A membrane electrode catalytic layer with a gradient pore size structure and its fabrication method

Abstract

This invention relates to the field of membrane electrode technology, and more particularly to a membrane electrode catalytic layer with a gradient pore size structure and its fabrication method. The catalytic layer is hot-pressed onto the side of a proton exchange membrane. The catalytic layer comprises at least three catalytic sublayers. The constituent materials of each catalytic sublayer include ultrapure water, an organic solvent, a catalyst, a foaming agent, and an ionomer. Moving away from the proton exchange membrane, the mass ratio of catalyst to foaming agent in different catalytic sublayers gradually decreases, while the pore size and porosity of the catalytic layer gradually increase. The membrane electrode catalytic layer of this embodiment can reduce the probability of "flooding" of the gas diffusion layer (GDL) and improve the transport performance of battery gases and reactants.

Description

Technical Field

[0001] This invention relates to the field of membrane electrode technology, and in particular to a membrane electrode catalytic layer with a gradient pore size structure and a method for fabricating the same. Background Technology

[0002] The membrane electrode assembly (MEA) is the core component of a proton exchange membrane fuel cell (PEMFC), providing microchannels for multiphase mass transfer and the site for electrochemical reactions. The MEA consists of three parts: the proton exchange membrane (PEM), the catalyst layer (CL), and the gas diffusion layer (GDL), playing a crucial role in promoting the chemical reaction between hydrogen and oxygen to generate electricity. During MEA operation, the catalyst layer is the primary site of the hydrogen-oxygen reaction, and this reaction region involves not only the transfer of electrons and protons but also the transfer of heat and gases, as well as the migration of moisture. Therefore, the design quality of the catalyst layer largely determines the performance of the fuel cell. Since the reaction rate at the anode in a fuel cell is typically several times that at the cathode, the battery's electrical performance is mainly influenced by the design of the cathode catalyst layer.

[0003] To improve the electrical performance of fuel cells, improvements to the fuel cell catalyst layer mainly focus on two aspects: First, by enhancing the performance of materials such as catalysts, carbon paper, and bipolar plates, the performance and lifespan of the fuel cell are improved, while manufacturing costs are reduced. Second, with the development of manufacturing processes, the performance and lifespan of fuel cells are improved, while manufacturing costs are reduced. To date, catalyst layer manufacturing technology has evolved from the gas diffusion electrode (GDE) process to the catalyst-coated proton exchange membrane (CCM) process. Currently, the mainstream manufacturing technology for catalyst layers has shifted to gradient design. This gradient design not only improves the electrical performance of the MEA but also reduces the amount of platinum (Pt) used in the catalyst layer, meeting the operating requirements of fuel cells under low humidity, high current density, and low platinum loading conditions. However, the probability of "flooding" in the gas diffusion layer (GDL) is still high in existing technologies. When excessive water accumulates in the GDL, it blocks gas transport channels, affecting the transport of gases and reactants, thereby reducing battery performance. Summary of the Invention

[0004] To address the problems mentioned above in the background art, the first objective of this invention is to provide a membrane electrode catalytic layer with a gradient pore size structure, which can reduce the probability of "flooding" of the gas diffusion layer (GDL) and improve the performance of battery gas and reactant transport.

[0005] The solution adopted by the present invention to solve its technical problem is: a membrane electrode catalytic layer with a gradient pore size structure, which is hot-pressed onto the side of a proton exchange membrane, and the catalytic layer includes at least three catalytic sublayers;

[0006] The catalyst sublayer is composed of ultrapure water, organic solvent, catalyst, foaming agent and ionomer; in the direction away from the proton exchange membrane, the mass ratio of catalyst to foaming agent in different catalyst sublayers gradually decreases, and the pore size and porosity in the catalyst layer gradually increase.

[0007] Furthermore, the catalyst layer includes a first catalyst sublayer, a second catalyst sublayer, and a third catalyst sublayer; the first catalyst sublayer is formed by coating a first slurry onto the surface of a proton exchange membrane and then drying it, the first slurry including ultrapure water, organic solvent, catalyst, foaming agent, and ionomer; the content of catalyst in the first slurry is 1wt% to 50wt%, the content of organic solvent is 1wt% to 80wt%, the content of ultrapure water is 10wt% to 90wt%, the content of foaming agent is 1wt% to 10wt%, and the content of ionomer is 0.8 to 2 times the content of catalyst;

[0008] The second catalyst layer is formed by coating a second slurry onto the side of the first catalyst layer away from the proton exchange membrane and then drying it. The second slurry includes ultrapure water, an organic solvent, a catalyst, a foaming agent, an ionomer, and a hydrophobic agent. The catalyst content in the second slurry is 1 wt% to 50 wt%, the organic solvent content is 1 wt% to 80 wt%, the ultrapure water content is 10 wt% to 90 wt%, the ionomer content is 0.8 to 2 times the catalyst content, the foaming agent content is 1 wt% to 10 wt%, and the hydrophobic agent content is 1 wt% to 30 wt%. The catalyst content in the second slurry is lower than the catalyst content in the first slurry, and the ionomer content in the second slurry is lower than the ionomer content in the first slurry.

[0009] The third catalyst layer is formed by coating a third slurry onto the side of the second catalyst layer away from the first catalyst layer and then drying it. The third slurry includes ultrapure water, organic solvent, catalyst, foaming agent, ionomer, and hydrophobic agent. The catalyst content in the third slurry is 1wt% to 50wt%, the organic solvent content is 1wt% to 80wt%, the ultrapure water content is 10wt% to 90wt%, the foaming agent content is 1wt% to 10wt%, and the hydrophobic agent content is 1wt% to 30wt%. The catalyst content in the third slurry is lower than that in the second slurry. The ionomer content in the third slurry is lower than that in the second slurry. The hydrophobic agent content in the third slurry is higher than that in the second slurry.

[0010] Furthermore, in the first slurry, the mass ratio of catalyst, ultrapure water, and organic solvent is 1:7:3; the mass ratio of catalyst to foaming agent and ionomer is 1:2:(2-6.9); in the second slurry, the mass ratio of catalyst, ultrapure water, and organic solvent is 1:7:3; the mass ratio of catalyst to foaming agent, ionomer, and hydrophobic agent is 1:(2-3):6.9:0.05; in the third slurry, the catalyst is carbon powder, and the mass ratio of catalyst, ultrapure water, and organic solvent is 1:6:3; the mass ratio of catalyst to foaming agent, ionomer, and hydrophobic agent is 1:5:3.45:0.08.

[0011] Furthermore, the catalyst on the first and second slurries is one or more of Pt / C, PtRu, PtRu / C, PtFe / C, PtCo / C, PtNi / C, PtAu / C, PtPd / C, PtPb / C, and PtMn / C, and the Pt loading in the catalyst is 30wt%-70wt%.

[0012] Furthermore, the hydrophobic agent is one or any combination of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

[0013] Furthermore, the foaming agent is one or more of polystyrene, DNTA, NTA, and ammonium bicarbonate in any combination.

[0014] Furthermore, the ionomer is one or any combination of D2020, D520, and D79-25BS.

[0015] Optionally, the organic solvent in this application may be one or any combination of ethanol, isopropanol, n-propanol, n-butanol, etc.

[0016] The second objective of this invention is to provide a simple method for preparing a membrane electrode catalytic layer, comprising the following steps:

[0017] S1, Preparation of the first slurry

[0018] The catalyst, ultrapure water, and organic solvent were weighed separately. Ultrapure water was added to the catalyst and shaken well. Then the organic solvent was added and sheared and dispersed for 20 minutes to obtain a dispersion. An ionomer solution and a foaming agent were added to the dispersion and sheared and dispersed for another 20 minutes to obtain the first slurry.

[0019] S2, Preparation of the second slurry

[0020] Weigh out the catalyst, ultrapure water and organic solvent separately. Add ultrapure water to the catalyst, shake well and then add the organic solvent. Then shear and disperse the mixture for 20 minutes to obtain a dispersion. Add ionomer solution, foaming agent and hydrophobic agent to the dispersion and shear and disperse it for another 20 minutes to obtain a second slurry.

[0021] S3, Preparation of the third slurry

[0022] Weigh out the catalyst, ultrapure water and organic solvent separately. Add ultrapure water to the catalyst, shake well and then add the organic solvent. Then shear and disperse the mixture for 20 minutes to obtain a dispersion. Add ionomer solution, foaming agent and hydrophobic agent to the dispersion and shear and disperse it for another 20 minutes to obtain the third slurry.

[0023] S4, Fabrication of gradient pore structure membrane electrode

[0024] The first slurry, the second slurry, and the third slurry are sequentially applied to both sides of the proton exchange membrane using a slit coating method. The proton exchange membrane is then placed in a dry air atmosphere for foaming until foaming is complete, forming a cathode catalytic layer and an anode catalytic layer with a gradient pore structure. The cathode catalytic layer includes a first cathode catalytic sublayer, a second cathode catalytic sublayer, and a third cathode catalytic sublayer, and the anode catalytic layer includes a first anode catalytic sublayer, a second anode catalytic sublayer, and a third anode catalytic sublayer.

[0025] Furthermore, in step S4, the foaming temperature is 30-100℃ and the foaming time is 10min-24h.

[0026] In summary, the beneficial effects of the present invention are as follows: by the different foaming speeds of slurries with different concentrations of foaming agent and the influence of temperature gradient transmission on different levels of catalyst sublayers during heating, a gradient distribution of pore structure is formed in the catalyst layer, thereby reducing the probability of "flooding" of the gas diffusion layer and improving the transmission performance of battery gas and reactants.

[0027] Simultaneously, by adjusting the concentrations of catalyst and polytetrafluoroethylene to form a gradient catalyst layer structure and a hydrophilic-hydrophobic structure, an ordered hydrophilic-hydrophobic structure and a gradual pore distribution are achieved, improving the maximum power and stability of the proton exchange membrane fuel cell (PEMFC), thereby producing a high-efficiency, low-cost, and long-life PEMFC.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0029] To make the content of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0030] The D520-Naf ion ionomer solution in the following examples is a Nafi ion solution with a mass concentration of 5%.

[0031] Example 1

[0032] S1, Preparation of the first slurry

[0033] Weigh 1g of Pt / C, 7g of ultrapure water, and 3g of isopropanol, respectively. The platinum content in Pt / C is 50wt%. Add ultrapure water to Pt / C, shake well, and then add isopropanol. Then, shear and disperse the mixture for 20 minutes to obtain a dispersion. Add 6.9g of D520-Nafion ionomer solution and 2g of ammonium bicarbonate to the dispersion, and then shear and disperse it for another 20 minutes to obtain the first slurry.

[0034] S2, Preparation of the second slurry

[0035] Weigh 1g of Pt / C, 7g of ultrapure water, and 3g of isopropanol, respectively. The Pt / C contains 50wt% platinum. Add ultrapure water to the Pt / C, shake well, and then add isopropanol. Shear the mixture for 20 minutes to obtain a dispersion. Add 6.9g of D520-Naf ion ionomer solution, 3g of polystyrene, and 0.05g of 20% PTFE emulsion to the dispersion, and shear the mixture for another 20 minutes to obtain a second slurry.

[0036] S3, Preparation of the third slurry

[0037] Weigh out 2g of VC-72R superconducting carbon powder, 12g of ultrapure water, and 6g of isopropanol. Add ultrapure water to the VC-72R superconducting carbon powder, shake well, and then add isopropanol. Then, shear and disperse the mixture for 20 minutes to obtain a dispersion. Add 3.45g of D520-Naf ion ionomer solution, 5g of polystyrene, and 0.08g of 20% PTFE emulsion to the dispersion, and then shear and disperse the mixture for another 20 minutes to obtain the third slurry.

[0038] S4, Fabrication of gradient pore structure membrane electrode

[0039] The first, second, and third slurries were sequentially applied to both sides of the proton exchange membrane using a slit coating method, until the target Pt loading or carbon loading reached 0.3 mg Pt / cm³. 2 0.1 mg Pt / cm 2 and 0.3 mg C / cm 2 The proton exchange membrane was then placed in a dry air atmosphere at 95°C for foaming for 6 hours. After foaming was complete, a cathode catalytic layer and an anode catalytic layer with a gradient pore structure were formed. The cathode catalytic layer includes a first cathode catalytic sublayer, a second cathode catalytic sublayer, and a third cathode catalytic sublayer. The anode catalytic layer includes a first anode catalytic sublayer, a second anode catalytic sublayer, and a third anode catalytic sublayer.

[0040] Example 2

[0041] S1, Preparation of the first slurry

[0042] Weigh 1g of PtCo / C, 7g of ultrapure water, and 3g of isopropanol, respectively. The platinum content in PtCo / C is 25wt%. Add ultrapure water to PtCo / C, shake well, and then add isopropanol. Then, shear and disperse the mixture for 20 minutes to obtain a dispersion. Add 2g of D520-Naf ion ionomer solution and a foaming agent, wherein the foaming agent is a mixture of 2g of ammonium bicarbonate and 1g of DNTA, to the dispersion. Then, shear and disperse the mixture for another 20 minutes to obtain the first slurry.

[0043] S2, Preparation of the second slurry

[0044] Weigh 1g of Pt / C, 7g of ultrapure water, and 3g of isopropanol, respectively. The Pt / C contains 50wt% platinum. Add ultrapure water to the Pt / C, shake well, and then add isopropanol. Shear the mixture for 20 minutes to obtain a dispersion. Add 6.9g of D520-Naf ion ionomer solution, 3g of polystyrene, and 0.05g of 20% PTFE emulsion to the dispersion, and shear the mixture for another 20 minutes to obtain a second slurry.

[0045] S3, Preparation of the third slurry

[0046] Weigh out 2g of VC-72R superconducting carbon powder, 12g of ultrapure water, and 6g of isopropanol. Add ultrapure water to the VC-72R superconducting carbon powder, shake well, and then add isopropanol. Then, shear and disperse the mixture for 20 minutes to obtain a dispersion. Add 3.45g of D520-Naf ion ionomer solution, 5g of polystyrene, and 0.08g of 20% PTFE emulsion to the dispersion, and then shear and disperse the mixture for another 20 minutes to obtain the third slurry.

[0047] S4, Fabrication of gradient pore structure membrane electrode

[0048] The first, second, and third slurries were sequentially applied to both sides of the proton exchange membrane using a slit coating method, until the target Pt loading or carbon loading reached 0.2 mg Pt / cm³. 2 0.05 mg Pt / cm 2 and 0.2 mg C / cm 2 The proton exchange membrane was then placed in a dry air atmosphere at 95°C for foaming for 6 hours. After foaming was complete, a cathode catalytic layer and an anode catalytic layer with a gradient pore structure were formed. The cathode catalytic layer includes a first cathode catalytic sublayer, a second cathode catalytic sublayer, and a third cathode catalytic sublayer. The anode catalytic layer includes a first anode catalytic sublayer, a second anode catalytic sublayer, and a third anode catalytic sublayer.

[0049] Example 3

[0050] S1, Preparation of the first slurry

[0051] 1g of Pt / C, 7g of ultrapure water, and 3g of isopropanol were weighed separately. The platinum content in the Pt / C was 50wt%. Ultrapure water was added to the Pt / C, and the mixture was shaken well before adding isopropanol. The mixture was then sheared and dispersed for 20 minutes to obtain a dispersion. 6.9g of D520-Nafion ionomer solution and 2g of ammonium bicarbonate were added to the dispersion, and the mixture was sheared and dispersed for another 20 minutes to obtain the first slurry.

[0052] S2, Preparation of the second slurry

[0053] 1g of Pt / C, 0.01g of IrO2, 7g of ultrapure water, and 3g of isopropanol were weighed separately, wherein the platinum content in Pt / C was 50wt%. Pt / C and IrO2 were mixed together to form a catalyst mixture. Ultrapure water was added to the catalyst mixture, and after shaking, isopropanol was added. The mixture was then sheared and dispersed for 20 minutes to obtain a dispersion. 6.9g of D520-Nafion ionomer solution, 2g of polystyrene, and 0.05g of 20% PTFE emulsion were added to the dispersion, and the mixture was sheared and dispersed for another 20 minutes to obtain a second slurry.

[0054] S3, Preparation of the third slurry

[0055] Weigh out 2g of VC-72R superconducting carbon powder, 12g of ultrapure water, and 6g of isopropanol. Add ultrapure water to the VC-72R superconducting carbon powder, shake well, and then add isopropanol. Shear and disperse the mixture for 20 minutes to obtain a dispersion. Add 3.45g of D520-Nafion ionomer solution, 5g of polystyrene, and 0.08g of 20% PTFE emulsion to the dispersion, and shear and disperse the mixture for another 20 minutes to obtain the third slurry.

[0056] S4, Fabrication of gradient pore structure membrane electrode

[0057] The first, second, and third slurries were sequentially applied to both sides of the proton exchange membrane using a slit coating method, until the target Pt loading or carbon loading reached 0.25 mg Pt / cm³. 2 0.1 mg Pt / cm 2 and 0.2 mg C / cm 2 The proton exchange membrane was then placed in a dry air atmosphere at 95°C for foaming for 6 hours. After foaming was complete, a cathode catalytic layer and an anode catalytic layer with a gradient pore structure were formed. The cathode catalytic layer includes a first cathode catalytic sublayer, a second cathode catalytic sublayer, and a third cathode catalytic sublayer. The anode catalytic layer includes a first anode catalytic sublayer, a second anode catalytic sublayer, and a third anode catalytic sublayer.

[0058] The embodiments described above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and modifications made by those skilled in the art based on the invention shall fall within the scope of protection of the present invention.

Claims

1. A membrane electrode catalytic layer with a gradient pore size structure, characterized in that, The catalyst layer is hot-pressed onto the side of the proton exchange membrane, and the catalyst layer includes a first catalyst sublayer, a second catalyst sublayer and a third catalyst sublayer. The catalyst sublayer is composed of ultrapure water, organic solvent, catalyst, foaming agent and ionomer; in the direction away from the proton exchange membrane, the mass ratio of catalyst to foaming agent in different catalyst sublayers gradually decreases, and the pore size and porosity in the catalyst layer gradually increase. The first catalyst sublayer is formed by coating a first slurry onto the surface of a proton exchange membrane and then drying it. The first slurry includes ultrapure water, organic solvent, catalyst, foaming agent, and ionomer. The catalyst content in the first slurry is 1wt% to 50wt%, the organic solvent content is 1wt% to 80wt%, the ultrapure water content is 10wt% to 90wt%, the foaming agent content is 1wt% to 10wt%, and the ionomer content is 0.8 to 2 times the catalyst content. The second catalyst layer is formed by coating a second slurry onto the side of the first catalyst layer away from the proton exchange membrane and then drying it. The second slurry includes ultrapure water, an organic solvent, a catalyst, a foaming agent, an ionomer, and a hydrophobic agent. The catalyst content in the second slurry is 1 wt% to 50 wt%, the organic solvent content is 1 wt% to 80 wt%, and the ultrapure water content is [missing information]. The content of the catalyst in the second slurry is 10wt% to 90wt%, the content of the ionomer is 0.8% to 2 times the content of the catalyst, the content of the foaming agent is 1wt% to 10wt%, and the content of the hydrophobic agent is 1wt% to 30wt%. The content of the catalyst in the second slurry is lower than the content of the catalyst in the first slurry. The content of the ionomer in the second slurry is lower than the content of the ionomer in the first slurry. The third catalyst layer is formed by coating a third slurry onto the side of the second catalyst layer away from the first catalyst layer and then drying it. The third slurry includes ultrapure water, organic solvent, catalyst, foaming agent, ionomer, and hydrophobic agent. The catalyst content in the third slurry is 1wt% to 50wt%, the organic solvent content is 1wt% to 80wt%, the ultrapure water content is 10wt% to 90wt%, the foaming agent content is 1wt% to 10wt%, and the hydrophobic agent content is 1wt% to 30wt%. The catalyst content in the third slurry is lower than that in the second slurry. The ionomer content in the third slurry is lower than that in the second slurry. The hydrophobic agent content in the third slurry is higher than that in the second slurry.

2. The membrane electrode catalytic layer with a gradient pore size structure according to claim 1, characterized in that, The mass ratio of catalyst, ultrapure water, and organic solvent in the first slurry is 1:7:3; the mass ratio of catalyst to foaming agent and ionomer is 1:2:(2-6.9). The mass ratio of catalyst, ultrapure water, and organic solvent in the second slurry is 1:7:3; the mass ratio of catalyst to foaming agent, ionomer, and hydrophobic agent is 1:(2-3):6.9:0.

05. The catalyst in the third slurry is carbon powder, and the mass ratio of the catalyst, ultrapure water, and organic solvent in the third slurry is 1:6:3; the mass ratio of the catalyst to the foaming agent, ionomer, and hydrophobic agent is 1:5:3.45:0.

08.

3. The membrane electrode catalytic layer with a gradient pore size structure according to claim 1, characterized in that, The catalyst on the first and second slurries is one or a mixture of several of Pt / C, PtRu, PtRu / C, PtFe / C, PtCo / C, PtNi / C, PtAu / C, PtPd / C, PtPb / C, and PtMn / C, and the Pt loading in the catalyst is 30wt%-70wt%.

4. The membrane electrode catalytic layer with a gradient pore size structure according to claim 1, characterized in that, The hydrophobic agent is one or any combination of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

5. The membrane electrode catalytic layer with a gradient pore size structure according to claim 1, characterized in that, The foaming agent is one or more of polystyrene, DNTA, NTA, and ammonium bicarbonate in any combination.

6. The membrane electrode catalytic layer with a gradient pore size structure according to claim 1, characterized in that, The ionomer is one or any combination of D2020, D520, and D79-25BS.

7. A method for preparing the membrane electrode catalytic layer according to any one of claims 1-6, characterized in that, Includes the following steps: S1, Preparation of the first slurry The catalyst, ultrapure water, and organic solvent were weighed separately. Ultrapure water was added to the catalyst and shaken well. Then the organic solvent was added and sheared and dispersed for 20 minutes to obtain a dispersion. An ionomer solution and a foaming agent were added to the dispersion and sheared and dispersed for another 20 minutes to obtain the first slurry. S2, Preparation of the second slurry Weigh out the catalyst, ultrapure water and organic solvent separately. Add ultrapure water to the catalyst, shake well and then add the organic solvent. Then shear and disperse the mixture for 20 minutes to obtain a dispersion. Add ionomer solution, foaming agent and hydrophobic agent to the dispersion and shear and disperse it for another 20 minutes to obtain a second slurry. S3, Preparation of the third slurry Weigh out the catalyst, ultrapure water and organic solvent separately. Add ultrapure water to the catalyst, shake well and then add the organic solvent. Then shear and disperse the mixture for 20 minutes to obtain a dispersion. Add ionomer solution, foaming agent and hydrophobic agent to the dispersion and shear and disperse it for another 20 minutes to obtain the third slurry. S4, Fabrication of gradient pore structure membrane electrode The first slurry, the second slurry, and the third slurry are sequentially applied to both sides of the proton exchange membrane using a slit coating method. The proton exchange membrane is then placed in a dry air atmosphere for foaming until foaming is complete, forming a cathode catalytic layer and an anode catalytic layer with a gradient pore structure. The cathode catalytic layer includes a first cathode catalytic sublayer, a second cathode catalytic sublayer, and a third cathode catalytic sublayer, and the anode catalytic layer includes a first anode catalytic sublayer, a second anode catalytic sublayer, and a third anode catalytic sublayer.

8. The preparation method according to claim 7, characterized in that, In step S4, the foaming temperature is 30-100℃ and the foaming time is 10min-24h.