A Pt alloy electrocatalyst for fuel cells and a co-reduction preparation method

Abstract

The present invention belongs to the fields of fuel cells and electrochemistry technologies, and particularly relates to a Pt alloy electrocatalyst for fuel cells and a co-reduction preparation method. By studying the reduction mechanism of alloy ions, the present invention realizes the one-step co-reduction to form an alloy catalyst under the action of the same reducing agent; by pre-reducing the platinum precursor, the difference in redox potentials between platinum ions and transition metal ions is initially narrowed; by screening a suitable complexing agent, noble metal ions and transition metal ions are complexed with the complexing agent together, further adjusting the redox potentials between the two metal ions to a similar level, and finally an alloy catalyst is obtained through a one-step co-reduction reaction; the alloy catalyst prepared by this scheme does not require subsequent high-temperature heat treatment, has a smaller particle size and a uniform distribution, is more uniformly dispersed on the carbon support, and has a high degree of alloying; when applied to the catalytic process of hydrogen-oxygen proton exchange membrane fuel cells, compared with the prior art, the reaction activity of the catalyst is higher.

Description

Technical Field

[0001] The present invention belongs to the technical fields of fuel cells and electrochemistry, and particularly relates to a Pt alloy electrocatalyst for fuel cells and a co-reduction preparation method thereof. Background Art

[0002] With the rapid growth of global energy demand and the possible climate change caused by carbon dioxide emissions, the development of clean and sustainable energy has become an important challenge to address the above issues. Fuel Cells (FCs) can directly convert the chemical energy in fuels into electrical energy under the action of catalysts, and are a sustainable new energy device with high efficiency and pollution-free products. Among them, Proton Exchange Membrane Fuel Cells (PEMFCs) have the advantages of cleanliness, high efficiency, high power density, and rapid start-up at low temperatures, and have broad application prospects in fields such as vehicle power supplies and distributed power generation. In PEMFCs, Pt-based electrocatalysts are the key components of fuel cells, accounting for more than 40% of the total cost of the entire fuel cell. Due to the scarcity and high price of Pt, the cost of PEMFCs remains high, restricting their large-scale application. In addition, the commercially available Pt / C catalyst still has problems such as high price and low catalytic performance in the actual application of fuel cells, thus affecting the output efficiency of fuel cells. Therefore, developing high-performance electrocatalysts for PEMFCs to achieve the commercialization process of fuel cells has become an urgent problem to be solved.

[0003] Studies have found that transition metal Pt alloy catalysts have better electrocatalytic activity than pure Pt. After Pt forms an alloy with a transition metal, the introduction of the second transition metal can change the d-band center of Pt and the electron arrangement on the surface, and the geometric effect and electron effect generated by alloying can optimize the adsorption mode of oxygen molecules and the binding strength between the catalyst surface and reaction intermediates, thereby improving the catalytic activity of the oxygen reduction reaction (ORR) at the cathode of fuel cells.

[0004] At present, the preparation methods of Pt alloy electrocatalysts include impregnation reduction method, organic solvent thermal method, reverse emulsion method, polyol reduction method, etc. Among them, the organic solvent thermal method, reverse emulsion method, and polyol reduction method usually require the use of toxic and harmful organic solvents, structure-directing agents, surfactants, etc., and often require multi-step reactions to form alloys. The impregnation liquid phase reduction method usually uses water as the metal precursor solvent and forms an alloy catalyst under the action of a water-soluble reducing agent.

[0005] The impregnation reduction method using water as a solvent is a simple and environmentally friendly synthesis method, which has the feasibility of industrial production. Chinese Patent (CN109331844B) invented a method for preparing MoS2 microsphere / PtCo alloy nanocomposite with MoS2 microspheres loaded with PtCo alloy using polyvinylpyrrolidone (PVP) as a complexing agent by a two-step method, which has a low platinum content and catalytic activity comparable to that of platinum. Chinese Patent (CN103949272B) invented a method for preparing a NiPt@RGO composite nanocatalyst for hydrogen production from hydrazine borane. Using sodium borohydride (NaBH4) as a reducing agent, it was prepared by one-step reduction of Ni, Pt precursors and graphene oxide in an aqueous solution. The NiPt@RGO composite material has excellent catalytic activity, but the Pt loading is also low and the alloying degree of NiPt is not high.

[0006] Therefore, on the premise of matching the complexing agent and the reducing agent, synthesizing a Pt alloy catalyst with a smaller particle size, a higher degree of alloying and uniform dispersion on the carrier by a one-step method under aqueous phase conditions is the key to realizing the industrial production and further commercial application of fuel cells. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies in the prior art of Pt alloy catalysts, such as complex preparation methods, low alloying degree, uneven dispersion and low catalytic activity, and to provide a Pt alloy electrocatalyst for fuel cells and a co-reduction preparation method.

[0008] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0009] A preparation method of a Pt alloy electrocatalyst, characterized by comprising the following preparation steps:

[0010] S1. After mixing the Pt metal precursor solution and the transition metal precursor solution evenly, adding a complexing agent solution, and then adjusting the pH of the solution to 7-10, stirring to completely complex the metal ions to form a first solution;

[0011] S2. Dispersing the carbon carrier in ultrapure water to form a carbon slurry. After ultrasonic treatment, adding the carbon slurry into the first solution, adjusting the pH to 7-10 again, and stirring and impregnating for 2-24 h to uniformly adsorb and disperse the metal ions on the surface of the carbon carrier to form a second solution;

[0012] S3. Under the conditions of normal temperature and stirring, dropping a reducing agent solution into the second solution at a dropping rate of 0.1-10 mL / min. After the dropping is completed, continue to stir for 0.5-24 h to allow the solution to undergo a sufficient co-reduction reaction. After the reaction is completed, filter by suction and wash to neutrality to obtain the Pt alloy electrocatalyst.

[0013] Through the research on the reduction mechanism of metal ions, the present invention realizes the one-step co-reduction to form an alloy catalyst under the action of the same reducing agent; by researching and screening suitable complexing agents and reducing agents, noble metal ions and transition metal ions are coordinated with the complexing agent together, and further the ORP between the two metal ions is adjusted to a similar level, and then a platinum alloy catalyst is prepared through a one-step co-reduction reaction under environmentally friendly and mild conditions; the alloy catalyst prepared by this solution has a smaller particle size, uniform particle size, and is more uniformly dispersed on the carbon support; and no subsequent high-temperature heat treatment is required; the degree of alloying is higher; compared with the prior art, when applied to the catalytic process of a hydrogen-oxygen proton exchange membrane fuel cell, the reaction activity of the catalyst is higher.

[0014] In the process of studying the optimal performance of the Pt-alloy catalyst, the inventors found that during the preparation of the alloy catalyst, the large difference in the redox potential between most Pt metal precursor solutions and transition metal ions such as Fe 3+ , Co 2+ , Ni 2+ prevented them from co-reducing to form alloy particles in one step under the same reduction conditions. In order to narrow the potential difference between the above-mentioned ions, as a preferred technical solution of the present invention, sodium citrate is selected as the complexing agent to coordinate platinum ions and transition metal ions to form a stable complex; further narrow the gap of the ORP of the two metal ions, so as to co-reduce and prepare a platinum alloy catalyst in one step under the action of a reducing agent.

[0015] Preferably, the complexing agent is sodium citrate, and the molar ratio between the sodium citrate and the total metal ions is 50:1 to 1:1.

[0016] As a preferred technical solution of the present invention, the ratio between platinum metal ions and transition metal ions is 3:1 to 1:3.

[0017] Through experimental research, it is found that the pH value of the impregnation solution will significantly affect the reduction of metal ions and the particle size of Pt alloy nanoparticles. When the solution is acidic (pH < 7), sodium citrate mainly exists in the form of citric acid in the reaction system and cannot form a stable complex with metal ions; when the pH value of the solution is too high (pH > 10), too much OH - in the reaction system will cause hydrolysis of platinum ions and transition metal ions, which will also affect the formation of a stable complex. When the solution is weakly alkaline, after sodium citrate ionizes, it mainly exists as C6H5O7 3-The sodium citrate and the metal ions form a stable metal complex, which can provide sufficient protection to prevent the metal atoms from agglomerating during the reduction process, thereby achieving the purpose of controlling the particle size of the alloy nanoparticles. As a preferred technical solution of the present invention, the pH value range of step S1 and step S2 is 8-9.

[0018] Under the condition that the aforementioned complexing agent is determined, the inventor has studied the process of preparing alloy catalyst by one-step method with reducing agent. After the metal ions form a stable complex with the complexing agent, the difficulty of reducing the metal ions increases. Through a large number of reducing agent reduction experiments, it is found that the reasonable combination of the complexing agent and the reducing agent has a great influence on the one-step preparation of alloy catalyst. When the complexing agent is sodium citrate, the use of NaBH4 as a reducing agent can be used for co-reduction to prepare alloy catalyst with smaller particle size and better performance. This is because the redox potential of sodium citrate, Pt and transition metal ions are close after the complexing. Under the same conditions, when formaldehyde or formic acid is used as a reducing agent, alloy catalyst cannot be obtained, and transition metal ions (Co, Fe, Ni) are difficult to be completely reduced to metal atoms. This is because after the transition metal forms a stable complex with complexing agents such as sodium citrate, such as ([Co(C6H5O7)2] 4- ), compared with simple metal ions (such as Co 2+ ), the difficulty of being reduced to metal atoms will increase, so it is difficult to be reduced to metal elements by formaldehyde or formic acid with weaker reducing properties at room temperature, and thus cannot be reduced with Pt ions to form alloys; only a small part of the transition metal ions are reduced, resulting in a low degree of alloying of the prepared catalyst; using NaBH4 as a reducing agent, the transition metal ions can be completely reduced, and the prepared catalyst has a higher degree of alloying and a higher electrocatalytic activity. This further proves that: the complexing agent and the reducing agent have a matching relationship to a certain extent. When the matching properties of the selected reducing agent and the complexing agent are appropriate, an alloy catalyst with suitable particle size, higher alloying degree and better catalytic performance can be obtained. As a preferred technical solution of the present invention, the reducing agent is sodium borohydride.

[0019] As a preferred technical solution of the present invention, the molar ratio of the reducing agent to the total metal ions is 40:1 to 1:1.

[0020] As a preferred technical solution of the present invention, the Pt metal precursor solution contains Pt 2+ ions; wherein the Pt metal precursor solution is obtained by the following steps: using any one of chloroplatinic acid, potassium chloroplatinate, and potassium chloroplatinite as a raw material, and performing a pre-reduction reaction with a NaHSO3 solution to obtain the Pt 2+ Solution.

[0021] Specifically, the ratio of chloroplatinic acid or potassium chloroplatinate or sodium chloroplatinate or platinum chloride to the NaHSO3 is 1:3 to 1:30; more preferably, the ratio of chloroplatinic acid or potassium chloroplatinate or sodium chloroplatinate or platinum chloride to the NaHSO3 is 1:3 to 1:9.

[0022] Using the weak reducing agent NaHSO3 to pre-reduce any one of H2PtCl6, potassium chloroplatinate, sodium chloroplatinate, and platinum chloride to generate the intermediate product H3Pt(SO3)2OH, and reducing [PtCl6] 2- to Pt 2+ , which is beneficial to react with a complexing agent (such as C6H5O7 3- ) to form a complex, and at the same time can initially narrow the difference in the redox potential between Pt 2+ and transition metal ions, which is beneficial to the co-reduction for preparing the Pt alloy catalyst.

[0023] The transition metal precursor solution includes any one of an iron ion solution, a cobalt ion solution, and a nickel ion solution.

[0024] The cobalt ion solution includes any one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and cobalt sulfate heptahydrate.

[0025] The iron ion solution includes one of iron nitrate nonahydrate, iron chloride hexahydrate, ferric sulfate, etc.;

[0026] The nickel ion solution includes one of nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate, etc.;

[0027] As a preferred technical solution of the present invention, the pH regulator is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 0.1 - 2 mol / L.

[0028] The carbon carrier includes any one of Vulcan XC-72, Vulcan XC-72R, Ketjenblack EC 600JD, and Ketjenblack EC 300J;

[0029] As a preferred technical solution of the present invention, the dropping rate of the reducing agent is 1 - 10 mL / min.

[0030] A Pt-alloy catalyst prepared according to the above method, with a particle size of 3 - 5 nm, and the mass percentage of metallic Pt in the overall loaded catalyst is 20% - 80%.

[0031] Compared with the prior art, the beneficial effects of the present invention:

[0032] 1. The carbon-supported alloy catalyst prepared by the one-step co-reduction method has a smaller particle size, a better distribution on the carbon support, and excellent ORR catalytic activity, and can be used as an efficient cathode catalyst in the field of hydrogen fuel cells.

[0033] 2. The carbon-supported alloy catalyst is prepared by one-step co-reduction under normal temperature and aqueous phase conditions. This method is environmentally friendly, easy to control, and has the application prospect of industrial production.

[0034] 3. The platinum metal precursor is pre-reduced first, and [PtCl6] 2- is reduced to Pt 2+ , which is beneficial to react with a complexing agent (such as C6H5O7 3- ) to form a stable complex, and at the same time can also initially narrow the difference in redox potentials between Pt ions and transition metal ions.

[0035] 4. A suitable complexing agent needs to be selected for the co-reduction of two metal ions. After platinum ions and iron, cobalt, and nickel ions form complexes with sodium citrate respectively, the oxidation reduction potentials (ORP) of the two can be close, and they are co-reduced to form an alloy in one step by the reducing agent NaBH4, with uniform particle size and showing excellent ORR catalytic activity. Description of the Drawings

[0036] Figure 1 XRD patterns of the PtCo / C, PtFe / C, and PtNi / C catalysts prepared according to the schemes of Example 1, Example 2, and Example 3;

[0037] Figure 2 TEM images of the PtCo / C, PtFe / C, and PtNi / C catalysts prepared according to the schemes of Example 1, Example 2, and Example 3;

[0038] Figure 3 LSV curves of the PtCo / C, PtFe / C, and PtNi / C catalysts prepared according to the schemes of Example 1, Example 2, and Example 3;

[0039] Figure 4 XRD patterns of the PtCo / C-1, PtCo / C-2, PtCo / C-3, and PtCo / C-4 prepared according to the schemes of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4;

[0040] Figure 5 TEM images of the PtCo / C-1, PtCo / C-2, PtCo / C-3, and PtCo / C-4 catalysts prepared according to the schemes of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4;

[0041] Figure 6 XRD patterns of PtCo / C-5, PtCo / C-6, and PtCo / C-7 prepared in Comparative Example 5, Comparative Example 6, and Comparative Example 7;

[0042] Figure 7 TEM images of PtCo / C-5 and PtCo / C-6 prepared in Comparative Example 5 and Comparative Example 6;

[0043] Figure 8 LSV curves of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 6, and Comparative Example 7. Detailed Description of the Invention

[0044] The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present invention is limited to the following embodiments. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0045] Example 1

[0046] Accurately measure 40 mL of an aqueous solution of H2PtCl6 with a concentration of 5 mg / mL and an NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:3. Then, stir and react at room temperature for 1 h. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) and a certain amount of sodium citrate (the molar ratio of sodium citrate to the total metal ions is 1:1) to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 7-8 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions. Then, weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it uniformly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution to 8, and continue to stir and impregnate for 2-12 h to make the metal ions uniformly adsorb and disperse on the surface of the carbon support.

[0047] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, a certain amount of freshly prepared NaBH4 solution is added dropwise to the above suspension with a peristaltic pump, and the dropping rate is maintained at 10 mL / min. After the addition of the NaBH4 solution is completed, continue to stir at room temperature for 5 h to ensure that the metal ions are co-reduced and form an alloy. After the reduction is completed, filter by suction, and wash repeatedly with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a platinum-cobalt alloy catalyst, denoted as (PtCo / C).

[0048] Example 2

[0049] Accurately measure 40 mL of an aqueous solution of K2PtCl6 with a concentration of 5 mg / mL and an NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to K2PtCl6 is 1:6. Then stir and react for 1 h at room temperature. After that, add a certain amount of Fe(NO3)3·9H2O solution (5 mg / mL) and a certain amount of sodium citrate (the molar ratio of sodium citrate to the total metal ions is 3:1) to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 8.5 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions. Then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, sonicate for 30 min to make it uniformly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution to 8.5, and continue to stir and impregnate for 2 - 12 h to uniformly adsorb and disperse the metal ions on the surface of the carbon support.

[0050] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, use a peristaltic pump to drop a certain amount of freshly prepared NaBH4 solution into the above suspension, and maintain the dropping rate at 5 mL / min. After the addition of the NaBH4 solution is completed, continue to stir at room temperature for 12 h to ensure that the metal ions undergo co-reduction and form an alloy. After the reduction is completed, filter by suction, and repeatedly wash with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a PtFe alloy catalyst, denoted as (PtFe / C).

[0051] Example 3

[0052] Accurately measure 40 mL of an aqueous solution of Na2PtCl6 with a concentration of 5 mg / mL and an NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to Na2PtCl6 is 1:9. Then stir and react for 1 h at room temperature. After that, add a certain amount of Ni(NO3)2·6H2O solution (5 mg / mL) and a certain amount of sodium citrate (the molar ratio of sodium citrate to the total metal ions is 5:1) to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 9 with Na2CO3 solution, and continue to stir for a certain time to completely complex the metal ions. Then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, sonicate for 30 min to make it uniformly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution to 9, and continue to stir and impregnate for 2 - 24 h to uniformly adsorb and disperse the metal ions on the surface of the carbon support.

[0053] After the above-mentioned stirring and impregnation is completed, under normal temperature and stirring conditions, a certain amount of freshly prepared NaBH4 solution is added dropwise to the above-mentioned suspension using a peristaltic pump, and the dropping rate is maintained at 1 mL / min. After the addition of the NaBH4 solution is completed, stirring is continued for 5 h under normal temperature conditions to ensure that the metal ions undergo co-reduction and form an alloy. After the reduction is completed, filtration is carried out by suction, and the product is repeatedly washed with ultrapure water until the filtrate is neutral, and then dried in a vacuum drying oven at 70 °C for 12 h to obtain a PtNi alloy (PtNi / C) catalyst.

[0054] In the above Examples 1 to 3, sodium citrate was used as a complexing agent and NaBH4 as a reducing agent to prepare three kinds of carbon-supported Pt-based alloy electrocatalysts (PtCo / C, PtFe / C, and PtNi / C). The above three catalysts were subjected to XRD tests, and the obtained XRD patterns are as Figure 1 shown. The characteristic diffraction peaks of Pt in the XRD shifted to a higher angle, indicating the formation of the Pt alloy. The corresponding XRD particle sizes were 3.08 nm, 4.56 nm, and 4.17 nm respectively, and the lattice constants were 0.3842 nm, 0.3847 nm, and 0.3846 nm respectively (see Summary Table 1 of Experimental Data). The TEM test results of the PtCo / C catalyst are shown in Figure 2 , specifically, Figure 2 a is the TEM image of the PtCo / C catalyst at a scale of 50 nm, Figure 2 b is the TEM image of the PtFe / C catalyst at a scale of 50 nm, Figure 2 c is the TEM image of the PtNi / C catalyst at a scale of 50 nm; from the Figure 2 TEM results in, it can be seen that the PtCo, PtFe, and PtNi alloy particles have smaller particle sizes and are evenly distributed on the carrier.

[0055] In addition, the ORR performance tests were carried out on the PtCo / C, PtFe / C, and PtNi / C catalysts prepared in the above Examples 1 to 3, and the corresponding LSV curves are as Figure 3 shown. It can be seen from the figure that PtCo / C, PtFe / C, and PtNi / C all show good ORR activity. Among them, PtCo / C has the best ORR activity, and its mass activity is 0.442 A / mg Pt .

[0056] In order to study the influence of the complexing agent on the preparation of the Pt alloy catalyst, using NaBH4 as the reducing agent, PtCo / C catalysts were prepared without a complexing agent, with ammonia water, ethylenediamine, and CTAB as complexing agents.

[0057] Comparative Example 1 (without using a complexing agent for the complexation reaction)

[0058] Accurately measure 40 mL of an aqueous H2PtCl6 solution with a concentration of 5 mg / mL and a NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:3. Then stir and react for 1 h at room temperature. After that, add a certain amount of Co(NO3)2·6H2O solution to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 9 with NaOH solution and continue stirring for a certain time. Then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it evenly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and continue stirring and impregnating for 5 h to make the metal ions evenly adsorbed and dispersed on the surface of the carbon support.

[0059] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, use a peristaltic pump to drop a certain amount of freshly prepared NaBH4 solution into the above suspension, and maintain the dropping rate at 5 mL / min. After the NaBH4 solution is added dropwise, continue to stir at room temperature for 5 h to ensure that the metal ions are co-reduced and form an alloy. After the reduction is completed, filter by suction, and repeatedly wash with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a platinum-cobalt alloy catalyst, denoted as PtCo / C-1.

[0060] Comparative Example 2 (Ammonia water as a complexing agent)

[0061] Accurately measure 40 mL of an aqueous H2PtCl6 solution with a concentration of 5 mg / mL and a NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:3. Then stir and react for 1 h at room temperature. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) to the above solution, and then adjust the pH value of the solution to 8.5 with ammonia water solution, and then continue to stir for a certain time to completely complex the metal ions. Then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it evenly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution to 8.5 with ammonia water solution, and continue stirring and impregnating for 24 h to make the metal ions evenly adsorbed and dispersed on the surface of the carbon support.

[0062] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, use a peristaltic pump to drop a certain amount of freshly prepared NaBH4 solution into the above suspension, and maintain the dropping rate at 0.5 mL / min. After the NaBH4 solution is added dropwise, continue to stir at room temperature for 12 h to ensure that the metal ions are co-reduced and form an alloy. After the reduction is completed, filter by suction, and repeatedly wash with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a PtCo alloy catalyst, denoted as PtCo / C-2.

[0063] Comparative Example 3 (ethylenediamine as complexing agent)

[0064] Accurately measure 40 mL of an aqueous solution of H2PtCl6 with a concentration of 5 mg / mL and an NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:6. Then, stir and react at room temperature for 1 h. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) and ethylenediamine solution to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 9 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions; weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it uniformly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution, and continue to stir and impregnate for 24 h to uniformly adsorb and disperse the metal ions on the surface of the carbon support.

[0065] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, use a peristaltic pump to drop a certain amount of freshly prepared NaBH4 solution into the above suspension, and keep the dropping rate at 1 mL / min. After the addition of the NaBH4 solution is completed, continue to stir at room temperature for 10 h to ensure that the metal ions are co-reduced and form an alloy. After the reduction is completed, filter by suction, and repeatedly wash with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a PtCo alloy catalyst, denoted as PtCo / C-3.

[0066] Comparative Example 4 (CTAB as complexing agent)

[0067] Accurately measure 40 mL of an aqueous solution of H2PtCl6 with a concentration of 5 mg / mL and an NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:9. Then, stir and react at room temperature for 1 h. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) and a certain amount of CTAB (the molar ratio of CTAB to total metal ions is 2:1) to the above solution, stir at room temperature for 30 min, and then adjust the pH value of the solution to 8 with KOH solution, and continue to stir for a certain time to completely complex the metal ions; then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it uniformly dispersed, and then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution to 8, and continue to stir and impregnate for 24 h to uniformly adsorb and disperse the metal ions on the surface of the carbon support.

[0068] After the above stirring impregnation is completed, under normal temperature and stirring conditions, a certain amount of freshly prepared NaBH4 solution is added dropwise to the above suspension using a peristaltic pump, and the dropping rate is maintained at 8 mL / min. After the addition of the NaBH4 solution is completed, stirring is continued for 12 h under normal temperature conditions to ensure that the metal ions are co-reduced to form an alloy. After the reduction is completed, filtration is carried out, and the product is repeatedly washed with ultrapure water until the filtrate is neutral, and then dried in a vacuum drying oven at 70 °C for 12 h to obtain the PtCo alloy catalyst PtCo / C-4.

[0069] For the above Comparative Examples 1-4, PtCo / C catalysts prepared using NaBH4 as a reducing agent without using a complexing agent or using different complexing agents were characterized by XRD. The results are as Figure 4 shown. It can be seen from the XRD data that the XRD diffraction peaks of the PtCo / C catalysts prepared without using a complexing agent or using ammonia water as a complexing agent did not shift, indicating that no alloy was formed; while the shift of the Pt characteristic diffraction peaks occurred when ethylenediamine and CTAB were used as complexing agents, indicating that an alloy catalyst was successfully obtained. The XRD particle sizes corresponding to Comparative Examples 1-4 were 9.84 nm, 7.47 nm, 6.63 nm, and 5.91 nm, respectively, and the corresponding lattice constants were 0.3920 nm, 0.3914 nm, 0.3879 nm, and 0.3876 nm (as shown in the summary table of experimental data 1). Compared with using sodium citrate as a complexing agent (Example 1), their XRD particle sizes were larger. The TEM test results of the PtCo / C catalysts prepared in Comparative Examples 1-4 are as Figure 5 shown, Figure 5 a corresponds to the TEM image of PtCo / C-1 in Comparative Example 1 (without adding a complexing agent), Figure 5 b corresponds to the TEM image of PtCo / C-2 in Comparative Example 2 (using ammonia water as a complexing agent), Figure 5 c corresponds to the TEM image of PtCo / C-3 in Comparative Example 3 (using ethylenediamine as a complexing agent), Figure 5 d corresponds to the TEM image of PtCo / C-4 in Comparative Example 4 (using CTAB as a complexing agent); it shows that when no complexing agent (Comparative Example 1) or an inappropriate complexing agent (Comparative Examples 2, 3, 4) is used, the particle size of the prepared Pt alloy nanoparticles is larger and the agglomeration is serious, which will greatly reduce the catalytic activity of the catalyst.

[0070] Through the comparative experiments using different complexing agents, it was found that the catalyst prepared using sodium citrate as a complexing agent had a smaller particle size, better dispersion on the carrier, and the most excellent electrocatalytic activity.

[0071] Furthermore, in order to verify the compatibility between sodium citrate and sodium borohydride, the inventor also conducted experiments on the reducing agent. While keeping the complexing agent as sodium citrate, experiments with different reducing agents were carried out:

[0072] Comparative Example 5 (Sodium citrate as complexing agent, formic acid as reducing agent)

[0073] Accurately measure 40 mL of an aqueous H2PtCl6 solution with a concentration of 5 mg / mL and a NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:3. Then, stir and react at room temperature for 1 h. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) and a certain amount of sodium citrate (the molar ratio of sodium citrate to total metal ions is 1:1) to the above solution, stir at room temperature for 30 min, then adjust the pH value of the solution to 9 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions; Weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it uniformly dispersed, then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution, and continue to stir and impregnate for 12 h to make the metal ions uniformly adsorbed and dispersed on the surface of the carbon support.

[0074] After the above stirring and impregnation is completed, stir and heat up to 80 - 100 °C, and use a peristaltic pump to drop a certain amount of formic acid solution into the above suspension, keeping the dropping rate at 0.1 - 10 mL / min. After the formaldehyde aqueous solution is dropped, continue to stir at 80 - 100 °C for 12 h to reduce the metal ions. After the reduction is completed, filter by suction, and repeatedly wash with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain a PtCo alloy (PtCo / C-5) catalyst.

[0075] Comparative Example 6 (Sodium citrate as complexing agent, formaldehyde as reducing agent)

[0076] Accurately measure 40 mL of an aqueous H2PtCl6 solution with a concentration of 5 mg / mL and a NaHSO3 solution into a three-necked flask, where the molar ratio of NaHSO3 to H2PtCl6 is 1:3. Then, stir and react at room temperature for 1 h. After that, add a certain amount of Co(NO3)2·6H2O solution (5 mg / mL) and a certain amount of sodium citrate (the molar ratio of sodium citrate to total metal ions is 1:1) to the above solution, stir at room temperature for 30 min, then adjust the pH value of the solution to 9 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions; Then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, ultrasonically treat it for 30 min to make it uniformly dispersed, then add the dispersed carbon slurry to the metal precursor solution and adjust the pH value of the solution, and continue to stir and impregnate for 2 - 12 h to make the metal ions uniformly adsorbed and dispersed on the surface of the carbon support.

[0077] After the previous step of stirring and impregnation is completed, the temperature is raised to 60 - 80 °C with stirring, and a certain amount of aqueous formaldehyde solution is added dropwise to the above suspension using a peristaltic pump, maintaining a dropping rate of 1 mL / min. After the addition of the aqueous formaldehyde solution is completed, stirring is continued for 5 h at a temperature of 60 - 80 °C to reduce the metal ions. After the reduction is completed, suction filtration is carried out, and the product is repeatedly washed with ultrapure water until the filtrate is neutral, and then dried in a vacuum drying oven at 70 °C for 12 h to obtain a PtCo alloy (PtCo / C-6) catalyst.

[0078] In Comparative Example 5 and Comparative Example 6, the effects of using different reducing agents on the preparation of alloy catalysts were investigated under the premise of a certain complexing agent. Using sodium citrate as the complexing agent, when formaldehyde and formic acid were used as reducing agents, alloy catalysts could not be obtained, and the characteristic diffraction peaks of their XRD did not shift as Figure 6 shown. Their XRD particle sizes were 3.37 nm and 3.24 nm respectively. The corresponding lattice constants were 0.3911 nm and 0.3917 nm respectively. After the metal ions form stable complexes with the complexing agent, the difficulty of their reduction increases. When formaldehyde and formic acid were used as reducing agents, only a small part of the transition metal ions were reduced, resulting in a low degree of alloying of the prepared catalyst. However, due to the protective effect of sodium citrate, the catalyst has good particle size and dispersion. The TEM images are shown in Figure 7 shown. Figure 7 a is the TEM image of the (PtCo / C-5) catalyst obtained in Comparative Example 5; Figure 7 b is the TEM image of the (PtCo / C-5) catalyst obtained in Comparative Example 6.

[0079] The ORR performance tests were carried out on the alloy catalysts of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 6, and the obtained LSV curves are shown in Figure 8 . From Figure 8 it can be obtained that the ORR activity of Example 1 among these catalysts is better than that of Comparative Example 1, Comparative Example 2, and Comparative Example 6.

[0080] Comparative Example 7 (H2PtCl6 not pre-reduced)

[0081] Accurately measure 40 mL of an aqueous solution of H2PtCl6 with a concentration of 5 mg / mL, Co(NO3)2·6H2O solution, and a certain amount of sodium citrate (the molar ratio of sodium citrate to total metal ions is 1:1) into a three-necked flask, then stir for 30 min at room temperature, and then adjust the pH value of the solution to 8 with NaOH solution, and continue to stir for a certain time to completely complex the metal ions; then weigh a certain amount of carbon support and disperse it in 50 mL of ultrapure water, sonicate for 30 min to make it evenly dispersed, and then add the dispersed carbon slurry into the metal precursor solution and adjust the pH value of the solution to 7-10, and continue to stir and impregnate for 2-24 h to make the metal ions evenly adsorb and disperse on the surface of the carbon support.

[0082] After the above stirring and impregnation is completed, under the conditions of room temperature and stirring, a certain amount of freshly prepared NaBH4 solution is added dropwise to the above suspension with a peristaltic pump, and the dropping rate is maintained at 0.1-10 mL / min. After the addition of the NaBH4 solution is completed, continue to stir at room temperature for 0.5-12 h to ensure that the metal ions are co-reduced to form an alloy. After the reduction is completed, filter by suction, and wash repeatedly with ultrapure water until the filtrate is neutral, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain the PtCo alloy catalyst PtCo / C-7.

[0083] In Comparative Example 7, the effect of not using NaHSO3 to pre-reduce H2PtCl6 on the preparation of the alloy catalyst was investigated. On the premise that H2PtCl6 was not pre-reduced, sodium citrate was used as a complexing agent and NaBH4 was used as a reducing agent to co-reduce and prepare the PtCo / C alloy catalyst, and the XRD diffraction peaks of the corresponding catalyst also shifted towards higher angles, as Figure 6 shown. The corresponding XRD particle size and lattice constant are 4.33 nm and 0.3888 nm respectively. However, compared with Example 1 (using NaHSO3 to pre-reduce H2PtCl6), its alloy degree is lower, indicating that [PtCl6] 2- is first pre-reduced to generate Pt 2+ After that, it is more conducive to complexing with sodium citrate, and at the same time, under the action of the reducing agent, a PtCo / C catalyst with a high alloy degree is co-reduced and prepared.

[0084] Table 1 is a summary table of the experimental data of the above Examples 1-3 and Comparative Examples 1-6

[0085]

[0086] Through the research on the reduction mechanism of alloy ions, the present invention realizes the one-step co-reduction to form an alloy catalyst under the action of the same reducing agent; by pre-reducing H2PtCl6 to obtain Pt 2+, which is more conducive to its complexation reaction with the complexing agent and reduces the gap in the redox potential with the transition metal. By researching and screening a suitable complexing agent, the noble metal ions and transition metal ions are coordinated with the complexing agent together, and the redox potential between the two metal ions is adjusted to a similar level. Then, an alloy catalyst is prepared through a one-step co-reduction reaction under environmentally friendly and mild conditions; this solution is simple to operate and does not require subsequent high-temperature heat treatment. The prepared alloy catalyst has a smaller particle size and a uniform particle size distribution, is more uniformly dispersed on the carbon support, and has a higher degree of alloying; when applied to the catalytic process of a hydrogen-oxygen proton exchange membrane fuel cell, compared with the prior art, the reaction activity of the catalyst is higher.

[0087] The foregoing are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a Pt alloy electrocatalyst, characterized in that, It includes the following preparation steps: S1. After uniformly mixing the Pt metal precursor solution and the transition metal precursor solution, add the complexing agent solution, and then adjust the pH of the solution to 8 - 9. Stir to completely complex the metal ions to form a first solution; the ratio between the platinum metal ions and the transition metal ions is 3:1 to 1:3; the complexing agent is sodium citrate, and the molar ratio between the sodium citrate and the total metal ions is 1:1 to 5:1; The transition metal precursor solution includes Co(NO3)2·6H2O solution, Fe(NO3)3·9H2O solution, Ni(NO3)2·6H2O solution; The Pt metal precursor solution is obtained through the following steps: using any one of chloroplatinic acid, potassium chloroplatinate, and potassium chloroplatinate(II) as a raw material, and obtaining the Pt2 + solution through a pre-reduction reaction with a NaHSO3 solution; The ratio between chloroplatinic acid or potassium chloroplatinate or sodium chloroplatinate or platinum chloride and the NaHSO3 is 1:3 to 1:9; S2. Disperse the carbon support in ultrapure water to form a carbon slurry. After ultrasonic treatment, add the carbon slurry into the first solution, and adjust the pH to 9 again. Stir and impregnate for 2 - 12 h to uniformly adsorb and disperse the metal ions on the surface of the carbon support to form a second solution; S3. Under the conditions of normal temperature and stirring, dropwise add the reducing agent solution to the second solution. The reducing agent is sodium borohydride, and the dropping rate is 1 - 10 mL / min. After the dropping is completed, continue to stir for 0.5 - 24 h to allow the solution to undergo a full co - reduction reaction. After the reduction is completed, perform suction filtration, and repeatedly wash with ultrapure water until the filtrate is neutral. Then dry in a vacuum drying oven at 70 °C for 12 h to obtain a platinum - cobalt alloy catalyst or a platinum - iron alloy catalyst or a platinum - nickel alloy catalyst; the mass percentage of metal Pt in the overall loaded catalyst is 20% - 80%.

2. The preparation method of the Pt alloy electrocatalyst according to claim 1, wherein, The pH regulator is any one of sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution, and the concentration of the pH regulator is 0.1 - 2 mol / L.

3. A Pt alloy catalyst prepared according to any one of claims 1-2, characterized in that, The particle size range of the catalyst is 3 - 5 nm, and the proportion of metal Pt in the overall loaded catalyst is 20% - 80%.

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