Medium-temperature carbon dioxide reduction electrode and system

Abstract

The invention discloses a medium-temperature carbon dioxide reduction electrode and system, and belongs to the technical field of electrolysis of carbon dioxide. The medium-temperature carbon dioxide reduction electrode comprises a bipolar plate, a membrane electrode and a diaphragm, the bipolar plate comprises a cathode and an anode; the membrane electrode comprises a cathode membrane electrode and an anode membrane electrode; the cathode, the cathode membrane electrode, the diaphragm, the anode membrane electrode and the anode are arranged in sequence; a multifunctional proton buffer layer is attached to the cathode membrane electrode; the multifunctional proton buffer layer is made of an inorganic material or a covalent organic framework material. The arrangement of the multifunctional proton buffer layer inhibits HER from the double dimensions of physical confinement and chemical regulation, enhances the adsorption and mass transfer of CO2, significantly improves the Faraday efficiency of ECR, and solves the technical problem of intense competition of hydrogen evolution reaction of the existing medium temperature catalytic system.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide electrolysis, and particularly relates to a medium-temperature carbon dioxide reduction electrode and system. Background Art

[0002] As a key path for realizing carbon cycle utilization, the performance of the core equipment electrolyzer in carbon dioxide electrolysis reduction technology directly determines the energy conversion efficiency and economic feasibility. Currently, commercial electrolyzers are mainly divided into two major technical routes: low-temperature liquid electrolyte electrolyzers and high-temperature solid oxide electrolyzers (SOECs). There are significant differences in the reaction temperature ranges between the two, and each has its own advantages and disadvantages. Low-temperature electrolyzers usually use alkaline or neutral liquid electrolytes (such as KOH solution, KHCO3 solution), and the operating temperature is maintained in the normal temperature range of 20 - 80°C. Its technology maturity is relatively high, the system construction cost is relatively low, and it has the response characteristics of fast start and stop. However, limited by the slow reaction kinetics in the low-temperature environment, the cathodic hydrogen evolution side reaction (HER) is highly competitive, resulting in the Faraday efficiency of CO2 reduction generally being lower than 90%, and the current density is mostly limited to 200 mA / cm 2 Below, there is a theoretical bottleneck in improving the energy efficiency.

[0003] In contrast, solid oxide electrolyzers (SOECs) use oxygen ion conductors (such as YSZ) or proton-electron mixed conductors (such as BCZY) as electrolytes and operate in a high-temperature environment of 600 - 1000°C. The high-temperature conditions significantly improve the reaction thermodynamics characteristics: on the one hand, the theoretical electrolysis voltage is reduced by reducing the change in Gibbs free energy, and on the other hand, the gas diffusion and charge transfer processes are accelerated, enabling a high current density of more than 1 A / cm 2 However, SOECs face high-temperature degradation problems such as ceramic electrode sintering and sealing material failure. The system needs to be equipped with a complex thermal management module, the start-up time is up to several hours, and the insufficient thermal cycle tolerance seriously restricts its commercial deployment.

[0004] It should be noted that there is an obvious technical gap in the medium-temperature range of 100-200 °C in the existing technology system. In theory, this temperature range can take into account the advantages of two types of electrolyzers: retaining the mechanical stability of polymer electrolyte membranes (such as modified Nafion), and improving the CO2 activation efficiency by moderately increasing the temperature. Specifically, the medium-temperature environment can reduce the formation energy barrier of intermediates on the surface of the cathode catalyst (such as Sn, Cu-based materials) by about 0.3 eV, while suppressing the carbonate crystallization problem of liquid electrolytes. At present, the research in this field focuses on the development of new composite electrolytes. For example, a mixed conductor system is formed by doping phosphotungstic acid into a polybenzimidazole (PBI) membrane and molten carbonate, or a porous ionomer structure with a nanoconfinement effect is constructed, in order to achieve a performance target of a proton conductivity exceeding 0.1 S / cm and a CO2 permeability lower than 10^-6 mol / (m·s·Pa) at about 150 °C. The breakthrough of such medium-temperature electrolyzers is expected to establish a new paradigm of synergistic optimization of "temperature-efficiency-life", providing a better technical solution for distributed carbon capture, utilization, and storage (CCUS) systems.

[0005] The competition mechanism between electrochemical CO2 reduction (ECR) and hydrogen evolution reaction (HER) is one of the core challenges restricting the efficiency of this technology. Under medium-temperature operating conditions of 100-200 °C, the reaction kinetics on the electrode surface are significantly affected by the mass transfer process and the interfacial microenvironment. Since the current medium-temperature electrochemical system mainly relies on phosphoric acid-impregnated proton exchange membranes (such as the high-temperature proton exchange membrane fuel cell technology route), its unique proton conduction mechanism results in a much higher proton (H + ) concentration at the cathode catalyst interface than the effective partial pressure of dissolved CO2. In the case of a conventional membrane electrode assembly electrolyzer, the proton activity in the electrolyte comes from phosphoric acid, while CO2 usually reacts by gas adsorption on the active sites of the catalyst. These two raw material sources form a concentration difference of several orders of magnitude. Therefore, HER has an absolute advantage under medium-temperature conditions.

[0006] Even more complicated is that the negative impact of temperature increase on the gas adsorption process further exacerbates the competition imbalance between ECR and HER. According to the Langmuir adsorption theory, under atmospheric pressure, the coverage of CO2 on the catalyst surface decays exponentially with increasing temperature. This leads to a significant inhibition of the core elementary reaction of ECR - the chemisorption and activation of CO2 molecules on the active sites of the catalyst. At the same time, since the reaction path of HER has sufficient proton supply and does not rely on gas adsorption, its kinetic parameters can still maintain a positive response with increasing temperature. Summary of the Invention

[0007] The purpose of the present invention is to provide a medium-temperature carbon dioxide reduction electrode and system to solve the technical problem of intense competition of hydrogen evolution reaction in the existing medium-temperature catalytic system.

[0008] To achieve the above object, the present invention is implemented by the following technical solutions:

[0009] The present invention discloses a medium-temperature carbon dioxide reduction electrode, comprising a bipolar plate, a membrane electrode and a diaphragm; the bipolar plate includes a cathode and an anode; the membrane electrode includes a cathode membrane electrode and an anode membrane electrode; the cathode, the cathode membrane electrode, the diaphragm, the anode membrane electrode and the anode are arranged in sequence; a multifunctional proton buffer layer is attached to the cathode membrane electrode;

[0010] The material of the multifunctional proton buffer layer is an inorganic material or a covalent organic framework material.

[0011] Further, the inorganic material includes one or more of inorganic reagents having proton buffering properties such as disodium hydrogen phosphate, sodium dihydrogen phosphate and potassium bicarbonate.

[0012] Further, the covalent organic framework material is a COF containing basic functional groups; the COF containing basic functional groups has regular pores; the pore diameter of the regular pores is 2-3 nm.

[0013] Further, a cathode gas inlet and a cathode gas outlet are arranged on one side surface of the cathode; a cathode channel is arranged on the other side surface of the cathode; a cathode tab is arranged at the upper end of the cathode; the side surface provided with the cathode channel is in contact with the cathode membrane electrode.

[0014] Further, a cathode heating rod port is arranged on the end surface of the cathode perpendicular to the side surface provided with the cathode channel; a temperature sensor is arranged on the side provided with the cathode tab.

[0015] Further, the cathode membrane electrode includes a cathode electrode carrier and a cathode catalyst; one side surface of the cathode electrode carrier is in contact with the cathode; a cathode catalyst is arranged on the other side surface of the cathode electrode carrier; the multifunctional proton buffer layer is attached to the cathode catalyst; the side surface provided with the cathode catalyst is in contact with one side surface of the diaphragm.

[0016] Further, the diaphragm includes a cathode electrode diaphragm, an ion exchange membrane and an anode electrode diaphragm arranged in sequence; the cathode electrode diaphragm is in contact with the cathode catalyst; the anode electrode diaphragm is in contact with the anode.

[0017] Further, an anode gas inlet and an anode gas outlet are arranged on one side surface of the anode; an anode channel is arranged on the other side surface of the cathode; an anode tab is arranged at the upper end of the cathode; the side surface provided with the anode channel is in contact with the anode membrane electrode;

[0018] The anode membrane electrode includes an anode electrode carrier and an anode catalyst; one side of the anode electrode carrier is in contact with the anode; the anode catalyst is disposed on the other side of the anode electrode carrier; the side where the cathode catalyst is disposed is in contact with the other side of the diaphragm.

[0019] The present invention also discloses a medium-temperature carbon dioxide reduction system including the above medium-temperature carbon dioxide reduction electrode.

[0020] Further, the operating temperature of the multifunctional proton buffer layer is 100 - 200 °C.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention discloses a medium-temperature carbon dioxide reduction electrode. By adding a multifunctional proton buffer layer between the cathode catalyst layer and the proton exchange membrane, the addition of the buffer layer increases the proton transport distance, and the migration time of H + from the membrane to the catalyst is increased; the basic sites of the multifunctional proton buffer layer can capture part of H + (such as the combination of amino group and H + to form -NH2 + ), controlling the H + concentration at the catalyst interface within a lower concentration range; the addition of the buffer layer prolongs the residence time of CO2 in the buffer layer, and the interface CO2 concentration is increased to 2 - 3 times that of the bulk phase, inhibiting HER from both the physical confinement and chemical regulation dimensions, while strengthening the adsorption and mass transfer of CO2, and significantly improving the Faraday efficiency of ECR.

[0023] Further, the material of the multifunctional proton buffer layer includes disodium hydrogen phosphate, sodium dihydrogen phosphate, and potassium bicarbonate. Its weakly basic local environment can physically adsorb CO2 molecules, forming a local CO2 enrichment area on the catalyst surface to promote the ECR reaction kinetics; the selected covalent organic framework material is a COF containing basic functional groups. Its regular pores (pore diameter 2 - 3 nm) and amino / pyridine groups can selectively adsorb CO2 through chemical action, and the phenolic hydroxyl groups on some benzene rings can provide protons for ECR.

[0024] Further, according to relevant experimental results, the addition of the multifunctional proton buffer layer prolongs the residence time of CO2 in the buffer layer by 3 - 8 times, and the interface CO2 concentration is increased to 2 - 3 times that of the bulk phase.

[0025] The present invention also discloses a reduction system composed of the above medium-temperature carbon dioxide reduction electrode. The electrolytic cell has a channel design inside, which is suitable for various electrolysis reactions such as H2O, CO2, N2, etc., and has broad application prospects. Description of the Drawings

[0026] Figure 1Schematic diagram of the structure of the medium-temperature carbon dioxide reduction electrode of the present invention;

[0027] Figure 2 SEM image of the catalyst applied to medium-temperature carbon dioxide reduction in Example 2 of the present invention;

[0028] Figure 3 SEM image of the catalyst applied to medium-temperature carbon dioxide reduction in Example 3 of the present invention;

[0029] Figure 4 Schematic diagram of the principle of the medium-temperature carbon dioxide reduction electrode of the present invention;

[0030] Wherein: 1 - bipolar plate; 101 - cathode inlet; 102 - cathode outlet; 103 - anode inlet; 104 - anode outlet; 105 - cathode channel; 106 - anode channel; 107 - cathode heating rod port; 108 - anode heating rod port; 109 - cathode tab; 110 - anode tab; 111 - temperature sensor; 2 - membrane electrode; 201 - cathode electrode carrier; 202 - cathode catalyst; 203 - anode catalyst; 204 - anode electrode carrier; 301 - ion exchange membrane; 302 - cathode electrode diaphragm; 303 - anode electrode diaphragm. Detailed implementation manners

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art with respect to the present invention. In case of conflict, the definition in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0033] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0034] In this article, unless otherwise specified, the terms "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0035] In this text, for the sake of brevity in description, not all possible combinations of all technical features in each implementation or embodiment are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation or embodiment can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0036] The present invention provides a medium-temperature carbon dioxide reduction electrode, which includes a bipolar plate 1, a membrane electrode 2, and a diaphragm 3; the bipolar plate 1 includes a cathode and an anode; the membrane electrode 2 includes a cathode membrane electrode and an anode membrane electrode; the cathode, the cathode membrane electrode, the diaphragm 3, the anode membrane electrode, and the anode are arranged in sequence; a multifunctional proton buffer layer is attached to the cathode membrane electrode; the material of the multifunctional proton buffer layer is an inorganic material or a covalent organic framework material; the setting of this multifunctional proton buffer layer inhibits HER from both the physical confinement and chemical regulation dimensions, while strengthening the adsorption and mass transfer of CO2, and significantly improving the Faraday efficiency of ECR.

[0037] Preferably, the inorganic material includes one or more of inorganic reagents with proton buffering properties such as disodium hydrogen phosphate, sodium dihydrogen phosphate, and potassium bicarbonate. Its weakly basic local environment can physically adsorb CO2 molecules, forming a local CO2 enrichment area on the catalyst surface and promoting the reaction kinetics of ECR.

[0038] Preferably, for the covalent organic framework material (COFs): COFs containing basic functional groups are selected. Their regular pores (pore diameter 2 - 3 nm) and amino / pyridine groups can selectively adsorb CO2 through chemical action, and the phenolic hydroxyl groups on some benzene rings can provide protons for ECR.

[0039] Preferably, the buffer layer of the multifunctional proton buffer layer contains NH3 groups in the COF material, which can selectively adsorb CO2 molecules and increase the local concentration of CO2 on the catalyst surface.

[0040] Preferably, the introduction of the multifunctional proton buffer layer can make ECR have a Faraday efficiency of more than 2% under medium-temperature conditions.

[0041] Preferably, the introduction of the multifunctional proton buffer layer can further increase the Faraday efficiency of CO by 3 percentage points compared with the KHCO3 buffer material.

[0042] The loading amount of the COF buffer layer has a positive correlation with the Faraday efficiency of CO.

[0043] The action mechanism of the buffer layer of the multifunctional proton buffer layer in the present invention:

[0044] (1) Physical barrier of protons: The addition of the buffer layer increases the proton transport distance, making H +Migration time from the membrane to the catalyst is increased; Chemical consumption: The basic sites of COFs can capture part of H + (such as amino groups binding with H + to form -NH2 + ), controlling the H + concentration at the catalyst interface within a lower concentration range.

[0045] (2) CO2 adsorption and mass transfer enhancement for adsorption enrichment: The addition of the buffer layer extends the residence time of CO2 in the buffer layer by 3 - 8 times, and the interfacial CO2 concentration is increased to 2 - 3 times that of the bulk phase.

[0046] The present invention also discloses a reduction system composed of the above medium-temperature carbon dioxide reduction electrode. The electrolytic cell used specifically includes: a membrane electrode assembly (MEA) electrolytic cell, a temperature control module, and a gas and liquid feed management unit;

[0047] Among them, metallic titanium (Ti) is used as the main material of the electrolytic cell. The interior of the electrolytic cell has a channel design, which is suitable for various electrolysis reactions such as H2O, CO2, N2, etc. The temperature control module consists of a heating jacket, a thermocouple, and a PID controller, and is used to stably control the temperature of the entire system. The gas and liquid feed management unit includes a humidifier, a liquid thermostat, a back pressure valve, and a gas flow controller. By evaporating the liquid into gaseous reactants through the scrubbing method and combining the linkage control of the back pressure valve and the liquid vapor pressure, precise supply of gas flow is achieved.

[0048] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0049] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0050] Such as Figure 1 and Figure 4As shown in the figure, a medium-temperature carbon dioxide reduction electrode disclosed by the present invention includes a bipolar plate 1, a membrane electrode 2, and a diaphragm 3. Among them, the bipolar plate 1 has a cathode and an anode. A cathode gas inlet 101 and a cathode gas outlet 102 are provided on one side surface of the cathode; a cathode channel 105 is provided on the other side surface of the cathode; a cathode tab 109 is provided at the upper end of the cathode; the side surface provided with the cathode channel 105 is in contact with the cathode membrane electrode; a cathode heating rod port 107 is provided on the end surface of the cathode perpendicular to the side surface provided with the cathode channel 105; a temperature sensor is provided on the side where the cathode tab 109 is provided; an anode gas inlet 103 and an anode gas outlet 104 are provided on one side surface of the anode; an anode channel 106 is provided on the other side surface of the anode; an anode tab 110 is provided at the upper end of the anode; the side surface provided with the anode channel 106 is in contact with the anode membrane electrode; the cathode membrane electrode includes a cathode electrode carrier 201 and a cathode catalyst 202; one side surface of the cathode electrode carrier 201 is in contact with the cathode; a cathode catalyst 202 is provided on the other side surface of the cathode electrode carrier 201; a multifunctional proton buffer layer is attached to the cathode catalyst 202; the side surface provided with the cathode catalyst 202 is in contact with one side surface of the diaphragm 3; the anode membrane electrode includes an anode electrode carrier 204 and an anode catalyst 203; one side surface of the anode electrode carrier 204 is in contact with the anode; an anode catalyst 203 is provided on the other side surface of the anode electrode carrier 204; the side surface provided with the cathode catalyst 202 is in contact with the other side surface of the diaphragm 3; the diaphragm 3 includes a cathode electrode diaphragm 302, an ion exchange membrane 301, and an anode electrode diaphragm 303 arranged in sequence; the cathode electrode diaphragm 302 is in contact with the cathode catalyst 202; the anode electrode diaphragm 303 is in contact with the anode; the material of the multifunctional proton buffer layer is an inorganic material or a covalent organic framework material; the inorganic material includes one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate, and potassium bicarbonate; the covalent organic framework material is a COF containing basic functional groups; the COF containing basic functional groups has regular pores; the pore diameter of the regular pores is 2-3 nm.

[0051] When performing carbon dioxide electroreduction using the system composed of the medium-temperature carbon dioxide reduction electrode disclosed by the present invention, the following steps are included:

[0052] The entire electrolytic cell is heated by inserting heating rods into the anode heating rod port 108 and the cathode heating rod port 107. The temperature sensor 111 performs real-time temperature feedback, and the temperature is ensured to be controlled at 150 °C through a PID program, and there is no temperature overshoot.

[0053] The raw material gas CO2 for the cathode reaction enters the electrolytic cell through the cathode gas inlet 101, flows through the cathode channel 105, and then flows out of the electrolytic cell through the cathode gas outlet 102; the raw material gas H2O for the anode reaction enters the electrolytic cell through the anode gas inlet 103, flows through the anode channel 106, and then flows out of the electrolytic cell through the anode gas outlet 104;

[0054] The cathode ear 109 and the anode ear 110 are respectively connected to the cathode and anode of the DC power supply;

[0055] The cathode catalyst 202 is dispersed in isopropanol, and after being prepared into a uniformly dispersed ink, the catalyst is loaded onto the cathode electrode support 201 (carbon paper) after hydrophobic treatment by the CCS (Catalyst Coated Substrate) method. After loading the catalyst layer, a multifunctional proton buffer layer is loaded again by the CCS method;

[0056] The anode catalyst 203 is dispersed in isopropanol, and after being prepared into a uniformly dispersed ink, the catalyst is loaded onto the anode electrode support 204 (carbon paper) by the CCS method;

[0057] The ion exchange membrane 301 is pretreated so that it has ion exchange ability and does not leak air under the condition of 100 - 200 °C;

[0058] The cathode electrode diaphragm 302 and the anode electrode diaphragm 303 have certain elasticity and thermal stability to ensure that the whole system still has a sealing effect under the working condition of 100 - 200 °C.

[0059] Example 1

[0060] Step 1: Spray the silver catalyst (1 mg / cm -2 ) on the hydrophobic carbon paper and place it on the cathode side of the titanium bipolar plate. Spray IrO2 on the hydrophilic carbon paper and place it on the anode side of the titanium bipolar plate. The middle is a PBI (polybenzimidazole) membrane loaded with infiltrated H3PO4. Assemble the electrolytic cell and fasten it with bolts (torque 12 N·m). Place the electrolytic cell in the thermoelectric coupling module, and connect the heating tape and the thermocouple probe;

[0061] Step 2: After Step 1 is completed, purge the electrolytic cell and the pipeline with argon (flow rate 100 sccm) for 10 minutes, and monitor the oxygen content in the tail gas by chromatography until the content < 5 ppm;

[0062] Step 3: After Step 2 is completed, set the target temperature to 150 °C, and correct the power in real time through the PID algorithm to prevent the electrolytic cell from overheating due to thermal inertia, and finally stabilize at 150 ± 0.5 °C;

[0063] Step 4: After step 3 is completed, set the temperature of the constant-temperature water storage tank to 80 °C, introduce water vapor into the electrode chamber through the carrier gas, and adjust the pressure value of the back pressure valve to 2 bar so that the water vapor pressure inside the electrode chamber reaches the preset value;

[0064] Step 5: After step 4 is completed, apply a voltage of 2 V to the electrolytic cell, monitor the current density and hydrogen production rate in real time, and the system automatically records the temperature fluctuation (±0.5 °C), gas flow error (≤1%), and voltage-current curve;

[0065] Step 6: After step 5 is completed, switch the valve back to purge gas purging (100 sccm, 30 minutes), and cool down to room temperature.

[0066] Example 2

[0067] Step 1: Spray the silver catalyst (1 mg / cm 2 ) on the hydrophobic carbon paper and place it on the cathode side of the titanium bipolar plate. Then, spray 1 mg / cm 2 of KHCO3 (dissolved in water / acetone) outside the silver catalyst; spray IrO2 on the hydrophilic carbon paper and place it on the anode side of the titanium bipolar plate, with a polystyrene benzimidazole (PBI) membrane loaded with infiltrated H3PO4 in the middle; assemble the electrolytic cell and fasten it with bolts (torque 12 N·m). Place the electrolytic cell in the thermoelectric coupling module, and connect the heating tape and thermocouple probe;

[0068] Step 2: After step 1 is completed, purge the electrolytic cell and pipelines with argon (flow rate 100 sccm) for 10 minutes, and monitor the oxygen content in the tail gas through chromatography until the content < 5 ppm;

[0069] Step 3: After step 2 is completed, set the target temperature to 150 °C, and use the PID algorithm to correct the power in real time to prevent the electrolytic cell from overheating due to thermal inertia, and finally stabilize at 150 ± 0.5 °C;

[0070] Step 4: After step 3 is completed, set the temperature of the constant-temperature water storage tank to 80 °C, introduce water vapor into the electrode chamber through the carrier gas, and adjust the pressure value of the back pressure valve to 2 bar so that the water vapor pressure inside the electrode chamber reaches the preset value;

[0071] Step 5: After step 4 is completed, apply a voltage of 2 V to the electrolytic cell, monitor the current density and hydrogen production rate in real time, and the system automatically records the temperature fluctuation (±0.5 °C), gas flow error (≤1%), and voltage-current curve;

[0072] Step 6: After step 5 is completed, switch the valve back to purge gas purging (100 sccm, 30 minutes), and cool down to room temperature.

[0073] Example 3

[0074] Step 1: Spray the silver catalyst (1 mg / cm 2 ) on the hydrophobic carbon paper and place it on the cathode side of the titanium bipolar plate. Then, spray 1 mg / cm 2 of COF (dissolved in water / acetone) outside the silver catalyst; spray IrO2 on the hydrophilic carbon paper and place it on the anode side of the titanium bipolar plate. In the middle is a polybenzimidazole (PBI) membrane loaded with infiltrated H3PO4; assemble the electrolytic cell and fasten it with bolts (torque 12 N·m); place the electrolytic cell in the thermoelectric coupling module and connect the heating tape and thermocouple probe;

[0075] Step 2: After Step 1 is completed, purge the electrolytic cell and pipelines with argon (flow rate 100 sccm) for 10 minutes, and monitor the oxygen content in the tail gas through chromatography until the content is < 5 ppm;

[0076] Step 3: After Step 2 is completed, set the target temperature to 150 °C, and use the PID algorithm to correct the power in real time to prevent the electrolytic cell from overheating due to thermal inertia, and finally stabilize at 150 ± 0.5 °C;

[0077] Step 4: After Step 3 is completed, set the temperature of the constant temperature water storage tank to 80 °C, introduce water vapor into the electrode chamber through the carrier gas, and adjust the pressure value of the back pressure valve to 2 bar so that the water vapor pressure inside the electrode chamber reaches the preset value;

[0078] Step 5: After Step 4 is completed, apply a voltage of 2 V to the electrolytic cell, monitor the current density and hydrogen production rate in real time, and the system automatically records the temperature fluctuation (±0.5 °C), gas flow error (≤1%), and voltage-current curve;

[0079] Step 6: After Step 5 is completed, switch the valve back to purge gas for purging (100 sccm, 30 minutes), and cool down to room temperature.

[0080] Example 4

[0081] Step 1: Spray the silver catalyst (1 mg / cm 2 ) on the hydrophobic carbon paper and place it on the cathode side of the titanium bipolar plate. Then, spray 2 mg / cm 2 of COF (dissolved in water / acetone) outside the silver catalyst; spray IrO2 on the hydrophilic carbon paper and place it on the anode side of the titanium bipolar plate. In the middle is a polybenzimidazole (PBI) membrane loaded with infiltrated H3PO4; assemble the electrolytic cell and fasten it with bolts (torque 12 N·m); place the electrolytic cell in the thermoelectric coupling module and connect the heating tape and thermocouple probe;

[0082] Step 2: After Step 1 is completed, purge the electrolytic cell and pipelines with argon (flow rate 100 sccm) for 10 minutes, and monitor the oxygen content in the tail gas through chromatography until the content is < 5 ppm;

[0083] Step 3: After Step 2 is completed, set the target temperature to 150 °C, and use the PID algorithm to correct the power in real time to prevent the electrolytic cell from overheating due to thermal inertia, and finally stabilize at 150 ± 0.5 °C;

[0084] Step 4: After Step 3 is completed, set the temperature of the constant temperature water storage tank to 80 °C, introduce water vapor into the electrode chamber through the carrier gas, and adjust the pressure value of the back pressure valve to 2 bar so that the water vapor pressure inside the electrode chamber reaches the preset value;

[0085] Step 5: After Step 4 is completed, apply a voltage of 2 V to the electrolytic cell, monitor the current density and hydrogen production rate in real time, and the system automatically records the temperature fluctuation (±0.5 °C), gas flow error (≤1%), and voltage-current curve;

[0086] Step 6: After Step 5 is completed, switch the valve back to purge gas purging (100 sccm, 30 minutes) and cool down to room temperature.

[0087] Figure 2 This is the SEM image of the catalyst applied in Example 2 of the present invention for medium-temperature carbon dioxide reduction, and it can be seen that the morphology of granular KHCO3; Figure 3 This is the SEM image of the catalyst applied in Example 3 of the present invention for medium-temperature carbon dioxide reduction, and it can be seen that the morphological characteristics of the two-dimensional structure.

[0088] Table 1 shows the statistical results of the catalytic performance of medium-temperature ECR under different buffer layer strengths in Examples 1 to 4. From the data in the table, it can be seen that the present invention reveals the key influence of the buffer layer on the medium-temperature CO2 electrochemical reduction performance. Under the condition of no buffer layer, HER dominates absolutely; after introducing the buffer layer, although HER is still the main reaction, the Faraday efficiency of CO is significantly improved. It is particularly worth noting that with the increase of the COF buffer layer loading, the Faraday efficiency of CO shows an obvious upward trend. Comparative studies have found that the performance of the COF buffer layer is significantly better than that of the traditional KHCO3 buffer, which is mainly attributed to the specific adsorption effect of the amino functional groups rich in the COF structure on CO2 molecules. This adsorption characteristic effectively increases the local concentration of CO2 on the catalyst surface, thus better suppressing the HER competitive reaction under medium-temperature conditions (100 - 200 °C) and promoting the selective conversion of CO2 to CO. This discovery provides an important theoretical basis and technical path for the development of an efficient medium-temperature CO2 electroreduction system.

[0089] Table 1: Catalytic performance of medium-temperature ECR under different buffer layer strengths

[0090] Embodiment 1 2 3 4 <![CDATA[FE CO / %]]> 0 2.18 3.47 4.84

[0091] The present invention discloses a carbon dioxide (CO2) reduction electrode applicable to the medium temperature range of 100 - 200 °C. By optimizing the electrode structure design, the selectivity and reaction efficiency of electrochemical CO2 reduction (ECR) are significantly improved. The core innovation of this electrode lies in introducing a multifunctional proton buffer layer between the cathode catalyst layer and the proton exchange membrane (PEM). This buffer layer suppresses the hydrogen evolution side reaction (HER) from both the physical confinement and chemical regulation dimensions by regulating the proton (H + ) transport kinetics and CO2 mass transfer process, while enhancing the adsorption and activation of CO2, thereby greatly improving the Faraday efficiency (FE) and current density of ECR.

[0092] Design principle of the multifunctional proton buffer layer:

[0093] In the cathode structure of traditional CO2 electrolyzers, the catalyst layer is usually in direct contact with the proton exchange membrane, resulting in the rapid migration of H + to the catalyst active sites, triggering HER at low overpotentials and severely reducing the selectivity of ECR. The multifunctional proton buffer layer proposed in the present invention optimizes the reaction microenvironment through the following mechanisms:

[0094] The introduction of the buffer layer increases the migration path of H + from the membrane to the catalyst, prolonging its diffusion time and thus reducing the H + concentration at the catalyst interface. The basic sites (such as amino, pyridyl, phosphate groups) in the buffer layer can partially capture H + (such as -NH2 + H + → -NH3 + ), forming a local weakly basic environment and further suppressing the HER competitive reaction.

[0095] The buffer layer has the ability to selectively adsorb CO2. Its porous structure can extend the residence time of CO2 molecules, increasing the CO2 concentration at the catalyst interface to 2 - 3 times that of the bulk solution; experimental data show that this buffer layer can extend the residence time of CO2 at the electrode interface by 3 - 8 times, thus significantly improving the reaction rate of ECR.

[0096] The buffer layer not only physically adsorbs CO2 through its pore structure (such as 2 - 3 nm regular pores), but also the basic functional groups (such as amino, phenolic hydroxyl) modified on its surface can form weak chemical interactions with CO2 (such as the formation of a carbamate intermediate between amino and CO2), further promoting the activation of CO2.

[0097] Selection and optimization of buffer layer materials:

[0098] The materials of the buffer layer need to have both proton conductivity, CO2 adsorption ability and chemical stability. The present invention preferably selects the following types of materials:

[0099] 1) Inorganic weak acid salts: such as disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), potassium bicarbonate (KHCO3). These compounds can form a weakly alkaline microenvironment in the hydrated state, which can not only regulate the H + concentration, but also enrich CO2 through physical adsorption;

[0100] 2) Covalent organic framework materials (COFs): Select COFs containing functional groups such as amino groups, pyridyl groups, and phenolic hydroxyl groups. Their regular pores (2-3 nm) can provide a high specific surface area and CO2 selective adsorption sites. For example, pyridyl-containing COF-TpPa-1 can stably exist under medium-temperature conditions and promote the chemisorption of CO2.

[0101] The present invention also discloses a medium-temperature CO2 electrolysis system based on the above electrode, and its core innovations include:

[0102] Modular electrolyzer design: Adopting a flow channel optimization structure, suitable for electrolysis of various gases such as H2O, CO2, N2, etc., and enabling continuous production;

[0103] Thermal-electric co-management: The system operates at 100-200 °C, which not only avoids the material degradation problem of high-temperature SOEC, but also utilizes medium-temperature conditions to enhance the reaction kinetics, and the energy efficiency is increased by more than 20% compared with traditional low-temperature electrolyzers;

[0104] Broad raw material adaptability: It can directly utilize low-concentration CO2 (10-30%) in industrial waste gases (such as tail gas from coal-fired power plants and blast furnace gas from steel plants) without high-cost purification treatment.

[0105] The present invention significantly improves the catalytic activity of the CO2 reduction reaction by introducing a buffer layer on the electrode surface. It is found that under medium-temperature conditions of 100-200 °C, the introduction of the buffer layer can effectively block the direct contact between protons and the catalyst, inhibit the competition of the hydrogen evolution reaction (HER), and improve the Faraday efficiency of CO. In particular, the present invention compares the performance differences between KHCO3 buffer and COF buffer materials, and finds that due to the selective adsorption of CO2 by the unique NH3 group of the COF material, it can significantly increase the local concentration of CO2 on the catalyst surface, thereby obtaining better catalytic performance. This technical solution provides a new technical path for the performance optimization of medium-temperature CO2 electrolysis systems.

[0106] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A medium-temperature carbon dioxide reduction electrode, characterized in that: The invention comprises a bipolar plate (1), a membrane electrode (2) and a diaphragm (3); the bipolar plate (1) comprises a cathode and an anode; the membrane electrode (2) comprises a cathode membrane electrode and an anode membrane electrode; the cathode, the cathode membrane electrode, the diaphragm (3), the anode membrane electrode and the anode are arranged in sequence; a multifunctional proton buffer layer is attached to the cathode membrane electrode; The material of the multifunctional proton buffer layer is inorganic material or covalent organic framework material.

2. A medium-temperature carbon dioxide reduction electrode according to claim 1, characterized in that: The inorganic material includes one or more of disodium monohydrogen phosphate, sodium dihydrogen phosphate and potassium bicarbonate.

3. The medium-temperature carbon dioxide reduction electrode according to claim 1, characterized in that: The covalent organic framework material is COFs containing alkaline functional groups; the COFs containing alkaline functional groups have regular pores; and the pore diameter of the regular pores is 2-3 nm.

4. The medium-temperature carbon dioxide reduction electrode according to claim 1, characterized in that: A cathode gas inlet (101) and a cathode gas outlet (102) are arranged on one side of the cathode; a cathode channel (105) is arranged on the other side of the cathode; a cathode pole ear (109) is arranged at the upper end of the cathode; and the side provided with the cathode channel (105) is in contact with the cathode membrane electrode.

5. The medium-temperature carbon dioxide reduction electrode according to claim 4, characterized in that: A cathode heating rod opening (107) is arranged on the end surface of the cathode which is perpendicular to the side surface where the cathode channel (105) is arranged; and a temperature sensor is arranged on the side where the cathode pole ear (109) is arranged.

6. The medium-temperature carbon dioxide reduction electrode according to claim 4, characterized in that: The cathode membrane electrode comprises a cathode electrode carrier (201) and a cathode catalyst (202); one side of the cathode electrode carrier (201) is in contact with the cathode; the cathode catalyst (202) is arranged on the other side of the cathode electrode carrier (201); a multifunctional proton buffer layer is attached to the cathode catalyst (202); and the side on which the cathode catalyst (202) is arranged is in contact with one side of the diaphragm (3).

7. The medium-temperature carbon dioxide reduction electrode according to claim 6, characterized in that: The diaphragm (3) comprises a cathode electrode diaphragm (302), an ion exchange membrane (301) and an anode electrode diaphragm (303) which are arranged in sequence; the cathode electrode diaphragm (302) is in contact with the cathode catalyst (202); and the anode electrode diaphragm (303) is in contact with the anode.

8. The medium-temperature carbon dioxide reduction electrode according to claim 7, characterized in that: An anode gas inlet (103) and an anode gas outlet (104) are provided on one side of the anode; an anode channel (106) is provided on the other side of the cathode; an anode pole ear (110) is provided at the upper end of the cathode; and the side provided with the anode channel (106) is in contact with the anode membrane electrode; The anode membrane electrode comprises an anode electrode carrier (204) and an anode catalyst (203); one side of the anode electrode carrier (204) is in contact with the anode; the anode catalyst (203) is arranged on the other side of the anode electrode carrier (204); and the side on which the cathode catalyst (202) is arranged is in contact with the other side of the diaphragm (3).

9. A medium temperature carbon dioxide reduction system, characterized in that: The invention comprises the medium-temperature carbon dioxide reduction electrode as described in any one of claims 1 to 8.

10. A medium temperature carbon dioxide reduction system according to claim 9, characterized in that: The working temperature of the multifunctional proton buffer layer is 100-200°C.

Images