Method for preparing orr catalyst and application in high temperature proton exchange membrane fuel cell

Abstract

The application relates to the technical field of fuel cells and discloses an ORR catalyst preparation method and application in a high-temperature proton exchange membrane fuel cell, which comprises the following steps: S1, preparing an h-TiN porous framework; S2, immersing the h-TiN porous framework in a platinum precursor solution, and then obtaining a Pt / h-TiN framework after reduction; S3, completely immersing the Pt / h-TiN framework in an acidophilic inorganic sol to perform single limited infiltration, wherein the acidophilic inorganic sol is ZrO2 sol and / or Nb2O5 sol; and S4, after multiple limited infiltrations, gradient drying is performed to obtain an ORR catalyst. The application constructs a through electronic continuous network by using TiN, anchors a Pt catalytic phase in a pore structure, and constructs a continuous and connected acid phase / proton network, so that the acid phase is macroscopically connected in a catalytic layer and discontinuously covers a platinum surface, thereby improving the performance and durability at high temperatures.

Description

Technical Field

[0001] This invention relates to the technical field of fuel cells, and in particular to a method for preparing ORR catalysts and their application in high-temperature proton exchange membrane fuel cells. Background Technology

[0002] High-temperature proton exchange membrane fuel cells (HT-PEMFCs) typically employ phosphoric acid-doped polybenzimidazole (PA-PBI) or related acid-based membrane systems, enabling the cells to operate in the 120–200 °C range and under low or no external humidification conditions. This simplifies hydrothermal management at the system level and improves tolerance to impurities such as CO. However, the performance and durability of HT-PEMFCs are significantly influenced by the distribution and dynamic migration of phosphoric acid in the membrane-electrode system: phosphoric acid serves as both a proton conduction medium and a potential source of "acid phase coverage / poisoning" of the cathode catalyst.

[0003] Patents and research generally indicate that the PA-PBI system may experience local enrichment of phosphoric acid, infiltration along the pore structure, migration to the electrode / gas diffusion layer, and acid loss during operation. This can lead to: changes in the connectivity of proton channels within the catalyst layer, resulting in fluctuations in ion / proton-related impedance; continuous coverage of the acid phase near the Pt active site, causing an increase in charge transfer impedance and a reduction in the effective three-phase interface; and changes in the morphology of acid intrusion in the GDL / microporous layer, resulting in obstructed gas diffusion and enhanced mass transfer polarization.

[0004] To address the performance and durability issues caused by phosphoric acid distribution / migration, existing patents and engineering practices have shown a diversified trend in catalyst material improvement strategies. For example, patent CN120164971A uses manganese dioxide to coat Pt nanoparticles. Manganese dioxide not only serves as a protective layer but also forms a new proton conductor with phosphoric acid, improving the proton transport channels of the membrane electrode under high-temperature conditions and enhancing the performance of high-temperature proton fuel cells. Patent CN119153716A describes a molybdenum oxide-modified carbon-supported platinum alloy catalyst with excellent initial oxygen reduction activity, phosphoric acid resistance, and electrochemical stability, effectively solving the phosphoric acid poisoning problem of platinum-based catalysts in high-temperature proton exchange membrane fuel cells. Patent CN116682977A, through doping and coating platinum-based carbon-supported catalysts with silica followed by heat treatment, endows the catalyst with phosphoric acid poisoning resistance and enhances C binding force, reducing Pt particle agglomeration at high temperatures, thereby improving the catalyst's performance and lifespan in high-temperature proton exchange membrane fuel cell applications.

[0005] While the above approach can reduce the poisoning of platinum active sites by phosphoric acid to some extent, its technical route inherently suffers from the following drawbacks: (1) The trade-off between anti-poisoning and interfacial reaction / mass transfer is hard to avoid; to achieve anti-phosphoric acid effect, oxide coating or modification layer often requires high coverage or strong interfacial effect; however, increased coverage will lead to limited path of oxygen / reactants to the platinum surface, and decrease the effective area of ​​the three-phase interface, thereby causing an increase in charge transfer impedance and loss of activity, that is, the contradiction of "the stronger the protection, the more passivated the interface" appears. (2) It is difficult to ensure a continuous low proton impedance at the catalyst layer scale. Existing schemes focus on the regulation of platinum surface adsorption behavior or the formation of local proton conductors, but do not construct a controllable, interconnected and stable continuous proton / acid phase network in the catalyst layer pore structure. Under high temperature operation and acid phase dynamic migration conditions, the connectivity of proton channels in the catalyst layer is prone to fluctuate with time, resulting in high or drifting proton / ion transport related impedance. (3) The carbon carrier chassis limits the structure retention and durability limit under high temperature acid environment; even if the combination of carbon and platinum is enhanced by inorganic coating or particle agglomeration is inhibited, the carbon skeleton still faces the risk of pore structure degradation and mass transfer deterioration under high temperature acid environment, which will accelerate performance decay. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing an ORR catalyst and its application in a high-temperature proton exchange membrane fuel cell. A continuous electronic network (E-network) is constructed using TiN, with the Pt catalytic phase anchored in the reachable region of the TiN pore walls (forming ORR active sites). Furthermore, an acid-loving inorganic sol-gel network is used to construct a continuous acid phase / proton network (P-network) within the pore structure. The resulting catalyst, under high-temperature operating conditions, ensures low proton impedance while avoiding the formation of a continuous acid film on the Pt surface, thus balancing electron conduction, proton conduction, and oxygen mass transfer, and improving durability.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing an ORR catalyst, comprising the following steps: S1: h-TiN porous framework was prepared using F127 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, poloxamer F127) and PS microspheres (polystyrene microspheres) as template agents. S2: The h-TiN porous framework is immersed in a platinum precursor solution and then reduced to obtain a Pt / h-TiN framework. S3: Perform a single restricted immersion, completely immersing the Pt / h-TiN framework in an acid-loving inorganic sol for 20-40 s. The acid-loving inorganic sol is ZrO2 sol and / or Nb2O5 sol. Then, maintain a vacuum of -0.10 to -0.06 MPa for 10-20 s, release the gas, remove the framework, remove excess sol from the outer surface, and let it stand at room temperature for 2-10 min. S4: Repeat S3, perform multiple restricted impregnations, and then perform gradient drying to obtain the ORR catalyst.

[0008] The ORR catalyst comprises an electron continuous network (E-network), a proton continuous network (P-network), and a Pt catalytic phase supported on the electron continuous network.

[0009] This invention achieves a synergistic effect of "low proton impedance" and "phosphoric acid resistance coverage" through structural topology design rather than simple surface coating: a continuous electronic network (E-network) is constructed using TiN to improve conductivity and pore structure stability under high-temperature acid conditions; the Pt catalytic phase is anchored in the reachable region of the TiN pore walls (forming ORR active sites); an acid-loving inorganic sol-gel network is used to construct a continuous and interconnected acid phase / proton network (P-network) within the pore structure to reduce proton / ion transport-related impedance; and the spatial distribution of the acid phase is controlled by pore confinement, segmented restricted wetting, and gradient solidification, so that the acid phase is macroscopically interconnected in the catalytic layer but discontinuously covered on the platinum surface, thereby maintaining low proton impedance while avoiding the increase in charge transfer impedance and the shielding of active sites, thus improving performance and durability at high temperatures.

[0010] TiN combines electrical conductivity, thermal stability, and framework retention, making it more suitable as a stable electronic framework in high-temperature, acidic environments. Other carbon materials may be oxidized under high temperature and pressure conditions, leading to the destruction of the conductive framework and affecting electrode stability. Pt precursors adsorb on the TiN pore wall surface and undergo in-situ reduction nucleation, forming a stable Pt-TiN interface contact. Simultaneously, the pore wall confinement further inhibits Pt particle migration and aggregation. Furthermore, the TiN framework exhibits better structure retention under high-temperature, acidic environments, effectively preventing the deactivation of active sites due to structural collapse.

[0011] Meanwhile, TiN is more conducive to the synergistic construction of bicontinuous phase structures with acid-loving inorganic networks. The h-TiN porous framework provides a three-dimensional spatial support for the restricted entry, gradual bridging, and continuous network formation of acid-loving inorganic sol-gel networks within the porous structure. Due to the spatial confinement of the h-TiN porous framework, the sol preferentially remains on the pore walls, pore necks, and local interfaces after entry, rather than forming a uniform continuous liquid film on all surfaces. Negative pressure assistance is used to improve the accessibility of the inner pores, aiming to promote the sol's entry into the three-dimensional framework rather than enhancing the outer surface thickness. The purpose of removing excess sol from the outer surface is to prevent the formation of a continuous thick film on the outer surface. This operation does not remove the sol that has entered the pores and adhered to the pore walls or the Pt adjacent area, ultimately achieving restricted wetting and discontinuous coverage. In addition, the TiN framework has better structure retention capabilities under high-temperature acidic environments, which is beneficial for maintaining a bicontinuous phase topology where the electron network and proton network interweave, are continuous, and do not obscure each other.

[0012] Preferably, in S1, the pore size of the h-TiN porous framework is 5~20 nm and the porosity is 45~75%, more preferably, the porosity is 55~70%.

[0013] In the h-TiN porous framework, an appropriate interconnected pore structure facilitates oxygen diffusion and reduces local acid retention. Reasonable pore size and porosity help alleviate thermal stress, acid phase migration stress, and structural shrinkage stress, thereby improving the long-term stability of the catalyst layer. However, if the pore size is too large or the proportion of macropores is too high, it may cause localized sol accumulation and form a thick capping layer, which is detrimental to maintaining a discontinuous capping layer on the Pt surface. Pores that are too small will restrict the entry of inorganic sol into the framework, leading to a discontinuous proton network. Excessive porosity weakens the continuity and mechanical stability of the framework; excessively low porosity results in an overly dense structure, which is detrimental to oxygen mass transfer and the formation of an acid-loving network within the pores.

[0014] Preferably, S1 includes the following steps: dissolving F127 in a mixed solvent of isopropanol and water, adding TiN powder and dispersant and stirring to disperse, then adding PS microspheres and stirring to obtain a slurry; after the slurry is graded and dried, it is soaked in ethanol to dissolve F127, then soaked in THF (tetrahydrofuran) to dissolve PS microspheres, and finally dried to obtain an h-TiN porous framework.

[0015] Preferably, the volume ratio of isopropanol to water in the mixed solvent is 70-80%:20-30%; the average particle size of the TiN powder is 50-100 nm; the mass ratio of the TiN powder, F127, and PS microspheres is 1:0.1-0.2:0.7-0.9; the average particle size of the PS microspheres is 1-2 μm; the graded drying includes: standing at room temperature for 5-15 min, drying at 40-50 °C for 20-30 min, and then drying at 90-100 °C for 1-3 h.

[0016] Preferably, in S2, the platinum precursor solution comprises an aqueous solution of H2PtCl6 with a concentration of 15-25 mg·mL. -1 The impregnation time of the TiN porous framework in the platinum precursor solution is 30~60 min.

[0017] Preferably, in step S2, the reducing agent used for reduction is ethylene glycol, the reduction temperature is 120~150 ℃, and the reduction time is 30~60 min.

[0018] Preferably, in step S2, the reduction includes: transferring the impregnated TiN porous framework into a mixed solvent of ethylene glycol and water, reducing it at 120~150℃ for 30~60 min, and then removing and drying it to obtain a Pt / h-TiN framework; the volume ratio of ethylene glycol to water in the mixed solvent is 70~80%:20~30%.

[0019] Preferably, in S3, the solid content of the acid-loving inorganic sol is 10-20 wt%, and the particle size is 2-20 nm; more preferably, the solid content is 12-14 wt%, and the particle size is 3-10 nm.

[0020] Preferably, in step S3, the vacuum degree is -0.10 to -0.08 MPa, and more preferably, the vacuum degree is -0.10 MPa.

[0021] Preferably, in S4, the number of times the restricted impregnation is 2 to 4; the gradient drying includes: vacuum drying at 40 to 50 ℃ for 20 to 30 min, followed by curing at 110 to 130 ℃ for 40 to 60 min.

[0022] Gradient drying achieves a balance between "proton network continuity" and "discontinuous Pt surface coverage." First, low-temperature slow drying gently removes the solvent, inhibiting the migration of the sol to the outer surface during evaporation and preferentially fixing it to the pore walls, necks, and local interfaces. Then, higher-temperature curing promotes condensation / gelation, transforming it into a stable acid-loving network. Direct, rapid, high-temperature drying easily leads to sol migration and accumulation to the outer surface or pore openings, forming continuous films or locally thick films, which is detrimental to maintaining discontinuous coverage on the Pt surface.

[0023] If the low-temperature stage is not long enough, the solvent will not be removed sufficiently, and the sol will still have high fluidity; if the low-temperature stage temperature is too high, it will approach rapid drying, which is not conducive to maintaining the restricted distribution.

[0024] If the high-temperature phase is insufficient, the inorganic network will not shrink sufficiently, resulting in insufficient stability and continuity of the P-network. If the high-temperature phase is too high or too long, it may lead to excessive network shrinkage, local aggregation, thickening of the overlay layer, or clogging of the orifices.

[0025] Preferably, the content of ZrO2 and / or Nb2O5 in the ORR catalyst is 8~22 wt%, more preferably, the content of ZrO2 and / or Nb2O5 is 10~18 wt%; the Pt loading in the Pt / h-TiN framework is 10~30 wt%, more preferably, the Pt loading is 15~25 wt%.

[0026] Secondly, the present invention also provides an application of the ORR catalyst prepared by the above preparation method in a high-temperature proton exchange membrane fuel cell, wherein the ORR catalyst is used as a cathode electrode material.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The interconnected pore structure in the TiN porous framework ensures the main oxygen diffusion channel and the liquid / acid drainage channel, which alleviates mass transfer polarization. At the same time, the continuous TiN framework enhances the structure retention ability under high temperature acid environment, reduces the mass transfer deterioration and performance degradation caused by pore structure degradation, and is more suitable for the structural stability under high temperature conditions. (2) An acid-loving inorganic sol-gel network (ZrO2 / Nb2O5) is used as the P-network. The probability of intrapore connectivity is increased by multiple short-term confined wetting, forming a continuous proton channel. Through pore confinement and confined wetting / gradient solidification, the acid phase is connected in the pore and forms a discontinuous coverage on the Pt surface, avoiding the increase of Rct and the shielding of active sites caused by the continuous acid film. (3) TiN forms a through E-network and P-network forms a through proton channel. The double continuous interpenetrating structure reduces polarization loss. Attached Figure Description

[0028] Figure 1 The morphology and elemental distribution characterization diagrams of the Pt / h-TiN-Nb2O5 catalyst obtained in Example 2 are shown below. Figure 2 The Pt / h-TiN-ZrO2 catalyst in Example 1 was used at 160 °C and 0.5 A·cm⁻¹. -2 Voltage-time curve of constant current endurance test under certain conditions; Figure 3 The Pt / h-TiN-Nb2O5 catalyst in Example 2 was tested at 160 °C and 0.5 A·cm⁻¹. -2 Voltage-time curve of constant current endurance test under certain conditions; Figure 4 The Pt / h-TiN catalyst in Comparative Example 1 was tested at 160 °C and 0.5 A·cm⁻¹. -2 Voltage-time curve of constant current endurance test under certain conditions; Figure 5 The commercial 20% Pt / C catalyst in Comparative Example 2 was tested at 160 °C and 0.5 A·cm⁻¹. -2 Voltage-time curve of constant current endurance test under certain conditions. Detailed Implementation

[0029] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] The preparation of ZrO2 sol in the following examples and comparative examples includes the following steps: Zr(OPr)4 zirconium propoxide is added to anhydrous isopropanol and stirred for 10-30 min; acetylacetone is added and stirring is continued for 30-60 min to obtain solution I; deionized water is added to anhydrous isopropanol to obtain solution II; solution II is added dropwise to solution I while stirring is maintained; after the addition is complete, stirring is continued for 30-60 min; the mixture is allowed to stand for 10-30 min and then filtered through a 0.45 μm PTFE membrane to obtain ZrO2 sol.

[0031] The preparation of Nb2O5 sol in the following examples and comparative examples includes the following steps: adding niobium pentaethoxy to anhydrous isopropanol and stirring for 10-30 min; adding acetylacetone and continuing to stir for 30-60 min to obtain solution I; adding deionized water to anhydrous isopropanol to obtain solution II; adding solution II dropwise to solution I while maintaining stirring; after the addition is complete, continuing to stir for 30-60 min; allowing to stand for 10-30 min; and filtering with a 0.45 μm PTFE membrane to obtain Nb2O5 sol.

[0032] Example 1: Preparation of dual-continuous phase catalyst Pt / h-TiN-ZrO2 S1: h-TiN (E-network) construction (1) Take 18 mg of F127 and add it to 1.5 mL of isopropanol / water mixed solvent (volume ratio 80 / 20), stir for 30 min to completely dissolve it; then add 100 mg of TiN powder (average particle size 70 nm) and ultrasonically disperse for 15 min, add 1 mg of polyvinylpyrrolidone (PVP, K30) and stir for 30 min; finally add 80 mg of PS microspheres (average particle size 1 μm) and stir at 500 rpm for 60 min to obtain a uniform slurry; (2) Let the above slurry stand at room temperature for 10 min, then pre-dry at 50 ℃ for 30 min; then dry at 90 ℃ for 2 h; (3) Soak the dried sample in ethanol for 2 hours to dissolve it, then replace the ethanol and soak for another 2 hours; rinse with ethanol twice after taking it out. (4) Soak in THF for 4 hours to dissolve, then replace the THF and soak for another 4 hours; rinse twice with ethanol after taking it out. (5) The h-TiN porous framework was obtained by vacuum drying at 80 °C for 4 h with a pore size of 5~20 nm and a porosity of 62%.

[0033] S2: Pt catalyst phase supported (Pt / h-TiN) Take 3.54 mL of solution with a concentration of 20 mg / mL. -1An aqueous solution of H2PtCl6 was prepared, and 80 mg of h-TiN porous framework was added and ultrasonically dispersed for 30 min. The impregnated h-TiN porous framework was then transferred into 50 mL of ethylene glycol / water mixed solvent (volume ratio 80 / 20) and reduced at 120 °C for 60 min. After reduction, the framework was washed three times each with deionized water and ethanol by centrifugation and then vacuum dried at 80 °C for 6 h to obtain a Pt / h-TiN framework with a Pt loading of 20.5 wt%.

[0034] S3: Preparation of Pt / h-TiN-ZrO2 Single-time restricted immersion: 275 mg of Pt / h-TiN framework was completely immersed in ZrO2 sol (solid content 15 wt%, average particle size 16 nm) for 30 s. After removal, it was immediately transferred to a vacuum desiccator and kept for 20 s, and the gas was slowly released. The sample was removed and the excess sol on the outer surface was gently wiped off with a lint-free paper (avoid wiping the pore surface). The sample was allowed to stand at room temperature for 5 min.

[0035] Perform three restricted impregnations according to the above steps; then perform gradient solidification on the impregnated sample, vacuum dry at 50 ℃ for 20 min, and then solidify at 110 ℃ for 45 min to obtain the Pt / h-TiN-ZrO2 catalyst with a ZrO2 content of 12.0 wt%.

[0036] Example 2: Preparation of the dual-continuous phase catalyst Pt / h-TiN-Nb2O5 S1 and S2 are the same as in Example 1.

[0037] S3: Preparation of Pt / h-TiN-Nb2O5 Single-time restricted immersion: 530 mg of Pt / h-TiN framework (Pt loading of 20.5 wt%) was completely immersed in Nb2O5 sol (solid content of 20 wt%, average particle size of 15 nm) for 30 s. After removal, it was immediately transferred to a vacuum desiccator and kept for 20 s, and the gas was slowly released. The sample was removed and the excess sol on the outer surface was gently wiped off with a lint-free paper (avoid wiping the pore surface). The sample was then allowed to stand at room temperature for 5 min.

[0038] The above steps were followed to perform three restricted impregnations. The impregnated sample was then subjected to gradient curing, vacuum drying at 50 °C for 20 min, followed by curing at 110 °C for 45 min to obtain the Pt / h-TiN-Nb2O5 catalyst, in which the Nb2O5 sol content was 13.9 wt%.

[0039] Example 3: Preparation of dual-continuous phase catalyst Pt / h-TiN-ZrO2 S1: h-TiN (E-network) construction (1) Take 13 mg of F127 and add it to 1.5 mL of isopropanol / water mixed solvent (volume ratio 80 / 20), stir for 30 min to completely dissolve it; then add 100 mg of TiN powder (average particle size 70 nm) and ultrasonically disperse for 15 min, add 1 mg of polyvinylpyrrolidone (PVP, K30) and stir for 30 min; finally add 70 mg of PS microspheres (average particle size 2 μm) and stir at 500 rpm for 60 min to obtain a uniform slurry; (2) Let the above slurry stand at room temperature for 10 min, then pre-dry at 50 ℃ for 30 min; then dry at 90 ℃ for 2 h; (3) Soak the dried sample in ethanol for 2 h to dissolve it, then replace the ethanol and soak for another 2 h; rinse with ethanol twice after taking it out. (4) Soak in THF for 4 hours to dissolve, then replace the THF and soak for another 4 hours; rinse twice with ethanol after taking it out. (5) The h-TiN porous framework was obtained by vacuum drying at 80 °C for 4 h with a pore size of 5~20 nm and a porosity of 55%.

[0040] S2: Pt catalyst phase supported (Pt / h-TiN) Take 1.78 mL of solution with a concentration of 20 mg / mL. -1 80 mg of h-TiN porous framework was added to an aqueous solution of H2PtCl6 and ultrasonically dispersed for 30 min. The impregnated h-TiN porous framework was then transferred to 50 mL of ethylene glycol / water mixed solvent (volume ratio 80 / 20) and reduced at 120 °C for 60 min. After reduction, the framework was washed three times each with deionized water and ethanol by centrifugation and then vacuum dried at 80 °C for 6 h to obtain a Pt / h-TiN framework with a Pt loading of 10.4 wt%.

[0041] S3: Preparation of Pt / h-TiN-ZrO2 Single-time restricted immersion: Immerse 275 mg of Pt / h-TiN framework completely in ZrO2 sol (solid content 15 wt%, average particle size 16 nm) for 30 s, remove and immediately transfer to a vacuum desiccator for 20 s, slowly release the gas; remove the sample and gently blot away excess sol on the outer surface with lint-free paper (avoid wiping the pore surface); let stand at room temperature for 5 min.

[0042] The above steps were followed to perform three restricted impregnations. The impregnated sample was then subjected to gradient curing, vacuum drying at 50 °C for 20 min, followed by curing at 110 °C for 45 min to obtain the Pt / h-TiN-ZrO2 catalyst with a ZrO2 content of 12.2 wt%.

[0043] Comparative Example 1: Preparation of Pt / h-TiN catalyst The difference from Example 1 is that the ZrO2 sol was not impregnated.

[0044] S1: h-TiN (E-network) construction (1) Take 18 mg of F127 and add it to 1.5 mL of isopropanol / water mixed solvent (volume ratio 80 / 20), stir for 30 min to completely dissolve it; then add 100 mg of TiN powder (average particle size 70 nm) and ultrasonically disperse for 15 min, add 1 mg of polyvinylpyrrolidone (PVP, K30) and stir for 30 min; finally add 80 mg of PS microspheres (average particle size 1 μm) and stir at 500 rpm for 60 min to obtain a uniform slurry; (2) Let the above slurry stand at room temperature for 10 min, then pre-dry at 50℃ for 30 min; then dry at 90℃ for 2 h; (3) Soak the dried sample in ethanol for 2 h to dissolve it, then replace the ethanol and soak for another 2 h; rinse with ethanol twice after taking it out. (4) Soak in THF for 4 hours to dissolve, then replace the THF and soak for another 4 hours; rinse twice with ethanol after taking it out. (5) The h-TiN porous framework was obtained by vacuum drying at 80℃ for 4 h with a pore size of 5~20 nm and a porosity of 62%.

[0045] S2: Pt catalyst phase supported (Pt / h-TiN) Take 3.54 mL of solution with a concentration of 20 mg / mL. -1 An aqueous solution of H2PtCl6 was prepared, and 80 mg of h-TiN porous framework was added and ultrasonically dispersed for 30 min. The impregnated h-TiN porous framework was then transferred to 50 mL of ethylene glycol / water mixed solvent (volume ratio 80 / 20) and reduced at 120 °C for 60 min. After reduction, the framework was washed three times each with deionized water and ethanol by centrifugation and then vacuum dried at 80 °C for 6 h to obtain a Pt / h-TiN framework with a Pt loading of 20.5 wt%.

[0046] Comparative Example 2: Commercial 20% Pt / C catalyst Comparative Example 3: Preparation of the dual-continuous phase macroporous catalyst Pt / h-TiN-ZrO2-1 The difference from Example 1 is that too much F127 was added during the construction of the h-TiN porous framework, resulting in excessively large pore size and porosity.

[0047] S1: h-TiN (E-network) construction (1) Take 25 mg of F127 and add it to 1.5 mL of isopropanol / water mixed solvent (volume ratio 80 / 20), stir for 30 min to completely dissolve it; then add 100 mg of TiN powder (average particle size 70 nm) and ultrasonically disperse for 15 min, add 1 mg of polyvinylpyrrolidone (PVP, K30) and stir for 30 min; finally add 80 mg of PS microspheres (average particle size 2 μm) and stir at 500 rpm for 60 min to obtain a uniform slurry; (2) Let the above slurry stand at room temperature for 10 min, then pre-dry at 50 ℃ for 30 min; then dry at 90 ℃ for 2 h; (3) Soak the dried sample in ethanol for 2 h to dissolve it, then replace the ethanol and soak for another 2 h; rinse with ethanol twice after taking it out. (4) Soak in THF for 4 hours to dissolve, then replace the THF and soak for another 4 hours; rinse twice with ethanol after taking it out. (5) The h-TiN porous framework was obtained by vacuum drying at 80℃ for 4 h with a pore size of 20~40 nm and a porosity of 77%.

[0048] S2: Pt catalyst phase supported (Pt / h-TiN) Take 3.54 mL of solution with a concentration of 20 mg / mL. -1 80 mg of h-TiN porous framework was added to an aqueous solution of H2PtCl6 and ultrasonically dispersed for 30 min. The impregnated h-TiN porous framework was then transferred to 50 mL of ethylene glycol / water mixed solvent (volume ratio 80 / 20) and reduced at 120 °C for 60 min. After reduction, the framework was washed three times each with deionized water and ethanol by centrifugation and then vacuum dried at 80 °C for 6 h to obtain a Pt / h-TiN framework with a Pt loading of 21.6 wt%.

[0049] S3: Preparation of Pt / h-TiN-ZrO2 Single-time restricted immersion: 275 mg of Pt / h-TiN framework was completely immersed in ZrO2 sol (solid content 15 wt%, average particle size 16 nm) for 30 s. After removal, it was immediately transferred to a vacuum desiccator and kept for 20 s, and the gas was slowly released. The sample was removed and the excess sol on the outer surface was gently wiped off with a lint-free paper (avoid wiping the pore surface). The sample was allowed to stand at room temperature for 5 min.

[0050] The above steps were followed to perform three restricted impregnations. The impregnated sample was then subjected to gradient curing, vacuum drying at 50 °C for 20 min, followed by curing at 110 °C for 45 min to obtain the Pt / h-TiN-ZrO2-1 catalyst, in which the ZrO2 content was 15.1 wt%.

[0051] Comparative Example 4: Preparation of the dual-continuous phase catalyst Pt / h-TiN-ZrO2-2 The difference from Example 1 is that the gradient curing parameters in S3 are set differently.

[0052] S1: h-TiN (E-network) construction (1) Take 18 mg of F127 and add it to 1.5 mL of isopropanol / water mixed solvent (volume ratio 80 / 20), stir for 30 min to completely dissolve it; then add 100 mg of TiN powder (average particle size 70 nm) and ultrasonically disperse for 15 min, add 1 mg of polyvinylpyrrolidone (PVP, K30) and stir for 30 min; finally add 80 mg of PS microspheres (average particle size 1 μm) and stir at 500 rpm for 60 min to obtain a uniform slurry; (2) Let the above slurry stand at room temperature for 10 min, then pre-dry at 50 ℃ for 30 min; then dry at 90 ℃ for 2 h; (3) Soak the dried sample in ethanol for 2 h to dissolve it, then replace the ethanol and soak for another 2 h; rinse with ethanol twice after taking it out. (4) Soak in THF for 4 hours to dissolve, then replace the THF and soak for another 4 hours; rinse twice with ethanol after taking it out. (5) The h-TiN porous framework was obtained by vacuum drying at 80 °C for 4 h with a pore size of 5~20 nm and a porosity of 62%.

[0053] S2: Pt catalyst phase supported (Pt / h-TiN) Take 3.54 mL of solution with a concentration of 20 mg / mL. -1 An aqueous solution of H2PtCl6 was prepared, and 80 mg of h-TiN porous framework was added and ultrasonically dispersed for 30 min. The impregnated h-TiN porous framework was then transferred into 50 mL of ethylene glycol / water mixed solvent (volume ratio 80 / 20) and reduced at 120 °C for 60 min. After reduction, the framework was washed three times each with deionized water and ethanol by centrifugation and then vacuum dried at 80 °C for 6 h to obtain a Pt / h-TiN framework with a Pt loading of 20.5 wt%.

[0054] S3: Preparation of Pt / h-TiN-ZrO2 Single-time restricted immersion: 275 mg of Pt / h-TiN framework was completely immersed in ZrO2 sol (solid content 15 wt%, average particle size 16 nm) for 30 s. After removal, it was immediately transferred to a vacuum desiccator and kept for 20 s, and the gas was slowly released. The sample was removed and the excess sol on the outer surface was gently wiped off with a lint-free paper (avoid wiping the pore surface). The sample was allowed to stand at room temperature for 5 min.

[0055] Perform three restricted impregnations according to the above steps; then perform gradient solidification on the impregnated sample, vacuum dry at 30 ℃ for 10 min, and then solidify at 140 ℃ for 55 min to obtain the Pt / h-TiN-ZrO2-2 catalyst with a ZrO2 content of 12.0 wt%.

[0056] Performance testing (1) ECSA test: The catalysts from Examples 1-3 and Comparative Examples 1-4 were prepared into catalyst inks. 5 mg of catalyst was dispersed in 1 mL of ethanol / water (volume ratio 3:1) mixed solution, and 16 μL of Nafion solution was added. After sonication for 30 min, the catalyst ink was formed. The catalyst ink was drop-coated onto the surface of a glassy carbon rotating disk electrode (RDE) to achieve a Pt loading of 15 μg Pt·cm⁻¹ on the electrode. -2 After drying at room temperature, it was used as the working electrode. Using a platinum wire as the counter electrode and a reversible hydrogen electrode (RHE) as the reference electrode, dissolved oxygen was removed by purging with N2 for 20 min in a 0.10 M HClO4 electrolyte. Subsequently, the working electrode underwent cyclic voltammetry pretreatment (potential range 0.05–1.00 V vs RHE, scan rate 50 mV·s). -1 To stabilize the surface state, the potential was maintained at 0.10 V vs RHE, and CO was introduced for 10 min to saturate the Pt surface with CO adsorption. Then, N2 was purged for 20 min to remove dissolved CO from the solution, followed by purging with 20 mV·s⁻¹. -1 A single scan was performed in the range of 0.05–1.00 V vs RHE to obtain the CO-stripping peak, and the ECSA under phosphoric acid-free conditions was obtained by integration.

[0057] H3PO4 was added to the electrolyte to a concentration of 10 mM while keeping other conditions constant. The above CO adsorption-purge-stripping scanning process was repeated to obtain ECSA under phosphoric acid conditions. The ECSA retention rate was calculated as ECSA (with phosphoric acid) / ECSA (without phosphoric acid) to characterize the degree of occupancy of Pt active sites by phosphoric acid adsorption and the catalyst's resistance to phosphoric acid poisoning.

[0058] (2) Electrochemical performance testing: The catalysts from Examples 1-3 and Comparative Examples 1-4 were used to prepare cathode electrodes and composited with a gas diffusion layer. A commercially available carbon paper-type gas diffusion layer was used as the substrate, with its microporous layer facing the catalyst layer. The catalyst ink was uniformly sprayed onto the surface of the gas diffusion layer using a spraying method and dried at 80 °C. The cathode Pt loading was controlled at 0.2 mgPt·cm⁻¹. -2The cathode electrode was obtained. A commercial Pt / C electrode was used as the anode, and a phosphoric acid-doped PBI membrane (PA-PBI) was used as the proton exchange membrane. After aligning the membrane with the cathode and anode electrodes, the MEA was prepared by hot pressing at 160 °C and 1.0 MPa for 3 min and then installed in a single-cell fixture and sealed to the test bench. First, N2 was introduced into the anode and cathode at 100 sccm each for 10 min at room temperature for purging. Then, the temperature was gradually increased to 160 °C (holding at 120 °C for 15 min, then increasing to 160 °C and holding for 30 min). Subsequently, the anode gas was switched to H2 and the cathode gas was switched to O2, with the back pressure set to 100 kPa (gauge pressure) and kept constant.

[0059] First, stabilize at 160 °C using OCV for 15 min, then activate using a constant current method: 0.10 A·cm. -2 Maintain for 10 min at 0.20 A·cm -2 Maintain for 10 min at 0.50 A·cm -2 Maintain for 20 min, then at 0.20 A·cm -2 The system was allowed to stabilize for 10 minutes, and the voltage at that operating point was recorded as the initial performance. Then, a constant current endurance test was performed at 160 °C with constant gas supply and back pressure: 0.50 A·cm. -2 The system was continuously operated for 100 hours, and the voltage-time curve was recorded in real time. The voltage decay rate (mV·h) was calculated by comparing the voltage at the end of the endurance test with the initial voltage. -1 (This is used to evaluate the operational stability and anti-attenuation ability of the catalyst layer under 160 °C conditions.)

[0060] Table 1 Performance test data of catalysts in Examples 1-3 and Comparative Examples 1-4

[0061] like Figure 1 The image shows the morphology and elemental distribution characterization of the Pt / h-TiN-Nb2O5 catalyst obtained in Example 2. The left side is a low-magnification morphology image, showing the porous aggregated structure of the catalyst formed by the stacking of nanoparticles; the middle side is a high-magnification morphology image, with the arrow indicating the brighter Pt nanoparticles supported on the framework surface; the right side shows the elemental distribution maps of Pt, Nb, and Ti, showing that Pt is distributed in discrete particles, Nb is relatively uniformly distributed in the sample, and Ti is continuously distributed as a framework element.

[0062] like Figure 2 , Figure 3 , Figure 4 , Figure 5 The figures shown are of the catalysts used in Examples 1-2 and Comparative Examples 1-2 at 160 °C and 0.5 A·cm⁻¹. -2The voltage-time curves of the constant current durability test under the given conditions are shown in the figure. The figure shows the catalyst at 160 °C and 0.5 A·cm⁻¹. -2 The voltage decay behavior during 100 h of continuous operation under the specified conditions was investigated. Table 1 shows the calculated voltage decay rate. It can be seen that the voltage decay rate of the catalysts in Examples 1-3 is significantly lower than that of the commercial 20% Pt / C catalyst in Comparative Example 2, indicating that the catalyst prepared in this invention has excellent operational stability and anti-decay ability at 160 °C. In Comparative Example 1, the catalyst did not introduce an acid-loving inorganic sol-gel network as a P-network, thus failing to form continuous proton channels, and the Pt active sites were more easily occupied by phosphate, resulting in poor anti-decay ability. In Comparative Example 3, the pore size and porosity of the h-TiN porous framework were relatively large, leading to poor sol-wetting effect and weakening of framework continuity and mechanical stability, resulting in poor operational stability. The drying conditions in Comparative Example 4 resulted in insufficient low-temperature slow drying and excessive high-temperature curing, leading to easier sol migration, local agglomeration, thickening of the capping layer, or pore blockage, thereby reducing the continuity and stability of the P-network and significantly affecting the voltage decay rate.

[0063] Table 1 shows that the ECSA retention rates of Examples 1-3 under phosphoric acid conditions were significantly higher than those of Comparative Examples 1-4, indicating that the present invention, by constructing an acid-loving inorganic sol-gel network, can effectively reduce the coverage of Pt active sites by phosphoric acid and improve the catalyst's resistance to phosphoric acid poisoning. Among them, Comparative Example 1, due to the absence of a P-network, had a relatively low ECSA retention rate. Although Comparative Examples 3 and 4 introduced ZrO2, their resistance to phosphoric acid poisoning was relatively poor because the framework pore structure parameters or gradient drying conditions deviated from the limits defined in this invention. Although Comparative Example 2 had the highest ECSA retention rate under phosphoric acid-free conditions, its ECSA retention rate was only 75.5%, indicating that commercial Pt / C is more prone to active site coverage under phosphoric acid conditions. In summary, the synergistic optimization of the h-TiN framework pore structure, restricted wetting, and gradient drying conditions in this invention is key to forming a high-quality P-network and improving the catalyst's resistance to phosphoric acid poisoning.

[0064] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing an ORR catalyst, characterized in that, Includes the following steps: S1: An h-TiN porous framework was prepared using F127 and PS microspheres as template agents; the pore size of the h-TiN porous framework was 5~20 nm, and the porosity was 45~75%. S2: The h-TiN porous framework is immersed in a platinum precursor solution and then reduced to obtain a Pt / h-TiN framework. S3: Perform a single restricted immersion, completely immersing the Pt / h-TiN framework in an acid-loving inorganic sol for 20-40 s. The acid-loving inorganic sol is ZrO2 sol and / or Nb2O5 sol. Then, maintain a vacuum of -0.10 to -0.06 MPa for 10-20 s, release the gas, remove the framework, remove excess sol from the outer surface, and let it stand at room temperature for 2-10 min. S4: Repeat S3, perform multiple restricted impregnations, and then perform gradient drying, which includes: vacuum drying at 40~50 ℃ for 20~30 min, followed by curing at 110~130 ℃ for 40~60 min to obtain the ORR catalyst.

2. The method for preparing the ORR catalyst according to claim 1, characterized in that, S1 includes the following steps: F127 is dissolved in a mixed solvent of isopropanol and water, TiN powder and dispersant are added and stirred to disperse, and then PS microspheres are added and stirred to obtain a slurry; the slurry is graded and dried, then soaked in ethanol to dissolve F127, then soaked in THF to dissolve PS microspheres, and finally dried to obtain h-TiN porous framework.

3. The method for preparing the ORR catalyst according to claim 2, characterized in that, The mass ratio of TiN powder, F127 and PS microspheres is 1:0.1~0.2:0.7~0.9; the average particle size of the PS microspheres is 1~2 μm.

4. The method for preparing the ORR catalyst according to claim 2 or 3, characterized in that, The graded drying process includes: standing at room temperature for 5-15 minutes, drying at 40-50°C for 10-30 minutes, and then drying at 90-100°C for 1-3 hours.

5. The method for preparing the ORR catalyst according to claim 1, characterized in that, In S2, the platinum precursor solution includes an aqueous solution of H2PtCl6; the reducing agent used in the reduction is ethylene glycol, the reduction temperature is 120~150 ℃, and the reduction time is 30~60 min.

6. The method for preparing the ORR catalyst according to claim 1, characterized in that, In S3, the solid content of the acid-loving inorganic sol is 10~20 wt%, and the particle size is 2~20 nm.

7. The method for preparing the ORR catalyst according to claim 1, 5, or 6, characterized in that, In S4, the number of times the restricted wetting is performed is 2 to 4.

8. The method for preparing the ORR catalyst according to claim 1, 5, or 6, characterized in that, The ORR catalyst contains 8-22 wt% ZrO2 and / or Nb2O5; the Pt loading in the Pt / h-TiN framework is 10-30 wt%.

9. The application of an ORR catalyst prepared by any one of claims 1-8 in a high-temperature proton exchange membrane fuel cell.

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