Gas diffusion electrode for electrochemical reduction of carbon dioxide

Abstract

This invention relates to a gas diffusion electrode for the electrochemical reduction of carbon dioxide, comprising: a conductive porous gas diffusion layer; at least one porous catalyst layer disposed adjacent to the gas diffusion layer, the at least one porous catalyst layer comprising a first porous catalyst layer comprising a copper-based first catalyst material, wherein the first porous catalyst layer comprises a mixture of the copper-based first catalyst material and a hydrophobic material, the porous catalyst layer being obtained from a precursor material free of any ionomers; and an ionomer layer disposed adjacent to the at least one porous catalyst layer, the ionomer layer being obtained from a precursor material free of any catalysts. The invention also relates to an electrochemical cell comprising such a gas diffusion electrode, and a method for manufacturing such a gas diffusion electrode.

Description

Technical Field

[0001] This invention relates to a gas diffusion electrode for the electrochemical reduction of carbon dioxide (CO2) to valuable carbon-based products such as carbon monoxide (CO) or ethylene (C2H4) . The invention also relates to a method for manufacturing such a gas diffusion electrode and an electrochemical cell using such a gas diffusion electrode. Background Technology

[0002] Significant advancements in energy conversion and storage technologies have driven the growing demand for highly efficient electrochemical systems. Among these, gas diffusion electrodes (GDEs) have become key components, revolutionizing the field by facilitating enhanced mass transfer and electrode kinetics. With their unique construction and versatile applications, GDEs have garnered considerable attention across various sectors, including fuel cells, electrochemical sensors, and electrolyzers. Also known as three-phase electrodes, GDEs play a crucial role in bridging electrochemical processes and gaseous reactants occurring at the solid electrode-electrolyte interface. Their unique architecture enables efficient transport of reactant gases, electron transfer, and electrolyte management, thereby improving the overall performance of electrochemical devices. The construction of GDEs involves a carefully designed, layered structure combining a porous catalyst layer, a gas diffusion layer, and a hydrophobic binder. The porous catalyst layer acts as the site of electrochemical reactions, where catalytic materials (such as platinum, palladium, or other transition metals) facilitate the conversion of reactant gases. It provides a high surface area for efficient catalysis and promotes efficient electron transfer between the electroactive material and the electrode. The porosity of this layer allows for the entry and exit of reactant gases and facilitates the transport of ions and products. The gas diffusion layer, positioned adjacent to the catalyst layer, acts as a conductive pathway for both gaseous reactants and electrons. Typically composed of carbon-based materials such as carbon cloth or paper, carbon nanotubes, or graphene, the gas diffusion layer must exhibit high gas permeability, electrical conductivity, and mechanical stability. It not only contributes to the uniform distribution of reactant gases within the catalyst layer but also aids in the effective removal of reaction byproducts and water, thus preventing flooding and ensuring sustained electrochemical activity. To enhance the stability and durability of the gas diffusion electrode, hydrophobic binders are introduced, imparting water repellency to the gas diffusion layer. This hydrophobicity prevents flooding and helps maintain the desired gas diffusion characteristics by minimizing the intrusion of liquid water into the electrode structure. Commonly used binders include polytetrafluoroethylene (PTFE) and various perfluorosulfonic acid (PFSA) polymers.

[0003] Gas diffusion electrodes have diverse applications in various electrochemical devices: in fuel cells, they act as catalyst supports for oxygen reduction and fuel oxidation reactions, facilitating the conversion of chemical energy into electrical energy. They also play a crucial role in electrochemical sensors, providing rapid and selective detection of various analytes by utilizing the electrochemical signals generated at the electrode-electrolyte interface. Furthermore, gas diffusion electrodes are an essential component of electrolyzers, such as in chlor-alkali electrolysis.

[0004] In recent years, the use of gas diffusion electrodes for the electrochemical reduction of carbon dioxide has become a rapidly growing research area, especially because burning fossil fuels (which still account for the majority of global energy demand) involves the emission of carbon dioxide into the atmosphere, leading to environmental crises such as climate change and ocean acidification. To mitigate the problems associated with the release of carbon dioxide into the environment, technologies aimed at capturing and reusing carbon dioxide, such as from the atmosphere or directly from carbon dioxide-producing sources, have been investigated in recent years. However, carbon dioxide is a very stable molecule, requiring a significant energy input to convert it into other valuable carbon-based products. Particularly promising technologies for such applications involve electrochemical CO2 reduction reactions, especially when using energy from renewable energy sources. Typical valuable products obtained from electrochemical CO2 reduction are C1-C3 products, such as carbon monoxide (CO) and ethylene (C2H4).

[0005] Initially, the gas diffusion electrode for electrochemical CO2 reduction was based on a gas diffusion electrode originally developed for fuel cells. Typically, a catalyst layer is deposited on a microporous layer by spraying a mixture of catalyst and ionomer onto the microporous layer. The resulting structure exhibits several beneficial features, such as a thin overall structure that enhances carbon dioxide accessibility and ensures good ionic conductivity of the electrolyte in the catalyst region. However, the structural effect of the ionomer can cause problems regarding the structure's conductivity and durability because ionomers are typically electrically insulating. Furthermore, stability issues caused by carbonate precipitation can arise.

[0006] International patent application WO 2019 / 020239 A1 describes an electrolyzer design for the electrochemical reduction of carbon dioxide. The cathode of this electrolyzer is based on a mixture of a powdered electrocatalyst for carbon dioxide reduction and an anion-exchange ionomer. The cathode described in this prior art document still contains a mixture of catalyst and ionomer, and therefore still suffers from the aforementioned problems regarding reduced conductivity and durability of the structure.

[0007] Ramato Ashu TUFA et al. in " Towards highly efficient electrochemical CO 2 reduction: Cell designs, membranes and electrocatalystsIn Applied Energy, Elsevier Science Publishers, GB, Vol. 277, August 12, 2020, it is described that binders and ionomers can be used in the catalyst layer to bind the catalyst and facilitate ion transport.

[0008] International patent application WO 2023 / 004505 A1 describes a multilayer cathode for the electrochemical reduction of carbon dioxide. This multilayer cathode comprises a gas diffusion layer, a cathode catalyst layer sputtered onto the gas diffusion layer, and a permeable carbon dioxide regeneration layer comprising anion-exchange ionomers (from which an ionomer solution is applied to the cathode catalyst layer). The cathode catalyst may be a copper-based catalyst.

[0009] Therefore, the object of this invention is to provide a gas diffusion electrode that solves problems related to electrochemical CO2 reduction. Specifically:

[0010] Due to the poor solubility of CO2 in liquid electrolytes and its limited diffusion range, good gas accessibility must be ensured throughout the entire structure to minimize the competitive hydrogen evolution reaction caused by water electrolysis.

[0011] In addition, good electrical conductivity of the overall structure must be ensured to allow electrons to come into contact with the catalyst and assist the reduction reaction.

[0012] In addition, it is essential to ensure the presence of sufficient liquid electrolyte in the catalyst region while avoiding immersion of the entire structure, which would also lead to the takeover of the aforementioned competitive hydrogen evolution reaction.

[0013] Finally, carbonate precipitation must be limited, which can occur when using alkaline hydroxides as electrolytes. This is because CO2 reacts with hydroxyl ions generated during the electrochemical reduction of CO2 or provided by alkaline electrolytes (such as metal hydroxides (MOHs)), which undergo further conversion into metal carbonates in an alkaline environment. The precipitation of solid metal carbonates can disrupt the electrode structure and lead to a reduction in the overall process efficiency. Summary of the Invention

[0014] Various aspects of the invention are set forth in the appended claims.

[0015] In one aspect, the present invention relates to a gas diffusion electrode for the electrochemical reduction of carbon dioxide, comprising: a conductive porous gas diffusion layer; at least one porous catalyst layer disposed adjacent to the gas diffusion layer, the at least one porous catalyst layer comprising a first porous catalyst layer comprising a copper-based first catalyst material, wherein the first porous catalyst layer comprises a mixture of the copper-based first catalyst material and a hydrophobic material, the catalyst layer being obtained from a precursor material free of any ionomers; and an ionomer layer disposed adjacent to the at least one porous catalyst layer, the ionomer layer being obtained from a precursor material free of any catalyst. In the sense of the present invention, the catalyst layer and the ionomer layer are structurally separated layers obtained from different precursor materials. Compared to the prior art described above, the precursor material for the catalyst layer is free of any ionomers, and the precursor material for the ionomer layer is free of any catalyst. This results in the presence of two separate layers, which provides a new way to regulate the permeation of electrolyte solution into the structure of the gas diffusion electrode, and thus can be customized according to the electrochemical process of interest.

[0016] Depending on the manufacturing process, some penetration of the ionomer into the catalyst layer can still occur, thus an interfacial region comprising a mixture of catalyst and ionomer can still exist between the porous catalyst layer and the ionomer layer. However, according to the present invention, in addition to providing the catalyst and ionomer in separate layers, the catalyst layer also comprises a mixture of a copper-based first catalyst material (e.g., catalyst powder or catalyst precursor powder) and a hydrophobic material (e.g., a hydrophobic resin such as a fluoropolymer). The hydrophobic material in the catalyst layer minimizes the penetration of the ionomer into the catalyst layer during manufacturing, and thus also minimizes the thickness of this interfacial region of mixed catalyst and ionomer.

[0017] Therefore, according to the invention, the at least one porous catalyst layer disposed to the gas diffusion layer is substantially free of any ionomers, and the ionomer layer disposed adjacent to the at least one porous catalyst layer is substantially free of any catalyst. In the context of this invention, the terms "substantially free of ionomers" or "catalyst," respectively, mean that while the catalyst layer precursor material is free of any ionomers and the ionomer layer precursor material is free of any catalyst, exceptions may be made in the small interface region between the porous catalyst layer and the ionomer layer, which comprises a mixture of catalyst and ionomer. However, in the above context, the term "small" means that the interface region has a thickness much smaller than the thickness of the corresponding layer itself. For example, the thickness of the interface region may be less than 25% of the thickness of the corresponding catalyst layer or ionomer layer, preferably less than 10% of the thickness of the catalyst layer or ionomer layer.

[0018] Since ionomers are typically hydrophilic, the ionomer layer increases the hydrophilicity of the electrode surface without compromising the overall catalyst layer structure.

[0019] In the context of this invention, a "hydrophobic" material is one that ensures the resulting porous catalyst layer exhibits hydrophobic properties, i.e., a water contact angle greater than 90°, preferably greater than 120°. Since ionomers are generally hydrophilic, the hydrophobic porous surface layer ensures that no ionomers permeate into the porous catalyst layer during the fabrication of the gas diffusion electrode of this invention, thereby minimizing or completely avoiding the interface region containing a mixture of catalyst and ionomers. Therefore, according to one embodiment, the catalyst layer is ionomer-free. Thus, the pathway of reactants to the catalyst material can be independently optimized by adjusting the properties of the ionomer layer and the porous catalyst layer.

[0020] In one embodiment, the copper-based first catalyst material comprises copper particles and / or copper oxide particles, preferably in the form of microparticles or nanoparticles. Microparticles are particles whose size (e.g., diameter for spherical particles, or effective diameter for non-spherical particles) is in the micrometer range. Nanoparticles have sizes in the nanometer range. Copper particles or copper oxide particles are suitable catalysts for the electrochemical reduction of carbon dioxide to carbon monoxide (CO) and ethylene (C₂H₄).

[0021] In a particularly preferred embodiment, the copper oxide particles comprise a mixture of copper (II) oxide (also known as copper oxide (CuO)) and copper (I) oxide (also known as cuprous oxide (Cu2O)). A corresponding catalyst layer is obtained by sintering a catalyst layer made of cuprous oxide (Cu2O) in an oxygen-containing atmosphere, such as air, which converts a portion of the cuprous oxide to copper oxide. Surprisingly, it has been found that, for the electrochemical reduction of carbon dioxide, the catalyst layer containing a mixture of copper oxide and cuprous oxide exhibits increased Faraday efficiency compared to a catalyst layer containing only cuprous oxide, particularly with increased selectivity for the production of alcohols such as ethanol (C2H5OH) and propanol (C3H7OH).

[0022] The gas diffusion electrode of the present invention is constructed to allow the ionomer layer to be applied on top of a pre-formed catalyst layer, enabling the catalyst layer and the ionomer layer to be manufactured separately. Separate treatment of the two layers allows for heat treatment on the catalyst layer, ensuring enhanced stability and hydrophobicity to the desired level. Such heat treatment cannot be performed using conventional mixtures of catalyst and ionomer, as most ionomers are unstable at high temperatures. Furthermore, the gas diffusion electrode of the present invention allows for the use of a catalyst precursor material that can be converted into the final catalyst material through in-situ heat treatment prior to the application of the ionomer layer. Thus, in one embodiment of the invention, the at least one porous catalyst layer is obtained by heat treating the precursor layer applied to the gas diffusion layer.

[0023] In addition to the catalyst material, the catalyst layer may contain components that adjust conductivity, such as carbon powder; components that adjust porosity, such as fibrous materials like cellulose; and components that adjust hydrophobicity, such as fluoropolymers.

[0024] In one embodiment, the at least one porous catalyst layer comprises not only the first catalyst layer described above, but also a second catalyst layer comprising a second catalyst material different from the copper-based first catalyst material. In certain electrochemical processes, it can be advantageous to deposit two or more different catalysts in separate layers, for example, to achieve a tandem effect, which is beneficial for the production of certain desired products. The weight ratio of the first catalyst layer to the second catalyst layer is preferably selected in the range of 20:1 to 2:1.

[0025] The gas diffusion electrode is specifically configured to promote the electrochemical reduction of carbon dioxide. Therefore, the second catalyst material is preferably selected from transition metal complexes, metal microparticles, metal nanoparticles, metal oxides, metal oxide microparticles, metal oxide nanoparticles, or combinations thereof. Transition metal complexes are preferably selected from porphyrins, phthalocyanines, metalloporphyrins, metal phthalocyanines, or metal-organic frameworks (MOFs), especially nickel-based MOFs. Microparticles and nanoparticles are preferably selected from gold (Au), silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), or alloys thereof. The copper particles or copper oxide particles in the copper-based first catalyst layer preferably have a diameter in the range of 20 nm to 10 μm. If two catalyst layers are used, the second catalyst layer is particularly preferably composed of silver nanoparticles with a diameter in the range of 20 nm to 200 nm.

[0026] The catalyst loading in at least one catalyst layer is preferably between 0.3 and 10 mg / cm³. 2 between.

[0027] In some embodiments, the conductive porous gas diffusion layer of the gas diffusion electrode of the present invention comprises a macroporous layer acting as a support and a microporous layer disposed between the macroporous layer and the at least one catalyst layer. According to the present invention, "Macroporous layer" Typically, they are carbon-based fiber structures, such as cloth, paper, or felt, in which the fibers have a diameter of 5-50 μm, and "Microporous layer" It is typically a carbon-based continuous structure that includes pores with an average diameter of 0.5–15 μm.

[0028] Preferably, the macroporous layer is a carbon base layer, such as carbon cloth or carbon paper, and its thickness is preferably selected in the range of 90 μm to 200 μm.

[0029] The microporous layer preferably comprises a mixture of carbon and a hydrophobic material. The thickness of the microporous layer is preferably selected in the range of 45 μm to 140 μm. Similar to the above definition, in the sense of this invention, "hydrophobic material" is a material that ensures the microporous layer exhibits hydrophobic properties (i.e., a water contact angle greater than 90°, preferably greater than 120°).

[0030] The hydrophobic material of the at least one porous catalyst layer and / or the hydrophobic material of the microporous layer is preferably a hydrophobic resin, preferably a fluoropolymer, such as a polytetrafluoroethylene (PTFE) polymer or a perfluorosulfonic acid (PFSA) polymer.

[0031] The ionomer layer arranged adjacent to at least one porous catalyst layer may comprise anion-exchange polymers or cation-exchange polymers. Depending on the electrochemical process of interest, the ionomer layer can be tailored in such a way that unwanted counterions from the electrolyte reach the catalytic reaction site, thereby preventing the diffusion of unwanted side reactions and thus improving the overall efficiency of the electrochemical process. In the case of the electrochemical reduction of carbon dioxide, the ionomer layer is made of anion-exchange polymer, which preferably has ammonium functional groups, such as piperidinium and imidazolium functional groups. The anion-exchange polymer may also include phosphonium and sulfonium structural moieties.

[0032] The present invention also relates to an electrochemical cell comprising an anode chamber, a cathode chamber, and a separator disposed between the anode chamber and the cathode chamber, wherein at least one of the anode chamber and the cathode chamber comprises a gas diffusion electrode as described above. The separator may be a membrane or a diaphragm. Typically, the anode chamber and the cathode chamber comprise current collectors that are in electrical contact with the electrodes in the respective chambers. The current collectors may be part of the gas diffusion electrode of the present invention and may, for example, be bonded to the outer surface of a gas diffusion layer, or, in the case of a real gas diffusion layer, to the outer surface of a microporous layer.

[0033] The present invention also relates to a method for manufacturing a gas diffusion electrode, particularly a gas diffusion electrode as described above, comprising the following steps:

[0034] a) A catalyst ink is prepared by dispersing a copper-based first catalyst material and a hydrophobic material in a first solvent, wherein the catalyst ink does not contain any ionomers;

[0035] b) Ionomer-based ink is prepared by dispersing the ionomer in a second solvent, wherein the ionomer-based ink does not contain any catalyst;

[0036] c) Prepare a conductive porous gas diffusion layer;

[0037] d) Coating the conductive porous gas diffusion layer with the catalyst ink to form a catalyst layer;

[0038] e) Drying and / or heat-treating the catalyst layer to allow the catalyst material to migrate over the gas diffusion layer; and

[0039] f) Coating the catalyst layer with the ionomer-based ink.

[0040] The catalyst ink in step a) is typically prepared by dissolving catalyst powder in a first solvent (e.g., in water). The ink also contains a hydrophobic material, such as a hydrophobic resin, like a fluoropolymer selected from polytetrafluoroethylene (PTFE) and perfluorosulfonic acid (PFSA) polymers. The catalyst ink may also contain a surfactant, such as a nonionic surfactant polymer having a hydrophilic polyether moiety and a hydrophobic aromatic moiety. The catalyst ink may also include a viscosity modifier, preferably a cellulose derivative. In some embodiments, the catalyst ink may also include carbon, preferably a mixture of hydrophobic and hydrophilic acetylene black.

[0041] The ionomer-based ink in step b) is obtained by dispersing an ionomer (e.g., anion-exchange ionomer and / or cation-exchange ionomer) in a second solvent (which is typically a water-alcohol mixture). The water-alcohol solvent mixture is preferably in a weight ratio of about 1:1.

[0042] The coating in step d) can be accomplished using various deposition techniques, such as brush coating, roll-to-roll gravure printing, slot die coating, or similar techniques. Typically, coating is performed until a concentration of 0.3 to 10 mg / cm³ is obtained. 2 Until the catalyst loading is reached.

[0043] In step e), the applied coating may be dried to form a catalyst layer on the gas diffusion layer. In some embodiments, step e) may include heat treatment at a higher temperature to increase the adhesion of the catalyst layer to the gas diffusion layer and / or to convert the catalyst precursor material into a finer catalyst material. Preferably, the heat treatment in step e) includes baking the porous gas diffusion layer and catalyst layer assembly at a temperature of 170°C to 350°C for 10 minutes to 24 hours.

[0044] In one embodiment, a first catalyst layer comprising metallic copper is desired. The copper-based first catalyst material may comprise metallic copper powder as a starting material, and the heat treatment of the catalyst layer in step e) is carried out in an oxygen-containing atmosphere, such as air. The metallic copper powder is partially oxidized to copper oxide, thereby obtaining a catalyst layer comprising a mixture of metallic copper (Cu) and copper oxide (CuO).

[0045] In another embodiment, where it is desirable to include a first catalyst layer containing copper oxide, the copper-based first catalyst material may also include copper oxide powder as a starting material, specifically cuprous oxide (Cu₂O) particles, and the heat treatment of the catalyst layer in step e) can be carried out in an oxygen-containing atmosphere, such as air. The cuprous oxide (Cu₂O) particles are partially oxidized to copper oxide (CuO), thereby obtaining a catalyst layer containing a mixture of cuprous oxide (Cu₂O) and copper oxide (CuO).

[0046] In the embodiment, wherein the conductive porous gas diffusion layer comprises a macroporous layer and a microporous layer, step c) preferably includes the following detailed sub-steps c1)-c3) performed prior to step d):

[0047] c1) Provide a macroporous layer, such as carbon cloth or carbon paper.

[0048] c2) A carbon-based ink, such as a mixture of acetylene black and water, may be provided, but mixtures of different carbons may also be used. Hydrophobic carbon materials are preferred for gas diffusion electrodes. The carbon-based ink may also contain a hydrophobic resin, typically a fluoropolymer, preferably with a particle size in the range of 0.005 to 10 μm.

[0049] c3) The carbon-based ink is deposited on the macroporous layer to form a microporous layer. In step c3), a deposition technique similar to that described above can be used, such as brush coating, roll-to-roll gravure printing, slot die coating, or similar methods.

[0050] In some implementations, depending on the deposition technique used in sub-step c3), step c) may include an additional sub-step c4) performed after sub-steps c1)-c3) and before step d):

[0051] c4) Bake the assembly of the macroporous layer and the applied microporous layer in air at a temperature of 170°C to 350°C for 10 minutes to 24 hours.

[0052] Carbon loading is typically 25-100 g / m³ 2 Within the range, preferably 58-63 g / m 2 Within the range.

[0053] In step f), various deposition techniques can be used, but preferably, the ionomer-based ink is deposited onto the catalyst layer by spraying. The final ionomer loading is preferably 0.05 to 0.4 mg / cm³. 2 .

[0054] The gas diffusion electrode of this invention can be used in a variety of applications. A preferred application is the electrochemical reduction of carbon dioxide to valuable carbon-based products such as CO and ethylene. Other possible applications include anion exchange membrane (AEM) fuel cells, including regenerative modular fuel cells (URFCs), which can operate in fuel cell mode to combine oxygen and hydrogen to generate electricity and in regenerative electrolyzer mode to electrolyze water. Other possible applications include acting as a cathode in AEM water electrolysis. The gas diffusion electrode of this invention ensures good performance and stability during operation. Attached Figure Description

[0055] The invention will now be described in more detail with reference to certain preferred embodiments and the accompanying drawings.

[0056] In the attached diagram:

[0057] Figure 1 A schematic diagram of a first embodiment of the gas diffusion electrode of the present invention is shown;

[0058] Figure 2 A second embodiment of the gas diffusion electrode of the present invention is shown; and

[0059] Figure 3 A schematic diagram of an electrolytic cell including the gas diffusion electrode of the present invention is shown. Detailed Implementation

[0060] Figure 1 A first embodiment of the gas diffusion electrode 10 according to the present invention is shown, wherein a single catalyst layer is provided. As can be seen from the figure, the gas diffusion electrode 10 is provided with a gas diffusion layer 11, which comprises a macroporous layer 12 and a microporous layer 13. The macroporous layer 12 acts as a support for the microporous layer 13 deposited on the macroporous layer 12. A copper-based catalyst layer 14 is applied on top of the microporous layer 13. An ionomer layer 15 is applied on top of the catalyst layer 14. The side of the macroporous layer 12 opposite to the side where the microporous layer 13 is applied contacts a current collector 16.

[0061] Figure 2 A second embodiment of the gas diffusion electrode 20 according to the invention is shown, which substantially corresponds to Figure 1 The second embodiment of the gas diffusion electrode 20 further includes a gas diffusion layer 21, which comprises a macroporous layer 22 and a microporous layer 23. A catalyst layer 24 is disposed on top of the microporous layer 23. An ionomer layer 25 is applied on top of the catalyst layer 24. The macroporous layer 22 is also in contact with the current collector 26. Figure 1Compared to the previous implementation, the catalyst layer 24 is formed by multiple layers 24a and 24b, wherein the multiple layers differ in their catalyst composition. For example, the first catalyst layer 24a may be a copper-based catalyst layer, while the second catalyst layer 24b may contain silver nanoparticles.

[0062] Figure 3 An electrochemical cell 30 with an anode chamber 31 and a cathode chamber 32 is shown. The anode chamber 31 includes an anode current collector 32 with an anode gas flow channel 33, and the cathode chamber 32 includes a cathode current collector 35 with a cathode gas flow channel 36. The anode chamber 31 and the cathode chamber 34 are separated by a membrane 37. In an embodiment of the invention, the anode chamber includes an anode gas diffusion electrode 38 with an anode catalyst layer 39, such as an iridium-based catalyst. The cathode chamber 34 includes a cathode gas diffusion electrode 40 according to the invention, such as according to... Figure 1 and 2 One embodiment of the cathode gas diffusion electrode is described. The cathode gas diffusion electrode 40 includes a cathode catalyst layer 41, which may be, for example, a silver-based catalyst, a MOF-based catalyst, or a copper-based catalyst as described in more detail below. The cathode chamber 34 also includes a CO2 gas inlet 42 and a reduction product outlet 43. The anode chamber 31 includes an anolyte inlet 45 and a reaction product outlet 44.

[0063] When using, such as Figure 3 In the battery depicted for the electrochemical reduction of carbon dioxide, the reduction takes place in the cathode chamber. The specific reactions and products can vary depending on the catalyst, electrolyte, applied voltage, and product selectivity required for a particular application. In the anode chamber, an oxidation reaction occurs to maintain charge balance within the electrolyzer. The specific reaction depends on the choice of electrolyte, system design, and operating conditions. For example, a primary desired reaction in the cathode chamber is the reduction of carbon dioxide to carbon monoxide. This reaction is often targeted due to the industrial importance of carbon monoxide as a versatile chemical feedstock. This reaction can be represented as follows:

[0064] Cathode: CO2 + 2e - +H₂O→2OH - +CO

[0065] Another common reaction is the reduction of carbon dioxide to formate, which can be used as a precursor for various organic compounds. This reaction can be represented as follows:

[0066] Cathode: CO2 + 2e - +H₂O→HCOO - +OH -

[0067] The choice of catalyst on the cathode surface plays a crucial role in determining the selectivity of carbon dioxide reduction and the formation of specific products. Different catalyst materials can promote different reaction pathways, thus affecting the formation of the desired products.

[0068] If an aqueous electrolyte is used in a neutral or alkaline environment, the reaction in the anode chamber can be represented as follows:

[0069] Anode: 2OH - →H₂O + 1 / 2O₂ + 2e -

[0070] In non-aqueous or solid electrolytes, other substances present in the electrolyte can undergo oxidation to maintain charge balance. For example, in non-aqueous electrolytes, the anodic half-cell reaction may involve the oxidation of anions or other substances. The specific reaction will depend on the properties of the electrolyte and the available oxidizable substances.

[0071] Anode: X - →X+e -

[0072] The invention will now be described with reference to certain embodiments.

[0073] Example

[0074] Example 1: Copper-based electrode

[0075] 1.1: Preparation of Catalyst Ink

[0076] A water-based ink was prepared by mixing metallic copper powder, a fluoropolymer (such as polytetrafluoroethylene (PTFE)), a surfactant (such as Triton X100), and a thickener (such as carboxymethyl cellulose) with water. The resulting ink was stirred for 15 minutes under vigorous magnetic stirring.

[0077] 1.2: Preparation of Ionomer-Based Ink

[0078] A diluted solution of anion exchange ionomer ink is prepared by dissolving the anion exchange ionomer (in this embodiment, a functionalized poly(arylpiperidinium) resin) in a water-alcoholic solvent to obtain a diluted solution.

[0079] 1.3: Preparation of a conductive porous gas diffusion layer

[0080] A suitable conductive porous gas diffusion layer can be prepared as follows: Acetylene black is mixed with water, a nonionic surfactant, an aqueous dispersant, a fluoropolymer (such as PTFE), and a poly(ethylene oxide) (PEO) polymer. The resulting ink is stirred for 60 to 200 minutes. The ink, acting as a microporous layer, is then deposited onto commercially available carbon cloth (acting as the microporous layer) using a slit die or gravure coating machine, and subsequently baked at 250–320°C for 1 to 14 hours. The final gas diffusion layer has a thickness of 320–370 μm. The water contact angle of the microporous layer is in the range of 130–140°, and the in-plane conductivity measured on the microporous layer side is in the range of 40–60 S / cm. -1 Within the range.

[0081] 1.4: Coat a conductive porous gas diffusion layer with catalyst ink.

[0082] Then, the catalyst ink is coated onto the microporous layer of the gas diffusion layer obtained in step 1.3 through multiple (two or more) brushing cycles to achieve 1.0 mg / cm². 2 The final catalyst loading. Between cycles, a drying step is performed, including heat-treating the manufactured product at 50 to 100°C for 5 to 30 minutes.

[0083] 1.5: Fixing the catalyst material

[0084] The resulting components were then baked in air at 300°C for 2 hours to produce a catalyst mixture of metallic copper (Cu) and cuprous oxide (CuO).

[0085] The final samples had a thickness of 370–400 μm. The water contact angle of the catalyst layer ranged from 100° to 120°, and the in-plane conductivity measured on the catalyst layer side ranged from 45 to 55 S / cm. -1 Within the range.

[0086] 1.6: Coating with ionomer-based ink

[0087] The ionomer ink prepared in step 1.2 was uniformly sprayed onto the top of the catalyst layer of the component obtained in step 1.5. The resulting layer was dried at room temperature. The final ionomer loading was 0.05-0.4 mg / cm³. 2 .

[0088] Example 2: Copper oxide-based electrode

[0089] The preparation of the copper oxide-based electrode corresponds to the preparation of the metallic copper-based electrode in Example 1, except that cuprous oxide (Cu₂O) powder is used instead of metallic copper powder as the starting material in step 1.1. Similar to step 1.5 of Example 1 (fixing the catalyst material), heat treatment is performed in air. In Example 2, the heat treatment partially oxidizes the cuprous oxide to copper oxide, thereby producing a Cu₂O / CuO catalyst mixture.

[0090] CuO-based gas diffusion electrodes with a catalyst mixture of Cu2O / CuO exhibit enhanced performance against C. 2+ The activity of the product. Targeting C 2+ The Faraday efficiency of the product is 35%-50%. (At 3 kA / m) 2 At the given current density, the battery voltage is below 2.8 V.

[0091] Example 3: Copper oxide-based electrode with a silver-based second catalyst layer

[0092] 3.1: As in Example 2, steps 1.1 to 1.5 of Example 1 are performed to prepare a copper oxide-based first catalyst layer, i.e., cuprous oxide (Cu2O) powder is used as the starting material in step 1.1.

[0093] 3.2: Preparation of the second catalyst ink

[0094] A second water-based ink was prepared by mixing metallic silver nanoparticles, isopropanol, and a thickener (such as hydroxypropyl methylcellulose) with water. The resulting ink was then sonicated for 15 minutes.

[0095] 3.3: Preparation of the second catalyst layer

[0096] Then, the second catalyst ink is coated onto the first catalyst layer obtained in step 3.2 by spray coating, and multiple (two or more) cycles are performed to achieve 0.1 mg / cm³. 2 The final catalyst loading. Between cycles, a drying step is performed, including heat-treating the manufactured product at 50-100°C for 5-30 minutes, preferably at 80°C for 15 minutes.

[0097] 3.4: Fixing the second catalyst material

[0098] The resulting components were then baked at 300°C for 2 hours in an inert air atmosphere.

[0099] 3.5: Coating with ionomer-based ink, corresponding to step 1.6 of Example 1.

[0100] CuO-based gas diffusion electrodes with a catalyst mixture of Cu2O / CuO exhibit enhanced performance against C. 2+The product's activity was improved, and its battery voltage was also enhanced. (Regarding C) 2+ The Faraday efficiency of the product is 40%-55%. (At 3 kA / m) 2 At the given current density, the battery voltage is below 2.6 V.

[0101] The above description is not intended to limit the invention, which can be used in various embodiments without departing from its purpose, and its scope is defined only by the appended claims.

[0102] In the specification and claims of this application, the terms “comprising,” “including,” and “containing” are not intended to exclude the presence of other additional elements, components, or process steps.

[0103] The discussions of documents, articles, materials, devices, and other materials included in this specification are intended only to provide context for the invention. They do not imply that any or all of these subjects constitute part of the prior art or formed common general knowledge in the relevant field prior to the priority date of each claim of this application.

[0104] The project that gave rise to this application was funded by the EU’s Horizon 2020 research and innovation program under grant agreement number 101037389.

Claims

1. A gas diffusion electrode for the electrochemical reduction of carbon dioxide, comprising: Conductive porous gas diffusion layer; At least one porous catalyst layer is arranged adjacent to the gas diffusion layer, the at least one porous catalyst layer comprising a first porous catalyst layer comprising a copper-based first catalyst material, wherein the first porous catalyst layer comprises a mixture of the copper-based first catalyst material and a hydrophobic material, the porous catalyst layer being obtained from a precursor material free of any ionomers; and An ionomer layer is arranged adjacent to the at least one porous catalyst layer, the ionomer layer being obtained from a precursor material that does not contain any catalyst.

2. The electrode according to claim 1, wherein the copper-based first catalyst material comprises copper particles and / or copper oxide particles, wherein the copper oxide particles preferably comprise a mixture of copper oxide (CuO) and cuprous oxide (Cu2O).

3. The electrode according to any one of claims 1 to 2, wherein the at least one porous catalyst layer is obtained by heat-treating a precursor layer applied to the gas diffusion layer.

4. The electrode according to any one of claims 1 to 3, wherein the at least one porous catalyst layer further comprises a second catalyst layer, the second catalyst layer comprising a second catalyst material, and the weight ratio of the first catalyst layer to the second catalyst layer is preferably selected from the range of 20:1 to 2:

1.

5. The electrode according to claim 4, wherein the second catalyst material is selected from transition metal complexes, metal microparticles, metal nanoparticles, metal oxides, metal oxide microparticles, metal oxide nanoparticles, or combinations thereof.

6. The electrode according to claim 5, wherein the second catalyst material comprises silver nanoparticles.

7. The electrode according to any one of claims 1 to 6, wherein the conductive porous gas diffusion layer comprises a macroporous layer and a microporous layer, the microporous layer being disposed between the macroporous layer and the at least one catalyst layer, the macroporous layer preferably being carbon cloth or carbon paper, and the microporous layer preferably comprising a mixture of carbon and a hydrophobic material.

8. The electrode according to any one of claims 1 to 7, wherein the hydrophobic material is a hydrophobic resin selected from polytetrafluoroethylene (PTFE) and perfluorosulfonic acid (PFSA) polymers.

9. An electrochemical cell comprising an anode chamber, a cathode chamber, and a partition disposed between the anode chamber and the cathode chamber, wherein at least one of the anode chamber and the cathode chamber comprises a gas diffusion electrode according to any one of claims 1 to 8.

10. A method for manufacturing a gas diffusion electrode, comprising the following steps: a) A catalyst ink is prepared by dispersing a copper-based first catalyst material and a hydrophobic material in a first solvent, wherein the catalyst ink does not contain any ionomers; b) Ionomer-based ink is prepared by dispersing the ionomer in a second solvent, wherein the ionomer-based ink does not contain any catalyst; c) Prepare a conductive porous gas diffusion layer; d) Coating the conductive porous gas diffusion layer with the catalyst ink to form a catalyst layer; e) Dry and / or heat-treat the catalyst layer to fix the catalyst material onto the gas diffusion layer; and f) Coating the catalyst layer with the ionomer-based ink.

11. The method according to claim 11, wherein in step a), the hydrophobic material is a hydrophobic resin selected from polytetrafluoroethylene (PTFE) and perfluorosulfonic acid (PFSA) polymers.

12. The method according to any one of claims 10 or 11, wherein step e) comprises baking the assembly of the porous gas diffusion layer and the catalyst layer at a temperature of 170°C to 350°C for 10 minutes to 24 hours.

13. The method of claim 12, wherein the copper-based first catalyst material comprises metallic copper powder or cuprous oxide powder, and step e) comprises heat-treating the catalyst layer in an oxygen-containing atmosphere.

14. The method according to any one of claims 10 to 13, wherein in step c), the preparation of the conductive porous gas diffusion layer comprises the following steps: c1) providing a macroporous layer, c2) providing carbon-based ink, c3) depositing the carbon-based ink onto the macroporous layer to form a microporous layer, and optionally, c4) baking the assembly of the macroporous layer and the microporous layer in air at a temperature of 170°C to 350°C for 10 minutes to 24 hours.

15. The method according to any one of claims 10 to 14, wherein in step f), the ionomer-based ink is deposited on the catalyst layer by spraying.

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