Gas diffusion electrode and electrolytic cell with same

Abstract

The utility model relates to a gas diffusion electrode and an electrolytic tank with the gas diffusion electrode. In particular to a gas diffusion electrode of an electrolytic tank for electrochemically reducing CO2 into CO, an anode chamber and a cathode chamber are separated by an anion exchange membrane (AEM), and the electrode is provided with at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer.

Description

Technical Field

[0001] The utility model relates to the field of electrolysis technology, and particularly to the electrochemical reduction of carbon dioxide.

[0002] In particular, the utility model relates to a gas diffusion electrode preferably used for the electrochemical reduction of carbon dioxide.

[0003] The utility model also relates to an electrolytic cell for the electrochemical reduction of carbon dioxide. Background Art

[0004] In an aqueous environment, valuable chemical raw material products such as carbon monoxide, alcohols, aldehydes, ketones, and carboxylic acids can be obtained from carbon dioxide by means of electrochemical reduction.

[0005] In addition to extracting valuable raw materials, the electrochemical reduction of carbon dioxide also has the following advantages: the greenhouse gas CO 2 can be removed from the environment, or can be collected and further processed, for example, after a combustion process or an industrial process, and thus will not even be released into the environment. With the expansion of renewable energy and related carbon dioxide-based energy production, carbon dioxide electrolysis is expected to become more important, especially because it can both extract valuable raw materials for the chemical industry and save fossil raw materials.

[0006] Currently, in an electrolytic cell, for CO 2 reduction and CO reduction, a single-layer catalyst layer (CL) containing a polymer, a single-layer catalyst layer (CL) containing an ionomer, and a single-layer catalyst layer (CL) containing a polymer and an ionomer are adopted.

[0007] In an electrode with a polymer-containing CL, the catalyst substance is bound by the polymer on a porous gas diffusion layer (GDL) or a porous transport layer (PTL). For this purpose, a mixture of a catalyst and a polymer binder is usually applied to the porous GDL or porous PTL by a wet manufacturing process (such as spraying). As other manufacturing processes, hot pressing or doctor blading is also particularly used for applying a dry powder mixture.

[0008] For the catalyst layer, fluoropolymers such as polytetrafluoroethylene (PTFE) are usually adopted because they can utilize their hydrophobic properties to reduce the problem of excessive water flooding the electrode pores and related CO 2 mass transfer problems. This is particularly important in processes using gaseous reactants. In addition to CO 2In addition to electrolysis and CO electrolysis, examples of using such fluoropolymer-based catalyst layers also include fuel cell technology and chlor-alkali electrolysis.

[0009] In the field of CO 2 electrolysis, single-layer polymer-containing catalyst layers (CLs) have so far been mainly applied to gas-liquid electrolyzers because this can slow down the unwanted penetration of the liquid electrolyte into the gas diffusion electrode (GDE) and reduce the associated limitations of carbon dioxide mass transfer.

[0010] Studies have shown that appropriate hydrophobicity in the catalyst layer is the key to selective CO 2 reduction. By applying a catalyst-free, ionomer-containing coating, the ionic conductivity and surface wettability of the catalyst layer in the gas-liquid electrolyzer can be improved, thereby improving the product selectivity of CO 2 reduction at industrial current densities (Junge Puring K, Siegmund D, Timm J et al., Electrochemical CO 2 Reduction (Electrochemical CO 2 reduction): Tailoring Catalyst Layers in Gas Diffusion Electrodes. Adv. Sustainable Syst. (Gas diffusion electrodes in the custom catalyst layer. Advanced Sustainable Systems) 2021; 5(1): 2000088).

[0011] In addition, studies have shown that the catalyst layer is the first protective layer against electrode flooding, and the long-term stability of the electrode can be significantly improved by the appropriate hydrophobicity of the binder (Nwabara UO, Hernandez AD, Henckel DA et al., Binder-Focused Approaches to Improve the Stability of Cathodes for CO 2 Electroreduction. ACS Appl. Energy Mater (Binder-centered methods to improve the stability of cathodes for CO 2 electroreduction. ACS Applied Energy Issues) 2021; 4(5): 5175–86).

[0012] However, using such electrodes in gas-liquid electrolyzers is not very economical because the limited electrolyte conductivity requires high energy demands for the electrochemical process. Application in a typically strongly basic electrolyte, which is preferably used for CO 2 reduction, is also disadvantageous because of the reaction between hydroxide and gaseous CO 2Neutralization and carbonate formation occur due to the reaction of. In particular, the formation of carbonate leads to the continuous hydrophilicity of the gas diffusion electrode and thus to the electro-wetting and overflow of the electrode. At an industrial current density of ≥ 300 mA cm -2 it is rarely possible to achieve an electrolysis duration of ≥ 10 h.

[0013] Even in a zero-gap electrolyzer, i.e., an electrolyzer in which the catalyst layer is in direct contact with a solid polymer electrolyte made of an ion-conductive polymer, excessive water accumulates in the pores of the gas diffusion electrode on the cathode side, despite the lack of liquid electrolyte on the cathode. Therefore, the use of a hydrophobic polymer-containing catalyst layer can also help to minimize the overflow process.

[0014] So far, hydrophobic polymer-containing catalyst layers have only been used occasionally for CO 2 reduction. This shows that as the proportion of PTFE in the polymer-containing catalyst layer increases, the overflow behavior decreases, and it is advantageous to use a thin film usually less than 40 μm. However, the partial current density of less than 100 mA cm -2 achieved at a cell voltage of 3 V and an electrolysis duration of 25 minutes is still far from the industrially relevant results of a partial current density greater than or equal to 300 mA cm -2 and an electrolysis duration of ≥ 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 (Managing cathode hydration enables efficient CO 2 electrolysis. ACS Energy Lett 2020); 5(5):1612–8).

[0015] In the field of CO 2 reduction, the disadvantage of using a hydrophobic polymer-containing catalyst layer in gas-liquid electrolyzers as well as zero-gap electrolyzers is the lack of ionic conductivity of the catalyst. One way to improve these systems could be an ionomer coating; however, due to the application of a low-viscosity ionomer within the polymer-containing catalyst layer, pore closure or inhomogeneity leading to mass transport limitations may occur.

[0016] Furthermore, the ionomer coating itself does not contain any catalyst and thus has neither catalytic activity nor electrical conductivity, which is why inactive regions may occur in the hydrophobic polymer-containing CL. The currently used single-layer, hydrophobic polymer-containing catalyst layer and the single-layer, hydrophobic polymer-containing catalyst layer with an ionomer coating are not suitable for achieving an industrially relevant ≥300 mA cm -2 current density at a cell voltage ≤ 3 V and an electrolysis duration ≥ 10 h.

[0017] Compared with the single-layer polymer-containing catalyst layer, the use of an ion-conductive single-layer ionomer-containing catalyst layer enables a significantly lower cell voltage to be achieved at higher partial current densities and longer electrolysis durations. They represent the state of the art for CO 2 reduction in zero-gap electrolyzers. To prepare the ionomer-containing gas diffusion electrode, a wet manufacturing process, such as spraying, is typically used to apply the catalyst ink onto the porous conductive gas diffusion layer (GDL). As another manufacturing process, for example, the doctor blade process is also employed. Through the ionomer in the catalyst layer, good ionic contact between the catalyst layer and the liquid electrolyte in the gas-liquid electrolyzer or the solid electrolyte membrane (SPE-membrane) in the zero-gap electrolyzer can be achieved.

[0018] In the field of CO 2 reduction, at the industrially relevant current density in zero-gap electrolyzers, a significantly lower cell voltage and longer electrolysis duration can be achieved compared to using the above-mentioned polymer-containing catalyst layer. In a zero-gap electrolyzer with an anion-conducting single-layer ionomer-containing catalyst layer, in combination with an anion exchange membrane (AEM), at an industrially relevant current density ≥ 300 mA cm -2 the electrolysis duration has reached ≥ 200 h at a cell voltage ≤ 3 V.

[0019] By using an ionomer with poly(arylpiperidinium) groups (Piperion) in the solid electrolyte membrane (SPE membrane) and the catalyst layer, for example, in a zero-gap electrolyzer, a partial current density of up to 420 mA cm -2 was achieved at 3.2 V for more than 200 hours for the target product carbon monoxide. B, Samu A, Kecsenovity E, Halmágyi T, D, Janáky 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).

[0020] Using a solid polymer electrolyte membrane (SPE membrane) and a catalyst layer (CL) containing an imidazolium group-based ionomer (sustainion), a current density of 400 mA cm 池 can be achieved at a cell voltage (U -2 ) of approximately 3.2 V and an electrolysis duration of ≥70 h (Liu Z, Yang H, Kutz R, Masel RI. Electrolysis to CO and O2 at High Selectivity, Stability and Efficiency Using Sustainion Membranes (J. Electrochem. Soc. 2018; 165(15): J3371-J3377)). 2 to CO and O 2 )

[0021] In addition to these results, further studies were also carried out on ionomer-containing catalyst layers in zero-gap electrolyzers at industrial current densities. However, at a current density of ≥300 mA cm -2 and a cell voltage of ≤3.2 V, they were unable to achieve an electrolysis duration of more than 70 h. In particular, it can be shown here that, in addition to using AEMs and PEMs, promising results can also be obtained if an anion-conducting ionomer is used in the catalyst layer of the cathode, thereby obtaining a bipolar boundary layer. This structure seems to have an advantage over using bipolar membranes, as a significantly reduced cell voltage can be achieved. Nevertheless, it is still difficult for CO 2 to be transferred 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 CO 2Reduction from Gas Phase at Low Temperature (for efficient reduction of CO from the gas phase at low temperature 2 (co-electrolyzer design), July 24, 2017).

[0022] In addition to being applied in zero-gap electrolyzers, the ionomer-containing catalyst layer is also applied in gas-liquid electrolyzers. However, due to the above-mentioned strong overflow, the electrolysis duration of these systems is limited. In one publication, contrary to most publications, a porous polymer membrane was used as the gas diffusion layer (GDL) instead of a porous hydrophobic carbon fabric. The catalyst was applied to the porous polymer membrane using a PVD process so that the catalyst could then be adhered by spraying an ionomer. Thus, at a current density of 1 A cm -2 and FE C2H4 ≥ 50%, an electrolysis duration of ≥ 60 h could be achieved (García de Arquer FP, Dinh C-T, Ozden A et al., CO 2 electrolysis to multicarbon products at activities greater than 1 A cm -2 (at greater activities than 1 A cm -2 reduce CO 2 to multicarbon products). Science 2020; 367(6478): 661–6).

[0023] Thus, so far, in the field of CO 2 reduction, at an industrial current density ≥ 300 mA cm -2 the electrolysis duration of the ionomer-containing catalyst layer in gas-liquid electrolyzers is limited to 60 h, and in zero-gap electrolyzers it is limited to 2000 h, where a reciprocal proportional correlation between the electrolysis duration and the current density can usually be observed. The lack of long-term stability of the catalyst layer is due to the insufficient hydrophobicity of the catalyst layer. Although hydrophobicity can be achieved in the polymer-containing catalyst layer by selecting the ratio and type of the polymer used and by adjusting pore formation through a sintering process, this is not possible for the currently used ionomer-containing CL. Since the ionomer-containing catalyst layer does not have sufficient hydrophobicity to slow down the overflow of the gas diffusion electrode, they rely on a highly hydrophobic gas diffusion layer (GDL).

[0024] In addition to using a single-layer catalyst layer containing a polymer and a single-layer catalyst layer containing an ionomer, a single-layer catalyst layer containing a polymer and an ionomer is also used to combine the properties of the two types of binders in one catalyst layer. However, when examining various single-layer catalyst layers containing both a hydrophobic polymer and a hydrophilic ionomer, no flooding behavior was found in a zero-gap electrolyzer or the achievable electrolysis duration was improved compared to hydrophobic, purely polymer-containing or purely ionomer-containing catalyst layers, because the overall hydrophobicity can be reduced by the proportion of the ionomer and the ionic conductivity of the SPE membrane can be reduced by the proportion of the polymer.

[0025] In fuel cell technology, electrodes with multiple different catalyst layers are employed to improve water management on the corresponding electrodes. On the one hand, a multilayer-structured ionomer-containing catalyst layer (CL) is used to achieve a gradient in terms of ionic conductivity or porosity. In addition, multilayer structures with hydrophobic and hydrophilic catalyst layers have been used. For example, such a structure is used to improve catalyst utilization in methanol fuel cells, as disclosed in DE 601 33 879T2, and to improve catalyst utilization in PEM fuel cells, as described in CN 100521313C. Generally, the water content of the catalyst should be adjusted and sufficient mass transfer of gaseous substances should be ensured, whereby a higher power density and long-term stability can be achieved. However, the hydrophobic catalyst layer according to CN 100521313C always contains a certain proportion of ionomer, which results in good ionic conductivity but ultimately leads to flooding of the electrode. The same also applies to the multilayer structure according to DE 601 33 879T2.

[0026] Similar to fuel cell technology, in the field of electrochemical CO 2 reduction, water management at the cathode is also crucial. The multilayer-structured catalyst layers developed in the field of fuel cell technology cannot be directly used for CO 2 reduction because CO 2 reduction is much more complex. While the goal of a PEM-fuel cell is to achieve mass transfer of gaseous segregation products with sufficient ionic conductivity introduced by water, a large number of influencing factors must be considered in the reduction of CO 2 In the reduction of CO 2 two reactants, CO 2 and water, must be provided on the catalyst layer (CL) of the cathode, the parasitic hydrogen evolution reaction (HER) must be suppressed and the desired product must be obtained. This mainly depends on the direct catalyst environment. In addition to adjusting the water content by the hydrophobicity of the layer, for the corresponding CO 2The reduction process is used to adjust the local pH value, porosity, and catalyst availability. Currently, the corresponding multi-layer catalyst layer has not been developed and optimized for CO 2 reduction. Since the formation of carbonate in the catalyst layer (CL) and gas diffusion layer (GDL) plays no role in the field of fuel cell technology, it is also important to develop a suitable catalyst layer to inhibit the formation of carbonate for COx electrolysis. Therefore, the multi-layer catalyst layer currently used in the field of fuel cells is not suitable for the requirements of CO 2 reduction in electrolyzers, although the water management in the case of fuel cells and the CO 2 reduction targets in zero-gap electrolyzers are similar. SUMMARY OF THE UTILITY MODEL

[0027] Now, an object of the present utility model is to avoid or at least mitigate the previously described disadvantages associated with the prior art.

[0028] In particular, an object of the present utility model is to provide an electrode, especially a gas diffusion electrode, which can operate persistently at industrial current intensities and has a high current yield, and is particularly suitable for reducing CO2.

[0029] Therefore, according to the first aspect of the present utility model, the subject matter of the present utility model is a gas diffusion electrode for an electrolytic cell for electrochemically reducing CO2 to CO, wherein the anode chamber and the cathode chamber are separated by an anion exchange membrane (AEM), and the electrode has at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer. Other advantageous designs of this aspect of the present utility model are the subject matter of the relevant dependent claims.

[0030] According to the second aspect of the present utility model, another subject matter of the present utility model is an electrolytic cell, especially for electrochemically reducing carbon dioxide to carbon monoxide, having the electrode described above.

[0031] It goes without saying that in the following - in order to avoid unnecessary repetition - the special features, characteristics, designs, and implementation manners, as well as advantages, etc., which are only explained for one aspect of the present utility model, of course, correspondingly apply to the remaining aspects of the present utility model without explicitly mentioning this.

[0032] In addition, all the values or parameter information, etc., mentioned below can in principle be determined using standardized or clearly specified determination methods or using determination methods familiar to those skilled in the art. Furthermore, it goes without saying that all percentages related to weight or quantity are interpreted by those skilled in the art in a way that the sum is 100%.

[0033] That being said, the present utility model will be described in more detail below.

[0034] According to the present utility modelFirst In one aspect, the subject matter of the present utility model is a gas diffusion electrode especially for the electrochemical reduction of CO 2 , wherein the electrode has at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer.

[0035] Because, as the applicant has surprisingly found, the main problems of the gas diffusion electrodes used hitherto can be avoided by using a gas diffusion electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer. In particular, the disadvantages of the hydrophilic ionomer-containing catalyst layer, namely the gradual flooding of the cathode chamber and thus the deterioration of mass transfer and ultimately the interruption of electrolysis, can be avoided. At the same time, the disadvantages of a pure hydrophobic polymer-containing catalyst layer, namely low mass conversion rate and low available current density, can also be avoided.

[0036] In the context of the present utility model, it is generally stipulated that a hydrophobic catalyst layer (Catalyst Layer, CL) is first applied to a commercially available gas diffusion layer (GDL) or a porous support material (PTL), and then a hydrophilic catalyst layer (Catalyst Layer, CL) is applied. At the phase boundary between the electrode and the substrate, especially in the interfacial region between the hydrophobic and hydrophilic catalyst layers, effective reduction of the substrate, especially carbon dioxide, can be achieved. The effective reduction of the substrate is achieved in particular by the fact that there is no three-phase boundary between the electrode, the electrolyte and the substrate, but rather the substrate (i.e., carbon dioxide) is not guided through the aqueous phase at the interface between the hydrophilic and hydrophobic catalyst layers, but only wetted. Due to the use of hydrophobic and hydrophilic catalyst layers, the electrode is not flooded with liquid water, but only wetted enough for the electrochemical reduction of carbon dioxide to occur. The rapid transport of the ions formed is also possible by using a hydrophilic catalyst layer.

[0037] As an alternative to the electrode preparation described previously, it is also possible to first apply the hydrophilic catalyst layer to an ion-conducting membrane, and then apply the hydrophobic catalyst layer to the hydrophilic catalyst layer. This structure is then applied to the gas diffusion layer with the hydrophobic catalyst layer.

[0038] Due to the multi-layer structure of the gas diffusion electrode described in the present utility model, the gas diffusion electrode has a plurality of catalyst layers, the catalyst layers having at least one hydrophobic, especially polymer-containing, catalyst layer and at least one hydrophilic, especially ionomer-containing, catalyst layer, so that the physical properties of the electrode can be adjusted according to the CO 2 reduction and the corresponding process conditions. In addition to gas, ion and electron transport, wettability and ion transport can also be adjusted separately and decoupledly on the one hand at the phase boundary between the electrode and the substrate and on the other hand at the phase boundary between the electrode and the electrolyte.

[0039] Here, by means of a hydrophobic, especially polymer-containing CL, the binding to the GDL, the pore distribution, and the overall hydrophobicity can be improved, and the cost of the CL can be reduced. By means of a hydrophilic, especially ionomer-containing CL, the cell voltage can be reduced due to the improved ionic conductivity, and the local pH value at the catalyst can be appropriately adjusted to reduce CO 2 2 . By means of a multilayer structure having at least two catalyst layers, further advantages are also achieved: Since the active region in the gas diffusion electrode is not a two-dimensional plane, but a three-dimensional region having a certain depth perpendicular to the plane, by providing a catalyst and continuous conductivity on both sides of the phase boundary, the region having an active catalyst substance in the catalyst layer can be enlarged. In addition, the use of a hydrophilic catalyst layer and a hydrophobic catalyst layer enables a synergistic combination of the performances of different catalyst layers. The hydrophobic catalyst layer prevents the electrode from being flooded with water, while the hydrophilic layer can rapidly transport the generated ions to the membrane. The combination of these two characteristics results in a significant improvement in the electrochemical reduction efficiency of carbon dioxide, with a higher current density, a higher yield, and a longer operating time.

[0040] In the context of the present invention, the hydrophobic catalyst layer should be understood to mean a catalyst layer in which the contact angle of the material of the catalyst layer with water is at least 90°, preferably at least 120°, preferably at least 140°, particularly preferably at least 160°.

[0041] In contrast, in the context of the present invention, the hydrophilic catalyst layer should be understood to mean a catalyst layer in which the contact angle of the material of the catalyst layer with water is less than 90°, preferably less than 50°, preferably less than 40°, particularly preferably less than 30°.

[0042] The contact angle can be determined, for example, by static contact angle measurement using an optical method.

[0043] In the context of the present invention, an ionomer should be understood to mean a copolymer composed of electrically neutral repeating units and repeating units having ionic functional groups. Based on the polymer, the proportion of ionic repeating units generally does not exceed 15% (mol). The ionic groups are usually carboxylic acid functional groups or carboxylates or sulfonic acid groups or sulfonates. Ionomers generally have high ionic conductivity but no electrical conductivity and are usually used as solid electrolytes in electrolytic cells or as ion-conducting membranes, especially proton-conducting membranes.

[0044] Particularly important in the context of the present utility model is that both the hydrophilic catalyst layer and the hydrophobic catalyst layer have a certain proportion of catalysts for electrochemical reactions, especially reduction. Only in this way can the excellent improved performance of the electrode according to the present utility model be achieved. Using a hydrophobic layer without a catalyst (on which a hydrophilic catalyst layer or a hydrophobic catalyst layer is applied and on which a catalyst-free hydrophilic layer is applied) does not result in improved performance. Sometimes the performance of the mixed layer with hydrophilic and hydrophobic regions used in the prior art also cannot compare with the system according to the present utility model. Only an electrode with a hydrophobic catalyst layer and a hydrophilic catalyst layer can lead to an increase in the area of the region with active catalyst substance, and the electrode will not face the risk of being flooded.

[0045] In addition, the electrode according to the present utility model is different from the electrodes with hydrophobic and hydrophilic catalyst layers used in the fuel cell technology field in that the binder, i.e., the adhesive, used in the context of the present utility model does not have an ionomer for the hydrophobic layer.

[0046] The multi-layer structure according to the present utility model has at least one hydrophobic, especially polymer-containing, catalyst layer and at least one hydrophilic, especially ionomer-containing, catalyst layer. Through this multi-layer structure, compared with the conventional single-layer polymer-containing catalyst layer (CL), single-layer ionomer-containing catalyst layer (CL), and single-layer polymer- and ionomer-containing catalyst layer (CL), at least 10 times higher current yield, lower cell voltage, higher energy efficiency, and improved long-term stability can be achieved. Thus, when reducing CO 2 using the system according to the present utility model, a current yield increased by up to 16% can be obtained at a cell voltage (U 池 ) of approximately 100 mV, and the long-term stability is improved by at least 10 times. In addition, the amount of ionomer used can be greatly reduced, preferably by about 20%, so that a corresponding reduction in material cost can be achieved.

[0047] In order to reduce CO 2For applications in the fields of reduction, CO reduction or other electrochemical processes, the multilayer structure according to the present invention having at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer is preferably applied to a commercially available GDL or PTL. The application of the coating composition can be carried out by dry or wet coating methods, such as by spraying, knife coating, drop coating, printing or by a combination of these methods. The catalyst layer can be applied to a porous carrier layer (catalyst-coated matrix) or an ion-conducting membrane (catalyst-coated membrane), and a combination of these two methods is also possible. The catalyst is usually combined with the corresponding structure through a suitable binder such as a hydrophobic polymer or an ionomer. By adjusting the type of catalyst used, the type of binder, the ratio of binder to catalyst, and the catalyst loading in each layer, the performance of the structure with multiple catalyst layers can be further adjusted.

[0048] Hydrophilic polymers, especially ionomers and resins with or without ion-exchange groups, and hydrophobic polymers have proven to be particularly suitable binders in the above sense.

[0049] The gas diffusion electrode according to the present invention is very suitable for applications in the electrochemical processes already mentioned. For the described applications, the electrode usually acts as a cathode for the reduction of CO 2 、CO、N 2 or O 2 or the electroreduction (e.g., hydrogenation) of organic molecules. Depending on the application, it can also be used as an anode for oxidation reactions (H 2 、N 2 or CO 2 oxidation, oxidation of organic compounds). The electrolytic cell also includes another electrode on which appropriate oxidation or reduction processes can occur.

[0050] The most important advantage of the present invention described here is the application of at least one hydrophobic, especially polymer-containing, catalyst layer and at least one hydrophilic, especially ionomer-containing, catalyst layer. As a result, the hydrophobicity and porosity in the hydrophobic, especially polymer-containing, layer facing the GDL can be adjusted independently of the ionic conductivity and chemical environment, such as independently of the cocatalytic effect of the ionomer, which allows, for example, the control of the local pH value in the catalyst layer of the hydrophilic, especially ionomer-containing, layer facing the electrolyte. Thus, ideal conditions for the reduction of CO 2 can be set at the formed three-phase boundary layer, thereby achieving a higher current density, an improved current yield of the target product, a reduced cell voltage, and an improved electrolysis duration.

[0051] In the context of the present utility model, it is generally stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer are porous. In this way, on the one hand, sufficient mass transfer can be carried out through the electrodes, and on the other hand, a large surface area is available for electrochemical reactions.

[0052] In the context of the present utility model, it can be stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer are in direct or indirect contact with each other. Direct contact means that the hydrophilic catalyst layer is applied to the hydrophobic catalyst layer, or vice versa. The hydrophilic and hydrophobic catalyst layers are preferably in direct contact with each other.

[0053] Similarly, within the scope of the present utility model, it can be stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly or indirectly one above the other. Preferably, the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly one above the other.

[0054] Within the scope of the present utility model, it can also be stipulated that a plurality of hydrophobic or hydrophilic catalyst layers are used in order to locally or gradually specifically adjust the hydrophobicity and hydrophilicity. The electrode according to the present utility model preferably has a hydrophobic catalyst layer and a hydrophilic catalyst layer.

[0055] According to a preferred embodiment of the present utility model, it is stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged on a porous layer, in particular on a porous carrier layer, preferably on a gas diffusion layer.

[0056] The porous layer preferably has a porosity, that is, based on the volume of the porous layer, the volume ratio of the pores is in the range of 50 - 90%, in particular 50 - 80%, preferably 55 - 75%, preferably 55 - 70%. The porous layer is designed as macroporous or microporous. In the context of the present utility model, the porosity should be understood as the ratio of the pore volume (also called void volume) of an object to the total volume of the relevant object. The porosity (in percentage) of the porous layer can be determined in particular by mercury porosimetry or by calculation according to the BET model or as the oil absorption rate. Similarly, the porosity can also be determined by computer tomography (CT), in particular by means of micro-CT or nano-CT.

[0057] Preferably, the porous layer is microporous or has at least one microporous layer. In the context of the present utility model, it has proven particularly beneficial to use a conventional gas diffusion layer or material as the porous layer, in particular as the carrier material. Then the hydrophobic and hydrophilic catalyst layers are applied thereon, thereby obtaining a porous or microporous catalyst layer.

[0058] Particularly good results are obtained when the pore diameter of the porous layer is in the range of 0.001 - 200 μm, in particular 0.001 - 150 μm, preferably 0.01 - 100 μm, and most preferably 0.01 - 100 μm. The pore diameter can be determined in particular by mercury porosimetry or by calculation according to the BET model.

[0059] If the porous layer is macroporous, it can be stipulated that the porous layer has a pore diameter in the range of 0.05 μm - 200 μm, in particular 0.5 μm - 150 μm, preferably 0.5 μm - 100 μm, and most preferably 1 μm - 100 μm. Preferably, the porous layer is designed to be microporous or has a microporous layer. In this case, the pore diameter of the porous layer or the microporous layer of the layer is in the range of 0.001 - 5 μm, in particular 0.001 - 0.5 μm, preferably 0.01 - 0.5 μm, and most preferably 0.01 - 0.2 μm. Through the porous or microporous structure of the porous layer, the porous or microporous structure of the catalyst layer is usually also obtained.

[0060] In the context of the present utility model, it is generally stipulated that a hydrophobic catalyst layer is arranged on the porous layer, and a hydrophilic catalyst layer is arranged on the hydrophobic catalyst layer. Alternatively, it can also be stipulated that the hydrophilic catalyst layer is arranged on the porous layer and the hydrophobic catalyst layer is arranged on the hydrophilic catalyst layer, but preferably it is stipulated that the hydrophobic catalyst layer is arranged on the porous layer and the hydrophilic catalyst layer is arranged on the hydrophobic catalyst layer.

[0061] Therefore, in the context of the present utility model, it is preferably stipulated that the hydrophobic catalyst layer is applied to the porous layer, and then the hydrophilic catalyst layer is applied to the hydrophobic catalyst layer. In this way, the penetration of polar electrolytes, especially water, into the electrode is prevented. On the other hand, sufficient absorption of water and sufficient ion transport can be achieved in the hydrophilic region, so that electrochemical reduction of especially carbon dioxide can be particularly effectively achieved.

[0062] As already explained above, in the context of the present utility model, it is preferred that the porous layer, in particular the porous carrier layer, is a conventional gas diffusion layer (Gas Diffusion Layer, GDL). Particularly good results are obtained when the porous carrier layer is selected from the group consisting of carbon fabric, carbon fiber paper, graphite fabric, metal felt, metal mesh, sintered metal particles, and mixtures thereof. In the context of the present utility model, if the carrier layer contains or consists of a metal, it has been proven beneficial that the metal is selected from the following group: silver, copper, platinum, titanium, nickel, zinc, iron, aluminum, and stainless steel, and mixtures and alloys thereof. Particularly good results are obtained in this regard if the metal is selected from the group consisting of copper, silver, platinum, and mixtures and alloys thereof.

[0063] In the context of the present utility model, it has also proven beneficial that the porous layer, in particular the porous support layer, is selected from carbon-containing materials. Particularly preferably, the material of the porous layer is selected from the group consisting of carbon fabric, carbon fiber paper, and mixtures thereof. Particularly preferably, the porous layer, in particular the porous support layer, is carbon fabric. When selecting the porous support layer, it is particularly important that the material is conductive and does not have any undesirable catalytic properties.

[0064] Regarding the thickness of the porous layer, in particular the porous support layer, it can of course vary within a wide range. However, in the context of the present utility model, particularly good results will be obtained if the porous support layer has a thickness of 50 - 1,000 μm, in particular 50 μm - 800 μm, preferably 100 μm - 600 μm, and most preferably 150 μm - 500 μm.

[0065] As described above, in the context of the present utility model, it is generally stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer each contain at least one catalyst.

[0066] Furthermore, within the scope of the present utility model, it can be stipulated that the hydrophobic catalyst layer and the hydrophilic catalyst layer contain the same or different catalysts. In the context of the present utility model, particularly good results will be obtained when the hydrophobic catalyst layer and the hydrophilic catalyst layer contain the same catalyst.

[0067] Regarding the selection of the catalyst, in principle, it can be selected from all catalysts suitable for electrolysis, in particular catalysts suitable for the electrochemical reduction of carbon dioxide. The catalyst is generally selected from the group consisting of metal particles, in particular metal nanoparticles, single-atom catalysts, metal carbides, metal oxides, metal chalcogenides, molecular catalysts, and mixtures thereof. Particularly good results will be obtained in this regard if the catalyst is selected from metal particles, in particular metal nanoparticles. It has proven beneficial in this regard that the catalyst is selected from the group consisting of metal particles of Au, Ag, Zn, Pd, Ga, Cd, In, Hg, Tl, Pb, Bi, Cu, in particular metal nanoparticles, and mixtures and alloys thereof, metal carbides, metal oxides, metal chalcogenides, molecular catalysts, and mixtures thereof.

[0068] Particularly good results will be obtained if the catalyst is selected from the group consisting of metal particles of Au, Ag, Zn, Pd, Ga, Cd, In, Hg, Tl, Pb, Bi, Cu, in particular metal nanoparticles, and mixtures and alloys thereof.

[0069] In the context of the present utility model, particularly good results will be obtained if the catalyst is selected from the group consisting of metal particles of Au, Ag, Cu, in particular metal nanoparticles, and mixtures and alloys thereof.

[0070] As for the amount of catalyst in the catalyst layer, it can also vary within a wide range. However, it has proven beneficial that the hydrophobic catalyst layer and the hydrophilic catalyst layer mainly contain the catalyst.

[0071] In this regard, particularly good results will be obtained if, based on the hydrophobic catalyst layer and the hydrophilic catalyst layer, the hydrophobic catalyst layer and the hydrophilic catalyst layer contain 10 - 99.9% by weight, especially 25 - 99.9% by weight, preferably 40 - 99.9% by weight, preferably 50 - 99.8% by weight of the catalyst.

[0072] In particular, it can be stipulated that, based on the hydrophilic catalyst layer, the hydrophilic catalyst layer contains 50 - 99.9% by weight, especially 55 - 99.9% by weight, preferably 60 - 99.9% by weight, preferably 70 - 99.8% by weight of the catalyst.

[0073] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the hydrophilic catalyst layer, the hydrophilic catalyst layer contains 50 - 99.9% by weight, especially preferably 55 - 99% by weight, preferably 60 - 99.9% by weight, preferably 90 - 99.8% by weight of the catalyst.

[0074] Alternatively, if a bipolar membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the hydrophilic catalyst layer, the hydrophilic catalyst layer contains 50 - 99.8% by weight, especially 55 - 99% by weight, preferably 60 - 97% by weight, preferably 70 - 95% by weight of the catalyst.

[0075] It can also be stipulated that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 10 - 99.8% by weight, especially 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight of the catalyst.

[0076] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 10 - 99.8% by weight, especially 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight of the catalyst.

[0077] Alternatively, if a bipolar membrane (BPM) is used to separate the anodic chamber and the cathodic chamber, it can be stipulated that, based on the weight of the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight of catalyst.

[0078] It can also be stipulated that, based on the solid content of the coating composition, the amount of catalyst contained in the hydrophobic catalyst layer and the hydrophilic catalyst layer is 10 - 99.8% by weight, in particular 25 - 99.8% by weight, preferably 40 - 99.8% by weight, preferably 50 - 99.5% by weight, and the hydrophobic catalyst layer and the hydrophilic catalyst layer are obtained from the coating composition.

[0079] The solid content of the coating composition, in particular the catalyst ink, should be understood to mean the part of the coating composition that remains after removing the solvent and other volatile components.

[0080] In this context, it can be stipulated that, based on the solid content of the coating composition, the hydrophilic catalyst layer preferably contains 50 - 99.8% by weight, in particular 55 - 99.8% by weight, preferably 60 - 99.8% by weight, preferably 66 - 99.5% by weight of catalyst, and the hydrophilic catalyst layer is obtained from the coating composition.

[0081] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anodic chamber and the cathodic chamber, it can be stipulated that, based on the solid content of the coating composition, the hydrophilic catalyst layer contains 50 - 99.8% by weight, in particular 80 - 99% by weight, preferably 89 - 99.8% by weight, preferably 89 - 99.5% by weight of catalyst, and the hydrophilic catalyst layer is obtained from the coating composition.

[0082] Alternatively, if a bipolar membrane (BPM) is used to separate the anodic chamber and the cathodic chamber, it can be stipulated that, based on the solid content of the coating composition, the hydrophilic catalyst layer contains 50 - 99.8% by weight, in particular 55 - 95% by weight, preferably 60 - 92% by weight, preferably 66 - 86% by weight of catalyst, and the hydrophilic catalyst layer is obtained from the coating composition.

[0083] It can also be stipulated that, based on the solid content of the coating composition, the hydrophobic catalyst layer contains 10 - 99.8% by weight, in particular 25 - 96% by weight, preferably 40 - 96% by weight, preferably 50 - 96% by weight of catalyst, and the hydrophobic catalyst layer is obtained from the coating composition.

[0084] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the solid content of the coating composition, the hydrophobic catalyst layer contains 10 - 99.8% (by weight), particularly 25 - 96% (by weight), preferably 40 - 96% (by weight), preferably 50 - 96% (by weight) of the catalyst, and a hydrophilic catalyst layer is obtained from the coating composition.

[0085] Alternatively, if a bipolar membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the solid content of the coating composition, the hydrophobic catalyst layer contains 10 - 99.8% (by weight), particularly 25 - 96% (by weight), preferably 40 - 96% (by weight), preferably 50 - 96% (by weight) of the catalyst, and a hydrophilic catalyst layer is obtained from the coating composition.

[0086] Based on the surface area of the hydrophobic catalyst layer or the hydrophilic catalyst layer, the hydrophobic catalyst layer and the hydrophilic catalyst layer generally contain 0.001 - 100 mg / cm -2 、particularly 0.05 - 50 mg / cm -2 、preferably 0.1 - 10 mg / cm -2 、preferably 0.5 - 3 mg / cm -2 of the catalyst.

[0087] In the context of the present utility model, it is generally also stipulated that the hydrophilic catalyst layer has at least one hydrophilic polymer, particularly at least one ionomer. The polymer acts as a binder for the catalyst, i.e., a binder, and particularly ensures that the catalyst adheres to a carrier layer such as a gas diffusion layer or an ion conductive membrane. The hydrophilic catalyst layer preferably contains a hydrophilic polymer or a mixture of hydrophilic polymers, particularly one or more ionomers, as the sole polymer, i.e., as the sole binder.

[0088] In the context of the present utility model, it is not particularly stipulated that the hydrophilic catalyst layer has a hydrophilic polymer and a hydrophobic polymer.

[0089] It has been found beneficial that the hydrophilic polymer is selected from the group consisting of: polyelectrolytes, ionomers, ionomers and mixtures thereof. Preferably, the hydrophilic polymer is selected from the group consisting of: polyacrylic acid, acrylic acid copolymers, acrylamide copolymers, polyethyleneimine, alginates, pectins, lignins, lignosulfonates, celluloses, cellulose ethers, polyvinylpyrrolidone, polyvinylamine, polyvinylpyridine, polymers having sulfonic acid groups, polymers having perfluorosulfonic acid groups, polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, polymers having phosphonium groups, polymers having sulfonium groups, polymers having organometallic complexes cationically functionalized and mixtures thereof.

[0090] Preferably, the hydrophilic polymer is an ionomer.

[0091] In the context of the present invention, particularly good results are obtained if the hydrophilic polymer, especially the ionomer, is selected from polymers having sulfonic acid groups, polymers having perfluorosulfonic acid groups, polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, polymers having phosphorus groups, polymers having sulfonium groups, polymers having organometallic complexes cationically functionalized, and mixtures thereof. Generally, in the context of the present invention, hydrophilic polymers having ionic groups or groups that easily form ions are preferably used.

[0092] In the present context, particularly good results are obtained if the hydrophilic polymer, especially the ionomer, is selected from polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, polymers having phosphorus groups, polymers having sulfonium groups, polymers having organometallic complexes cationically functionalized, and mixtures thereof. Particularly good results are obtained when the hydrophilic polymer, especially the ionomer, is selected from polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, and mixtures thereof.

[0093] So far, the best results have been obtained when the hydrophilic polymer, especially the ionomer, is selected from ionomers containing piperidinium groups, ionomers containing imidazolium groups, ionomers containing benzimidazolium groups, and mixtures thereof.

[0094] Suitable ionomers are, for example, polymers and copolymers containing sulfonic acid groups, especially perfluorosulfonic acid-based polymers and copolymers, and hydrocarbon-based polymers and copolymers, which, for example, have hydrocarbons based on aromatic compounds and have sulfonic acid groups, and are commercially available, for example, from DuPont In addition, polymers and copolymers containing ammonium groups or polymers having quaternary nitrogen heterocycles are also suitable as ionomers and are commercially available, for example, as those from Dioxide Materials from Versogen or Fumasep-FAA3 from Fumatec.

[0095] As for the amount of the hydrophilic polymer contained in the hydrophilic catalyst layer, it can vary within a wide range. The hydrophilic catalyst layer usually contains a smaller amount of the hydrophilic polymer, especially the ionomer, than the catalyst. Particularly good results can be obtained if, based on the hydrophilic catalyst layer, the hydrophilic catalyst layer contains 0.01 - 50% (by weight), especially 0.01 - 40% (by weight), preferably 0.01 - 30% (by weight), and preferably 0.1 - 18% (by weight) of the hydrophilic polymer, especially the ionomer.

[0096] In the context of the present utility model, according to a preferred embodiment, it is thus stipulated that, based on the hydrophilic catalyst layer respectively, the hydrophilic catalyst layer has:

[0097] (a) a catalyst in an amount of 50 - 99.9% (by weight), especially 55 - 99.9% (by weight), preferably 60 - 99.9% (by weight), preferably 70 - 99.8% (by weight); and

[0098] (b) a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.01 - 40% (by weight), preferably 0.1 - 30% (by weight), preferably 0.1 - 18% (by weight).

[0099] All of the foregoing features, advantages and characteristics apply accordingly to this embodiment.

[0100] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that the hydrophilic catalyst layer contains a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.01 - 10% (by weight), preferably 0.01 - 5% (by weight), preferably 0.1 - 5% (by weight), based on the hydrophilic catalyst layer.

[0101] In the case where an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it is stipulated that, based on the hydrophilic catalyst layer respectively, the hydrophilic catalyst layer has:

[0102] (a) a catalyst in an amount of 50 - 99.9% (by weight), especially 55 - 99.9% (by weight), preferably 60 - 99.9% (by weight), preferably 90 - 99.8% (by weight); and

[0103] (b) a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.01 - 10% (by weight), preferably 0.01 - 5% (by weight), preferably 0.1 - 5% (by weight).

[0104] All of the foregoing features, advantages and characteristics apply accordingly to this embodiment.

[0105] Alternatively, if a bipolar membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that the hydrophilic catalyst layer contains a hydrophilic polymer, especially an ionomer, in an amount of 0.01% - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 8 - 18% (by weight), based on the hydrophilic catalyst layer.

[0106] In the case where a bipolar exchange membrane (BPM) is used to separate the anodic chamber and the cathodic chamber, according to a preferred embodiment, based on the hydrophilic catalyst layer respectively, the hydrophilic catalyst layer has:

[0107] (a) a catalyst in an amount of 50 - 99.8% by weight, in particular 55 - 99% by weight, preferably 60 - 97% by weight, preferably 70 - 95% by weight; and

[0108] (b) a hydrophilic polymer, in particular an ionomer, in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 8 - 18% by weight.

[0109] All of the foregoing features, advantages and characteristics accordingly apply to this embodiment.

[0110] It can also be provided that, based on the solid content of the coating composition, the hydrophilic catalyst layer contains a hydrophilic polymer, in particular an ionomer, in an amount of 0.01 - 50% by weight, in particular 0.01 - 40% by weight, preferably 0.01 - 30% by weight, 0.05 - 33% by weight, and the hydrophilic catalyst layer is obtained from the coating composition.

[0111] Therefore, according to a preferred embodiment, based on the solid content of the coating composition respectively - from which the hydrophilic catalyst layer is obtained, the hydrophilic catalyst layer has:

[0112] (a) a catalyst in an amount of 50 - 99.8% by weight, in particular 55 - 99.8% by weight, preferably 60 - 99.8% by weight, preferably 66 - 99.5% by weight; and

[0113] (b) a hydrophilic polymer, in particular an ionomer, in an amount of 0.01 - 50% by weight, in particular 0.01 - 40% by weight, preferably 0.01 - 30% by weight, preferably 0.05 - 33% by weight.

[0114] All of the foregoing features, advantages and characteristics accordingly apply to this embodiment.

[0115] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anodic chamber and the cathodic chamber, it can be provided that, based on the solid content of the coating composition - from which the hydrophilic catalyst layer is obtained, the hydrophilic catalyst layer contains a hydrophilic polymer, in particular an ionomer, in an amount of 0.01 - 50% by weight, in particular 0.01 - 40% by weight, preferably 0.01 - 10% by weight, preferably 0.05 - 10% by weight.

[0116] In the case of using an anion exchange membrane (AEM) to separate the anode chamber and the cathode chamber, according to a preferred embodiment, based on the solid content of the coating composition respectively - a hydrophilic catalyst layer is obtained from the coating composition, and the hydrophilic catalyst layer has:

[0117] (a) a catalyst in an amount of 50 - 99.8% (by weight), especially 80 - 99.8% (by weight), preferably 89 - 99.8% (by weight), preferably 89 - 99.5% (by weight); and

[0118] (b) a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.01 - 40% (by weight), preferably 0.01 - 10% (by weight), preferably 0.05 - 10% (by weight).

[0119] All of the foregoing features, advantages and characteristics apply accordingly to this embodiment.

[0120] Alternatively, if a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be provided that, based on the solid content of the coating composition respectively - a hydrophilic catalyst layer is obtained from the coating composition, and the hydrophilic catalyst layer contains a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 13 - 33% (by weight).

[0121] In the case of using a bipolar exchange membrane (BPM) to separate the anode chamber and the cathode chamber, according to a preferred embodiment, based on the solid content of the coating composition respectively - a hydrophilic catalyst layer is obtained from the coating composition, and the hydrophilic catalyst layer has:

[0122] (a) a catalyst in an amount of 50 - 99.8% (by weight), especially 55 - 95% (by weight), preferably 60 - 92% (by weight), preferably 66 - 86% (by weight); and

[0123] (b) a hydrophilic polymer, especially an ionomer, in an amount of 0.01 - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 13 - 33% (by weight).

[0124] All of the foregoing features, advantages and characteristics apply accordingly to this embodiment.

[0125] In the context of the present utility model, it can also be stipulated that the thickness of the hydrophilic catalyst layer is in the range of 0.05 μm - 100 μm, in particular 0.5 μm - 100 μm, preferably 0.5 μm - 50 μm, preferably 0.5 μm - 20 μm, particularly preferably 0.5 - 10 μm, very particularly preferably 0.5 - 5 μm, particularly preferably 0.5 - 3 μm, particularly preferably 0.5 - 1 μm.

[0126] Particularly good results will be obtained when the pore size of the hydrophilic catalyst layer is 0.001 - 1 μm, in particular 0.001 - 0.8 μm, preferably 0.01 - 0.5 μm.

[0127] Furthermore, it has proven beneficial that the weight per unit area of the hydrophilic catalyst layer is 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 .

[0128] Furthermore, it can be stipulated that the weight per unit area of the hydrophilic catalyst layer is in the range of 0.2 - 10 mg·cm -2 、in particular 0.3 - 7 mg·cm -2 、preferably 0.4 - 5 mg·cm -2 、preferably 0.5 - 1 mg·cm -2 .

[0129] As for the hydrophobic catalyst layer, it usually has at least one hydrophobic polymer. Preferably, the hydrophobic catalyst layer has only one or more hydrophobic polymers as the polymer, i.e., the binder.

[0130] In the context of the present utility model, it has proven beneficial that the hydrophobic polymer is selected from the following group: polyolefins, polyfluoroolefins, silicones, fluorinated polymers, polyaromatic polymers, and their copolymers and mixtures. In this regard, particularly good results will be obtained if the hydrophobic polymer is selected from the group consisting of polyolefins, polyfluoroolefins, fluorinated polymers, polyaromatic polymers, and their copolymers and mixtures.

[0131] Preferably, the hydrophobic polymer is selected from the group consisting of: polyethylene, polypropylene, cycloolefin copolymer (COC), polystyrene (PS), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and their copolymers and mixtures, especially polyethylene, polypropylene, polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE).

[0132] Using the aforementioned hydrophobic polymer, it is possible to effectively prevent, in particular, water from penetrating into the electrode, especially the cathode.

[0133] Regarding the amount of the hydrophobic polymer in the hydrophobic catalyst layer, it can vary within a wide range - like the hydrophilic polymer. However, for the hydrophobic catalyst layer, it has also proven beneficial that the hydrophobic catalyst layer contains a larger amount of catalyst than the hydrophobic polymer.

[0134] It is generally specified that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 0.01 - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight) of the hydrophobic polymer.

[0135] According to a preferred embodiment, it is thus specified that, respectively based on the hydrophobic catalyst layer, the hydrophobic catalyst layer has:

[0136] (a) a catalyst in an amount of 10 - 99.8% (by weight), especially 25 - 99% (by weight), preferably 40 - 97% (by weight), preferably 50 - 95% (by weight); and

[0137] (b) a hydrophobic polymer in an amount of 0.01 - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight).

[0138] All the aforementioned features, advantages, and characteristics correspondingly apply to this embodiment.

[0139] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be specified that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 0.01 - 50% (by weight), especially 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight) of the hydrophobic polymer.

[0140] In the case where an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, based on the hydrophobic catalyst layer respectively, the hydrophobic catalyst layer has:

[0141] (a) a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight; and

[0142] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight.

[0143] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0144] In the context of the present utility model, if a bipolar membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight.

[0145] In the case where a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, based on the hydrophobic catalyst layer respectively, the hydrophobic catalyst layer has:

[0146] (a) a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight; and

[0147] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight.

[0148] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0149] It can also be stipulated that, based on the solid content of the coating composition, the hydrophobic catalyst layer can contain a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.05 - 40% by weight, preferably 0.08 - 30% by weight, preferably 0.08 - 16% by weight, and the hydrophobic catalyst layer is obtained from the coating composition.

[0150] According to a preferred embodiment, it is thus provided that, based on the solids content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, the hydrophobic catalyst layer having:

[0151] (a) a catalyst in an amount of 10 - 99.8% by weight, especially 25 - 96% by weight, preferably 40 - 96% by weight, preferably 50 - 96% by weight; and

[0152] (b) a hydrophobic polymer, especially an ionomer, in an amount of 0.01 - 50% by weight, especially 0.05 - 40% by weight, preferably 0.08 - 30% by weight, preferably 0.08 - 16% by weight.

[0153] All of the foregoing features, advantages, and characteristics accordingly apply to this embodiment.

[0154] In the context of the present utility model, if an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be provided that, based on the solids content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, the hydrophobic catalyst layer comprising a hydrophobic polymer in an amount of 0.01 - 50% by weight, especially 0.05 - 40% by weight, preferably 0.08 - 30% by weight, preferably 0.08 - 16% by weight.

[0155] In the case of using an anion exchange membrane (AEM) to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it is provided that, based on the solids content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, the hydrophobic catalyst layer having:

[0156] (a) a catalyst in an amount of 10 - 99.8% by weight, especially 25 - 96% by weight, preferably 40 - 96% by weight, preferably 50 - 96% by weight; and

[0157] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, especially 0.05 - 40% by weight, preferably 0.08 - 30% by weight, preferably 0.08 - 16% by weight.

[0158] All of the foregoing features, advantages, and characteristics accordingly apply to this embodiment.

[0159] Alternatively, if a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the solid content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer contains 0.01 - 50% (by weight), in particular 0.08 - 40% (by weight), preferably 0.08 - 30% (by weight), preferably 0.08 - 16% (by weight) of a hydrophobic polymer.

[0160] In the case where a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it is stipulated that, respectively based on the solid content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer has:

[0161] (a) A catalyst in an amount of 10 - 99.8% (by weight), in particular 25 - 96% (by weight), preferably 40 - 96% (by weight), preferably 50 - 96% (by weight); and

[0162] (b) A hydrophobic polymer in an amount of 0.01 - 50% (by weight), in particular 0.08 - 40% (by weight), preferably 0.08 - 30% (by weight), preferably 0.08 - 16% (by weight).

[0163] All of the foregoing features, advantages, and characteristics correspondingly apply to this embodiment.

[0164] In addition, within the scope of the present utility model, it can be stipulated that the hydrophobic catalyst layer has a conductivity improver, that is, an improver for conductivity. In this regard, particularly good results will be obtained if the conductivity improver is selected from carbon black, graphite, carbon nanotubes, and mixtures thereof. The conductivity improver can be added to the hydrophobic coating composition to improve the performance of the electrode, and in particular to ensure that the hydrophobic catalyst layer does not act as an electrical insulator. Additionally, the porosity of the hydrophobic catalyst layer can be increased by adding the conductivity improver.

[0165] If the hydrophobic catalyst layer has a conductivity improver, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer generally contains 0.05 - 90% (by weight), in particular 0.5 - 75% (by weight), preferably 5 - 60% (by weight), preferably 6 - 45% (by weight) of the conductivity improver.

[0166] It can also be stipulated that, based on the solid content of the coating composition - a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer contains 0.05 - 90% (by weight), in particular 0.5 - 75% (by weight), preferably 1 - 60% (by weight), preferably 4 - 45% (by weight) of the conductivity improver.

[0167] If the hydrophobic catalyst layer has a conductivity improver, it is preferably provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight, of catalyst.

[0168] If the hydrophobic catalyst layer has a conductivity improver, it is preferably provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer contains 10 - 99.8% by weight, in particular 25 - 95% by weight, preferably 40 - 90% by weight, preferably 50 - 80% by weight, of catalyst.

[0169] Furthermore, according to this embodiment, it can be provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight, of a hydrophobic polymer.

[0170] According to this embodiment, it can likewise be provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer contains 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight, of a hydrophobic polymer.

[0171] According to a preferred embodiment, it is thus provided that, based on the hydrophobic catalyst layer respectively, the hydrophobic catalyst layer has:

[0172] (a) a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight;

[0173] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight; and

[0174] (c) a conductivity improver in an amount of 0.05 - 90% by weight, in particular 0.5 - 75% by weight, preferably 5 - 60% by weight, preferably 6 - 45% by weight.

[0175] All of the foregoing features, advantages, and characteristics correspondingly apply to this embodiment.

[0176] According to a further preferred embodiment, based on the solids content of the coating composition, a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer has:

[0177] (a) a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 95% by weight, preferably 40 - 90% by weight, preferably 50 - 80% by weight;

[0178] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight; and

[0179] (c) a conductivity improver in an amount of 0.05 - 90% by weight, in particular 0.5 - 75% by weight, preferably 1 - 60% by weight, preferably 4 - 45% by weight.

[0180] All the foregoing features, advantages and characteristics accordingly apply to this embodiment.

[0181] In the context of the present invention, if the hydrophobic catalyst layer has a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, then according to this embodiment, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 99% by weight, preferably 40 - 97% by weight, preferably 50 - 95% by weight.

[0182] In the context of the present invention, if the hydrophobic catalyst layer has a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, then it can be provided that, based on the solids content of the coating composition, a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer contains a catalyst in an amount of 10 - 99.8% by weight, in particular 25 - 95% by weight, preferably 40 - 90% by weight, preferably 50 - 80% by weight.

[0183] In the context of the present invention, if the hydrophobic catalyst layer has a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, then it can be provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight.

[0184] In the context of the present utility model, if the hydrophobic catalyst layer has a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, it can be stipulated that, based on the solid content of the coating composition - from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer contains 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight) of a hydrophobic polymer.

[0185] In the case where an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it is stipulated that, respectively based on the hydrophobic catalyst layer, the hydrophobic catalyst layer has:

[0186] (a) a catalyst in an amount of 10 - 99.8% (by weight), in particular 25 - 99% (by weight), preferably 40 - 97% (by weight), preferably 50 - 95% (by weight);

[0187] (b) a hydrophobic polymer in an amount of 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight); and

[0188] (c) a conductivity improver in an amount of 0.05 - 90% (by weight), in particular 0.5 - 75% (by weight), preferably 5 - 60% (by weight), preferably 6 - 45% (by weight).

[0189] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0190] In the case where an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it can also be stipulated that, respectively based on the solid content of the coating composition - from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer has:

[0191] (a) a catalyst in an amount of 10 - 99.8% (by weight), in particular 25 - 95% (by weight), preferably 40 - 90% (by weight), preferably 50 - 80% (by weight);

[0192] (b) a hydrophobic polymer in an amount of 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight); and

[0193] (c) a conductivity improver in an amount of 0.05 - 90% (by weight), in particular 0.5 - 75% (by weight), preferably 1 - 60% (by weight), preferably 4 - 45% (by weight).

[0194] All of the foregoing features, advantages, and characteristics accordingly apply to this embodiment.

[0195] Alternatively, if the hydrophobic catalyst layer has a conductivity improver and a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it may be provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 10% - 99.8%, preferably 25 - 95% (by weight), preferably 40 - 92% (by weight), preferably 50 - 90% (by weight) of the catalyst.

[0196] As an alternative, if a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it may be provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer contains 10 - 99.8% (by weight), in particular 25 - 95% (by weight), preferably 40 - 92% (by weight), preferably 50 - 80% (by weight) of the catalyst.

[0197] If a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it may be provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer contains 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight) of the hydrophobic polymer.

[0198] If a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, it may be provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer contains 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight) of the hydrophobic polymer.

[0199] In the case where a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, according to a preferred embodiment, it is provided that, based on the hydrophobic catalyst layer respectively, the hydrophobic catalyst layer has:

[0200] (a) a catalyst in an amount of 10 - 99.8% (by weight), in particular 25 - 95% (by weight), preferably 40 - 92% (by weight), preferably 50 - 90% (by weight);

[0201] (b) a hydrophobic polymer in an amount of 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight); and

[0202] (c) A conductivity improver in an amount of 0.05 - 90% by weight, especially 0.5 - 75% by weight, preferably 5 - 60% by weight, more preferably 6 - 45% by weight.

[0203] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0204] In the case of using a bipolar membrane (BPM) to separate the anodic chamber and the cathodic chamber, according to a preferred embodiment, it can also be provided that, based on the solid content of the coating composition respectively - a hydrophobic catalyst layer is obtained from the coating composition, and the hydrophobic catalyst layer has:

[0205] (a) A catalyst in an amount of 10 - 99.8% by weight, especially 25 - 95% by weight, preferably 40 - 92% by weight, more preferably 50 - 80% by weight;

[0206] (b) A hydrophobic polymer in an amount of 0.01 - 50% by weight, especially 0.1 - 40% by weight, preferably 1 - 30% by weight, more preferably 1 - 10% by weight; and

[0207] (c) A conductivity improver in an amount of 0.05 - 90% by weight, especially 0.5 - 75% by weight, preferably 1 - 60% by weight, more preferably 4 - 45% by weight.

[0208] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0209] If the hydrophobic catalyst layer does not have a conductivity improver and an anion exchange membrane (AEM) is used to separate the anodic chamber and the cathodic chamber, then according to a preferred embodiment, based on the hydrophobic catalyst layer respectively, the hydrophobic catalyst layer has:

[0210] (a) A catalyst in an amount of 50 - 99.8% by weight, especially 55 - 99% by weight, preferably 60 - 97% by weight, more preferably 70 - 95% by weight; and

[0211] (b) A hydrophobic polymer in an amount of 0.01 - 50% by weight, especially 0.1 - 40% by weight, preferably 1 - 30% by weight, more preferably 1 - 10% by weight.

[0212] All of the foregoing features, advantages and characteristics correspondingly apply to this embodiment.

[0213] If the hydrophobic catalyst layer does not have a conductivity improver and an anion exchange membrane (AEM) is used to separate the anode chamber and the cathode chamber, then according to a preferred embodiment, it can also be provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer has:

[0214] (a) a catalyst in an amount of 50 - 99.8% by weight, in particular 55 - 96% by weight, preferably 60 - 96% by weight, preferably 70 - 96% by weight; and

[0215] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.05 - 40% by weight, preferably 0.08 - 30% by weight, preferably 0.08 - 16% by weight.

[0216] All of the foregoing features, advantages and characteristics accordingly apply to this embodiment.

[0217] If the hydrophobic catalyst layer does not have a conductivity improver and a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, then according to a preferred embodiment, it is provided that, based on the hydrophobic catalyst layer, the hydrophobic catalyst layer has:

[0218] (a) a catalyst in an amount of 50 - 99.8% by weight, in particular 55 - 99% by weight, preferably 60 - 97% by weight, preferably 70 - 95% by weight; and

[0219] (b) a hydrophobic polymer in an amount of 0.01 - 50% by weight, in particular 0.1 - 40% by weight, preferably 1 - 30% by weight, preferably 1 - 10% by weight.

[0220] All of the foregoing features, advantages and characteristics accordingly apply to this embodiment.

[0221] If the hydrophobic catalyst layer does not have a conductivity improver and a bipolar exchange membrane (BPM) is used to separate the anode chamber and the cathode chamber, then according to a preferred embodiment, it can also be provided that, based on the solid content of the coating composition from which the hydrophobic catalyst layer is obtained, the hydrophobic catalyst layer has:

[0222] (a) a catalyst in an amount of 50 - 99.8% by weight, in particular 55 - 96% by weight, preferably 60 - 96% by weight, preferably 70 - 96% by weight; and

[0223] (b) A hydrophobic polymer in an amount of 0.01 - 50% (by weight), especially 0.08 - 40% (by weight), preferably 0.08 - 30% (by weight), preferably 0.08 - 16% (by weight).

[0224] All of the foregoing features, advantages, and characteristics apply correspondingly to this embodiment.

[0225] Furthermore, within the scope of the present utility model, it is generally stipulated that the thickness of the hydrophobic catalyst layer is in the range of 0.05 μm - 100 μm, especially 0.5 μm - 100 μm, preferably 0.5 μm - 50 μm, preferably 0.5 μm - 20 μm, particularly preferably 0.5 μm - 10 μm, very particularly preferably 0.5 - 5 μm, particularly preferably 0.5 - 4 μm, particularly preferably 0.5 - 3 μm.

[0226] Particularly good results will be obtained when the hydrophobic catalyst layer has a pore diameter of at most 5 μm, especially at most 3 μm, preferably at most 2 μm.

[0227] Likewise, it has proven beneficial that the hydrophobic catalyst layer has a pore diameter in the range of 0.001 - 5 μm, especially 0.001 - 3 μm, preferably 0.01 - 2 μm.

[0228] Furthermore, it has proven beneficial that the weight per unit area of the hydrophobic catalyst layer is less than 10 mg·cm -2 、especially less than 7 mg·cm -2 、preferably less than 5 mg·cm -2 、preferably less than 3 mg·cm -2 .

[0229] Furthermore, it can be stipulated that the weight per unit area of the hydrophobic catalyst layer is in the range of 0.5 - 10 mg·cm -2 、especially 0.8 - 7 mg·cm -2 、preferably 1 - 5 mg·cm -2 、preferably 1 - 3 mg·cm -2 .

[0230] In addition, within the scope of the present utility model, it is generally stipulated that the total thickness of the hydrophilic catalyst layer and the hydrophobic catalyst layer is in the range of 0.1 μm - 100 μm, especially 0.1 μm - 100 μm, preferably 0.5 μm - 50 μm, preferably 0.5 - 20 μm, particularly preferably 0.5 - 10 μm, very particularly preferably 1 - 5 μm, particularly preferably 1 - 4 μm, particularly preferably 1 - 3 μm.

[0231] Furthermore, it is preferably stipulated that the electrode has 0.5 - 50,000 cm 2 、especially 1 - 10,000 cm2 , preferably 10 - 5,000 cm 2 , preferably 100 - 2,500 cm 2 in the area range.

[0232] Particularly good results will be obtained if the total thickness of the electrode is in the range of 2 μm - 200 μm, especially 2 μm - 100 μm, preferably 2 μm - 50 μm, preferably 3 - 30 μm, particularly preferably 4 - 20 μm, and very particularly preferably 5 - 15 μm. Description of the Drawings

[0233] Figure 1 shows a schematic diagram of the electrode according to the present invention;

[0234] Figure 2 shows an electrolytic cell containing the electrode according to the present invention;

[0235] Figure 3 shows the relationship between the cell voltage and current yield of constant - current electrolysis and the PTFE content in the cathode catalyst ink;

[0236] Figure 4 shows the relationship between the cell voltage and current yield of constant - current electrolysis and the ionomer content in the cathode catalyst ink;

[0237] Figure 5 shows the relationship between the cell voltage and current yield of constant - current electrolysis and the catalyst loading in the hydrophobic and hydrophilic catalyst layers;

[0238] Figure 6 shows the cell voltage and current yield of constant - current electrolysis for only a hydrophobic catalyst layer, a hydrophobic and hydrophilic catalyst layer, and a pure hydrophilic catalyst layer;

[0239] Figure 7 shows the relationship between the current yield of constant - current electrolysis using the electrode and an anion - exchange membrane and time, where the electrode has a hydrophobic catalyst layer and a hydrophilic catalyst layer;

[0240] Figure 8 shows the relationship between the cell voltage of constant - current electrolysis using the electrode and an anion - exchange membrane and time, where the electrode has a hydrophobic catalyst layer and a hydrophilic catalyst layer;

[0241] Figure 9 shows the relationship between the current yield of constant - current electrolysis using the electrode and a bipolar exchange membrane and time, where the electrode has a hydrophobic catalyst layer and a hydrophilic catalyst layer;

[0242] Figure 10Shows the relationship between the cell voltage and time of constant current electrolysis using an electrode and a bipolar exchange membrane, the electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer;

[0243] Figure 11 Shows the relationship between the current yield and time of constant current electrolysis using an electrode and a bipolar exchange membrane, the electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer; and

[0244] Figure 12 Shows the relationship between the cell voltage and time of constant current electrolysis using an electrode and a bipolar exchange membrane, the electrode having a hydrophobic catalyst layer and a hydrophilic catalyst layer. Detailed Description

[0245] The gas diffusion electrode according to the present invention is particularly used as a cathode and / or anode in electrolysis, preferably as a cathode.

[0246] For the described applications, the electrode is generally used as a cathode, especially for the reduction of CO 2 (but also for the reduction of CO, N 2 , O 2 and organic molecules), especially by hydrogenation.

[0247] However, the gas diffusion electrode can also be used as an anode for oxidation reactions.

[0248] The electrode according to the present invention is particularly suitable as a cathode for the electrochemical reduction of carbon dioxide in an excellent manner, wherein valuable chemical raw materials, especially carbon monoxide (but also alcohols, aldehydes, ketones and carboxylic acids) can be obtained.

[0249] A method for preparing the aforementioned electrode, which can be carried out in the following manner:

[0250] (i) In a first process step, a first coating composition is applied to a porous carrier material or an ion-conducting membrane to produce a first catalyst layer that is hydrophilic or hydrophobic, preferably hydrophobic; and

[0251] (ii) In a second process step after 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.

[0252] In the context of the present utility model, it is preferred to apply the coating composition to a porous carrier material to obtain a coated substrate (a catalyst-coated substrate). However, the coating composition can also be applied to an ion-conducting membrane of an electrolytic cell, in particular an anion exchange membrane (AEM), a proton exchange membrane (PEM), or a bipolar exchange membrane (BPM) (a catalyst-coated membrane), and such a structure with a catalyst layer is applied to the porous carrier material. A combination of the two methods is also possible.

[0253] The porous carrier material corresponds to the above-mentioned porous layer.

[0254] In the context of the present utility model, it is specifically provided that if the hydrophilic catalyst layer is first applied to the porous carrier material, then the hydrophobic coating is applied in a second step, or if the hydrophobic coating composition is applied to the porous carrier material in a first process step, then the hydrophilic coating composition is applied in a second process step. It is preferred to dry or cure the coating composition to obtain the corresponding catalyst layer.

[0255] The application of the coating composition can be carried out by dry or wet coating methods, such as spraying, scraping, drop coating, printing, or by a combination of these methods.

[0256] The hydrophilic coating composition usually contains a hydrophilic polymer, in particular the aforementioned hydrophilic polymer.

[0257] The hydrophobic coating composition usually contains a hydrophobic polymer, in particular the aforementioned hydrophobic polymer.

[0258] The hydrophilic coating composition and the hydrophobic coating composition can contain different forms of hydrophilic polymers or hydrophobic polymers. Usually, the hydrophilic coating composition and the hydrophobic coating composition contain hydrophilic polymers or hydrophobic polymers in the form of solid particles, such as in the form of a dispersion or a film, preferably in the form of solid particles.

[0259] Generally, within the scope of the present utility model, it is provided that the first and / or second coating composition, which is hydrophilic and / or hydrophobic, exists in the form of a dispersion. Preferably, both the first and / or second coating composition, which is hydrophilic and / or hydrophobic, exist in the form of a dispersion.

[0260] If the first or second coating composition is present in the form of a dispersion, it is generally provided that the dispersion medium is removed during or after the application of the first coating composition. The removal of the dispersion medium is particularly preferably carried out before the second process step ii. Thus, in the context of the present invention, it is preferably provided that the first catalyst layer is obtained from the first coating composition first, before applying the second coating composition to produce the second catalyst layer.

[0261] Likewise, within the scope of the present invention, it is generally provided that the dispersion medium is removed during or after the application of the second coating composition. Thus, the second coating composition is preferably also dried or cured.

[0262] 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 possible crosslinking reaction can proceed immediately. The polymer particles can also be applied directly and adhered to the heated carrier material. Particularly preferred herein is that the carrier material is heated during the application of the first coating composition and during the application of the second coating composition. By heating during the application of the coating composition, the dispersion medium evaporates rapidly, and the layer thickness of the catalyst layer can be adjusted specifically by applying multiple times if necessary.

[0263] Regarding the temperature to which the carrier material is heated, it has been shown to be beneficial that the carrier material is heated to a temperature in the range of 25 - 140 °C, particularly 40 - 120 °C, particularly 60 - 120 °C, preferably 70 - 100 °C.

[0264] Within the scope of the present invention, it can be provided that after the application of the first or second coating composition, particularly after the application of the hydrophobic coating composition, a thermal or mechanical post-treatment step is carried out on the electrode. In particular, the electrode can undergo a sintering step and / or a pressing step.

[0265] Herein, it can be provided that after the application of the first or second coating composition and, if necessary, the removal of the dispersion medium, a sintering step is carried out on the electrode. Preferably, after the application of the hydrophobic coating composition and the removal of the dispersion medium, a sintering step is carried out on the electrode. In the sintering step, the adhesion of the coating composition to the carrier layer or another catalyst layer is improved, and the uniformity of the catalyst layer is promoted.

[0266] If a sintering step is carried out, the carrier material is generally heated to a temperature in the range of 150 - 400 °C, particularly 150 - 350 °C, preferably 150 - 300 °C, preferably 200 - 300 °C.

[0267] The duration of the sintering step can vary widely. However, sintering is typically carried out for 1 - 100 minutes, especially 5 - 30 minutes, preferably 5 - 15 minutes, and preferably 10 - 15 minutes.

[0268] As mentioned above, the hydrophobic coating composition usually has a hydrophobic polymer. In this regard, particularly good results will be obtained when the hydrophobic coating composition contains 0.05 - 5% (by weight), especially 0.1 - 3% (by weight), preferably 0.2 - 1% (by weight), and preferably 0.3 - 0.5% of the hydrophobic polymer based on the hydrophobic coating composition.

[0269] Similarly, within the scope of the present utility model, it can be stipulated that the hydrophobic coating composition contains 0.1 - 10% (by weight), especially 0.5 - 5% (by weight), preferably 1 - 3% (by weight), and preferably 1% - 2% of the catalyst based on the hydrophobic coating composition.

[0270] As mentioned above, the hydrophobic coating composition has a dispersion medium. Based on the hydrophobic coating composition, the hydrophobic coating composition usually contains 85 - 99.9% (by weight), especially 92 - 99.4% (by weight), preferably 96 - 98.8% (by weight), and preferably 97 - 98.7% (by weight) of the dispersion medium.

[0271] In the context of the present utility model, particularly good results will be obtained if 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.

[0272] If the dispersion medium is selected from water, alcohols, and mixtures thereof, it has been shown to be beneficial if the dispersion medium is selected from water, methanol, ethanol, isopropanol, and mixtures thereof, preferably mixtures thereof. In this regard, particularly good results will be obtained if the dispersion medium is selected from water, isopropanol, and mixtures thereof, preferably mixtures thereof.

[0273] Furthermore, it can be stipulated that the hydrophobic coating composition has additives. If the hydrophobic coating composition has additives, the additives are usually selected from the group consisting of pore - forming agents, stabilizers, rheological additives, surfactants, or mixtures thereof.

[0274] If the hydrophobic coating composition contains additives, based on the hydrophobic coating composition, the coating composition usually contains 0.01 - 2% (by weight), especially 0.05 - 1% (by weight), preferably 0.1 - 0.5% (by weight), and preferably 0.1 - 0.3% (by weight) of the additives.

[0275] According to a preferred embodiment of the present invention, the hydrophobic coating composition comprises a conductivity improver. As described above in conjunction with the electrode according to the present invention, it has been shown to be beneficial that the conductivity improver is selected from the group consisting of carbon black, graphite, carbon nanotubes and mixtures thereof.

[0276] If the hydrophobic coating composition contains a conductivity improver, it is generally specified that the amount of the conductivity improver contained in the hydrophobic coating composition is 0.01-2% (weight), especially 0.05-1% (weight), preferably 0.1-0.5% (weight), preferably 0.1-0.3% (weight), based on the hydrophobic coating composition.

[0277] With respect to the hydrophilic coating composition, it is generally provided that the hydrophilic coating composition comprises a hydrophilic polymer.

[0278] In this context, particularly good results will be obtained if the hydrophilic coating composition contains a hydrophilic polymer in an amount of 0.01-2% by weight, in particular 0.05-1.5% by weight, preferably 0.1-1% by weight, preferably 0.3-0.5% by weight, based on the hydrophilic coating composition.

[0279] Likewise, within the scope of the present invention it can be provided that the hydrophilic coating composition contains a catalyst in an amount of 0.1-10% by weight, in particular 0.5-5% by weight, preferably 1-3% by weight, preferably 1%-2% by weight, based on the coating composition.

[0280] As also mentioned above, the hydrophilic coating composition usually contains a dispersion medium. If the hydrophilic coating composition has a dispersion medium, it has been found to be beneficial if the hydrophilic coating composition contains a dispersion medium in an amount of 85% to 99.9% by weight, in particular 92% to 99.4% by weight, preferably 96% to 98.8% by weight, preferably 97 to 98.7% by weight, based on the coating composition.

[0281] Likewise, good results will be obtained if the dispersion medium is selected from water, alcohol, N,N-dimethylformamide, acetone, ethyl acetate, acetonitrile and mixtures thereof, preferably mixtures thereof. In this context, particularly good results will be obtained if the dispersion medium is selected from water, alcohol and mixtures thereof, preferably mixtures thereof.

[0282] If the dispersion medium is selected from water, alcohols and mixtures thereof, it has been found to be advantageous 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.

[0283] Regarding the hydrophilic coating composition, it can also be stipulated that the coating composition has additives. If the hydrophilic coating composition has additives, it can be stipulated that the additives are selected from pore formers, stabilizers, rheological additives, surfactants or mixtures thereof.

[0284] Similarly, it can be stipulated herein that, based on the hydrophilic coating composition, the hydrophilic coating composition contains an additive in an amount of 0.01 - 2% (by weight), especially 0.05 - 1% (by weight), preferably 0.1 - 0.5% (by weight), preferably 0.1 - 0.3% (by weight).

[0285] Another subject matter of the present invention - according to the present invention Second aspect - is an electrolytic cell, especially for the electrochemical reduction of carbon dioxide, which has at least one of the previously described electrodes.

[0286] Generally speaking, the electrolytic cell according to the present invention has at least two chambers, namely an anode chamber and a cathode chamber.

[0287] The electrode according to the present invention, especially the gas diffusion electrode, usually forms an interface between a liquid and / or gaseous matrix and a liquid or solid electrolyte. The diffusion layer composed of a porous carrier layer and a catalyst layer is preferably at least partially penetrated by the liquid matrix. The matrix, electrolyte and catalyst then form a triple-phase boundary, at which the electrochemical process occurs.

[0288] The gas diffusion electrode according to the present invention can form the cathode and / or anode of the electrolytic cell, preferably the cathode.

[0289] In the context of the present invention, it is preferably stipulated that the electrode according to the present invention forms the cathode in the electrolytic cell according to the present invention.

[0290] The electrode according to the present invention is preferably used as the cathode, especially for the reduction of, for example, CO 2 (and CO, N 2 , O 2 and organic molecules). It can also be used as the anode for oxidation reactions.

[0291] In addition to the electrode according to the present invention, the electrolytic cell also has at least one other electrode, especially the anode. A suitable oxidation or reduction process can be carried out on the other electrode, and the other electrode can also be the electrode according to the present invention. At the anode, as part of the electrochemical reduction of CO 2 water is especially oxidized to oxygen.

[0292] The second electrode, in particular the anode, can also be composed of all suitable materials, in particular porous materials such as metal felts, sintered metal particles, metal meshes and mixtures thereof. In addition, it is generally provided that the second electrode is also coated with a catalyst. The catalyst is usually a metal or a metal oxide, such as iridium oxide.

[0293] There is usually a diaphragm or semipermeable membrane, in particular an anion exchange membrane (AEM), between the anode and the cathode of the electrolytic cell according to the present invention. Alternatively, a proton exchange membrane (PEM) or a bipolar exchange membrane (BPM) is also conceivable.

[0294] In order to increase the output, in addition to expanding the electrode area, due to the conductivity, a plurality of individual cells can also be stacked vertically to the electrode plane into a bipolar stack.

[0295] According to a preferred embodiment of the present invention, the electrolytic cell is a so-called zero-gap electrolytic cell.

[0296] For further details of the electrolytic cell according to the present invention, reference can be made to the statements above regarding another aspect of the present invention, which correspondingly apply to the electrolytic cell according to the present invention.

[0297] The subject matter of the present invention will be explained below in a non-limiting manner by means of the accompanying drawings and exemplary embodiments.

[0298] Figure 1 An electrode 1 according to the present invention is shown, which has a hydrophobic catalyst layer (CL) 2 and a hydrophilic catalyst layer (CL) 3.

[0299] The catalyst layers 2 and 3 are each porous and have a pore size in the range of 0.001 - 5 μm, in particular 0.001 - 3 μm, preferably 0.01 - 2 μm.

[0300] The hydrophobic catalyst layer 2 preferably has at least one hydrophobic polymer, and based on the hydrophobic catalyst layer, the amount thereof is 0.01 - 50% (by weight), in particular 0.1 - 40% (by weight), preferably 1 - 30% (by weight), preferably 1 - 10% (by weight).

[0301] The hydrophobic polymer is preferably selected from the group consisting of polyethylene, polypropylene, cycloolefin copolymer (COC), polystyrene (PS), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and their copolymers and mixtures, especially polyethylene, polypropylene, polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE).

[0302] Furthermore, it can be specified that the hydrophobic catalyst layer 2 has a conductivity improver, which is especially selected from carbon black, graphite, carbon nanotubes, and their mixtures.

[0303] The hydrophilic catalyst layer 3 preferably has at least one hydrophilic polymer, especially an ionomer. In the context of the present invention, it is particularly preferred that the hydrophilic polymer is selected from cationic and anionic exchange polymers, especially anionic exchange polymers. In this article, particularly good results will be obtained if the hydrophilic polymer is selected from the group consisting of polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, polymers having phosphonium groups, polymers having sulfonium groups, polymers having organometallic complexes cationically functionalized, and their mixtures. Polymers having quaternary ammonium groups, polymers having quaternary nitrogen heterocycles, and their mixtures are particularly preferred. In this article, it is particularly preferred that the hydrophilic polymer, especially the ionomer, is selected from the group consisting of ionomers containing piperidinium groups, ionomers containing imidazolium groups, ionomers containing benzimidazolium groups, and their mixtures.

[0304] Based on the hydrophilic catalyst layer, the amount of the hydrophilic polymer contained in the hydrophilic catalyst layer 3 is generally 0.01 - 50% (by weight), especially 0.01 - 40% (by weight), preferably 0.01 - 30% (by weight), preferably 0.1 - 18% (by weight).

[0305] The hydrophilic catalyst layer 3 and the hydrophobic catalyst layer 2 generally have a thickness of 0.05 μm - 100 μm, especially 0.5 μm - 100 μm, preferably 0.5 μm - 50 μm, preferably 0.5 - 20 μm.

[0306] In the context of the present invention, it is also specified that both the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 have 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 each other. However, usually the same catalyst is used in the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3.

[0307] The catalyst is distributed as evenly as possible in each layer. The catalyst is usually selected from the following group: metal particles, especially metal nanoparticles, single atom catalysts, metal carbides, metal oxides, metal chalcogenides, molecular catalysts, and mixtures thereof.

[0308] Particularly good results are obtained if the catalyst is selected from the group consisting of metal particles, especially metal nanoparticles, such as silver, gold, zinc, palladium, gallium, cadmium, indium, mercury, thallium, lead, bismuth, copper, and mixtures and alloys thereof. Particularly preferred herein is that the catalyst is selected from the group: metal particles, especially metal nanoparticles, silver, gold, copper, and mixtures and alloys thereof.

[0309] Based on the hydrophobic catalyst layer 2 or the hydrophilic catalyst layer 3, the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 usually contain 50 - 99.9% (by weight), especially 55 - 99.9% (by weight), preferably 60 - 99.8% (by weight), preferably 70 - 99.8% (by weight) of the catalyst.

[0310] Preferably, it is also specified that the hydrophobic catalyst layer 2 and the hydrophilic catalyst layer 3 are applied to a porous layer, especially the gas diffusion layer 4.

[0311] The porous layer, especially the gas diffusion layer 4, is especially a common gas diffusion layer, Gas Diffusion Layer, (GDL). The material of the porous layer, especially the gas diffusion layer 4, is usually selected from the following group: carbon fabric, carbon fiber paper, graphite fabric, metal felt, metal mesh, sintered metal, and mixtures thereof. Particularly good results are obtained if the material of the porous layer, especially the gas diffusion layer 4, is selected from the group consisting of carbon fabric, carbon fiber paper, and mixtures thereof. The porous layer, especially the gas diffusion layer 4, is particularly preferably carbon fabric. The porous layer, especially the gas diffusion layer 4, preferably has a thickness of 50 - 1,000 μm, especially 50 μm - 800 μm, preferably 100 μm - 600 μm, preferably 150 μm - 500 μm.

[0312] According to a preferred embodiment, the electrode according to the present invention has the following structure: the hydrophobic catalyst layer 2 is applied to the gas diffusion layer 4, and the hydrophilic catalyst layer 3 is applied to this hydrophobic catalyst layer.

[0313] The electrode 1 according to the present invention is excellently suitable for use as a cathode in an electrolytic cell, especially a zero-gap electrolytic cell, for reducing carbon dioxide.

[0314] Figure 2 An electrolytic cell 5 according to the present invention is shown, especially an electrolytic cell in the form of a zero-gap electrolytic cell.

[0315] The electrode structure consists of an electrode 1 with a gas diffusion layer 4, a hydrophobic catalyst layer 2, and a hydrophilic catalyst layer 3 according to the present utility model. The electrode 1 according to the present utility model is preferably formed as a cathode.

[0316] The anode 6 of the electrolytic cell 5 is preferably composed of a titanium felt, on which an iridium oxide catalyst is applied.

[0317] These electrodes are separated by a semipermeable membrane 7 (i.e., an anion exchange membrane).

[0318] On the cathode side, carbon dioxide is introduced, particularly using an inert carrier gas moistened with water vapor, such as nitrogen or argon, and diffuses through the porous support layer to the catalyst layers 2 and 3. On the anode side, water is introduced through the anode chamber, through the porous anode 6 to the membrane 7.

[0319] At the electrode 1 acting as the cathode, CO 2 is preferably reduced to carbon monoxide. The reaction products are again flushed out of the cathode chamber by the carrier gas stream. On the anode side, water is oxidized to oxygen, while protons migrate through the semipermeable membrane 7 and react with the reduced CO 2 to form organic residues.

[0320] The following examples illustrate the subject matter of the present utility model in a non - limiting manner.

[0321] Examples

[0322] 1. Reference Example A: GDE with a hydrophobic polymer - containing CL

[0323] As a reference example, a GDE with a single - layer, hydrophobic polymer - containing catalyst layer (CL) was prepared. For this purpose, a carbon fabric (W1S1010, fuelcellstore) with a microporous layer was coated with a polymer - containing catalyst ink.

[0324] 1.1 Preparation of the catalyst ink:

[0325] The catalyst (AgNP, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink was equal to 16.67 mg ml -1 . In addition, Triton X - 100 was added as an ink stabilizer and pore - former. Before adding the PTFE dispersion, the ink was homogenized at 13,400 rpm for 90 seconds (Ultra - Turrax T18D, IKA). Finally, the catalyst ink was sonicated for 15 minutes for further homogenization.

[0326] Table 1: Exemplary composition of the polymer - containing catalyst ink, based on the weighed amount of the catalyst (AgNP), having 15% (by weight) of the polymer (PTFE)

[0327] Number Component Amount 1 Ultra-pure water 7.5ml 2 AgNPs (Alfa Aesar) 500 mg 3 Isopropanol 22.5ml 4 Triton X-100 75 mg 5 PTFE-dispersion (60% (by weight)) 125 mg

[0328] 1.2. Preparation of GDE:

[0329] The prepared catalyst ink was sprayed onto the carbon fabric using a spray gun (Eclipse, Iwata) until a catalyst loading of 2.5 mg cm -2 of AgNP was reached. To ensure rapid solvent evaporation, the carbon fabric was heated to 90 °C during spraying. Then the GDE was sintered in air at 300 °C for 15 minutes. The prepared GDE contained 1%; 3.75%; 7.5%; 15% and 30% (by weight) of PTFE in the catalyst ink, based on the weight of the catalyst used.

[0330] 1.3 CO 2 Electrolysis:

[0331] CO 2 The electrolysis was carried out in a zero-gap electrolytic cell with an active cell area of 2 cm 2 . A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 of IrO 2 (Alfa Aesar) was used at the anode. The anode chamber was continuously flushed with 16.6 ml min -1 of 0.1 M KHCO 3 . A prepared GDE containing 2.5 mg cm -2 of AgNP (Alfa Aesar) was used at the cathode. Five different GDEs with a hydrophobic polymer-containing CL were studied. The corresponding PTFE contents in the catalyst ink were 1%; 3.75%; 7.5%; 15% and 30% (by weight). During electrolysis, the cathode chamber was flushed with 50 ml min -1 of CO 2 and 5 ml min -1 of Ar. Argon was used as an internal standard here. Before entering the cathode chamber, the gas input stream was adjusted to a relative humidity of 79% (dew point: 55 °C) using a saturated steam humidifier. The 40-μm-thick Piperion membrane used was activated directly in 1 M KOH for 30 minutes before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm, MilliQ). All electrocatalytic studies were carried out at a constant current of 300 mA cm -2 for 3 hours. Samples of the gaseous product stream generated at the cathode were analyzed by GC-MS every 20 minutes.

[0332] For all prepared GDEs with polymer-containing CLs (1%, 3.75%, 7.5%, 15%, and 30% (by weight) PTFE), the current yield of the target product CO (FE CO ), and the measured cell voltage (U 池 ) are as Figure 3 shown.

[0333] Figure 3 Shows U -2 and FE 池 as a function of the PTFE content in the cathode catalyst ink during constant current electrolysis at 300 mA cm CO . The test time after reaching the steady state (2 - 3 h) is shown.

[0334] The hydrophobic polymer-containing CLs were studied at an industrially relevant current density of 300 mA cm -2 . FE 池 values of 28 - 44% can be achieved at U CO values of 3.5 - 5.5 V. It can be seen that the cell voltage increases with increasing PTFE content in the CL. The highest FE CO was achieved in the CL where 7.5% (by weight) PTFE was used based on the amount of catalyst used in the catalyst ink of the CL. When the PTFE content was 30% (by weight), the SPE membrane dried repeatedly and thus ruptured.

[0335] 2. Reference Example B: GDE with a hydrophilic ionomer-containing CL

[0336] As a second reference example, a GDE with a hydrophilic ionomer-containing CL was prepared. For this purpose, a carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated with an ionomer-containing catalyst ink.

[0337] 2.1 Preparation of the catalyst ink:

[0338] The catalyst (AgNP, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture to give a catalyst concentration in the ink of 16.67 mg ml -1 . The catalyst ink was homogenized at 13,400 rpm for 90 s (Ultra Turrax T18D, IKA). Finally, the catalyst ink was sonicated for 15 min to further homogenize.

[0339] Table 2. Exemplary composition of the polymer-containing catalyst ink, with 15% (by weight) ionomer (Piperion) based on the amount of catalyst (AgNP) weighed

[0340] Number Component Amount 1 Ultra-pure water 7.5ml 2 AgNPs (Alfa Aesar) 500 mg 3 Isopropanol 22.5ml 4 Piperion A5 (5% (by weight) in EtOH) 1.5 mg

[0341] 2.2 Preparation of GDE:

[0342] Use a spray gun (Eclipse, Iwata) to spray the catalyst ink onto the carbon fabric until a catalyst loading of 2.5 mg cm - 2 of AgNP is achieved. To ensure rapid solvent evaporation, the carbon fabric is heated to 90 °C during spraying. The prepared GDE contains 1%; 3.75%; 7.5%; 15% and 30% (by weight) of Piperion in the catalyst ink based on the weighed amount of catalyst.

[0343] 2.3 CO 2 Electrolysis:

[0344] CO 2 The electrolysis is carried out in a zero-gap electrolytic cell with an active cell area of 2 cm 2 On the anode, a porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrO 2 (Alfa Aesar) is used. The anode chamber is continuously flushed with 16.6 ml min -1 of 0.1 M KHCO 3 On the cathode, a GDE with a AgNP (Alfa Aesar) loading of 2.5 mg cm -2 is used. Five different GDEs with an ionomer-containing CL are studied. The corresponding PTFE content in the catalyst ink is 1%; 3.75%; 7.5%; 15% and 30% (by weight). During electrolysis, the cathode chamber is flushed with 50 ml min -1 CO 2 and 5 ml min -1 Ar. Argon is used as an internal standard here. Before entering the cathode chamber, the gas input stream is adjusted to a relative humidity of 79% (dew point: 55 °C) using a saturated steam humidifier. Whether it is a 40-μm-thick Piperion membrane or a GDE, it is activated directly in 1 M KOH for 30 minutes before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic studies are carried out at a constant current of 300 mA cm -2 for 3 hours. Samples of the gaseous product stream generated from the cathode are analyzed by GC-MS every 20 minutes.

[0345] For all the prepared GDEs with a polymer-containing CL (1 - 30% (by weight) of Piperion), Figure 4Shows the current yield of the target product CO (FE CO ), and the measured cell voltage (U_cell).

[0346] Figure 4 Shows the relationship between the cell voltage (A) and the current yield of the product CO (B) during constant current electrolysis at 300 mA cm -2 and the Piperion content in the cathode catalyst ink. The test time after reaching the steady state (2 - 3 hours) is shown respectively.

[0347] At an industrially relevant current density of 300 mA cm -2 , the hydrophilic ionomer-containing CL was studied. At U 池 of 3.2 - 3.4 V, an FE of 12 - 49% can be achieved CO . It can be seen that as the Piperion content increases, the FE CO decreases and the U 池 increases. At a Piperion of 1% (by weight), the highest FE of 49% CO and the lowest U 池 will be achieved.

[0348] 3. Example 1 of the present utility model: (Multi-layer catalyst layer)

[0349] As an example of the present utility model described herein having multiple catalyst layers (CL) for CO 2 reduction, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated with a hydrophobic polymer-containing catalyst layer in the first step and a hydrophilic ionomer-containing catalyst layer in the second step.

[0350] 3.1 Preparation of the polymer-containing catalyst ink:

[0351] The catalyst (AgNP, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture so that the concentration of the catalyst in the ink was equal to 16.67 mg ml -1 . In addition, Triton X-100 was added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink was homogenized at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, the catalyst ink was treated in an ultrasonic bath for 15 minutes to further homogenize. Based on the weighed amount of the catalyst, the PTFE content in the catalyst ink was 7.5% (by weight).

[0352] 3.2 Preparation of the ionomer-containing catalyst ink:

[0353] The catalyst (AgNP, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture to give a catalyst concentration in the ink equal to 16.67 mg ml -1 The catalyst ink was homogenized at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, the catalyst ink was treated with ultrasound for 15 minutes for further homogenization. The Piperion content in the catalyst ink was 1% by weight, based on the weighed catalyst.

[0354] 3.3 Preparation of GDE:

[0355] To prepare the catalyst layer, in a first step, the polymer-containing catalyst ink was sprayed onto a commercial carbon fabric using a spray gun (Eclipse, Iwata) until the desired catalyst loading was reached. The total AgNP loading in the catalyst layer was 2.5 mg cm 2 Five GDEs were prepared with different catalyst loadings of polymer-containing or ionomer-containing CLs. The corresponding compositions of the CLs are shown in Table 5. The PTFE content in the polymer-containing catalyst ink was 7.5% by weight based on the weighed catalyst, and the Piperion content in the ionomer-containing catalyst ink was 1% by weight based on the weighed catalyst. The polymer-containing CL was directly coated onto the GDL, and the ionomer-containing CL was directly coated onto the polymer-containing CL.

[0356] Table 3. Overview of AgNP loading of prepared multilayered CLs. The multilayered CLs consist of a polymer-containing CL located underneath and an ionomer-containing CL applied on top. The loading of the polymer-containing CL located underneath is shown in the middle column and the loading of the ionomer-containing CL is shown in the right column.

[0357]

[0358] 3.4 Preparation of 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 a spray gun (Eclipse, Iwata) until the desired catalyst loading was reached (see Table 3). The GDEs thus prepared were then sintered in air at 300 °C for 15 min. In a second step, the prepared ionomer-containing catalyst ink was sprayed onto the PTFE-CL until the target catalyst loading of 2.5 mg cm-3 was reached for the entire multilayer CL. 2 , PTFE-CL was previously coated onto the GDL heated to 90°C, the GDL having the polymer-containing CL.

[0360] 3.5CO 2 Electrolysis

[0361] CO 2 Electrolysis was carried out in a zero-gap electrolytic cell with an active cell area of 2 cm 2 On the anode, a porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrO 2 (Alfa Aesar) was used. The anode chamber was continuously flushed with 16.6 ml min -1 of 0.1 M KHCO 3 On the cathode, the prepared GDE was used, with an AgNP (Alfa Aesar) loading of 2.5 mg cm -2 . Five different GDEs with multilayer CLs were studied.

[0362] During electrolysis, the cathode chamber was flushed with 50 ml min -1 CO 2 and 5 ml min -1 Ar. Argon was used as an internal standard here. Before entering the cathode chamber, the gas input stream was adjusted to a relative humidity of 79% (dew point: 55 °C) using a saturated steam humidifier. Whether it was the 40-μm-thick Piperion membrane or the GDE, they were directly activated in 1 M KOH for 30 minutes before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All the electrocatalytic studies carried out were conducted at a constant current of 300 mA cm 2 for 3 hours. Samples of the gaseous product stream generated from the cathode were analyzed by GC-MS every 20 minutes.

[0363] For all the prepared GDEs with multilayer-structured CLs, Figure 5 the current yield (FE CO ) of the target product CO and the measured cell voltage (U 池 ) are shown.

[0364] Figure 5 Shown is at 300 mA cm -2The relationship between the cell voltage (A) and current yield of the product CO(B) of constant current electrolysis and the catalyst loading in the CL based on Piperion and PTFE, which produces a multi-layer structure according to the present utility model. Based on the weighed catalyst, the PTFE content in the polymer-based catalyst ink is 7.5% (by weight), and this catalyst ink is used to prepare the polymer-based CL. Based on the weighed catalyst, the Piperion content in the ionomer-based catalyst ink is 1% (by weight), and this catalyst ink is used to prepare the ionomer-based CL. The test time (2 - 3 hours) after reaching the steady state is shown respectively.

[0365] It can be seen from Figure 5 that compared with using the best polymer-containing CL (Reference A-3, left column) and the best ionomer-containing CL (Reference B-1, right column), higher current yield FE is achieved using all the multi-layer structures prepared according to the present utility model (Examples 1-A to 1-E, middle column). CO and lower cell voltage U 池 .

[0366] Figure 6 The cell voltage (A) and current yield of the product CO(B) of constant current electrolysis at 300 mA cm -2 are shown, which are achieved using the polymer-containing CL (Reference A), the ionomer-containing CL (Reference B), and the multi-layer structure according to the present utility model (Example 1-1). The polymer-containing CL (Reference A) has a catalyst loading of 2.5 mg cm -2 , and is prepared by spraying the catalyst ink, which contains 7.5% (by weight) of PTFE based on the catalyst AgNP. The ionomer-containing CL (Reference B) has a catalyst loading of 2.5 mg cm -2 , and is prepared by spraying the catalyst ink, which contains 1% (by weight) of Piperion based on the catalyst AgNP. The structure according to the present utility model (Example 1-1) consists of a polymer-containing first CL (7.5% (by weight) of PTFE) with an AgNP loading of 2.0 mg cm 2 and an ionomer-containing second CL (PiperIon) with an AgNP loading of 0.5 mg cm -2 , so the total AgNP loading is equivalent to 2.5 mg cm -2 . The test time (2 - 3 hours) after reaching the steady state is shown respectively.

[0367] 4. Example 2 of the present utility model (multi-layer structure with carbon in a hydrophobic polymer-containing CL)

[0368] As an embodiment of the present utility model described herein, this embodiment has the structure of a catalyst layer, and the catalyst layer has carbon in a hydrophobic polymer-containing CL for CO 2 reduction. A commercially available carbon fabric (W1S1010, fuelcellstore) with a microporous layer is coated with a polymer- and carbon black-containing CL in a first step and then with an ionomer-containing CL in a second step.

[0369] 4.1 Preparation of polymer-containing catalyst ink:

[0370] The catalyst (AgNP, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink is equivalent to 16.67 mg ml -1 . Then, based on the weighed amount of the catalyst, 20% (by weight) of carbon (Ensaco 250G) is added to the catalyst ink, and Triton X-100 is added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink is homogenized at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, the catalyst ink is sonicated for 15 minutes to further homogenize. Based on the catalyst, the content of PTFE in the catalyst ink is 7.5% (by weight).

[0371] Table 4: Exemplary composition of the polymer-containing catalyst ink. Based on the weighed amount of the catalyst AgNP, the catalyst ink has 15% (by weight) of polymer (PTFE). Additionally, based on the weighed amount of the catalyst AgNP, 20% (by weight) of carbon (Ensaco 250G) is added.

[0372] Number Component Amount 1 Ultra-pure water 7.5ml 2 AgNPs (Alfa Aesar) 500 mg 3 Carbon (Ensaco 250G) 100 mg 4 Isopropanol 22.5ml 5 Triton X-100 75 mg 6 PTFE dispersion (60% (by weight)) 125 mg

[0373] 4.2 Preparation of ionomer-containing catalyst ink:

[0374] The catalyst (AgNP, Alfa Aesar) is dispersed in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink is equivalent to 16.67 mg ml -1 . The catalyst ink is homogenized at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, the catalyst ink is sonicated for 15 minutes to further homogenize. The content of Piperion in the catalyst ink based on the catalyst is 1% (by weight).

[0375] 4.3 Preparation of GDE:

[0376] To ensure rapid solvent evaporation, the carbon fabric was heated to 90 °C during spraying. Then, the prepared catalyst ink containing the polymer was sprayed onto the microporous side of the carbon fabric using a spray gun (Eclipse, Iwata) until the desired catalyst loading was reached (see Table 1). The thus-prepared GDE was then sintered in air at 300 °C for 15 minutes. In the second step, the prepared catalyst ink containing the ionomer was sprayed onto the previously coated PTFE-CL until the target loading of 2.5 mg cm 2 was reached, and the PTFE-CL was applied to the GDL heated to 90 °C, and the GDL had a polymer-containing CL.

[0377] 4.4CO 2 Electrolysis

[0378] CO 2 The electrolysis was carried out using an in-house developed zero-gap electrolyzer with an effective cell area of 2 cm 2 . A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrO 2 (Alfa Aesar) was used at the anode. The anode chamber was continuously flushed with 16.67 ml min -1 of 0.1 M KHCO 3 . The prepared GDE was used at the cathode with a AgNP (Alfa Aesar) loading of 2.5 mg cm -2 .

[0379] During electrolysis, the cathode chamber was flushed with 50 ml min -1 CO 2 and 5 ml min -1 Ar. Argon was used as an internal standard. Before entering the cathode chamber, the gas input stream was adjusted to a relative humidity of 79% (dew point: 55 °C) using a saturated steam humidifier. Whether it was a 40-μm-thick Piperion membrane or a GDE with a CL of multilayer structure, both were activated directly in 1 M KOH for 30 minutes before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic studies were carried out at a constant current of 300 mA cm -2 for 3 hours. Samples of the gaseous product stream generated at the cathode were analyzed by GC-MS every 20 minutes.

[0380] As Example 2-1, the current yield of the target product CO (FE Figure 7 and Figure 8 ) and the measured cell voltage (U CO ) for the prepared GDE are shown in 池) The GDE has a multi-layer structure and carbon according to the present utility model in a hydrophobic polymer-containing layer.

[0381] Figure 7 Shows the current yield of the target product CO (FE CO ) Figure 8 Shows at 300 mA cm -2 During the 180-minute constant current electrolysis, the corresponding measured cell voltage (U 池 ). The average FE is shown as a percentage on the left Y-axis CO (gray) and FE H2 (white), and the average U in volts can be seen on the right Y-axis 池 . Both are shown as the electrolysis duration (t 电解 )(in minutes) on the x-axis. The stable region after the adjustment phase in the last hour of electrolysis is highlighted in gray.

[0382] By additionally introducing 20% (by weight) of carbon based on the weighed catalyst into a polymer-containing catalyst ink having 15% (by weight) of PTFE based on the weighed catalyst, an additional carbon-containing multi-layer structured CL (AsfB 2-1) was produced. Based on the weighed catalyst, the catalyst ink of the ionomer-containing CL contains 1% (by weight) of Piperion (see Table 4). By using such a multi-layer structure with carbon in the polymer-containing layer, at a cell voltage of 3 V and an applied current density of 300 mA cm -2 , compared with Examples 1-1 to 1-5, FE CO Can be increased to 75%, as Figure 7 And 8 Shown.

[0383] 5. According to Example 3 of the present utility model (when using a bipolar solid electrolyte membrane, a CL having a multi-layer structure with carbon in the polymer-containing CL)

[0384] As an example of the present utility model described herein of a CL having a multi-layer structure with carbon in the polymer-containing CL when using a bipolar solid electrolyte membrane for CO 2 R, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was first coated with a polymer-containing and carbon black-containing CL in the first step and then coated with an ionomer-containing CL in the second step.

[0385] 5.1 Preparation of the polymer-containing catalyst ink:

[0386] Disperse the catalyst (AgNP, Alfa Aesar) in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink is equivalent to 16.67 mg / ml -1 。Then, based on the weighed amount of the catalyst, add 20% (by weight) of carbon (Ensaco 250G) to the catalyst ink, and add Triton X-100 as an ink stabilizer and pore former. Before adding the PTFE dispersion, homogenize the ink at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, sonicate the catalyst ink for 15 minutes to further homogenize it. The PTFE content in the catalyst ink based on the catalyst is 7.5% (by weight).

[0387] Table 5: Exemplary composition of the polymer-containing catalyst ink, with 7.5% (by weight) of polymer (PTFE) based on the weighed amount of the catalyst AgNP. Additionally, 20% (by weight) of carbon (Ensaco 250G) is added based on the weighed amount of the catalyst AgNP.

[0388] Number Component Amount 1 Ultra-pure water 7.5ml 2 AgNPs (Alfa Aesar) 500 mg 3 Carbon (Ensaco 250G) 100 mg 4 Isopropanol 22.5ml 5 Triton X-100 75 mg 6 PTFE dispersion (60% (by weight)) 62.5 mg

[0389] 5.2 Preparation of the ionomer-containing catalyst ink:

[0390] Disperse the catalyst (AgNP, Alfa Aesar) in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink is equivalent to 16.67 mg / ml -1 。Homogenize the catalyst ink at 13,400 rpm for 90 seconds (Ultra-Turrax T18D, IKA). Finally, sonicate the catalyst ink for 15 minutes to further homogenize it. The Piperion content in the catalyst ink based on the catalyst is 1% (by weight).

[0391] 5.3 Preparation of the GDE:

[0392] To ensure rapid solvent evaporation, heat the carbon fabric to 90 °C during the spraying process. Then spray the prepared polymer-containing catalyst ink onto the microporous side of the carbon fabric using a spray gun (Eclipse, Iwata) until the desired catalyst loading is reached (see Table 1). Then sinter the GDE prepared in this way in air at 300 °C for 15 minutes. In the second step, spray the prepared ionomer-containing catalyst ink onto the previously coated PTFE-CL until the target loading of 2.5 mg / cm 2 is reached, and the PTFE-CL is applied to the GDL heated to 90 °C, and the GDL has a polymer-containing CL.

[0393] 5.4 Preparation of the bipolar membrane

[0394] The bipolar membrane was prepared by laminating a 40-μm thick Piperion membrane and a 50-μm thick Nafion 212 membrane in a hot press at 50 °C and 10 bar pressure for a pressing time of 90 s.

[0395] 5.5CO 2 Electrolysis

[0396] CO 2 The electrolysis was carried out using an in-house developed zero-gap electrolyzer with an effective cell area of 12.57 cm 2 . A porous titanium felt (2-GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrO2 (Alfa Aesar) was used on the anode. The anode chamber was continuously flushed with 66.67 ml min -1 ultrapure water (18.2 MΩ cm). The prepared GDE was used on the cathode, which had a loading of 2.5 mg cm -2 of AgNP (Alfa Aesar).

[0397] During the electrolysis, the cathode chamber was flushed with 50 ml min -1 CO 2 and 5.5 ml min -1 Ar. Argon was used as an internal standard. Both the bipolar membrane prepared by lamination and the GDE with a multi-layer structured CL were activated directly in 1 M KOH for 30 min before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic studies were carried out at a constant current of 300 mA cm -2 for 3 h. Samples of the gaseous product stream generated at the cathode were analyzed by GC-MS every 20 min.

[0398] Figure 9 shows the current yield of the target product CO (FE CO ), Figure 10 shows the measured cell voltage (U 池 ) of the GDE prepared using the bipolar membrane, with a multi-layer structured CL that has carbon in the polymer-containing layer. The electrolysis was carried out at a constant current of 300 mA cm -2 for more than 180 min. The average FE CO (gray) and FE H2 (white) are shown as percentages on the left Y-axis, and the average U 池 in volts can be seen on the right Y-axis. Both are shown against the electrolysis duration (t 电解 ) (in minutes) on the x-axis.

[0399] By additionally introducing 20% (by weight) of carbon based on the weight of the catalyst into the polymer-containing catalyst ink containing 7.5% (by weight) of PTFE, an additional carbon-containing multi-layer structured CL (AsfB.2-1) was produced. The catalyst ink of the ionomer-containing CL contains 1% (by weight) of Piperion based on the weight of the catalyst (see Table 4). Using a laminated bipolar membrane composed of a 40 μm thick Piperion membrane and a 50 μm thick Nafion 212 membrane, at a current density of 300 mA cm -2 a current density of, a FE of up to 50% can be achieved at a cell voltage of 3.3 - 3.4 V CO .

[0400] 6. According to Example 4 of the present invention (a CL having a multi-layer structure with carbon in a polymer-containing CL when using a bipolar solid electrolyte membrane)

[0401] As an example of the CL of the present invention described herein having a multi-layer structure with carbon in a polymer-containing CL when using a bipolar solid electrolyte membrane for CO 2 R, a commercially available carbon fabric with a microporous layer (W1S1010, fuelcellstore) was coated with a polymer-containing and carbon black-containing CL in the first step and with an ionomer-containing CL in the second step.

[0402] 6.1 Preparation of the polymer-containing catalyst ink:

[0403] The catalyst (AgNP, Alfa Aesar) was dispersed in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink was equivalent to 16.67 mg ml -1 . Then, 20% (by weight) of carbon (Ensaco250G) was added to the catalyst ink based on the weight of the catalyst, and Triton X-100 was added as an ink stabilizer and pore former. Before adding the PTFE dispersion, the ink was homogenized at 13,400 rpm for 90 seconds (Ultra-TurraxT18D, IKA). Finally, the catalyst ink was sonicated for 15 minutes for further homogenization. The PTFE content based on the catalyst in the catalyst ink was 7.5% (by weight).

[0404] Table 6: Exemplary composition of the polymer-containing catalyst ink, having 7.5% (by weight) of polymer (PTFE) based on the weight of the catalyst AgNP. Additionally, 20% (by weight) of carbon (Ensaco250G) was added based on the weight of the catalyst AgNP.

[0405] Number Component Amount 1 Ultra-pure water 7.5ml 2 AgNPs (Alfa Aesar) 500 mg 3 Carbon (Ensaco 250G) 100 mg 4 Isopropanol 22.5ml 5 Triton X-100 75 mg 6 PTFE dispersion (60% (by weight)) 62.5 mg

[0406] 6.2 Preparation of Catalyst Ink Containing Ionomer:

[0407] Disperse the catalyst (AgNP, Alfa Aesar) in a 3:1 isopropanol / water mixture such that the concentration of the catalyst in the ink is equivalent to 16.67 mg ml -1 . Homogenize the catalyst ink at 13,400 rpm for 90 seconds (Ultra - Turrax T18D, IKA). Finally, sonicate the catalyst ink for 15 minutes for further homogenization. The content of Piperion in the catalyst ink is 1% (by weight) based on the catalyst.

[0408] 6.3 Preparation of GDE:

[0409] To ensure rapid solvent evaporation, heat the carbon fabric to 90 °C during the spraying process. Then spray the prepared polymer - containing catalyst ink onto the microporous side of the carbon fabric using a spray gun (Eclipse, Iwata) until the desired catalyst loading is reached (see Table 1). Then sinter the thus - prepared GDE in air at 300 °C for 15 minutes. In the second step, spray the prepared catalyst ink containing ionomer onto the previously coated PTFE - CL until a target loading of 2.5 mg cm 2 is reached, and the PTFE - CL is applied to the GDL heated to 90 °C, and the GDL has a polymer - containing CL.

[0410] 6.4 Preparation of Bipolar Membrane

[0411] The bipolar membrane is prepared by spraying a Piperion solution (1% (by weight) in ethanol) onto a 50 - μm - thick Nafion 212 membrane and then treating it in a hot press at 50 °C and 10 bar pressure for a pressing time of 90 seconds.

[0412] 6.5 CO 2 Electrolysis

[0413] CO 2 The CO electrolysis is carried out using an in - house developed zero - gap electrolyzer with an effective cell area of 12.57 cm 2 . Use a porous titanium felt (2 - GDL40, Bekaert) with a catalyst loading of 1 mg cm -2 IrO2 (Alfa Aesar) on the anode. Continuously rinse the anode chamber with 66.67 ml min -1 ultrapure water (18.2 MΩ cm). Use the prepared GDE with a AgNP (Alfa Aesar) loading of 2.5 mg cm -2 on the cathode.

[0414] During electrolysis, the cathode chamber was flushed with 50 ml min -1 CO 2 and 5.5 ml min -1 Ar. Argon served as the internal standard. Whether the bipolar membrane was prepared by lamination or the GDE with a CL of multilayer structure, it was activated directly in 1 M KOH for 30 minutes before the start of electrolysis and then rinsed with ultrapure water (18.2 MΩ cm). All electrocatalytic studies were carried out at a constant current of 300 mA cm -2 for 3 hours. Samples of the gaseous product stream generated from the cathode were analyzed by GC-MS every 20 minutes.

[0415] Figure 11 shows the current yield of the target product CO (FE CO ), Figure 12 shows the measured cell voltage (U 池 ) of the GDE prepared using a bipolar membrane, the GDE having a CL of multilayer structure with carbon in the polymer-containing layer. Electrolysis was carried out at a constant current of 300 mA cm -2 for more than 180 minutes. The average FE CO (gray) and FE H2 (white) are shown as percentages on the left Y-axis, and the average U 池 in volts can be seen on the right Y-axis. Both are shown against the electrolysis duration (t 电解 )(in minutes) on the x-axis.

[0416] An additional carbon-containing multilayer-structured CL (AsfB.2-1) was produced by additionally introducing 20% (by weight) of carbon based on the weight of the catalyst into the polymer-containing catalyst ink containing 7.5% (by weight) PTFE. The catalyst ink of the ionomer-containing CL contained 1% (by weight) of Piperion based on the weight of the catalyst (see Table 4). Using a bipolar membrane, at a current density of 300 mA cm -2 , an FE CO of up to 43% could be achieved at a cell voltage of 3.3 - 3.6 V, and the bipolar membrane was prepared by spraying a Piperion solution (1% (by weight) in ethanol) onto a 50-μm-thick Nafion 212 membrane.

[0417] List of reference numerals:

[0418] 1 Electrode

[0419] 2 Hydrophobic catalyst layer

[0420] 3 Hydrophilic catalyst layer

[0421] 4 Gas diffusion layer

[0422] 5 Electrolytic cell

[0423] 6 Anode

[0424] 7 Membrane

Claims

1. A gas diffusion electrode, wherein: The anode and cathode compartments are separated by an anion exchange membrane (AEM). It is characterized in that The electrode has at least one hydrophobic catalyst layer and at least one hydrophilic catalyst layer.

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

3. The electrode according to claim 1 or 2, characterized in that The hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged directly or indirectly above each other.

4. The electrode according to claim 1 or 2, characterized in that: The hydrophobic catalyst layer and the hydrophilic catalyst layer are arranged on a porous support layer, in particular a gas diffusion layer.

5. The electrode according to claim 4, characterized in that The porous support layer is carbon fabric, carbon fiber paper, graphite fabric, metal felt, metal mesh or sintered metal.

6. The electrode according to claim 5, characterized in that The porous carrier layer is carbon fabric or carbon fiber paper.

7. The electrode according to claim 1 or 2, characterized in that: The hydrophobic catalyst layer and the hydrophilic catalyst layer each contain a catalyst.

8. The electrode according to claim 1 or 2, characterized in that: The catalyst is a metal particle, a single atom catalyst, a metal carbide, a metal oxide, a metal chalcogenide or a molecular catalyst.

9. The electrode according to claim 8, characterized in that The metal particles are metal nanoparticles.

10. The electrode according to claim 1 or 2, characterized in that: The hydrophilic catalyst layer has a hydrophilic polymer.

11. The electrode according to claim 10, characterized in that The hydrophilic polymer is an ionomer.

12. The electrode according to claim 10, characterized in that The hydrophilic polymer is a cation exchange polymer or an anion exchange polymer.

13. The electrode according to claim 1 or 2, characterized in that: The hydrophobic catalyst layer has a hydrophobic polymer.

14. The electrode according to claim 13, characterized in that The hydrophobic polymer is a polyolefin, a polyfluoroolefin, a silicone, a fluorinated polymer or a polyaromatic polymer.

15. An electrolytic cell, characterized in that: The electrolytic cell comprises at least one electrode according to any one of claims 1 to 14 .

16. The electrolytic cell according to claim 15, characterized in that It is used for the electrochemical reduction of carbon dioxide to carbon monoxide.

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