A method for preparing an efficient and stable porous PtCoV fuel cell cathode catalyst

Abstract

The present invention relates to a method for preparing an efficient and stable porous PtCoV fuel cell cathode catalyst, belonging to the field of new energy nanomaterials and catalytic technology. The main purpose is to solve the problems of low utilization rate of precious metal atoms, limited activity, and poor stability in Pt catalysts. The main scheme is to use electrospinning technology to prepare cobalt acetate tetrahydrate Co(Ac)2·4H20, vanadium diacetylacetonate C 10 H 14 PAN / Pt / Co / V composite nanofibers were constructed using O5V, chloroplatinic acid (H2PtCI6·6H2O), polyacrylonitrile (PAN), and N,N-dimethylformamide. These fibers were then hydrolyzed in a mixture of ethanol, water, and ammonia, and tetraethyl orthosilicate was added. This resulted in a layer of silicon dioxide (SiO2) coating the composite fibers. This was then pyrolyzed and etched with HF to remove the inactive SiO2 and excess metal precursors. Leveraging the confinement effects of the excess transition metal salt, PAN, and SiO2 coating, along with the high-temperature-driven Kirkendall effect, a porous PtCoV alloy catalyst embedded within a hollow, porous carbon fiber support was effectively prepared.

Description

Technical Field

[0001] The present invention relates to a method for preparing an efficient and stable porous PtCoV fuel cell cathode catalyst, belonging to the field of new energy nanomaterials and catalysis technology. Background Art

[0002] As a sustainable clean energy conversion technology, proton exchange membrane fuel cells can convert high-energy-density hydrogen fuel into electrical energy, playing a key role in a carbon-neutral economy. Platinum group metals are the most efficient cathode oxygen reduction reaction catalysts in proton exchange membrane fuel cells. However, the amount of Pt used in commercialized automotive proton exchange membrane fuel cells is still as high as 30g. Considering the limited resources and commercialization costs of Pt, a key development goal of proton exchange membrane fuel cells is to reduce the content of Pt catalyst in a 100kW battery pack from 30g to less than 10g, so that fuel cell vehicles can achieve large-scale commercial application. Obviously, improving the activity, stability and utilization of Pt-based catalysts are issues that urgently need to be addressed.

[0003] Recent advances in nanotechnology have provided promising avenues for improving catalytic efficiency and reducing platinum usage. Fabricating nanostructured platinum alloys by introducing transition metals into the Pt lattice has become an effective strategy. These alloys benefit from ligand and strain effects, significantly improving the intrinsic activity of the catalyst, thereby reducing the Pt content without compromising performance. What is easily overlooked is that a large number of non-functional precious metal atoms are still buried inside the alloy nanoparticles. Single-atom Pt catalysts can maximize the utilization of Pt atoms, but this structure is generally not conducive to accelerating the 4-electron oxygen reduction reaction. Cage-like, hollow, or porous nanoparticles can help achieve this goal and enhance mass transfer. In addition, this porous structure in nanoscale form is rich in low-coordinated boundary atoms and has been shown to have high ORR activity. However, under typical proton exchange membrane fuel cell operating conditions (pH <1, operating voltage 0.6-1.5V, cell temperature 60-80°C), these low-coordinated boundary atoms are highly susceptible to oxidation and dissolution, causing the nanoporous structure to collapse. Furthermore, the small nanoparticles have high surface energy and are prone to migration and aggregation, leading to rapid degradation of catalytic performance. Currently, the preparation of nano-Pt alloy catalysts with high Pt utilization, high catalytic activity, and high durability remains a significant challenge. Summary of the Invention

[0004] The purpose of the present invention is to provide a simple and efficient technical route, which mainly solves the problems of low utilization rate of precious metal atoms, limited activity and poor stability in Pt catalysts. A small-sized porous PtCoV alloy embedded in the porous structure of a hollow carbon fiber carrier is synthesized. While improving the Pt utilization rate and electrocatalytic oxygen reduction reaction activity, it also ensures the excellent durability of the catalyst.

[0005] In order to solve the above problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing an efficient and stable porous PtCoV fuel cell cathode catalyst. First, an N,N-dimethylformamide solution containing Co, V, Pt and polyacrylonitrile (PAN) is electrospinned into PAN / Pt / Co / V composite nanofibers. Then, a layer of silicon dioxide (SiO2) is coated on the surface of the nanofibers. Subsequently, high-temperature pyrolysis and HF etching are performed to finally obtain a porous PtCoV alloy catalyst embedded in a hollow porous carbon fiber carrier.

[0007] In the above technical solution, the preparation method comprises the following steps:

[0008] Step 1: Cobalt acetate tetrahydrate Co(Ac)2·4H2O, vanadium diacetylacetonate C 10 H 14 After dissolving O5V and chloroplatinic acid H2PtCl6·6H2O in N,N-dimethylformamide by ultrasonication, polyacrylonitrile PAN was added and stirred to obtain a uniform mixed solution;

[0009] Step 2: electrospinning the mixed solution to obtain PAN / Pt / Co / V composite nanofibers;

[0010] Step 3, vacuum drying the PAN / Pt / Co / V composite nanofibers to obtain nanofibers;

[0011] Step 4: placing the dried nanofibers in a mixed solution of ethanol, water, and ammonia, adding tetraethyl orthosilicate, and hydrolyzing them to coat a layer of SiO2 on the surface of the composite fibers. After drying, a PAN / Pt / Co / V@SiO2 composite is obtained;

[0012] Step 5, pyrolyzing the PAN / Pt / Co / V@SiO2 composite at high temperature;

[0013] Step 6: The carbonized sample is subjected to HF etching, filtration, washing, and vacuum drying to obtain PtCoV-EPNF.

[0014] In the above technical solution, in step 1, H2PtCl6·6H2O, Co(Ac)2·4H2O, C 10 H14 The mass ratio of O5V to PAN is 1:1.5:1.2:3.8; the mass percentage concentration of PAN in N,N-dimethylformamide solution is 11wt%.

[0015] In the above technical solution, the voltage of electrospinning in step 2 is 17 kV and the pushing speed is 0.003 mL min -1 , the spinning temperature was 50 °C, and the distance between the syringe needle tip and the collector was 18 cm.

[0016] In the above technical solution, the vacuum drying temperature in step 3 is 60° C. and the drying time is 12 h.

[0017] In the above technical solution, the volume ratio of ethanol, water, ammonia water and tetraethyl orthosilicate in step 4 is 19:1:1:4; the mass ratio of composite fiber to tetraethyl orthosilicate is controlled at 25:1; the reaction time is 3 hours, the drying temperature is 60°C, and the drying time is 24 hours.

[0018] In the above technical solution, the temperature of the high-temperature heat treatment in step 5 is 800-1000°C, the heat treatment time is 1-6h, and the atmosphere is Ar / H2 mixed gas.

[0019] In the above technical solution, the heat treatment temperature is 900°C and the heat treatment time is 2 hours.

[0020] In the above technical solution, the pickling conditions in step 6 are 2% HF, etching at room temperature for 3 hours; after pickling, filtering is performed and washing with deionized water until neutral; the vacuum drying temperature is 60° C. and the drying time is 12 hours.

[0021] The present invention has the following advantages:

[0022] 1) By utilizing the encapsulation of metal ions by PAN and the physical separation effect of excess Co and V ions on Pt precursors, small-sized PtCoV alloy nanoparticles were prepared under high temperature conditions, effectively avoiding the sintering problem of metal nanoparticles in an open system;

[0023] 2) Utilizing the confinement effects of excess transition metal salts, PAN, and SiO2 coatings, along with the high-temperature-driven Kirkendall effect, a carbon fiber support with a hollow structure, high specific surface area, and abundant mesopores was constructed, simultaneously enabling the preparation of porous nanoparticles. On the one hand, the hollow porous structure of the support and the porous structure of the catalyst nanoparticles themselves can increase the exposure of active sites and improve the utilization of precious metal atoms in the catalyst. On the other hand, the abundant low-coordinated boundary atoms in the porous nanoalloy can significantly enhance the activity of the electrocatalytic oxygen reduction reaction. The resulting porous PtCoV alloy catalyst embedded in the hollow porous carbon fiber support exhibited high Pt utilization, high activity, and stability in the oxygen reduction reaction at the cathode of a fuel cell.

[0024] 3) The migration and agglomeration of PtCoV alloy nanoparticles embedded in the porous structure of the carrier are inhibited during the electrocatalytic process. The doping of V atoms enhances the interaction between atoms within the alloy, effectively inhibits the dissolution of metal elements in the alloy, and thus improves the stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) SEM image and (b) XRD pattern of the PtCoV-EPNF catalyst prepared in Example 1;

[0026] Figure 2 (a) SEM image and (b) XRD pattern of the PtCo-EPNF catalyst prepared in Example 2;

[0027] Figure 3 (a) SEM image and (b) XRD pattern of the PtCoV-ENF catalyst prepared in Example 3;

[0028] Figure 4 (a) HAADF-STEM image and (b) EDX element mapping distribution of the PtCoV-EPNF catalyst prepared in Example 1;

[0029] Figure 5 (a) N2 adsorption-desorption curve and (b) pore size distribution of the PtCoV-EPNF catalyst prepared in Example 1;

[0030] Figure 6 (a) is the oxygen reduction reaction polarization curve of the PtCoV-EPNF, PtCo-EPNF, PtCoV-ENF catalysts prepared in Examples 1, 2, and 3, and the commercial Pt / C catalyst, and (b) is the oxygen reduction reaction polarization curve of the PtCoV-EPNF catalyst before and after accelerated aging test;

[0031] Figure 7 (a) Polarization curve and power density curve of the membrane electrode prepared based on the PtCoV-EPNF catalyst prepared in Example 1 and commercial Pt / C as the cathode catalyst, (b) Polarization curve and power density curve of the membrane electrode prepared based on the PtCoV-EPNF catalyst prepared in Example 1 as the cathode before and after 30,000 square wave cycles. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific implementation examples.

[0033] First, an N,N-dimethylformamide solution containing Co, V, Pt precursors and polyacrylonitrile (PAN) was electrospinned into PAN / Pt / Co / V composite nanofibers, and then a layer of silica SiO2 was coated on its surface. Subsequently, high-temperature pyrolysis and HF etching were performed to finally obtain a porous PtCoV alloy catalyst (PtCoV-EPNF) embedded in a hollow porous carbon fiber support.

[0034] The principle is that under high-temperature thermal drive and the action of the SiO2 coating layer, the metal ions in the PAN / Pt / Co / V composite nanofibers migrate to the outside of the fibers and promote the decomposition of the PAN inside. Over time, a hollow porous structure is gradually formed. In this process, the different types of metal ions that come into contact with each other alloy, and due to the coating of PAN, the outward diffusion rate of Pt is greater than the inward diffusion rate of Co / V inside the formed nano-alloy particles, thus forming pores inside the nanoparticles. After etching, washing, and drying, the porous PtCoV alloy catalyst embedded in the hollow porous structure of the carbon fiber is finally obtained.

[0035] The preparation process of the above-mentioned efficient and stable porous PtCoV fuel cell cathode catalyst is as follows:

[0036] Step 1) Cobalt acetate tetrahydrate C o (Ac)2·4H2O, vanadium diacetylacetonate C 10 H 14 After dissolving O5V and chloroplatinic acid H2PtCl6·6H2O in N,N-dimethylformamide by ultrasonication, polyacrylonitrile PAN was added and stirred to obtain a uniform mixed solution;

[0037] Step 2) electrospinning the mixed solution to obtain PAN / Pt / Co / V composite nanofibers;

[0038] step 3) vacuum drying the PAN / Pt / Co / V composite nanofibers to obtain nanofibers;

[0039] Step 4) placing the dried nanofibers in a mixed solution of ethanol, water, and ammonia, and adding tetraethyl orthosilicate for hydrolysis, coating the surface of the composite fibers with a layer of SiO2, and drying to obtain a PAN / Pt / Co / V@SiO2 composite;

[0040] Step 5) pyrolyzing the PAN / Pt / Co / V@SiO2 composite at high temperature;

[0041] Step 6) The carbonized sample is subjected to HF etching, filtration, washing, and vacuum drying to obtain PtCoV-EPNF.

[0042] In the above step 1), H2PtCl6·6H2O, Co(Ac)2·4H2O, C 10 H 14 The mass ratio of O5V to PAN is 1:1.5:1.2:3.8; the mass percentage concentration of PAN in N,N-dimethylformamide solution is 11wt%.

[0043] In step 2), the electrospinning voltage was 17 kV and the pushing speed was 0.003 mL min -1 , the spinning temperature was 50 °C, and the distance between the syringe needle tip and the collector was 18 cm.

[0044] In the above step 3), the vacuum drying temperature is 60° C. and the drying time is 12 h.

[0045] In the above step 4), the volume ratio of ethanol, water, ammonia water and tetraethyl orthosilicate is 19:1:1:4; the mass ratio of composite fiber to tetraethyl orthosilicate is controlled at 25:1; the reaction time is 3 hours, the drying temperature is 60°C, and the drying time is 24 hours.

[0046] In the above step 5), the temperature of the high temperature heat treatment is 800-1000° C., the heat treatment time is 1-6 hours, and the atmosphere is an Ar / H 2 mixed gas.

[0047] In the above technical solution, the heat treatment temperature is 900°C and the heat treatment time is 2 hours.

[0048] In the above step 6), the pickling conditions are 2% HF and etching at room temperature for 3 hours; after pickling, the product is filtered and washed with deionized water until neutral; the vacuum drying temperature is 60° C. and the drying time is 12 hours.

[0049] Example 1

[0050] Efficient and stable porous PtCoV fuel cell cathode catalyst was prepared by electrospinning-SiO2 coating-high temperature thermal reduction.

[0051] The specific preparation steps are as follows:

[0052] 1) 133mg H2PtCl6·6H2O, 200mg Co(Ac)2·4H2O, 160mg C 10 H 14 After O5V was dissolved in 4.6 mL of N,N-dimethylformamide solution by ultrasonication, 500 mg of PAN was added and stirred to obtain a uniform mixed solution;

[0053] 2) The above solution was electrospun with the positive and negative voltages set to 17 kV and the pushing speed set to 0.003 mL min -1, the spinning temperature was 50 °C, and the distance between the syringe needle tip and the collector was 18 cm;

[0054] 3) drying the above spinning composite under vacuum conditions at 60° C. for 12 h;

[0055] 4) 120 mg of the composite fiber was placed in a mixed solution of ethanol, water, and ammonia, with volumes of 19 mL, 1 mL, and 1 mL, respectively. 4 mL of tetraethyl orthosilicate was then added. After hydrolysis for 3 hours, the mixture was placed in an oven at 60°C and dried for 24 hours.

[0056] 5) The composite was heat treated at 900°C for 2 h in a tube furnace under an Ar / H2 atmosphere;

[0057] 6) The carbonized sample was etched with 2% HF at room temperature for 3 h, then filtered, washed with deionized water until neutral, and vacuum dried at 60° C. for 12 h to obtain PtCoV-EPNF. Figure 1 1 is the SEM image and XRD pattern of PtCoV-EPNF prepared in Example 1. Figure 1 It can be seen from a that the prepared carbon fiber is a hollow tubular structure. Figure 1 The XRD pattern in b confirms that the metal precursor forms PtCoV alloy after high-temperature annealing.

[0058] Example 2

[0059] The steps of Example 2 are similar to those of Example 1, except that 160 mg of C is not added in step 1). 10 H 14 O5V, other conditions remain unchanged. Figure 2 The SEM and XRD images of the PtCo-EPNF prepared in Example 2 are shown. Figure 2 The test results of a show that after removing C 10 H 14 After O5V, hollow carbon fiber can still be obtained, and Figure 2 From the XRD results in b, it can be seen that PtCo alloy nanoparticles were synthesized.

[0060] Example 3

[0061] The steps of Example 3 are similar to those of Example 1, except that step 4) is removed and there is no need to coat the composite fiber surface with a SiO2 layer. Other conditions remain unchanged. Figure 3 : The SEM image and XRD pattern of PtCoV-ENF prepared in Example 3. Figure 3 From the SEM of a, it can be seen that in the absence of SiO2 coating on the surface of the nanofibers, a hollow structure cannot be obtained and only solid fibers can be obtained. Figure 3 The XRD pattern of b shows that the obtained nanocrystals are also Pt alloy particles.

[0062] Figure 4 : HAADF-STEM image and EDX element mapping distribution diagram of PtCoV-EPNF prepared in Example 1. Figure 4 It can be concluded from Figure a that the prepared nanoparticles exhibit a porous structure with an average size of 4.9 nm and are evenly distributed on the carbon fibers, effectively avoiding the sintering problem of metal nanoparticles at high temperatures. The EDX element mapping distribution diagram shows the uniform distribution of Pt, Co, and V in the particles, further confirming the formation of the PtCoV alloy ( Figure 4 b).

[0063] Figure 5 The specific surface area and pore size distribution of PtCoV-EPNF prepared in Example 1 are shown in FIG. According to the test results, the specific surface area of ​​PtCoV-EPNF is as high as 656.7 m 2 g -1 , and has a rich mesoporous structure, which can promote the exposure of active sites on the one hand, and on the other hand strengthen the anchoring of nanoparticles, inhibit the migration and aggregation during the electrochemical process, thereby improving the activity and stability of the catalyst.

[0064] Figure 6 The LSV curves of PtCo-EPNF, PtCoV-EPNF, PtCoV-ENF and commercial Pt / C (20%) catalysts prepared in Example 1, Example 2 and Example 3 were tested under the following conditions: 0.1 M HClO4 electrolyte, scan rate: 50 mV s -1 , electrode speed: 1600rpm. The test results show that: at the same Pt ​​metal loading, PtCoV-EPNF presents the highest half-wave potential: 0.934V vs.RHE, which is 17mV, 8mV and 53mV higher than PtCo-EPNF, PtCoV-ENF and commercial Pt / C catalyst respectively. Figure 6 In addition, the PtCoV-EPNF catalyst also showed excellent stability in a 60,000-cycle accelerated aging test (voltage range: 0.6-1.0 V; O2-saturated 0.1 M HClO4 electrolyte; scan rate: 100 mV s -1 ), the half-wave potential only decayed by 4mV ( Figure 6 b).

[0065] Figure 7 The PtCoV-EPNF prepared in Example 1 or the commercial Pt / C catalyst was used as the cathode (the loading was 0.06 mg Pt cm -2 ), commercial Pt / C as the anode (loading 0.1 mg Pt cm -2) assembled into a proton exchange membrane fuel cell. Under the same test conditions, the H2-O2 fuel cell based on the PtCoV-EPNF cathode can provide 1.74W cm -2 The peak power density of the fuel cell with commercial Pt / C catalyst as cathode can only reach a maximum power density of 1.19 W cm -2 ( Figure 7 a). In the subsequent 30,000-cycle square wave accelerated aging test (0.6V holding voltage for 3s; 0.9V holding voltage for 3s), the peak power density only decreased by 80mW cm -2 , at 0.8A cm -2 At a current density of 1.5, the voltage decayed by only 15mV ( Figure 7 b), demonstrating the excellent activity and stability of the PtCoV-EPNF catalyst.

Claims

1. A method for preparing an efficient and stable porous PtCoV fuel cell cathode catalyst, characterized in that: First, an N,N-dimethylformamide solution containing Co, V, Pt and polyacrylonitrile (PAN) was electrospun into PAN / Pt / Co / V composite nanofibers. The fibers were then coated with a layer of silicon dioxide (SiO2). The fibers were then pyrolyzed and etched with HF to obtain a porous PtCoV alloy catalyst embedded in a hollow porous carbon fiber support. The steps include: Step 1: Cobalt acetate tetrahydrate Co(Ac)2·4H2O, vanadium diacetylacetonate C 10 H 14 After dissolving O5V and chloroplatinic acid H2PtCl6·6H2O in N,N-dimethylformamide by ultrasonication, polyacrylonitrile PAN was added and stirred to obtain a uniform mixed solution; Step 2: electrospinning the mixed solution to obtain PAN / Pt / Co / V composite nanofibers; Step 3, vacuum drying the PAN / Pt / Co / V composite nanofibers to obtain nanofibers; Step 4: placing the dried nanofibers in a mixed solution of ethanol, water, and ammonia, adding tetraethyl orthosilicate, and hydrolyzing them to coat a layer of SiO2 on the surface of the composite fibers. After drying, a PAN / Pt / Co / V@SiO2 composite is obtained; Step 5, pyrolyzing the PAN / Pt / Co / V@SiO2 composite at high temperature; Step 6: The carbonized sample is subjected to HF etching, filtration, washing, and vacuum drying to obtain PtCoV-EPNF; In step 1, H2PtCl6·6H2O, Co(Ac)2·4H2O, C 10 H 14 O5V, and PAN mass ratio of 1: 1.5: 1.2: 3.8; PAN N, N- dimethylformamide solution concentration of the mass percentage is 11wt%; In step 4, the volume ratio of ethanol, water, ammonia and tetraethyl orthosilicate is 19:1:1:4; the mass ratio of the composite fiber to tetraethyl orthosilicate is controlled at 25:1; the reaction time is 3 hours, the drying temperature is 60 ° C, and the drying time is 24 h; In step 5, the high temperature heat treatment temperature is 800-1000 ℃, the heat treatment time is 1-6 h, and the atmosphere is an Ar / H2 gas mixture; The pickling conditions in step 6 are 2% HF and etching at room temperature for 3 h. After pickling, the product is filtered and washed with deionized water until neutral. The vacuum drying temperature is 60°C and the drying time is 12 h.

2. The method for preparing a highly efficient and stable porous PtCoV fuel cell cathode catalyst according to claim 1, characterized in that: The electrospinning voltage in step 2 was 17 kV and the spinning speed was 0.003 mL min -1 , the spinning temperature was 50 ℃, and the distance between the syringe needle tip and the collector was 18 cm.

3. The method for preparing a highly efficient and stable porous PtCoV fuel cell cathode catalyst according to claim 1, characterized in that: The vacuum drying temperature in step 3 is 60°C and the drying time is 12 h.

4. The method for preparing a highly efficient and stable porous PtCoV fuel cell cathode catalyst according to claim 1, characterized in that: The heat treatment temperature is 900 °C and the heat treatment time is 2 h.

Images