Modified membrane electrode catalyst layer, membrane electrode assembly and proton exchange membrane electrolytic tank

Abstract

The invention provides a modified membrane electrode catalyst layer, a membrane electrode assembly and a proton exchange membrane electrolytic tank, and relates to the technical field of proton exchange membrane electrolyzed water. The modified membrane electrode catalyst layer comprises an anode catalyst and an ionomer, and the surface of one side of the modified membrane electrode catalyst layer is formed by plasma etching treatment; wherein gas used in the plasma etching treatment comprises at least one of ozone, oxygen and nitrogen. The modified membrane electrode catalyst layer has excellent electron conduction performance, water vapor transmission and long-period operation stability.

Description

Technical Field

[0001] The present invention relates to the technical field of proton exchange membrane water electrolysis, and in particular to a modified membrane electrode catalyst layer, a membrane electrode assembly and a proton exchange membrane electrolysis cell. Background Art

[0003] As the core site of multiphase material transport and energy conversion, the catalytic layer is an indispensable and important component of the proton exchange membrane water electrolysis system. The catalytic layer is composed of catalyst particles, perfluorosulfonated ionomers (PFSA) and pore structures, which respectively undertake the functions of electron conduction, proton transport and water vapor transport during the reaction process. The microstructure of the catalytic layer and the distribution of each component have a decisive influence on the electrolysis performance and long-term stability. However, in the long-term stability test, the ionomer may migrate and swell, resulting in limited exposure of the catalyst active sites. In addition, some of the lost ionomers may block the pore structure in the catalytic layer, thereby reducing the transmission efficiency. Therefore, optimizing the transmission path to improve the performance and stability of the catalytic layer is still a key issue that needs to be solved urgently. Summary of the invention

[0004] The main purpose of the present invention is to provide a modified membrane electrode catalyst layer, a membrane electrode assembly and a proton exchange membrane electrolyzer to solve the problems of limited electron conduction and obstructed water vapor transmission exposed by the catalyst layer in the long-cycle life test process in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a modified membrane electrode catalyst layer is provided, wherein the modified membrane electrode catalyst layer includes an anode catalyst and an ionomer, and one side surface of the modified membrane electrode catalyst layer is treated by plasma etching; wherein the gas used for the plasma etching treatment includes at least one of ozone, oxygen, and nitrogen.

[0006] Further, the flow rate of the gas is 50 to 200 mL / min; and / or,

[0007] The discharge power of the plasma etching treatment is 5 to 30 W, the temperature is 20 to 25° C., and the time is 10 to 30 minutes.

[0008] Further, the anode catalyst includes a supported iridium-based catalyst;

[0009] Preferably, the supported iridium-based catalyst comprises a carrier and iridium oxide supported on the carrier; wherein the carrier comprises at least one of titanium oxide, niobium oxide, tin oxide, silicon oxide, zirconium oxide, tantalum oxide, cerium oxide, aluminum oxide, and titanium nitride;

[0010] Preferably, the loading amount of iridium oxide on the carrier is 10% to 80%.

[0011] Furthermore, the ionomer includes at least one of perfluorosulfonic acid resin, sulfonated polyetheretherketone resin, and sulfonated trifluorostyrene resin.

[0012] Furthermore, the mass ratio of the anode catalyst to the ionomer is 100:(5-40).

[0013] Furthermore, the preparation of the anode catalyst comprises the following steps:

[0014] S11, ultrasonically mixing the carrier, the iridium precursor and isopropanol to obtain a first mixture;

[0015] S12, drying the first mixed material to obtain a dried product;

[0016] S13, mixing the dried product with a molten salt to obtain a second mixed material, and calcining the second mixed material to obtain a calcined product;

[0017] S14, washing the calcined product to obtain an anode catalyst.

[0018] Preferably, the calcination temperature is 400-500° C. and the calcination time is 0.5-2 h.

[0019] Preferably, the molten salt comprises NaNO 3 .

[0020] Preferably, the molar ratio of the molten salt to the iridium element in the iridium precursor is (20-80):1.

[0021] Preferably, the iridium precursor comprises H 2 IrCl 6 .

[0022] The second aspect of the present invention provides a membrane electrode assembly, comprising an anode catalyst layer, a polymer electrolyte membrane and a cathode catalyst layer stacked in sequence, the anode catalyst layer is the modified membrane electrode catalyst layer mentioned in the first aspect, and the other side surface of the modified membrane electrode catalyst layer is in contact with the polymer electrolyte membrane.

[0023] Furthermore, the method for preparing the membrane electrode assembly comprises the following steps:

[0024] S1, mixing an anode catalyst, a solution containing an ionomer, an alcohol compound and water to obtain a first slurry;

[0025] S2, ball milling and defoaming the first slurry to obtain a second slurry;

[0026] S3, coating the second slurry on the substrate, and after drying, forming an initial anode catalyst layer on the surface of the substrate;

[0027] S4, transferring the initial anode catalyst layer on the surface of the substrate to one side of the polymer electrolyte membrane by hot pressing, and preparing a cathode catalyst layer on the other side of the polymer electrolyte membrane by hot pressing transfer or coating to obtain an initial membrane electrode;

[0028] S5, performing plasma etching on the surface of the initial anode catalyst layer in the initial membrane electrode away from the polymer electrolyte membrane to obtain a membrane electrode assembly.

[0029] Further, the mass content of the anode catalyst in the first slurry is 15% to 40%; and / or,

[0030] The mass of the ionomer in the solution containing the ionomer is 5% to 40% of the mass of the anode catalyst; and / or,

[0031] The mass ratio of water to alcohol compound is (5-8): (2-5); and / or,

[0032] Alcohol compounds are monohydric or polyhydric liquid alcohols with 1 to 8 carbon atoms;

[0033] Preferably, the alcohol compound includes at least one of methanol, ethanol, n-propanol, isopropanol, propylene glycol, glycerol, n-butanol, isobutanol, and ethylene glycol.

[0034] A third aspect of the present invention provides a proton exchange membrane electrolyzer, comprising the membrane electrode assembly provided in the second aspect.

[0035] By applying the technical solution of the present invention, the distribution of ionomers in the catalyst layer can be optimized by plasma etching the surface of the catalyst layer, the exposure of the catalyst can be increased, the number of active sites can be effectively increased, and the electronic conduction of the catalyst layer can be improved; by appropriately removing the blocking substances in the catalyst layer through plasma etching, the pore structure can be optimized, which is conducive to the rapid diffusion and discharge of gases and reduces the resistance in the gas transmission process. In addition, the hydrophilicity of the surface of the catalyst layer after treatment is significantly enhanced, which improves the wettability of the catalyst layer, which in turn is also conducive to the rapid discharge of gases. Therefore, the present invention not only optimizes the electronic conduction performance of the catalyst layer through plasma etching treatment, but also improves the water vapor transmission channel, which helps to improve the overall performance of the membrane electrode and the stability of its long-term operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a polarization performance curve diagram of the membrane electrode in Examples 1-2 and Comparative Example 1;

[0037] Figure 2 The electrochemical impedance spectra of the membrane electrodes in Examples 1 to 2 and Comparative Example 1 are shown;

[0038] Figure 3The stability test curves of the membrane electrodes of Examples 1 to 2 and Comparative Example 1 are shown;

[0039] Figure 4 The electrochemical impedance spectra after the membrane electrode stability test in Examples 1 to 2 and Comparative Example 1 are shown;

[0040] Figure 5 This is a contact angle test diagram of the anode catalyst layer in the membrane electrode of comparative example 1;

[0041] Figure 6 This is a contact angle test diagram of the anode catalyst layer in the membrane electrode of Example 1;

[0042] Figure 7 This is a contact angle test diagram of the anode catalyst layer in the membrane electrode in Example 2. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0044] As described in the background of the present invention, the catalyst layer in the prior art exposes the problems of limited electron conduction and obstructed water vapor transmission during the long-cycle life test. In order to solve the above problems, in a typical embodiment of the present invention, a modified membrane electrode catalyst layer is provided, the modified membrane electrode catalyst layer includes an anode catalyst and an ionomer; one side surface of the modified membrane electrode catalyst layer is treated by plasma etching; wherein the gas used for the plasma etching treatment includes at least one of ozone, oxygen, and nitrogen.

[0045] The modified membrane electrode catalyst layer is mainly composed of an anode catalyst and an ionomer. The anode catalyst is a substance that promotes the water oxidation reaction. Common catalyst active components include iridium oxide (IrO 2 ), these catalysts are usually supported on inert carriers such as titanium oxide (TiO 2 ) etc. The ionomer is used to enhance the proton conductivity and mechanical stability of the catalytic layer.

[0046] The modified membrane electrode catalyst layer has two side surfaces arranged opposite to each other. In the specific implementation process of the present invention, one side surface of the modified membrane electrode catalyst layer is located on the outside, and the other side surface is used to fit with the polymer electrolyte membrane, and only the side surface located on the outside is plasma-etched. Plasma etching is a surface modification technology that allows the active components such as free radicals, ions and ultraviolet rays in the plasma to react with the surface of the catalyst layer to remove unnecessary substances on the surface, improve surface properties, optimize the distribution of catalyst active sites and ionomers, thereby improving the electronic conductivity, water vapor transmission performance and long-term operation stability of the catalyst layer.

[0047] First, plasma etching treatment optimizes the distribution of ionomers in the catalyst layer, and the optimized distribution of ionomers promotes the full exposure of catalytic active sites. The increase and optimized distribution of active sites improves the conduction path of electrons in the catalyst layer, reduces the resistance of electron transmission, and thus significantly improves the efficiency of electron conduction.

[0048] Secondly, through moderate plasma etching treatment, blocking substances in the catalyst layer, such as excessive ionomers or other impurities, can be removed. The removal of these substances helps to maintain the structural stability of the catalyst layer.

[0049] In addition, plasma etching treatment improves the pore structure of the catalyst layer, increases the openness and connectivity of the pores, facilitates the rapid diffusion and discharge of gases, and reduces the resistance during gas transmission. The optimization of the gas diffusion channel ensures that the reaction products can be discharged quickly while providing fresh reactants, which is crucial to improving the efficiency and stability of the water electrolysis reaction.

[0050] Plasma etching treatment significantly increases the hydrophilicity of the catalyst layer surface, improves its wettability, and promotes better penetration of water molecules into the catalyst layer. At the same time, the entry of water helps the rapid discharge of gas in the catalyst layer, building a good water-gas transmission channel. During the plasma etching process, the gas used can be ozone (O 3 ), oxygen (O 2 ), nitrogen (N 2 ) or any combination of these three gases. These gases are more active in the plasma state and can react more effectively with the surface of the catalyst layer. Different gas selections will bring different surface modification effects. For example, oxygen (O 2 ), ozone (O 3 ) treatment can introduce (-OH) or oxide functional groups (such as -COOH, C=O) on the surface of the material, significantly increasing the hydrophilicity. 2 ) can introduce nitrogen-containing functional groups (such as -NH 2, -C≡N), which will increase polarity and enhance hydrophilicity, but the effect is not as significant as oxygen. In the specific implementation of the present invention, a combination of different gases can be selected according to actual needs.

[0051] In some embodiments, the flow rate of the gas is 50 to 200 mL / min, for example, 50 mL / min, 80 mL / min, 100 mL / min, 120 mL / min, 150 mL / min, 180 mL / min, 200 mL / min or a range consisting of any two of them. The control of the gas flow rate directly affects the density and etching rate of the plasma and the uniformity of the distribution of the plasma on the surface of the catalyst layer. By accurately adjusting the gas flow rate to 50 to 200 mL / min, the appropriate flow rate can ensure that the plasma uniformly covers the entire surface, the speed of the etching process can be controlled, the over-etching or under-etching of the catalyst layer can be avoided, the uniformity and consistency of the surface modification of the catalyst layer can be ensured, and the overall performance and stability of the catalyst layer can be further improved.

[0052] In some embodiments, the discharge power of the plasma etching treatment is 5 to 30 W, such as 5 W, 10 W, 15 W, 20 W, 25 W, 30 W or any two of them, the temperature is 20 to 25 ° C, such as 20 ° C, 21 ° C, 22 ° C, 23 ° C, 24 ° C, 25 ° C or any two of them, and the time is 10 to 30 min, such as 10 min, 15 min, 20 min, 25 min, 30 min or any two of them. By precisely controlling the parameters of the plasma etching treatment, excessive damage to the catalyst layer can be avoided, while ensuring the effect of surface modification, so that the number and distribution of active sites in the catalyst layer are more uniform, and the stability and life of the membrane electrode are improved.

[0053] The present invention does not limit the specific type of catalyst, which may be a conventional catalyst in the art. In some embodiments, the anode catalyst includes a supported iridium-based catalyst; for example, the supported iridium-based catalyst includes a carrier and iridium oxide supported on the carrier; wherein the carrier includes titanium oxide (TiO 2 ), niobium oxide (NbO x ), tin oxide (SnO 2 ), silicon oxide (SiO 2 )、ZrO 2 ), tantalum oxide (TaO 2 ), cerium oxide (CeO 2 ), aluminum oxide (Al 2 O 3 ), at least one of titanium nitride (TiN).

[0054] The loading amount of iridium oxide on the carrier refers to the percentage of the mass of iridium oxide to the total mass of the mixture of the carrier and iridium oxide. In some embodiments, the loading amount of iridium oxide on the carrier is 10% to 80%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or a range consisting of any two of them. By limiting the loading amount of iridium oxide to 10% to 80%, the stability and activity of the catalyst can be improved, and the electronic conductivity of the membrane electrode can be further improved.

[0055] Ionomers are polymers containing ionic groups and having proton conduction function, which can dissociate ions under specific conditions, thereby forming channels in the material that can conduct protons. In some embodiments, the ionomer includes at least one of perfluorosulfonic acid resin, sulfonated polyetheretherketone resin, and sulfonated trifluorostyrene resin. The sulfonic acid groups in these ionomers can not only dissociate H + ions, forming protons (H + ), and can also help the protons in the reaction to be conducted in the base membrane and the catalytic layer; secondly, the ionomer can also provide mechanical stability in the catalytic layer, preventing the catalyst particles from migrating or aggregating during operation and maintaining the integrity of the catalytic layer structure, which is crucial for long-term stable operation.

[0056] In some embodiments, the mass ratio of the anode catalyst to the ionomer is 100:(5-40), such as 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, 100:35, 100:40 or any two thereof. By adjusting the mass ratio of the anode catalyst to the ionomer, the structure and performance of the catalyst layer can be optimized, and while ensuring the activity of the catalyst, the transmission of its electrons, protons and their water vapor is enhanced, which helps to improve the efficiency of the battery and extend its service life.

[0057] In some embodiments, the preparation of the anode catalyst comprises the following steps:

[0058] S11, ultrasonically mixing the carrier, the iridium precursor and isopropanol to obtain a first mixture;

[0059] S12, drying the first mixed material to obtain a dried product;

[0060] S13, mixing the dried product with a molten salt to obtain a second mixed material, and calcining the second mixed material to obtain a calcined product;

[0061] S14, washing the calcined product to obtain an anode catalyst.

[0062] Specifically, the carrier, the iridium precursor and the isopropanol can be ultrasonically mixed, and the ultrasonic wave can effectively break up the solid particles, promote uniform dispersion, ensure the full contact between the two in the whole solution, and facilitate the subsequent chemical reaction. As a solvent, isopropanol can dissolve certain substances and promote subsequent reactions. The loading amount of iridium oxide on the carrier can be controlled by adjusting the mass ratio of the precursor iridium precursor to the carrier.

[0063] The first mixed material needs to be dried to remove the solvent isopropanol, leaving a solid mixture (i.e., dried product). Next, the dried product is mixed with a molten salt, the role of which is to act as a flux, promoting the uniform distribution and fixation of iridium oxide on the surface of the carrier in subsequent high-temperature treatment. After the dried product is fully mixed with the molten salt, it is necessary to calcine under high temperature conditions. High-temperature calcination promotes the formation of iridium oxide, while promoting the combination of iridium oxide and the carrier, and the stability of iridium oxide particles on the surface of the carrier, while through the fluxing effect of the molten salt, the iridium oxide is dispersed more evenly, forming a higher active site density.

[0064] The molten salt will react with iridium oxide and the carrier at high temperature or form residues on the surface. These residues may affect the performance and stability of the catalytic layer. Therefore, the calcined product needs to be washed multiple times (3 to 5 times) with deionized water to remove excess molten salt and other possible impurities.

[0065] The washed calcined product needs to be dried again and then ground to obtain a uniform powder state. Drying ensures that the catalyst is in an anhydrous state and avoids the influence of moisture on the subsequent membrane electrode preparation. Grinding is to increase the surface area of ​​the catalyst, which is beneficial for subsequent coating and improving the activity of the catalytic layer.

[0066] In some embodiments, the calcination temperature is 400-500°C, for example 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C or a range consisting of any two thereof, and the calcination time is 0.5-2h, for example 0.5h, 1h, 1.5h, 2h or a range consisting of any two thereof.

[0067] In some embodiments, the molar ratio of the molten salt to the iridium element in the iridium precursor is (20-80):1, such as 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1 or any two thereof. This ratio helps to control the distribution density of the catalyst particles on the carrier to avoid shielding of active sites due to local over-density or reduced catalytic efficiency due to local over-sparseness.

[0068] The present invention does not limit the specific selection of raw materials. For example, in some embodiments, the molten salt includes NaNO3 , iridium precursors include chloroiridic acid (H 2 IrCl 6 ).

[0069] The second aspect of the present invention provides a membrane electrode assembly, comprising an anode catalyst layer, a polymer electrolyte membrane and a cathode catalyst layer stacked in sequence, the anode catalyst layer is the modified membrane electrode catalyst layer provided in the first aspect, and the other side surface of the modified membrane electrode catalyst layer is in contact with the polymer electrolyte membrane.

[0070] The membrane electrode assembly is a stacked structure. The polymer electrolyte membrane is the base membrane, which provides structural support and proton conduction functions. It is usually a proton exchange membrane (PEM) such as a Nafion membrane, which has good chemical stability and proton conduction ability. A modified membrane electrode catalyst layer is provided on one side of the polymer electrolyte membrane, and a cathode catalyst layer is provided on the other side. It can be understood that one side surface of the modified membrane electrode catalyst layer is away from the polymer electrolyte membrane, and the other side surface is in contact with the polymer electrolyte membrane. Since one side surface of the modified membrane electrode catalyst layer is treated with plasma etching, the membrane electrode assembly has excellent electronic conductivity and water vapor transmission performance, and can achieve long-term stability testing.

[0071] Specifically, the modified membrane electrode catalyst layer is used as the anode catalyst layer. In the process of water electrolysis, the main function of the polymer electrolyte membrane is to conduct protons (H + ions), while blocking the passage of electrons and other molecules such as oxygen. The modified membrane electrode catalyst layer is responsible for splitting water molecules into oxygen and protons, while the cathode catalyst layer is responsible for combining protons and electrons to form hydrogen.

[0072] In some embodiments, the method for preparing a membrane electrode assembly comprises the following steps:

[0073] S1, mixing an anode catalyst, a solution containing an ionomer, an alcohol compound and water to obtain a first slurry;

[0074] S2, ball milling and defoaming the first slurry to obtain a second slurry;

[0075] S3, coating the second slurry on the substrate, and after drying, forming an initial anode catalyst layer on the surface of the substrate;

[0076] S4, transferring the initial anode catalyst layer on the surface of the substrate to one side of the polymer electrolyte membrane by hot pressing, and preparing a cathode catalyst layer on the other side of the polymer electrolyte membrane by hot pressing transfer or coating to obtain an initial membrane electrode;

[0077] S5, performing plasma etching on the surface of the initial anode catalyst layer in the initial membrane electrode away from the polymer electrolyte membrane to obtain a membrane electrode assembly.

[0078] In S1, the anode catalyst, the solution containing the ionomer, the alcohol compound and the deionized water are mixed in a container. The alcohol compound and the water act together to disperse the anode catalyst and the ionomer to form a uniform first slurry. The ionomer solution serves to provide proton conductivity, while the mixture of the alcohol compound and the water contributes to the fluidity and dispersibility of the slurry, which is convenient for subsequent coating.

[0079] In S2, the first slurry is transferred to a ball mill and ball milled together with ball mill beads. The purpose of ball milling is to further refine the particles in the slurry, ensure that the anode catalyst and ionomer are evenly distributed in the slurry, and destroy any possible agglomeration to promote its uniform laying in the subsequent coating process. The slurry after ball milling needs to be degassed to remove any residual bubbles to prevent the formation of voids or uneven coatings during the coating process, which affects the performance of the catalytic layer. The degassing process is usually carried out under vacuum conditions to ensure that the bubbles are effectively removed, and the second slurry obtained is more stable and suitable for the next step of coating.

[0080] In S3, the second slurry is evenly coated on the substrate. This step is intended to form a thin and uniform catalyst layer. The coating process can be carried out using equipment such as a slit coater. The coating parameters are adjusted according to the required catalyst loading. For example, the loading can be set to 0.100-1.000 mg Ir / cm 2 After coating, it is necessary to dry at a suitable temperature to remove the solvent and moisture and solidify the catalyst layer. The drying conditions (such as temperature and time) should match the slurry composition to ensure the formation of a stable coating. The substrate can be a polytetrafluoroethylene membrane (PTFE membrane).

[0081] In S4, the initial catalytic layer on the surface of the substrate is transferred to the surface of one side of the base membrane by hot pressing, and the cathode catalytic layer is attached to the surface of the other side of the base membrane to obtain an initial membrane electrode. The present invention tightly combines the initial catalytic layer on the surface of the substrate, the cathode catalytic layer and the base membrane through hot pressing transfer technology to form an initial membrane electrode. The hot pressing transfer process needs to be carried out at high temperature and high pressure to ensure good contact and adhesion between the catalytic layer and the base membrane, thereby improving the electrochemical performance of the membrane electrode. The cathode catalytic layer can be a Pt loading of 0.3 mg / cm 2 Pt catalytic layer.

[0082] In S5, the surface of the initial catalyst layer in the initial membrane electrode away from the base membrane is subjected to plasma etching to modify the initial catalyst layer to form a modified membrane electrode catalyst layer. Plasma etching uses active gas (such as ozone, 3 、Oxygen 2 、Nitrogen 2At least one of the above) reacts with the surface of the initial catalytic layer in a plasma state to remove or reshape the ionomers and other possible blocking substances on the surface, optimize the pore structure, enhance the mass transfer efficiency, and at the same time improve the hydrophilicity and reduce the resistance to gas transmission.

[0083] In some embodiments, the mass content of the anode catalyst in the first slurry is 15% to 40%, such as 15%, 20%, 25%, 30%, 35%, 40% or any two thereof. The ionomer is 5% to 40% of the mass of the anode catalyst, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or any two thereof.

[0084] The mass of the ionomer in the solution containing the ionomer is 5% to 40% of the mass of the anode catalyst, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or any two thereof.

[0085] The alcohol compound may be a conventional liquid alcohol in the art. In some embodiments, the alcohol compound includes a monovalent or polyvalent liquid alcohol having a carbon number of 1 to 8. For example, the alcohol compound includes at least one of methanol, ethanol, n-propanol, isopropanol, propylene glycol, glycerol, n-butanol, isobutanol, and ethylene glycol. In some embodiments, the mass ratio of water to the alcohol compound is (5 to 8): (2 to 5).

[0086] The present invention does not limit the specific operation steps of ball milling, and conventional ball milling in the art can be used. For example, in some embodiments, the ball milling beads used in ball milling are ZrO 2 The ball milling beads have a particle size of 2.0 to 4.5 mm; the ball milling temperature is 15 to 25° C., the rotation speed is 300 to 1000 rpm, and the time is 2 to 12 hours.

[0087] A third aspect of the present invention provides a proton exchange membrane electrolyzer, comprising the membrane electrode assembly provided in the second aspect.

[0088] Due to the inclusion of the above-mentioned membrane electrode assembly, the proton exchange membrane electrolyzer has excellent electronic conductivity and water gas transmission performance, and can achieve long-term stability testing.

[0089] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0090] Example 1

[0091] The preparation of the modified membrane electrode catalyst layer of this embodiment includes the following steps:

[0092] S1, 0.74g of deionized water, 0.5g of anode catalyst, 0.33g of 15% perfluorosulfonic acid solution, 0.28g of n-propanol and 0.14g of propylene glycol are added to a glass bottle in sequence, and the glass bottle is placed on a magnetic stirrer, and after stirring and dispersing, a first slurry is obtained; the anode catalyst includes TiO 2 Support and loaded on TiO 2 IrO 2 , TiO 2 Support and IrO 2 The mass ratio is 100:50;

[0093] S2, the first slurry is transferred to a ball milling tank filled with ball milling beads for ball milling. After ball milling dispersion, a deaerator is used for mixing and deaeration to obtain a second slurry; a 3.0 mm ZrO 2 Ball milling: constant temperature ball milling at 20 °C, speed of 600 rpm, time of 4 h;

[0094] S3, the second slurry is coated on the PTFE membrane using a slit coater, and the coating amount is 0.500 mg Ir / cm 2 After drying, an initial anode catalyst layer was formed on the surface of the PTFE membrane. The average loading of iridium element was 0.491 mg / cm by XRF detection. 2 ;

[0095] S4, the initial anode catalyst layer on the surface of the PTFE membrane is transferred to one side of the polymer electrolyte membrane by hot pressing, and the anode catalyst layer coated on the PTFE membrane with a loading of 0.3 mg Pt / cm 2 The cathode catalyst layer is transferred to the other side surface of the polymer electrolyte membrane by hot pressing to obtain an initial membrane electrode;

[0096] S5, the initial anode catalyst layer of the initial membrane electrode is placed in the plasma etching chamber with the surface away from the proton exchange membrane upward, and after vacuum evacuation, ozone (O 3 ), maintaining the gas flow rate at 100 mL / min, adjusting the discharge power to 30 W, and the treatment time to 15 min, to obtain the modified membrane electrode of this embodiment.

[0097] Example 2

[0098] The difference from Example 1 is that in S5, the processing time is 60 minutes.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that S5 is omitted and the initial membrane electrode is directly used as the membrane electrode.

[0101] Test example

[0102] 1. Hydrophilicity test

[0103] A drop of water is dropped on the surface of the anode catalyst layer in the membrane electrode, and the angle of contact between the water drop and the material surface is measured. A contact angle of less than 90 degrees indicates a higher hydrophilicity, while a contact angle of more than 90 degrees indicates a lower hydrophilicity.

[0104] 2. Assemble the electrolytic cell in the order of insulating end plate, cathode plate, 0.15mm gasket, carbon paper, membrane electrode, 2.05mm gasket, titanium felt, titanium mesh and anode plate, tighten the electrolytic cell diagonally with a torque wrench (3N·m), and clamp the electrode clamp. Pass water under the working condition of 80℃, and perform the following electrochemical performance tests:

[0105] (1) Polarization performance test method: Use the proton exchange membrane water electrolysis (PEMWE) working condition test equipment to record the current density from the low current density of 0.025A / cm 2 To high current density 5A / cm 2 The cell pressure value of the electrolytic cell is plotted with the current density as the horizontal axis and the cell pressure value of the electrolytic cell as the vertical axis, and a graph of the relationship between the cell pressure value of the electrolytic cell and the current density is drawn.

[0106] (2) Stability test method: Use the proton exchange membrane water electrolysis (PEMWE) working condition test equipment at a temperature of 80°C and a flow rate of 2A / cm 2 The current density was subjected to an 800 h stability test, and the current and voltage values ​​were recorded in real time to evaluate the stability of the electrolytic cell.

[0107] Test results see Figures 1 to 7 .

[0108] Figure 1 The polarization performance curves of the membrane electrodes in Examples 1 to 2 and Comparative Example 1 are shown in FIG. Figure 2 It can be seen that there is no obvious difference in the polarization performance of the membrane electrode of Examples 1-2 and Comparative Example 1.

[0109] Figure 2 The electrochemical impedance spectra of the membrane electrodes in Examples 1 to 2 and Comparative Example 1 are shown in FIG. Figure 3 It can be seen that compared with Comparative Example 1, the charge transfer resistance (Rct) of the membrane electrode of Example 1 is significantly reduced, and the Rct of the membrane electrode of Example 2 is significantly increased. The reduction of Rct means that the transfer of electrons in the catalyst layer is smoother, indicating that the electronic conductivity is improved, which is conducive to the electrochemical reaction. By comparing Example 1 and Example 2, it can be seen that the electron transfer performance and its stability are further improved by moderately etching the catalyst layer, but excessive etching may destroy the catalyst layer structure.

[0110] Figure 3 The stability test curve of the membrane electrode of Examples 1 to 2 and Comparative Example 1 is shown in FIG. Figure 3 It can be seen that compared with Comparative Example 1, the membrane electrode of Example 1 has excellent electron conductivity and water vapor transport performance, and the long-term durability test performance is more stable. By comparing Example 1 and Example 2, it can be seen that moderate etching can ensure that the catalytic layer structure is not damaged, and further improve the electron transport performance, water vapor transport and long-term operation stability, but excessive etching may damage the catalytic layer structure.

[0111] Figure 4 The electrochemical impedance spectra after the membrane electrode stability test in Examples 1 to 2 and Comparative Example 1 are shown in FIG. Figure 4 It can be seen that compared with Comparative Example 1, the mass transfer resistance (Rmt) of the membrane electrode of Example 1 does not change much after 800 hours of long-term operation stability test, indicating that the gas transmission efficiency is good and is conducive to the long-term stable operation of the reaction. The mass transfer resistance of the comparative example and Example 2 increases significantly after the long-term stability test, indicating that the water vapor transmission channels of both are blocked.

[0112] Figures 5 to 7 The contact angle test diagram of the anode catalyst layer in the membrane electrode of Examples 1-2 and Comparative Example 1 is shown in FIG. Figures 5 to 7 It can be seen that the anode catalyst layer in Comparative Example 1 that has not been treated with plasma etching has the largest contact angle and the strongest hydrophobicity, while the anode catalyst layers of Examples 1 and 2 are highly hydrophilic. Among them, the plasma etching treatment time of Example 2 is long, and the contact angle is smaller than that of Example 1, and the hydrophilicity is stronger.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modified membrane electrode catalyst layer, characterized in that: The material of the modified membrane electrode catalyst layer includes an anode catalyst and an ionomer, and one side surface of the modified membrane electrode catalyst layer is treated by plasma etching; wherein the gas used for the plasma etching treatment includes at least one of ozone, oxygen, and nitrogen.

2. The modified membrane electrode catalyst layer according to claim 1, characterized in that: The flow rate of the gas is 50 to 200 mL / min; and / or, The plasma etching process has a discharge power of 5 to 30 W, a temperature of 20 to 25° C., and a time of 10 to 30 min.

3. The modified membrane electrode catalyst layer according to claim 1 or 2, characterized in that: The anode catalyst comprises a supported iridium-based catalyst; Preferably, the supported iridium-based catalyst comprises a carrier and iridium oxide supported on the carrier; wherein the carrier comprises at least one of titanium oxide, niobium oxide, tin oxide, silicon oxide, zirconium oxide, tantalum oxide, cerium oxide, aluminum oxide, and titanium nitride; Preferably, the loading amount of the iridium oxide on the carrier is 10% to 80%.

4. The modified membrane electrode catalyst layer according to claim 1 or 2, characterized in that: The ionomer includes at least one of perfluorosulfonic acid resin, sulfonated polyetheretherketone resin, and sulfonated trifluorostyrene resin.

5. The modified membrane electrode catalyst layer according to claim 1 or 2, characterized in that: The mass ratio of the anode catalyst to the ionomer is 100:(5-40).

6. The modified membrane electrode catalyst layer according to claim 1 or 2, characterized in that: The preparation of the anode catalyst comprises the following steps: S11, ultrasonically mixing the carrier, the iridium precursor and isopropanol to obtain a first mixture; S12, drying the first mixed material to obtain a dried product; S13, mixing the dried product with a molten salt to obtain a second mixed material, and calcining the second mixed material to obtain a calcined product; S14, washing the calcined product to obtain the anode catalyst; Preferably, the calcination treatment is carried out at a temperature of 400 to 500° C. and for a time of 0.5 to 2 h; Preferably, the molten salt comprises NaNO3; Preferably, the molar ratio of the molten salt to the iridium element in the iridium precursor is (20-80):1; Preferably, the iridium precursor comprises H2IrCl6.

7. A membrane electrode assembly, characterized in that: It comprises an anode catalyst layer, a polymer electrolyte membrane and a cathode catalyst layer which are stacked in sequence, wherein the anode catalyst layer is a modified membrane electrode catalyst layer as claimed in any one of claims 1 to 6, and the other side surface of the modified membrane electrode catalyst layer is in contact with the polymer electrolyte membrane.

8. The membrane electrode assembly according to claim 7, characterized in that: The method for preparing the membrane electrode assembly comprises the following steps: S1, mixing an anode catalyst, a solution containing an ionomer, an alcohol compound and water to obtain a first slurry; S2, ball milling and defoaming the first slurry to obtain a second slurry; S3, coating the second slurry on a substrate, and after drying, forming an initial anode catalyst layer on the surface of the substrate; S4, transferring the initial anode catalyst layer on the surface of the substrate to one side of the polymer electrolyte membrane by hot pressing, and preparing a cathode catalyst layer on the other side of the polymer electrolyte membrane by hot pressing transfer or coating to obtain an initial membrane electrode; S5, performing plasma etching on the surface of the initial anode catalyst layer in the initial membrane electrode away from the polymer electrolyte membrane to obtain the membrane electrode assembly.

9. The membrane electrode assembly according to claim 8, characterized in that: The mass content of the anode catalyst in the first slurry is 15% to 40%; and / or, The mass of the ionomer in the solution containing the ionomer is 5% to 40% of the mass of the anode catalyst; and / or, the mass ratio of the water to the alcohol compound is (5 to 8): (2 to 5); and / or, The alcohol compound is a monovalent or polyvalent liquid alcohol having 1 to 8 carbon atoms; Preferably, the alcohol compound includes at least one of methanol, ethanol, n-propanol, isopropanol, propylene glycol, glycerol, n-butanol, isobutanol and ethylene glycol.

10. A proton exchange membrane electrolyzer, characterized in that: A membrane electrode assembly comprising the membrane electrode assembly according to any one of claims 7 to 9.

Images