Method for preparing a continuous graded gradient catalytic layer for an anion exchange membrane electrolysis anode side

Abstract

This invention relates to a method for preparing a continuous gradient catalytic layer on the anode side of anion exchange membrane electrolysis of water, comprising the following steps: (1) Anode catalytic layer slurry preparation: Gradient slurries are prepared for the near-membrane side, the near-PTL side, and the intermediate transition layer of the catalytic layer, respectively. Each slurry includes catalyst particles, ionomer dispersion, and a mixed solvent of isopropanol and water. A stable dispersion system is formed by mixing and ultrasonic vibration; (2) Porous transport layer pretreatment to obtain a sprayable substrate; (3) Gradient catalytic layer preparation: The porous transport layer is used as the substrate, and the catalytic layer is sprayed on one side of the porous transport layer. A slurry with a low mass fraction of ionomer is sprayed on the near-PTL side; a slurry with a high mass fraction of ionomer is sprayed on the near-membrane side; and a transition layer is sprayed in the middle. After spraying, heat treatment is performed; (4) Assembly and testing of the membrane electrode.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water electrolysis, specifically relating to a method for preparing a continuously gradient structure catalyst layer for anodes in water electrolysis. Background Technology

[0002] Anion exchange membrane electrolyzers (AEMWEs) combine the advantages of low cost and non-precious metal compatibility of alkaline water electrolysis (AWE) with the high current density and high gas purity of proton exchange membrane electrolysis (PEMWE). They represent a core technology for next-generation low-cost green hydrogen production and are widely used in renewable energy consumption and other fields. The membrane electrode assembly (MEA) is the core component of AEMWE, with the anode catalyst layer being the site of the oxygen evolution reaction (OER). Its performance directly determines the energy efficiency, cost, and stability of the electrolyzer, making it a crucial element in its development.

[0003] Unlike PEMWE, the ionomers in the AEMWE anode catalyst layer are used to construct continuous OH groups. - The content and distribution of the core medium in the transmission network play a decisive role in the structure and performance of the catalyst layer. Traditional catalyst layers with uniform ionomer distribution have inherent bottlenecks: excessive ionomer content can easily clog pores and cause mass transfer polarization, while insufficient ionomer content can prevent the formation of continuous ion pathways and lead to an increase in ohmic impedance. Especially under pure water or low-concentration alkaline conditions, it is difficult to balance ion conduction and gas diffusion, which becomes the core obstacle to performance improvement.

[0004] Furthermore, existing research largely focuses on the development of catalysts and ionomer materials, lacking systematic studies on the spatial distribution of ionomers, thus failing to fundamentally resolve the contradiction between ion transport and mass transfer. Therefore, by optimizing the spatial distribution of ionomers and constructing a highly efficient gradient anode catalyst layer, the bottleneck of homogeneous structure can be overcome, improving the electrochemical performance of AEMWE, reducing energy consumption and cost, and providing core technological support for its commercial application. The catalyst layer referred to below is the AEMWE anode catalyst layer. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing a continuously graded gradient catalyst layer on the anode side of anion exchange membrane water electrolysis. Specifically, the following solutions are proposed to address the above technical issues: A method for preparing a continuously gradient catalyst layer on the anode side of anion exchange membrane water electrolysis includes the following steps: (1) Preparation of anodic catalyst layer slurry: Gradient slurries for the near-film side, near-PTL side, and intermediate transition layer of the catalyst layer are prepared respectively. Each slurry includes catalyst particles, ionomer dispersion, and a mixed solvent of isopropanol and water. A stable dispersion system is formed by mixing and ultrasonic vibration. The first slurry is the near-PTL side slurry, the second slurry is the intermediate transition layer slurry, and the third slurry is the near-film side slurry of the catalyst layer. The first slurry is a slurry with a low mass fraction of ionomer, the third slurry is a slurry with a low mass fraction of ionomer, and the second slurry is a slurry with an ionomer mass fraction between the two. (2) Pretreatment of porous transport layer to obtain a sprayable substrate; (3) Gradient catalyst layer preparation: The porous transport layer is used as the substrate, and the catalyst layer is sprayed on one side of the porous transport layer. A slurry of low mass fraction ionomer is sprayed on the side near the PTL; a slurry of high mass fraction ionomer is sprayed on the side near the membrane; a transition layer is sprayed in the middle; and heat treatment is performed after the spraying is completed. (4) Assembly and testing of membrane electrode: The gradient catalyst layer prepared in step (3) is stacked and packaged with the anion exchange membrane to complete the assembly of the anion exchange membrane electrolyzer and the electrochemical performance is tested.

[0006] Furthermore, ferric nickel tetraoxonate was used as the catalyst particles; the isopropanol and water mixed solvent was prepared by mixing isopropanol and ultrapure water in a mass ratio of (1.8-2.2):1; the ionomer dispersion was PiperION B5 ionomer dispersion.

[0007] Furthermore, the mass fractions of the ionomer dispersions in the near-film side, near-PTL side, and intermediate transition layer slurry are 5 wt%, 10 wt%, and 30 wt%, respectively.

[0008] Further, the method of step (2) is as follows: the porous transport layer substrate is subjected to decontamination treatment, deoxidation treatment and final treatment in sequence to obtain a sprayable substrate with optimized coating adhesion.

[0009] Furthermore, the method for step (3) is as follows: (1) Preparation of the catalyst layer near the PTL side: The first slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours; (2) Preparation of intermediate transition layer catalyst layer: The second slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours; (3) Preparation of the near-membrane side catalyst layer: The third slurry is sprayed onto the porous transport layer substrate; (4) Vacuum dry for 10 hours at 60°C.

[0010] The technical principles of this invention are explained below: This method involves sequentially spraying a gradient slurry onto a porous transport layer on the anode side, forming a membrane electrode assembly (MEA) together with an anion exchange membrane, a cathode catalyst layer, and a cathode gas diffusion layer. The anode catalyst layer is a three-layer gradient structure prepared using a spraying technique. A low-ionomer mass fraction slurry is sprayed near the porous transport layer to retain efficient water replenishment, while a high-ionomer mass fraction slurry is sprayed near the membrane to construct a continuous ion transport network. This also achieves adequate wettability to optimize bubble desorption, and a transition layer is constructed in the middle to eliminate abrupt compositional changes. This structure can be specifically matched to the needs of different regions, ensuring interfacial bonding strength and ion transport continuity while maximizing the mass transfer efficiency of the catalyst layer. Compared with existing technologies, the above technical solution of this invention has the following advantages: This invention fundamentally solves the inherent contradiction between ion conduction and gas mass transfer in traditional homogenized catalyst layers by constructing a three-layer continuous gradient structure consisting of a high-mass-fraction ionomer near the membrane side and a low-mass-fraction ionomer near the porous transport layer side. The high-mass-fraction ionomer layer is located close to the membrane side, allowing for the construction of a continuous and complete OH- ionomer layer. - The transmission network significantly reduces ohmic impedance, solving the bottleneck of ion transport under pure water conditions; the low mass fraction ionomers near the porous transport layer retain sufficient interconnected pore structure, significantly improving oxygen bubble desorption efficiency and reducing mass transfer polarization; the intermediate transition layer eliminates abrupt changes in interlayer composition and stress concentration, achieving a smooth transition of wettability, ion transport and mass transfer characteristics, enabling the catalyst layer to form an integrated continuous structure, and simultaneously optimizing interfacial bonding strength and structural stability.

[0011] The gradient design of this invention effectively suppresses catalyst particle agglomeration, fully exposes active sites, and improves catalyst utilization. Simultaneously, it optimizes the distribution and stability of the three-phase interface (TPB), significantly reducing the activation overpotential of the oxygen evolution reaction (OER). Experimental data show that the membrane electrode based on the three-layer gradient structure achieves a high activation overpotential at 0.5 A cm⁻¹. -2 The polarization voltage at current density is only 2.1 V, achieving a further performance leap compared to the homogenized structure; its stripping loss rate is as low as 0.147%, which is 8.7% lower than that of the homogenized catalyst layer structure (0.161%), significantly improving the interfacial bonding strength and effectively suppressing the risk of catalyst layer shedding and interfacial delamination during long-term operation. Attached Figure Description

[0012] Appendix Figure 1 Schematic diagram of the gradient catalyst layer Appendix Figure 2 Two-dimensional image of a homogenized catalyst layer cross-section taken using a scanning electron microscope. Appendix Figure 3 This is a two-dimensional image of the gradient catalyst layer cross-section taken using a scanning electron microscope according to the present invention. Appendix Figure 4This is a comparison diagram of the polarization performance of the gradient catalyst layer and the homogenized catalyst layer of the present invention. Appendix Figure 5 This is a comparison of the electrochemical impedance spectroscopy (EIS) of the gradient catalyst layer and the homogenized catalyst layer of this invention. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0014] The technical route for preparing a continuous gradient catalyst layer on the anode side of anion exchange membrane water electrolysis according to the present invention is as follows: (1) Preparation of anodic catalyst layer slurry: Gradient slurries were prepared for the near-membrane side and the near-PTL (Porous Transport Layer) side of the catalyst layer and the intermediate transition layer, respectively. The slurry included catalyst particles, ionomer dispersion, and a mixed solvent of isopropanol and ultrapure water. A stable dispersion system was formed by mixing and ultrasonic vibration. (2) Pretreatment of porous transport layer: The porous transport layer substrate is subjected to decontamination treatment, deoxidation treatment and final treatment in sequence to obtain a sprayable substrate with optimized coating adhesion; (3) Gradient catalyst layer preparation: The porous transport layer is used as the substrate, and the catalyst layer is sprayed on one side of the porous transport layer. A slurry of low mass fraction ionomer is sprayed near the porous transport layer; a slurry of high mass fraction ionomer is sprayed near the membrane side; a transition layer is sprayed in the middle, and heat treatment is performed after the spraying is completed. (4) Assembly and testing of membrane electrode: The gradient catalyst layer prepared in step (3) is stacked and packaged with the anion exchange membrane to complete the assembly of the anion exchange membrane electrolyzer and the electrochemical performance is tested.

[0015] Comparative Example 1: As a comparison, the preparation of the homogenized film electrode follows these steps: (1) Weigh 80 mg of ferric tetroxide using a balance of 0.001 g and place it in a centrifuge tube as catalyst particles.

[0016] (2) Inject the isopropanol and ultrapure water mixture into a centrifuge tube, and then add 10% PiperION B5 ionomer dispersion dropwise to ensure that the catalyst particles and ionomer can be fully dissolved. The mass fraction of PiperION B5 is 30wt%, and the ratio of isopropanol to ultrapure water is 2:1.

[0017] (3) Seal the centrifuge tube and place it on a solution homogenizer for thorough and uniform dispersion.

[0018] (4) Place the mixed solution in an ultrasonic cleaner and treat it at 20°C for 40 minutes; every 10 minutes, take out the centrifuge tube and place it in a vortex mixer for 2 minutes to make the catalyst ink disperse evenly.

[0019] (5) Take an appropriate amount of acetone in a beaker, place the sprayed base stainless steel felt in the beaker, and place the beaker in an ultrasonic cleaner for 15 minutes to thoroughly remove surface oil and grease. (6) Take an appropriate amount of dilute hydrochloric acid into another beaker, place the stainless steel felt in the beaker and sonicate for 15 minutes to remove the surface oxide layer; (7) Place the stainless steel felt substrate in anhydrous ethanol and sonicate for 15 minutes to quickly dehydrate and prevent secondary oxidation, while washing away residual Cl. - To avoid corrosion later; (8) Use nitrogen to dry the stainless steel felt substrate to complete the final treatment of the porous transport layer.

[0020] (9) Take the prepared anode side slurry and spray it evenly on the stainless steel felt substrate. After the spraying is completed, weigh it with a balance and calculate the catalyst loading.

[0021] (10) After the calculation is completed, vacuum dry for 10 hours at 60°C.

[0022] (11) Assemble the homogenized catalyst layer with the anion exchange membrane, the cathode catalyst layer and the cathode gas diffusion layer to form a membrane electrode, and apply a torque of 3 N·m to complete the assembly of the AEMWE electrolyzer.

[0023] (12) The assembled electrolytic cell was tested using an electrochemical workstation.

[0024] Example 1: Preparation of a gradient catalytic membrane electrode on the anode side (this invention) (1) Weigh 80 mg of ferric tetroxide using a balance of 0.001 g / L, divide it into three equal portions and place them in three centrifuge tubes as catalyst particles.

[0025] (2) Inject the isopropanol and ultrapure water mixture into three centrifuge tubes, and then add 10% PiperION B5 ionomer dispersion dropwise to ensure that the catalyst particles and ionomer can be fully dissolved.

[0026] (3) Prepare three different slurries: The first slurry consisted of 30 wt% PiperION B5 and a ratio of isopropanol to ultrapure water of 2:1.

[0027] The second slurry consisted of 10 wt% PiperION B5 and a 2:1 ratio of isopropanol to ultrapure water.

[0028] The third slurry: PiperION B5 with a mass fraction of 5 wt%, and isopropanol to ultrapure water in a ratio of 2:1.

[0029] (4) Seal the centrifuge tube and place it on a solution homogenizer for thorough and uniform dispersion.

[0030] (5) Place the mixed solution in an ultrasonic cleaner and treat it at 20°C for 40 minutes; every 10 minutes, take out the centrifuge tube and place it in a vortex mixer for 2 minutes to make the catalyst ink disperse evenly.

[0031] (6) Take an appropriate amount of acetone in a beaker, place the sprayed base stainless steel felt in the beaker, and place the beaker in an ultrasonic cleaner for 15 minutes to thoroughly remove surface oil and grease. (7) Take an appropriate amount of dilute hydrochloric acid into another beaker, place the stainless steel felt in the beaker and sonicate for 15 minutes to remove the surface oxide layer; (8) Place the stainless steel felt substrate in anhydrous ethanol and sonicate for 15 minutes to rapidly dehydrate and prevent secondary oxidation, while washing away residual Cl. - To avoid corrosion later; (9) Use nitrogen to dry the stainless steel felt substrate to complete the final treatment of the porous transport layer.

[0032] (10) Preparation of catalyst layer near porous transport layer: The first slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours.

[0033] (11) Preparation of intermediate transition layer catalyst: The second slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours.

[0034] (12) Preparation of near-membrane side catalyst layer: The third slurry was sprayed onto the porous transport layer substrate, weighed using a balance, and the catalyst loading was calculated.

[0035] (13) After the calculation is completed, vacuum dry for 10 hours at 60°C.

[0036] (14) Assemble the gradient catalyst layer with the anion exchange membrane, the cathode catalyst layer and the cathode gas diffusion layer to form a membrane electrode, and apply a torque of 3 N·m to complete the assembly of the AEMWE electrolyzer.

[0037] (15) The assembled electrolytic cell was tested using an electrochemical workstation.

[0038] In this embodiment of the invention, two control groups were set up for the experiment on the anolyte catalyst layer. After being assembled into membrane electrodes, they were respectively referred to as the homogenized membrane electrode and the gradient membrane electrode. The cathodes used were both commercially available platinum with a loading of 1 mg / cm³. 2The catalyst layer, the homogenized catalyst layer on the anode side, and the gradient catalyst layer used in this invention both have a ferric tetraoxonate loading of 2.0 mg / cm³. 2 The two-dimensional morphologies of the two anode catalyst layers are as follows: Figure 2 , Figure 3 As shown, polarization performance is compared to, for example Figure 4 As shown, electrochemical impedance spectroscopy for example Figure 5 As shown.

[0039] By controlling the gradient spatial distribution and microstructure of ionomers within the anode catalyst layer, the following key breakthroughs were achieved: (1) Synergistic optimization of transport performance: Construct a three-layer continuous gradient structure with high ionomer near the membrane side and low ionomer near the PTL side to form a continuous and complete OH group on the membrane side. - The transmission network reduces ohmic impedance, retains sufficient interconnected pores on the PTL side to enhance O2 bubble desorption, and the intermediate transition layer eliminates interface abrupt changes, simultaneously optimizing ion conduction and gas-liquid mass transfer, significantly reducing activation and mass transfer overpotential.

[0040] (2) Improved interface stability and lifespan: Gradient distribution effectively alleviates interlayer stress concentration, significantly improves the interfacial bonding strength between the catalyst layer and the membrane and PTL, and reduces the peeling loss rate by more than 8% compared with the uniform structure. It effectively inhibits interfacial delamination and catalyst layer shedding during long-term operation and significantly extends the service life of the membrane electrode.

[0041] (3) Synergistic improvement in performance and cost: at 0.5 A cm -2 At current density, the polarization voltage of the gradient catalyst layer is reduced by more than 6% compared with the homogenized structure, resulting in a significant improvement in electrolysis efficiency.

[0042] This design, starting from the perspective of catalyst layer microstructure engineering, provides a scalable technical path for the efficient, long-life, and low-cost commercial application of AEMWE in pure water conditions.

Claims

1. A method for preparing a continuously gradient catalyst layer on the anode side of anion exchange membrane water electrolysis, comprising the following steps: (1) Preparation of anodic catalyst layer slurry: Gradient slurries for the near-film side, near-PTL side, and intermediate transition layer of the catalyst layer are prepared respectively. Each slurry includes catalyst particles, ionomer dispersion, and a mixed solvent of isopropanol and water. A stable dispersion system is formed by mixing and ultrasonic vibration. The first slurry is the near-PTL side slurry, the second slurry is the intermediate transition layer slurry, and the third slurry is the near-film side slurry of the catalyst layer. The first slurry is a slurry with a low mass fraction of ionomer, the third slurry is a slurry with a low mass fraction of ionomer, and the second slurry is a slurry with an ionomer mass fraction between the two. (2) Pretreatment of porous transport layer to obtain a sprayable substrate; (3) Gradient catalyst layer preparation: The porous transport layer is used as the substrate, and the catalyst layer is sprayed on one side of the porous transport layer. A slurry of low mass fraction ionomer is sprayed on the side near the PTL; a slurry of high mass fraction ionomer is sprayed on the side near the membrane; a transition layer is sprayed in the middle; and heat treatment is performed after the spraying is completed. (4) Assembly and testing of membrane electrode: The gradient catalyst layer prepared in step (3) is stacked and packaged with the anion exchange membrane to complete the assembly of the anion exchange membrane electrolyzer and the electrochemical performance is tested.

2. The method for preparing a continuous gradient catalytic layer on the anode side of anion exchange membrane water electrolysis according to claim 1, characterized in that, Ferric nickel tetraoxonate was used as the catalyst particles; the isopropanol and water mixed solvent was prepared by mixing isopropanol and ultrapure water in a mass ratio of (1.8-2.2):1; the ionomer dispersion was PiperION B5 ionomer dispersion.

3. The method for preparing a continuous gradient catalyst layer on the anode side of anion exchange membrane water electrolysis according to claim 1, characterized in that, The mass fractions of the ionomer dispersions in the near-film side, near-PTL side, and intermediate transition layer slurry were 5 wt%, 10 wt%, and 30 wt%, respectively.

4. The method for preparing a continuous gradient catalytic layer on the anode side of anion exchange membrane water electrolysis according to claim 1, characterized in that, The method of step (2) is as follows: the porous transport layer substrate is subjected to decontamination treatment, oxide layer removal treatment and final treatment in sequence to obtain a sprayable substrate with optimized coating adhesion.

5. The method for preparing a continuous gradient catalyst layer on the anode side of anion exchange membrane water electrolysis according to claim 1, characterized in that, The method for step (3) is as follows: (1) Preparation of the catalyst layer near the PTL side: The first slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours; (2) Preparation of intermediate transition layer catalyst layer: The second slurry was sprayed onto the porous transport layer substrate and heat-treated at 60°C for 2 hours; (3) Preparation of the near-membrane side catalyst layer: The third slurry is sprayed onto the porous transport layer substrate; (4) Vacuum dry for 10 hours at 60°C.

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