Proton exchange membranes, membrane electrodes, etching methods, and applications for electrochemical carbon dioxide reduction
By etching vertical channels on a proton exchange membrane using radio frequency magnetron sputtering technology, the problem of limited mass transfer in electrochemical carbon dioxide reduction was solved, achieving efficient catalyst utilization and product selectivity, and improving reaction performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI ELECTRICGROUP CORP
- Filing Date
- 2026-04-02
- Publication Date
- 2026-06-09
AI Technical Summary
In existing electrochemical carbon dioxide reduction processes, CO2 mass transfer is limited, catalyst utilization is low, product selectivity is poor, and reaction stability is insufficient. Commercial proton exchange membranes have limited specific surface area, resulting in low reaction current density and unsatisfactory product selectivity.
Radio frequency magnetron sputtering technology was used to etch proton exchange membranes. By applying bias voltage and controlling atmosphere conditions, vertical channels with a depth of 2-5.5 μm were formed, which improved the specific surface area and catalyst loading capacity and optimized the mass transfer path.
It significantly improves the performance of electrochemical carbon dioxide reduction, increases the reaction current density and the selectivity of multi-carbon products, and achieves a Faraday efficiency of over 75%. Moreover, the etching method is simple and controllable, making it suitable for temperature-sensitive substrates.
Smart Images
Figure CN122169158A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a proton exchange membrane for electrochemical carbon dioxide reduction, a membrane electrode, an etching method, and its application. Background Technology
[0002] Electrochemical carbon dioxide reduction (CO2RR) is a key technology for converting CO2 into high-value-added fuels and chemicals (such as ethylene and ethanol). Its core component is the membrane electrode, in which the proton exchange membrane (PEM) not only needs to conduct protons, but also plays an important role in isolating the cathode and anode and providing the reaction interface.
[0003] An ideal PEM for CO2 RR should possess the following characteristics: 1) a three-dimensional structure with a high specific surface area to support highly active and selective catalysts; 2) an optimized pore structure to promote mass transfer of CO2 gas to the catalyst layer and accelerate the removal of liquid products, preventing pore blockage; 3) good proton conductivity to maintain the reaction interface; and 4) suitable surface properties to regulate local wettability and balance the transport of gas, ions, and products.
[0004] Currently, commercially available PEMs (such as the Nafion series) have flat surfaces and limited specific surface areas. Direct coating with catalysts results in a dense catalytic layer structure with high CO2 mass transfer resistance, leading to low reaction current density and unsatisfactory product selectivity. Therefore, structural treatment of PEM surfaces to increase specific surface area and optimize mass transfer pathways has become a research hotspot.
[0005] To increase specific surface area and improve catalyst adhesion, the industry has tried various PEM membrane surface treatment technologies, but all have significant shortcomings. For example, mechanical embossing: forming micron-scale patterns on the membrane surface through physical imprinting, but this method easily leads to changes in polymer chain orientation and local stress concentration, which may become crack initiation points during fuel cell operation. Chemical etching: treating the membrane surface with strong acids or strong oxidants, but sulfonic acid groups may be damaged, resulting in a 20%-40% decrease in surface proton conductivity, and reagent residues may poison the catalyst. Plasma treatment: although it can improve surface hydrophilicity, the treatment depth is shallow and the uniformity is poor, making it difficult to form a controllable three-dimensional structure. Summary of the Invention
[0006] The technical problem this invention aims to solve is to overcome at least one of the defects in existing electrochemical carbon dioxide reduction technologies, such as limited CO2 mass transfer, low catalyst utilization, poor product selectivity, and insufficient reaction stability. This invention provides a proton exchange membrane (PEM) for electrochemical carbon dioxide reduction, a membrane electrode assembly (MEA), an etching method, and its applications. The structured PEM prepared by this invention has deep pores, providing a high specific surface area and significantly improving the performance of electrochemical CO2 reduction.
[0007] The present invention solves the above-mentioned technical problems through the following technical solution:
[0008] In a first aspect, the present invention provides an etching method for a proton exchange membrane for electrochemical carbon dioxide reduction, comprising the following steps: performing radio frequency magnetron sputtering on the proton exchange membrane using a radio frequency power supply; wherein the bias voltage applied to the proton exchange membrane by the radio frequency power supply is 100-1000 V.
[0009] RF power supply
[0010] In this invention, the frequency of the radio frequency power supply is 13.56 MHz.
[0011] In this invention, radio frequency magnetron sputtering is a key technology upgrade based on magnetron sputtering by introducing a radio frequency power supply (usually 13.56MHz), which can process insulating materials that cannot be processed using ordinary magnetron sputtering for CeO2 targets.
[0012] RF magnetron sputtering parameters
[0013] In this invention, the bias voltage applied to the proton exchange membrane by the radio frequency power supply can be 200-1000 V, for example 400 V.
[0014] In this invention, the power of the radio frequency power supply can be 0.5-2 kW, for example 1.5 kW.
[0015] In this invention, the radio frequency magnetron sputtering time can be 300-7200 s, for example 1800-4800 s.
[0016] In this invention, the atmosphere of the radio frequency magnetron sputtering can be Ar and O2; the volume ratio of Ar to O2 is preferably (50-80):1, for example 65:1.
[0017] In this invention, the absolute pressure of the gas pressure in the radio frequency magnetron sputtering can be 0.01-1 Pa, for example 0.4 Pa.
[0018] In this invention, the sputtering target for the radio frequency magnetron sputtering can be CeO2.
[0019] In this invention, the radio frequency magnetron sputtering may not require an ion source power supply.
[0020] In this invention, at the same power, radio frequency magnetron sputtering can cause the substrate temperature rise to be lower than that of DC sputtering, which is advantageous for coating temperature-sensitive substrates (such as plastics) and is more suitable for etching PEM films.
[0021] [RF magnetron sputtering pretreatment]
[0022] In this invention, the proton exchange membrane can be cleaned before the radio frequency magnetron sputtering. The cleaning process can be gas purging. The gas used for gas purging can be nitrogen or a rare gas.
[0023] In this invention, the proton exchange membrane can be made of perfluorosulfonic acid resin.
[0024] [Specific Implementation Cases]
[0025] In some specific embodiments of the present invention, the bias voltage applied to the proton exchange membrane by the radio frequency power supply is 400 V, and the power of the radio frequency power supply is 1.5 kW; the radio frequency magnetron sputtering time is 1800 s, the atmosphere is Ar and O2, the volume ratio of Ar to O2 is 65:1, and the absolute pressure is 0.4 Pa.
[0026] In some specific embodiments of the present invention, the bias voltage applied to the proton exchange membrane by the radio frequency power supply is 200 V, and the power of the radio frequency power supply is 1.5 kW; the radio frequency magnetron sputtering time is 1800 s, the atmosphere is Ar and O2, the volume ratio of Ar to O2 is 65:1, and the absolute pressure is 0.4 Pa.
[0027] Secondly, the present invention provides a proton exchange membrane for electrochemical carbon dioxide reduction prepared by the etching method described above.
[0028] Thirdly, the present invention provides a proton exchange membrane for electrochemical carbon dioxide reduction, wherein at least one side surface is provided with channels; the depth of the channels is 2-5.5 μm.
[0029] In this invention, the depth of the channel can be 4-5.5 μm, for example 5.3 μm.
[0030] In this invention, the direction of the pores can be perpendicular to the surface of the proton exchange membrane.
[0031] In this invention, the proton exchange membrane may be a proton exchange membrane used for the electrochemical reduction of carbon dioxide.
[0032] In this invention, the proton exchange membrane for electrochemical carbon dioxide reduction can be prepared by the etching method described above.
[0033] Fourthly, the present invention provides a membrane electrode comprising the proton exchange membrane for electrochemical carbon dioxide reduction as described above.
[0034] Fifthly, the present invention provides an application of the membrane electrode as described above in the electrochemical reduction of carbon dioxide.
[0035] The positive and progressive effects of this invention are as follows:
[0036] (1) In this invention, the etched proton exchange membrane has a pore depth of at least 2 μm in the micrometer range, providing a low-resistance diffusion channel for gas and a discharge path for liquid products. The pore structure can increase the specific surface area, which can be used for efficient catalyst loading. It can also optimize the local wettability of the membrane surface to balance gas transport and ion conduction.
[0037] (2) In this invention, the etched proton exchange membrane may have nearly vertical channels. The vertical sidewalls can ensure the uniform flow of the reaction gas and liquid and avoid the formation of dead zones.
[0038] (3) The etching method of the present invention adopts radio frequency (RF) magnetron sputtering technology, introduces anisotropic etching capability, and by controlling the magnitude of the bias voltage applied to the substrate, it can achieve a nearly vertical sidewall etching morphology, which significantly improves the pattern transfer fidelity of micro-nano structures.
[0039] (4) The etching method of the present invention adopts radio frequency (RF) magnetron sputtering technology, which does not require the introduction of plasma treatment, which is conducive to the formation of three-dimensional ordered structure, can deposit non-conductive target material, and at the same time ensures sufficient etching depth.
[0040] (5) The etching method of the present invention adopts dry etching, which is carried out at room temperature, thus avoiding the problems of film swelling and thermal expansion. The process is simple and controllable. Attached Figure Description
[0041] Figure 1 This is a cross-sectional SEM image of the proton exchange membrane in Example 1;
[0042] Figure 2 Here is a SEM image of the proton exchange membrane surface from Example 1;
[0043] Figure 3 This is a cross-sectional SEM image of the proton exchange membrane in Example 2;
[0044] Figure 4 Here is a SEM image of the proton exchange membrane surface in Example 2;
[0045] Figure 5 This is a cross-sectional SEM image of the proton exchange membrane in Comparative Example 1.
[0046] Figure 6 This is a SEM image of the proton exchange membrane surface in Comparative Example 1.
[0047] Figure 7 This is a cross-sectional SEM image of the proton exchange membrane in Comparative Example 2;
[0048] Figure 8 Here is a SEM image of the proton exchange membrane surface in Comparative Example 2;
[0049] Figure 9Here is a cross-sectional SEM image of the proton exchange membrane in Comparative Example 3;
[0050] Figure 10 Here is a SEM image of the proton exchange membrane surface in Comparative Example 3;
[0051] Figure 11 Here is a cross-sectional SEM image of the proton exchange membrane in Comparative Example 4;
[0052] Figure 12 Here is a SEM image of the proton exchange membrane surface in Comparative Example 4;
[0053] Figure 13 Here is a cross-sectional SEM image of the proton exchange membrane in Comparative Example 5;
[0054] Figure 14 Here is a SEM image of the proton exchange membrane surface in Comparative Example 5; Detailed Implementation
[0055] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.
[0056] PEM, perfluorosulfonic acid membrane, manufacturer: Gore, grade: M788.12.
[0057] Example 1
[0058] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0059] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0060] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. After evacuating the equipment to 0.002 Pa, Ar and O2 were introduced in a volume ratio of 65:1, and the furnace pressure was controlled at 0.4 Pa. Then, the RF sputtering power supply was turned on, with the power controlled at 1.5 kW. The sputtering target was CeO2, and a bias voltage of 400 V was applied. The etching time was 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0061] Example 2
[0062] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0063] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0064] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. After evacuating the equipment to 0.002 Pa, Ar and O2 were introduced in a volume ratio of 65:1, and the furnace pressure was controlled at 0.4 Pa. Then, the RF sputtering power supply was turned on, with the power controlled at 1.5 kW. The sputtering target was CeO2, and a bias voltage of 200 V was applied. The etching time was 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0065] Comparative Example 1
[0066] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0067] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0068] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. After evacuating the equipment to 0.002 Pa, Ar and O2 were introduced in a volume ratio of 65:1, and the furnace pressure was controlled at 0.4 Pa. Then, the RF sputtering power supply was turned on, with the power controlled at 1.5 kW. The sputtering target was CeO2, and no bias voltage was applied. The etching time was 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0069] Comparative Example 2
[0070] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0071] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0072] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. After evacuating the equipment to 0.002 Pa, Ar and O2 were introduced at a volume ratio of 65:1, and the furnace pressure was controlled at 0.4 Pa. Subsequently, the RF sputtering power supply and ion source power supply were turned on. The RF sputtering power supply power was controlled at 1.5 kW, the sputtering target was CeO2, and a bias voltage of 200 V was applied. The ion source power supply current was controlled at 300 mA, and the etching was performed for 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0073] Comparative Example 3
[0074] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0075] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0076] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. After evacuating the equipment to 0.002 Pa, Ar and O2 were introduced at a volume ratio of 65:1, and the furnace pressure was controlled at 0.4 Pa. Subsequently, the RF sputtering power supply and ion source power supply were turned on. The RF sputtering power supply power was controlled at 1.5 kW, the sputtering target was CeO2, and a bias voltage of 400 V was applied. The ion source power supply current was controlled at 300 mA, and the etching was performed for 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0077] Comparative Example 4
[0078] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0079] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0080] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. The equipment was evacuated to 0.002 Pa, and Ar and O2 were introduced in a volume ratio of 17:1, with the furnace pressure controlled at 0.2 Pa. Then, the ion source power supply was turned on, the ion source current was controlled at 300 mA, no target material was used, and a bias voltage of 200 V was applied. Etching was performed for 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0081] Comparative Example 5
[0082] A proton exchange membrane for carbon dioxide reduction and its preparation method, comprising the following steps:
[0083] 1. Membrane cleaning: Use nitrogen to purge the PEM surface to remove surface dirt. Do not use liquid washing to avoid deformation of the PEM.
[0084] 2. Film Etching: The cleaned PEM was placed in a magnetron sputtering coating machine. The equipment was evacuated to 0.002 Pa, and Ar and O2 were introduced in a volume ratio of 17:1, with the furnace pressure controlled at 0.2 Pa. Then, the ion source power supply was turned on, the ion source power supply current was controlled at 300 mA, no target material was used, and a bias voltage of 400 V was applied. Etching was performed for 1800 s to obtain a proton exchange membrane for carbon dioxide reduction.
[0085] The main parameters of each embodiment and comparative example are summarized in the table below.
[0086]
[0087] Example 1: Morphology of the proton exchange membrane
[0088] 1. Test objects: Proton exchange membranes prepared in each embodiment and comparative example.
[0089] 2. Test method: The cross-section and surface of the proton exchange membrane were observed using a scanning electron microscope.
[0090] 3. Test Results:
[0091] The proton exchange membrane of Example 1, such as Figure 1 As shown, the etching depth is approximately 5.3 μm, as Figure 2 As shown, the proton exchange membrane has no surface covering, numerous etched channels, and good verticality, which facilitates the diffusion of gaseous and liquid products and effectively increases the specific surface area.
[0092] The proton exchange membrane of Example 2, such as Figure 3 As shown, the etching depth is approximately 4 μm, as Figure 4 As shown, complete etched channels are visible on the surface, resulting in an increased specific surface area.
[0093] The proton exchange membrane of Comparative Example 1, such as Figure 5 As shown, the etching depth is approximately 1.4 μm, as Figure 6 As shown, the surface is largely covered by sediments, resulting in very few complete channels and an inability to effectively increase the specific surface area.
[0094] The proton exchange membrane of Comparative Example 2, such as Figure 7 As shown, the etching depth is approximately 1.5 μm, as... Figure 8 As shown, although there are many channels, their verticality is poor.
[0095] The proton exchange membrane of Comparative Example 3, such as Figure 9 As shown, the etching depth is approximately 1 μm, as Figure 10 As shown, the number of channels is small, which cannot effectively increase the specific surface area.
[0096] The proton exchange membrane of Comparative Example 4, such as Figure 11 As shown, the etching depth is approximately 370 nm, as Figure 12 As shown, the number of channels is small, and the structure is needle-like with a thicker bottom and a thinner top, which cannot effectively increase the specific surface area.
[0097] The proton exchange membrane of Comparative Example 5, such as Figure 13 As shown, the etching depth is approximately 380 nm, as Figure 14 As shown, the surface structure has collapsed and there are no porous channels.
[0098] Example 2: Faraday efficiency of membrane electrode
[0099] 1. Test objects: membrane electrodes made from the proton exchange membranes of each embodiment and comparative example.
[0100] 2. Testing Method:
[0101] (1) Preparation of membrane electrode: When filling the tank, the components are stacked in the following order: titanium felt anode, PTFE gasket matching the thickness of titanium felt, etched proton exchange membrane, PTFE gasket corresponding to the thickness of gas diffusion electrode, and cathode gas diffusion electrode.
[0102] After stacking, a torque wrench was used to press the flow field plates on both sides together, with the torque strictly controlled at 5 N·m to ensure minimal contact resistance between components and avoid pressure damage to the membrane. The cathode used a low-loading Au / C gas diffusion electrode (approximately 0.4 mg·cm³). -2 The anode uses an iridium (Ir) catalyst layer, and the effective reaction area of the membrane electrode is uniformly set to 5 cm × 5 cm.
[0103] (2) Test procedure: The test was conducted at a constant temperature of approximately 40°C. The CO2 gas flow rate on the cathode side was maintained at 150 sccm, and the electrolyte flow rate (usually deionized water or dilute acid) on the anode side was controlled at 80 mL·min. -1 The cathode outlet gas path is directly connected to a gas chromatograph to monitor the gas phase products in real time, and sampling and analysis are performed according to standard test procedures. The CO2 electroreduction performance of the membrane electrode is systematically evaluated mainly by the selectivity of the product CO (Faraday efficiency) and the steady-state current density (volt-ampere curve) at different potentials.
[0104] The Faraday efficiency (FE) of CO is calculated using the following formula:
[0105]
[0106] In the formula:
[0107] n represents the number of electrons transferred; for CO, this value is 2.
[0108] p0 is standard atmospheric pressure, 101 kPa;
[0109] v represents the gas flow rate of the gaseous product detected by gas chromatography.
[0110] x i This indicates the mole fraction of CO in the gaseous products detected by gas chromatography.
[0111] F is the Faraday constant, 96485 C·mol⁻¹ -1 ;
[0112] I represents the current density, mA·cm. -2 ;
[0113] R is the ideal gas constant, 8.314 J·mol⁻¹-1 ·K -1 ;
[0114] T is the absolute temperature, 273 K.
[0115] 3. Test Results:
[0116] The CO and H2 Faraday efficiencies of the membrane electrodes prepared by the proton exchange membranes in each embodiment and comparative example are shown in the table below.
[0117]
[0118] The structured proton exchange membrane prepared by this invention has deep pores, providing a high specific surface area for PEM. Under the same catalyst loading, it can achieve higher reaction current density and better selectivity for multi-carbon products, with a Faraday efficiency of over 75%, and significantly improved performance in electrochemical CO2 reduction.
[0119] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.
Claims
1. A method for etching a proton exchange membrane for electrochemical carbon dioxide reduction, characterized in that, It includes the following steps: The proton exchange membrane is sputtered by radio frequency magnetron sputtering using a radio frequency power supply; the bias voltage applied to the proton exchange membrane by the radio frequency power supply is 100-1000 V.
2. The etching method for the proton exchange membrane for electrochemical carbon dioxide reduction according to claim 1, characterized in that, It meets one or more of the following conditions: (1) The bias voltage applied to the proton exchange membrane by the radio frequency power supply is 200-1000 V, for example 400 V; (2) The power of the radio frequency power supply is 0.5-2 kW, for example 1.5 kW; (3) The radio frequency magnetron sputtering time is 300-7200 s, for example 1800-4800 s; (4) The atmosphere for the radio frequency magnetron sputtering is Ar and O2; the volume ratio of Ar and O2 is preferably (50-80):1, for example 65:1; (5) The absolute pressure of the gas pressure in the radio frequency magnetron sputtering is 0.01-1 Pa, for example 0.4 Pa.
3. The etching method for the proton exchange membrane for electrochemical carbon dioxide reduction according to claim 2, characterized in that, It meets one of the following conditions: (1) The bias voltage applied to the proton exchange membrane by the radio frequency power supply is 400 V, and the power of the radio frequency power supply is 1.5 kW; the radio frequency magnetron sputtering time is 1800 s, the atmosphere is Ar and O2, the volume ratio of Ar and O2 is 65:1, and the absolute pressure is 0.4 Pa. (2) The bias voltage applied to the proton exchange membrane by the radio frequency power supply is 200 V, and the power of the radio frequency power supply is 1.5 kW; the radio frequency magnetron sputtering time is 1800 s, the atmosphere is Ar and O2, the volume ratio of Ar and O2 is 65:1, and the absolute pressure is 0.4 Pa.
4. The etching method for a proton exchange membrane for electrochemical carbon dioxide reduction according to claim 1, characterized in that, It meets one or more of the following conditions: (1) The frequency of the radio frequency power supply is 13.56 MHz; (2) The sputtering target for the radio frequency magnetron sputtering is CeO2; (3) The radio frequency magnetron sputtering does not use an ion source power supply; (4) Before the radio frequency magnetron sputtering, the proton exchange membrane is cleaned; (5) The proton exchange membrane is made of perfluorosulfonic acid resin.
5. The etching method for a proton exchange membrane for electrochemical carbon dioxide reduction according to claim 4, characterized in that, It meets one or two of the following conditions: (1) The cleaning process is gas purging; (2) The gas used for the gas purging is nitrogen or a rare gas.
6. A proton exchange membrane for electrochemical carbon dioxide reduction prepared by the etching method according to any one of claims 1-5.
7. A proton exchange membrane for electrochemical carbon dioxide reduction, characterized in that, It has channels distributed on at least one side surface; the depth of the channels is 2-5.5 μm.
8. The proton exchange membrane for electrochemical carbon dioxide reduction according to claim 7, characterized in that, It meets one or more of the following conditions: (1) The depth of the channel is 4-5.5 μm, for example 5.3 μm; (2) The direction of the pores is perpendicular to the surface of the proton exchange membrane for electrochemical carbon dioxide reduction; (3) The proton exchange membrane for electrochemical carbon dioxide reduction is prepared by the etching method described in any one of claims 1-5.
9. A membrane electrode, characterized in that, It includes the proton exchange membrane for electrochemical carbon dioxide reduction as described in any one of claims 4-6.
10. The application of a membrane electrode as described in claim 9 in the electrochemical reduction of carbon dioxide.