Fuel cell gradient pore distribution dual-catalyst layer cathode and preparation method thereof

Abstract

The application discloses a preparation method of a fuel cell gradient hole distribution double-catalyst layer cathode, which comprises the following steps: preparing a diffusion layer; coating outer catalyst layer slurry on the surface of the diffusion layer to obtain an outer catalyst layer; the outer catalyst layer slurry comprises a precious metal platinum carrier-based catalyst, an ionomer and a pore-forming agent; the porosity of the outer catalyst layer is 40%-50%, and the average pore size is 0.5-5 mu m; coating inner catalyst layer slurry on the surface of the outer catalyst layer to obtain an inner catalyst layer; the inner catalyst layer slurry comprises a precious metal platinum carrier-based catalyst, an ionomer and a pore-forming agent; the porosity of the inner catalyst layer is 20%-30%, and the average pore size is 0.05-1 mu m. The application further discloses a fuel cell gradient hole distribution double-catalyst layer cathode obtained by the above method. The application can effectively construct an electrochemical reaction three-phase interface, improve the utilization rate of a precious metal catalyst, and realize controllable preparation of a low-platinum high-efficiency gas diffusion electrode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to a high-temperature proton exchange membrane fuel cell gradient pore distribution double-catalyst layer cathode and a preparation method thereof. BACKGROUND

[0002] High-temperature proton exchange membrane fuel cells (HT-PEMFCs) can effectively solve the hydrogen source problem and help achieve the dual-carbon target due to strong CO tolerance, direct reforming gas feeding, and simple water thermal management. As the core component of HT-PEMFCs, HT-PEMFC membrane electrodes have attracted much attention in recent years, especially the phosphoric acid-doped polybenzimidazole (PA-PBI) membrane electrode with the most promising application.

[0003] The structure, components and preparation process of the HT-PEMFC membrane electrode of the phosphoric acid-doped PBI system are different from those of the low-temperature PEMFC. In addition, due to the adsorption of phosphate ions on the surface of the catalyst and the low solubility of O2 in phosphoric acid, the HT-PEMFC membrane electrode has problems such as high catalyst consumption and low utilization rate. Therefore, improving catalyst utilization efficiency and reducing Pt loading have become the main goals of the development of HT-PEMFC membrane electrodes.

[0004] The traditional high-temperature proton exchange membrane membrane electrode cathode is mostly single-layer, with single porosity and pore size. The cathode catalyst near the phosphoric acid impregnated proton exchange membrane is easily flooded by acid, and the catalyst in the internal cathode catalyst layer is difficult to build a three-phase interface for electrochemical reaction due to the lack of phosphoric acid, which cannot be effectively utilized, resulting in a high cathode catalyst loading of 1.0-2.0 mg / cm 2 , which not only increases the preparation cost, but also causes the thickness of the catalyst layer to increase, affecting gas mass transfer and further reducing the utilization rate of the catalyst. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned defects, and provide a fuel cell gradient pore distribution double-catalyst layer cathode and a preparation method thereof, which solves the technical problem of low utilization rate of the existing high-temperature proton exchange membrane membrane electrode cathode catalyst. The present application can effectively build a three-phase interface for electrochemical reaction, improve the utilization rate of noble metal catalysts, and realize the controllable preparation of low-platinum high-efficiency gas diffusion electrodes.

[0006] To achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The application discloses a high-temperature proton exchange membrane fuel cell gradient pore distribution double catalytic layer cathode, mainly comprising a diffusion layer, an outer catalytic layer and an inner catalytic layer; the diffusion layer is composed of a support layer and a microporous layer. The outer catalytic layer is composed of a noble metal-based catalyst and an ionomer, has a relatively high porosity and a relatively large pore diameter; the inner catalytic layer is composed of a platinum-based catalyst and an ionomer, has a relatively low porosity and a relatively small pore diameter; the gradient pore distribution double catalytic layer cathode is prepared by using a GDE process, and the gradient pore distribution double catalytic layer cathode is prepared by adding a pore-forming agent into the slurry of the outer catalytic layer and the inner catalytic layer and adjusting the type and content of the pore-forming agent. Compared with a traditional cathode with uniform pore distribution, the gradient pore distribution double catalytic layer cathode prepared by the application can realize uniform distribution of phosphoric acid, avoid local acid flooding, effectively construct an electrochemical reaction three-phase interface, improve the utilization rate of the noble metal catalyst and realize controllable preparation of a low-platinum high-efficiency gas diffusion electrode.

[0008] Specifically, a preparation method of a fuel cell gradient pore distribution double catalytic layer cathode comprises the following steps.

[0009] Preparation of the diffusion layer

[0010] Coating of the outer catalytic layer slurry on the surface of the diffusion layer to obtain the outer catalytic layer; the outer catalytic layer slurry comprises a noble metal platinum-based catalyst, an ionomer and a pore-forming agent; the porosity of the outer catalytic layer is 40% to 50%, and the average pore size is 0.5 to 5 mu m;

[0011] Coating of the inner catalytic layer slurry on the surface of the outer catalytic layer to obtain the inner catalytic layer; the inner catalytic layer slurry comprises a noble metal platinum-based catalyst, an ionomer and a pore-forming agent; the porosity of the inner catalytic layer is 20% to 30%, and the average pore size is 0.05 to 1 mu m.

[0012] Further, the diffusion layer comprises a support layer and a microporous layer, and the method for preparing the diffusion layer comprises the following steps.

[0013] Immersion of carbon cloth or carbon paper into a PTFE emulsion, and obtaining the hydrophobic carbon cloth or carbon paper after taking out;

[0014] Heat treatment of the hydrophobic carbon cloth or carbon paper to obtain the support layer;

[0015] Mixing of carbon powder and the PTFE emulsion to obtain a microporous layer slurry;

[0016] Coating of the microporous layer slurry on the surface of the support layer to obtain the microporous layer, and then heat treatment of the obtained product to obtain the diffusion layer.

[0017] Further, the mass percentage of PTFE in the support layer is 5% to 25%;

[0018] The heat treatment condition of the hydrophobic carbon cloth or carbon paper is heat treatment at 340 to 360 DEG C for 0.1 to 2 hours;

[0019] The carbon powder has a loading of 1-3 mg / cm in the microporous layer 2 The PTFE has a mass percentage of 10%-30%;

[0020] The heat treatment of the obtained product is performed at 340-360℃ for 0.1-2h.

[0021] Further, the noble metal in the noble metal supported platinum-based catalyst is one or more of Pt, Pd or PtPd alloy;

[0022] The ionomer is one or more of PTFE or PVDF;

[0023] The pore-forming agent is one or more of ammonium bicarbonate, ammonium oxalate, ammonium nitrate, ammonium carbonate or ammonium sulfate.

[0024] Further, the preparation method of the outer catalytic layer slurry comprises:

[0025] The noble metal supported platinum-based catalyst is uniformly dispersed in the solvent to obtain a first catalyst slurry;

[0026] The ionomer aqueous solution is prepared, and the pore-forming agent is added into the ionomer aqueous solution to obtain a first solution which is uniform and transparent after uniform dispersion; the mass percentage of the ionomer in the ionomer aqueous solution is 0.5-10%, and the mass ratio of the ionomer to the pore-forming agent in the first solution is 1 / 10-10 / 1;

[0027] The first solution is dropped into the first catalyst slurry to obtain an outer catalytic layer slurry after uniform dispersion; in the outer catalytic layer slurry, the mass of the pore-forming agent is 10%-20% of the total mass of the noble metal supported platinum-based catalyst, the ionomer and the pore-forming agent (not including the solvent).

[0028] Further, the preparation method of the inner catalytic layer slurry comprises:

[0029] The noble metal supported platinum-based catalyst is uniformly dispersed in the solvent to obtain a second catalyst slurry;

[0030] The ionomer aqueous solution is prepared, and the pore-forming agent is added into the ionomer aqueous solution to obtain a second solution which is uniform and transparent after uniform dispersion; the mass percentage of the ionomer in the ionomer aqueous solution is 0.5-10%, and the mass ratio of the ionomer to the pore-forming agent in the first solution is 1 / 10-10 / 1;

[0031] The second solution is dropped into the second catalyst slurry to obtain an inner catalytic layer slurry after uniform dispersion; in the inner catalytic layer slurry, the mass of the pore-forming agent is 5%-10% of the total mass of the noble metal supported platinum-based catalyst, the ionomer and the pore-forming agent (not including the solvent).

[0032] Further, the method for coating the outer catalytic layer slurry on the surface of the diffusion layer includes ultrasonic spraying, silk screen printing or slit direct coating, after coating the outer catalytic layer slurry on the surface of the diffusion layer, the obtained product is placed into a muffle furnace and calcined at 300-400 DEG C for 0.5-2 hours, to obtain the outer catalytic layer;

[0033] The method for coating the inner catalytic layer slurry on the surface of the outer catalytic layer includes ultrasonic spraying, silk screen printing or slit direct coating, after coating the inner catalytic layer slurry on the surface of the outer catalytic layer, the obtained product is placed into a muffle furnace and calcined at 300-400 DEG C for 0.5-2 hours, to obtain the inner catalytic layer.

[0034] Further, in the obtained outer catalytic layer, the mass percentage of the pore-forming agent is 10-20%; in the obtained inner catalytic layer, the mass percentage of the pore-forming agent is 5-10%;

[0035] In the outer catalytic layer and the inner catalytic layer, the loading of the precious metal platinum-based catalyst is 0.05-0.5 mg / cm 2 .

[0036] Further, the total thickness of the diffusion layer, the outer catalytic layer and the inner catalytic layer is 120-300 mu m.

[0037] A fuel cell gradient pore distribution double catalytic layer cathode is obtained by the above-mentioned method for preparing a fuel cell gradient pore distribution double catalytic layer cathode, and includes a diffusion layer, an outer catalytic layer and an inner catalytic layer.

[0038] In the outer catalytic layer and the inner catalytic layer, the loading of the precious metal platinum-based catalyst is 0.05-0.5 mg / cm 2 .

[0039] The porosity of the outer catalytic layer is 40-50%, and the average pore size is 0.5-5 mu m;

[0040] The porosity of the inner catalytic layer is 20-30%, and the average pore size is 0.05-1 mu m.

[0041] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0042] (1) The present application creatively proposes a method for preparing a double catalytic layer cathode, and a gradient pore distribution double catalytic layer cathode is prepared on the surface of the diffusion layer, which can effectively construct an electrochemical reaction three-phase interface and improve the utilization rate of the precious metal catalyst;

[0043] (2) By adding a pore-forming agent to the outer catalytic layer and the inner catalytic layer slurry and adjusting the type and content of the pore-forming agent, the present application can realize controllable preparation of a low-platinum high-efficiency gas diffusion electrode;

[0044] (3) The present application gives the optimal porosity and pore size range of the double catalytic layer, under which the double catalytic layer cathode can achieve the optimal cost and performance at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 SEM image of the cross section of the gradient-pore-distribution double catalytic layer cathode obtained in Example 1 of the present application;

[0046] Figure 2 Polarization curves of membrane electrodes with different cathode catalytic layer structures;

[0047] Figure 3 Impedance diagrams of membrane electrodes with different cathode catalytic layer structures;

[0048] Figure 4 Cyclic voltammograms of membrane electrodes with different cathode catalytic layer structures. DETAILED DESCRIPTION

[0049] The features and advantages of the present application will become more apparent from the detailed description in which:

[0050] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. Unless specifically stated otherwise, the present disclosure is not to be construed as using terms or phrases such as "example," "for example," or "exemplary" in a way that would require one of skill in the art to conclude that a feature described in relation to only one implementation is a required feature of all implementations. The terms "plurality" and "a plurality" as used herein mean "two or more than two." The terms "another," "an additional" and "yet another" as used herein mean "at least a second" or "at least a third."

[0051] The present application provides a gradient-pore-distribution double catalytic layer cathode for high-temperature proton exchange membrane fuel cells and a preparation method thereof.

[0052] The gradient-pore-distribution double catalytic layer cathode of the present application mainly comprises a diffusion layer, an outer catalytic layer, and an inner catalytic layer.

[0053] The diffusion layer comprises a support layer and a microporous layer. The gradient-pore-distribution double catalytic layer cathode is prepared by the GDE process, and by adding pore-forming agents to the slurry of the outer catalytic layer and the inner catalytic layer and adjusting the types and contents of the pore-forming agents, the gradient-pore-distribution double catalytic layer cathode is prepared.

[0054] The support layer is prepared by immersing carbon cloth or carbon paper in 2%-20% PTFE emulsion for about 10-100 seconds, and the percentage of PTFE in the support layer is calculated accordingly. The above-mentioned immersion and drying process is repeated until the PTFE loading of the support layer is 5-25 wt.%. Finally, the hydrophobic carbon cloth or carbon paper is placed in a muffle furnace and heat-treated at 340-360℃ for 0.1-2h, and then taken out after cooling to room temperature.

[0055] The preparation method of the microporous layer is as follows: carbon powder and PTFE emulsion are mixed, a proper amount of ethanol is added, and a slurry is prepared by ultrasonic stirring; the microporous layer is prepared by coating the slurry on the surface of the support layer treated with hydrophobic agent by using the silk screen printing technology; and then the loading of the carbon powder is determined by the weighing method to be 1-3 mg / cm 2 , the PTFE content is 10%-30%. The diffusion layer is obtained by placing it in a muffle furnace and heat treating it at 340-360℃ for 0.1-2h, and then reducing it to room temperature. After heat treatment at this temperature, the carbon powder and PTFE are more uniformly distributed. The pore size of the microporous layer is generally 0.1-1 microns, and the porosity is 20%-50%.

[0056] The outer catalytic layer of the double-catalytic-layer cathode comprises a noble metal platinum-based catalyst, an ionomer and a pore-forming agent.

[0057] 1) The preparation process of the catalyst slurry of the outer catalytic layer is as follows:

[0058] a) 5%-50% (mass percentage) platinum carbon catalyst is dispersed in an isopropyl alcohol / water solution, and ultrasonic stirring is circularly performed for 2-3 times, each time for 0.1-1h, so that the catalyst is uniformly dispersed, to obtain catalyst slurry ①; the isopropyl alcohol / water solution refers to a mixed solution of isopropyl alcohol and water;

[0059] b) PTFE or PVDF is used as the ionomer, and ammonium bicarbonate, ammonium oxalate, ammonium nitrate, ammonium sulfate and the like are used as the pore-forming agent; 0.5wt%-10wt% PTFE or PVDF aqueous solution is weighed, a certain amount of pore-forming agent is added, the mass ratio of PTFE or PVDF to the pore-forming agent is controlled to be between 1 / 10 and 10 / 1, and ultrasonic stirring is performed to uniformly disperse the solution to obtain a uniform transparent solution ②;

[0060] c) according to the mass ratio of the pore-forming agent to the catalyst layer being between 10% and 20%, a certain amount of solution ② is slowly dropped into solution ①, and ultrasonic stirring is circularly performed for 2-3 times, each time for 0.1-1h, so that the catalyst is uniformly dispersed to obtain catalyst slurry ③;

[0061] 2) the catalyst slurry ③ is coated on the diffusion layer by using ultrasonic spraying, silk screen printing, slot direct coating and the like, and then placed in a muffle furnace to be calcined at 300℃-400℃ for 0.5h-2h, to obtain the outer catalytic layer; the loading of the noble metal catalyst of the outer catalytic layer is 0.05-0.5 mg / cm 2 , the porosity is 40%-50%, and the average pore size is between 0.5-5μm;

[0062] The inner catalytic layer of the double-catalytic-layer cathode comprises a noble metal platinum-based catalyst, an ionomer and a pore-forming agent.

[0063] 1) The preparation process of the catalyst slurry of the inner catalytic layer is as follows:

[0064] a) disperse the noble metal supported platinum-based catalyst in isopropyl alcohol / water solution, ultrasonic, stirring cycle 2-3 times, 0.1-1h each time to make it evenly dispersed, to obtain catalyst slurry ④;

[0065] b) using PTFE or PVDF as ionomer, taking 0.5wt%-10wt% of PTFE or PVDF aqueous solution, adding a certain amount of pore-forming agent, controlling the mass ratio of PTFE or PVDF to pore-forming agent between 1 / 10-10 / 1, ultrasonic, stirring to make it evenly dispersed to obtain a uniform transparent solution ⑤;

[0066] c) according to the mass proportion of the pore-forming agent in the catalyst layer is between 5%-10%, take a certain amount of solution ⑤, slowly drop into solution ④, ultrasonic, stirring cycle 2-3 times, 0.1-1h each time to make it evenly dispersed to obtain catalyst slurry ⑥;

[0067] 2) use ultrasonic spraying, screen printing, slot direct coating and other technologies to coat the catalyst slurry ⑥ on the outer catalyst layer, then put it into the muffle furnace and calcine at 300℃-400℃ for 0.5h-2h to obtain the inner catalyst layer, the noble metal catalyst loading of the inner catalyst layer is 0.05-0.5mg / cm 2 , the porosity is 20%-30%, and the average pore size is between 0.05-1μm;

[0068] The noble metal of the above-mentioned gradient pore distribution double catalyst layer cathode is Pt, Pd and their alloys, the thickness of the cathode is between 120μm-300μm, and the working temperature of the high-temperature proton exchange membrane fuel cell is between 120℃-250℃.

[0069] Compared with the traditional uniform pore distribution cathode, the pore-forming agent is added in the slurry of the outer catalyst layer and the inner catalyst layer, and the type and content of the pore-forming agent are adjusted to prepare the gradient pore distribution double catalyst layer cathode, which can realize uniform distribution of phosphoric acid, avoid local acid flooding, effectively build the three-phase interface of electrochemical reaction, improve the utilization rate of noble metal catalyst, and realize the controllable preparation of low-platinum high-efficiency gas diffusion electrode.

[0070] Example 1:

[0071] Example 1 is a membrane electrode with a gradient pore distribution double catalyst layer, which mainly consists of an electrolyte membrane and cathode and anode gas diffusion electrodes. The cathode and anode gas diffusion electrodes are composed of cathode and anode gas diffusion layers and cathode and anode catalyst layers. The cathode and anode gas diffusion layers have the same structure and are composed of a support layer and a microporous layer. The cathode gas diffusion electrode is the gradient pore distribution double catalyst layer cathode provided by the present application. See Figure 1The gradient pore distribution double catalytic layer cathode is mainly composed of a gas diffusion layer, an inner catalytic layer and an outer catalytic layer. The thickness of the gas diffusion layer is 180 microns. The mass ratio of the pore-forming agent ammonium carbonate in the inner catalytic layer to the catalytic layer is 20%, and the thickness of the inner catalytic layer is about 10 microns. The mass ratio of the pore-forming agent ammonium carbonate in the outer catalytic layer to the catalytic layer is 10%, and the thickness of the outer catalytic layer is about 20 microns. The specific preparation process of the gradient pore distribution double catalytic layer cathode membrane electrode is as follows:

[0072] Hydrophobic treatment of the support layer: 2wt.% PTFE emulsion is used to treat Torray carbon paper. First, the commercial carbon paper is weighed, then immersed in the PTFE emulsion for about 30s, taken out and dried with a hair dryer, weighed again, and the percentage of PTFE immersed is calculated. Repeat the above immersion, drying process until the PTFE loading of the support layer is 10wt.%. Finally, the hydrophobicized carbon paper is placed in a muffle furnace and heat treated at 350°C for 40min, then taken out after cooling to room temperature.

[0073] Preparation process of microporous layer: first mix Vulcan XC-72 carbon powder and PTFE emulsion, add appropriate amount of ethanol, ultrasonic stirring to prepare slurry, use screen printing technology to coat the microporous layer on the surface of the hydrophobic treated support layer, the fixed carbon powder loading is 1mg / cm 2 , the PTFE content is 20%. Place it in a muffle furnace and heat treat at 350°C for 30min, then get the diffusion layer after cooling to room temperature.

[0074] Preparation of anode catalytic layer: disperse 30% Pt / C catalyst in isopropyl alcohol / water solution, ultrasonic, stirring cycle 3 times, 0.2h each time to make it uniformly dispersed, get catalyst slurry ①; use 60% PTFE F as ionomer, dilute with water, ultrasonic, stirring to make it uniformly dispersed to get 2wt% PTFE aqueous solution ②; take out a certain amount of solution ②, slowly drop into solution ①, ultrasonic, stirring cycle 3 times, 0.2h each time to make it uniformly dispersed to get catalyst slurry ③; use ultrasonic spraying technology to coat the catalyst slurry ③ on the diffusion layer, then place it in a muffle furnace and calcine at 350°C for 0.5h to get the anode catalytic layer, the noble metal catalyst loading in the catalytic layer is 0.5mg / cm 2 .

[0075] Preparation of the outer catalytic layer of the cathode: 30% Pt / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and stirred for 3 cycles of 0.2 h each to make it uniformly dispersed, to obtain a catalyst slurry ①; PTFE was used as the ionomer, and ammonium carbonate was used as the pore-forming agent; 2 wt% of the PTFE water solution was weighed out, a certain amount of the pore-forming agent was added, the mass ratio of PTFE to the pore-forming agent was controlled to be 1 / 1, and the solution was ultrasonically and stirred to make it uniformly dispersed to obtain a uniform and transparent solution ②; according to the mass ratio of the pore-forming agent in the catalytic layer being 20%, a certain amount of the solution ② was taken out and slowly dropped into the solution ①, which was ultrasonically and stirred for 3 cycles of 0.2 h each to make it uniformly dispersed to obtain a catalyst slurry ③; the catalyst slurry ③ was coated on the diffusion layer by using the ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 350°C for 0.5 h to obtain the outer catalytic layer; the loading of the noble metal catalyst of the outer catalytic layer was 0.3 mg / cm 2 , the porosity was 50%, and the average pore size was between 0.5-5 μm.

[0076] Preparation of the inner catalytic layer of the cathode: 50% PtCo / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and stirred for 3 cycles of 0.15 h each to make it uniformly dispersed, to obtain a catalyst slurry ④; PTFE was used as the ionomer, and ammonium carbonate was used as the pore-forming agent; 2 wt% of the PTFE water solution was weighed out, a certain amount of the pore-forming agent was added, the mass ratio of PTFE to the pore-forming agent was controlled to be 2 / 1, and the solution was ultrasonically and stirred to make it uniformly dispersed to obtain a uniform and transparent solution ⑤; according to the mass ratio of the pore-forming agent in the catalytic layer being 10%, a certain amount of the solution ⑤ was taken out and slowly dropped into the solution ④, which was ultrasonically and stirred for 3 cycles of 0.2 h each to make it uniformly dispersed to obtain a catalyst slurry ⑥; the catalyst slurry ⑥ was coated on the outer catalytic layer by using the ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 340°C for 0.5-2 h to obtain the inner catalytic layer; the loading of the noble metal catalyst of the inner catalytic layer was 0.2 mg / cm 2 , the porosity was 30%, and the average pore size was between 0.05-1 μm.

[0077] Preparation of the electrolyte membrane: a PBI / H3PO4 composite electrolyte membrane was prepared by using the impregnation method; first, the PBI membrane was cut into a certain size as needed, second, the cut membrane was soaked in 85 wt% phosphoric acid at 120°C for a corresponding time, the excess phosphoric acid on the surface of the membrane was absorbed with filter paper, and the membrane was quickly weighed to obtain the phosphoric acid adsorption amount of the membrane; the mass ratio of phosphoric acid to the resin was used to investigate the phosphoric acid adsorption amount MPA / PBI of the membrane; steps 2 and 3 were repeated until the phosphoric acid adsorption amount reached 380 wt%.

[0078] The prepared anode and cathode gas diffusion electrodes and the PBI / H3PO4 composite electrolyte membrane were stacked in a mold in a certain order. Then, the membrane electrode was hot-pressed and formed in a hot press, and then was placed in a sealed bag for storage for use.

[0079] Example 2

[0080] Example 2 is a membrane electrode of the cathode with gradient pore distribution double catalytic layer, which is different from Example 1 in that the mass ratio of the pore-forming agent ammonium carbonate added in the inner catalytic layer to the catalytic layer is 5%, and the mass ratio of the pore-forming agent ammonium carbonate added in the outer catalytic layer to the catalytic layer is 10%. The specific preparation process of the inner and outer catalytic layers of the cathode is as follows:

[0081] Preparation of the outer catalytic layer of the cathode: 30% Pt / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and circularly stirred for 3 times, 0.2 h each time, to make it uniformly dispersed, to obtain catalyst slurry ①; PTFE was used as the ionomer, and ammonium carbonate was used as the pore-forming agent. 2wt% PTFE aqueous solution was weighed, a certain amount of pore-forming agent was added, and the mass ratio of PTFE to pore-forming agent was controlled to be 1 / 1. Ultrasonic stirring was used to make it uniformly dispersed to obtain a uniform transparent solution ②; according to the mass ratio of the pore-forming agent to the catalytic layer being 10%, a certain amount of solution ② was slowly added dropwise into solution ①, and was ultrasonically and circularly stirred for 3 times, 0.2 h each time, to make it uniformly dispersed to obtain catalyst slurry ③; the catalyst slurry ③ was coated on the diffusion layer by using ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 350°C for 0.5 h to obtain the outer catalytic layer. The loading of the noble metal catalyst of the outer catalytic layer was 0.3 mg / cm 2 , the porosity was 41%, and the average pore size was between 0.5-5 μm.

[0082] Preparation of the inner catalytic layer of the cathode: 50% PtCo / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and circularly stirred for 3 times, 0.15 h each time, to make it uniformly dispersed, to obtain catalyst slurry ④; PTFE was used as the ionomer, and ammonium carbonate was used as the pore-forming agent. 2wt% PTFE aqueous solution was weighed, a certain amount of pore-forming agent was added, and the mass ratio of PTFE to pore-forming agent was controlled to be 2 / 1. Ultrasonic stirring was used to make it uniformly dispersed to obtain a uniform transparent solution ⑤; according to the mass ratio of the pore-forming agent to the catalytic layer being 5%, a certain amount of solution ⑤ was slowly added dropwise into solution ④, and was ultrasonically and circularly stirred for 3 times, 0.2 h each time, to make it uniformly dispersed to obtain catalyst slurry ⑥; the catalyst slurry ⑥ was coated on the outer catalytic layer by using ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 340°C for 0.5-2 h to obtain the inner catalytic layer. The loading of the noble metal catalyst of the inner catalytic layer was 0.2 mg / cm 2 , the porosity was 23%, and the average pore size was between 0.05-1 μm.

[0083] Comparative Example 1

[0084] Comparative Example 1 is a traditional membrane electrode with uniform pore distribution, which differs from Example 1 in that the cathode catalytic layer is a single layer of uniform pore distribution structure, and no pore-forming agent is added in the catalytic layer. The specific preparation process is as follows:

[0085] Preparation of the cathode catalytic layer: 50% PtCo / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and stirred for 3 cycles, each for 0.15 h, to make it uniformly dispersed, to obtain a catalyst slurry ④; 60% PTFE was used as an ionomer, diluted with water, and was ultrasonically and stirred to make it uniformly dispersed to obtain a uniform and transparent 2 wt% PTFE aqueous solution ⑤; a certain amount of solution ⑤ was slowly dropped into solution ④, and was ultrasonically and stirred for 3 cycles, each for 0.2 h, to make it uniformly dispersed to obtain a catalyst slurry ⑥; the catalyst slurry ⑥ was coated on the diffusion layer by using ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 340°C for 1 h, to obtain a cathode catalytic layer. The loading of the noble metal catalyst of the catalytic layer was 0.5 mg / cm 2 , the porosity was 20%, and the average pore size was between 0.05-1 μm.

[0086] Comparative Example 2:

[0087] Comparative Example 3 is a membrane electrode with a gradient pore distribution double-catalytic layer cathode, which differs from Example 1 in that the mass ratio of the pore-forming agent ammonium carbonate added in the inner catalytic layer to the catalytic layer is 10%, and the mass ratio of the pore-forming agent ammonium carbonate added in the outer catalytic layer to the catalytic layer is 5%. The specific preparation process of the inner and outer catalytic layers of the cathode is as follows:

[0088] Preparation of the outer catalytic layer of the cathode: 30% Pt / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and stirred for 3 cycles, each for 0.2 h, to make it uniformly dispersed, to obtain a catalyst slurry ①; PTFE was used as an ionomer, and ammonium carbonate was used as a pore-forming agent. A certain amount of pore-forming agent was added to 2 wt% PTFE aqueous solution, and the mass ratio of PTFE to the pore-forming agent was controlled to be 1 / 1, to make it uniformly dispersed to obtain a uniform and transparent solution ②; according to the mass ratio of the pore-forming agent to the catalytic layer being 5%, a certain amount of solution ② was slowly dropped into solution ①, and was ultrasonically and stirred for 3 cycles, each for 0.2 h, to make it uniformly dispersed to obtain a catalyst slurry ③; the catalyst slurry ③ was coated on the diffusion layer by using ultrasonic spraying technology, and then was placed in a muffle furnace for calcination at 350°C for 0.5 h, to obtain an outer catalytic layer. The loading of the noble metal catalyst of the outer catalytic layer was 0.3 mg / cm 2 , the porosity was 23%, and the average pore size was between 0.5-5 μm.

[0089] Preparation of the inner catalytic layer of the cathode: 50% PtCo / C catalyst was dispersed in an isopropyl alcohol / water solution, and was ultrasonically and stirred for 3 cycles of 0.15 h each to make it uniformly dispersed, to obtain a catalyst slurry ④; PTFE was used as an ionomer, and ammonium carbonate was used as a pore-forming agent; 2 wt% of the PTFE water solution was weighed out, a certain amount of the pore-forming agent was added, and the mass ratio of PTFE to the pore-forming agent was controlled to be 2 / 1; the mixture was ultrasonically and stirred to make it uniformly dispersed to obtain a uniform and transparent solution ⑤; according to the mass proportion of the pore-forming agent in the catalytic layer being 10%, a certain amount of the solution ⑤ was taken out and slowly dropped into the solution ④; the mixture was ultrasonically and stirred for 3 cycles of 0.2 h each to make it uniformly dispersed to obtain a catalyst slurry ⑥; the catalyst slurry ⑥ was coated on the outer catalytic layer by using an ultrasonic spraying technology, and then was placed into a muffle furnace for calcination at 340℃ for 0.5-2 h to obtain an inner catalytic layer; the loading of the noble metal catalyst of the inner catalytic layer was 0.2 mg / cm 2 , the porosity was 41%, and the average pore size was between 0.05-1 μm.

[0090] After the membrane electrode with different cathode catalytic layer structures was assembled into a single cell, the following tests were performed:

[0091] According to GB / T 20042.5-2009, polarization curve tests were performed on the obtained high-temperature proton exchange membrane fuel cell membrane electrode; the specific operation conditions were as follows: the single cell working temperature was 160℃, the anode was fed with pure hydrogen gas, the cathode was fed with normal-pressure air, and the feeding ratio of the cathode to the anode was 3 / 1.5 times.

[0092] According to GB / T 20042.5-2009, impedance detection of the high-temperature proton exchange membrane fuel cell membrane electrode was performed; the specific operation conditions were as follows: the single cell working temperature was 160℃, the anode was fed with pure hydrogen gas, the cathode was fed with normal-pressure air, and the feeding ratio of the cathode to the anode was 3 / 1.5 times @ 0.5 A cm -2 ; the discharge current density was 0.5 A cm -2 .

[0093] According to GB / T 20042.5-2009, cyclic voltammetry detection of the high-temperature proton exchange membrane fuel cell membrane electrode was performed; the specific operation conditions were as follows: the single cell working temperature was 160℃, dry N2 was fed into the cathode at a flow rate of 4.6 ml min-1cm -2 ; dry H2 was fed into the anode at a flow rate of 6.9 ml min -1 cm -2 ; the voltage range was 0.05 V-1.2 V, and the scanning speed was 0.05 V s -1 .

[0094] The detection results are shown in the attached Figures 2-4, #1 is the cathode structure of Comparative Example 1, #2 is the cathode structure of Example 1, #3 is the cathode structure of Example 2, and #4 is the cathode structure of Comparative Example 2

[0095] Referring to Figure 2 , the membrane electrode polarization characteristic curves of the cathode structures of Example 1 and Example 2 and the cathode structures of Comparative Examples 1 and 2 were measured. As can be seen from the figure, the voltage of the membrane electrode corresponding to the cathode structure of Example 1, the cathode structure of Example 2 and the cathode structures of Comparative Examples 1 and 2 was 0.68 V, 0.67 V, 0.67 V and 0.66 V respectively at 0.1 A / cm 2 , the voltage of the membrane electrode corresponding to the cathode structure of Example 1, the cathode structure of Example 2 and the cathode structures of Comparative Examples 1 and 2 was 0.548 V, 0.509 V, 0.5 V and 0.491 V respectively at 0.5 A / cm 2 , the voltage of the membrane electrode corresponding to the cathode structure of Example 1, the cathode structure of Example 2 and the cathode structures of Comparative Examples 1 and 2 was 0.428 V, 0.363 V, 0.339 V and 0.346 V respectively at 1.0 A / cm 2 , the voltage of the membrane electrode corresponding to the cathode structure of Example 1, the cathode structure of Example 2 and the cathode structures of Comparative Examples 1 and 2 was 0.428 V, 0.363 V, 0.339 V and 0.346 V respectively at 1.0 A / cm

[0096] Referring to Figure 3 , the membrane electrode impedance diagrams of the cathode structures of Example 1 and Example 2 and the cathode structures of Comparative Examples 1 and 2 were measured. The results show that, compared with the membrane electrodes of the cathode structures of Comparative Examples 1 and 2, the internal resistance and the cathode charge transfer resistance and mass transfer resistance of the membrane electrodes of the cathode structures of Example 1 and Example 2 are greatly reduced, indicating that the cathode gradient pore distribution double catalyst layer structure of Example 1 and Example 2 is more conducive to the uniform distribution of phosphoric acid, avoiding the acid flooding caused by local phosphoric acid being too high and the low three-phase interface area caused by less phosphoric acid, thereby reducing the cathode activation polarization loss and mass transfer polarization loss and improving the performance.

[0097] Referring to Figure 4 , the cyclic voltammograms of the cathode structures of Example 1 and Example 2 and the cathode structures of Comparative Examples 1 and 2 were measured. The results show that, compared with the cathode electrochemical active areas of 21.27 and 32.45 g / m 2 , the cathode electrochemical active areas of Example 1 and Example 2 were 51.94 and 35.72 g / m 2 , respectively, the electrochemical active area was greatly improved, indicating that the gradient pore distribution double catalyst layer of Example 1 and Example 2 is conducive to the uniform distribution of phosphoric acid, the cathode three-phase interface is effectively constructed, and the utilization rate of the catalyst is greatly improved.

[0098] The above detailed description has shown, among other things, specific embodiments of the application. The description and specific examples, however, should not be construed as limiting the scope of the application. Those skilled in the art will recognize that equivalents for the specific embodiments described herein can be made with the treating of the application, and that it is intended to cover all adaptations, modifications, and equivalents that fall within the scope of the application. The scope of the application should be determined by a fair reading of the appended claims in accordance with the legal principles of patent claims interpretation.

[0099] Any procedural model, steps, or details not described in detail in the specification are known to those skilled in the art.

Claims

1. A method for making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution dual catalyst layer, characterized in that, The application relates to a preparation method of a diffusion layer and a catalyst layer. The diffusion layer is prepared; An outer catalytic layer slurry is coated on the surface of the diffusion layer to obtain an outer catalytic layer; The outer catalytic layer slurry comprises a noble metal platinum carrier-based catalyst, an ionomer and a pore-forming agent; the porosity of the outer catalytic layer is 40%-50%, and the average pore size is 0.5-5 mu m; An inner catalytic layer slurry is coated on the surface of the outer catalytic layer to obtain an inner catalytic layer; the inner catalytic layer slurry comprises a noble metal platinum carrier-based catalyst, an ionomer and a pore-forming agent; the porosity of the inner catalytic layer is 20%-30%, and the average pore size is 0.05-1 mu m; The pore-forming agent is one or more of ammonium bicarbonate, ammonium oxalate, ammonium nitrate, ammonium carbonate or ammonium sulfate; The preparation method of the outer catalytic layer slurry comprises the following steps: The noble metal platinum carrier-based catalyst is uniformly dispersed in a solvent to obtain a first catalyst slurry; An ionomer aqueous solution is prepared, the pore-forming agent is added into the ionomer aqueous solution, and after uniform dispersion, a first solution is obtained; the mass percentage of the ionomer in the ionomer aqueous solution is 0.5-10%, and the mass ratio of the ionomer to the pore-forming agent in the first solution is 1 / 10-10 / 1; The first solution is dropped into the first catalyst slurry, and after uniform dispersion, the outer catalytic layer slurry is obtained; in the outer catalytic layer slurry, the mass of the pore-forming agent accounts for 10%-20% of the total mass of the noble metal platinum carrier-based catalyst, the ionomer and the pore-forming agent; The preparation method of the inner catalytic layer slurry comprises the following steps: The noble metal platinum carrier-based catalyst is uniformly dispersed in a solvent to obtain a second catalyst slurry; An ionomer aqueous solution is prepared, the pore-forming agent is added into the ionomer aqueous solution, and after uniform dispersion, a second solution is obtained; the mass percentage of the ionomer in the ionomer aqueous solution is 0.5-10%, and the mass ratio of the ionomer to the pore-forming agent in the first solution is 1 / 10-10 / 1; The second solution is dropped into the second catalyst slurry, and after uniform dispersion, the inner catalytic layer slurry is obtained; in the inner catalytic layer slurry, the mass of the pore-forming agent accounts for 5%-10% of the total mass of the noble metal platinum carrier-based catalyst, the ionomer and the pore-forming agent.

2. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 1, wherein, The diffusion layer comprises a support layer and a microporous layer, and the preparation method of the diffusion layer comprises the following steps: The carbon cloth or carbon paper is immersed into a PTFE emulsion, and after being taken out, the hydrophobic carbon cloth or carbon paper is obtained; After the hydrophobic carbon cloth or carbon paper is subjected to heat treatment, the support layer is obtained; The carbon powder and the PTFE emulsion are mixed to obtain a microporous layer slurry; The microporous layer slurry is coated on the surface of the support layer to obtain a microporous layer, and then the obtained product is subjected to heat treatment to obtain the diffusion layer.

3. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 2, wherein, The mass percentage of PTFE in the support layer is 5-25%; The heat treatment condition of the hydrophobic carbon cloth or carbon paper is heat treatment at 340-360 DEG C for 0.1-2 h; The carbon powder has a loading of 1 to 3 mg / cm2in the microporous layer 2 The mass percentage of PTFE is 10% to 30%. The heat treatment condition of the obtained product is heat treatment at 340-360 DEG C for 0.1-2 h.

4. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 1, wherein, The noble metal in the noble metal platinum carrier-based catalyst is one or more of Pt, Pd or PtPd alloy; The ionomer is one or more of PTFE or PVDF.

5. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 1, wherein, The method for coating the outer catalytic layer slurry on the surface of the diffusion layer comprises ultrasonic spraying, silk screen printing or slit direct coating; after the outer catalytic layer slurry is coated on the surface of the diffusion layer, the obtained product is placed into a muffle furnace and calcined at 300 DEG C-400 DEG C for 0.5 h-2 h to obtain the outer catalytic layer. The method for coating the inner catalytic layer slurry on the surface of the outer catalytic layer includes ultrasonic spraying, silk screen printing or slit direct coating. After the inner catalytic layer slurry is coated on the surface of the outer catalytic layer, the obtained product is placed into a muffle furnace for calcination at 300-400 ℃ for 0.5-2 h to obtain the inner catalytic layer.

6. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 1, wherein, In the obtained outer catalytic layer, the mass percentage of the pore-forming agent is 10-20%; in the obtained inner catalytic layer, the mass percentage of the pore-forming agent is 5-10%; The loadings of the platinum-based catalysts supported on noble metals in the outer catalytic layer and the inner catalytic layer are both 0.05-0.5 mg / cm2 2 .

7. The method of making a high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution and dual catalyst layers of claim 1, wherein, The total thickness of the diffusion layer, the outer catalytic layer and the inner catalytic layer is 120-300 μm.

8. A high temperature proton exchange membrane fuel cell cathode with a gradient pore distribution dual catalyst layer, characterized in that, The preparation method of the gradient-pore-distribution double-catalytic-layer cathode of the high-temperature proton exchange membrane fuel cell is obtained by using the method of any one of claims 1-7, and includes a diffusion layer, an outer catalytic layer and an inner catalytic layer. The loadings of the platinum-based catalysts supported on noble metals in the outer catalytic layer and the inner catalytic layer are both 0.05-0.5 mg / cm2 2 ; The porosity of the outer catalytic layer is 40-50%, and the average pore size is 0.5-5 μm. The porosity of the inner catalytic layer is 20-30%, and the average pore size is 0.05-1 μm.

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