flow-through cell for electrolysis.

[0307] In the flow cell, the cathode used was a corresponding gas diffusion electrode (GDE) with an active area of ​​3.3 cm 2 The carbon dioxide gas supply rate on the cathode side is 50 mL / min, and the electrolyte flow rate on both sides is 130 mL / min. The anode is iridium oxide on a titanium support with an active area of ​​10 cm 2The cathode electrolyte was a 1 M KHCO3 solution, wherein the KHCO3 concentration was 1 M, and the anode electrolyte was 1 M KHCO3, each in deionized water (18 MΩ), each in an amount of 100 mL, at a temperature of 25° C. In addition, 0.5 M K2SO4 as the cathode electrolyte and 2.5 M KOH as the anode electrolyte were also tried.

[0308] Due to the pronounced electrolyte permeability of the gas diffusion electrodes, it is not possible to ensure stable electrolysis operation.

[0309] Example 2: Preparation of a bilayer GDE with a hydrophobic base layer and a hydrophilic exchange layer having powdered cation exchange resin and catalyst powder

[0310] 42.5 g of copper powder (85% by weight) and 7.5 g of PTFE powder Dyneon TF 1750 (15% by weight) are mixed in an IKA A10 cutting mill with a hard metal mallet for 6 minutes. After mixing for 15 seconds, a pause of 15 seconds is respectively carried out. The powder mixture is sieved through a 0.5 mm thick template onto a current distributor (copper mesh with a mesh size of 0.375 mm and a wire thickness of 0.14 mm) and excess material is removed with a scraper. The mesh with the sieved powder layer is rolled on a two-roll calender to a thickness of 500 μm. Preferably, the rollers in this step are heated to a temperature of 60-80° C. In a further step, the mixture containing the ion exchange resin from Example 1 is sieved through a 0.2 mm template onto the prepared base layer and calibrated with the help of a scraper. The two layers are rolled on a two-roll calender with a gap width of 0.5 mm to obtain the electrode.

[0311] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 2 was used as cathode.

[0312] With the help of the double-layer variant, the GDE can be prevented from completely overflowing.

[0313] Example 3: Preparation of a single-layer GDE from a base layer and an ion exchange layer sprayed with a cation exchange resin suspension

[0314] 42.5 g of copper powder (85% by weight) and 7.5 g of PTFE powder Dyneon TF 1750 (15% by weight) were mixed in an IKA A 10 cutting mill with a hard metal mallet for 6 minutes. After 15 seconds of mixing, a 15-second pause was performed. The powder mixture was sieved through a 0.5 mm thick template onto a current distributor (copper mesh with a mesh size of 0.375 mm and a wire thickness of 0.14 mm), and the excess material was removed with a scraper. The mesh with the sieved powder layer was rolled on a two-roll calender to a thickness of 500 μm.

[0315] A 20 wt% microdispersion of IRA 900 ion exchange resin (see Example 1) or ionomer Tokuyama AS4 (Tokuyama) was sprayed onto the calendered gas diffusion electrode to form a thin film. A total of 10 ml was sprayed onto 40 cm².

[0316] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 3 was used as cathode.

[0317] Figure 15 The results for a pure copper GDE as a comparison electrode are shown, which was not sprayed with the corresponding dispersion, Figure 16 The results for GDE impregnated with Tokuyama AS4 are shown. Figure 17 Results are shown for GDEs impregnated with IRA 900. The figures give the Faradaic efficiency (FE) as a function of current density J. Comparison of the experimental data shows that the use of ion exchange resins or ionomers does not have any adverse effect on ethylene selectivity. In addition, at higher current densities, hydrogen formation is slightly suppressed compared to pure copper catalysts. See Figure 16 and 17 ,and Figure 15 In comparison.

[0318] Example 4: Coating a hydrophobic substrate with an acidic cation exchanger - ionomer poly(4-styrenesulfonic acid)

[0319] In a 4 mL snap-cap glass vial, 60 mg of an 18 wt% suspension of the dendritic copper catalyst and 60 mg of the cation exchanger (ionomer poly(4-styrenesulfonic acid)) in water were weighed, diluted with 2 mL of isopropanol, and the mixture homogenized in an ultrasonic bath for 15 minutes. The resulting dispersion was applied to a pre-prepared substrate (4 cm x 10 cm, 0.5 mm thick) consisting of 15 wt% PTFE and 85 wt% copper powder, with a particle size of 100-150 μm. The coating process was repeated three times, dried under an argon stream, and the electrode was dried under an argon stream for 12 hours before use. No significant change in thickness was observed.

[0320] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 4 was used as cathode.

[0321] Figure 18The results for the product selectivity achievable with this electrode as a function of current density are shown. As can be seen from the figure, the acidic ionomer promotes the formation of methane (FE = 15%). The Faradaic efficiency of the undesired H2 is approximately 45%. This indicates that the acidic ion exchanger is not very suitable for the formation of CO and hydrocarbons. Therefore, in a configuration with direct contact between the acidic Nafion membrane and the catalyst, little or no hydrocarbons or CO are usually obtained, and only hydrogen is usually formed.

[0322] Example 5: Using anion exchange resin IRA 900 (Me4N + Cl - ; Me=CH3) composed of microemulsion coating hydrophobic base

[0323] In a 4 mL snap-cap glass vial, 60 mg of dendritic copper catalyst powder and 120 mg of a 16.7 wt% microemulsion (20 g IRA 900 (see Example 1), 80 g HO, and 20 g isopropanol) were weighed, diluted with 2 mL of isopropanol, and the mixture homogenized in an ultrasonic bath for 15 minutes. The resulting dispersion was applied to a pre-prepared substrate (4 cm x 10 cm) consisting of 15 wt% PTFE and 85 wt% copper powder, with a copper particle size of 100-150 μm during preparation. The electrode was dried under an argon stream for 12 hours before use.

[0324] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 5 was used as cathode.

[0325] Figure 19 Results are shown for the product selectivity achieved with this electrode as a function of current density. As shown, the anion exchange resin suppresses hydrogen formation to approximately 20% FE. Methane formation is achieved at approximately 5% FE. As can be seen from the deviation from 100% gaseous product sum, the formation of liquid products such as ethanol and propanol is enhanced.

[0326] Example 6: Using R4N + Anion exchanger ionomer coated hydrophobic base

[0327] In a 4 mL snap-cap glass vial, 60 mg of dendritic copper catalyst powder and 120 mg of a 5 wt% dispersion (FUMA Tech AS4, n-propanol; FUMA Tech) were weighed and diluted with 2 mL of n-propanol. The mixture was homogenized in an ultrasonic bath for 15 minutes. The dispersion was applied to a pre-prepared substrate (4 cm x 10 cm) consisting of 15 wt% PTFE and 85 wt% copper powder. The copper particles had a particle size of 100-150 μm during preparation. The electrode was dried under an argon stream for 12 hours before use.

[0328] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 6 was used as cathode.

[0329] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 6 was used as cathode.

[0330] Figure 20 Results are shown regarding the product selectivity obtainable with this electrode as a function of current density. As shown, the anion exchanger ionomer suppresses hydrogen formation to a FE of approximately 10-20%. Methane formation is completely suppressed. CO formation (FE = 65-60%) is suppressed at 40-80 mA / cm 2 Similarly, compared to the higher current density (J = about 170 mA / cm 2 ) in all experiments performed under , the formation of ethylene was more selective.

[0331] Example 7: Coating a hydrophobic substrate with an acidic cation exchanger ionomer (Nafion)

[0332] In a 4 mL snap-cap glass vial, 60 mg of copper catalyst powder and 60 mg of a 20 wt% dispersion (solvent: 34 wt% water, remainder: fatty alcohol, DuPont) (Nafion, Aldrich) were weighed, diluted with 2 mL of isopropanol, and the mixture homogenized in an ultrasonic bath for 15 minutes. The prepared dispersion was applied to a pre-prepared substrate (4 cm x 10 cm) consisting of 15 wt% PTFE and 85 wt% copper powder. The copper particles had a particle size of 100-150 μm during the preparation process. The electrode was dried in an argon stream for 12 hours before use.

[0333] The cell configuration for examining the product selectivity corresponded to that from Example 1, except that a correspondingly prepared GDE from Example 7 was used as cathode.

[0334] Figure 21 Results are shown regarding the product selectivity achievable with this electrode as a function of current density. As shown, the acidic Nafion ionomer promotes the undesirable formation of hydrogen at elevated current densities with FE = approximately 40%. The formation of methane is completely suppressed. The formation of CO (FE = 45-35%) is significantly reduced at 40-80 mA / cm 2 The differences between them were observed at low current densities.

[0335] Example 8: Control experiment for CO production according to US2010 / 0251766A1

[0336] The experiment according to Example 4 of US 2016 / 0251766 A1 was performed without modification.

[0337] Figure 22 Shown at 50mA / cm 2 The Faradaic efficiency of the CO and H2 products was monitored over time at a constant current density of 1.5 Å. After 10 hours of operation, the configuration in the MEA arrangement with a catalyst-coated gas diffusion layer (silver cathode, iridium oxide anode) showed a reduction in CO production. After 10 hours, destruction of the anode was observed, as the ionomer could not withstand the oxidizing conditions and was destroyed.

[0338] Example 9: Coating of a hydrophobic substrate with an anion exchanger ionomer Tokuyama AS4 and additional use of a Tokuyama AEM 207 membrane in the case of a cell configuration with two membranes

[0339] According to Example 3, a GDE was prepared using Tokuyama AS4 as the anion exchanger ionomer.

[0340] The cell configuration used to examine the product selectivity corresponds to the cell configuration from Example 3, where the corresponding GDE has a Tokuyama AS4, except that a Tokuyama AEM 207 membrane is additionally used, which is in direct contact with the GDE. Thus, the experimental setup corresponds to Figure 13 The device shown in .

[0341] Figure 23 Results are shown regarding the product selectivity achievable with this electrode as a function of current density. As shown, the anion exchanger ionomer, Tokuyama AS4, suppresses unwanted hydrogen formation at elevated current densities. The cell configuration increases the Faradaic efficiency of ethylene by a factor of two to 30%. Methane formation is completely suppressed. CO formation (FE = 30%) is significantly reduced at 40-80 mA / cm 2 The differences between them were observed at low current densities.

[0342] The present invention relates to a method and an electrolysis system for the electrochemical utilization of carbon dioxide. Carbon dioxide (CO2) can be introduced into an electrolytic cell and reduced at the cathode side by means of a gas diffusion electrode (GDE). A GDE is a porous electrode in which a liquid phase, a solid phase, and a gas phase are present, and a conductive catalyst catalyzes the electrochemical reaction between the liquid phase and the gas phase. For the electrochemical utilization of carbon dioxide, it is preferred to use a catalyst-based gas diffusion electrode, which is similarly known from industrial-scale chlor-alkali electrolysis. The catalyst-based gas diffusion electrode can first be contacted with a liquid electrolyte, such as a salt-containing electrolyte, or directly adjacent to a diaphragm. In the latter case, the ionic bonding of the catalyst particles to the membrane is advantageous because the membrane in this operating mode can be used as a solid electrolyte. In order to achieve ionic conductivity, the ion transport material of the present invention is integrated into the gas diffusion electrode, and the ion transport material preferably has a functional group such as a quaternary ammonium group, thereby acting as an anion transporter.

[0343] The introduction of powdered ion transport materials, such as exchange resins, such as anion exchange materials, into catalyst-based gas diffusion electrodes is a novel approach for broadening the process window for the electrochemical reduction of CO2 and / or CO. Due to the reduced generation of hydrogen, this variant provides, in particular, a current of more than >150 mA / cm 2 The method offers the advantage of lower current density. For example, increased Faradaic efficiency for CO or ethylene can be achieved. The method also offers the possibility of increasing the ionic conductivity of the gas diffusion electrode, thereby reducing the generation of concentration gradients. Furthermore, the method offers the possibility of using catalyst-based gas diffusion electrodes within membrane-electrode structures, particularly within MEA (membrane electrode assembly) structures.

[0344] According to the present invention, a dimensionally stable gas diffusion electrode based on a catalyst powder can be produced, which can be used in industrial-scale electrolyzer applications within the scope of electrochemical CO₂ production and can improve the long-term stability of electrolysis operation. The use of ion transport materials, such as anion transport materials, particularly anion exchange resins, in the gas diffusion electrode provides a low-energy route for the removal of generated hydroxide and bicarbonate ions, while simultaneously preventing the inward diffusion of mobile cations from the electrolyte due to the positively charged polymer backbone structure.

Claims

1. An electrolysis cell comprising a gas diffusion electrode as cathode, the gas diffusion electrode comprising a metal M selected from the group consisting of Ag, Au, Cu, Pd and mixtures and / or alloys and / or salts thereof, and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein ion exchange material is at least partially contained in the pores and / or channels of the gas diffusion electrode, wherein the ion exchange material is an anion exchange material, wherein the anion exchange material does not have imidazolium-containing, pyridinium-containing and β-hydrogen-containing groups.

2. The electrolytic cell of claim 1 , wherein the ion exchange material is an ion exchange resin.

3. The electrolytic cell of claim 1 , wherein the ion exchange material is at least partially applied to the surface of the gas diffusion electrode.

4. The electrolytic cell of claim 1 , wherein the anion exchange material is stable at a pH greater than 7.

5. The electrolytic cell of claim 1 , wherein the anion exchange material has alkyl quaternary ammonium groups.

6. The electrolytic cell of claim 3, wherein the anion exchange material is at least partially fluorinated.

7. The electrolytic cell of claim 3, wherein the anion exchange material further comprises OH groups and / or NH2 groups.

8. The electrolytic cell according to any one of claims 1 to 7, comprising carrier, and A layer comprising a metal M, an ion exchange material and at least one binder, wherein the layer comprises hydrophilic and hydrophobic pores and / or channels.

9. The electrolytic cell of claim 8, wherein the weight proportion of the ion exchange material in the layer is greater than the weight proportion of the binder.

10. The electrolytic cell of claim 8, wherein the support is in the form of a sheet-like structure.

11. The electrolytic cell according to any one of claims 1 to 7, comprising carrier, and a first layer comprising a metal M, an ion exchange material and at least one binder, wherein said first layer comprises hydrophilic and hydrophobic pores and / or channels, Further comprising a second layer comprising a metal M and at least one binder, wherein the second layer is located on a support, and the first layer is located on the second layer, wherein the second layer comprises hydrophobic pores and / or channels.

12. The electrolytic cell of claim 11, wherein the binder content in the first layer is less than the binder content in the second layer.

13. The electrolytic cell of claim 11, wherein the second layer comprises 3 to 30 wt% binder, based on the second layer.

14. The electrolytic cell of claim 11, wherein the second layer comprises 10-30 wt% binder, based on the second layer.

15. The electrolytic cell of claim 11, wherein the second layer comprises 10-20 wt% binder, based on the second layer.

16. The electrolytic cell of claim 11, wherein the first layer comprises 0-10 wt% binder, based on the first layer.

17. The electrolytic cell of claim 11, wherein the first layer comprises 0.1 to 10 weight percent binder, based on the first layer.

18. The electrolytic cell of claim 11, wherein the first layer comprises 1 to 7 weight percent binder, based on the first layer.

19. The electrolytic cell of claim 11, wherein the first layer comprises 3-7 wt% binder, based on the first layer.

20. The electrolytic cell of claim 11, wherein the support is in the form of a sheet-like structure.

21. The electrolytic cell of claim 1 further comprising an anode and at least one membrane and / or at least one separator between the cathode and the anode.

22. The electrolytic cell of claim 1 further comprising an anode and at least one anion exchange membrane and / or anion exchange diaphragm between the cathode and the anode.

23. The electrolytic cell of claim 21 , wherein at least one membrane and / or one diaphragm is not in contact with the anode.

24. The electrolytic cell of claim 22, wherein the anion exchange membrane and / or anion exchange diaphragm is not in contact with the anode.

25. The electrolytic cell of claim 24, wherein at least one further membrane and / or further diaphragm is provided between the anion exchange membrane and / or the anion exchange diaphragm and the anode.

26. Method for the electrolysis of CO2 and / or CO, wherein an electrolysis cell according to any one of claims 1 to 25 is used.

27. Use of the electrolysis cell according to any one of claims 1 to 25 for the electrolysis of CO2 and / or CO.

28. A method for producing a gas diffusion electrode comprising a metal M selected from the group consisting of Ag, Au, Cu, Pd, and mixtures and / or alloys and / or salts thereof, and at least one binder, wherein the gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, wherein an ion exchange material is at least partially contained in the pores and / or channels of the gas diffusion electrode, wherein the ion exchange material is an anion exchange material, wherein the anion exchange material does not have imidazolium-containing, pyridinium-containing, and β-hydrogen-containing groups, the method comprising: - preparing a mixture comprising at least a metal M, an ion exchange material and at least one binder, - applying a mixture comprising at least a metal M, an ion exchange material and at least one binder to a support, and - rolling the mixture onto a support in a dry or wet manner to form a layer; or - preparing a first mixture comprising at least a metal M, an ion exchange material and at least one binder, - preparing a second mixture comprising at least a metal M and at least one binder, - applying a second mixture comprising at least a metal M and at least one binder to the support, - applying a first mixture comprising at least a metal M, an ion exchange material and at least one binder to the second mixture, and - rolling the second mixture and the first mixture onto a support in a dry or wet manner to form the second layer and the first layer; or - providing a gas diffusion electrode comprising said metal M and said at least one binder, wherein said gas diffusion electrode comprises hydrophilic and hydrophobic pores and / or channels, and - at least partially introducing the ion exchange material into the pores and / or channels of the gas diffusion electrode.

29. The method of claim 28, wherein: After applying the first mixture comprising at least the metal M, the ion exchange material and the at least one binder to the second mixture, the method further comprises: - applying the additional mixture to the first mixture, and - rolling the second mixture and the first mixture and the further mixture onto a support in a dry or wet manner to form the second layer and the first layer and the further layer.

30. The method of claim 28, wherein The carrier is a carrier in the form of a sheet-like structure.

31. An electrolysis system comprising the electrolysis cell according to any one of claims 1 to 27.

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