Carbon-supported low-platinum alloy nanocrystal catalyst, preparation method and application thereof, and fuel cell

Abstract

The application provides a carbon-supported low-platinum alloy nanocrystal catalyst and a preparation method and application thereof and a fuel cell, and relates to the technical field of fuel cell catalyst materials.The preparation method provided by the application comprises the following steps: (1) providing a mixed dispersion solution of formamide, a Pt precursor salt, a Ga precursor salt and a separation agent; the molar ratio of the Pt precursor salt to the Ga precursor salt is 1:1; the separation agent is Zn or ZnCl2; (2) performing a solvothermal reaction on the mixed dispersion solution to obtain a catalyst precursor; and (3) calcining the catalyst precursor in an inert atmosphere or a nitrogen atmosphere to obtain the carbon-supported low-platinum alloy nanocrystal catalyst.The carbon-supported low-platinum alloy nanocrystal (Ga2Pt / GaN) catalyst prepared by the application can reduce the use amount of the noble metal Pt on the basis of maintaining the activity of the Pt-based catalyst, and can efficiently catalyze the oxygen reduction reaction as a cathode catalyst of a fuel cell.

Description

Technical Field

[0001] This invention relates to the field of fuel cell catalyst materials technology, and in particular to a carbon-supported low-platinum alloy nanocrystalline catalyst, its preparation method and application, and fuel cells. Background Technology

[0002] In today's society, the energy and environmental crises caused by the overexploitation and incomplete combustion of fossil fuels are becoming increasingly severe. There is an urgent need to develop sustainable and clean energy technologies such as fuel cells and metal-air batteries to alleviate the environmental degradation caused by traditional energy use. Fuel cells are a highly efficient and sustainable clean energy source, considered an ideal energy storage and converter, characterized by high energy conversion efficiency, low environmental pollution, and high specific energy. However, the slow kinetics of the oxygen reduction reaction (ORR), a key reaction occurring at the fuel cell cathode, limit its large-scale expansion, often requiring a large amount of platinum-carbon catalyst to address this issue. To date, platinum-based materials are the most effective catalysts for promoting the ORR reaction, but the high cost and limited reserves of platinum severely restrict its widespread application. Therefore, there is an urgent need to find a substitute for Pt catalysts to reduce the amount of Pt used and improve its catalytic activity.

[0003] One method to modify the activity of Pt catalysts is through alloying. Introducing a second metal element can not only reduce the Pt loading but also alter the electronic structure of Pt, modulating the d-band center to a more ideal position. Current research on the introduction of second metal elements into Pt alloy catalysts mainly focuses on 3d transition metals such as Fe, Co, Ni, Cu, Mn, and Mo. These alloy catalysts, due to the electronic effects of dd-orbit coupling and the geometric effects caused by different atomic radii, result in a downward shift of the d-band center, thus generating more effective active sites; exhibiting excellent electrocatalytic performance in many reactions such as ORR and OER. Recently, Professor Huang Hongwen's research group at Hunan University prepared Pt-Ga ultrathin alloy nanowires and attributed the oxygen reduction catalytic activity to the pd hybrid coupling of Ga and Pt. Oxygen reduction tests showed that, compared to commercial Pt / C catalysts, carbon-supported ultrafine Pt… 4.31 The mass activity and specific activity of Ga alloy nanowire catalysts have been significantly improved. However, the Pt / Ga ratio in the prepared Pt-Ga alloy nanowire catalysts is close to 5 / 1, which keeps the cost of the catalyst high. Therefore, how to further reduce the amount of Pt used while maintaining the catalyst's activity and stability is the key to realizing the large-scale application of catalyst fuel cells. Summary of the Invention

[0004] In view of this, the present invention aims to provide a carbon-supported low-platinum alloy nanocrystalline catalyst, its preparation method, its application, and fuel cells. The carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the present invention maintains the activity of Pt-based catalysts while further reducing the amount of precious metal Pt used, thus reducing the cost of the catalyst.

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

[0006] This invention provides a method for preparing a carbon-supported low-platinum alloy nanocrystalline catalyst, comprising the following steps:

[0007] (1) Provide a mixed dispersion of formamide, Pt precursor salt, Ga precursor salt and a separating agent; wherein the molar ratio of Pt precursor salt to Ga precursor salt is 1:1; wherein the separating agent is Zn or ZnCl2;

[0008] (2) The mixed dispersion is subjected to a solvothermal reaction to obtain a catalyst precursor;

[0009] (3) The catalyst precursor is calcined in an inert atmosphere or a nitrogen atmosphere to obtain the carbon-supported low platinum alloy nanocrystalline catalyst.

[0010] Preferably, the Pt precursor salt in step (1) includes one or more of platinum acetylacetonate, chloroplatinic acid, ammonium chloroplatinate, and sodium hexachloroplatinate; the Ga precursor salt includes one or more of gallium chloride, gallium acetylacetonate, gallium oxalate, and gallium salicylate.

[0011] Preferably, in step (1), the ratio of formamide to Pt precursor salt is (80-120) mL: 1 mmol; and the molar ratio of the isolating agent to Pt precursor salt is 2:1 to 5:1.

[0012] Preferably, the mixed dispersion in step (1) further includes activated carbon; the ratio of activated carbon to Pt precursor salt is (100-200) mg: 0.3 mmol.

[0013] Preferably, the temperature of the solvothermal reaction in step (2) is 150-180°C and the time is 6-18h.

[0014] Preferably, the calcination temperature in step (3) is 900-1100℃ and the time is 1-3h; the heating rate to the calcination temperature is 5℃ / min.

[0015] The present invention provides a carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the preparation method described above, the composition of which includes carbon-supported Ga2Pt alloy and GaN.

[0016] This invention provides the application of the carbon-supported low-platinum alloy nanocrystalline catalyst described above as a cathode catalyst for fuel cells.

[0017] The present invention also provides a fuel cell, wherein the carbon-supported low-platinum alloy nanocrystalline catalyst described in the above technical solution is used as the cathode catalyst of the fuel cell.

[0018] Preferably, the fuel cell is a high-temperature proton exchange membrane fuel cell, wherein the proton exchange membrane of the high-temperature proton exchange membrane fuel cell is a phosphoric acid-doped PBI membrane, the electrolyte is an acidic electrolyte, and the operating temperature is 140–200°C.

[0019] This invention provides a method for preparing a carbon-supported low-platinum alloy nanocrystalline catalyst, comprising the following steps: (1) providing a mixed dispersion of formamide, Pt precursor salt, Ga precursor salt and a separating agent; wherein the molar ratio of the Pt precursor salt to the Ga precursor salt is 1:1; and the separating agent is Zn or ZnCl2; (2) subjecting the mixed dispersion to a solvothermal reaction to obtain a catalyst precursor; and (3) calcining the catalyst precursor in an inert atmosphere or a nitrogen atmosphere to obtain the carbon-supported low-platinum alloy nanocrystalline catalyst. This invention uses low-cost formamide as a reaction solvent, which promotes the uniform dispersion of Pt and Ga ions in Pt and Ga precursor salts, thus facilitating the solid-liquid reaction. The formamide also acts as a reducing agent for the Pt and Ga precursor salts, and the nitrogen-carbon material generated by the formamide polymerization reaction serves as a carbon support material. The invention adds a separating agent, Zn or ZnCl2, to better disperse the reduced Pt and Ga metals from the Pt and Ga precursor salts, ensuring the formation of the Ga2Pt alloy phase. This invention controls the molar ratio of Pt to Ga precursor salt at 1:1, making the Pt / Ga ratio of the product most favorable for the ORR reaction. Therefore, the carbon-supported low-platinum alloy nanocrystalline catalyst prepared by this invention can reduce the amount of precious metal Pt used in fuel cells while maintaining the activity of Pt-based catalysts, which is beneficial for improving Pt utilization and reducing catalyst costs. Furthermore, the preparation method provided by this invention has low raw material costs, is simple to operate, and has high reproducibility, which is conducive to the large-scale preparation and industrialization of the catalyst.

[0020] This invention provides a carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the preparation method described above. The carbon-supported low-platinum alloy nanocrystalline catalyst has the characteristics of low Pt / Ga ratio (Pt / Ga ratio is 1 / 2), high activity and strong stability. As a cathode catalyst for fuel cells, it can efficiently catalyze the oxygen reduction reaction.

[0021] The results of the examples show that the mass activity of the carbon-supported low-platinum alloy nanocrystalline catalyst prepared in this invention is 221.19–342.69 mA / mgPt, which is 2.68–4.14 times that of the 20wt% Pt / C catalyst (82.68 mA / mgPt), and the area-specific activity is 0.31–0.4 mA / cm². 2 It is a 20wt% Pt / C catalyst (0.14mA / cm). 2 It has a strength 2.21 to 2.86 times that of oxygen reduction, and is used as a cathode oxygen reduction catalyst. It exhibits excellent oxygen reduction reaction stability under acidic conditions, and its oxygen reduction activity remains essentially unchanged during long-term use (5000 cycles). Attached Figure Description

[0022] Figure 1 These are SEM images of the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2;

[0023] Figure 2 These are TEM images of the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2;

[0024] Figure 3 This is the XRD pattern of the carbon-supported low-platinum alloy nanocrystalline catalyst prepared in Example 1;

[0025] Figure 4 This is the XRD pattern of the carbon-supported low-platinum alloy nanocrystalline catalyst prepared in Example 2;

[0026] Figure 5 The LSV curves in HClO4 solution were measured by electrodes prepared with the catalysts obtained in Examples 2 and Comparative Examples 1-3, as well as by electrodes prepared with commercial Pt / C catalysts.

[0027] Figure 6 These are the CV and LSV curves of the electrode prepared with the catalyst obtained in Example 1, compared before and after 5000 cycles in HClO4 solution. Figure 6 In the middle, the left figure is the CV curve, and the right figure is the LSV curve;

[0028] Figure 7 These are the CV and LSV curves of the electrode prepared with the catalyst obtained in Example 2, compared before and after 5000 cycles in HClO4 solution. Figure 7 In the middle, the left figure is the CV curve, and the right figure is the LSV curve;

[0029] Figure 8 These are the voltage-current density curves and power-current density curves of the hydrogen-oxygen fuel cell prepared in Example 2, measured at 150°C.

[0030] Figure 9The LSV curve of the electrode prepared by the catalyst obtained by adjusting the different precursor salt ratios in Comparative Example 4 was tested in HClO4 solution.

[0031] Figure 10 The LSV curve of the electrode prepared by the catalyst obtained by adjusting the different precursor salt ratios in Comparative Example 4 was tested in HClO4 solution.

[0032] Figure 11 The image shows the XRD pattern of the catalyst prepared using ethylene glycol as a reducing agent in Comparative Example 6. Detailed Implementation

[0033] This invention provides a method for preparing a carbon-supported low-platinum alloy nanocrystalline catalyst, comprising the following steps:

[0034] (1) Provide a mixed dispersion of formamide, Pt precursor salt, Ga precursor salt and a separating agent; wherein the molar ratio of Pt precursor salt to Ga precursor salt is 1:1; wherein the separating agent is Zn or ZnCl2;

[0035] (2) The mixed dispersion is subjected to a solvothermal reaction to obtain a catalyst precursor;

[0036] (3) The catalyst precursor is calcined in an inert atmosphere or a reducing atmosphere to obtain the carbon-supported low-platinum alloy nanocrystalline catalyst.

[0037] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0038] This invention provides a mixed dispersion of formamide, a Pt precursor salt, a Ga precursor salt, and a separating agent. In this invention, the Pt precursor salt preferably includes one or more of platinum acetylacetonate, chloroplatinic acid, ammonium chloroplatinate, and sodium hexachloroplatinate; the Ga precursor salt preferably includes one or more of gallium chloride, gallium acetylacetonate, gallium oxalate, and gallium salicylate; the molar ratio of the Pt precursor salt to the Ga precursor salt is 1:1. In this invention, the preferred molar ratio of formamide to Pt precursor salt is (80–120) mL:1 mmol, more preferably 100 mL:1 mmol; the formamide serves as both a reaction solvent and a reducing agent. In this invention, the isolating agent is Zn or ZnCl2; the molar ratio of the isolating agent to the Pt precursor salt is preferably 2:1 to 5:1, more preferably 4:1 to 5:1; the isolating agent can promote the uniform dispersion of reduced Pt and Ga metals in the precursor salt, which is a necessary condition for the formation of the Ga2Pt phase. Without the addition of the isolating agent, the Ga2Pt phase cannot be generated. In this invention, the preferred method for preparing the mixed dispersion is to add Pt precursor salt, Ga precursor salt, and isolating agent to formamide, and then perform ultrasonic dispersion under heating conditions to obtain the mixed dispersion; the heating temperature is preferably 30 to 80°C, more preferably 60°C; this invention does not have special requirements for the ultrasonic dispersion conditions, as long as the components are dispersed evenly; the preparation of the mixed dispersion must be carried out under anhydrous conditions, as the presence of water will adversely affect the subsequent self-polymerization reaction of formamide. In this invention, the mixed dispersion preferably includes activated carbon; the preferred ratio of activated carbon to Pt precursor salt is (100-200) mg: 0.3 mmol, more preferably (100-150) mg: 0.3 mmol. In this invention, the activated carbon is preferably added to formamide for ultrasonic dispersion before the addition of Pt precursor salt, Ga precursor salt, and the separating agent.

[0039] After obtaining the mixed dispersion, the present invention subjectes the mixed dispersion to a solvothermal reaction to obtain a catalyst precursor. In the present invention, the temperature of the solvothermal reaction is preferably 150–180°C, more preferably 160°C, and the time is preferably 6–18 h, more preferably 12 h. The present invention preferably places the mixed dispersion in a sealed reaction vessel, and then places the sealed reaction vessel in an oven for the solvothermal reaction. During the solvothermal reaction, formamide self-polymerizes and grows, acting as a solvent and reducing agent. Pt precursor salt and Ga precursor salt react with formamide, and Pt in the Pt precursor salt... 2+ Ga and Ga precursor salts 3+ Restored, a portion of Ga 3+ The nitrogen in formamide reacts with nitrogen to form GaN, while the remaining Ga... 3+ and Pt 2+Ga₂Pt is formed, and the isolating agent Zn or ZnCl₂ is transformed into a Zn-containing component doped into the product. After the solvothermal reaction, the obtained solvothermal reaction solution is preferably subjected to cooling, solid-liquid separation, solid-phase washing, and drying in sequence to obtain the catalyst precursor. The cooling is preferably natural cooling to room temperature. The present invention does not have special requirements for the solid-liquid separation method, and any solid-liquid separation method well known to those skilled in the art can be used, such as filtration. The mother liquor obtained by filtration contains unreacted metal ions, which can be recovered. The washing liquid used for solid-phase washing is preferably ethanol, and the number of solid-phase washings is preferably 3 to 4 times. The present invention does not have special requirements for the drying temperature and time, and drying to constant weight is sufficient.

[0040] After obtaining the catalyst precursor, the present invention calcines the catalyst precursor in a nitrogen atmosphere or other inert atmosphere to obtain the carbon-supported low-platinum alloy nanocrystalline catalyst. For the inert atmosphere, the present invention can use any inert atmosphere well known to those skilled in the art, such as helium. In the present invention, the calcination temperature is preferably 900–1100℃, more preferably 900–1000℃, and the time is preferably 1–3 h, more preferably 1 h; the heating rate to the calcination temperature is preferably 5℃ / min. During the calcination process, the Zn-containing component escapes from the sample in a gaseous state, thereby achieving two purposes: firstly, to eliminate Zn, and secondly, the vacancies left by the escaped Zn allow for greater spacing between Pt and Ga, exposing more active surface area.

[0041] This invention provides a carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the method described above, comprising carbon-supported Ga₂Pt alloy and GaN. In this invention, the particle size of the carbon-supported low-platinum alloy nanocrystalline catalyst is preferably 5–50 nm. The carbon-supported low-platinum alloy nanocrystalline catalyst provided by this invention features a low Pt / Ga ratio (Pt / Ga ratio of 1 / 2), high activity, and strong stability.

[0042] This invention provides the application of the carbon-supported low-platinum alloy nanocrystalline catalyst described above as a cathode catalyst for fuel cells. The carbon-supported low-platinum alloy nanocrystalline catalyst, as a cathode catalyst for fuel cells, can efficiently catalyze the oxygen reduction reaction.

[0043] This invention also provides a fuel cell, using the carbon-supported low-platinum alloy nanocrystalline catalyst described in the above technical solution as the cathode catalyst of the fuel cell. In this invention, the fuel cell is preferably a high-temperature proton exchange membrane fuel cell; the proton exchange membrane of the high-temperature proton exchange membrane fuel cell is preferably a phosphoric acid-doped PBI membrane. This invention does not have special requirements for the phosphoric acid-doped PBI membrane; any phosphoric acid-doped PBI membrane well-known to those skilled in the art can be used. The electrolyte of the high-temperature proton exchange membrane fuel cell is preferably an acidic electrolyte, preferably commercially available 85% concentrated phosphoric acid. The anode catalyst of the high-temperature proton exchange membrane fuel cell is preferably a Pt / C catalyst. This invention does not have special requirements for the Pt / C catalyst; any commercially available Pt / C catalyst well-known to those skilled in the art can be used. The operating temperature of the high-temperature proton exchange membrane fuel cell is 140–200°C. The fuel cell provided by this invention has better power density and significantly improved performance. This invention does not have special requirements for the preparation method of the fuel cell; any fuel cell preparation method well-known to those skilled in the art can be used. In the embodiments of this invention, the preparation method of the fuel cell preferably includes the following steps:

[0044] (a) PTFE, deionized water, isopropanol and Pt / C catalyst are subjected to a first ultrasonic mixing to obtain an anode catalyst slurry;

[0045] (b) PTFE, deionized water, isopropanol and the carbon-supported low-platinum alloy nanocrystalline catalyst are subjected to a second ultrasonic mixing to obtain a cathode catalyst slurry;

[0046] (c) Under heating conditions, the anode catalyst slurry and the cathode catalyst slurry are respectively sprayed onto the gas diffusion layer to obtain a gas diffusion layer coated with the anode catalyst slurry and a gas diffusion layer coated with the cathode catalyst slurry.

[0047] (d) The gas diffusion layer coated with the anode catalyst slurry and the gas diffusion layer coated with the cathode catalyst slurry are calcined respectively to obtain the anode gas diffusion layer and the cathode gas diffusion layer.

[0048] (e) The anode gas diffusion layer, the cathode gas diffusion layer and the phosphoric acid-doped PBI film are combined to form a "sandwich" structure membrane electrode, wherein the "sandwich" structure has the phosphoric acid-doped PBI film as the core; the membrane electrode is cold-pressed to obtain a cold-pressed membrane electrode.

[0049] (f) The cold-pressed membrane electrode and the fuel cell fixture are assembled into a fuel cell.

[0050] In this invention, the preferred ratio of PTFE, deionized water, isopropanol, and Pt / C catalyst in step (a) is 8.8 μL: 5 mL: 15 mL and 40 mg; the preferred ratio of PTFE, deionized water, isopropanol, and carbon-supported low-platinum alloy nanocrystalline catalyst in step (b) is 11 μL: 5 mL: 15 mL and 50 mg. This invention does not have special requirements for the conditions of the first and second ultrasonic mixing, as long as the components are sufficiently dispersed. In this invention, the preferred heating temperature in step (c) is above 100°C, and the heating is used to evaporate the moisture in the anode and cathode catalyst slurries in a timely manner. This invention does not have special requirements for the gas diffusion layer; any gas diffusion layer well known to those skilled in the art can be used. In this invention, the preferred calcination temperature in step (d) is 350°C, and the preferred time is 0.5 h; the purpose of calcination is to adjust the dispersibility of PTFE on the gas diffusion layer, making the PTFE dispersion more uniform and increasing the three-phase interface of the reaction. In this invention, the phosphoric acid-doped PBI membrane in step (e) is pre-cut before use, ensuring that the cut area is slightly larger than the area of ​​the gas diffusion layer. The cold pressing is preferably performed using a dedicated hot press for membrane electrodes. Before cold pressing, it is preferable to drop 3 μL of phosphoric acid onto both sides of the membrane electrode and coat them evenly to minimize the impact of phosphoric acid overflow after cold pressing on the uniform dispersion of the coated phosphoric acid in the catalyst layer. In this invention, the fuel cell fixture in step (f) specifically includes flow channels, current collectors, end plates, and sealing and insulating components.

[0051] The following detailed description, in conjunction with embodiments, illustrates the carbon-supported low-platinum alloy nanocrystalline catalyst, its preparation method, its application, and its use in fuel cells provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] A carbon-supported low-platinum alloy nanocrystalline catalyst (carbon-supported platinum-gallium ORR catalyst) is prepared as follows:

[0054] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to 30 mL of formamide. Heat and sonicate at 60 °C until the mixture is evenly dispersed to obtain a mixed dispersion (solventothermic reaction mother liquor). (Note that the container should be completely dry, because the self-polymerization reaction of formamide cannot occur in the presence of water).

[0055] The solvothermal reaction mother liquor was placed in a sealed reaction vessel, and the reaction vessel was placed in an oven. The temperature was kept constant at 160℃ for 12 hours for continuous solvothermal reaction. Then, the mixture was allowed to cool to room temperature. The reaction vessel was opened and the reaction liquid was taken out. The mixture was washed repeatedly with ethanol 3 to 4 times and then dried to obtain a black solid material without formamide residue, which is the catalyst precursor, denoted as Pt-Ga-Zn@C.

[0056] The Pt-Ga-Zn@C obtained by solvothermal reaction was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was naturally cooled to room temperature and removed to obtain a carbon-supported low-platinum alloy nanocrystalline catalyst, denoted as Ga2Pt@C material.

[0057] Example 2

[0058] A carbon-supported low-platinum alloy nanocrystalline catalyst (activated carbon-supported platinum-gallium ORR catalyst) is prepared as follows:

[0059] Weigh 100 mg of activated carbon (AC) as the carbon support for the catalyst, add AC to 30 mL of formamide, and sonicate until evenly dispersed to obtain a solvothermal reaction preparation solution.

[0060] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to the solvothermal reaction preparation solution. Heat and sonicate at 60°C until the mixture is evenly dispersed to obtain a mixed dispersion (solvothermal reaction mother liquor). (Note that the container should be kept completely dry, because the self-polymerization reaction of formamide cannot occur in the presence of water.)

[0061] The solvothermal reaction mother liquor was placed in a sealed reaction vessel, and the reaction vessel was placed in an oven. The temperature was kept constant at 160℃ for 12 hours for continuous solvothermal reaction. Then, the mixture was allowed to cool to room temperature. The reaction vessel was opened and the reaction liquid was taken out. The mixture was washed repeatedly with ethanol 3 to 4 times and then dried to obtain a black solid material without formamide residue, which is the catalyst precursor, denoted as Pt-Ga-Zn@AC.

[0062] The Pt-Ga-Zn@AC obtained by solvothermal reaction was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was naturally cooled to room temperature and removed to obtain a carbon-supported low-platinum alloy nanocrystalline catalyst, denoted as Ga2Pt@AC material.

[0063] Comparative Example 1

[0064] A carbon-supported low-platinum alloy nanocrystalline catalyst (graphene oxide-supported platinum-gallium ORR catalyst) is prepared as follows:

[0065] Weigh 100 mg of graphene oxide (rGO) as the carbon support for the catalyst, add rGO to 30 mL of formamide, and sonicate until evenly dispersed to obtain a solvothermal reaction preparation solution.

[0066] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to the solvothermal reaction preparation solution. Heat and sonicate at 60°C until the mixture is evenly dispersed to obtain a mixed dispersion (solvothermal reaction mother liquor). (Note that the container should be kept completely dry, because the self-polymerization reaction of formamide cannot occur in the presence of water.)

[0067] The solvothermal reaction mother liquor was placed in a sealed reaction vessel, and the reaction vessel was placed in an oven. The temperature was kept constant at 160℃ for 12 hours for continuous solvothermal reaction. Then, the mixture was allowed to cool to room temperature. The reaction vessel was opened and the reaction liquid was taken out. The mixture was washed repeatedly with ethanol 3 to 4 times and then dried to obtain a black solid material without formamide residue, which is the catalyst precursor, denoted as Pt-Ga-Zn@rGO.

[0068] The obtained Pt-Ga-Zn@rGO was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was naturally cooled to room temperature and removed to obtain a carbon-supported low-platinum alloy nanocrystalline catalyst, denoted as Ga2Pt@rGO material.

[0069] Comparative Example 2

[0070] A carbon-supported low-platinum alloy nanocrystalline catalyst (conductive carbon black-supported platinum-gallium ORR catalyst) is prepared as follows:

[0071] Weigh 100 mg of conductive carbon black (Vulcan XC-72) as the carbon support for the catalyst, add Vulcan XC-72 to 30 mL of formamide, and sonicate until evenly dispersed to obtain a solvothermal reaction preparation solution.

[0072] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to the solvothermal reaction preparation solution. Heat and sonicate at 60°C until the mixture is evenly dispersed to obtain a mixed dispersion (solvothermal reaction mother liquor). (Note that the container should be kept completely dry, because the self-polymerization reaction of formamide cannot occur in the presence of water.)

[0073] The solvothermal reaction mother liquor was placed in a sealed reaction vessel, and the reaction vessel was placed in an oven. The temperature was kept constant at 160℃ for 12 hours for continuous solvothermal reaction. Then, the mixture was allowed to cool to room temperature. The reaction vessel was opened and the reaction liquid was taken out. The mixture was washed repeatedly with ethanol 3 to 4 times and then dried to obtain a black solid material without formamide residue, which is the catalyst precursor, denoted as Pt-Ga-Zn@XC.

[0074] The obtained Pt-Ga-Zn@XC was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was naturally cooled to room temperature and removed to obtain a carbon-supported low-platinum alloy nanocrystalline catalyst, denoted as Ga2Pt@XC material.

[0075] Comparative Example 3

[0076] A carbon-supported low-platinum alloy nanocrystalline catalyst (carbon nanotube-supported platinum-gallium ORR catalyst) is prepared as follows:

[0077] Weigh 100 mg of carbon nanotubes (CNTs) as the carbon support for the catalyst, add the CNTs to 30 mL of formamide, and sonicate until uniformly dispersed to obtain a solvothermal reaction preparation solution.

[0078] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to the solvothermal preparation solution. Heat and sonicate at 60°C until the mixture is evenly dispersed to obtain a mixed dispersion (solvothermal reaction mother liquor). (Note that the container should be completely dry, because the self-polymerization reaction of formamide cannot occur in the presence of water.)

[0079] The solvothermal reaction mother liquor was placed in a sealed reaction vessel, and the reaction vessel was placed in an oven. The temperature was kept constant at 160℃ for 12 hours for continuous solvothermal reaction. Then, the mixture was allowed to cool to room temperature. The reaction vessel was opened and the reaction liquid was taken out. The mixture was washed repeatedly with ethanol 3 to 4 times and then dried to obtain a black solid material without formamide residue, which is the catalyst precursor, denoted as Pt-Ga-Zn@CNT.

[0080] The Pt-Ga-Zn@CNT obtained by solvothermal reaction was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was naturally cooled to room temperature and removed to obtain a carbon-supported low-platinum alloy nanocrystalline catalyst, denoted as Ga2Pt@CNT material.

[0081] Comparative Example 4

[0082] Regulation of precursor ratio:

[0083] Several groups of molar ratios of platinum acetylacetonate and gallium acetylacetonate were compared. The experiment was divided into two parts: the first group had a fixed amount of gallium acetylacetonate added, while the amount of platinum acetylacetonate added was changed, and the molar ratios of platinum acetylacetonate: gallium acetylacetonate were 1:1, 2:1, 3:1, and 4:1, respectively; the second group had a fixed amount of platinum acetylacetonate added, while the amount of gallium acetylacetonate added was changed, and the molar ratios of platinum acetylacetonate: gallium acetylacetonate were 1:1, 1:1.5, 1:2, 1:3, and the case where no gallium acetylacetonate was added.

[0084] Comparative Example 5

[0085] Omitted Zn powder:

[0086] Weigh 118 mg of platinum acetylacetonate and 111 mg of gallium acetylacetonate and add them to 30 mL of formamide. Heat and sonicate at 60 °C until uniformly dispersed to obtain a mixed dispersion (solventothermal reaction mother liquor). Place the soventothermal reaction mother liquor into a sealed reaction vessel, place the reaction vessel into an oven, set the temperature to 160 °C and continuously soventothermically react for 12 h. Then let it stand and cool to room temperature. Open the reaction vessel and take out the reaction solution. Wash it repeatedly with ethanol 3 to 4 times and then filter it. No product was obtained.

[0087] Comparative Example 6

[0088] Replace formamide with ethylene glycol:

[0089] Weigh 98 mg of Zn powder, 118 mg of platinum acetylacetonate, and 111 mg of gallium acetylacetonate and add them to 30 mL of ethylene glycol. Heat and sonicate at 60 °C until uniformly dispersed to obtain a mixed dispersion. Place the mixed dispersion in an Erlenmeyer flask on an iron stand and incubate in an oil bath at 130 °C for 3–4 hours. After cooling, transfer the reaction solution to a vacuum filtration apparatus, wash repeatedly with ethanol 3–4 times, filter, and dry to obtain a black solid material.

[0090] The black solid material was placed in a ceramic boat and calcined at 900℃ for 1 hour under inert gas protection at a heating rate of 5℃ / min. After the reaction was completed, the sample was taken out after naturally cooling to room temperature.

[0091] The catalyst materials prepared in Examples 1-2 and Comparative Examples 1-6 were characterized and their electrochemical performance was tested. The results are as follows:

[0092] Figure 1 These are SEM images of the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2. Figure 1 It can be seen that the catalysts prepared in Examples 1 and 2 have relatively uniform particle distribution and particle size in the nanometer range.

[0093] Figure 2 These are TEM images of the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2. The average particle size of the catalyst particles prepared in Example 1 is 4.91 nm, and the average particle size of the catalyst particles prepared in Example 2 is 5.88 nm.

[0094] Figure 3 and Figure 4 The images show the XRD patterns of the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2, respectively. Figure 3 and Figure 4It can be seen that the carbon-supported low-platinum alloy nanocrystalline catalysts prepared in Examples 1 and 2 both contain Ga2Pt and GaN phases. However, the intensity of the GaN peak corresponding to the catalyst in Example 2 is very low, indicating that the GaN content of the catalyst in Example 2 is much lower than that in Example 1.

[0095] The carbon-supported low-platinum alloy nanocrystalline catalysts obtained in Examples 1-2 and the catalyst samples obtained in Comparative Examples 1-3 were used to prepare a rotating disk electrode. The preparation method is as follows: 5 mg of the catalyst materials prepared in Examples 1-2 and Comparative Examples 1-3 were dispersed in 490 μL of N,N-dimethylformamide, and 10 μL of 5% Nafion solution was added. The mixture was stirred evenly and sonicated for 30 min. 5 μL of the prepared active material solution was uniformly dropped onto a glassy carbon electrode. After the solution was dried, the electrode was tested. The catalysts obtained in Examples 1-2 were tested again after 5000 cycles of cyclic voltammetry. The test conditions were: linear sweep voltammetry (LSV) curves were measured in 0.1 mol / L HClO4 solution under oxygen saturation conditions at a rotation speed of 1600 rpm and a scan rate of 5 mv / s. A 20 wt.% commercial Pt / C catalyst was used as a control.

[0096] Figure 5 These are the LSV curves of HClO4 solution measured by electrodes prepared with the catalysts obtained in Examples 2 and Comparative Examples 1-3, as well as those prepared with 20 wt.% commercial Pt / C catalyst. The difference between Example 2 and Comparative Examples 1-3 is the use of different carbon material supports. LSV electrochemical tests were performed on these four samples. The half-wave potential of Example 2 reached 0.88 V, exceeding the 60 mV of 20 wt.% commercial Pt / C, while the corresponding half-wave potentials of the samples in Comparative Examples 1-3 were all lower than those of Pt / C. Therefore, the addition of activated carbon to the four carbon supports is effective in improving performance.

[0097] Figure 6 These are the CV and LSV curves of the electrode prepared with the catalyst obtained in Example 1, compared before and after 5000 cycles in HClO4 solution (denoted as Pt-Ga before cycling and Pt-Ga-5000 after cycling). Figure 6 In the image, the left figure shows the CV curve, and the right figure shows the LSV curve. (From...) Figure 6 It can be seen that the CV curve and LSV curve of the catalyst in Example 1 were measured before and after 5000 cycles. After 5000 cycles, the CV curve did not change much, and the half-wave potential of the LSV curve decreased by 55mV, indicating that the prepared catalyst has good stability.

[0098] Figure 7These are the CV and LSV curves of the electrode prepared with the catalyst obtained in Example 2, compared before and after 5000 cycles in the HClO4 solution (denoted as Pt-Ga@AC before cycling and Pt-Ga@AC-5000 after cycling). Figure 7 In the image, the left figure shows the CV curve, and the right figure shows the LSV curve. (From...) Figure 7 It can be seen that the CV curve and LSV curve of the catalyst in Example 2 were measured before and after 5000 cycles. It was found that the CV curve did not change much after 5000 cycles, while the half-wave potential of the LSV curve decreased by 20mV, which was much lower than 55mV in Example 1. This indicates that the catalyst in Example 2 has higher stability than that in Example 1.

[0099] The electrochemical active area (ECSA), mass activity (MA), and specific area activity (SA) of the two alloy catalysts, PtGa2@C from Example 1 and PtGa2@AC from Example 2, were calculated and compared with 20 wt.% commercial Pt / C. The test results are shown in Table 1. Table 1 clearly shows that the ECSA of PtGa2@C and PtGa2@AC are 1.2 times and 1.44 times that of Pt / C, respectively; the MA is 2.68 times and 4.14 times that of Pt / C, respectively; and the SA is 2.21 times and 2.86 times that of Pt / C, respectively, demonstrating better ORR activity than commercial Pt / C.

[0100] Table 1 ECSA, MA, and SA data for PtGa2@C and PtGa2@AC

[0101]

[0102] The catalyst obtained in Example 2 was used for testing in a hydrogen-oxygen fuel cell. The testing method was as follows: 50 mg of the catalyst from Example 2 was mixed with 15 mL of isopropanol, 11 μL of 60 wt.% PTFE, and 5 mL of deionized water to prepare a slurry of a certain concentration. This slurry was then sprayed onto the gas diffusion layer and calcined at 350°C for 0.5 h to serve as the cathode of the membrane electrode assembly (MEA). 40 mg of 40 wt.% Pt / C was mixed with 15 mL of isopropanol, 8.8 μL of 60 wt.% PTFE, and 5 mL of deionized water to prepare a slurry. This slurry was then sprayed onto the gas diffusion layer and calcined at 350°C for 0.5 h to serve as the anode of the MEA. The cathode, anode, and phosphoric acid-doped PBI membrane were combined to form a "sandwich" structure to form the MEA electrode. This MEA electrode was then assembled with a fuel cell fixture. Hydrogen and oxygen were then introduced into the pipelines on both sides, and the voltage and power of the self-assembled battery were tested at 150°C. Test conditions: Before the test, the internal air was purged with nitrogen for 0.5 hours. During the test, the hydrogen flow rate was 300 mL / min and the oxygen flow rate was 400 mL / min. Test results are as follows. Figure 8As shown, Figure 8 These are the voltage-current density curves and power-current density curves measured at 150°C for the hydrogen-oxygen fuel cell prepared in Example 2. Figure 8 It can be seen that the maximum power density of the fuel cell reaches 259 mW·cm². -2 At this point, the corresponding voltage is 0.32V and the current density is 812mA·cm. -2 .

[0103] Figure 9 and Figure 10 The LSV curves of the electrodes prepared using catalysts obtained by adjusting the proportions of different precursor salts in Comparative Example 4 are shown in HClO4 solution. Figure 9 and Figure 10 As can be seen, the half-wave potential of the catalyst sample obtained under the condition of platinum acetylacetonate: gallium acetylacetonate (molar ratio) = 1:1 is higher than that of the catalyst material under other ratios and exceeds that of Pt / C. Therefore, platinum acetylacetonate: gallium acetylacetonate (molar ratio) = 1:1 is the optimal ratio.

[0104] Figure 11 The XRD characterization results of the catalyst prepared by oil bath method using ethylene glycol as a reducing agent in Comparative Example 6 are shown below. The catalyst contains Ga phase. 2.8 Pt 17.2 Furthermore, it does not contain any Ga2Pt phase. From the chemical formula, the ratio of Pt to Ga has reached a level close to 6:1, indicating that using ethylene glycol as a reducing agent not only fails to obtain the Ga2Pt phase, but also fails to reduce the Pt content (for Ga2Pt, Ga:Pt = 2:1 is less than Ga:Pt = 1:6, which is less Pt).

[0105] As can be seen from the above embodiments, the carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the present invention has the characteristics of low Pt / Ga ratio (Pt / Ga ratio is 1 / 2), high activity and strong stability, and can efficiently catalyze the oxygen reduction reaction as a cathode catalyst for fuel cells.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-supported low-platinum alloy nanocrystalline catalyst, comprising the following steps: (1) A mixed dispersion of formamide, Pt precursor salt, Ga precursor salt and a separating agent is provided; the molar ratio of Pt precursor salt to Ga precursor salt is 1:1; the separating agent is Zn or ZnCl2; the amount ratio of formamide to Pt precursor salt is (80-120) mL:1 mmol; the molar ratio of the separating agent to Pt precursor salt is 2:1 to 5:1; the mixed dispersion also includes activated carbon; (2) The mixed dispersion is subjected to a solvothermal reaction to obtain a catalyst precursor; the temperature of the solvothermal reaction is 150-180℃ and the time is 6-18h. (3) The catalyst precursor is calcined in an inert atmosphere or a nitrogen atmosphere to obtain the carbon-supported low platinum alloy nanocrystalline catalyst.

2. The preparation method according to claim 1, characterized in that, The Pt precursor salt in step (1) includes one or more of platinum acetylacetonate, chloroplatinic acid, ammonium chloroplatinate, and sodium hexachloroplatinate; the Ga precursor salt includes one or more of gallium chloride, gallium acetylacetonate, gallium oxalate, and gallium salicylate.

3. The preparation method according to claim 1, characterized in that, In step (1), the ratio of activated carbon to Pt precursor salt is (100-200) mg: 0.3 mmol.

4. The preparation method according to claim 1, characterized in that, In step (3), the calcination temperature is 900-1100℃ and the time is 1-3h; the heating rate to the calcination temperature is 5℃ / min.

5. The carbon-supported low-platinum alloy nanocrystalline catalyst prepared by the preparation method according to any one of claims 1 to 4 comprises carbon-supported Ga2Pt alloy and GaN.

6. The application of the carbon-supported low-platinum alloy nanocrystalline catalyst of claim 5 as a cathode catalyst for fuel cells.

7. A fuel cell, wherein the carbon-supported low-platinum alloy nanocrystalline catalyst of claim 5 is used as the cathode catalyst of the fuel cell, the fuel cell is a high-temperature proton exchange membrane fuel cell, the proton exchange membrane of the high-temperature proton exchange membrane fuel cell is a phosphoric acid-doped PBI membrane, the electrolyte is an acidic electrolyte, and the operating temperature is 140-200°C.

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