A high-temperature proton exchange membrane fuel cell cathode and its preparation method, and membrane electrode assembly.

Abstract

This invention discloses a method for preparing a cathode for a high-temperature proton exchange membrane fuel cell, comprising: preparing a cathode diffusion layer; coating the surface of the cathode diffusion layer with an outer catalyst layer slurry, followed by heat treatment to obtain the outer catalyst layer; coating the surface of the outer catalyst layer with an inner catalyst layer slurry, followed by heat treatment to obtain the inner catalyst layer. This invention also discloses a high-temperature proton exchange membrane fuel cell cathode, wherein the outer catalyst layer has an average pore size of 60–150 nm and a porosity of 30%–45%; the inner catalyst layer has an average pore size of 30–50 nm and a porosity of 25%–30%. This invention further discloses a membrane electrode assembly, comprising the above-described cathode, proton exchange membrane, and anode arranged sequentially. This invention can effectively improve the catalyst utilization rate and the performance and lifespan of high-temperature proton exchange membrane fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature proton exchange membrane fuel cell technology, and specifically relates to a high-temperature proton exchange membrane fuel cell cathode and its preparation method, as well as a membrane electrode. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are considered a promising next-generation power source due to their advantages such as high energy conversion efficiency, high power density, zero pollutant emissions, and relatively simple design. Based on operating temperature, PEMFCs are divided into low-temperature PEMFCs (LT-PEMFCs) based on Nafion membranes and high-temperature PEMFCs (HT-PEMFCs) based on phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes. Currently, HT-PEMFCs, operating at temperatures up to 200°C, have attracted widespread attention due to their high tolerance to impurities, faster electrode reaction kinetics, large amounts of reusable thermal energy, and simplified water management. However, the slow kinetics of the oxygen reduction reaction (ORR) and catalyst deactivation caused by PA adsorption necessitate the use of large amounts of platinum catalyst at the cathode to ensure satisfactory performance. This leads to a significant high cost, a major obstacle to the commercialization of HT-PEMFCs. Therefore, improving platinum utilization efficiency and enhancing the performance of HT-PEMFCs is expected to promote their development.

[0003] Traditional cathode single catalyst layers (SCLs) used in high-temperature proton exchange membrane (HT-PEMFC) employ a single catalyst slurry coated onto the gas diaphragm layer (GDL). While this results in a relatively uniform pore structure, it also leads to catalyst flooding near the PEM (Proton Exchange Membrane) due to higher acid content, reducing the number of active sites. Furthermore, the reduced pore size near the GDL makes air or oxygen diffusion more difficult, significantly increasing mass transfer resistance and severely impacting the performance and lifespan of HT-PEMFCs. Compared to other types of fuel cells, the absence of liquid water in HT-PEMFCs, coupled with the more viscous phosphoric acid acting as a proton conductor, results in more severe coverage and poisoning of catalyst active sites. Therefore, there is an urgent need to design a novel HT-PEMFC catalyst layer structure to adapt to the high-temperature phosphoric acid environment, balance gas mass transfer channels, and improve catalyst utilization. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects and provide a high-temperature proton exchange membrane fuel cell cathode and its preparation method, as well as a membrane electrode assembly. This invention solves the technical problems of complex preparation process and low catalyst utilization rate of traditional high-temperature proton exchange membranes. This invention can effectively improve catalyst utilization rate and the performance and lifespan of the battery.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a high-temperature proton exchange membrane fuel cell cathode, comprising:

[0007] Preparation of cathode diffusion layer;

[0008] After coating the surface of the cathode diffusion layer with a cathode outer catalyst layer slurry, the cathode outer catalyst layer is obtained by heat treatment; the cathode outer catalyst layer slurry includes a catalyst, a binder and a pore-forming agent; the average pore size of the cathode outer catalyst layer is 60-150 nm and the porosity is 30%-45%;

[0009] A cathode inner catalyst layer slurry is coated onto the surface of the outer catalyst layer of the cathode, and then heated to obtain the cathode inner catalyst layer. The cathode inner catalyst layer slurry includes a catalyst, a binder, and a pore-forming agent. The average pore size of the cathode inner catalyst layer is 30–50 nm, and the porosity is 25%–30%.

[0010] Furthermore, the adhesive is a hydrophobic adhesive, specifically including at least one of PTFE, PVDF, FEP, ECTE, ETFE, PFA, or PDMS.

[0011] Furthermore, the catalyst in the cathode outer catalyst layer slurry is one or more of Pt / C, PtFe / C, or PtCo / C; in Pt / C, PtFe / C, or PtCo / C, the mass fraction of Pt is 5% to 70%;

[0012] The catalyst in the slurry of the inner catalytic layer of the cathode is one or more of Pt black, PtCo / C or PtNi / C.

[0013] Furthermore, the pore-forming agent is at least one of EG or PEG;

[0014] The ratio of the pore-forming agent content in the cathode outer catalyst layer slurry to the mass of the pore-forming agent in the cathode inner catalyst layer slurry is 1.5 to 1.

[0015] Furthermore, based on the total solids mass of the cathode outer catalyst layer slurry, the mass percentage of the pore-forming agent is 30%–50%, and the molecular weight of the pore-forming agent is 600–1000; based on the total solids mass of the cathode inner catalyst layer slurry, the mass percentage of the pore-forming agent in the cathode inner catalyst layer slurry is 0%–30%, and the molecular weight of the pore-forming agent is ≤600. The solids in the slurry, i.e., the solute, include the catalyst, binder, and pore-forming agent.

[0016] Furthermore, the cathode outer catalyst layer slurry or the cathode inner catalyst layer slurry is heated in an environment with a protective gas atmosphere.

[0017] The protective gas includes N2;

[0018] The temperature for heat treatment is 50℃~300℃.

[0019] A high-temperature proton exchange membrane fuel cell cathode, prepared by the above method, includes a cathode diffusion layer, an outer cathode catalyst layer, and an inner cathode catalyst layer;

[0020] The cathode diffusion layer includes a support layer and a microporous layer;

[0021] The total pore area of ​​the outer catalyst layer of the cathode is 60–90 m². 2 / g, median pore size V 200~800nm, average pore size 60~150nm, porosity 30%~45%; median pore size V is a term used in mercury porosimetry testing, specifically referring to the size of the pore size corresponding to the median pore volume when pores of the same pore size are arranged according to their pore volume. In this invention, the focus is on constructing oxygen transport channels, which requires a high pore volume. Therefore, the median pore size V is used as a characteristic to evaluate the pore volume.

[0022] The total pore area of ​​the inner catalyst layer in the cathode is 30–50 m². 2 / g, median pore size V 100-150nm, average pore size 30-50nm, porosity 25%-30%.

[0023] The pore size of the inner and outer catalyst layers is mainly controlled by the molecular weight of PEG. When the molecular weight of PEG is between 200 and 1000, the median pore size V is between 100 and 800 nm, and the average pore size is between 30 and 150 nm.

[0024] The loading of noble metals in both the outer and inner catalyst layers of the cathode is 0.05–2.0 mg / cm³. 2 Furthermore, the noble metal loading in the inner catalyst layer of the cathode is higher than that in the outer catalyst layer of the cathode.

[0025] A high-temperature proton exchange membrane fuel cell membrane electrode assembly includes a cathode, a proton exchange membrane, and an anode arranged sequentially; the cathode is the aforementioned high-temperature proton exchange membrane fuel cell cathode.

[0026] The anode includes an anode diffusion layer and an anode catalyst layer. The anode diffusion layer includes a support layer and a microporous layer.

[0027] The cathode diffusion layer, the outer cathode catalyst layer, the inner cathode catalyst layer, the proton exchange membrane, the anode catalyst layer, and the anode diffusion layer are arranged sequentially.

[0028] Both the support layer in the cathode diffusion layer and the support layer in the anode diffusion layer are located on the side away from the proton exchange membrane.

[0029] Furthermore, the aforementioned high-temperature proton exchange membrane fuel cell membrane electrode is prepared by sequentially bonding a cathode, a proton exchange membrane, and an anode, followed by hot pressing.

[0030] The proton exchange membrane is a phosphoric acid-doped PBI membrane.

[0031] Furthermore, the above-mentioned high-temperature proton exchange membrane fuel cell membrane electrode, the high-temperature proton exchange membrane fuel cell including the high-temperature proton exchange membrane fuel cell membrane electrode, has an operating temperature of 140℃~220℃.

[0032] When the high-temperature proton exchange membrane fuel cell is in operation, hydrogen is introduced into the anode side, and the HER reaction occurs at the anode. Air or oxygen is introduced into the cathode side, and the ORR reaction occurs at the cathode.

[0033] Compared with the prior art, the present invention has at least one of the following advantages:

[0034] (1) The present invention creatively prepares a cathode structure with a porosity gradient, which reduces the diffusion resistance of cathode reactive gas in the catalyst layer, increases the acid storage capacity of the catalyst layer, thereby regulating the distribution of phosphoric acid in the catalyst layer, avoiding acid flooding of the catalyst layer, greatly increasing the three-phase interface in the electrode, improving the catalyst utilization rate and the performance and life of the battery.

[0035] (2) The present invention defines the specific porosity, pore size and other parameters of the inner catalyst layer and the outer catalyst layer, which can achieve the best catalyst utilization rate;

[0036] (3) The preparation method of the present invention is simple and conducive to large-scale application. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the gradient cathode structure with adjustable pore size in the high-temperature proton exchange membrane fuel cell of the present invention.

[0038] Figure 2 The film electrode polarization characteristic curves of Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2 of the present invention are shown.

[0039] Figure 3 The membrane electrode impedance diagrams for Embodiment 1, Embodiment 2, Comparative Example 1, and Comparative Example 2 of the present invention are shown below.

[0040] Figure 4 The cyclic voltammetry curves of the membrane electrodes in Examples 1, 2, 1, and 2 of this invention are shown below.

[0041] Figure 5 The above are bar charts showing the oxygen gain of the membrane electrode in Embodiments 1, 2, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed Implementation

[0042] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0043] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0044] This invention provides a high-temperature proton exchange membrane fuel cell cathode and its preparation method, as well as a high-temperature proton exchange membrane fuel cell membrane electrode assembly (MEA). This invention, while facilitating production operations, reduces the diffusion resistance of the cathode reactant gas in the catalyst layer, increases the acid storage capacity of the catalyst layer, thereby regulating the distribution of phosphoric acid in the catalyst layer, preventing acid flooding, significantly increasing the three-phase interface within the electrode, and improving catalyst utilization, battery performance, and lifespan. The high-temperature proton exchange membrane fuel cell used in this invention operates in a high-temperature phosphoric acid environment. The gradient pore structure catalyst layer proposed in this invention aims to improve the proton and oxygen transport channels in the catalyst layer under high-temperature phosphoric acid conditions.

[0045] This invention discloses a high-temperature proton exchange membrane fuel cell membrane electrode with an adjustable-pore-size gradient cathode catalyst layer, comprising a cathode diffusion layer, an outer cathode catalyst layer, an inner cathode catalyst layer, a proton exchange membrane, an anode catalyst layer, and an anode diffusion layer arranged sequentially. The outer cathode catalyst layer includes an outer catalyst layer and a hydrophobic binder, possessing a large pore size and porosity. The inner cathode catalyst layer includes an inner catalyst layer and a hydrophobic binder, possessing a smaller pore size and porosity. The pore-forming agent content in the slurry for preparing the outer cathode catalyst layer is higher than that in the slurry for preparing the inner cathode catalyst layer. The dried catalyst layer semi-finished product containing the pore-forming agent is heated to allow the pore-forming agent to volatilize and create pores, thus preparing a complete catalyst layer. After air is uniformly dispersed through the gas diffusion layer, an ORR reaction first occurs in the more porous outer cathode catalyst layer, and the unreacted air diffuses into the inner cathode catalyst layer to continue the ORR reaction.

[0046] High-temperature proton exchange membrane fuel cells operate at temperatures ranging from 140℃ to 220℃, and the proton exchange membrane used is a phosphoric acid-doped PBI membrane. During operation, hydrogen is introduced to the anode side, triggering the HER reaction, while air or oxygen is introduced to the cathode side, triggering the ORR reaction.

[0047] In one specific embodiment, the pore-forming agent content in the outer catalyst layer of the cathode is higher than that in the inner catalyst layer, resulting in a richer pore structure in the outer catalyst layer compared to the inner catalyst layer. Specifically, the total pore area of ​​the outer catalyst layer is 60-90 μm². 2 / g, median pore size V 200-800nm, average pore size 60-150nm, porosity 30%-45%; while the total pore area of ​​the inner catalyst layer is 30-50m². 2 / g, median pore size V 100-150nm, average pore size 30-50nm, porosity 25%-30%.

[0048] It should be noted that precise control of the catalyst layer structure requires the organic combination of various materials. This invention proposes the optimal combination of the listed materials. When the catalyst activity is high and the Pt content is low, the difference in pore structure between the inner and outer catalyst layers will increase, reaching 30-800 nm. The outer catalyst layer requires a larger pore size to transport more oxygen. Considering the compatibility of the slurry solvent and the convenience of large-scale operation, pore-forming agents with similar properties are needed. This necessitates the use of PEG100-PEG1000 with different molecular weights to construct different pore sizes. Meanwhile, conventional volatile salts such as ammonium salts and carbonates, including low-molecular-weight EG, are easily volatilized with the solvent at low temperatures (below 80°C), failing to provide good pore-forming effects. A large amount of salt pore-forming agent dissolved in the slurry can also cause charge attraction to the alloy catalyst, leading to agglomeration and affecting the dispersion state of the slurry. In summary, this invention, on the one hand, uses PEG pore-forming agents of different molecular weights to control pore size and balance the relationship between phosphoric acid and oxygen transport; on the other hand, high-molecular-weight PEG is less volatile during the slurry drying stage, making it easier to apply in precise quantities.

[0049] This invention discloses a method for preparing a high-temperature proton exchange membrane fuel cell membrane electrode with an adjustable pore size gradient cathode catalyst layer, comprising:

[0050] Anode preparation:

[0051] S1: Coat the anode catalyst slurry onto the anode diffusion layer;

[0052] Cathode preparation:

[0053] S2: Coat the outer layer catalyst slurry of the cathode onto the cathode diffusion layer;

[0054] S3: The cathode diffusion layer coated with the outer catalyst layer slurry is heated at high temperature in an environment with protective gas to form the outer catalyst layer after pore formation.

[0055] S4: Coat the inner cathode catalyst slurry onto the outer catalyst layer after pore formation;

[0056] S5: The cathode diffusion layer coated with the inner catalyst layer slurry and the outer catalyst layer are heated at high temperature in an environment with protective gas to form the inner catalyst layer after pore formation.

[0057] Assembly of the anode, cathode, and proton exchange membrane:

[0058] S6: The anode diffusion layer coated with anode catalyst slurry and the proton exchange membrane, the cathode diffusion layer obtained by secondary pore formation and the double catalyst layer are sequentially bonded together, and finally composited by hot pressing.

[0059] In one specific embodiment, the slurry of the cathode outer catalyst layer includes an outer catalyst, a hydrophobic binder, and a pore-forming agent;

[0060] The slurry of the inner catalyst layer of the cathode includes an inner catalyst, a hydrophobic binder, and a pore-forming agent.

[0061] The pore size and porosity of the outer catalyst layer of the cathode after pore formation are higher than those of the inner catalyst layer of the cathode.

[0062] In one specific embodiment, the ratio of the content of pore-forming agent in the slurry used to prepare the outer catalyst layer of the cathode to the content of pore-forming agent in the slurry used to prepare the inner catalyst layer of the cathode is 1.5 / 1 to 5 / 1.

[0063] In one specific embodiment, the molecular weight of the pore-forming agent in the slurry for preparing the outer catalyst layer of the cathode is less than or equal to 600; the molecular weight of the pore-forming agent in the slurry for preparing the inner catalyst layer of the cathode is 600-1000. Molecular weight affects the pore size of the catalyst layer; larger molecular weights create larger pore structures that are more conducive to mass transfer, while smaller pore sizes, due to capillary forces, are more conducive to the diffusion of phosphoric acid. This invention defines a specific range of molecular weights within which both mass transfer and phosphoric acid diffusion can be optimized.

[0064] In one specific embodiment, the content (mass percentage) of pore-forming agent in the slurry for preparing the outer catalyst layer of the cathode is 30%-50%; the content of pore-forming agent in the slurry for preparing the inner catalyst layer of the cathode is 0%-30%.

[0065] In one specific embodiment, the pore-forming agent is any one or more of EG and PEG100-1000.

[0066] In one specific embodiment, the outer catalyst comprises Pt / C, PtFe / C, or PtCo / C; the mass fraction of noble metal in Pt / C, PtFe / C, or PtCo / C is 5%-70%, and the loading of noble metal in the outer catalyst layer is 0.05-2.0 mg / cm³. 2 ;

[0067] The inner catalyst layer includes Pt black, PtCo / C, or PtNi / C; the loading of noble metals in the inner catalyst layer is 0.05-2.0 mg / cm³. 2 ;

[0068] The inner catalyst loading of the inner catalyst layer of the cathode is higher than that of the outer catalyst loading of the outer catalyst layer of the cathode.

[0069] In one specific embodiment, the cathode includes a cathode diffusion layer, an outer cathode catalyst layer, and an inner cathode catalyst layer; the cathode catalyst layer includes an outer cathode catalyst layer and an inner cathode catalyst layer; both the cathode diffusion layer and the anode diffusion layer include a support layer and a microporous layer, with the support layer located on the side of the microporous layer away from the proton exchange membrane;

[0070] In one specific embodiment, the support layer is carbon paper or carbon cloth impregnated with PTFE, and the microporous layer includes carbon powder and PTFE.

[0071] In one specific embodiment, the carbon powder is any one of activated carbon, graphitized carbon, carbon nanotubes, carbon nanoribbons, and carbon nanospheres, and the PTFE content in the microporous layer is 5%-25%.

[0072] In one specific embodiment, during the preparation of the cathode catalyst layer, the inner and outer catalyst layers of the cathode are heated to create pores in an environment with a protective gas, and the heating temperature is 50℃-300℃.

[0073] In one specific embodiment, the hydrophobic adhesive is any one or more of PTFE, PVDF, FEP, ECTE, ETFE, PFA, and PDMS.

[0074] The tunable gradient cathode structure of this invention includes a cathode diffusion layer, an outer cathode catalyst layer, and an inner cathode catalyst layer. It can adjust the distribution of phosphoric acid in the cathode catalyst layer (including the cathode catalyst layer and the outer cathode catalyst layer), avoid acid flooding of the cathode catalyst layer, significantly increase the three-phase interface in the electrode, improve catalyst utilization, reduce oxygen transport resistance in the cathode catalyst layer, and after oxygen is uniformly dispersed through the cathode diffusion layer, it first undergoes an ORR reaction in the outer cathode catalyst layer. Unreacted oxygen further diffuses into the inner cathode catalyst layer to continue the ORR reaction.

[0075] This invention employs a novel porosity gradient cathode structure using different types of catalysts, catalyst ratios, and gradient pore structures. The pore size increases progressively from the inner to the outer catalytic layer of the cathode, while the relative Pt content decreases. The macropore content in the electrode also gradually increases, thereby reducing the mass transfer resistance of oxygen in both the inner and outer catalytic layers of the cathode, facilitating gas transport. The abundant pore structure also provides more acid storage sites, greatly ensuring the effective distribution of phosphoric acid within the catalytic layer. The smaller porosity and pore size in the inner catalytic layer reduce the contact resistance between the proton exchange membrane and the catalytic layer, while the larger porosity and pore size in the outer catalytic layer reduce the diffusion resistance of gas from the diffusion layer to the three-phase interface, thus increasing the number of gas transport channels, preventing acid flooding of the cathode catalytic layer, significantly increasing the three-phase interface within the electrode, and improving catalyst utilization, battery performance, and lifespan.

[0076] Example 1

[0077] See Figure 1 A gradient cathode structure with adjustable pore size for a high-temperature proton exchange membrane fuel cell includes a cathode diffusion layer 1, an outer cathode catalyst layer 2, and an inner cathode catalyst layer 3. After oxygen is uniformly dispersed through the cathode diffusion layer 1, it first undergoes an ORR reaction in the outer catalyst layer 2. Unreacted oxygen continues to diffuse into the inner catalyst layer 3 to complete the ORR reaction.

[0078] The fabrication method of a high-temperature proton exchange membrane fuel cell membrane electrode assembly with an adjustable pore size gradient cathode catalyst layer is as follows:

[0079] Preparation of the gas diffusion layer: First, Vulcan XC-72 toner and PTFE emulsion were mixed, and an appropriate amount of ethanol was added. The mixture was ultrasonically stirred to obtain a slurry, which was then coated onto the surface of commercially available Toray carbon paper. The toner loading and PTFE content were then determined by weighing. Finally, the mixture was placed in a muffle furnace and heat-treated at 340°C for 25 minutes. After cooling to room temperature, the gas diffusion layer was obtained. This gas diffusion layer serves as the anodic and cathodic diffusion layers in subsequent steps.

[0080] Preparation of the anode catalyst layer (anode GDE): Weigh out the required Pt / C catalyst (0.5 mg) Pt / cm 2 Add a small amount of deionized water and stir to wet the catalyst, then add a certain amount of PTFE aqueous alcohol solution, and after ultrasonic dispersion, obtain a catalyst slurry; the above slurry is uniformly coated on the microporous layer surface of the anode diffusion layer by ultrasonic spraying.

[0081] Preparation of the cathode double catalyst layer (cathode GDE): Weigh out the required Pt content of 60%, PtCo / C catalyst (0.25 mg) Pt / cm 2Add a small amount of deionized water and stir to wet the mixture. Add a certain amount of PTFE (20 wt% of total solids) aqueous alcohol solution, followed by a certain amount of PEG600 (30 wt%) as a pore-forming agent. After ultrasonic dispersion, a cathode outer catalyst slurry is obtained. The slurry is then uniformly coated onto the microporous surface of the cathode diffusion layer using an ultrasonic spraying method to obtain a cathode outer catalyst layer containing the pore-forming agent. The outer catalyst layer is then placed in a muffle furnace and calcined at 250°C for 1 hour under N2 protection to allow the pore-forming agent to volatilize and create pores, resulting in a pore-formed outer catalyst layer. The cathode outer catalyst layer is prepared by weighing the required PtCo / C catalyst, adding a small amount of deionized water and stirring to wet it, then adding a certain amount of PTFE (20wt%) water-alcohol solution, followed by a certain amount of PEG200 (10wt%). After ultrasonic dispersion, an inner catalyst layer slurry is obtained. The slurry is then uniformly coated onto the surface of the cathode outer catalyst layer using ultrasonic spraying to obtain a cathode inner catalyst layer containing a pore-forming agent. The catalyst layer is then placed in a muffle furnace and calcined at 250°C for 1 hour under N2 protection to obtain a pore-forming cathode double catalyst layer.

[0082] Preparation of PBI / H3PO4 composite membrane: The PBI / H3PO4 composite membrane was prepared by impregnation method. First, the PBI membrane was cut into a certain size as needed. Then, the cut membrane was soaked in 85wt% phosphoric acid at 120℃ for the corresponding time. The excess phosphoric acid on the membrane surface was absorbed with filter paper and weighed quickly to obtain the phosphoric acid adsorption capacity of the membrane.

[0083] The phosphoric acid adsorption capacity (MPA / PBI) of the membrane was determined using the mass ratio of phosphoric acid to resin. Steps 2 and 3 were repeated until the phosphoric acid adsorption capacity reached 400 wt%.

[0084] The prepared electrodes and PBI / H3PO4 composite membranes were stacked in a mold in a specific order. Then, the mold was placed in a hot press for hot pressing and shaping of the membrane electrode. Finally, it was placed in a sealed bag for storage.

[0085] The above methods are used to obtain the fuel cell membrane electrode.

[0086] The active area of ​​the prepared membrane electrode is 50 cm². 2 The cathode and anolyte gas diffusion layers have the same composition and structure, both consisting of a support layer and a microporous layer. The support layer is mainly Torray carbon paper with a thickness of 140 micrometers. The microporous layer is mainly composed of carbon powder and PTFE. The carbon powder type is Vulcan XC-72, and the carbon powder loading in the microporous layer is 4 mg / cm³. 2 The PTFE content is 25%, and the thickness is 40 micrometers. The anode catalyst layer consists of 40 wt% Pt / C catalyst (40 wt% is the percentage of Pt mass in the Pt / C catalyst) and PTFE, with a platinum loading of 0.5 mg / cm³.2 The PTFE content in the anode catalyst layer is 20%. The cathode catalyst layer consists of 60 wt% PtCo / C and PTFE, with a Pt loading of 0.5 mg / cm³. 2 The PTFE content is 20%. The cathode catalyst layer includes an inner cathode catalyst layer and an outer cathode catalyst layer. The inner cathode catalyst layer is close to the proton exchange membrane and has a PEG200 content of 10wt% before the pore-forming agent is heated and volatilized. The outer cathode catalyst layer is close to the microporous layer and has a PEG400 content of 30wt% before the pore-forming agent is heated and volatilized.

[0087] Example 2

[0088] The difference from Example 1 is that in Example 2, the pore-forming agent used in the outer layer slurry of the cathode catalyst layer in the high-temperature proton exchange membrane fuel cell membrane electrode assembly is PEG800, that is, the molecular weight of the pore-forming agent is 800; and the catalyst is a PtCo / C catalyst with a Pt content of 30%.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that the content of pore-forming agent in the cathode catalyst layer of the high-temperature proton exchange membrane fuel cell membrane electrode assembly in Comparative Example 1 is 0.

[0091] Comparative Example 2

[0092] The difference from Example 1 is that in Comparative Example 2, the PEG content in both the inner and outer catalyst layers of the cathode in the high-temperature proton exchange membrane fuel cell membrane electrode assembly is 20 wt%.

[0093] Performance testing

[0094] According to GB / T 20042.5-2009, the polarization curve of the obtained high-temperature proton exchange membrane fuel cell membrane electrode was tested. The specific operating conditions were: single cell operating temperature of 160℃, anode feed of pure hydrogen, cathode feed of atmospheric pressure air, and cathode / anode feed ratio of 3 / 1.5.

[0095] According to GB / T 20042.5-2009, the membrane electrode impedance of a high-temperature proton exchange membrane fuel cell was tested. The specific operating conditions were: single cell operating temperature 160℃, anode feed pure hydrogen, cathode feed atmospheric pressure air, and a cathode / anode feed ratio of 3 / 1.5 @ 0.5A cm. -2 The discharge current density is 0.5 A cm⁻¹. -2 .

[0096] Referring to GB / T 20042.5-2009, cyclic voltammetry testing of the membrane electrode assembly (MEA) of a high-temperature proton exchange membrane fuel cell was performed. The specific operating conditions were: single-cell operating temperature of 160℃, dry N2 introduced into the cathode at a flow rate of 4.6 ml / min. -1 cm -2 Dry H2 was introduced into the anode at a flow rate of 6.9 ml / min. -1 cm -2 The voltage range is 0.05V-1.2V, and the sweep speed is 0.05V / s. -1 .

[0097] Test results are attached to the instruction manual. Figure 2-5 In the figure, PEG0 represents Comparative Example 1, PEG20 represents Comparative Example 2, PEG10 / 30 represents Example 1, and PEG10 / 30 low Pt represents Example 2. PEG0 indicates that the PEG content in the solid components of the catalyst layer slurry is 0 wt%, PEG10 / 30 indicates that the PEG200 content in the solid components of the inner catalyst layer (close to the membrane) slurry is 10 wt%, while the PEG600 or PEG800 content in the solid components of the outer catalyst layer (far from the membrane) slurry is 30 wt%, and low Pt indicates that the Pt content of the catalyst used in Example 2 is 30%, which is lower than the 60% Pt content of Examples 1, 1, and 2.

[0098] See Figure 2 The membrane electrode polarization characteristic curves of the cathode structures in Examples 1 and 2 of this invention, and the cathode structures in Comparative Examples 1 and 2 were measured. As can be seen from the figures, at 0.1 A / cm... 2 Under these conditions, the measured voltages of the corresponding membrane electrodes for the cathode structures of Embodiments 1 and 2 of the present invention and the cathode structures of Comparative Examples 1 and 2 were 0.656V, 0.667V, 0.645V, and 0.654V, respectively; at 0.5A / cm 2 Under these conditions, the measured voltages of the corresponding membrane electrodes of the cathode structure in Example 1 of the present invention and the cathode structures in Comparative Examples 1 and 2 were 0.498V, 0.472V, and 0.483V, respectively; at 1.0 A / cm 2 The measured voltages of the membrane electrodes corresponding to the cathode structures of Embodiments 1 and 2 of the present invention and the cathode structures of Comparative Examples 1 and 2 were 0.359V, 0.531V, 0.325V, and 0.334V, respectively; the measured maximum power densities of the membrane electrodes corresponding to the cathode structures of Embodiments 1 and 2 of the present invention and the cathode structures of Comparative Examples 1 and 2 were 0.359W / cm², respectively. 2 0.446W / cm 2 0.325W / cm 2 0.339W / cm 2Compared to the membrane electrodes with cathode pore structures in Comparative Examples 1 and 2, the membrane electrodes with adjustable pore size gradient cathodes in Examples 1 and 2 of this invention exhibit lower polarization losses, and in particular, the reduction in mass transfer polarization results in higher overall battery performance. Referring to Examples 1 and 2, the gradient cathode structures with different pore sizes proposed in this invention, constructed using PEG, require higher external mass transfer channels after matching with catalysts with lower Pt content. Using PEG800 with a higher molecular weight to create pores in the external layer significantly improves battery performance.

[0099] See Figure 3 Impedance spectra show that, compared to Comparative Example 1, Examples 1 and 2 have lower internal resistance at high frequencies and lower cathode charge transfer resistance at mid frequencies. This is mainly because the cathode structure using 10wt% PEG (inner catalyst layer) and 30wt% PEG (outer catalyst layer) is more conducive to the uniform distribution of phosphoric acid, avoiding acid flooding caused by excessive local phosphoric acid and lower three-phase interface area caused by insufficient phosphoric acid, thereby reducing activation polarization and ohmic polarization and improving performance. Examples 1 and 2 show significant improvements over Comparative Example 2. This is mainly due to the coupling effect of the phosphoric acid distribution in the inner catalyst layer's pore structure on cathode polarization and the effect of the outer catalyst layer's pore structure on mass transfer polarization. In the 20wt% PEG cathode structure, the phosphoric acid distribution is more uniform, but the outer mass transfer channels are relatively fewer. In the 10wt% PEG (inner catalyst layer) and 30wt% PEG (outer catalyst layer) cathode structures, the phosphoric acid distribution is relatively uneven, but the mass transfer effect is better. This gradient pore structure blocks the large-scale diffusion of phosphoric acid to the outer layer at high current densities, protecting the outer layer's mass transfer channels. Simultaneously, the high pore-forming agent content in the outer layer itself provides more active sites. Therefore, Example 1 shows significant improvements at high current densities (0.8 A / cm²). -2 The mass transfer polarization under the condition of ) is significantly reduced. Compared with Examples 1 and 2, Example 2, after using PEG800 with a larger molecular weight for pore formation, significantly increased the capacity for phosphoric acid. At the same time, the mass transfer channel further expanded due to the increase in pore size. This was manifested in the gradual separation of the semicircular signals of anodic polarization and cathodic polarization on the impedance spectrum, while the radius of the semicircle formed by the merging of cathodic polarization and mass transfer polarization decreased.

[0100] See Figure 4 Cyclic voltammetry curves were used to measure the ECSA of the cathode structures in Examples 1 and 2 of this invention, as well as those in Comparative Examples 1 and 2, which were 44.571 m. 2 / g, 42.694m 2 / g, 36.952m 2 / g, 63.048m 2 / g. It can be seen that compared to Comparative Example 1, Examples 1 and 2 possess higher electrochemically active surface areas (ECSA), demonstrating the optimization of phosphoric acid distribution by PEG pore-forming, allowing for the storage of more phosphoric acid within the catalyst layer, indirectly proving the enhancement effect on cathode polarization. Compared to Comparative Example 2, Examples 1 and 2 have relatively lower peak integrated areas. This is because, in order to improve the acid flooding resistance of the cathode catalyst layer, Example 1 used a relatively low pore-forming agent content and molecular weight in the inner catalyst layer, resulting in a denser pore structure that hinders the flooding of the outer catalyst layer by phosphoric acid, effectively protecting the catalyst active sites from poisoning by excess phosphoric acid.

[0101] See Figure 5 The oxygen gain histogram shows that, compared to Comparative Examples 1 and 2, the voltage gain of Examples 1 and 2 decreases continuously with increasing current density when using pure oxygen feed. This indicates that the cathode structure using 10wt% PEG200 (inner catalyst layer) and 30wt% PEG600 (outer catalyst layer) is more conducive to the mass transfer of oxygen under hydrogen-air conditions, reducing the impact of mass transfer polarization on the battery.

[0102] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0103] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for preparing a high-temperature proton exchange membrane fuel cell cathode, characterized in that, include: Preparation of cathode diffusion layer; After coating the cathode diffusion layer with a cathode outer catalyst layer slurry, the cathode outer catalyst layer is obtained by heat treatment; The cathode outer catalyst layer slurry includes a catalyst, a binder, and a pore-forming agent; the average pore size of the cathode outer catalyst layer is 60~150nm, and the porosity is 30%~45%. A cathode inner catalyst layer slurry is coated onto the surface of the outer catalyst layer of the cathode, and then heated to obtain the cathode inner catalyst layer. The cathode inner catalyst layer slurry includes a catalyst, a binder, and a pore-forming agent. The average pore size of the cathode inner catalyst layer is 30-50 nm, and the porosity is 25%-30%. The pore-forming agent is at least one of EG or PEG; The ratio of the pore-forming agent content in the cathode outer catalyst layer slurry to the pore-forming agent mass in the cathode inner catalyst layer slurry is 1.5~1; based on the total solid mass of the cathode outer catalyst layer slurry, the mass percentage of the pore-forming agent is 30%~50%, and the molecular weight of the pore-forming agent is 600~1000; based on the total solid mass of the cathode inner catalyst layer slurry, the mass percentage of the pore-forming agent in the cathode inner catalyst layer slurry is 0%~30%, and the molecular weight of the pore-forming agent is ≤600; the cathode outer catalyst layer slurry or the cathode inner catalyst layer slurry is heat-treated under a protective gas atmosphere. The protective gas includes N2; The heat treatment temperature is 50℃~300℃; A high-temperature proton exchange membrane fuel cell cathode obtained according to the above method includes a cathode diffusion layer, an outer cathode catalyst layer, and an inner cathode catalyst layer; The cathode diffusion layer includes a support layer and a microporous layer; The total pore area of ​​the outer catalyst layer of the cathode is 60~90m². 2 / g, median pore size V 200~800nm, average pore size 60~150nm, porosity 30%~45%; The total pore area of ​​the inner catalyst layer in the cathode is 30~50m². 2 / g, median pore size V 100-150nm, average pore size 30-50nm, porosity 25%-30%; The loading of noble metals in both the outer and inner catalyst layers of the cathode is 0.05–2.0 mg / cm³. 2 Furthermore, the noble metal loading in the inner catalyst layer of the cathode is higher than that in the outer catalyst layer of the cathode.

2. The method for preparing a high-temperature proton exchange membrane fuel cell cathode according to claim 1, characterized in that, The adhesive is a hydrophobic adhesive, specifically including at least one of PTFE, PVDF, FEP, ECTE, ETFE, PFA, or PDMS.

3. The method for preparing a high-temperature proton exchange membrane fuel cell cathode according to claim 1, characterized in that, The catalyst in the cathode outer catalyst layer slurry is one or more of Pt / C, PtFe / C, or PtCo / C; the mass fraction of Pt in Pt / C, PtFe / C, or PtCo / C is 5% to 70%; The catalyst in the slurry of the inner catalyst layer of the cathode is one or more of Pt black, PtCo / C or PtNi / C.

4. A high-temperature proton exchange membrane fuel cell cathode, characterized in that, The preparation method described in any one of claims 1-3 is used to obtain a cathode diffusion layer, an outer cathode catalyst layer, and an inner cathode catalyst layer; The cathode diffusion layer includes a support layer and a microporous layer; The total pore area of ​​the outer catalyst layer of the cathode is 60~90m². 2 / g, median pore size V 200~800nm, average pore size 60~150nm, porosity 30%~45%; The total pore area of ​​the inner catalyst layer in the cathode is 30~50m². 2 / g, median pore size V 100-150nm, average pore size 30-50nm, porosity 25%-30%; The loading of noble metals in both the outer and inner catalyst layers of the cathode is 0.05–2.0 mg / cm³. 2 Furthermore, the noble metal loading in the inner catalyst layer of the cathode is higher than that in the outer catalyst layer of the cathode.

5. A membrane electrode assembly for a high-temperature proton exchange membrane fuel cell, characterized in that, It includes a cathode, a proton exchange membrane, and an anode arranged in sequence; the cathode is the high-temperature proton exchange membrane fuel cell cathode as described in claim 4; The anode includes an anode diffusion layer and an anode catalyst layer. The anode diffusion layer includes a support layer and a microporous layer. The cathode diffusion layer, the outer cathode catalyst layer, the inner cathode catalyst layer, the proton exchange membrane, the anode catalyst layer, and the anode diffusion layer are arranged in sequence. Both the support layer in the cathode diffusion layer and the support layer in the anode diffusion layer are located on the side away from the proton exchange membrane.

6. The membrane electrode assembly for a high-temperature proton exchange membrane fuel cell according to claim 5, characterized in that, It is made by sequentially bonding a cathode, a proton exchange membrane, and an anode together, followed by hot pressing. The proton exchange membrane is a phosphoric acid-doped PBI membrane.

7. The membrane electrode assembly for a high-temperature proton exchange membrane fuel cell according to claim 6, characterized in that, The high-temperature proton exchange membrane fuel cell, which includes a high-temperature proton exchange membrane fuel cell membrane electrode, operates at a temperature of 140℃~220℃. When the high-temperature proton exchange membrane fuel cell is in operation, hydrogen is introduced into the anode side, and the HER reaction occurs at the anode. Air or oxygen is introduced into the cathode side, and the ORR reaction occurs at the cathode.

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