Alloy catalyst and preparation method thereof

Abstract

The present application provides an alloy catalyst and a preparation method thereof, which belongs to the field of fuel cell technology. The preparation method of the alloy catalyst comprises: placing the alloy in an atmosphere containing oxygen for oxidation treatment to obtain a first precursor, and then placing the first precursor in an atmosphere containing carbon monoxide for annealing treatment, the annealing temperature is 650°C to 900°C, and the annealing time is 2h to 5h to obtain an alloy catalyst, wherein the alloy includes platinum and a transition metal. The preparation method of the alloy catalyst of the present application is simple and easy to mass produce, and a carbon-coated alloy catalyst with a structure that inhibits the agglomeration, dissolution and shedding of alloy nanoparticles is synthesized. The obtained alloy catalyst not only has a highly ordered core-shell structure, which can effectively inhibit the dissolution of base metals, but also has better catalytic performance and durability than the uncoated catalyst, truly achieving both high catalytic performance and long durability.

Description

Technical Field

[0001] The present application relates to the field of fuel cell technology, and in particular to an alloy catalyst and a preparation method thereof. Background Art

[0002] To achieve widespread commercialization of proton exchange membrane fuel cell (PEMFC) technology, it is necessary to improve catalyst activity and reduce costs. In PEMFCs, the slow rate of the oxygen reduction reaction (ORR) results in a large overpotential at low temperatures. Therefore, the development of highly active cathode electrocatalysts is crucial. To achieve high ORR activity, uniform dispersion and control of the Pt particle size are crucial. Pt particle agglomeration reduces the electrocatalyst surface area and subsequently reduces catalytic activity. To obtain high-quality and active Pt, various binary and ternary Pt-based alloy catalysts on high-surface-area supports have been reported. Compared to Pt / C, Pt alloys / C (e.g., PtCo, PtNi, etc.) exhibit 2–4 times higher ORR activity in PEMFCs. However, due to the instability of the transition metal elements in alloy catalysts, they are easily dissolved from the metal nanoparticles during the durability process, resulting in poor durability. Ordered alloy catalysts offer high durability due to their unique structure, but the formation of the ordered alloy structure requires higher temperatures, which can lead to agglomeration and growth of the alloy nanoparticles, affecting the active sites of the alloy catalyst and resulting in low ORR activity. Core-shell alloy catalysts have high ORR activity and high durability, but the formation of the platinum shell usually requires acid washing and secondary heat treatment, which involves many steps and the process is cumbersome and difficult to control. Summary of the Invention

[0003] The present application provides an alloy catalyst and a preparation method thereof, which have high catalytic performance and long durability.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, the present application provides an example method for preparing an alloy catalyst, comprising:

[0006] The initial alloy catalyst is placed in an atmosphere containing oxygen for oxidation treatment to obtain a first precursor, and then the first precursor is placed in an atmosphere containing carbon monoxide for annealing treatment. The annealing temperature is 650°C to 900°C, and the annealing time is 2h to 5h to obtain an alloy catalyst, wherein the initial alloy catalyst includes a carrier and initial alloy particles loaded on the carrier, and the initial alloy particles include platinum and a transition metal.

[0007] In the above technical solution, the initial alloy catalyst is first oxidized in an atmosphere containing oxygen to fully oxidize the transition metal. The first precursor is then annealed in an atmosphere containing carbon monoxide. The carbon monoxide gas not only induces platinum segregation, thereby forming the outermost platinum shell of the alloy nanoparticles, but also reduces the transition metal oxide to form oxygen vacancies, accelerating the diffusion of transition metal elements and promoting the formation of an ordered structure, thereby improving the order of the alloy nanoparticles. Furthermore, the carbon monoxide gas forms a carbon layer during the reaction with the transition metal oxide. This carbon layer physically coats the surface of the alloy nanoparticles, restricting their growth, ultimately resulting in an ordered core-shell alloy catalyst with smaller and evenly distributed particles.

[0008] The preparation method of the core-shell alloy catalyst of the present application is simpler and easier to mass produce than the conventional pickling and secondary heat treatment, and a carbon-coated alloy catalyst is synthesized that inhibits the agglomeration, dissolution and shedding of alloy nanoparticles. The prepared alloy catalyst not only has a highly ordered core-shell structure that can effectively inhibit the dissolution of base metals, but also has better catalytic performance and durability than uncoated catalysts, truly achieving both high catalytic performance and long durability.

[0009] In some possible embodiments, the molar ratio of platinum to transition metal in the initial alloy particles is 1:3 to 5:1; and / or the support comprises a carbon support or an oxide support.

[0010] In some possible embodiments, the atmosphere of the annealing treatment includes carbon monoxide and an inert gas, and the volume ratio of carbon monoxide to the inert gas is 10 mL:200 mL to 100 mL:300 mL.

[0011] In the above technical solution, by maintaining the volume ratio of carbon monoxide to inert gas within the aforementioned range, the carbon monoxide gas induces platinum segregation, thereby forming an outwardly outer platinum shell on the outermost side of the alloy nanoparticles. Simultaneously, the carbon monoxide gas reduces the transition metal oxide to form oxygen vacancies, accelerating the diffusion of transition metal elements and promoting the formation of an ordered structure, thereby improving the order of the alloy nanoparticles. Furthermore, the carbon monoxide gas forms a carbon layer during the reaction with the transition metal oxide. This carbon layer physically coats the surface of the alloy nanoparticles, restricting their growth. Ultimately, an ordered core-shell alloy catalyst with small, uniformly distributed particles is obtained.

[0012] In some possible embodiments, the temperature of the oxidation treatment is 80° C. to 100° C., and the time of the oxidation treatment is 2 h to 5 h.

[0013] In the above technical solution, by making the temperature and time of the oxidation treatment within the above ranges, it is beneficial to control the size of the alloy nanoparticles and at the same time ensure that the transition metal is fully oxidized.

[0014] In some possible embodiments, the atmosphere for the oxidation treatment is air.

[0015] In some possible embodiments, the initial alloy catalyst can be prepared by the following method: placing the freeze-dried material in an atmosphere containing hydrogen for heat treatment, the heat treatment temperature is 200°C to 400°C, and the heat treatment time is 2h to 5h; the freeze-dried material includes a mixture of a transition metal precursor, a platinum precursor and a carrier.

[0016] In the above technical solution, a freeze-dried mixture of a transition metal precursor, a platinum precursor, and a support is heat-treated in a hydrogen atmosphere to reduce the transition metal precursor and the platinum precursor to a transition metal and platinum, respectively, to form an alloy of the transition metal and platinum. In other possible embodiments, the initial alloy catalyst can also be prepared by conventional impregnation or colloid methods.

[0017] In some possible embodiments, the lyophilized material is prepared by the following method: after mixing the transition metal precursor, the platinum precursor and the carrier, the mixture is transferred to a glass watch glass within 5 minutes for rapid pre-freezing to obtain a pre-frozen material, and the pre-frozen material is transferred to a freeze dryer and frozen for 18 hours to 30 hours to obtain a lyophilized material.

[0018] In the above technical solution, the mixture is transferred to a glass surface dish for rapid pre-freezing within 5 minutes, so that the mixture including the transition metal precursor, the platinum precursor and the carrier can be locked while maintaining a uniform stirring state, which is beneficial to improving the order of the alloy nanoparticles.

[0019] In some possible embodiments, the transition metal includes any one or more of cobalt, nickel, iron, and manganese; and / or the platinum precursor includes any one or more of chloroplatinic acid, platinum acetylacetonate, and potassium chloroplatinate.

[0020] In a second aspect, the present application provides an alloy catalyst, which is prepared according to the preparation method of the alloy catalyst in the above embodiment.

[0021] In the above technical scheme, the alloy catalyst of the present application is an ultra-thin carbon layer-coated ordered core-shell alloy catalyst, which can inhibit the agglomeration, dissolution and shedding of alloy nanoparticles. It not only has a highly ordered core-shell structure, which can effectively inhibit the dissolution of base metals, but also has better catalytic performance and durability than uncoated catalysts, truly achieving both high catalytic performance and long durability.

[0022] In some possible embodiments, the alloy catalyst includes a carrier and alloy particles loaded on the carrier, the alloy particles include a core, a first shell and a second shell, the first shell is coated on the surface of the core, the second shell is coated on the surface of the first shell, the core is an alloy, the first shell is a platinum layer, and the second shell is a carbon layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a flow chart of a method for preparing an alloy catalyst according to an embodiment of the present application;

[0025] Figure 2 This is a schematic structural diagram of the alloy particles according to an embodiment of the present application;

[0026] Figure 3 TEM image of the alloy catalyst prepared in Example 1 of the present application;

[0027] Figure 4 These are the XRD patterns of Example 1 and Comparative Example 2 of the present application.

[0028] Icon: 10-alloy particle; 100-core; 200-first shell; 300-second shell. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0030] This application discovered that to address the unstable nature of transition metal elements and their tendency to dissolve easily from metal nanoparticles during the durability process, core-shell catalysts can be used. However, the formation of the platinum shell typically requires acid washing and secondary heat treatment, which involves multiple steps and is cumbersome and difficult to control. Overall, there is an urgent need for methods to prepare core-shell alloy catalysts that can produce highly ordered, controllable metal particle sizes.

[0031] Based on this, see Figure 1 The present application provides a method for preparing an alloy catalyst, which comprises the following steps:

[0032] S1. Preparation of lyophilized material

[0033] First, the transition metal precursor and the platinum precursor are uniformly mixed in water to prepare a mixed solution, and then the mixed solution and the carrier are added to a mixing tank for mixing. After the mixing is completed, the mixture is transferred to a glass watch glass within 5 minutes for rapid pre-freezing to obtain a pre-frozen material, and then the pre-frozen material is transferred to a freeze dryer and frozen for 18 hours to 30 hours to obtain a freeze-dried material.

[0034] The transition metal precursor includes a transition metal salt, and the transition metal includes any one or more of cobalt, nickel, iron and manganese.

[0035] For example, when the transition metal element is cobalt, the transition metal precursor includes soluble salts such as cobalt nitrate, cobalt chloride, and cobalt acetate.

[0036] The platinum precursor includes any one or more of chloroplatinic acid, platinum acetylacetonate and potassium chloroplatinate.

[0037] The molar ratio of platinum to transition metal elements in the mixed solution is 1:3 to 5:1.

[0038] As an example, the molar ratio of platinum to the transition metal element in the mixed solution may be 1:5, 1:3, 1:1, 2:5, 2:3, 2:1, 3:5 or 3:1.

[0039] Optionally, the method of uniformly mixing the transition metal precursor and the platinum precursor in water includes ultrasonic dispersion.

[0040] The support includes a carbon support or an oxide support.

[0041] The BET specific surface area of ​​the carbon support is ≥400m 2 / g.

[0042] Optionally, the carbon support comprises Ketjen Black and / or BP2000.

[0043] Rapid pre-freezing methods include liquid nitrogen pre-freezing or low-temperature refrigerator pre-freezing.

[0044] Optionally, the rapid pre-freezing method is liquid nitrogen pre-freezing.

[0045] After the transition metal precursor, platinum precursor and carrier are mixed, they are transferred to a glass watch glass within 5 minutes for rapid pre-freezing. This allows the mixture including the transition metal precursor, platinum precursor and carrier to be locked while maintaining a uniform stirring state, which is beneficial to improving the order of the alloy nanoparticles.

[0046] As an example, the freezing time of the pre-frozen material in the freeze dryer can be 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours or 30 hours.

[0047] S2. Preparation of initial alloy catalyst

[0048] The obtained freeze-dried material is placed in an atmosphere containing hydrogen for heat treatment at a temperature of 200° C. to 400° C. for a time of 2 h to 5 h to obtain an initial alloy catalyst, which is an alloy supported on a carbon carrier.

[0049] Optionally, the atmosphere of the heat treatment includes hydrogen and an inert gas, and the volume ratio of hydrogen to the inert gas is 10 mL:200 mL to 100 mL:300 mL.

[0050] The inert gas includes any one or more of nitrogen, helium, neon, argon and xenon.

[0051] As an example, the heat treatment temperature can be 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, 350℃, 380℃ or 400℃, and the heat treatment time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0052] Optionally, before the heat treatment is performed, the air in the container to be heat treated is exhausted by using an inert gas.

[0053] Optionally, before reaching the target temperature of the heat treatment, the heating rate is 10° C. / min to 50° C. / min.

[0054] A freeze-dried product of a mixture including a transition metal precursor, a platinum precursor and a carrier is heat-treated in an atmosphere containing hydrogen, so that the transition metal precursor and the platinum precursor are reduced to a transition metal and platinum, respectively, to form an alloy of the transition metal and platinum.

[0055] In other possible embodiments, the initial alloy catalyst can also be prepared by conventional impregnation method or colloid method.

[0056] It should be noted that the molar ratio of platinum to transition metal elements in the initial alloy particles is the same as the molar ratio of platinum to transition metal elements in the mixed solution, which is also 1:3 to 5:1.

[0057] S3. Preparation of alloy catalyst

[0058] The prepared initial alloy catalyst is placed in an atmosphere containing oxygen for oxidation treatment to obtain a first precursor, and then the first precursor is placed in an atmosphere containing carbon monoxide for annealing treatment. The annealing temperature is 650°C to 900°C, and the annealing time is 2h to 5h to obtain an alloy catalyst.

[0059] Optionally, the atmosphere for the oxidation treatment is air.

[0060] The temperature of the oxidation treatment is 80° C. to 100° C., and the time of the oxidation treatment is 2 h to 5 h.

[0061] As an example, the temperature of the oxidation treatment may be 80° C., 85° C., 90° C., 95° C., or 100° C., and the time of the oxidation treatment may be 2 h, 3 h, 4 h, or 5 h.

[0062] By setting the temperature and time of the oxidation treatment within the above ranges, it is advantageous to control the size of the alloy nanoparticles while allowing the transition metal to be fully oxidized.

[0063] Optionally, before reaching the target temperature of the oxidation treatment, the heating rate is 5° C. / min to 10° C. / min.

[0064] Optionally, the atmosphere of the annealing treatment includes carbon monoxide and an inert gas, and the volume ratio of carbon monoxide to the inert gas is 10 mL:200 mL to 100 mL:300 mL.

[0065] As an example, the volume ratio of carbon monoxide and inert gas can be 10mL:200mL, 20mL:200mL, 50mL:200mL, 80mL:200mL, 100mL:200mL, 10mL:250mL, 20mL:250mL, 50mL:250mL, 80mL:250mL, 100mL:250mL, 10mL:300mL, 20mL:300mL, 50mL:300mL, 80mL:300mL or 100mL:300mL.

[0066] As an example, the temperature of the annealing process may be 650° C., 700° C., 750° C., 800° C., 850° C., or 900° C., and the time of the annealing process may be 2 h, 3 h, 4 h, or 5 h.

[0067] Optionally, the annealing temperature is 700°C to 900°C.

[0068] Optionally, before the annealing process is performed, the air in the container where the annealing process is performed is exhausted by using an inert gas.

[0069] Optionally, before reaching the target temperature of the annealing treatment, the heating rate is 10° C. / min to 50° C. / min.

[0070] It should be noted that the raw material initial alloy catalyst in S3 can be prepared through the steps of S1 and S2 of the present application, or can be prepared through a conventional impregnation method or colloid method, or can be directly purchased.

[0071] The preparation method of the alloy catalyst of the present application first oxidizes the initial alloy catalyst in an atmosphere containing oxygen to fully oxidize the transition metal, and then anneals the first precursor in an atmosphere containing carbon monoxide. The carbon monoxide gas not only induces platinum segregation, thereby forming the outermost platinum shell of the alloy nanoparticles, but also reduces the transition metal oxide to form oxygen vacancies, accelerates the diffusion of transition metal elements, promotes the formation of an ordered structure, and improves the order of the alloy nanoparticles. In addition, the carbon monoxide gas forms a carbon layer during the reaction process with the transition metal oxide. The carbon layer physically coats the surface of the alloy nanoparticles to restrict the growth of the alloy nanoparticles, ultimately obtaining an ordered core-shell alloy catalyst with smaller and uniformly distributed particles.

[0072] The preparation method of the core-shell alloy catalyst of the present application is simpler and easier to mass produce than the conventional pickling and secondary heat treatment, and a carbon-coated alloy catalyst is synthesized that inhibits the agglomeration, dissolution and shedding of alloy nanoparticles. The prepared alloy catalyst not only has a highly ordered core-shell structure that can effectively inhibit the dissolution of base metals, but also has better catalytic performance and durability than uncoated catalysts, truly achieving both high catalytic performance and long durability.

[0073] The present application also provides an alloy catalyst, which is prepared according to the preparation method of the alloy catalyst in the above embodiment.

[0074] See also Figure 2 The alloy catalyst includes a carrier and alloy particles 10 loaded on the carrier. The alloy particles 10 include a core 100, a first shell 200 and a second shell 300. The first shell 200 is coated on the surface of the core 100, and the second shell 300 is coated on the surface of the first shell 200. The core 100 is an alloy, the first shell 200 is a platinum layer, and the second shell 300 is a carbon layer.

[0075] Optionally, the alloy particles have a particle size of 2.5 nm to 5 nm.

[0076] Optionally, the metal loading of the alloy catalyst is between 20% and 60%.

[0077] The alloy catalyst of the present application is an ultra-thin carbon layer-coated ordered core-shell alloy catalyst, which can inhibit the agglomeration, dissolution and shedding of alloy nanoparticles. It not only has a highly ordered core-shell structure that can effectively inhibit the dissolution of base metals, but also has better catalytic performance and durability than uncoated catalysts, truly achieving both high catalytic performance and long durability.

[0078] The following is a further detailed description of an alloy catalyst and a preparation method thereof of the present application in conjunction with examples.

[0079] Example 1

[0080] The present invention provides an alloy catalyst and a preparation method thereof, which comprises the following steps:

[0081] S1. Preparation of lyophilized material

[0082] First, cobalt nitrate and chloroplatinic acid are ultrasonically dispersed in water at a molar ratio of cobalt element to platinum element of 3:1 to prepare a mixed solution, and then the mixed solution and Ketjen black are added to a stirring tank for stirring and mixing treatment. The mixing time is 2 hours. After the mixing treatment is completed, it is transferred to a glass watch glass within 5 minutes for liquid nitrogen pre-freezing to obtain a pre-frozen material, and then the pre-frozen material is transferred to a freeze dryer for freezing for 24 hours to obtain a freeze-dried material.

[0083] S2. Preparation of initial alloy catalyst

[0084] The obtained freeze-dried material was transferred to a porcelain boat and heat-treated in a tube furnace. Before the heat treatment, nitrogen was introduced into the tube furnace at room temperature for 60 minutes to expel the air in the tube furnace. Then hydrogen and nitrogen were introduced into the tube furnace, and the volume ratio of hydrogen to nitrogen was 100 mL:300 mL. Then, the temperature was increased to 300°C at a heating rate of 5°C / min to 10°C / min, and kept at 300°C for 3 hours to obtain an initial alloy catalyst, which was an alloy supported on a carbon carrier.

[0085] S3. Preparation of alloy catalyst

[0086] The prepared alloy loaded on the carbon support is oxidized in air in a tubular furnace with a heating rate of 5°C / min to 10°C / min, and the temperature is raised to 90°C, and kept at 90°C for 3 hours to obtain a first precursor. The first precursor is then transferred to a porcelain boat and annealed in a tubular furnace. Before annealing, nitrogen is introduced into the tubular furnace at room temperature for 60 minutes to exhaust the air in the tubular furnace, and then carbon monoxide and nitrogen are introduced into the tubular furnace with a volume ratio of carbon monoxide to nitrogen of 30mL:500mL. The temperature is then raised to 700°C at a heating rate of 10°C / min to 50°C / min, and kept at 700°C for 3 hours to obtain an alloy catalyst with a metal loading of 50%.

[0087] Figure 3 TEM image of the alloy catalyst prepared in Example 1. Figure 3 It can be seen that the surface of the alloy nanoparticles is covered with an ultra-thin carbon shell, and the thickness of the ultra-thin carbon shell is 0.5 nm.

[0088] Example 2

[0089] The examples of the present application provide an alloy catalyst and a preparation method thereof. Example 2 changes the volume ratio of carbon monoxide and nitrogen in the annealing treatment to 10 mL:500 mL based on Example 1, while other parameters remain unchanged.

[0090] Example 3

[0091] The examples of the present application provide an alloy catalyst and a preparation method thereof. Example 3 changes the volume ratio of carbon monoxide and nitrogen in the annealing treatment to 50 mL:500 mL based on Example 1, while other factors remain unchanged.

[0092] Example 4

[0093] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 4, the annealing temperature in the annealing treatment is changed to 600° C. based on Embodiment 1, while other aspects remain unchanged.

[0094] Example 5

[0095] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 5, the annealing temperature in the annealing treatment is changed to 800° C. based on Embodiment 1, while other aspects remain unchanged.

[0096] Example 6

[0097] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 6, based on Embodiment 1, the annealing temperature in the annealing treatment is changed to 900° C., while other aspects remain unchanged.

[0098] Example 7

[0099] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 7, based on Embodiment 1, the annealing time in the annealing treatment is changed to 2 hours, while other aspects remain unchanged.

[0100] Example 8

[0101] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 8, based on Embodiment 1, the annealing time in the annealing treatment is changed to 5 hours, while other aspects remain unchanged.

[0102] Example 9

[0103] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 9, based on Embodiment 1, the oxidation temperature in the oxidation treatment is changed to 120° C., while other aspects remain unchanged.

[0104] Example 10

[0105] The embodiments of the present application provide an alloy catalyst and a preparation method thereof. In Embodiment 9, based on Embodiment 1, the oxidation time in the oxidation treatment is changed to 6 hours, while other aspects remain unchanged.

[0106] Comparative Example 1

[0107] The comparative example of the present application provides an alloy catalyst and a preparation method thereof, which comprises the following steps:

[0108] S1. Preparation of lyophilized material

[0109] First, cobalt nitrate and chloroplatinic acid are ultrasonically dispersed in water at a molar ratio of cobalt element to platinum element of 3:1 to prepare a mixed solution, and then the mixed solution and Ketjen black are added to a stirring tank for stirring and mixing treatment. The mixing time is 2 hours. After the mixing treatment is completed, it is transferred to a glass watch glass within 5 minutes for liquid nitrogen pre-freezing to obtain a pre-frozen material, and then the pre-frozen material is transferred to a freeze dryer for freezing for 24 hours to obtain a freeze-dried material.

[0110] S2. Preparation of initial alloy catalyst

[0111] The obtained freeze-dried material was transferred to a porcelain boat and heat-treated in a tube furnace. Before the heat treatment, nitrogen was introduced into the tube furnace at room temperature for 60 minutes to expel the air in the tube furnace. Then hydrogen and nitrogen were introduced into the tube furnace, and the volume ratio of hydrogen to nitrogen was 100 mL:300 mL. Then, the temperature was increased to 300°C at a heating rate of 5°C / min to 10°C / min, and kept at 300°C for 3 hours to obtain an initial alloy catalyst, which was an alloy supported on a carbon carrier.

[0112] S3. Preparation of alloy catalyst

[0113] The prepared alloy loaded on the carbon support was transferred to a porcelain boat and annealed in a tube furnace. Before annealing, nitrogen was introduced into the tube furnace at room temperature for 60 minutes to expel the air in the tube furnace. Then, carbon monoxide and nitrogen were introduced into the tube furnace in a volume ratio of 30 mL:500 mL. The temperature was then raised to 700°C at a heating rate of 10°C / min to 50°C / min, and the mixture was kept at 700°C for 3 hours to obtain an alloy catalyst. The metal loading of the alloy catalyst was 50%.

[0114] Comparative Example 2

[0115] The comparative example of the present application provides an alloy catalyst and a preparation method thereof, which comprises the following steps:

[0116] S1. Preparation of lyophilized material

[0117] First, cobalt nitrate and chloroplatinic acid are ultrasonically dispersed in water at a molar ratio of cobalt element to platinum element of 3:1 to prepare a mixed solution, and then the mixed solution and Ketjen black are added to a stirring tank for stirring and mixing treatment. The mixing time is 2 hours. After the mixing treatment is completed, it is transferred to a glass watch glass within 5 minutes for liquid nitrogen pre-freezing to obtain a pre-frozen material, and then the pre-frozen material is transferred to a freeze dryer for freezing for 24 hours to obtain a freeze-dried material.

[0118] S2. Preparation of initial alloy catalyst

[0119] The obtained freeze-dried material was transferred to a porcelain boat and heat-treated in a tube furnace. Before the heat treatment, nitrogen was introduced into the tube furnace at room temperature for 60 minutes to expel the air in the tube furnace. Then hydrogen and nitrogen were introduced into the tube furnace, and the volume ratio of hydrogen to nitrogen was 100 mL:300 mL. Then, the temperature was increased to 300°C at a heating rate of 5°C / min to 10°C / min, and kept at 300°C for 3 hours to obtain an initial alloy catalyst, which was an alloy supported on a carbon carrier.

[0120] S3. Preparation of alloy catalyst

[0121] The prepared alloy loaded on the carbon support was transferred to a porcelain boat and annealed in a tube furnace. Before annealing, nitrogen was introduced into the tube furnace at room temperature for 60 minutes to expel the air in the tube furnace. Then nitrogen was introduced into the tube furnace with a volume of 500 mL. The temperature was then raised to 700°C at a heating rate of 10°C / min to 50°C / min, and the temperature was kept at 700°C for 3 hours to obtain an alloy catalyst with a metal loading of 50%.

[0122] The process parameters of Examples 1 to 10 and Comparative Examples 1 to 2 are shown in Table 1.

[0123] Table 1 Process parameters of Examples 1 to 10 and Comparative Examples 1 to 2

[0124]

[0125]

[0126] Test Example 1

[0127] The alloy catalysts of Examples 1 to 10 and Comparative Examples 1 to 2 were taken to measure their order and particle size as well as their performance in the membrane electrode. The results are shown in Table 2 and Table 3. The XRD patterns of Example 1 and Comparative Example 2 are shown in Table 3. Figure 4 shown.

[0128] The test method is as follows:

[0129] 1. Orderliness test

[0130] To calculate the degree of order of different platinum-cobalt alloy samples, we use the ratio of the intensity or integrated area of ​​the superlattice reflection to the non-characteristic reflection as a quantitative assessment. For example, for PtCo, we use the ratio of the integrated area under the (110) plane to the sum of the areas under the (111), (200) and (002) planes, S(110) / (S(111)+S(200)+S(002)), as a quantitative assessment. For the 100% ordered intermetallic compound Wct-PtCo (JCPDS: 65-8969), the value of S(110) / (S(111)+S(200)+S(002)) is 0.1677. Then the ratio of the actual calculated ratio S(110) / (S(111)+S(200)+S(002)) to the theoretical ratio of Wct-PtCo is the corresponding degree of order of the catalyst. (DOI: 10.1038 / s41467-022-34037-7).

[0131] 2. Particle size test

[0132] The average particle size of 100 metal nanoparticles was obtained by HR-TEM testing.

[0133] 3. Performance test conditions of alloy catalysts in membrane electrode

[0134] Hydrogen (0.6 L / min) was distributed to the anode and air (1.1 L / min) to the cathode. The relative humidity at the anode was set to 30%, the relative humidity at the cathode to 55%, the anode inlet pressure to 90 kPa, the cathode inlet pressure to 80 kPa, and the stack temperature to 80°C. The cell was activated at a constant current under hydrogen and oxygen conditions for approximately 30 minutes. The cathode was then switched to air. After approximately 20 minutes of voltage stabilization, the membrane electrode performance was finally tested.

[0135] Table 2 Ordering degree and particle size of alloy catalysts of Examples 1 to 10 and Comparative Examples 1 to 2

[0136] project Order degree (%) Particle size (nm) Example 1 72 3.5 Example 2 54.4 4.2 Example 3 70.9 3.4 Example 4 41.8 3.3 Example 5 68.1 4.1 Example 6 61.3 5.2 Example 7 60.9 3.3 Example 8 73.2 3.8 Example 9 61.0 3.9 Example 10 64.7 3.8 Comparative Example 1 34.2 3.6 Comparative Example 2 24.9 4.9

[0137] Table 3 Performance of alloy catalysts in membrane electrode of Examples 1-10 and Comparative Examples 1-2

[0138]

[0139]

[0140] From the above, it can be seen that the oxidation treatment and the thermal annealing temperature in Example 1 are appropriate, and the performance of the alloy catalyst obtained is better.

[0141] Comparing Example 2 with Example 1, it can be seen that the CO concentration in Example 2 is lower, the confinement effect on the alloy particles is weaker, and the electrochemical active area (ECSA) of the obtained alloy catalyst is lower. However, due to the oxidation treatment, the final catalyst performance shows higher low-electrical density performance and poor high-electrical density performance.

[0142] Comparison between Example 3 and Example 1 shows that the CO concentration in Example 3 is higher, which may result in the formation of an excessively thick carbon shell that blocks the alloy active sites. Therefore, the performance of the obtained alloy catalyst is slightly worse than that in Example 1.

[0143] Comparison between Example 4 and Example 1 shows that the heat treatment temperature of Example 4 is lower, and the obtained alloy catalyst has a higher electrochemical active area (ECSA), but is not sufficiently ordered, so its performance is slightly worse than that of Example 1.

[0144] Comparison of Examples 5 and 6 with Example 1 shows that the heat treatment temperatures of Examples 5 and 6 are higher, the electrochemical active area (ECSA) of the obtained alloy catalysts is reduced, and the performance is slightly reduced.

[0145] Comparison between Example 7 and Example 1 shows that the annealing time in Example 7 is shorter. Although the catalyst obtained has a smaller particle size and a higher electrochemical active area (ECSA), it is not sufficiently ordered, and the catalyst activity is worse than that in Example 1, and the low electric density performance is reduced.

[0146] Comparison between Comparative Example 1 and Example 1 shows that Comparative Example 1 was not subjected to oxidation treatment. Although the alloy catalyst obtained had a higher electrochemical active area (ECSA), it was not sufficiently ordered, and its catalytic activity was worse than that of Example 1, and its low electric density performance decreased.

[0147] Comparison between Comparative Example 2 and Example 1 shows that the alloy catalyst prepared in Comparative Example 2 has no oxidation treatment and CO treatment, and the ordering and electrochemical active area (ECSA) are insufficient, and the overall performance is poor.

[0148] Test Example 2

[0149] The alloy catalysts of Examples 1 to 10 and Comparative Examples 1 to 2 were tested for long-term durability in membrane electrodes. The results are shown in Table 4.

[0150] Long-term durability test conditions of alloy catalysts in membrane electrodes:

[0151] Hydrogen (0.5 L / min) was distributed to the anode, and air (1 L / min) was distributed to the cathode. The anode relative humidity was set to 25%, the cathode humidity to 50%, the anode inlet pressure to 80 kPa, the cathode inlet pressure to 70 kPa, and the stack temperature to 75°C. The cells were activated at a constant current under hydrogen and oxygen conditions for approximately 30 minutes. The cathode was then switched to air. After approximately 15 minutes of voltage stabilization, the VI performance was finally tested.

[0152] Hydrogen (0.2 L / min) was distributed to the anode, and nitrogen (0.075 L / min) was distributed to the cathode. The relative humidity at the anode and cathode was set to 100%, the anode and cathode inlet pressure was at atmospheric pressure, and the stack temperature was 80°C. A square wave cycle of 0.6 V for 3 s and 0.95 V for 3 s was performed. A catalyst aging test was performed for 3 cycles.

[0153] Table 4 Long-term durability test of alloy catalysts of Examples 1 to 10 and Comparative Examples 1 to 2 in membrane electrodes

[0154]

[0155]

[0156] It can be seen from the above that the alloy catalysts of Examples 1 to 10 all have relatively high catalyst resistance performance.

[0157] Comparison between Comparative Example 1 and Example 1 shows that the catalyst durability of the alloy catalyst prepared in Comparative Example 1 is worse than that in Example 1 because no oxidation treatment is performed.

[0158] Comparison of Comparative Example 2 with Comparative Example 1 and Example 1 shows that the catalyst durability of the alloy catalyst prepared in Comparative Example 2 without oxidation treatment and CO treatment is worse than that in Example 1 and even worse than that in Comparative Example 1.

[0159] The foregoing description is merely a specific embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing an alloy catalyst, characterized in that: The preparation method of the alloy catalyst comprises: Placing an initial alloy catalyst in an atmosphere containing oxygen for oxidation treatment to obtain a first precursor, wherein the oxidation treatment is performed in a tube furnace, and then subjecting the first precursor to an annealing treatment, wherein the annealing treatment atmosphere comprises carbon monoxide and an inert gas, and the volume ratio of carbon monoxide to the inert gas is 10 mL:200 mL to 20 mL:250 mL, the annealing treatment temperature is 650° C. to 900° C., and the annealing treatment time is 2 h to 5 h, to obtain the alloy catalyst; The initial alloy catalyst includes a carrier and initial alloy particles supported on the carrier, wherein the initial alloy particles include platinum and a transition metal; The initial alloy catalyst can be prepared by the following method: The freeze-dried product is placed in an atmosphere containing hydrogen for heat treatment, wherein the heat treatment temperature is 200° C. to 400° C. and the heat treatment time is 2 h to 5 h; The lyophilized material includes a mixture of a transition metal precursor, a platinum precursor and the carrier; The lyophilized material was prepared by the following method: After mixing the transition metal precursor, the platinum precursor and the carrier, the mixture is transferred to a glass watch glass within 5 minutes for rapid pre-freezing to obtain a pre-frozen product, and the pre-frozen product is transferred to a freeze dryer for freezing for 18 hours to 30 hours to obtain the freeze-dried product; The temperature of the oxidation treatment is 80°C to 100°C, and the time of the oxidation treatment is 2h to 5h; The alloy catalyst includes a carrier and alloy particles loaded on the carrier, the alloy particles include a core, a first shell and a second shell, the first shell is coated on the surface of the core, the second shell is coated on the surface of the first shell, the core is an alloy, the first shell is a platinum layer, and the second shell is a carbon layer.

2. The method for preparing the alloy catalyst according to claim 1, wherein: The molar ratio of platinum to transition metal in the initial alloy particles is 1:3 to 5:1; and / or the carrier comprises a carbon carrier or an oxide carrier.

3. The method for preparing the alloy catalyst according to claim 1, wherein: The atmosphere for the oxidation treatment is air.

4. The method for preparing the alloy catalyst according to claim 1, wherein: The transition metal includes any one or more of cobalt, nickel, iron and manganese; and / or the platinum precursor includes any one or more of chloroplatinic acid, platinum acetylacetonate and potassium chloroplatinate.

5. An alloy catalyst, characterized in that: The alloy catalyst is prepared according to the preparation method of the alloy catalyst according to any one of claims 1 to 4.

6. The alloy catalyst according to claim 5, characterized in that The alloy catalyst includes a carrier and alloy particles loaded on the carrier, the alloy particles include a core, a first shell and a second shell, the first shell is coated on the surface of the core, the second shell is coated on the surface of the first shell, the core is an alloy, the first shell is a platinum layer, and the second shell is a carbon layer.

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