Gas diffusion electrode and use thereof

Abstract

The invention relates to a gas diffusion electrode and to a method for the production thereof.

Description

[0001] Gas diffusion electrode and its use

[0002] The present invention relates to the technical field of electrolysis, in particular the electrochemical reduction of carbon dioxide.

[0003] In particular, the present invention relates to a gas diffusion electrode, preferably for the electrochemical reduction of carbon dioxide, and its use.

[0004] Furthermore, the present invention relates to a method for producing an aforementioned gas diffusion electrode and an electrolysis cell for the electrochemical reduction of carbon dioxide.

[0005] By means of electrochemical reduction in an aqueous environment, valuable chemical raw products such as carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids can be obtained from carbon dioxide.

[0006] In addition to the extraction of valuable raw materials, the electrochemical reduction of carbon dioxide also has the advantage that the greenhouse gas CO2 can be removed from the environment or, for example, collected and further processed after combustion or industrial processes, thus preventing it from entering the environment in the first place. With the expansion of renewable energy and the associated carbon dioxide-neutral energy production, the electrolysis of carbon dioxide is expected to gain in importance, particularly since it enables both the extraction of valuable raw materials for the chemical industry and the saving of fossil fuels.

[0007] Currently, single-layer polymer-containing catalyst layers (Catalyst Layer, CL), single-layer ionomer-containing catalyst layers (Catalyst Layer, CL) and single-layer polymer- and ionomer-containing catalyst layers (Catalyst Layer, CL) are used in electrolyzers for CCh reduction and CO reduction.

[0008] In electrodes with polymer-containing CLs, the catalyst mass is bonded to a porous gas diffusion layer (GDL) or porous transport layer (PTL) using a polymer. For this purpose, a mixture of catalyst and a polymer binder is typically applied to a porous GDL or PTL using a wet manufacturing process, such as spraying. Other manufacturing processes include hot pressing or doctor blade coating for the application of dry powder mixtures.

[0009] Fluoropolymers such as polytetrafluoroethylene (PTFE) are often used for the catalyst layer because their hydrophobic properties can reduce the flooding of the electrode pores with excess water and the associated CCh mass transport problems. This is particularly relevant in processes with gaseous reactants. Examples of the use of such fluoropolymer-based catalyst layers include CCh electrolysis and CO electrolysis, fuel cell technology, and chlor-alkali electrolysis.

[0010] In the field of CCh electrolysis, single-layer polymer-containing catalyst layers (CL) have so far been used primarily in gas-liquid electrolyzers, as they can slow down the unwanted penetration of liquid electrolyte into the gas diffusion electrode (GDE) and reduce the associated limitations of CCh mass transport.

[0011] It has been shown that appropriate hydrophobicity in the catalyst layer is key to selective CO2 reduction. By applying a catalyst-free ionomer-containing top layer, the ionic conductivity and surface wetting of a catalyst layer in a gas-liquid electrolyzer can be increased, thus increasing the product selectivity for CO2 reduction under industrial current densities (Junge Puring K, Siegmund D, Timm J, et al. Electrochemical CO2 Reduction: Tailoring Catalyst Layers in Gas Diffusion Electrodes. Adv. Sustainable Syst. 2021 ; 5(1 ): 2000088).

[0012] Furthermore, it has been shown that the catalyst layer represents the first protective layer against flooding of the electrode, and that the long-term stability of the electrode can be significantly improved by appropriate hydrophobicity of the binder (Nwabara UO, Hernandez AD, Henckel DA, et al. Binder-Focused Approaches to Improve the Stability of Cathodes for CO2 Electroreduction. ACS Appl. Energy Mater. 2021 ; 4(5): 5175-86). However, the use of such electrodes in gas-liquid electrolyzers is not very economical, as the limited electrolyte conductivity results in high energy requirements for the electrochemical process. Likewise, the use in typically very alkaline electrolytes, which are preferred for CCh reduction, is disadvantageous, as neutralization and carbonate formation occur due to the reaction of the hydroxides with the gaseous CO2.Carbonate formation, in particular, leads to a constant hydrophilization of the gas diffusion electrode and thus to electrowetting and flooding of the electrode. Electrolysis times > 10 h at industrial current densities of > 300 mA cur are rarely possible. 2 can be achieved.

[0013] Even in zero-gap electrolyzers, i.e., electrolyzers in which the catalyst layer is in direct contact with a solid polymer electrolyte made of an ion-conducting polymer, excess water can accumulate in the pores of the cathode-side gas diffusion electrode, despite the absence of a liquid electrolyte at the cathode. Therefore, the use of hydrophobic polymer-containing catalyst layers can also help minimize flooding processes here.

[0014] To date, hydrophobic polymer-containing catalyst layers have only been used sporadically for CO2 reduction in zero-gap electrolyzers. It has been shown that flooding behavior decreases with increasing PTFE content in the polymer-containing catalyst layer, and the use of thin membranes, usually less than 40 pm, is advantageous. The achieved partial current densities of less than 100 mA cm -2 and electrolysis times of 25 minutes at a cell voltage of 3 V are, however, still far from industrially relevant results with partial current densities greater than or equal to 300 mAcm -2 over electrolysis durations > 10 h (Reyes A, Jansonius RP, Mowbray BAW, et al. Managing Hydration at the Cathode Enables Efficient CO 2 Electrolysis at Commercially Relevant Current Densities. ACS Energy Lett. 2020; 5(5): 1612-8)

[0015] A disadvantage of using hydrophobic polymer-containing catalyst layers in the field of CO2 reduction in gas-liquid electrolyzers and zero-gap electrolyzers is the lack of ionic conductivity at the catalyst. Ionomer coating layers could represent an approach to improving these systems; however, the application of the low-viscosity ionomer within the polymer-containing catalyst layer can lead to the closure of pores or inhomogeneities, which can lead to

[0016] lead to mass transport limitations.

[0017] Furthermore, the ionomer capping layer itself does not contain a catalyst and is therefore neither catalytically active nor electrically conductive, which is why inactive regions may occur in the hydrophobic polymer-containing catalyst layers. Currently used single-layer, hydrophobic polymer-containing catalyst layers and single-layer, hydrophobic polymer-containing catalyst layers with an ionomer capping layer are not suitable for achieving industrially relevant current densities of > 300 mA cm -2 suitable for cell voltages of < 3 V and electrolysis times > 10 h.

[0018] In contrast to single-layer polymer-containing catalyst layers, ionically conductive single-layer ionomer-containing catalyst layers can achieve significantly lower cell voltages at higher partial current densities and electrolysis times. They represent the state of the art for CCh reduction in zero-gap electrolyzers. To produce an ionomer-containing gas diffusion electrode, a catalyst ink is typically applied to a porous and electrically conductive gas diffusion layer (GDL) using a wet manufacturing process such as spraying. Other manufacturing processes include doctor blade coating. The ionomer in the catalyst layer enables good ionic contact between the catalyst layer and the liquid electrolyte in gas-liquid electrolyzers or the solid electrolyte membrane (SPE membrane) in zero-gap electrolyzers.

[0019] In the field of CCh reduction, significantly lower cell voltages and longer electrolysis times are currently achieved at industrial current densities in zero-gap electrolyzers than with the previously described polymer-containing catalyst layers. For example, in zero-gap electrolyzers with an anion-conducting single-layer ionomer-containing catalyst layer in combination with an anion exchange membrane (AEM), electrolysis times of > 200 h have already been achieved at cell voltages of < 3 V and industrially relevant current densities of > 300 mA cm. -2 can be achieved.

[0020] By using an ionomer with poly(arylpiperidinium) groups (Piperion) in a solid electrolyte membrane (SPE membrane) and the catalyst layer, partial current densities for the target product carbon monoxide of up to 420 mA cirr could be achieved, for example, in a zero-gap electrolyzer. 2over 200 h at 3.2 V (Endrödi B, Samu A, Kecsenovity E, Halmägyi T, Sebök D, Janäky C. Operando cathode activation with alkali metal cations for high current density operation of water-fed zero-gap carbon dioxide electrolyzers. Nat Energy 2021 ; 6(4): 439-48).

[0021] Using a solid electrolyte membrane (SPE membrane) and a catalyst layer (CL) containing an ionomer based on imidazolium groups (Sustainion), current densities of 400 mA cm -2 at a cell voltage (Uzeiie) of approximately 3.2 V over an electrolysis time of > 70 h. (Liu Z, Yang H, Kutz R, Masel RI. CO 2 Electrolysis to CO and O 2 at High Selectivity, Stability and Efficiency Using Sustainion Membranes. J. Electrochem. Soc. 2018; 165(15): J3371-J3377).

[0022] In addition to these results, further investigations were carried out with ionomer-containing catalyst layers under industrial current densities in zero-gap electrolyzers. However, these could not achieve electrolysis times exceeding 70 h at current densities > 300 mA cm -2and cell voltages of < 3.2 V. Among other things, it was demonstrated that promising results can be achieved in addition to the use of an AEM with a PEM if an anion-conducting ionomer is used in the catalyst layer of the cathode, thus creating a bipolar boundary layer. This design appears advantageous over the use of a bipolar membrane, as significantly lower cell voltages can be achieved while still hindering the transfer of CO2 from the anode to the cathode in the form of carbonate ions (Patru A, Schmidt T-J, Binninger T, Pribyl B, inventors. Co-Electrolysis Cell Design for Efficient CO2 Reduction from Gas Phase at Low Temperature. 2017 Jul 24).

[0023] In addition to their use in zero-gap electrolyzers, ionomer-containing catalyst layers are also used in gas-liquid electrolyzers. However, these systems are limited in their electrolysis duration due to the severe flooding described above. In one publication, in contrast to the majority of publications, a porous polymer film was used as the gas diffusion layer (GDL) instead of a porous hydrophobic carbon fabric. The catalyst was applied to the porous polymer film using a PVD process, and then bonded by spraying on an ionomer. An electrolysis time of > 60 h at a current density of 1 A cm-2 with an FEC2H4 of > 50 % could be achieved (Garcia de Arquer FP, Dinh CT, Özden A, et al. CO2 electrolysis to multicarbon products at activities greater than 1 A cm-2. Science 2020; 367(6478): 661-6).Ionomer-containing catalyst layers have so far been used for CO2 reduction at industrial current densities of > 300 mA cm. -2limited to electrolysis times of 60 h in gas-liquid electrolyzers and to electrolysis times of 2000 h in zero-gap electrolyzers, whereby a reciprocal-proportional correlation between electrolysis time and current density is generally observed. This lack of long-term stability of the catalyst layer is due to the insufficient hydrophobicity of the catalyst layer. While in polymer-containing catalyst layers, hydrophobicity is possible through the selection of the proportion and type of polymer used and the adjustment of pore formation through sintering processes, this is not possible with the ionomer-containing CLs currently used. Because the ionomer-containing catalyst layers do not have sufficient hydrophobicity to slow down flooding of the gas diffusion electrode, they depend on a highly hydrophobic gas diffusion layer (GDL).

[0024] In addition to the use of single-layer polymer-containing catalyst layers and single-layer ionomer-containing catalyst layers, single-layer polymer- and ionomer-containing catalyst layers were also used to combine the properties of both binder types in a single catalyst layer. However, when investigating various single-layer catalyst layers containing both hydrophobic polymer and hydrophilic ionomer in zero-gap electrolyzers, no improvement in flooding behavior or achievable electrolysis time could be observed compared to hydrophobic, purely polymer-containing, or purely ionomer-containing catalyst layers. This is because the bulk hydrophobicity is reduced by the ionomer content, and the ionic conductivity to the SPE membrane is reduced by the polymer content.

[0025] In fuel cell technology, electrodes with several different catalyst layers are used to improve water management at the corresponding electrode. On the one hand, multilayered ionomer-containing catalyst layers (CL) are used to achieve a gradient in ionic conductivity or porosity. Furthermore, multilayer structures with a hydrophobic and hydrophilic catalyst layer are already in use. For example, such a structure is used to improve catalyst utilization in methanol fuel cells, as disclosed in DE 601 33 879 T2, and in PEM fuel cells, as specified, for example, in CN 100521313 C. In general, the water content of the catalyst should be adjusted and sufficient mass transport of gaseous species should be ensured, thereby enabling higher power densities and long-term stability to be achieved.However, the hydrophobic catalyst layers according to CN 100521313 C always contain a proportion of ionomer, which results in good ionic conductivity but ultimately leads to flooding of the electrode. The same applies to multilayer structures according to DE 601 33 879 T2.

[0026] Similar to fuel cell technology, water management at the cathode is also crucial in the field of electrochemical CCh reduction. The multilayer catalyst layers developed in the field of fuel cell technology cannot be used directly for CCh reduction, as CCh reduction is significantly more complex. While in a PEM fuel cell, the goal is to achieve mass transport of gaseous reactants with sufficient ionic conductivity provided by the water, a multitude of influences must be considered in CCh reduction. In CCh reduction, two reactants, CO2 and water, must be provided at the catalyst layer (CL) of the cathode, the parasitic hydrogen evolution reaction (HER) must be suppressed, and the desired product must be obtained. This depends primarily on the direct catalyst environment.In addition to adjusting the water content through the hydrophobicity of the layers, the local pH, porosity, and catalyst availability can also be adapted for the respective CCh reduction process. A corresponding multilayer catalyst layer has not yet been developed and optimized for CCh reduction. Since the formation of carbonate in the catalyst layer (CL) and gas diffusion layer (GDL) plays no role in fuel cell technology, it is also necessary to develop suitable catalyst layers to suppress carbonate formation for CO reduction. xElectrolysis. Accordingly, currently used multilayer catalyst layers in fuel cells are not suitable for the requirements of electrolyzers for CO2 reduction, even though the goal of water management in fuel cells and CO2 reduction in zero-gap electrolyzers is similar. It is therefore an object of the present invention to avoid or at least mitigate the previously described disadvantages associated with the prior art.

[0027] In particular, it is an object of the present invention to provide an electrode, in particular a gas diffusion electrode, which can be operated continuously at industrial current intensities and with high current efficiencies and is particularly suitable for the reduction of CO2.

[0028] The subject matter of the present invention according to a first aspect of the present invention is thus an electrode according to claim 1; further advantageous embodiments of this aspect of the invention are the subject matter of the relevant subclaims.

[0029] A further subject matter of the present invention according to a second aspect of the present invention is the use of an electrode according to the invention according to claim 12.

[0030] Yet another subject matter of the present invention according to a third aspect of the present invention is the use of an electrode according to the invention according to claim 13.

[0031] A further subject matter of the present invention according to a fourth aspect of the present invention is a method for producing an electrode according to the invention according to claim 14; further advantageous embodiments of this aspect of the invention are the subject matter of the relevant subclaims.

[0032] Finally, according to a fifth aspect of the present invention, a further subject matter of the present invention is an electrolysis cell for the electrochemical reduction of carbon dioxide according to claim 17.

[0033] It goes without saying that special features, characteristics, configurations and embodiments as well as advantages or the like, which are explained below only with regard to one aspect of the invention in order to avoid unnecessary repetition, naturally apply accordingly to the remaining aspects of the invention without this requiring express mention. Furthermore, all values ​​or parameter specifications or the like mentioned below can generally be determined using standardized or explicitly stated determination procedures or using determination methods that are familiar to the person skilled in the art. Furthermore, it goes without saying that all weight- or quantity-related percentages are interpreted by the person skilled in the art in such a way that the total amounts to 100%.

[0034] With that in mind, the present invention will be described in more detail below.

[0035] The present invention - according to a first aspect of the present invention - relates to a gas diffusion electrode, in particular for the electrochemical reduction of CO2, wherein the electrode has at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer.

[0036] As the applicant has surprisingly discovered, the use of a gas diffusion electrode comprising a hydrophobic catalyst layer and a hydrophilic catalyst layer allows the main problems of previously used gas diffusion electrodes to be avoided. In particular, the disadvantage of hydrophilic ionomer-containing catalyst layers, namely gradual flooding of the cathode compartment and thus a deterioration in mass transfer and ultimately an interruption of electrolysis, can be avoided. At the same time, the disadvantages of a purely hydrophobic polymer-containing catalyst layer, namely low mass conversion and low usable current densities, can also be circumvented.

[0037] Within the scope of the present invention, it is usually provided that a hydrophobic catalyst layer (CL) is first applied to a commercially available gas diffusion layer (GDL) or a porous support material (PTL), followed by a hydrophilic catalyst layer (CL). At the phase boundary between electrode and substrate, in particular in the region of the interface between the hydrophobic and hydrophilic catalyst layer, an effective reduction of the substrate, in particular of carbon dioxide, can be achieved. An effective reduction of the substrate is achieved in particular by there being no three-phase boundary between electrode, electrolyte and substrate, but rather by the substrate, i.e. carbon dioxide, not being passed through an aqueous phase at the interface between the hydrophilic and hydrophobic catalyst layer, but rather being merely moistened.By using a hydrophobic and a hydrophilic catalyst layer, the electrode is not flooded with liquid water, but is only moist enough to allow the electrochemical reduction of carbon dioxide to occur. The use of a hydrophilic catalyst layer also enables the rapid transport of formed ions.

[0038] As an alternative to the electrode fabrication described above, a hydrophilic catalyst layer can be first applied to an ion-conducting membrane, followed by a hydrophobic catalyst layer. The assembly, including the hydrophobic catalyst layer, is then applied to a gas diffusion layer.

[0039] The multilayer structure of a gas diffusion electrode described in the present invention, comprising several catalyst layers with at least one hydrophobic, in particular polymer-containing, catalyst layer and at least one hydrophilic, in particular ionomer-containing, catalyst layer, allows the physical properties of the electrode to be tailored to the CCh reduction and the respective process conditions. In addition to gas, ion, and electron transport, the wettability and ion transport at the phase boundaries between the electrode and substrate, on the one hand, and between the electrode and electrolyte, on the other, can also be adjusted independently.

[0040] The hydrophobic, particularly polymer-containing, CL can improve the binding to the GDL, the pore distribution, and the bulk hydrophobicity, as well as reduce the costs of the CL. The hydrophilic, particularly ionomer-containing, CL can lower the cell voltage due to the improved ionic conductivity, and the local pH value at the catalyst can be adjusted appropriately for CO2 reduction. Further advantages arise from the multilayer structure with at least two catalyst layers: Since the active zone in a gas diffusion electrode is not a two-dimensional plane, but a three-dimensional zone with a certain depth perpendicular to the plane, the area in the catalyst layer with active catalyst mass can be increased by providing catalyst on both sides at the phase boundaries and ensuring continuous electrical conductivity.Furthermore, the use of a hydrophilic catalyst layer and a hydrophobic catalyst layer enables a synergistic combination of the properties of the different catalyst layers. The hydrophobic catalyst layer prevents the electrode from flooding with water, while the hydrophilic layer enables the rapid transport of resulting ions to the membrane. The combination of both properties enables significantly more efficient electrochemical reduction of carbon dioxide with higher current densities, greater yields, and extended operating times.

[0041] In the context of the present invention, a hydrophobic catalyst layer is understood to mean a catalyst layer whose material has a contact angle with water of at least 90°, preferably at least 120°, more preferably at least 140°, particularly preferably at least 160°.

[0042] In the context of the present invention, a hydrophilic catalyst layer is understood to mean a catalyst layer whose material has a contact angle with water of less than 90°, preferably less than 50°, more preferably less than 40°, particularly preferably less than 30°.

[0043] The contact angle can be determined, for example, by static contact angle measurement using optical methods.

[0044] For the purposes of the present invention, an ionomer is understood to be a copolymer of electrically neutral repeating units and repeating units with ionic functional groups. Typically, the proportion of ionic repeating units is no more than 15 mol%, based on the polymer. The ionic groups are often carboxylic acid functions or carboxylates or sulfonic acid groups or sulfonates. Ionomers generally exhibit high ionic conductivity but no electrical conductivity and are often used as solid electrolytes in electrolysis cells or as ion-conductive, particularly proton-conductive, membranes.

[0045] Particularly important within the scope of the present invention is that both the hydrophilic catalyst layer and the hydrophobic catalyst layer each contain a certain proportion of catalyst for the electrochemical reaction, in particular reduction. Only in this way can the outstanding, improved properties of the electrode according to the invention be achieved. The use of a hydrophobic layer without catalyst with a hydrophilic catalyst layer applied thereon, or a hydrophobic catalyst layer and a hydrophilic layer without catalyst applied thereon, does not lead to the improved properties. Even the mixed layers with hydrophilic and hydrophobic regions sometimes used in the prior art are not comparable in performance to the systems according to the invention.Only electrodes with a hydrophobic catalyst layer and a hydrophilic catalyst layer lead to an increase in the area with active catalyst mass without the risk of the electrode being flooded.

[0046] Furthermore, the electrode according to the invention differs from electrodes used in the field of fuel cell technology with hydrophobic and hydrophilic catalyst layers in that the binding agent used in the present invention, ie the binder, for the hydrophobic layer does not contain an ionomer.

[0047] The multilayer structure according to the invention with at least one hydrophobic, in particular polymer-containing catalyst layer and at least one hydrophilic, in particular ionomer-containing catalyst layer enables higher current efficiencies, lower cell voltages, higher energy efficiencies, and improved long-term stability, at least by a factor of 10, to be achieved compared to conventional single-layer polymer-containing catalyst layers (CL), single-layer ionomer-containing catalyst layers (CL), and single-layer polymer- and ionomer-containing catalyst layers (CL). Thus, in the case of CO2 reduction, the system according to the invention can achieve an increase in current efficiency of up to 16% at a cell voltage (Uzeiie) of approximately 100 mV and an improvement in long-term stability by at least a factor of 10. In addition, the amount of ionomer used can be greatly reduced, preferably by approximately20%, thus achieving a corresponding reduction in material costs.

[0048] For use in the field of CO2 reduction, CO reduction, or other electrochemical processes, the multilayer structure according to the invention comprising at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer is preferably applied to a commercially available GDL or PTL. The coating compositions can be applied by dry or wet coating methods, such as spraying, knife coating, drop-coating, printing, or a combination of these methods. The catalyst layers can be applied to a porous carrier layer (catalyst-coated substrate) or to an ion-conducting membrane (catalyst-coated membrane), although a combination of both methods is also possible. The catalyst is typically bound to the corresponding structure by a suitable binder, for example, a hydrophobic polymer or an ionomer.The properties of the structure with multiple catalyst layers can be further adjusted by adjusting the catalyst types, binder types, binder and catalyst content, as well as the catalyst loading in the respective layers.

[0049] Hydrophilic polymers, in particular ionomers and resins with or without ion-exchanging groups and hydrophobic polymers have proven to be particularly suitable binders in the above sense.

[0050] The gas diffusion electrode according to the invention is ideally suited for use in the electrochemical processes already mentioned. Typically, the electrode functions as a cathode for the reduction of CO2, CO, N2, or O2, or for the electroreduction of organic molecules (e.g., hydrogenation). Depending on the application, it can also be used as an anode for oxidation reactions (H2, N2, or CO2 oxidation, oxidation of organic compounds). The electrolysis cell also consists of an additional electrode at which suitable oxidation or reduction processes can take place.

[0051] The most important advantage of the invention described here is the application of at least one hydrophobic, in particular polymer-containing, catalyst layer and at least one hydrophilic, in particular ionomer-containing, catalyst layer. This allows the hydrophobicity and porosity in the hydrophobic, in particular polymer-containing, layer facing the GDL to be adjusted independently of the ionic conductivity and the chemical environment, e.g., co-catalytic effects of the ionomers. This allows, for example, control over the local pH value in the catalyst layer of the hydrophilic, in particular ionomer-containing, layer facing the electrolyte. Thus, ideal conditions for CO2 reduction can be established at the developing three-phase boundary layer, thereby achieving higher current densities, improved current yields for the target product, lower cell voltages, and improved electrolysis times.

[0052] In the context of the present invention, it is typically provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer are porous. This allows for sufficient mass transport through the electrode, while also providing a large surface area for conducting the electrochemical reaction.

[0053] Within the scope of the present invention, it can be provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer are in direct or indirect contact with one another. Direct contact is understood to mean that the hydrophilic catalyst layer is applied to the hydrophobic catalyst layer, or vice versa. Preferably, the hydrophilic and hydrophobic catalyst layers are in direct contact with one another.

[0054] Likewise, within the scope of the present invention, it can be provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly or indirectly on top of one another. Preferably, the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly on top of one another.

[0055] Within the scope of the present invention, it may also be provided that multiple hydrophobic or hydrophilic catalyst layers are used, in particular to adjust the hydrophobic and hydrophilic properties in a targeted manner, either locally or gradually. The electrode according to the invention preferably comprises a hydrophobic catalyst layer and a hydrophilic catalyst layer.

[0056] According to a preferred embodiment of the present invention, it is provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged on a porous layer, in particular a porous carrier layer, preferably a gas diffusion layer.

[0057] The porous layer preferably has a porosity, i.e. a volume fraction of pores in the range from 50 to 90%, in particular 50 to 80%, preferably 55 to 75%, more preferably 55 to 70%, based on the volume of the porous layer. The porous layer is macroporous or microporous. In the context of the present invention, porosity is understood to mean the ratio of the pore volume, also called void volume, of a body to the total volume of the body in question. The porosity of the porous layer in percent can be determined in particular by mercury porosimetry or by calculation according to the BET model or as an oil absorption coefficient. Likewise, the porosity can also be determined using computer tomography (CT), in particular by means of micro-CT or nano-CT.

[0058] Preferably, the porous layer is microporous or has at least one microporous layer or layer. Within the scope of the present invention, it has proven particularly useful to use conventional gas diffusion layers or materials as the porous layer, in particular as the support material. The hydrophobic and hydrophilic catalyst layers are then applied to these layers, thus obtaining porous and microporous catalyst layers, respectively.

[0059] Particularly good results are obtained when the porous layer has pore sizes in the range of 0.001 to 200 pm, in particular 0.001 to 150 pm, preferably 0.01 to 100 pm, preferably 0.01 to 100 pm. The pore size can be determined in particular by mercury porosimetry or by calculation according to the BET model.

[0060] If the porous layer is macroporous, it can be provided that the porous layer has pore sizes in the range from 0.05 to 200 μm, in particular 0.5 to 150 μm, preferably 0.5 to 100 μm, more preferably 1 to 100 μm. The porous layer is preferably microporous or has a microporous layer. In this case, the porous layer or the microporous layer of the layer has pore sizes in the range from 0.001 to 5 μm, in particular 0.001 to 0.5 μm, preferably 0.01 to 0.5 μm, more preferably 0.01 to 0.2 μm. The porous or microporous structure of the porous layer usually also maintains the porous or microporous structure of the catalyst layers.

[0061] Within the scope of the present invention, it is usually provided that the hydrophobic catalyst layer is arranged on the porous layer and the hydrophilic catalyst layer is arranged on the hydrophobic catalyst layer. Alternatively, it can also be provided that the hydrophilic catalyst layer is arranged on the porous layer and the hydrophobic catalyst layer is arranged on the hydrophilic catalyst layer. However, it is preferably provided that the hydrophobic catalyst layer is arranged on the porous layer and the hydrophilic catalyst layer is arranged on the hydrophobic catalyst layer.

[0062] Within the scope of the present invention, it is therefore preferably provided that a hydrophobic catalyst layer is applied to a porous layer, followed by a hydrophilic catalyst layer on top of the hydrophobic catalyst layer. This prevents polar electrolytes, especially water, from penetrating the electrode. On the other hand, sufficient water absorption and ion transport are enabled in the hydrophilic region, thus enabling particularly effective electrochemical reduction, especially of carbon dioxide.

[0063] As already explained above, it is preferred within the scope of the present invention if the porous layer, in particular the porous carrier layer, is a conventional gas diffusion layer (GDL). Particularly good results are obtained if the porous carrier layer is selected from the group consisting of carbon fabrics, carbon fiber paper, graphite fabrics, metal felts, metal meshes, sintered metal particles, and mixtures thereof. If, within the scope of the present invention, the carrier layer contains or consists of a metal, it has proven useful if the metal is selected from the group consisting of silver, copper, platinum, titanium, nickel, zinc, iron, aluminum, and stainless steel, and mixtures and alloys thereof. Particularly good results are obtained in this context if the metal is selected from the group consisting of copper, silver, platinum, and mixtures and alloys thereof.

[0064] Within the scope of the present invention, it has also proven useful if the porous layer, in particular the porous carrier layer, is selected from carbon-containing materials. In particular, it is preferred if the material of the porous layer is selected from the group of carbon fabrics, carbon fiber paper, and mixtures thereof. The porous layer, in particular the porous carrier layer, is particularly preferably a carbon fabric. When selecting the porous carrier layer, it is particularly important that the material is conductive and does not have any undesirable catalytic properties. As far as the thickness of the porous layer, in particular the porous carrier layer, is concerned, this can naturally vary within a wide range. However, particularly good results are obtained within the scope of the present invention if the porous carrier layer has a thickness in the range from 50 to 1.000 pm, in particular 50 pm to 800 pm, preferably 100 pm to 600 pm, more preferably 150 pm to 500 pm.

[0065] As already stated above, it is usually provided within the scope of the present invention that the hydrophobic catalyst layer and the hydrophilic catalyst layer each contain at least one catalyst.

[0066] Furthermore, within the scope of the present invention, it may be provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer contain identical or different catalysts. Particularly good results are obtained within the scope of the present invention when the hydrophobic catalyst layer and the hydrophilic catalyst layer contain identical catalysts.

[0067] As far as the selection of the catalyst is concerned, it can in principle be selected from any catalyst suitable for electrolysis, especially for the electrochemical reduction of carbon dioxide. Typically, the catalyst is selected from the group of metal particles, especially metal nanoparticles, single-atom catalysts, metal carbides, metal oxides, metal chalcogenides, molecular catalysts, and mixtures thereof. Particularly good results are obtained in this context when the catalyst is selected from metal particles, especially metal nanoparticles.In this context, it has proven useful if the catalyst is selected from the group of metal particles, in particular metal nanoparticles, selected from metal particles of Au, Ag, Zn, Pd, Ga, Cd, In, Hg, Ti, Pb, Bi, Cu and their mixtures and alloys, metal carbides, metal oxides, metal chalcogenides, molecular catalysts and their mixtures.

[0068] Particularly good results are obtained when the catalyst is selected from the group of metal particles, in particular metal nanoparticles, of Au, Ag, Zn, Pd, Ga, Cd, In, Hg, Ti, Pb, Bi, Cu, and mixtures and alloys thereof. Particularly good results are obtained within the scope of the present invention when the catalyst is selected from the group of metal particles, in particular metal nanoparticles, of Au, Ag, Cu, and mixtures and alloys thereof.

[0069] The amount of catalyst in the catalyst layers can vary widely. However, it has proven effective for the hydrophobic catalyst layer and the hydrophilic catalyst layer to contain predominantly the catalyst.

[0070] Particularly good results are obtained in this context when the hydrophobic catalyst layer and the hydrophilic catalyst layer comprise the catalyst in amounts of 10 to 99.9 wt.%, in particular 25 to 99.9 wt.%, preferably 40 to 99.9 wt.%, more preferably 50 to 99.8 wt.%, based on the hydrophobic catalyst layer and the hydrophilic catalyst layer.

[0071] In particular, it can be provided that the hydrophilic catalyst layer comprises the catalyst in amounts of 50 to 99.9 wt.%, in particular 55 to 99.9 wt.%, preferably 60 to 99.9 wt.%, preferably 70 to 99.8 wt.%, based on the hydrophilic catalyst layer.

[0072] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the catalyst in amounts of 50 to 99.9 wt.%, in particular 55 to 99.9 wt.%, preferably 60 to 99.9 wt.%, more preferably 90 to 99.8 wt.%, based on the hydrophilic catalyst layer.

[0073] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99 wt.%, preferably 60 to 97 wt.%, more preferably 70 to 95 wt.%, based on the hydrophilic catalyst layer.

[0074] Likewise, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, based on the hydrophobic catalyst layer.

[0075] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, based on the hydrophobic catalyst layer.

[0076] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, based on the hydrophobic catalyst layer.

[0077] Likewise, it can be provided that the hydrophobic catalyst layer and the hydrophilic catalyst layer comprise the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99.8 wt.%, preferably 40 to 99.8 wt.%, preferably 50 to 99.5 wt.%, based on the solids content of the coating compositions from which the hydrophobic catalyst layer and the hydrophilic catalyst layer are obtained.

[0078] The solids content of a coating composition, in particular a catalyst ink, is understood to mean the part of the coating composition which remains after removal of solvents and other volatile components.

[0079] In this context, it can be provided that the hydrophilic catalyst layer contains the catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99.8 wt.%, preferably 60 to 99.8 wt.%, more preferably 66 to 99.5 wt.%, based on the solids content of the

[0080] Coating composition from which the hydrophilic catalyst layer is obtained. If, within the scope of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the catalyst in amounts of 50 to 99.8 wt.%, in particular 80 to 99.8 wt.%, preferably 89 to 99.8 wt.%, more preferably 89 to 99.5 wt.%, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0081] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 95 wt.%, preferably 60 to 92 wt.%, more preferably 66 to 86 wt.%, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0082] Likewise, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 96 wt.%, preferably 40 to 96 wt.%, more preferably 50 to 96 wt.%, based on the solids content of a coating composition from which the hydrophobic catalyst layer is obtained.

[0083] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 96 wt.%, preferably 40 to 96 wt.%, more preferably 50 to 96 wt.%, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0084] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer contains the catalyst in amounts of 10 to 99.8 wt. %, in particular 25 to 96 wt. %, preferably 40 to 96 wt. %, more preferably 50 to 96 wt. %, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained. Typically, the hydrophobic catalyst layer and the hydrophilic catalyst layer contain the catalyst in amounts of 0.001 to 100 mg / cm -2 , especially 0.05 to 50 mg / cm -2 , preferably 0.1 to 10 mg / cm -2 , preferably 0.5 to 3 mg / cm -2 , based on the surface of the hydrophobic catalyst layer or the hydrophilic catalyst layer.

[0085] Within the scope of the present invention, it is also typically provided that the hydrophilic catalyst layer comprises at least one hydrophilic polymer, in particular at least one ionomer. The polymer serves as a binding agent, i.e., a binder, for the catalyst and, in particular, ensures that the catalyst adheres to a support layer, such as, for example, a gas diffusion layer or an ion-conducting membrane. Preferably, the hydrophilic catalyst layer contains a hydrophilic polymer or a mixture of hydrophilic polymers, in particular one or more ionomers, as the sole polymer, i.e., as the sole binder.

[0086] In particular, within the scope of the present invention, it is not intended that the hydrophilic catalyst layer comprises hydrophilic polymers and hydrophobic polymers.

[0087] It has proven effective if the hydrophilic polymer is selected from the group of polyelectrolytes, ionic polymers, ionomers, and mixtures thereof. Preferably, the hydrophilic polymer is selected from the group of polyacrylic acid, acrylic acid copolymers, acrylamide copolymers, polyethyleneimine, alginate, pectin, lignin, ligninsulfonate, cellulose, cellulose ethers, polyvinylpyrrolidone, polyvinylamine, polyvinylpyridine, polymers with sulfonic acid groups, polymers with perfluorosulfonic acid groups, polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, polymers with phosphonium groups, polymers with sulfonium groups, polymers with organometallic complexes as cationic functionalization, and mixtures thereof.

[0088] Preferably, the hydrophilic polymer is an ionomer.

[0089] Particularly good results are obtained within the scope of the present invention when the hydrophilic polymer, in particular the ionomer, is selected from the group of polymers with sulfonic acid groups, polymers with perfluorosulfonic acid groups, polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, polymers with phosphonium groups, polymers with sulfonium groups, polymers with organometallic complexes as cationic functionalization, and mixtures thereof. In general, hydrophilic polymers with ionic groups or groups that readily form ions are preferably used within the scope of the present invention.

[0090] Particularly good results are obtained in this context when the hydrophilic polymer, in particular the ionomer, is selected from the group of polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, polymers with phosphonium groups, polymers with sulfonium groups, polymers with organometallic complexes as cationic functionalization, and mixtures thereof. Particularly good results are obtained when the hydrophilic polymer, in particular the ionomer, is selected from the group of polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, and mixtures thereof.

[0091] The best results to date are obtained when the hydrophilic polymer, in particular ionomer, is selected from the group of piperidinium group-containing ionomers, imidazolium group-containing ionomers, benzimidazolium group-containing ionomers and mixtures thereof.

[0092] Suitable ionomers include, for example, polymers and copolymers containing sulfonic acid groups, in particular polymers and copolymers based on perfluorosulfonic acid, and hydrocarbon-based polymers and copolymers, for example, with aromatic hydrocarbons, containing sulfonic acid groups, commercially available, for example, as Nafion® from DuPont. Other suitable ionomers include polymers and copolymers containing ammonium groups or polymers with quaternary nitrogen heterocycles, commercially available, for example, as Sustainion® from Dioxide Materials, PiperlON® from Versogen, or Fumasep-FAA3 from Fumatec.

[0093] As for the amount of hydrophilic polymer contained in the hydrophilic catalyst layer, this can vary widely. Typically, the hydrophilic catalyst layer contains the hydrophilic polymer, especially ionomer, in smaller amounts than the catalyst. Particularly good results can be achieved if the hydrophilic catalyst layer contains the hydrophilic polymer, especially ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 30 wt.%, more preferably 0.1 to 18 wt.%, based on the hydrophilic catalyst layer.

[0094] Within the scope of the present invention, according to a preferred embodiment, it is thus provided that the hydrophilic catalyst layer

[0095] (a) a catalyst in amounts of 50 to 99.9 wt.%, in particular 55 to 99.9 wt.%, preferably 60 to 99.9 wt.%, preferably 70 to 99.8 wt.%, and

[0096] (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.1 to 30 wt.%, more preferably 0.1 to 18 wt.%, in each case based on the hydrophilic catalyst layer.

[0097] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0098] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 10 wt.%, preferably 0.01 to 5 wt.%, more preferably 0.1 to 5 wt.%, based on the hydrophilic catalyst layer.

[0099] In the case that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophilic catalyst layer

[0100] (a) a catalyst in amounts of 50 to 99.9 wt.%, in particular 55 to 99.9 wt.%, preferably 60 to 99.9 wt.%, preferably 90 to 99.8 wt.%, and

[0101] (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 10 wt.%, preferably 0.01 to 5 wt.%, more preferably 0.1 to 5 wt.%, in each case based on the hydrophilic catalyst layer. All of the aforementioned features, advantages, and special features apply accordingly to this embodiment.

[0102] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, preferably 8 to 18 wt.%, based on the hydrophilic catalyst layer.

[0103] In the case that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophilic catalyst layer

[0104] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99 wt.%, preferably 60 to 97 wt.%, more preferably 70 to 95 wt.%, and

[0105] (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, preferably 8 to 18 wt.%, in each case based on the hydrophilic catalyst layer.

[0106] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0107] Likewise, it can be provided that the hydrophilic catalyst layer contains the hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 30 wt.%, preferably 0.05 to 33 wt.%, based on the solids content of the

[0108] Coating composition from which the hydrophilic catalyst layer is obtained.

[0109] According to a preferred embodiment, it is therefore provided that the hydrophilic catalyst layer

[0110] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99.8 wt.%, preferably 60 to 99.8 wt.%, preferably 66 to 99.5 wt.%, and (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 30 wt.%, preferably 0.05 to 33 wt.%, in each case based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0111] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0112] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 10 wt.%, preferably 0.05 to 10 wt.%, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0113] In the case that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophilic catalyst layer

[0114] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 80 to 99.8 wt.%, preferably 89 to 99.8 wt.%, preferably 89 to 99.5 wt.%, and

[0115] (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 10 wt.%, preferably 0.05 to 10 wt.%, in each case based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0116] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0117] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophilic catalyst layer comprises the hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, preferably 13 to 33 wt.%, based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0118] In the case that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophilic catalyst layer

[0119] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 95 wt.%, preferably 60 to 92 wt.%, preferably 66 to 86 wt.%, and

[0120] (b) a hydrophilic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, preferably 13 to 33 wt.%, in each case based on the solids content of the coating composition from which the hydrophilic catalyst layer is obtained.

[0121] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0122] Within the scope of the present invention, it can further be provided that the hydrophilic catalyst layer has a thickness in the range from 0.05 pm to 100 pm, in particular 0.5 pm to 100 pm, preferably 0.5 pm to 50 pm, preferably 0.5 to 20 pm, particularly preferably 0.5 to 10 pm, very particularly preferably 0.5 to 5 pm, particularly preferably 0.5 to 3 pm, particularly particularly preferably 0.5 to 1 pm.

[0123] Particularly good results are obtained when the hydrophilic catalyst layer has pore sizes of 0.001 to 1 pm, in particular 0.001 to 0.8 pm, preferably 0.01 to 0.5 pm.

[0124] In addition, it has proven useful if the hydrophilic catalyst layer has a surface weight of less than 10 mg . cm -2 , in particular less than 7 mg cm -2 , preferably less than 5 mg cm 2 , preferably less than 3m g . cm -2 , has.

[0125] Furthermore, it can be provided that the hydrophilic catalyst layer has a surface weight in the range of 0.2 to 10 mg . cm 2 , especially 0.3 to 7 mg . cr r 2 , preferably 0.4 to 5 mg cm 2 , preferably 0.5 to 1 mg cm 2 . As for the hydrophobic catalyst layer, this typically comprises at least one hydrophobic polymer. Preferably, the hydrophobic catalyst layer comprises exclusively one or more hydrophobic polymers as the polymer, ie, binder.

[0126] In the context of the present invention, it has proven useful if the hydrophobic polymer is selected from the group consisting of polyolefins, polyfluoroolefins, silicones, fluorinated polymers, polyaromatic polymers, and their copolymers and mixtures. Particularly good results are obtained in this context if the hydrophobic polymer is selected from the group consisting of polyolefins, polyfluoroolefins, fluorinated polymers, polyaromatic polymers, and their copolymers and mixtures.

[0127] Preferably, the hydrophobic polymer is selected from the group of polyethylene, polypropylene, cycloolefin copolymers (COC), polystyrene (PS), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluoroethylene-propylene (FEP), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymers (PFA), ethylene-tetrafluoroethylene copolymers (ETFE) and their copolymers and mixtures, in particular polyethylene, polypropylene, polyvinylidene fluoride (PVDF), fluoroethylene-propylene (FEP) and polytetrafluoroethylene (PTFE).

[0128] The aforementioned hydrophobic polymers can effectively prevent the penetration of water into the electrode, especially the cathode.

[0129] As for the amount of hydrophobic polymer in the hydrophobic catalyst layer, this can vary widely—as is the case with the hydrophilic polymer. However, with regard to the hydrophobic catalyst layer, it has proven advantageous for the hydrophobic catalyst layer to contain larger amounts of catalyst than the hydrophobic polymer.

[0130] Typically, the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer. According to a preferred embodiment, it is therefore provided that the hydrophobic catalyst layer

[0131] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, and

[0132] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, in each case based on the hydrophobic catalyst layer.

[0133] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0134] If, in the context of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer.

[0135] In the case that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0136] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, and

[0137] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, in each case based on the hydrophobic catalyst layer.

[0138] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0139] If, in the context of the present invention, a bipolar membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer.

[0140] In the case that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0141] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, and

[0142] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, in each case based on the hydrophobic catalyst layer.

[0143] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0144] Likewise, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.05 to 40 wt.%, preferably 0.08 to 30 wt.%, more preferably 0.08 to 16 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0145] According to a preferred embodiment, it is therefore provided that the hydrophobic catalyst layer

[0146] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 96 wt.%, preferably 40 to 96 wt.%, more preferably 50 to 96 wt.%, and

[0147] (b) a hydrophobic polymer, in particular ionomer, in amounts of 0.01 to 50 wt.%, in particular 0.05 to 40 wt.%, preferably 0.08 to 30 wt.%, preferably 0.08 to 16 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0148] All of the aforementioned features, advantages, and special features apply accordingly to this embodiment. If, within the scope of the present invention, an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt. %, in particular 0.05 to 40 wt. %, preferably 0.08 to 30 wt. %, more preferably 0.08 to 16 wt. %, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0149] In the case that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0150] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 96 wt.%, preferably 40 to 96 wt.%, more preferably 50 to 96 wt.%, and

[0151] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.05 to 40 wt.%, preferably 0.08 to 30 wt.%, more preferably 0.08 to 16 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0152] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0153] If, in the context of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.08 to 40 wt.%, preferably 0.08 to 30 wt.%, more preferably 0.08 to 16 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0154] In the case that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0155] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 96

[0156] % by weight, preferably 40 to 96 wt. %, preferably 50 to 96 wt. %, and (b) a hydrophobic polymer in amounts of 0.01 to 50 wt. %, in particular 0.08 to 40 wt. %, preferably 0.08 to 30 wt. %, preferably 0.08 to 16 wt. %, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0157] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0158] Furthermore, within the scope of the present invention, it can be provided that the hydrophobic catalyst layer comprises a conductivity enhancer, ie, an improver for electrical conductivity. Particularly good results are obtained in this context if the conductivity enhancer is selected from carbon black, graphite, carbon nanotubes, and mixtures thereof. Conductivity enhancers can be added to the hydrophobic

[0159] A conductivity enhancer can be added to the coating composition to increase the performance of the electrode and, in particular, to ensure that the hydrophobic catalyst layer does not act as an electrical insulator. Furthermore, the porosity of the hydrophobic catalyst layer can be increased by adding a conductivity enhancer.

[0160] If the hydrophobic catalyst layer comprises a conductivity improver, the hydrophobic catalyst layer typically comprises the conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 5 to 60 wt.%, more preferably 6 to 45 wt.%, based on the hydrophobic catalyst layer.

[0161] Likewise, it can be provided that the hydrophobic catalyst layer comprises the conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 1 to 60 wt.%, more preferably 4 to 45 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0162] If the hydrophobic catalyst layer comprises a conductivity improver, it is preferably provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, based on the hydrophobic catalyst layer.

[0163] If the hydrophobic catalyst layer comprises a conductivity improver, it is preferably provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 90 wt.%, preferably 50 to 80 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0164] Furthermore, according to this embodiment, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer.

[0165] Likewise, according to this embodiment, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0166] According to a preferred embodiment, it is therefore provided that the hydrophobic catalyst layer

[0167] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%,

[0168] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0169] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 5 to 60 wt.%, more preferably 6 to 45 wt.%, in each case based on the hydrophobic catalyst layer. All of the aforementioned features, advantages, and special features apply accordingly to this embodiment.

[0170] According to a further preferred embodiment, it is provided that the hydrophobic catalyst layer

[0171] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 90 wt.%, more preferably 50 to 80 wt.%,

[0172] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0173] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 1 to 60 wt.%, more preferably 4 to 45 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0174] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0175] If, in the context of the present invention, the hydrophobic catalyst layer comprises a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided according to this embodiment that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%, based on the hydrophobic catalyst layer.

[0176] If, in the context of the present invention, the hydrophobic catalyst layer comprises a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 90 wt.%, more preferably 50 to 80 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained. If, in the context of the present invention, the hydrophobic catalyst layer comprises a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.-%, based on the hydrophobic catalyst layer.

[0177] If, in the context of the present invention, the hydrophobic catalyst layer comprises a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0178] In the case that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0179] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 99 wt.%, preferably 40 to 97 wt.%, more preferably 50 to 95 wt.%,

[0180] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0181] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 5 to 60 wt.%, more preferably 6 to 45 wt.%, in each case based on the hydrophobic catalyst layer.

[0182] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0183] In the event that an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can also be provided according to a preferred embodiment that the hydrophobic catalyst layer (a) contains a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95

[0184] % by weight, preferably 40 to 90 % by weight, preferably 50 to 80 % by weight,

[0185] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0186] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 1 to 60 wt.%, more preferably 4 to 45 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0187] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0188] If, however, within the scope of the present invention, the hydrophobic catalyst layer comprises a conductivity improver and a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 92 wt.%, more preferably 50 to 90 wt.%, based on the hydrophobic catalyst layer.

[0189] If, within the scope of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the catalyst in amounts of 10 to 99.8% by weight, in particular 25 to 95% by weight, preferably 40 to 92% by weight, more preferably 50 to 80% by weight, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0190] If, according to this embodiment of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer. If, according to this embodiment of the present invention, a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can be provided that the hydrophobic catalyst layer comprises the hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0191] In the case that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0192] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 92 wt.%, more preferably 50 to 90 wt.%,

[0193] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0194] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 5 to 60 wt.%, more preferably 6 to 45 wt.%, in each case based on the hydrophobic catalyst layer.

[0195] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0196] In the event that a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can also be provided according to a preferred embodiment that the hydrophobic catalyst layer

[0197] (a) a catalyst in amounts of 10 to 99.8 wt.%, in particular 25 to 95 wt.%, preferably 40 to 92 wt.%, more preferably 50 to 80 wt.%,

[0198] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, and

[0199] (c) a conductivity improver in amounts of 0.05 to 90 wt.%, in particular 0.5 to 75 wt.%, preferably 1 to 60 wt.%, more preferably 4 to 45 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0200] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0201] If the hydrophobic catalyst layer does not have a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0202] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99 wt.%, preferably 60 to 97 wt.%, more preferably 70 to 95 wt.%, and

[0203] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, in each case based on the hydrophobic catalyst layer.

[0204] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0205] If the hydrophobic catalyst layer does not have a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode and cathode compartments, it can also be provided according to a preferred embodiment that the hydrophobic catalyst layer

[0206] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 96 wt.%, preferably 60 to 96 wt.%, preferably 70 to 96 wt.%, and

[0207] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.05 to 40 wt.%, preferably 0.08 to 30 wt.%, more preferably 0.08 to 16 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0208] For this embodiment, all the aforementioned features, advantages, and special features apply accordingly. If the hydrophobic catalyst layer does not contain a conductivity enhancer and a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it is provided according to a preferred embodiment that the hydrophobic catalyst layer

[0209] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 99 wt.%, preferably 60 to 97 wt.%, more preferably 70 to 95 wt.%, and

[0210] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, in each case based on the hydrophobic catalyst layer.

[0211] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0212] If the hydrophobic catalyst layer does not have a conductivity improver and a bipolar exchange membrane (BPM) is used to separate the anode and cathode compartments, it can also be provided according to a preferred embodiment that the hydrophobic catalyst layer

[0213] (a) a catalyst in amounts of 50 to 99.8 wt.%, in particular 55 to 96 wt.%, preferably 60 to 96 wt.%, preferably 70 to 96 wt.%, and

[0214] (b) a hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.08 to 40 wt.%, preferably 0.08 to 30 wt.%, more preferably 0.08 to 16 wt.%, in each case based on the solids content of the coating composition from which the hydrophobic catalyst layer is obtained.

[0215] All the aforementioned features, advantages and special features apply accordingly to this embodiment.

[0216] Furthermore, within the scope of the present invention, it is typically provided that the hydrophobic catalyst layer has a thickness in the range from 0.05 pm to 100 pm, in particular from 0.5 pm to 100 pm, preferably from 0.5 pm to 50 pm, preferably from 0.5 to 20 pm, particularly preferably from 0.5 to 10 pm, very particularly preferably from 0.5 to 5 pm, particularly preferably from 0.5 to 4 pm, particularly particularly preferably from 0.5 to 3 pm. Particularly good results are obtained when the hydrophobic catalyst layer has pore sizes of at most 5 pm, in particular at most 3 pm, preferably at most 2 pm.

[0217] It has also proven to be advantageous if the hydrophobic catalyst layer has pore sizes in the range of 0.001 to 5 pm, in particular 0.001 to 3 pm, preferably 0.01 to 2 pm.

[0218] In addition, it has proven useful if the hydrophobic catalyst layer has a surface weight of less than 10 mg . cm -2 , in particular less than 7 mg cm-2 , preferably less than 5 mg cm 2 , preferably less than 3 mg cm -2 , has.

[0219] Furthermore, it can be provided that the hydrophobic catalyst layer has a surface weight in the range of 0.5 to 10 mg . cm 2 , especially 0.8 to 7 mg . cr r 2 , preferably 1 to 5 mg cm 2 , preferably 1 to 3 mg cm 2 , has.

[0220] Furthermore, within the scope of the present invention, it is usually provided that the hydrophilic catalyst layer and the hydrophobic catalyst layer have a total thickness in the range 0.1 pm to 100 pm, in particular 0.1 pm to 100 pm, preferably 0.5 pm to 50 pm, preferably 0.5 to 20 pm, particularly preferably 0.5 to 10 pm, very particularly preferably 1 to 5 pm, particularly preferably 1 to 4 pm, particularly particularly preferably 1 to 3 pm.

[0221] Furthermore, it is preferably provided that the electrode has an area in the range of 0.5 to 50,000 cm 2 , especially 1 to 10,000 cm 2 , preferably 10 to 5,000 cm 2 , preferably 100 to 2,500 cm 2 , has.

[0222] Particularly good results are obtained when the electrode has a total thickness in the range 2 pm to 200 pm, in particular 2 pm to 100 pm, preferably 2 pm to 50 pm, preferably 3 to 30 pm, particularly preferably 4 to 20 pm, very particularly preferably 5 to 15 pm.

[0223] The figure representations show

[0224] Fig. 1 shows a schematic representation of an electrode according to the invention;

[0225] Fig. 2 shows an electrolysis cell containing an electrode according to the invention; Fig. 3 shows cell voltage and current yields of a galvanostatic electrolysis as a function of the PTFE content in the catalyst ink of the cathode;

[0226] Fig. 4 Cell voltage and current yields of a galvanostatic electrolysis as a function of the ionomer content in the catalyst ink of the cathode;

[0227] Fig. 5 Cell voltage and current efficiency of a galvanostatic electrolysis as a function of the catalyst loadings in the hydrophobic and hydrophilic catalyst layer;

[0228] Fig. 6 Cell voltage and current efficiency of a galvanostatic electrolysis with a purely hydrophobic catalyst layer as well as with a hydrophobic and a hydrophilic catalyst layer and with a purely hydrophilic catalyst layer;

[0229] Fig. 7 Current yields of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer and an anion exchange membrane as a function of time;

[0230] Fig. 8 Cell voltage of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer and an anion exchange membrane as a function of time;

[0231] Fig. 9 Current yields of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer and a bipolar exchange membrane as a function of time;

[0232] Fig.10 Cell voltage of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer and a bipolar exchange membrane as a function of time;

[0233] Fig. 11 Current yields of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer, and a bipolar exchange membrane as a function of time; and

[0234] Fig. 12 Cell voltage of a galvanostatic electrolysis with an electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer and a bipolar exchange membrane as a function of time.

[0235] A further object of the present invention - according to a second aspect of the present invention - is the use of an aforementioned electrode in electrolysis.

[0236] The gas diffusion electrode according to the invention is used in particular as a cathode and / or anode, preferably cathode, in electrolysis.

[0237] Typically, the electrode for the described applications acts as a cathode for the reduction of CO2, CO, N2, O2 and organic molecules, especially by hydrogenation.

[0238] However, it is also possible to use the gas diffusion electrode as an anode for oxidation reactions, in particular for the oxidation of H2, N2, CO2 and organic compounds.

[0239] For further details on this aspect of the invention, reference can be made to the above statements on the electrode according to the invention, which apply accordingly with regard to the use of the electrode according to the invention.

[0240] Yet another object of the present invention - according to a third aspect of the present invention - is the use of an aforementioned electrode as a cathode in the electrochemical reduction of carbon dioxide.

[0241] The electrode according to the invention is particularly suitable for the electrochemical reduction of carbon dioxide, whereby valuable chemical raw materials, in particular carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids can be obtained.

[0242] For further details on this aspect of the invention, reference can be made to the statements on the above aspects of the invention, which apply accordingly with regard to the use according to the invention. Yet another subject of the present invention - according to a further aspect of the present invention - is a method for producing a pre-printed electrode, wherein

[0243] (i) in a first process step, a first coating composition for producing a first hydrophilic or hydrophobic, preferably hydrophobic, catalyst layer is applied to a porous support material or an ion-conducting membrane and

[0244] (ii) in a second process step following the first process step (i), a second coating composition different from the first coating composition is applied to the hydrophobic or hydrophilic, preferably hydrophobic, first catalyst layer to produce a second hydrophilic or hydrophobic, preferably hydrophilic, catalyst layer.

[0245] In the context of the present invention, the coating compositions are preferably applied to a porous support material, thus obtaining a coated substrate (catalyst-coated substrate). However, it is also possible to apply the coating compositions to an ion-conducting membrane, in particular an anion exchange membrane (AEM), a proton exchange membrane (PEM), or a bipolar exchange membrane (BPM), of an electrolysis cell (catalyst-coated membrane), and to apply this structure with the catalyst layers to a porous support material. A combination of both processes is also possible.

[0246] The porous carrier material corresponds to the porous layer described above.

[0247] Within the scope of the present invention, it is particularly provided that, if a hydrophilic catalyst layer is first applied to the porous support material, a hydrophobic coating is applied in the second step, or if a hydrophobic coating composition is applied to the porous support material in the first process step, a hydrophilic coating composition is applied in the second process step. The coating compositions are preferably dried or cured to obtain the respective catalyst layers.

[0248] The coating compositions can be applied by dry or wet coating methods such as spraying, doctoring, dropping, printing or by a combination of these methods.

[0249] The hydrophilic coating composition usually contains a hydrophilic polymer, in particular a hydrophilic polymer mentioned above.

[0250] The hydrophobic coating composition typically contains a hydrophobic polymer, in particular a hydrophobic polymer mentioned above.

[0251] The hydrophilic coating composition and the hydrophobic coating composition may contain the hydrophilic polymer or the hydrophobic polymer in different forms; usually, the hydrophilic and the hydrophobic coating composition contain the hydrophilic polymer or the hydrophobic polymer in the form of solid particles, for example as a dispersion, or films, preferably in the form of solid particles.

[0252] Typically, within the scope of the present invention, the hydrophilic and / or hydrophobic first and / or second coating composition is in the form of a dispersion. Preferably, both the hydrophilic and / or hydrophobic first and / or second coating composition are in the form of a dispersion.

[0253] If the first or second coating composition is in the form of a dispersion, it is usually provided that the dispersion medium is removed during or after application of the first coating composition. The removal of the dispersion medium particularly preferably takes place before carrying out the second process step ii. Within the scope of the present invention, it is therefore preferably provided that a first catalyst layer is first obtained from the first coating composition before the second coating composition is applied to produce the second catalyst layer. Likewise, it is usually provided within the scope of the present invention that the dispersion medium is removed during or after application of the second coating composition. The second coating composition is therefore also preferably dried or cured.

[0254] According to a preferred embodiment of the present invention, the carrier material is heated during or after the application of the first or second coating composition. In this way, the dispersion medium can be removed quickly, and any crosslinking reaction that may occur can take place immediately. Polymer particles can also be applied directly and adhere to the heated carrier material. In this context, it is particularly preferred if the carrier material is heated during the application of the first coating composition and during the application of the second coating composition. Heating during the application of the coating composition causes the dispersion medium to evaporate quickly, and the layer thickness of the catalyst layer can be specifically adjusted by applying it multiple times if necessary.

[0255] As far as the temperatures to which the carrier material is heated are concerned, it has proven advantageous if the carrier material is heated to temperatures in the range of 25 to 140 °C, in particular 40 to 120 °C, in particular 60 to 120 °C, preferably 70 to 100 °C.

[0256] Within the scope of the present invention, it can be provided that the electrode is subjected to a thermal or mechanical post-treatment step after application of the first or second coating composition, in particular after application of a hydrophobic coating composition. In particular, the electrode can be subjected to a sintering step and / or a pressing step.

[0257] In this context, it may be provided that the electrode is subjected to a sintering step after application of the first or second coating composition and, if appropriate, removal of the dispersion medium. Preferably, the electrode is subjected to a sintering step after application of the hydrophobic coating composition and removal of the dispersion medium. During a sintering step, the adhesion of the coating composition to the carrier layer or the further catalyst layer is improved and the homogeneity of the catalyst layer is promoted.

[0258] If a sintering step is carried out, the support material is usually heated to temperatures in the range of 150 to 400 °C, in particular 150 to 350 °C, preferably 150 to 300 °C, more preferably 200 to 300 °C.

[0259] The duration of the sintering step can vary widely. However, sintering is typically carried out over a period of 1 to 100 minutes, in particular 5 to 30 minutes, preferably 5 to 15 minutes, and more preferably 10 to 15 minutes.

[0260] As already stated above, the hydrophobic coating composition typically comprises a hydrophobic polymer. Particularly good results are obtained in this context when the hydrophobic coating composition comprises the hydrophobic polymer in amounts of 0.05 to 5 wt.%, in particular 0.1 to 3 wt.%, preferably 0.2 to 1 wt.%, more preferably 0.3 to 0.5 wt.%, based on the hydrophobic coating composition.

[0261] Likewise, it can be provided within the scope of the present invention that the hydrophobic coating composition contains the catalyst in amounts of 0.1 to 10 wt.%, in particular 0.5 to 5 wt.%, preferably 1 to 3 wt.%, more preferably 1 to 2 wt.%, based on the hydrophobic

[0262] coating composition.

[0263] As already stated above, the hydrophobic coating composition comprises a dispersion medium. Typically, the hydrophobic coating composition comprises the dispersion medium in amounts of 85 to 99.9 wt.%, in particular 92 to 99.4 wt.%, preferably 96 to 98.8 wt.%, more preferably 97 to 98.7 wt.%, based on the hydrophobic coating composition.

[0264] Particularly good results are obtained in the present invention when the dispersion medium is selected from water, alcohols, N,N-dimethylformamide, acetone, ethyl acetate, acetonitrile, and mixtures thereof. The dispersion medium is preferably selected from water, alcohols, and mixtures thereof, preferably mixtures thereof.

[0265] If the dispersion medium is selected from water, alcohols, and mixtures thereof, it has proven effective if the dispersion medium is selected from water, methanol, ethanol, isopropanol, and mixtures thereof, preferably mixtures thereof. Particularly good results are obtained in this context if the dispersion medium is selected from water, isopropanol, and mixtures thereof, preferably mixtures thereof.

[0266] Furthermore, it may be provided that the hydrophobic coating composition comprises an additive. If the hydrophobic coating composition comprises an additive, the additive is typically selected from the group of pore formers, stabilizers, rheology additives, surfactants, or mixtures thereof.

[0267] If the hydrophobic coating composition comprises an additive, the coating composition usually comprises the additive in amounts of 0.01 to 2 wt.%, in particular 0.05 to 1 wt.%, preferably 0.1 to 0.5 wt.%, more preferably 0.1 to 0.3 wt.%, based on the hydrophobic

[0268] coating composition.

[0269] According to a preferred embodiment of the present invention, the hydrophobic coating composition comprises a conductivity enhancer. As previously described in connection with the electrode according to the invention, it has proven advantageous if the conductivity enhancer is selected from the group consisting of carbon black, graphite, carbon nanotubes, and mixtures thereof.

[0270] In the case where the hydrophobic coating composition contains a conductivity enhancer, it is generally intended that the hydrophobic coating composition comprise the conductivity enhancer in amounts of 0.01 to 2 wt.%, in particular 0.05 to 1 wt.%, preferably 0.1 to 0.5 wt.%, more preferably 0.1 to 0.3 wt.%, based on the hydrophobic coating composition. Regarding the hydrophilic coating composition, it is usually intended that the hydrophilic coating composition comprise a hydrophilic polymer.

[0271] In this context, particularly good results are obtained when the hydrophilic coating composition comprises the hydrophilic polymer in amounts of 0.01 to 2 wt.%, in particular 0.05 to 1.5 wt.%, preferably 0.1 to 1 wt.%, preferably 0.3 to 0.5 wt.%, based on the hydrophilic coating composition.

[0272] Likewise, within the scope of the present invention, it may be provided that the hydrophilic coating composition comprises the catalyst in amounts of 0.1 to 10 wt.%, in particular 0.5 to 5 wt.%, preferably 1 to 3 wt.%, preferably 1 to 2 wt.%, based on the coating composition.

[0273] As already stated above, the hydrophilic coating composition typically comprises a dispersion medium. If the hydrophilic coating composition comprises a dispersion medium, it has proven advantageous for the hydrophilic coating composition to contain the dispersion medium in amounts of 85 to 99.9 wt.%, in particular 92 to 99.4 wt.%, preferably 96 to 98.8 wt.%, more preferably 97 to 98.7 wt.%, based on the coating composition.

[0274] Likewise, good results are obtained when the dispersion medium is selected from water, alcohols, N,N-dimethylformamide, acetone, ethyl acetate, acetonitrile, and mixtures thereof, preferably mixtures thereof. Particularly good results are obtained in this context when the dispersion medium is selected from water, alcohols, and mixtures thereof, preferably mixtures thereof.

[0275] If the dispersion medium is selected from water, alcohols, and mixtures thereof, it has proven effective if the dispersion medium is selected from water, methanol, ethanol, isopropanol, and mixtures thereof, preferably mixtures thereof. Best results are obtained if the dispersion medium is selected from water, isopropanol, and mixtures thereof, preferably mixtures thereof. With regard to the hydrophilic coating composition, it can also be provided that the coating composition comprises an additive. If the hydrophilic coating composition comprises an additive, it can be provided that the additive is selected from pore formers, stabilizers, rheology additives, surfactants, or mixtures thereof.

[0276] Likewise, in this context, it may be provided that the hydrophilic coating composition comprises the additive in amounts of 0.01 to 2 wt.%, in particular 0.05 to 1 wt.%, preferably 0.1 to 0.5 wt.%, more preferably 0.1 to 0.3 wt.%, based on the hydrophilic coating composition.

[0277] For further details on this aspect of the invention, reference can be made to the statements on the above aspect of the invention, which apply accordingly with regard to the method according to the invention.

[0278] Yet another subject matter of the present invention - according to a fifth aspect of the present invention - is an electrolysis cell, in particular for the electrochemical reduction of carbon dioxide, comprising at least one electrode as described above.

[0279] In general, the electrolysis cell according to the invention has at least two chambers, namely an anode chamber and a cathode chamber.

[0280] The electrode according to the invention, in particular a gas diffusion electrode, typically forms the interface between a liquid and / or gaseous substrate and a liquid or solid electrolyte. The diffusion layer, consisting of a porous support layer and the catalyst layers, is preferably at least partially infiltrated with the liquid substrate. Thus, a three-phase boundary is formed between the substrate, electrolyte, and catalyst, at which the electrochemical process takes place.

[0281] The gas diffusion electrode according to the invention can form the cathode and / or the anode, preferably the cathode, of the electrolysis cell. Within the scope of the present invention, it is preferably provided that the electrode according to the invention forms the cathode in the electrolysis cell according to the invention.

[0282] The electrode according to the invention is preferably used as a cathode for the reduction of CO2, CO, N2, O2, and organic molecules, for example, in hydrogenation reactions. However, it can also be used as an anode for oxidation reactions, for example, for the oxidation of H2, N2, and organic compounds.

[0283] In addition to the electrode according to the invention, the electrolysis cell also has at least one further electrode, in particular an anode. Suitable oxidation or reduction processes can take place at the further electrode, which can also be an electrode according to the invention. At an anode, water, in particular, is oxidized to oxygen during the electrochemical reduction of CO2.

[0284] The second electrode, in particular the anode, can also be made of any suitable material, especially porous materials such as metal felts, sintered metal particles, metal meshes, and mixtures thereof. Furthermore, it is usually provided that the second electrode is also coated with a catalyst. The catalyst is often a metal or metal oxide, such as iridium oxide.

[0285] Between the anode and the cathode of the electrolyte cell according to the invention, there is usually a diaphragm or a semipermeable membrane, in particular an anion exchange membrane (AEM), a proton exchange membrane (PEM), or a bipolar exchange membrane (BPM). Bipolar exchange membranes typically consist of laminated PEM and AEM membranes and can be installed with either forward bias or reverse bias.

[0286] To increase conversion, in addition to scaling the electrode area, several individual cells can be stacked to form a bipolar stack, depending on the conductivity perpendicular to the electrode plane. According to a preferred embodiment of the present invention, the electrolysis cell is a so-called zero-gap electrolyzer.

[0287] For further details on the electrolysis cell according to the invention, reference can be made to the above statements on the other aspects of the invention, which apply accordingly with regard to the electrolysis cell according to the invention.

[0288] The subject matter of the present invention is explained below by way of example in a non-limiting manner with reference to the description of the figures and the exemplary embodiments.

[0289] Fig. 1 shows an electrode 1 according to the invention, which has a hydrophobic catalyst layer (Catalyst Layer, CL) 2 and a hydrophilic catalyst layer (Catalyst Layer, CL) 3.

[0290] The catalyst layers 2 and 3 are each porous and have pore sizes in the range of 0.001 to 5 pm, in particular 0.001 to 3 pm, preferably 0.01 to 2 pm.

[0291] The hydrophobic catalyst layer 2 preferably comprises at least one hydrophobic polymer in amounts of 0.01 to 50 wt.%, in particular 0.1 to 40 wt.%, preferably 1 to 30 wt.%, more preferably 1 to 10 wt.%, based on the hydrophobic catalyst layer.

[0292] The hydrophobic polymer is preferably selected from the group of polyethylene, polypropylene, cycloolefin copolymers (COC), polystyrene (PS), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluoroethylene-propylene (FEP), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymers (PFA), ethylene-tetrafluoroethylene copolymers (ETFE) and their copolymers and mixtures, in particular polyethylene, polypropylene, polyvinylidene fluoride (PVDF), fluoroethylene-propylene (FEP) and polytetrafluoroethylene (PTFE).

[0293] Furthermore, it can be provided that the hydrophobic catalyst layer 2 comprises a conductivity enhancer, in particular selected from carbon black, graphite, carbon nanotubes, and mixtures thereof. The hydrophilic catalyst layer 3 preferably comprises at least one hydrophilic polymer, in particular an ionomer. Within the scope of the present invention, it is particularly preferred if the hydrophilic polymer is selected from cation and anion exchange polymers, in particular anion exchange polymers. Particularly good results are obtained in this context if the hydrophilic polymer is selected from the group of polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, polymers with phosphonium groups, polymers with sulfonium groups, polymers with organometallic complexes as cationic functionalization, and mixtures thereof.Particularly preferred are polymers with quaternary ammonium groups, polymers with quaternary nitrogen heterocycles, and mixtures thereof. In this context, it is particularly preferred if the hydrophilic polymer, in particular ionomer, is selected from the group of piperidinium-containing ionomers, imidazolium-containing ionomers, benzimidazolium-containing ionomers, and mixtures thereof.

[0294] Typically, the hydrophilic catalyst layer 3 contains the hydrophilic polymer in amounts of 0.01 to 50 wt.%, in particular 0.01 to 40 wt.%, preferably 0.01 to 30 wt.%, more preferably 0.1 to 18 wt.%, based on the hydrophilic catalyst layer.

[0295] The hydrophilic catalyst layer 3 and the hydrophobic catalyst layer 2 usually have thicknesses in the range of 0.05 pm to 100 pm, in particular 0.5 pm to 100 pm, preferably 0.5 pm to 50 pm, more preferably 0.5 to 20 pm.

[0296] Within the scope of the present invention, it is further provided that both the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 comprise at least one catalyst. The catalysts of the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 can be the same or different from one another. However, the same catalysts are usually used in the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3.

[0297] The catalysts are distributed as evenly as possible in the respective layers. The catalyst is typically selected from the group of metal particles, especially metal nanoparticles, single-atom catalysts, metal carbides, metal oxides, metal chalcogenides, molecular catalysts, and mixtures thereof.

[0298] Particularly good results are obtained when the catalyst is selected from the group of metal particles, in particular metal nanoparticles of silver, gold, zinc, palladium, gallium, cadmium, indium, mercury, thallium, lead, bismuth, copper, and mixtures and alloys thereof. In this context, it is particularly preferred if the catalyst is selected from the group of metal particles, in particular metal nanoparticles of silver, gold, copper, and mixtures and alloys thereof.

[0299] Typically, the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 contain the catalyst in amounts of 50 to 99.9 wt.%, in particular 55 to 99.9 wt.%, preferably 60 to 99.8 wt.%, more preferably 70 to 99.8 wt.%, based on the hydrophobic catalyst layer 2 or the hydrophilic catalyst layer 3.

[0300] Preferably, it is further provided that the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 are applied to a porous layer, in particular a gas diffusion layer 4.

[0301] The porous layer, in particular gas diffusion layer 4, is in particular a conventional gas diffusion layer (GDL). The material of the porous layer, in particular gas diffusion layer 4, is generally selected from the group consisting of carbon fabrics, carbon fiber paper, graphite fabrics, metal felts, metal meshes, sintered metals, and mixtures thereof. Particularly good results are obtained when the material of the porous layer, in particular gas diffusion layer 4, is selected from the group consisting of carbon fabrics, carbon fiber paper, and mixtures thereof. The porous layer, in particular gas diffusion layer 4, is particularly preferably a carbon fabric. Preferably, the porous layer, in particular gas diffusion layer 4, has a thickness in the range of 50 to 1,000 pm, in particular 50 pm to 800 pm, preferably 100 pm to 600 pm, preferably 150 pm to 500 pm.

[0302] According to a preferred embodiment, the electrode according to the invention has the following structure: A hydrophobic catalyst layer 2 is applied to a gas diffusion layer 4, onto which in turn a hydrophilic catalyst layer 3 is applied.

[0303] The electrode 1 according to the invention is outstandingly suitable for use as a cathode in electrolyzers, in particular zero-gap electrolyzers for the reduction of carbon dioxide.

[0304] Fig. 2 shows an electrolysis cell 5 according to the invention, in particular an electrolyzer, in the form of a zero-gap electrolyzer.

[0305] The electrode structure consists of an electrode 1 according to the invention with a gas diffusion layer 4, a hydrophobic catalyst layer 2 and a hydrophilic catalyst layer 3. The electrode 1 according to the invention preferably forms the cathode.

[0306] The anode 6 of the electrolysis cell 5 preferably consists of a titanium felt with an iridium oxide catalyst applied thereto.

[0307] The electrodes are separated by a semipermeable membrane 7, in particular an anion exchange membrane, a proton exchange membrane or a bipolar exchange membrane, preferably a proton exchange membrane.

[0308] On the cathode side, carbon dioxide is introduced, in particular with an inert carrier gas humidified with water vapor, such as nitrogen or argon, and diffuses through the porous carrier layer to the catalyst layers 2 and 3. On the anode side, water is passed through the anode chamber, which passes through the porous anode 6 to the membrane 7.

[0309] At the electrode 1, which acts as the cathode, CO2 is preferably reduced to organic substances, in particular carbon monoxide, alcohols, aldehydes, ketones, and carboxylic acids. The corresponding reaction products are flushed out of the cathode chamber with the carrier gas stream. At the anode side, they are oxidized with water to oxygen, while the protons migrate through the semipermeable membrane 7 and react with the reduced CO2 to form organic residues. The subject matter of the present invention is described below. non-limitingly illustrated by the examples.

[0310] Examples of implementation

[0311] 1. Reference example A: GDE with hydrophobic polymer-containing CL

[0312] As a reference example, GDEs with a single-layer, hydrophobic polymer-containing catalyst layer (CL) were fabricated. For this purpose, a carbon fabric with a microporous layer (W1 S1010, fuelcellstore) was coated with a polymer-containing catalyst ink.

[0313] 1.1 Preparation of the catalyst ink:

[0314] The catalyst (AgNPs, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink is 16.67 mg ml' 1 In addition, Triton X-100 is added as an ink stabilizer and pore-forming agent. Before adding the PTFE dispersion, the ink is pressed for 90 seconds at 13,400 rpm. -1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink is treated with ultrasound for 15 minutes for further homogenization.

[0315] Table 1: Example composition of a polymer-containing catalyst ink with 15 wt.% polymer (PTFE) based on the weighed catalyst quantity (AgNPs)

[0316] 1.2. Production of the GDE:

[0317] The prepared catalyst ink was sprayed onto the carbon fabric using an airbrush gun (Eclipse, Iwata) until a catalyst loading of 2.5 mg cm -2 AgNPs is reached. To ensure rapid evaporation of the solvent, the carbon fabric is heated to 90 °C during the spraying process. The GDE was then sintered in air at 300 °C for 15 minutes. GDEs were prepared with PTFE contents in the catalyst ink of 1, 3.75, 7.5, 15, and 30 wt.% based on the weighed catalyst quantity. 1.3 CO2 Electrolysis:

[0318] The CCh electrolysis was carried out in a zero-gap electrolyzer with an active cell area of ​​2 cm 2At the anode, a porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrCh (Alfa Aesar) was used. The anode chamber was continuously filled with 16.6 ml min -1 0.1 M KHCO3. At the cathode, the prepared GDE were added with 2.5 mg cm -2 AgNPs (Alfa Aesar) were used. Five different GDEs with hydrophobic polymer-containing CLs were investigated. The PTFE content in the respective catalyst inks was 1, 3.75, 7.5, 15, and 30 wt.%. During electrolysis, the cathode compartment was filled with 50 ml min -1 CO2 and 5 ml min -1Ar was used as an internal standard. Before entering the cathode chamber, the gas inlet stream was brought to a relative humidity of 79% (dew point: 55 °C) using a saturation steam humidifier. The 40 μm thick Piperion membrane was activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MQ cm, MilliQ). All electrocatalytic tests were carried out galvanostatically at 300 mA cm. 2 over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0319] The current efficiency for the target product CO (FEco) as well as the measured cell voltage (Uzeiie) are shown in Fig. 3 for all manufactured GDE with polymer-containing CL (1; 3.75; 7.5; 15 and 30 wt% PTFE).

[0320] Fig. 3 shows Uzeiie (A) and FEco (B) of a galvanostatic electrolysis at 300 mA cm' 2 depending on the PTFE content in the cathode catalyst ink. The test periods after reaching a steady state (2-3 hours) are shown.

[0321] With an industrially relevant current density of 300 mA cm' 2 For the hydrophobic polymer-containing CLs investigated, FEco values ​​of 28–44% were achieved at voltages of 3.5–5.5 V. It can be seen that the cell voltage increases with the proportion of PTFE in the CL. The highest FEco is achieved in the CL whose catalyst ink contained a PTFE content of 7.5 wt.% based on the amount of catalyst used. At a PTFE content of 30 wt.%, drying out and consequent rupture of the SPE membrane reproducibly occurs. 2. Reference Example B: GDE with hydrophilic ionomer-containing CLs

[0322] As a second reference example, GDEs were fabricated with a hydrophilic ionomer-containing CL. For this purpose, a carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated with an ionomer-containing catalyst ink.

[0323] 2.1 Preparation of the catalyst ink:

[0324] The catalyst (AgNPs, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink is 16.67 mg ml' 1 The catalyst ink is pressed for 90 seconds at 13,400 rpm -1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink is treated with ultrasound for 15 minutes for further homogenization.

[0325] Table 2. Example composition of a polymer-containing catalyst ink with 15 wt.% ionomer (Piperion) based on the weighed catalyst quantity (AgNPs)

[0326] 2.2 Production of the GDE:

[0327] The catalyst ink was sprayed onto the carbon fabric using an airbrush gun (Eclipse, Iwata) until a catalyst loading of 2.5 mg cm -2 AgNPs was achieved. To ensure rapid evaporation of the solvent, the carbon fabric is heated to 90 °C during the spraying process. GDEs were prepared with Piperion concentrations in the catalyst ink of 1, 3.75, 7.5, 15, and 30 wt.% based on the weighed catalyst amount.

[0328] 2.3 CO2 electrolysis:

[0329] The CCh electrolysis was carried out in a zero-gap electrolyzer with an active cell area of ​​2 cm 2 At the anode, a porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrCh (Alfa Aesar) was used. The anode chamber was continuously filled with 16.6 ml min -1 0.1 M KHCO3. At the cathode, the GDE were coated with an AgNPs (Alfa Aesar) loading of 2.5 mg cm- 2 Five different GDEs with ionomer-containing CLs were investigated. The piperion content in the respective catalyst inks was 1, 3.75, 7.5, 15, and 30 wt.%. During electrolysis, the cathode compartment was filled with 50 ml min -1 CO2 and 5 ml min -1 Ar was used as an internal standard. Before entering the cathode compartment, the gas inlet stream was brought to a relative humidity of 79% (dew point: 55 °C) using a saturation steam humidifier. Both the 40 μm thick Piperion membrane and the GDE were activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic tests were carried out galvanostatically at 300 mA cm. -2 over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0330] The current efficiency for the target product CO (FEco) as well as the measured cell voltage (Uzeiie) are shown in Fig. 4 for all GDEs produced with polymer-containing CL (1-30 wt.% Piperion).

[0331] Fig. 4 shows the cell voltage (A) and current yields for the product CO (B) of a galvanostatic electrolysis at 300 mA cm -2 depending on the piperion content in the cathode catalyst ink. The test periods after reaching a steady state (2-3 hours) are shown.

[0332] With an industrially relevant current density of 300 mA cm -2 For the hydrophilic ionomer-containing CLs investigated, FEco values ​​of 12–49% were achieved at Uzeiie values ​​of 3.2–3.4 V. It can be seen that with increasing piperion content, there is a decrease in FEco and an increase in Uzeiie. The highest FEco of 49% and the lowest Uzeiie are achieved at 1 wt% piperion.

[0333] 3. Inventive embodiment 1 : (Several

[0334] catalyst layers)

[0335] As an exemplary embodiment of the invention described here with multiple catalyst layers (CL) for CO2 reduction, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated in a first step with a hydrophobic polymer-containing catalyst layer and in a second step with a hydrophilic ionomer-containing catalyst layer. 3.1 Preparation of the polymer-containing catalyst ink:

[0336] The catalyst (AgNPs, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink is 16.67 mg ml' 1 In addition, Triton X-100 is added as an ink stabilizer and pore-forming agent. Before adding the PTFE dispersion, the ink is pressed for 90 seconds at 13,400 rpm. -1homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with an ultrasonic bath for 15 minutes for further homogenization. The PTFE content in the catalyst ink, based on the weighed catalyst quantity, was 7.5 wt.%.

[0337] 3.2 Preparation of the ionomer-containing catalyst ink:

[0338] The catalyst (AgNPs, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink is 16.67 mg ml' 1 The catalyst ink is pressed for 90 seconds at 13,400 rpm -1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The Piperion content in the catalyst ink, based on the weighed catalyst, was 1 wt.%.

[0339] 3.3 Production of the GDE:

[0340] To prepare the catalyst layers, a polymer-containing catalyst ink is sprayed onto the commercial carbon fabric using an airbrush (Eclipse, Iwata) until the desired catalyst loading is achieved. Five GDEs with different catalyst loadings of the polymer-containing or ionomer-containing CLs were tested, with a total AgNP loading of the catalyst layers of 2.5 mg cm. -2 The corresponding compositions of the CLs are shown in Table 5. The PTFE content in the polymer-containing catalyst ink was 7.5 wt.% based on the weighed catalyst amount, and the Piperion content in the ionomer-containing catalyst ink was 1 wt.% based on the weighed catalyst. The polymer-containing CL is applied directly to the GDL, and the ionomer-containing CL is applied to the polymer-containing CL.

[0341] Table 3. Overview of the AgNP loadings of the prepared multilayered CLs. The multilayered CL consists of a polymer-containing CL at the bottom and an ionomer-containing CL applied on top. The loading of the polymer-containing CL at the bottom is shown in the middle column, and the loading of the ionomer-containing CL is shown in the right column.

[0342] 3.4 Production of the GDE

[0343] To ensure rapid evaporation of the solvent, the carbon fabric was heated to 90°C during the spraying process. The prepared polymer-containing catalyst ink is then sprayed onto the microporous side of the carbon fabric using an airbrush (Eclipse, Iwata) until the desired catalyst loading is achieved (see Table 3). The GDE thus prepared is then sintered for 15 minutes in air at 300°C. In a second step, the prepared ionomer-containing catalyst ink is sprayed onto the previously applied PTFE-CL onto the GDL with polymer-containing CL heated to 90°C until the target catalyst loading of the entire multilayer CL of

[0344] 2.5 mg cm -2 is reached.

[0345] 3.5 CO2 electrolysis

[0346] The CO2 electrolysis was carried out in a zero-gap electrolyzer with an active cell area of ​​2 cm 2At the anode, a porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 lrÜ2 (Alfa Aesar) was used. The anode chamber was continuously filled with 16.6 ml min -1 0.1 M KHCO3. At the cathode, the prepared GDE with an AgNPs (Alfa Aesar) loading of 2.5 mg cm - 2 Five different GDEs with multilayered CL were investigated. During electrolysis, the cathode chamber was filled with 50 ml min -1 CO2 and 5 ml mim 1Ar was used as an internal standard. Before entering the cathode chamber, the gas inlet stream was brought to a relative humidity of 79% (dew point: 55 °C) using a saturation steam humidifier. Both the 40 μm thick Piperion membrane and the GDE were activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic tests were carried out galvanostatically at 300 mA cirrus. 2 over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0347] The current efficiency for the target product CO (FEco) as well as the measured cell voltage (Uzeiie) are shown in Fig. 5 for all manufactured GDEs with multilayered CL.

[0348] Fig. 5 shows the cell voltage (A) and the current yields for the product CO (B) of a galvanostatic electrolysis at 300 mA cm -2 depending on the catalyst loadings in the Piperion- and PTFE-based CL, which result in the multilayer structure according to the invention. The PTFE content in the polymer-based catalyst ink used to produce the polymer-based CL was 7.5 wt.% based on the weighed-in catalyst. The Piperion content in the ionomer-based catalyst ink used to produce the ionomer-based CL was 1 wt.% based on the weighed-in catalyst. The test periods after reaching a steady state (2-3 hours) are shown in each case.

[0349] In Fig. 5 it can be seen that with all manufactured multilayer structures according to the invention (Example 1-A to 1-E, middle columns) higher current efficiencies FEco and lower cell voltages Uzeiie are achieved than with the best polymer-containing CL (Ref. A-3, left column) and the best ionomer-containing CL (Ref. B-1, right column).

[0350] Fig. 6 shows the cell voltage (A) and the current yields for the product CO (B) of a galvanostatic electrolysis at 300 mA cm -2 which were achieved with the polymer-containing CL (Reference A), ionomer-containing CL (Reference B), and the multilayer structure according to the invention (Example 1-1). The polymer-containing CL (Reference A) had a catalyst loading of 2.5 mg cm -2 and a catalyst ink containing 7.5 wt.% PTFE based on the catalyst AgNPs was prepared by spraying. The ionomer-containing CL (Reference B) had a catalyst loading of 2.5 mg cm -2and was prepared by spraying a catalyst ink containing 1 wt.% piperion based on the catalyst AgNPs. The inventive structure (Example 1-1) consists of a first polymer-containing CL (7.5 wt.% PTFE) with an AgNPs loading of 2.0 mg cm -2 and a second ionomer-containing CL (Piperlon) with an AgNPs loading of 0.5 mg cm -2 , so that the total AgNPs loading is 2.5 mg cm -2 The test periods after reaching a steady state (2-3 hours) are shown.

[0351] 4. Inventive embodiment 2 (multilayer structure with carbon in hydrophobic polymer-containing CL)

[0352] As an embodiment of the invention described here with a structure of the catalyst layers with carbon in the hydrophobic polymer-containing CL for CO2 reduction, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated in a first step with a polymer- and soot-containing CL and in a second step with an ionomer-containing CL.

[0353] 4.1 Production of the polymer-containing catalyst ink:

[0354] The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture, so that the concentration of the catalyst in the ink was 16.67 mg ml' 1 Subsequently, 20 wt.% carbon (Ensaco 250G) was added to the catalyst ink, based on the weighed catalyst quantity, and Triton X-100 was added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink was spun for 90 s at 13,400 rpm. -1homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The PTFE content of the catalyst ink was 7.5 wt.%.

[0355] Table 4: Example composition of a polymer-containing catalyst ink with 15 wt.% polymer (PTFE) based on the weighed catalyst amount of AgNPs. Additionally, 20 wt.% carbon (Ensaco 250G) based on the weighed catalyst amount of AgNPs was added.

[0356] 4.2 Preparation of the ionomer-containing catalyst ink:

[0357] The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink was 16.67 mg ml' 1 The catalyst ink was heated for 90 s at 13,400 rpm - 1homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The piperion content in the catalyst ink, based on the catalyst, was 1 wt.%.

[0358] 4.3 Production of the GDE:

[0359] To ensure rapid evaporation of the solvent, the carbon fabric was heated to 90°C during the spraying process. The prepared polymer-containing catalyst ink was then sprayed onto the microporous side of the carbon fabric using an airbrush (Eclipse, Iwata) until the desired catalyst loading was achieved (see Table 1). The prepared GDE was subsequently sintered in air at 300°C for 15 minutes. In a second step, the prepared ionomer-containing catalyst ink was sprayed onto the previously applied PTFE-CL onto the GDL with polymer-containing CL heated to 90°C until the target loading of 2.5 mg cm was reached. -2 was reached.

[0360] 4.4 CO2 electrolysis

[0361] The CCh electrolysis was carried out using an internally developed zero-gap electrolyzer with an active cell area of ​​2 cm 2A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrCh (Alfa Aesar) was used. The anode chamber was continuously filled with 16.67 ml min -1 0.1 M KHCO3. At the cathode, the prepared GDE were coated with an AgNPs (Alfa Aesar) loading of 2.5 mg cm - 2 During electrolysis, the cathode chamber was filled with 50 ml min -1 CO2 and 5 ml mim 1 Ar was used as an internal standard. Before entering the cathode chamber, the gas inlet stream was brought to a relative humidity of 79% (dew point: 55 °C) using a saturation vapor humidifier. Both the 40 μm thick Piperion membrane and the GDE with multilayered CL were activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic tests were carried out galvanostatically at 300 mA cm. 2over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0362] The current efficiency for the target product CO (FEco) as well as the measured cell voltage (Uzeiie) are shown for the manufactured GDE with multilayer structure according to the invention and carbon in the hydrophobic polymer-containing layer in Fig. 7 and 8 as embodiment 2-1.

[0363] Fig. 7 shows the current efficiency for the target product CO (FEco) and Fig. 8 the corresponding measured cell voltage (Uzeiie) of a galvanostatic electrolysis over 180 min at 300 mA cm' 2The averaged FEco (gray) and FEHZ (white) are shown as percentages on the left y-axis, and the averaged Uz in volts is shown on the right y-axis. Both are plotted against the electrolysis duration (tEiectroilyse) in minutes on the x-axis. The stable range after the conditioning phase in the last hour of electrolysis is highlighted in gray.

[0364] By incorporating 20 wt.% carbon, based on the weighed catalyst, into a polymer-containing catalyst ink with 15 wt.% PTFE, based on the weighed catalyst, an additional carbon-containing multilayered CL was produced (AsfB. 2-1 ). The catalyst ink of the ionomer-containing CL contained 1 wt.% piperion, based on the weighed catalyst. (See Table 4.) By using this multilayer structure with carbon in the polymer-containing layer, the FEco could be increased to 75% at a cell voltage of 3 V and an applied current density of 300 mA cm -2 compared to the embodiments 1-1 to 1-5, as shown in Figs. 7 and 8. 5. Inventive embodiment 3 (multilayered CL with carbon in polymer-containing CL using a bipolar solid electrolyte membrane)

[0365] As an embodiment of the invention described here of a multilayered CL with carbon in the polymer-containing CL when using a bipolar solid electrolyte membrane for the CO2R, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated in a first step with a polymer- and carbon black-containing CL and in a second step with an ionomer-containing CL.

[0366] 5.1 Production of the polymer-containing catalyst ink:

[0367] The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture, so that the concentration of the catalyst in the ink was 16.67 mg ml' 1Subsequently, 20 wt.% carbon (Ensaco 250G) was added to the catalyst ink, based on the weighed catalyst quantity, and Triton X-100 was added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink was spun for 90 s at 13,400 rpm. -1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The PTFE content of the catalyst ink was 7.5 wt.%.

[0368] Table 5: Example composition of a polymer-containing catalyst ink with 7.5 wt.% polymer (PTFE) based on the weighed catalyst amount of AgNPs. Additionally, 20 wt.% carbon (Ensaco 250G) based on the weighed catalyst amount of AgNPs was added.

[0369] 5.2 Preparation of the ionomer-containing catalyst ink: The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink was 16.67 mg ml' 1 The catalyst ink was heated for 90 s at 13,400 rpm 1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The piperion content in the catalyst ink, based on the catalyst, was 1 wt.%.

[0370] 5.3 Production of the GDE:

[0371] To ensure rapid evaporation of the solvent, the carbon fabric was heated to 90°C during the spraying process. The prepared polymer-containing catalyst ink was then sprayed onto the microporous side of the carbon fabric using an airbrush (Eclipse, Iwata) until the desired catalyst loading was achieved (see Table 1). The prepared GDE was subsequently sintered in air at 300°C for 15 minutes. In a second step, the prepared ionomer-containing catalyst ink was sprayed onto the previously applied PTFE-CL onto the GDL with polymer-containing CL heated to 90°C until the target loading of 2.5 mg cm was reached. -2 was reached.

[0372] 5.4 Production of the bipolar membrane

[0373] The bipolar membrane was fabricated by laminating a 40 pm thick Piperion membrane and a 50 pm thick Nation 212 membrane in a hot press at 50 °C and a pressure of 10 bar with a pressing time of 90 s.

[0374] 5.5 CO2 electrolysis

[0375] The CCh electrolysis was carried out using an internally developed zero-gap electrolyzer with an active cell area of ​​12.57 cm 2 A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrCh (Alfa Aesar) was used. The anode chamber was continuously filled with 66.67 ml min -1 Ultrapure water (18.2 MQ cm). At the cathode, the prepared GDE with an AgNPs (Alfa Aesar) loading of 2.5 mg cm - 2 used.

[0376] During electrolysis, the cathode chamber was filled with 50 ml min -1 CO2 and 5.5 ml mim 1Ar was used as an internal standard. Both the bipolar membrane produced by lamination and the GDE with multilayered CL were activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic tests were carried out galvanostatically at 300 mA cm. -2 over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0377] Fig. 9 shows the current efficiency for the target product CO (FEco) and Fig. 10 the measured cell voltage (Uzeiie) for the manufactured GDE with multilayered CLs with carbon in the polymer-containing layer using a bipolar membrane. Galvanostatic electrolysis over 180 min at 300 mA cm 2The averaged FEco (gray) and FEH2 (white) are plotted as percent on the left y-axis, and the averaged U line in volts is plotted on the right y-axis. Both are plotted against the electrolysis time (tEiectroilyse) in minutes on the x-axis.

[0378] By incorporating 20 wt.% carbon, based on the weighed catalyst, into a polymer-containing catalyst ink with 7.5 wt.% PTFE, an additional carbon-containing multilayered CL was produced (AsfB. 2-1 ). The catalyst ink of the ionomer-containing CL contained 1 wt.% Piperion based on the weighed catalyst. (See Table 4.) When using a laminated bipolar membrane consisting of a 40 pm thick Piperion membrane and a 50 pm thick Nafion 212 membrane, an FEco of up to 50% was achieved at a cell voltage of 3.3 - 3.4 V at an applied current density of 300 mA cirr 2 can be achieved.

[0379] 6. Inventive embodiment 4 (multilayered CL with carbon in polymer-containing CL using a bipolar solid electrolyte membrane)

[0380] As an embodiment of the invention described here of a multilayered CL with carbon in the polymer-containing CL when using a bipolar solid electrolyte membrane for the CO2R, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated in a first step with a polymer- and carbon black-containing CL and in a second step with an ionomer-containing CL.

[0381] 6.1 Preparation of the polymer-containing catalyst ink:

[0382] The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture, so that the concentration of the catalyst in the ink was 16.67 mg ml -1Subsequently, 20 wt.% carbon (Ensaco 250G) was added to the catalyst ink, based on the weighed catalyst quantity, and Triton X-100 was added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink was spun for 90 s at 13,400 rpm. 1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The PTFE content of the catalyst ink was 7.5 wt.%.

[0383] Table 6: Example composition of a polymer-containing catalyst ink with 7.5 wt.% polymer (PTFE) based on the weighed catalyst amount of AgNPs. Additionally, 20 wt.% carbon (Ensaco 250G) based on the weighed catalyst amount of AgNPs was added.

[0384] 6.2 Preparation of the ionomer-containing catalyst ink:

[0385] The catalyst (AgNPs, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink was 16.67 mg ml' 1 The catalyst ink was heated for 90 s at 13,400 rpm 1 homogenized (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The piperion content in the catalyst ink, based on the catalyst, was 1 wt.%.

[0386] 6.3 Production of the GDE:

[0387] To ensure rapid evaporation of the solvent, the carbon fabric was heated to 90°C during the spraying process. The prepared polymer-containing catalyst ink was then sprayed onto the microporous side of the carbon fabric using an airbrush (Eclipse, Iwata) until the desired catalyst loading was achieved (see Table 1). The prepared GDE was subsequently sintered in air at 300°C for 15 minutes. In a second step, the prepared ionomer-containing catalyst ink was sprayed onto the previously applied PTFE-CL onto the GDL with polymer-containing CL heated to 90°C until the target loading of 2.5 mg cm was reached. -2 was reached.

[0388] 6.4 Production of the bipolar membrane

[0389] The bipolar membrane was prepared by spraying a piperion solution (1 wt.% in ethanol) onto a 50 pm thick Nafion 212 membrane and then treating it in a hot press at 50 °C and a pressure of 10 bar with a pressing time of 90 s.

[0390] 6.5 CO2 electrolysis

[0391] The CO2 electrolysis was carried out using an internally developed zero-gap electrolyzer with an active cell area of ​​12.57 cm 2 A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrOz (Alfa Aesar) was used. The anode chamber was continuously filled with 66.67 ml min -1 Ultrapure water (18.2 MQ cm). At the cathode, the prepared GDE with an AgNPs (Alfa Aesar) loading of 2.5 mg cm - 2 used.

[0392] During electrolysis, the cathode chamber was filled with 50 ml min -1 CO2 and 5.5 ml min -1Ar was purged. Argon served as an internal standard. Both the bipolar membrane produced by lamination and the GDE with multilayered CL were activated in 1 M KOH for 30 minutes immediately before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic tests were carried out galvanostatically at 300 mA cirrus. 2 over an electrolysis period of 3 hours. Samples of the resulting gaseous product stream from the cathode were analyzed every 20 minutes by GC-MS.

[0393] Fig. 11 shows the current efficiency for the target product CO (FEco) and Fig. 12 the measured cell voltage (Uzeiie) for the manufactured GDE with multilayered CLs with carbon in the polymer-containing layer using a bipolar membrane. Galvanostatic electrolysis for 180 min at 300 mA cm 2The averaged FEco (gray) and FEH2 (white) are shown in percent on the left y-axis, the averaged voltage in volts is on the right y-axis. Both are plotted against the electrolysis time (tElectrolysis) in minutes on the x-axis. By additionally incorporating 20 wt.% carbon, based on the weighed catalyst, into a polymer-containing catalyst ink with 7.5 wt.% PTFE, an additional carbon-containing multilayered CL was produced (Figure 2-1). The catalyst ink of the ionomer-containing CL contained 1 wt.% piperion, based on the weighed catalyst. (See Table 4.)

[0394] Using a bipolar membrane, prepared by spraying a piperion solution (1 wt.% in ethanol) onto a 50 pm thick Nafion 212 membrane, an FEco of up to 43% could be achieved at a cell voltage of 3.3 - 3.6 V at an applied current density of 300 mA cm -2 can be achieved.

[0395] List of reference symbols: Electrode 5 Electrolysis cell hydrophobic catalyst layer 6 Anode hydrophilic catalyst layer 7 Membrane gas diffusion layer

Claims

Patent claims:

1. Gas diffusion electrode, in particular for the electrochemical reduction of CO2, characterized in that the electrode has at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer.

2. Electrode according to claim 1, characterized in that the hydrophobic catalyst layer and the hydrophilic catalyst layer are porous.

3. Electrode according to claim 1 or 2, characterized in that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly or indirectly, preferably directly, on one another.

4. Electrode according to one of the preceding claims, characterized in that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged on a porous carrier layer, in particular a gas diffusion layer.

5. Electrode according to claim 4, characterized in that the porous carrier layer is selected from the group of carbon fabrics, carbon fiber paper, graphite fabrics, metal felts, metal meshes, sintered metals and mixtures thereof, in particular is selected from the group of carbon fabrics, carbon fiber paper and mixtures thereof, preferably a carbon fabric.

6. Electrode according to one of the preceding claims, characterized in that the hydrophobic catalyst layer and the hydrophilic catalyst layer each contain at least one catalyst.

7. Electrode according to one of the preceding claims, characterized in that the catalyst is selected from the group of metal particles, in particular metal nanoparticles, single atom catalysts, metal carbides, metal oxides, metal chalcogenides, molecular catalysts and mixtures thereof.

8. Electrode according to one of the preceding claims, characterized in that the hydrophilic catalyst layer comprises at least one hydrophilic polymer, in particular an ionomer.

9. Electrode according to claim 8, characterized in that the hydrophilic polymer is selected from the group of cation exchange polymers, anion exchange polymers and mixtures thereof.

10. Electrode according to one of the preceding claims, characterized in that the hydrophobic catalyst layer comprises at least one hydrophobic polymer.

11. Electrode according to claim 10, characterized in that the hydrophobic polymer is selected from the group of polyolefins, polyfluoroolefins, silicones, fluorinated polymers, polyaromatic polymers and their copolymers and mixtures.

12. Use of an electrode according to one of claims 1 to 11 in electrolysis.

13. Use of an electrode according to one of claims 1 to 11 as a cathode in the electrochemical reduction of carbon dioxide.

14. A method for producing an electrode according to any one of claims 1 to 13, characterized in that (i) in a first process step, a first coating composition for producing a first hydrophilic or hydrophobic, preferably hydrophobic, catalyst layer is applied to a porous support material or an ion-conducting membrane and (ii) in a second process step following the first process step (I), a second coating composition different from the first coating composition is applied to produce a second hydrophilic or hydrophobic, preferably hydrophilic, catalyst layer on the hydrophobic or hydrophilic, preferably hydrophobic, first catalyst layer is applied.

15. The method according to claim 14, characterized in that the hydrophilic and / or hydrophobic first and / or second coating composition is in the form of a dispersion, in particular wherein preferably the first and the second hydrophilic and / or hydrophobic coating composition are in the form of a dispersion.

16. The method according to claim 14 or 15, characterized in that the hydrophobic coating composition comprises a conductivity improver, in particular wherein the conductivity improver is selected from carbon black, graphite, carbon nanotubes and mixtures thereof.

17. Electrolysis cell, in particular for the electrochemical reduction of carbon dioxide, comprising at least one electrode according to one of claims 1 to 11.

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