Method for preparing platinum-based alloy catalyst by using plasma enhanced chemical vapor deposition low-temperature technology

Abstract

The invention discloses a method for preparing a platinum-based alloy catalyst by using a plasma enhanced chemical vapor deposition low-temperature technology, relates to a preparation method of a platinum-based alloy catalyst, and aims to solve the technical problems that a carbon layer is not uniformly coated and metal particles of the catalyst are easy to agglomerate in a high-temperature calcination process in the existing platinum-based alloy catalyst prepared by carbon coating. The method comprises the following steps: 1, preparing Pt / C by a polyhydric alcohol reduction method; 2, pre-treating a Pt / C catalyst; 3, preparing M-Pt / C by a dipping evaporation method; 4, PECVD carbon shell coating is carried out; (5) alloying; and 6, removing a part of carbon shell to obtain the platinum-based alloy catalyst. When the Pt / C catalyst is used for preparing a membrane electrode of a proton exchange membrane fuel cell, the peak power density can reach 1.72-1.89 W / cm < 2 > under a hydrogen-air condition, which is improved by 20.3% and 32.2% compared with a membrane electrode of a commercial 20% Pt / C catalyst, and the Pt / C catalyst can be used in the field of proton exchange membrane fuel cells.

Description

Technical Field

[0001] The invention relates to a method for realizing carbon coating to prevent agglomeration of catalyst metal particles using low-temperature technology, and belongs to the field of new energy materials. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) hold enormous potential as a promising clean, renewable energy technology to address the global fossil energy crisis and environmental pollution. However, the cathode electrocatalysts of current PEMFCs primarily rely on the precious metal platinum (Pt), which is expensive and scarce, limiting their widespread application and commercialization. Furthermore, the practical performance of PEMFCs is severely limited by the sluggish kinetics of the oxygen reduction reaction (ORR) in acidic environments. Therefore, the commercialization of fuel cell vehicles urgently requires high-performance, long-life, and low-Pt electrocatalysts for the oxygen reduction reaction (ORR) to significantly reduce the use of expensive Pt.

[0003] The introduction of transition metals (such as Ni, Co, and Fe) modulates the electronic structure of Pt through strain and ligand effects, optimizing the bonding strength between the catalyst and oxygen-containing intermediates, thereby improving catalytic activity and stability. However, during the preparation of Pt-based alloy catalysts, high-temperature alloying can easily lead to sintering and growth of nanoparticles, thereby reducing the specific surface area and activity of the catalyst. To address this issue, carbon coatings have been introduced as a physical barrier to prevent direct contact and aggregation between particles. However, traditional carbon coating methods (such as chemical vapor deposition (CVD)) typically require high temperatures, which can lead to uneven carbon coating or sintering of particles during the coating process. Although plasma-enhanced chemical vapor deposition (PECVD) technology can perform carbon coating at low temperatures, highly active carbon groups preferentially deposit at the entrances of the catalyst's mesopores, forming a dense layer that hinders the diffusion of precursors into the pores. Due to the lack of carbon coating, some Pt particles in the mesopores are prone to migration, agglomeration (Ostwald ripening), and sintering during subsequent high-temperature processing or catalytic reactions. Therefore, it is of great significance to develop a technology to achieve uniform carbon coating at lower temperatures. Summary of the Invention

[0004] The present invention aims to address the technical issues of uneven carbon coating and the tendency of metal particles to agglomerate during high-temperature calcination in existing platinum-based alloy catalysts prepared by carbon coating. The present invention provides a method for preparing a platinum-based alloy catalyst using low-temperature plasma-enhanced chemical vapor deposition (PECVD) technology. The present invention utilizes low-temperature plasma-enhanced chemical vapor deposition (PECVD) to achieve carbon coating and improve the degree of alloying of the platinum-based alloy catalyst. Through methods such as PECVD gradient power low-temperature carbon layer deposition, optimized carbon shell removal process parameters, and gradient temperature alloying, the present invention effectively suppresses particle agglomeration during the carbon layer deposition process. Furthermore, through the synergistic effect of the spatial confinement of the carbon layer and the metal nanoparticles, a platinum-based alloy catalyst with high dispersibility, high structural stability, and excellent catalytic performance is prepared.

[0005] The method of preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology of the present invention is carried out according to the following steps:

[0006] 1. Preparation of Pt / C by polyol reduction method: The carbon support is dispersed in a mixed solution of ethylene glycol and isopropanol, and uniformly dispersed by ultrasonic and magnetic stirring. Then, an ethylene glycol solution of chloroplatinic acid is added, and the pH is adjusted to alkaline. Under the protection of inert gas, microwave heating is used for reduction. After cooling to room temperature, the pH is adjusted to acidic, and the mixture is stirred. The filtrate is filtered and washed until it is neutral and then dried under vacuum to obtain the Pt / C catalyst.

[0007] 2. Pt / C catalyst pretreatment: Disperse the Pt / C catalyst in nitric acid solution, heat it in a water bath, cool it to room temperature, filter and wash it with deionized water until it is neutral, vacuum dry it and grind it;

[0008] Preparation of M-Pt / C by immersion evaporation: The Pt / C powder treated in step 2 is dispersed in ultrapure water and uniformly dispersed by ultrasonic and magnetic stirring; a metal salt solution of a transition metal M is then added, stirred uniformly, and the solvent is evaporated in a water bath, vacuum dried, and ground to obtain M-Pt / C powder; wherein the transition metal M is Co, Ni, Cu, or Fe;

[0009] 4. PECVD carbon shell coating: The M-Pt / C powder is spread flat on a porcelain boat, and then the porcelain boat is placed in a PECVD tube furnace. The PECVD tube furnace is first evacuated to a vacuum state, and then a mixture of carbon source gas and Ar is introduced. The radio frequency power supply is started to generate plasma. The deposition is carried out under low power conditions of 10-60W for 0.5-3h, and then under high power conditions of 150-250W for 0.5-3h. The temperature is maintained at 300-500°C during deposition. After the carbon coating layer is deposited, it is cooled to room temperature, the porcelain boat is taken out, the powder is poured out and ground to obtain carbon shell-coated M-Pt / C powder.

[0010] 5. Alloying: The carbon-shell-coated M-Pt / C powder is placed in a high-temperature furnace and, under a hydrogen-argon atmosphere, heated to 300-500°C and maintained for 1-3 hours, then to 600-900°C and maintained for 2-12 hours for alloying. After cooling to room temperature, the powder is ground to obtain a carbon-shell-coated platinum-based alloy catalyst. A gradient heating strategy is used in this step: the initial low temperature stage promotes the uniform distribution of the metal precursor, and then the temperature is gradually increased to the high temperature stage to complete the alloying.

[0011] VI. Removal of Partial Carbon Shell: The carbon-shelled platinum alloy catalyst is placed in a muffle furnace and heated to 200-500°C in an air atmosphere for calcination and oxidation for 0.5-3 hours to remove the carbon shell. After cooling, it is acid-washed with dilute sulfuric acid to remove residual carbon and metal oxides. The filtrate is filtered and washed until neutral and then dried under vacuum to obtain a highly dispersed platinum alloy catalyst prepared using plasma-enhanced chemical vapor deposition low-temperature technology. This is represented by PtM / C, where M is Co, Ni, Cu, or Fe.

[0012] Furthermore, the carbon support in step 1 is one or a combination of Vulcan XC-72, ECP-600JD, ECP-300JD or mesoporous carbon.

[0013] Furthermore, the volume ratio of ethylene glycol to isopropyl alcohol in the mixed solution of ethylene glycol and isopropyl alcohol described in step 1 is (1-4):1.

[0014] Furthermore, the ratio of the mass of the carbon support described in step 1 to the volume of the mixed solution of ethylene glycol and isopropanol is 100 mg: (20-200) ml.

[0015] Furthermore, in step 1, the ultrasonic treatment is carried out at an ultrasonic power of 200 to 400 W for 30 to 60 minutes; and the magnetic stirring is carried out at a rotation speed of 500 to 1000 rpm for 1 to 2 hours.

[0016] Furthermore, the concentration of the ethylene glycol solution of chloroplatinic acid in step 1 is 7-12 mg / ml.

[0017] Furthermore, the liquid used to adjust the pH value to alkaline in step 1 is 1M NaOH ethylene glycol solution.

[0018] Furthermore, the step of adjusting the pH of the slurry to be alkaline in step 1 is to adjust the pH value to 10 to 12;

[0019] Furthermore, the inert gas in step 1 is N2 or Ar.

[0020] Furthermore, the microwave heating reduction in step 1 is performed by microwave heating at a power of 300 to 600 W for 0.5 to 3 minutes.

[0021] Furthermore, the liquid used to adjust the pH value to acidic in step 1 is 0.1 M HNO3 ethylene glycol solution.

[0022] Furthermore, the step of adjusting the pH of the slurry to be acidic in step 1 is to adjust the pH value to 0.5-4.

[0023] Furthermore, the vacuum drying in step 1 is carried out at a temperature of 60 to 80° C. and for a time of 6 to 12 hours.

[0024] Furthermore, the concentration of the nitric acid solution in step 2 is 1-4 mol / L.

[0025] Furthermore, the ratio of the mass of the Pt / C catalyst described in step 2 to the volume of the nitric acid solution is 100 mg: (25-100) ml.

[0026] Furthermore, the water bath heating temperature in step 2 is 40-80° C., and the heating time is 0.5-2 h.

[0027] Furthermore, the vacuum drying in step 2 is carried out at a temperature of 60 to 80° C. and for a time of 6 to 12 hours.

[0028] Furthermore, the ratio of the mass of the Pt / C powder after the treatment in step 2 described in step 3 to the volume of ultrapure water is 100 mg: (25-100) mL.

[0029] Furthermore, the ultrasonic treatment in step 3 is carried out at an ultrasonic power of 200 to 400 W for 30 to 60 minutes; and the magnetic stirring is carried out at a rotation speed of 500 to 1000 rpm for 1 to 2 hours.

[0030] Furthermore, the concentration of the metal salt in step 3 is 5 to 20 mg / ml;

[0031] Furthermore, the metal salt of the transition metal M in step 3 is cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, iron nitrate nonahydrate, cobalt chloride or cobalt sulfate;

[0032] Furthermore, the molar ratio of platinum to transition metal salt in the Pt / C powder described in step 3 is (3-0.5):1.

[0033] Furthermore, the water bath temperature in step 3 is 60-80° C., the vacuum drying temperature is 60-80° C., and the time is 6-12 h.

[0034] Furthermore, the water bath temperature in step 3 is 60-80° C.; the vacuum drying temperature is 60-80° C., and the time is 6-12 hours.

[0035] Furthermore, the vacuum state described in step 4 refers to a pressure of 10 -1 ~10 -3 Pa.

[0036] Furthermore, the carbon source gas in step 4 is C2H2, CH4 or C2H4.

[0037] Furthermore, the volume ratio of the carbon source gas to Ar in step 4 is (0.5-2):1, and the gas flow rate is 10-50 sccm.

[0038] Furthermore, the hydrogen-argon atmosphere in step five is a mixture of 5% H2 and 95% Ar in a volume ratio.

[0039] Furthermore, the concentration of the dilute sulfuric acid in step six is 0.5M to 1M, and the pickling time is 2 to 12 hours.

[0040] The platinum-based alloy catalyst prepared by the above method is represented by PtM / C, wherein M is Co, Ni, Cu or Fe; the mass fraction of platinum in the catalyst is 20% to 60%, and the molar ratio of the transition metal M to the Pt content is (3 to 0.3):1.

[0041] The membrane electrode is prepared using the platinum-based alloy catalyst obtained by the above method. The specific method is:

[0042] 1. Using a mixture of deionized water and isopropanol in a volume ratio of 1:(1-5) as a solvent, the PtM / C catalyst was added to the solvent and ultrasonically dispersed uniformly. Then, a 5 wt% Nafion solution was added and sheared and dispersed using a high-speed shearing machine at a speed of 5000-10000 rpm for 10-30 minutes to obtain slurry I; wherein the ratio of the dry weight of Nafion to the mass of the carbon support in the PtM / C catalyst was 0.5-0.9, that is, the I / C ratio was 0.5-0.9;

[0043] A Pt / C catalyst is added to a mixture of deionized water and isopropanol in a volume ratio of 1:(1-5) as a solvent and ultrasonically dispersed uniformly. A 5 wt% Nafion solution is then added and sheared and dispersed using a high-speed shearing machine at a speed of 5000-10000 rpm for 10-30 minutes to obtain slurry II. The ratio of the dry weight of Nafion to the mass of the carbon support in the Pt / C catalyst is 0.5-0.9, i.e., I / C is 0.5-0.9.

[0044] 2. Inject slurry I into an ultrasonic spraying device and evenly spray it on the surface of the proton exchange membrane at 60-90°C as the cathode; inject slurry II into an ultrasonic spraying device and evenly spray it on the other side of the proton exchange membrane at 60-90°C as the anode to obtain a proton exchange membrane fuel cell membrane electrode.

[0045] Furthermore, the power of the ultrasonic dispersion in step 1 is 200-400W, and the time is 30-60 minutes.

[0046] Furthermore, the rotation speed of the high-speed shearing machine in step 1 is 5000-10000 rpm, and the shearing and dispersion time is 10-30 min.

[0047] Furthermore, the Pt loading in the cathode of the membrane electrode in step 2 is 0.1-0.4 mg / cm 2 , the Pt loading in the anode is 0.1 mg / cm 2 .

[0048] The beneficial effects of the present invention compared to the prior art are as follows:

[0049] (1) HNO3 solution is used to remove oxides and impurities on the surface of Pt / C catalyst, and polar groups such as hydroxyl groups are introduced at the same time, so that transition metal salt solution (Co, Ni, etc.) can more easily infiltrate the support surface, avoiding the formation of droplets on the hydrophobic surface and causing excessive local concentration. 2+ 、Ni 2+ ) forms strong electrostatic adsorption, reducing the capillary migration effect during the immersion drying process. The introduced hydroxyl groups promote the adsorption of carbon sources during PECVD treatment.

[0050] (2) Plasma-enhanced chemical vapor deposition (PECVD) technology is used to deposit the carbon shell with gradient power. In the low-power zone, the precursor (such as CH4) is promoted to enter the deep of the mesoporous carbon. Increasing the power to high speed accelerates the internal deposition. The difference in deposition rate between the pore entrance and the interior is reduced, and the uniformity of the carbon layer thickness is improved.

[0051] (3) By regulating the annealing process parameters for carbon shell removal, the carbon shell was selectively removed, preserving the carbon layer generated in situ by plasma-enhanced chemical vapor deposition (PECVD). This strategy successfully constructed a synergistic interface structure between the carbon layer and the alloy particles, achieving confined anchoring of the alloy nanoparticles and improving the stability of the catalyst.

[0052] The preparation flow chart of the present invention using plasma enhanced chemical vapor deposition low temperature technology to prepare platinum-based alloy catalyst is as follows: Figure 1 The membrane electrode prepared by the platinum-based alloy catalyst of the present invention can achieve a peak power density of 1.72 to 1.89 W / cm under hydrogen-air conditions.2 , which is 63% and 80% higher than that of the catalyst membrane electrode without PECVD carbon shell coating, and 20.3% and 32.2% higher than that of the commercial 20% Pt / C catalyst membrane electrode, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a preparation flow chart of a platinum-based alloy catalyst prepared by utilizing plasma enhanced chemical vapor deposition low-temperature technology of the present invention;

[0054] Figure 2 This is a transmission electron microscope image of the product obtained in step 5 of Example 1 after alloying without removing the carbon coating;

[0055] Figure 3 is a transmission electron microscope image of the platinum-cobalt alloy catalyst PtCo / C obtained in step 6 of Example 1;

[0056] Figure 4 1 is a transmission electron microscope image and a particle size distribution diagram of the platinum-cobalt alloy catalyst PtCo / C prepared in Example 1;

[0057] Figure 5 1 is an element distribution diagram of the platinum-cobalt alloy catalyst PtCo / C prepared in Example 1;

[0058] Figure 6 1. Transmission electron microscope image and particle size distribution diagram of the platinum-based alloy catalyst prepared in Comparative Example 1;

[0059] Figure 7 This is an element distribution diagram of the platinum-based alloy catalyst prepared in Comparative Example 1;

[0060] Figure 8 CV curves of proton exchange membrane fuel cell membrane electrodes prepared using platinum-cobalt alloy catalysts PtCo / C according to Examples 1, 2, and 3;

[0061] Figure 9 1 is an ORR aging graph of the platinum-cobalt alloy catalyst PtCo / C of Example 1 and the catalyst of Comparative Example 1;

[0062] Figure 10 It is a polarization performance curve of the catalyst membrane electrode of Example 1, Comparative Example 1, Example 4 and the commercial Pt / C membrane electrode under hydrogen-air. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0064] Example 1: The method for preparing a PtCo / C catalyst using plasma enhanced chemical vapor deposition low temperature technology in this embodiment is carried out according to the following steps:

[0065] 1. Preparation of Pt / C by polyol reduction method: 50 mg of ECP-600JD was weighed into a beaker and dispersed in 50 ml of a mixed solution of ethylene glycol and isopropanol, wherein the volume ratio of ethylene glycol to isopropanol was 3:1. Ultrasonic dispersion was performed for 1 hour and magnetic stirring was performed for 2 hours to uniformly disperse the mixture. Then, 1.35 ml of a 9.28 mg / ml chloroplatinic acid ethylene glycol solution was added and ultrasonic dispersion was performed for 1 hour to uniformly disperse the mixture. Then, the pH was adjusted to 10 with 1 M NaOH ethylene glycol solution. Under N2 protection, the Pt precursor was reduced by microwave heating. After cooling to room temperature, the pH was adjusted to 4 with 0.1 M HNO3 ethylene glycol solution. After stirring for 12 hours, the mixture was filtered and washed until the filtrate was neutral. The mixture was vacuum dried at 60°C for 8 hours to obtain the Pt / C catalyst.

[0066] 2. Pt / C catalyst pretreatment: Disperse 200 mg of Pt / C catalyst in 40 ml of 3 M HNO3 solution and heat in a water bath at 60°C for 1.5 h. After cooling to room temperature, immediately filter and wash with deionized water until neutral, dry in a vacuum at 60°C for 8 h, and grind.

[0067] 3. Preparation of Co-Pt / C by impregnation and evaporation: 40 mg of the Pt / C powder treated in step 2 was weighed and dispersed in 40 ml of ultrapure water, ultrasonically dispersed for 30 minutes, and magnetically stirred for 1 hour to obtain a mixed solution; 0.6 ml of a 20 mg / ml cobalt nitrate hexahydrate solution was added, wherein the molar ratio of platinum to cobalt was 1:1; after stirring evenly, the solvent was evaporated in a water bath at 70°C, and the mixture was vacuum dried at 70°C for 8 hours. After cooling to room temperature, the mixture was ground to obtain Co-Pt / C powder;

[0068] 4. PECVD carbon shell coating: Spread the Co-Pt / C powder on the porcelain boat, then place the porcelain boat in the PECVD tube furnace, first evacuate the PECVD tube furnace to a pressure of 10 -1 Pa, and then a mixed gas of CH4 and Ar was introduced at a gas flow rate of 30 sccm, wherein the volume ratio of CH4:Ar was 1:1; after purging for 1 hour, the RF power was started to generate plasma at a temperature of 300°C and a gas pressure of 10 Pa. The RF power was first applied at 50 W for 30 minutes, and then increased to 150 W for another 30 minutes to form a carbon layer; after the temperature dropped to room temperature, the porcelain boat was removed, the powder was poured out and ground into powder to obtain a carbon shell-coated Co-Pt / C powder;

[0069] 5. Alloying: The carbon-shell-coated Co-Pt / C powder is placed in a high-temperature furnace and heated to 400°C for 3 hours and then to 700°C for 4 hours in a hydrogen-argon atmosphere for annealing and alloying. The hydrogen-argon mixture is composed of 5% H2 and 95% Ar by volume. After cooling to room temperature, the powder is ground to obtain a carbon-shell-coated platinum alloy catalyst. A gradient heating strategy is used in this step: the initial low temperature stage promotes the uniform distribution of the metal precursor, and then the temperature is gradually increased to the high temperature stage to complete the alloying.

[0070] 6. Removal of part of the carbon shell: The carbon-shell-coated platinum-based alloy catalyst was placed in a muffle furnace, heated to 300°C in an air atmosphere, and calcined for 2 hours to oxidize and remove the carbon shell; after cooling, it was pickled with 60 ml of a 0.5M dilute sulfuric acid solution in a 70°C water bath for 4 hours to remove residual carbon and metal oxides, and the filtrate was filtered and washed until the filtrate was neutral, and vacuum dried at 60°C for 8 hours to obtain a platinum-cobalt alloy catalyst prepared by plasma-enhanced chemical vapor deposition low-temperature technology, which was recorded as PtCo / C.

[0071] Comparative Example 1: In this comparative example, a catalyst PtCo / C without carbon coating treatment was prepared. The difference between this comparative example and Example 1 is that the PECVD carbon shell coating step in step 4 is omitted, and the other steps and parameters are the same as those in Example 1.

[0072] Comparative Example 2: The catalyst prepared in this comparative example does not adopt gradient power coating during PECVD carbon coating. The difference between this comparative example and Example 1 is that the RF power supply is started to generate plasma during deposition in step 4, and 150W of RF power is applied for deposition for 1 hour. The other steps and parameters are the same as those in Example 1.

[0073] The transmission electron microscope image of the product obtained in step 5 of Example 1 after alloying without removing the carbon coating is as follows: Figure 2 As shown in the figure, it can be seen that there is a carbon layer covering the particles. The transmission electron microscope image of the platinum-cobalt alloy catalyst PtCo / C obtained in step 6 of Example 1 is as follows: Figure 3 As shown in the figure, it can be seen that the carbon layer coating the alloy particles is partially removed, and the interface synergistic structure of the carbon layer-alloy particles is constructed to achieve confined anchoring of the platinum-cobalt alloy particles.

[0074] The transmission electron microscope photo of the platinum-cobalt alloy catalyst PtCo / C prepared in Example 1 is as follows: Figure 4 The element distribution diagram is shown in Figure 5 As shown, from Figure 4 and Figure 5 It can be seen that after high-temperature calcination, the platinum-cobalt alloy particles are evenly distributed without obvious agglomeration, and the average particle size is 2.13 nm.

[0075] The transmission electron microscope photo of the platinum-based alloy catalyst prepared in Comparative Example 1 is as follows: Figure 6 The element distribution diagram is shown in Figure 7 As shown, from Figure 6 and Figure 7 It can be seen that the largest particle size is 5-6 nm, the smallest particle size is 1-2 nm, the platinum-based alloy particles are unevenly distributed, with obvious agglomeration, and the average particle size is 3.14 nm.

[0076] The pore area and pore volume of the products of Example 1 and Comparative Example 2 after alloying in step 5 without removing the carbon coating were measured using the BET method. The results are shown in Table 1.

[0077] Table 1: Pore surface area and pore volume of different pore size regions of the products of Example 1 and Comparative Example 2 measured by BET method after alloying in step 5 without removing the carbon coating

[0078]

[0079] As can be seen from Table 2, compared with Example 1, a large number of mesopores in the product prepared in Comparative Example 2 after step five were blocked during the carbon coating process, resulting in a decrease in the surface area and pore volume of the carbon carrier. The PECVD gradient power deposition of the carbon shell weakened the phenomenon of pore entrance blocking caused by the shadow effect of the carbon carrier, thereby improving the uniformity of the carbon layer.

[0080] Example 2: This example differs from Example 1 in that the calcination time for removing the carbon shell in step 6 is 1 h, and the other steps and parameters are the same as those in Example 1.

[0081] Example 3: This example differs from Example 1 in that the calcination time for removing the carbon shell in step 6 is 3 h, and the other steps and parameters are the same as those in Example 1.

[0082] The membrane electrode was prepared using Example 1, Comparative Example 1, and the 20% Pt / C prepared by the polyol reduction method in Step 1 of Example 1, respectively. The specific steps are as follows:

[0083] 1. Using a mixture of 6.7 ml of deionized water and 8.5 ml of isopropanol as the solvent, 90 mg of the PtM / C catalyst was added to the solvent and ultrasonically dispersed uniformly. 1.09 ml of a 5 wt% Nafion solution was then added and sheared and dispersed using a high-speed shearing machine at 5000 rpm for 30 minutes to obtain slurry I (I / C in slurry I = 0.7).

[0084] 90 mg of 20% Pt / C catalyst was added to a mixture of 6.7 ml of deionized water and 8.5 ml of isopropanol as the solvent and ultrasonically dispersed. 1.09 ml of a 5 wt% Nafion solution was then added and sheared and dispersed using a high-speed shearing machine at 5000 rpm for 30 minutes to obtain slurry II (I / C = 0.7 in slurry II).

[0085] 2. Inject slurry I into ultrasonic spraying equipment and spray it evenly on the surface of proton exchange membrane Nafion 212 at 75°C as cathode. The cathode Pt loading is 0.1 mg / cm 2 The slurry II was injected into the ultrasonic spraying equipment and evenly sprayed on the other side of the proton exchange membrane Nafion 212 at 75 ° C as the anode. The anode Pt loading was 0.1 mg / cm 2 , and obtain a proton exchange membrane fuel cell membrane electrode.

[0086] The proton exchange membrane fuel cell membrane electrodes prepared using the platinum-cobalt alloy catalysts PtCo / C of Examples 1, 2, and 3 were subjected to CV performance tests. The CV tests were conducted in a nitrogen-saturated 0.1 M HClO4 electrolyte with a scanning potential of 0.05 V to 1.2 V and a scanning rate of 0.05 V s -1 The CV graph obtained is as follows Figure 8 As shown, from Figure 8 It can be seen that the electrochemically active area (ECSA) of the catalyst increases with the extension of the annealing time of the catalyst in air atmosphere. When the catalyst is annealed for 1 h, the electrochemical active area of the catalyst only reaches 25.6 m 2 g Pt -1 ,As shown in Table 2, although the ECSA of the catalyst annealed for 2 h is slightly smaller than that of the catalyst annealed for 3 h with the carbon shell completely removed, by controlling the annealing time and sacrificing part of the electrochemical activity, the interface synergistic structure of the carbon layer-alloy particles is constructed to achieve the anchoring of the metal particles.

[0087] Table 2 Electrochemical active areas of platinum-cobalt alloy catalysts PtCo / C of Examples 1, 2 and 3

[0088] Example No. 300℃ annealing time <![CDATA[Electrochemical active surface area (ECSA) (m 2 g Pt -1 )]]> Example 2 1h 58.7 Example 1 2h 47.9 Example 3 3h 25.6

[0089] The catalysts prepared in Example 1 and Comparative Example 1 were subjected to ORR aging performance tests. The aging tests were conducted by conducting potential cycling in an oxygen-saturated 0.1 M HClO4 electrolyte to study the stability of the catalysts at a scan rate of 0.1 V s -1 , the scanning range is 0.6~1.0V, and the ORR polarization diagrams before and after aging are as follows Figure 9As shown, from Figure 9 It can be seen that the stability of the platinum-cobalt alloy catalyst PtCo / C prepared in Example 1 is better than that in Comparative Example 1. The half-wave of the platinum-cobalt alloy catalyst PtCo / C prepared in Example 1 only drops by 4 mV after 30,000 cycles of aging, showing excellent stability.

[0090] Example 4: The method for preparing a PtCo / C catalyst using plasma enhanced chemical vapor deposition low temperature technology in this embodiment is carried out according to the following steps:

[0091] 1. Preparation of Pt / C by polyol reduction method: This step is the same as step 1 of Example 1 to obtain a Pt / C catalyst;

[0092] 2. Pt / C catalyst pretreatment: This step is the same as step 2 of Example 1;

[0093] 3. Preparation of Ni-Pt / C by impregnation and evaporation: 40 mg of the Pt / C powder treated in step 2 was weighed and dispersed in 40 ml of ultrapure water, ultrasonically dispersed for 30 minutes, and magnetically stirred for 1 hour to obtain a mixed solution; 0.6 ml of a 20 mg / ml nickel nitrate hexahydrate solution was added, wherein the molar ratio of platinum to nickel was 1:1; after stirring evenly, the solvent was evaporated in a water bath at 60°C, and vacuum dried at 60°C for 8 hours. After cooling to room temperature, the mixture was ground to obtain Ni-Pt / C powder;

[0094] 4. PECVD carbon shell coating: This step is the same as step 4 of Example 1;

[0095] 5. Alloying: The carbon-shell-coated Ni-Pt / C powder is placed in a high-temperature furnace and heated to 500°C for 4 hours and then to 800°C for 4 hours in a hydrogen-argon atmosphere for annealing and alloying. The hydrogen-argon mixture is composed of 5% H2 and 95% Ar by volume. After cooling to room temperature, the powder is ground to obtain a carbon-shell-coated platinum-based alloy catalyst. A gradient heating strategy is adopted in this step: the initial low temperature stage promotes the uniform distribution of the metal precursor, and then the temperature is gradually increased to the high temperature stage to complete the alloying.

[0096] 6. Removal of carbon shell: The alloyed catalyst was placed in a muffle furnace and calcined at 300°C for 2 hours in an air atmosphere to oxidize and remove the carbon shell; after cooling, it was pickled with 60 ml of a 0.5M dilute sulfuric acid solution in a 70°C water bath for 6 hours to remove residual carbon and metal oxides, and the catalyst was filtered and washed until the filtrate was neutral, and vacuum dried at 70°C for 8 hours to obtain a platinum-nickel alloy catalyst, recorded as PtNi / C.

[0097] The same method as in Example 1 was used to prepare a PtNi / C film electrode.

[0098] The membrane electrode hydrogen-oxygen polarization performance of Example 1, Comparative Example 1, Example 4, and commercial Pt / C membrane electrode was tested using the Qunyi 850e membrane electrode test system. The test conditions were as follows: temperature 80°C, relative humidity 100%, hydrogen-air flow through the anode and cathode respectively, and the back pressure was 200kPa. The polarization performance curves are shown in Figure 2. Figure 10 The specific membrane electrode performance comparison is shown in Table 3.

[0099] Table 3 Membrane electrode performance of Example 1, Comparative Example 1, Example 4, and commercial Pt / C

[0100]

[0101]

[0102] From Table 3 and Figure 10 It can be seen that under hydrogen-air conditions, the peak power density of the membrane electrode prepared in Example 1 can reach 1.72 W / cm 2 The peak power density of the membrane electrode prepared in Example 4 can reach 1.89W / cm 2 , with a higher peak power density. The peak power density of the membrane electrode of Comparative Example 1 is only 1.05W / cm 2 The performance of the membrane electrode of Example 1 and Example 4 is improved by 63% and 80% compared with the membrane electrode of Comparative Example 1. Figure 6 ) As can be seen, the catalyst particles without carbon coating are unevenly sized and exhibit agglomeration, which impairs mass transfer across the membrane electrode and results in poor performance. The performance of the membrane electrodes of Examples 1 and 4 is 20.3% and 32.2% higher than that of a commercial 20% Pt / C catalyst-based membrane electrode, respectively, demonstrating practical application value.

Claims

1. A method for preparing a platinum-based alloy catalyst using plasma enhanced chemical vapor deposition low-temperature technology, characterized in that: The method proceeds as follows:

1. Preparation of Pt / C by polyol reduction method: The carbon support is dispersed in a mixed solution of ethylene glycol and isopropanol, and uniformly dispersed by ultrasonic and magnetic stirring. Then, an ethylene glycol solution of chloroplatinic acid is added, and the pH is adjusted to alkaline. Under the protection of inert gas, microwave heating is used for reduction. After cooling to room temperature, the pH is adjusted to acidic, and the mixture is stirred. The filtrate is filtered and washed until it is neutral and then dried under vacuum to obtain the Pt / C catalyst.

2. Pt / C catalyst pretreatment: Disperse the Pt / C catalyst in nitric acid solution, heat it in a water bath, cool it to room temperature, filter and wash it with deionized water until it is neutral, vacuum dry it and grind it; Preparation of M-Pt / C by immersion evaporation: The Pt / C powder treated in step 2 is dispersed in ultrapure water and uniformly dispersed by ultrasonic and magnetic stirring; a metal salt solution of a transition metal M is then added, stirred uniformly, and the solvent is evaporated in a water bath, vacuum dried, and ground to obtain M-Pt / C powder; wherein the transition metal M is Co, Ni, Cu, or Fe; 4. PECVD carbon shell coating: The M-Pt / C powder is spread flat on a porcelain boat, and then the porcelain boat is placed in a PECVD tube furnace. The PECVD tube furnace is first evacuated to a vacuum state, and then a mixture of carbon source gas and Ar is introduced. The radio frequency power supply is started to generate plasma. The deposition is carried out under low power conditions of 10-60W for 0.5-3h, and then under high power conditions of 150-250W for 0.5-3h. The temperature is maintained at 300-500°C during deposition. After the carbon coating layer is deposited, it is cooled to room temperature, the porcelain boat is taken out, the powder is poured out and ground to obtain carbon shell-coated M-Pt / C powder.

5. Alloying: The carbon-shell-coated M-Pt / C powder is placed in a high-temperature furnace and heated to 300-500°C and maintained for 1-3 hours, then heated to 600-900°C and maintained for 2-12 hours in a hydrogen-argon atmosphere for alloying. After cooling to room temperature, the powder is ground to obtain a carbon-shell-coated platinum-based alloy catalyst.

6. Removal of part of the carbon shell: Place the carbon-shelled platinum-based alloy catalyst in a muffle furnace, heat it to 200-500°C in an air atmosphere, and calcine and oxidize it for 0.5-3 hours to remove the carbon shell; After cooling, the catalyst was pickled with a dilute sulfuric acid solution to remove residual carbon and metal oxides, filtered and washed until the filtrate was neutral, and vacuum dried to obtain a platinum-based alloy catalyst prepared by plasma enhanced chemical vapor deposition low-temperature technology.

2. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1, characterized in that: The molar ratio of platinum to transition metal salt in the Pt / C powder described in step 3 is (3-0.5):

1.

3. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1 or 2, characterized in that: The vacuum state described in step 4 refers to a pressure of 10 -1 ~10 -3 Pa.

4. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1 or 2, characterized in that: The carbon source gas in step 4 is C2H2, CH4 or C2H4.

5. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1 or 2, characterized in that: The volume ratio of the carbon source gas to Ar in step 4 is (0.5-2):1, and the gas flow rate is 10-50 sccm.

6. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1 or 2, characterized in that: The hydrogen-argon atmosphere described in step 5 is a mixture of 5% H2 and 95% Ar in a volume ratio.

7. The method for preparing a platinum-based alloy catalyst using plasma-enhanced chemical vapor deposition low-temperature technology according to claim 1 or 2, characterized in that: The concentration of the dilute sulfuric acid in step six is 0.5M to 1M, and the pickling time is 2 to 12 hours.

8. Use of the platinum-based alloy catalyst prepared by the method of claim 1, characterized in that: The platinum-based alloy catalyst is used to prepare a membrane electrode for a proton exchange membrane fuel cell.

9. The use of the platinum-based alloy catalyst according to claim 8, characterized in that: The method for preparing a membrane electrode for a proton exchange membrane fuel cell using a platinum-based alloy catalyst is specifically carried out in the following steps:

1. Using a mixture of deionized water and isopropanol in a volume ratio of 1:(1-5) as a solvent, the PtM / C catalyst was added to the solvent and ultrasonically dispersed uniformly. Then, a 5 wt% Nafion solution was added and sheared and dispersed using a high-speed shearing machine at a speed of 5000-10000 rpm for 10-30 minutes to obtain slurry I; wherein the ratio of the dry weight of Nafion to the mass of the carbon support in the PtM / C catalyst was 0.5-0.9, that is, the I / C ratio was 0.5-0.9; A Pt / C catalyst is added to a mixture of deionized water and isopropanol in a volume ratio of 1:(1-5) as a solvent and ultrasonically dispersed uniformly. A 5 wt% Nafion solution is then added and sheared and dispersed using a high-speed shearing machine at a speed of 5000-10000 rpm for 10-30 minutes to obtain slurry II. The ratio of the dry weight of Nafion to the mass of the carbon support in the Pt / C catalyst is 0.5-0.9, i.e., I / C is 0.5-0.

9.

2. Inject slurry I into an ultrasonic spraying device and evenly spray it on the surface of the proton exchange membrane at 60-90°C; inject slurry II into an ultrasonic spraying device and evenly spray it on the other side of the proton exchange membrane at 60-90°C to obtain a proton exchange membrane fuel cell membrane electrode.

10. The use of the platinum-based alloy catalyst according to claim 9, characterized in that: The cathode loading of the membrane electrode in step 2 is 0.1-0.4 mg / cm 2 , the anode loading is 0.1 mg / cm 2 .

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