PEM fuel cell membrane electrode and preparation method thereof

Abstract

The invention belongs to the technical field of fuel cells, and particularly relates to a PEM fuel cell membrane electrode and a preparation method thereof. The preparation method of the PEM fuel cell membrane electrode provided by the invention comprises the following steps: preparing composite hydrophilic resin and composite hydrophobic resin, preparing cathode first catalyst layer slurry by adopting the composite hydrophilic resin, and controlling the spraying rate to obtain a cathode first catalyst layer of which the content of the composite hydrophilic resin is gradually changed; preparing cathode second catalyst layer slurry by adopting composite hydrophobic resin, controlling the spraying rate to obtain a cathode second catalyst layer with gradually changed composite hydrophobic resin content, and performing transfer printing and hot pressing on the cathode first catalyst layer, the cathode second catalyst layer, the anode catalyst layer and a proton membrane to obtain a membrane electrode, wherein the content of the composite hydrophilic resin in the first catalyst layer of the cathode is uniformly reduced from top to bottom along the gravity direction, and the content of the composite hydrophobic resin in the second catalyst layer of the cathode is uniformly increased from top to bottom along the gravity direction.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a PEM fuel cell membrane electrode and its preparation method. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is a clean and efficient power generation device that directly converts chemical energy into electrical energy. During its operation, the membrane electrode assembly (MEA) is the core component where the electrochemical reaction occurs, and its internal water management is crucial. Ideally, the proton exchange membrane should be kept sufficiently wet to ensure high proton conductivity, while the reactant gas channels should not be blocked by excessive liquid water to ensure smooth transfer of reactant gases to the catalyst layer. However, in actual operation, especially under high current and high humidity conditions, a large amount of water is generated on the cathode side. Due to gravity, this liquid water naturally migrates and accumulates downwards in the fuel cell, causing "flooding" of the lower half of the MEA (near the ground). Flooding clogs the pores of the porous electrode, hindering the diffusion of reactant gases (such as hydrogen, air / oxygen) to the catalyst layer, resulting in increased mass transfer polarization and a sharp drop in output voltage and power density.

[0003] To address the aforementioned water management challenges, particularly the uneven water distribution between the upper and lower sections caused by gravity, the industry has proposed various technical solutions. These solutions primarily focus on applying hydrophilic or hydrophobic treatments to the catalyst layer (CCM) and gas diffusion layer (GDL) to regulate water distribution and discharge.

[0004] One common approach is to coat a microporous layer with uniform hydrophobicity onto the gas diffusion layer substrate. This homogeneous hydrophobic layer aims to prevent liquid water from accumulating within the pores and allow it to be expelled by gas purging. Another improvement is to attempt to construct a gradient hydrophobic structure, where the hydrophobicity gradually increases from the CCM to the GDL and then to the bilayer plate side, creating a driving force for water expulsion towards the flow channels. While the aforementioned existing technologies improve the water management capabilities of fuel cells to some extent, they still have significant limitations in addressing the specific problem of uneven water distribution at the top and bottom of the membrane electrode assembly due to gravity.

[0005] First, it's impossible to specifically address the difference between the upper and lower parts caused by gravity. Both uniform hydrophobic treatment and longitudinal gradient design involve global, uniform material modification of the entire membrane electrode or gas diffusion layer. This "one-size-fits-all" strategy ignores the objective fact that the bottom accumulates far more water than the top due to the gravitational field. Second, homogeneous hydrophobic treatment may cause the already easily dry upper part of the membrane electrode to become excessively dry, resulting in insufficient wetting of the proton exchange membrane, increased resistance, and poor low-density performance. Conversely, for the lower part with a large amount of accumulated water, its hydrophobicity may be insufficient to effectively drain the excess water, causing the membrane electrode to be flooded at high voltage levels and its performance to degrade.

[0006] Therefore, there is an urgent need for a new water management scheme that can match the distribution of the gravitational field and can treat different regions of the membrane electrode differently in order to simultaneously solve the risk of drying up in the upper part and the problem of flooding in the lower part. Summary of the Invention

[0007] This invention is based on the inventor's discoveries and understanding of the following facts and problems: CN116435525A discloses a gradient gas diffusion layer, with the gradient along the horizontal direction (from gas inlet to outlet), primarily to address the issue of the reactant gas concentration gradually decreasing along the flow channel and the gradual increase in generated water. However, in fuel cells, due to gravity, the accumulation and distribution of liquid water exhibit significant differences mainly in the vertical direction (from top to bottom), with flooding at the bottom being far more severe than at the top. A horizontal wettability gradient is insufficient to effectively remove excess water accumulated at the bottom of the fuel cell.

[0008] CN115241506A discloses a method for preparing a membrane electrode with an ionic liquid gradient distribution along the inlet and outlet directions. However, this method cannot achieve the two different functional requirements of "strong moisturizing" in the top region and "strong drainage" in the bottom region. Furthermore, the high viscosity of the ionic liquid forms a physical barrier, severely hindering the dissolution and diffusion of oxygen within the catalyst layer, leading to a sharp increase in mass transfer polarization. This not only reduces power output but may also alter the reaction pathway. The ionic liquid may also coat the active sites of the platinum catalyst through physical adsorption or specific chemical interactions, reducing the catalyst's activity and thus degrading the membrane electrode performance.

[0009] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for preparing a PEM fuel cell membrane electrode.

[0010] The method for preparing a PEM fuel cell membrane electrode according to an embodiment of the present invention includes the following steps: (1) Preparation of composite hydrophilic resin and composite hydrophobic resin; (2) The first catalytic layer slurry of the cathode is prepared using the composite hydrophilic resin in step (1), the slurry is sprayed onto the substrate, and the first catalytic layer of the cathode is formed after drying. The spraying flow rate is 0.3~3 mL / min, and the spraying rate is linearly increased from 0.1 m / min to 1 m / min. (3) The composite hydrophobic resin in step (1) is used to prepare the cathode second catalyst layer slurry. The slurry is sprayed onto the substrate and dried to form the cathode second catalyst layer. The spraying flow rate is 0.3~3 mL / min and the spraying rate is linearly reduced from 1 m / min to 0.1 m / min. (4) Prepare the anode catalyst layer slurry, spray the slurry onto the substrate, and dry it to form the anode catalyst layer; (5) The cathode first catalyst layer, cathode second catalyst layer, anode catalyst layer and proton membrane are transferred and hot-pressed to obtain membrane electrode; wherein the cathode first catalyst layer is close to the proton membrane, and the content of composite hydrophilic resin in the cathode first catalyst layer decreases uniformly from top to bottom along the direction of gravity, and the cathode second catalyst layer is far away from the proton membrane, and the content of composite hydrophobic resin in the cathode second catalyst layer increases uniformly from top to bottom along the direction of gravity.

[0011] The advantages and technical effects of the PEM fuel cell membrane electrode preparation method of this invention are as follows: 1. The method of this invention implements a structural design for differentiated moisture management in different regions of the membrane electrode (especially the upper and lower parts) to achieve moisture rebalancing that matches the gravitational field distribution; 2. The method of this invention establishes an active and directional moisture transport mechanism in the length direction parallel to the membrane electrode plane (i.e., the spatial dimension from the upper part to the lower part), thereby simultaneously alleviating the flooding phenomenon in the lower part and the tendency of membrane drying in the upper part, and improving the water management capability and overall performance stability of the fuel cell across the entire operating range.

[0012] In some embodiments, in step (1), the composite hydrophilic resin comprises a resin and a hydrophilic agent. The resin is a perfluorosulfonic acid resin. The hydrophilic agent includes at least one of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, fumed hydrophilic nano-silica, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes. The mass ratio of the hydrophilic agent to the resin is (1.5-3):1.

[0013] In some embodiments, the preparation method of the composite hydrophilic resin includes: mixing an aqueous solution of a hydrophilic agent and a n-propanol solution of a resin, then physically crosslinking the mixture in a reflux condenser at 150–200°C and 700–1000 rpm for 3–4 hours, followed by natural cooling, filtration separation, recrystallization purification, and drying.

[0014] In some embodiments, in step (1), the composite hydrophobic resin includes a resin and a hydrophobic agent; The resin is a perfluorosulfonic acid resin; The hydrophobic agent includes at least one of fumed hydrophobic nano silica, polytetrafluoroethylene, polyethylene propylene copolymer, perfluoroalkoxy vinyl ether copolymer, or polyethylene tetrafluoroethylene copolymer. The mass ratio of the hydrophobic agent to the resin is 1:(1.5-3).

[0015] In some embodiments, the preparation method of the composite hydrophobic resin includes: pulverizing a mixture of hydrophobic agent and ethanol in a cell disruptor to form a suspension; mixing the suspension, n-propanol and resin and then physically crosslinking them in a reflux condenser at 200-250 °C and 500-800 rpm for 3-4 hours; and then sequentially performing natural cooling, filtration separation, recrystallization purification and drying.

[0016] In some embodiments, the preparation method of the first catalyst layer slurry in step (2) includes: taking Pt / C catalyst into a ball milling jar, adding deionized water and stirring evenly, and then letting it stand; then adding n-propanol, composite hydrophilic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h; The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophilic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(10~40):(0.5~1.2):(150~250).

[0017] In some embodiments, the preparation method of the second catalyst layer slurry in step (3) includes: weighing Pt / C catalyst and placing it in a ball milling jar, adding deionized water and stirring evenly, and then letting it stand; adding n-propanol, composite hydrophobic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h; The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophobic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(20~40):(0.3~0.5):(150~250).

[0018] In some embodiments, the preparation method of the anode catalyst slurry in step (4) includes: placing Pt / C catalyst and IrO2 into a ball mill jar, adding deionized water to fully wet the catalyst, stirring evenly and then letting it stand; then adding n-propanol, short-chain resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h, wherein the mass ratio of Pt / C catalyst, IrO2, deionized water, n-propanol, short-chain resin and ZrO2 ball milling beads is (0.2~0.3):(20×10⁻⁶). -6 ~40×10 -6 ): (3~10): (20~40): (0.4~0.6): (150~250); And / or, in step (4), the spraying includes stirring the anode catalyst layer slurry at a speed of 200~400 r / min for 20~30 min, transferring the slurry into the injector of the spraying machine, with a spraying flow rate of 0.3~1 mL / min and a spraying rate of 0.1~1 m / min; And / or, in step (4), the drying temperature is 70~90℃ and the drying time is 5~8h.

[0019] In some embodiments, in step (5), the hot pressing temperature is 155~175℃, and the hot pressing pressure is 20~40 kgf / cm². 2 The hot pressing time is 75~200 s.

[0020] This invention also provides a PEM fuel cell membrane electrode, which is prepared using the above-described preparation method. Attached Figure Description

[0021] Figure 1 This is a comparison graph of battery performance for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The method for preparing a PEM fuel cell membrane electrode according to an embodiment of the present invention includes the following steps: (1) Preparation of composite hydrophilic resin and composite hydrophobic resin; (2) The first catalytic layer slurry of the cathode is prepared using the composite hydrophilic resin in step (1), the slurry is sprayed onto the substrate, and the first catalytic layer of the cathode is formed after drying. The spraying flow rate is 0.3~3 mL / min, and the spraying rate is linearly increased from 0.1 m / min to 1 m / min. (3) The composite hydrophobic resin in step (1) is used to prepare the cathode second catalyst layer slurry. The slurry is sprayed onto the substrate and dried to form the cathode second catalyst layer. The spraying flow rate is 0.3~3 mL / min and the spraying rate is linearly reduced from 1 m / min to 0.1 m / min. (4) Prepare the anode catalyst layer slurry, spray the slurry onto the substrate, and dry it to form the anode catalyst layer; (5) The cathode first catalyst layer, cathode second catalyst layer, anode catalyst layer and proton membrane are transferred and hot-pressed to obtain membrane electrode; wherein the cathode first catalyst layer is close to the proton membrane, and the content of composite hydrophilic resin in the cathode first catalyst layer decreases uniformly from top to bottom along the direction of gravity, and the cathode second catalyst layer is far away from the proton membrane, and the content of composite hydrophobic resin in the cathode second catalyst layer increases uniformly from top to bottom along the direction of gravity.

[0024] The method for fabricating the PEM fuel cell membrane electrode of this invention involves a structural design for differentiated moisture management in different regions of the membrane electrode (especially the upper and lower parts) to achieve moisture rebalancing that matches the gravitational field distribution. The method of this invention establishes an active and directional moisture transport mechanism in the length direction parallel to the membrane electrode plane (i.e., the spatial dimension from the upper to the lower part), thereby simultaneously alleviating the flooding phenomenon in the lower part and the tendency of membrane drying in the upper part, and improving the water management capability and overall performance stability of the fuel cell across the entire operating range.

[0025] In some embodiments, preferably, in step (1), the composite hydrophilic resin comprises a resin and a hydrophilic agent. The resin is a perfluorosulfonic acid resin. The hydrophilic agent includes at least one of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, fumed hydrophilic nano-silica, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes. The mass ratio of the hydrophilic agent to the resin is (1.5-3):1.

[0026] In this embodiment of the invention, a composite hydrophilic resin is prepared using perfluorosulfonic acid resin and a hydrophilic agent. Since the side chain of the perfluorosulfonic acid resin has a high affinity with the hydrophilic agent, the hydrophilic agent can be better introduced.

[0027] In some embodiments, preferably, the preparation method of the composite hydrophilic resin includes: mixing an aqueous solution of a hydrophilic agent and a n-propanol solution of a resin, then physically crosslinking the mixture in a reflux condenser at 150–200°C and 700–1000 rpm for 3–4 hours, followed by natural cooling, filtration, recrystallization purification, and drying. The reflux condenser treatment yields a more uniform composite hydrophilic resin solution.

[0028] In some embodiments, preferably, in step (1), the composite hydrophobic resin includes a resin and a hydrophobic agent; The resin is a perfluorosulfonic acid resin; The hydrophobic agent includes at least one of fumed hydrophobic nano silica, polytetrafluoroethylene, polyethylene propylene copolymer, perfluoroalkoxy vinyl ether copolymer, or polyethylene tetrafluoroethylene copolymer. The mass ratio of the hydrophobic agent to the resin is 1:(1.5-3).

[0029] In some embodiments, preferably, the preparation method of the composite hydrophobic resin includes: pulverizing a mixture of hydrophobic agent and ethanol in a cell disruptor to form a suspension; mixing the suspension, n-propanol and resin and then physically crosslinking them in a reflux condenser at 200-250 °C and 500-800 rpm for 3-4 hours; and then sequentially performing natural cooling, filtration separation, recrystallization purification and drying treatment.

[0030] In this embodiment of the invention, a composite hydrophobic resin is prepared using perfluorosulfonic acid resin and a hydrophobic agent, and then pulverized using a cell disruptor. The hydrophobic agent suspension pretreated by the cell disruptor has a small particle size, which makes it easier to achieve uniform dispersion of the hydrophobic agent in the resin matrix at the nano / submicron level during high-temperature physical cross-linking with the resin, forming "intrinsically hydrophobic" composite resin particles. If the hydrophobic agent powder is directly ball-milled and mixed with the resin solution, the hydrophobic agent is very prone to re-agglomeration due to its strong hydrophobicity, forming unstable large particles in the ink, causing cracks in the coating, and affecting the performance and durability of the membrane electrode.

[0031] In some embodiments, preferably, in step (2), the preparation method of the first catalyst layer slurry includes: taking Pt / C catalyst into a ball mill jar, adding deionized water and stirring evenly, and then letting it stand; then adding n-propanol, composite hydrophilic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h; The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophilic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(10~40):(0.5~1.2):(150~250).

[0032] In some embodiments, preferably, in step (2), the total platinum loading in the first catalytic layer of the cathode is 0.1~0.2 mg / cm³. 2 .

[0033] In some embodiments, preferably, in step (3), the preparation method of the second catalyst layer slurry includes: weighing Pt / C catalyst and placing it in a ball milling jar, adding deionized water and stirring evenly, and then letting it stand; adding n-propanol, composite hydrophobic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h; The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophobic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(20~40):(0.3~0.5):(150~250).

[0034] In some embodiments, preferably, in step (2), the total platinum loading in the second catalyst layer of the cathode is 0.2~0.3 mg / cm³. 2 The total platinum loading in the first and second cathode catalyst layers is controlled at 0.4 ± 0.01 mg / cm³. 2 .

[0035] In some embodiments, preferably, the preparation method of the anode catalyst slurry in step (4) includes: placing Pt / C catalyst and IrO2 into a ball mill jar, adding deionized water to fully wet the catalyst, stirring evenly and then letting it stand; then adding n-propanol, short-chain resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h, wherein the mass ratio of Pt / C catalyst, IrO2, deionized water, n-propanol, short-chain resin and ZrO2 ball milling beads is (0.2~0.3):(20×10⁻⁶). -6 ~40×10 -6 ): (3~10): (20~40): (0.4~0.6): (150~250); And / or, in step (4), the spraying includes stirring the anode catalyst layer slurry at a speed of 200~400 r / min for 20~30 min, transferring the slurry into the injector of the spraying machine, with a spraying flow rate of 0.3~1 mL / min and a spraying rate of 0.1~1 m / min; And / or, in step (4), the drying temperature is 70~90℃ and the drying time is 5~8h.

[0036] In some embodiments, preferably, in step (4), the total platinum loading in the anode catalyst layer is 0.05~0.07 mg / cm³. 2 .

[0037] In some embodiments, preferably, in step (5), the hot pressing temperature is 155~175℃, and the hot pressing pressure is 20~40 kgf / cm². 2 The hot pressing time is 75~200 s.

[0038] This invention also provides a PEM fuel cell membrane electrode, which is prepared using the above-described preparation method.

[0039] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0040] Example 1 (1) Preparation of composite hydrophilic resin: 2g of polyvinyl alcohol and 6g of ultrapure water were mixed in a flask. 1g of perfluorosulfonic acid resin dispersed in 25g of n-propanol was added to the flask and mixed. The dispersion was physically crosslinked at 200 ℃ and 800 rpm for 3 hours in a reflux condenser. After the reaction was completed, the mixture was naturally cooled at room temperature. The solution was filtered to obtain composite hydrophilic resin powder. The powder was then purified by recrystallization in ethanol three times and stored in an oven at 110℃ for later use. (2) Preparation of composite hydrophobic resin: 1g of polytetrafluoroethylene was added to 6g of ethanol and mixed. The mixture was crushed in a cell disruptor (250W, 3 seconds on, 2 seconds off) for 30 minutes to form a suspension. 4g of the suspension, 25g of n-propanol and 3g of perfluorosulfonic acid resin were added to a flask and stirred to obtain a dispersion. The dispersion was physically crosslinked in a reflux condenser at 200℃ and 600 rpm for 3 hours. After the reaction was completed, the mixture was naturally cooled at room temperature. The solution was filtered to obtain composite hydrophobic resin powder. The powder was then recrystallized and purified three times in ethanol and stored in an oven at 110℃ for later use. (3) Preparation of the first catalytic layer slurry for the cathode: Weigh 0.2 g of Pt / C catalyst on an analytical balance, place it in a ball mill jar, add 6 g of deionized water to fully wet the catalyst, stir evenly and let stand; add 20 g of n-propanol, 0.8 g of composite hydrophilic resin and 250 g of ZrO2 milling beads in sequence, after sealing the ball mill jar, put it in a ball mill and mill at a speed of 450 r / min for 10 h. Finally, stop the machine and take out the ball mill jar. Filter the milling beads to obtain the slurry, stir the slurry at 300 r / min for 30 min, transfer the slurry to the syringe of the spraying machine, spray flow rate of 0.5 mL / min, control the spraying rate through program logic, the spraying rate increases linearly from 0.1 m / min to 1 m / min, the linear increase rate is 0.1 m / min, and the active area of ​​the membrane electrode is 10 × 20 cm. 2 After spraying, the coating was dried in an oven at 80°C. The platinum loading was calculated using the differential gravimetric method until it reached 0.2 mg / cm³. 2 The coated catalyst layer is placed in a vacuum drying oven and dried at 80°C for 7 hours in a vacuum atmosphere. Then it is taken out and placed in a constant temperature and humidity oven for later use.

[0041] (4) Preparation of the second catalytic layer slurry for the cathode: Weigh 0.2 g of Pt / C catalyst on an analytical balance, place it in a ball mill jar, add 8 g of deionized water to fully wet the catalyst, stir evenly and let stand; add 25 g of n-propanol, 0.4 g of composite hydrophobic resin and 200 g of ZrO2 milling beads in sequence, after sealing the ball mill jar, place it in a ball mill and mill at a speed of 450 r / min for 10 h, finally stop the machine and remove the ball mill jar, filter the milling beads to obtain the slurry, stir the slurry at 300 r / min for 30 min, transfer the slurry to the syringe of the spraying machine, spray flow rate of 0.6 mL / min, control the spraying rate through program logic, the spraying rate decreases linearly from 1 m / min to 0.1 m / min, the linear decrease rate is 0.2 m / min, the active area of ​​the membrane electrode is 10 × 20 cm 2 After spraying, the coating was dried in an oven at 80℃. The platinum loading was calculated using the differential gravimetric method until it reached 0.2 mg / cm³. 2 The coated catalyst layer is placed in a vacuum drying oven and dried at 80°C for 7 hours in a vacuum atmosphere. Then it is taken out and placed in a constant temperature and humidity oven for later use.

[0042] (5) Preparation of anode catalyst slurry: Weigh 0.2g Pt / C catalyst and 25 μg IrO2 on an analytical balance and put them into a ball mill jar. Add 3-10 g of deionized water to fully wet the catalyst, stir evenly and let stand. Add 25g n-propanol, 0.6g short-chain resin and 200g ZrO2 particles in sequence. After the ball mill jar is sealed, put it into a ball mill and ball mill at a speed of 450 r / min for 10 h. Finally, stop the machine and take out the ball mill jar. Filter the ball mill beads to obtain slurry. Stir the slurry at 300 r / min for 30 min. Transfer the slurry to the syringe of the sprayer. Spray flow rate is 0.3 mL / min. Control the spraying rate through program logic. The spraying rate is 0.5 m / min. Place the coated catalyst layer in a vacuum drying oven and dry it at 80℃ for 5-8 h in a vacuum atmosphere. Then take it out and place it in a constant temperature and humidity oven for later use. The total platinum loading in the sprayed anode catalyst layer was calculated to be 0.05 mg / cm³ using the gravimetric method. 2 .

[0043] (6) Thermal transfer: loading of 0.4 / 0.05 mg Pt / cm 2 As cathode / anode catalyst layers, the anode catalyst layer and cathode catalyst layer were transferred onto the Gore 12 proton exchange membrane on a hot press at a temperature of 170°C and a pressure of 30 kgf / cm². 2 The hot pressing process takes 160 seconds. After the hot pressing is completed, the PTFE film is quickly peeled off to obtain the membrane electrode.

[0044] Comparative Example 1 (1) Preparation of composite hydrophilic resin, same as in Example 1; (2) Preparation of cathode catalyst slurry: Weigh 0.2 g of Pt / C catalyst on an analytical balance, place it in a ball mill jar, add 6 g of deionized water to fully wet the catalyst, stir evenly and let stand; add 20 g of n-propanol, 0.8 g of composite hydrophilic resin and 1250 g of ZrO2 milling beads in sequence. After the ball mill jar is sealed, place it in a ball mill and mill at a speed of 450 r / min for 10 h. Finally, stop the machine and remove the ball mill jar. Filter the milling beads to obtain the slurry. Stir the slurry at 300 r / min for 30 min. Transfer the slurry to the syringe of the sprayer. Spray flow rate is 0.5 mL / min. Control the spraying rate through program logic. The spraying rate is 0.5 m / min. The active area of ​​the membrane electrode is 10 × 20 cm. 2 After spraying, the coating was dried in an oven at 80°C. The platinum loading was calculated using the differential gravimetric method until it reached 0.4 mg / cm³. 2 The coated catalyst layer is placed in a vacuum drying oven and dried at 80°C for 5-8 hours in a vacuum atmosphere. Then it is taken out and placed in a constant temperature and humidity oven for later use.

[0045] (3) Prepare the anode catalyst layer slurry, as in Example 1; (4) Heat transfer printing, same as in Example 1.

[0046] Comparative Example 2 (1) Preparation of composite hydrophobic resin, same as in Example 1; (2) Preparation of cathode catalyst slurry: Weigh 0.2 g of Pt / C catalyst on an analytical balance, place it in a ball mill jar, add 8 g of deionized water to fully wet the catalyst, stir evenly and let stand; add 25 g of n-propanol, 0.4 g of composite hydrophobic resin and 200 g of ZrO2 milling beads in sequence. After sealing the ball mill jar, place it in a ball mill and mill at a speed of 450 r / min for 10 h. Finally, stop the machine and remove the ball mill jar. Filter the milling beads to obtain the slurry. Stir the slurry at 300 r / min for 30 min. Transfer the slurry to the syringe of the sprayer. Spray flow rate is 0.6 mL / min. Control the spraying rate through program logic. The spraying rate is 0.5 m / min. The active area of ​​the membrane electrode is 10 × 20 cm. 2 After spraying, the coating was dried in an oven at 80°C. The platinum loading was calculated using the differential gravimetric method until it reached 0.4 mg / cm³. 2 The coated catalyst layer is placed in a vacuum drying oven and dried at 80°C for 5-8 hours in a vacuum atmosphere. Then it is taken out and placed in a constant temperature and humidity oven for later use.

[0047] (3) Prepare the anode catalyst layer slurry, as in Example 1; (4) Heat transfer printing, same as in Example 1.

[0048] Comparative Example 3 (1) Preparation of cathodic layer slurry: Weigh 0.2g of Pt / C catalyst on an analytical balance, put it into a ball mill jar, add 3-10g of deionized water to fully wet the catalyst, stir evenly and let stand; add 25g of n-propanol, add 0.4g of short-chain resin and 200g of ZrO2 milling beads to the slurry, and after the ball mill jar is sealed, put it into a ball mill and mill at a speed of 450 r / min for 10 h. Finally, stop the machine and take out the ball mill jar. Filter the milling beads to obtain the slurry. Stir the slurry at 300 r / min for 30 min. Transfer the slurry to the syringe of the sprayer and spray at a flow rate of 0.5 mL / min. Control the spraying rate through the program logic. The spraying rate is 0.5 m / min. Place the coated catalyst layer in a vacuum drying oven and dry it at 80℃ in a vacuum atmosphere for 5-8 h. Then take it out and place it in a constant temperature and humidity oven for later use. The total platinum loading of the sprayed anode was calculated to be 0.4 mg / cm³ using the gravimetric method. 2 .

[0049] (3) Prepare the anode catalyst layer slurry, as in Example 1; (4) Heat transfer printing, same as in Example 1.

[0050] Comparative Example 4 The preparation method of this comparative example is the same as that of Example 1, except that: In step (3), the spraying rate is 0.5 m / min; In step (4), the spraying rate is 0.5 m / min.

[0051] Battery polarization performance, proton conduction, oxygen transport resistance, and constant current durability tests were conducted on the membrane electrodes of Examples 1 and 1-4. The results are as follows: Figure 1 As shown in Table 1: Among them, the battery polarization performance test: the anode and cathode areas are both 10×20 cm. 2 The prepared membrane electrode was directly clamped between two gas diffusion layers and tested using a fuel cell test fixture with a serpentine flow field. The cell temperature was 80℃, the humidification was RH 10% / 10%, the initial flow rates on the H2 side and the air side were set to 0.3 / 0.7 NLPM, the excess coefficient was 1.5 / 2.0, and the back pressure was 100kPa / 100kPa.

[0052] Proton conduction test: The area of ​​both the anode and cathode is 1×3 cm. 2The transferred CCM is directly sandwiched between two gas diffusion layers. The system is H2 / N2, with a battery temperature of 80℃, anode and cathode humidification at 80% / 80%RH, flow rate of 1 / 1 NLPM, back pressure of 0 / 0 kPa, purging for at least 30 minutes, voltage drop of less than 2mV within 5 minutes, bias voltage set at 0.45V, scan range of 0.2-100000Hz, and amplitude of 10mV.

[0053] Oxygen transport resistance test: Anode and cathode areas are both 1×3 cm² 2 With the battery temperature at 80℃ and humidification at 70% / 70%, the cathode gas was a 0.5% O2 / N2 mixture, the fixed flow rate was set to 1.8 / 4.5 NLPM, and the back pressure was 110 / 110 kPa. After the limiting current test was completed with low oxygen concentration gas, the limiting current tests were completed with all nine different oxygen concentrations under different back pressures in the order from low oxygen concentration to high oxygen concentration (1%, 2%, 3%, 4%, 8%, 12%, 16%, 21%).

[0054] Constant current endurance test: Anode and cathode areas are both 10 × 20 cm² 2 The transferred CCM is directly sandwiched between two gas diffusion layers. The battery temperature is 80℃, H2 / air flow rate is 2 / 6 NLPM, back pressure is 100 / 100 kPa, and anode / cathode humidification is 10% / 40%. The positive electrode of the electrochemical potentiostat is connected to the cathode of the battery, and the negative electrode is connected to the anode, with a constant current density of 0.3 A / cm². 2 and 1.7 A / cm 2 The voltage change over time was investigated.

[0055] Table 1

[0056] As shown in Table 1, proton conduction resistance tests were conducted on the membrane electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The proton transport resistance of Example 1 and Comparative Example 1 was lower than that of Comparative Example 2 and Comparative Example 3. This is because the membrane electrodes of Example 1 and Comparative Example 1 had a hydrophilic design in the first catalytic layer, which increased the water retention capacity of the membrane electrode. Protons could then jump from an oxygen atom on a water molecule to an oxygen atom on an adjacent water molecule through a hydrogen bond network, thus achieving directional conduction. Under low electron density and water-deficient conditions, the increased water retention capacity of the membrane electrode promotes directional proton conduction. The proton conduction resistance of Comparative Example 4 was higher than that of Example 1. This is because the homogeneous hydrophilic design may cause water to accumulate in the lower half of the membrane electrode under gravity, making the upper half more prone to dehydration and thus increasing the proton conduction resistance.

[0057] As shown in Table 1, oxygen transport resistance tests were conducted on the membrane electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The oxygen transport resistance of Example 1 and Comparative Example 2 was lower than that of Comparative Example 1 and Comparative Example 3. This is because the membrane electrodes of Example 1 and Comparative Example 2 incorporated a hydrophobic design in the second catalyst layer, making it easier for the membrane electrode to drain water, preventing flooding, and improving oxygen mass transfer capacity. The oxygen transport resistance of Comparative Example 4 was higher than that of Example 1. This is because the homogeneous hydrophobic design may cause the generated water to tend to accumulate in the lower half of the membrane electrode under gravity, leading to a "flooding" phenomenon in this area. Flooding hinders the diffusion of oxygen to the active sites of the catalyst, resulting in increased oxygen transport resistance and ultimately affecting battery performance.

[0058] As shown in Table 1, the membrane electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were subjected to a constant current density of 0.3 A / cm. 2 and 1.7A / cm 2 Durability test at 0.3 A / cm 2 After 500 hours of operation, the attenuation rates of Example 1 and Comparative Example 1 were lower than those of Example 2 and Comparative Example 3. This is because the membrane electrodes of Example 1 and Comparative Example 1 were designed with hydrophilic properties. When the electrostatic density is low and water production is low, the hydrophilic membrane electrode can absorb the reacting water to form bound water, which can wet the proton exchange membrane and reduce the polarization voltage loss caused by ohmic loss. At 1.7 A / cm 2 After 500 hours of operation, the decay rate of Example 1 and Comparative Example 2 was less than that of Comparative Example 1 and Comparative Example 4. This was because the membrane electrode of Example 1 and Comparative Example 2 was designed to be hydrophobic. Due to the high electrical density, more water was produced. Under the superimposed effect of gravity, more water was stored at the bottom of the membrane electrode. The hydrophobic gradient design could discharge the reaction water into the flow channel more efficiently, preventing the membrane electrode from being flooded. The ability of oxygen to diffuse to the reaction three-phase interface was increased, reducing the polarization loss of the oxygen reduction reaction.

[0059] from Figure 1 It can be seen from this that in the electrochemical polarization region (0-600 mA / cm) -2 In Example 1, the membrane electrode's battery performance is superior to that of Comparative Example 1. This is because the second layer of the membrane electrode in Example 1 features a hydrophobic design, which prevents flooding at the outlet where water is abundant due to gravity, thus improving oxygen transport capacity and slightly enhancing low-electrical-density performance. In the electrochemical polarization region, the membrane electrode in Comparative Example 1 outperforms the membrane electrodes in Comparative Examples 2 and 3. This is because the first layer of the membrane electrode in Comparative Example 1 features a hydrophilic design, making it easier to retain water at low electrical density, thus improving proton conductivity and low-electrical-density performance. In the mass transfer region (>1000 mA / cm²), -2The performance of the membrane electrode in Example 1 is close to that of the membrane electrode in Comparative Example 2, and superior to that of Comparative Example 1 and Comparative Example 3. This is because water generated under high electrical density is more likely to accumulate at the outlet due to gravity. The second layer of the membrane electrodes in Examples 1 and Comparative Example 2 features a hydrophobic design, making it easier for water accumulated at the outlet to drain, preventing flooding of the membrane electrode, thereby improving the oxygen mass transfer capacity of the membrane electrode and thus enhancing its performance under high electrical density. The performance of the membrane electrode in Comparative Example 1 is lower than that in Comparative Example 3. This is because the hydrophilic structure of the membrane electrode makes it more prone to flooding under high electrical density, hindering oxygen transport and thus reducing its performance in the high electrical density mass transfer region.

[0060] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a PEM fuel cell membrane electrode, characterized in that, Includes the following steps: (1) Preparation of composite hydrophilic resin and composite hydrophobic resin; (2) The first catalytic layer slurry of the cathode is prepared using the composite hydrophilic resin in step (1), the slurry is sprayed onto the substrate, and the first catalytic layer of the cathode is formed after drying. The spraying flow rate is 0.3~3 mL / min, and the spraying rate is linearly increased from 0.1 m / min to 1 m / min. (3) The composite hydrophobic resin in step (1) is used to prepare the cathode second catalyst layer slurry. The slurry is sprayed onto the substrate and dried to form the cathode second catalyst layer. The spraying flow rate is 0.3~3 mL / min and the spraying rate is linearly reduced from 1 m / min to 0.1 m / min. (4) Prepare the anode catalyst layer slurry, spray the slurry onto the substrate, and dry it to form the anode catalyst layer; (5) The cathode first catalyst layer, cathode second catalyst layer, anode catalyst layer and proton membrane are transferred and hot-pressed to obtain membrane electrode; wherein the cathode first catalyst layer is close to the proton membrane, and the content of composite hydrophilic resin in the cathode first catalyst layer decreases uniformly from top to bottom along the direction of gravity, and the cathode second catalyst layer is far away from the proton membrane, and the content of composite hydrophobic resin in the cathode second catalyst layer increases uniformly from top to bottom along the direction of gravity.

2. The method for preparing the PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (1), the composite hydrophilic resin includes a resin and a hydrophilic agent. The resin is a perfluorosulfonic acid resin. The hydrophilic agent includes at least one of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, fumed hydrophilic nano-silica, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes. The mass ratio of the hydrophilic agent to the resin is (1.5-3):

1.

3. The method for preparing the PEM fuel cell membrane electrode according to claim 2, characterized in that, The preparation method of the composite hydrophilic resin includes: mixing an aqueous solution of the hydrophilic agent and a n-propanol solution of the resin, and then physically crosslinking them in a reflux condenser at 150-200°C and 700-1000 rpm for 3-4 hours, followed by natural cooling, filtration separation, recrystallization purification and drying.

4. The method for preparing the PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (1), the composite hydrophobic resin includes a resin and a hydrophobic agent; The resin is a perfluorosulfonic acid resin; The hydrophobic agent includes at least one of fumed hydrophobic nano silica, polytetrafluoroethylene, polyethylene propylene copolymer, perfluoroalkoxy vinyl ether copolymer, or polyethylene tetrafluoroethylene copolymer. The mass ratio of the hydrophobic agent to the resin is 1:(1.5-3).

5. The method for preparing the PEM fuel cell membrane electrode according to claim 4, characterized in that, The preparation method of the composite hydrophobic resin includes: crushing a mixture of hydrophobic agent and ethanol in a cell disruptor to form a suspension; mixing the suspension, n-propanol and resin and then physically crosslinking them in a reflux condenser at 200-250 °C and 500-800 rpm for 3-4 hours; and then sequentially performing natural cooling, filtration separation, recrystallization purification and drying.

6. The method for preparing the PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (2), the preparation method of the first catalyst layer slurry includes: taking Pt / C catalyst into a ball mill jar, adding deionized water and stirring evenly, and then letting it stand; then adding n-propanol, composite hydrophilic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h. The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophilic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(10~40):(0.5~1.2):(150~250).

7. The method for preparing the PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (3), the preparation method of the second catalyst layer slurry includes: weighing Pt / C catalyst and putting it into a ball milling jar, adding deionized water and stirring evenly, and then letting it stand; adding n-propanol, composite hydrophobic resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h; The mass ratio of the Pt / C catalyst, deionized water, n-propanol, composite hydrophobic resin and ZrO2 milling beads is (0.2~0.3):(3~10):(20~40):(0.3~0.5):(150~250).

8. The method for preparing the PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (4), the preparation method of the anode catalyst slurry includes: placing Pt / C catalyst and IrO2 into a ball mill jar, adding deionized water to fully wet the catalyst, stirring evenly and then letting it stand; then adding n-propanol, short-chain resin and ZrO2 ball milling beads in sequence, and ball milling at a speed of 400~500 r / min for 8~12 h, wherein the mass ratio of Pt / C catalyst, IrO2, deionized water, n-propanol, short-chain resin and ZrO2 ball milling beads is (0.2~0.3):(20×10 -6 ~40×10 -6 ): (3~10): (20~40): (0.4~0.6): (150~250); And / or, in step (4), the spraying includes stirring the anode catalyst layer slurry at a speed of 200~400 r / min for 20~30 min, transferring the slurry into the injector of the spraying machine, with a spraying flow rate of 0.3~1 mL / min and a spraying rate of 0.1~1 m / min; And / or, in step (4), the drying temperature is 70~90℃ and the drying time is 5~8h.

9. The method for preparing a PEM fuel cell membrane electrode according to claim 1, characterized in that, In step (5), the hot pressing temperature is 155~175℃, and the hot pressing pressure is 20~40 kgf / cm². 2 The hot pressing time is 75~200 s.

10. A PEM fuel cell membrane electrode, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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