Carbon-supported metal catalyst and method for producing the same

Abstract

The application relates to the field of fuel cell technology, and mainly relates to a carbon-loaded metal catalyst and a preparation method thereof. The steps comprise: dispersing platinum acetylacetone, a transition metal acetylacetone salt and a carbon material in a solvent, drying to remove the solvent to obtain a precursor, and obtaining a mixture after first annealing under an air atmosphere; secondly annealing the mixture under a hydrogen-argon atmosphere, performing acid pickling after cooling, and then performing washing and drying, and thirdly annealing under a hydrogen-argon atmosphere to obtain the carbon-loaded metal catalyst. The platinum and the transition metal acetylacetone salt are used, the uniform impregnation is directly annealed under the air atmosphere, two-step gas-phase reduction is carried out under the hydrogen-argon atmosphere, platinum-based intermetallic compound nanoparticles wrapped by controllable carbon layers are prepared, particle agglomeration is effectively prevented, the prepared catalyst has high order degree, the particles are small, the distribution is uniform, and the catalyst has excellent activity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, and particularly relates to a carbon-supported metal catalyst and a preparation method thereof. BACKGROUND

[0002] The fuel cell currently proposed can effectively convert hydrogen energy into electric energy, and has good application prospects in the fields of energy conversion devices and heavy truck driving. Platinum and platinum-based alloy are necessary catalyst materials for proton exchange membrane fuel cells, and are also main factors affecting the conversion capacity and application cost of proton exchange membrane fuel cells. However, the platinum consumption in the currently commercial fuel cell vehicles is high, for example, the platinum loading in Toyota Mirai is about 36 g, and the high application cost becomes a main factor limiting the wide use of proton exchange membrane fuel cells.

[0003] An effective strategy to reduce the platinum loading at present is to alloy Pt with the first-row transition metal, that is, to add small transition metal atoms to the Pt-based alloy to cause beneficial strain and alloy effects, so as to improve the oxygen reduction reaction (ORR) rate of the platinum alloy catalyst. For platinum-based alloy catalysts, the order degree of the catalyst generally increases with the increase of temperature, and the order degree is positively correlated with the activity of the catalyst. However, high-temperature annealing is often required to achieve a high atomic order degree, and the high-temperature annealing treatment inevitably accelerates metal sintering, resulting in the aggregation of nanoparticles and the reduction of activity. At present, many preparation methods have been developed to prepare small nanoparticles, especially the nanoparticles of platinum-based catalyst materials applied to fuel cells, such as coating a polymer or metal oxide protective shell before annealing to limit the size of the particles, or preparing by small molecule assisted impregnation, but these methods are complicated to operate, the thickness of the protective shell is difficult to control, and the activity of the platinum-based catalyst is easily affected, therefore, the prior art still needs to be improved and developed. SUMMARY

[0004] In view of the above problems in the prior art, the present application aims to provide a carbon-supported metal catalyst and a preparation method thereof, and aims to solve the problems that the existing methods for controlling the aggregation of metal particles in the catalyst are complicated to operate and easily affect the activity of the catalyst.

[0005] The technical scheme of the present application is as follows:

[0006] In a first aspect, the present application provides a preparation method of a carbon-supported metal catalyst, which comprises the following steps:

[0007] The platinum acetylacetonate, the acetylacetonate salt of the transition metal and the carbon material are dispersed in a solvent, and a precursor is obtained after drying and removing the solvent, and a mixture is obtained after first annealing in an air atmosphere;

[0008] The mixture is annealed for the second time under a hydrogen argon atmosphere, and after cooling, the mixture is subjected to acid washing, and after washing and drying, the mixture is annealed for the third time under a hydrogen argon atmosphere to obtain the carbon-supported metal catalyst.

[0009] The present application can prepare platinum-based intermetallic compound nanoparticles wrapped by a controllable carbon layer by using platinum and acetylacetone salt of a transition metal, directly annealing by an air atmosphere after impregnation, and then performing two-step gas phase reduction under a hydrogen argon atmosphere, can effectively prevent particle agglomeration, and can prepare a carbon-supported metal catalyst with high order degree, small and uniform distribution of catalyst particles, and excellent activity.

[0010] Further, the temperature of the first annealing is 100-500℃, and the annealing time is 5-500min.

[0011] The weight loss rate of the mixture before and after the first annealing is 1-50%wt.

[0012] In the present application, by forming a carbon layer through acetylacetone groups, the thickness of the carbon layer formed subsequently and the wrapping performance on the reduced metal particles can be controlled by controlling the temperature and weight loss rate of the first annealing, which is beneficial to improve the catalytic effect of the catalyst.

[0013] Further, the temperature of the first annealing is 176℃, and the annealing time is 20-40min.

[0014] The weight loss rate of the mixture before and after the first annealing is 1-30%wt.

[0015] In the present application, the acetylacetone groups are adjusted, and by being at 176℃ and a weight loss rate of not more than 30%, the catalytic activity can be improved.

[0016] Further, the second annealing is performed at 400-1100℃ for 10min-8h.

[0017] In the present application, by annealing under an argon hydrogen atmosphere, the acetylacetone groups can be decomposed and form a carbon layer to wrap the reduced nanometer metal particles, effectively preventing particle agglomeration.

[0018] Further, the acid washing is performed in sulfuric acid with a concentration of 0.1-1mol / L at 60℃ for 12h.

[0019] Further, the third annealing is performed at 100-500℃ for 10min-6h.

[0020] In the present application, by performing the third annealing, the metal structure strength between platinum and the transition metal can be stabilized, and the stability can be improved.

[0021] Further, the carbon material includes graphitized carbon or commercialized carbon material.

[0022] The graphitized carbon is prepared by keeping non-amorphous carbon material at 1200-3000℃ for 10 min-6h in inert atmosphere or nitrogen atmosphere, and then naturally cooling to room temperature.

[0023] The commercialized carbon material is one of Vulcan XC72, KB300, KB600, BP 2000 or Toray carbon.

[0024] Further, the acetylacetone salt of transition metal is one or more than two of acetylacetone iron, acetylacetone nickel, acetylacetone molybdenum, acetylacetone vanadium, acetylacetone copper, acetylacetone manganese, acetylacetone zinc, acetylacetone titanium, acetylacetone tungsten, acetylacetone chromium and acetylacetone zirconium.

[0025] Further, the platinum loading in the carbon-supported metal catalyst is 1-60wt%.

[0026] In the second aspect, the application further provides a carbon-supported metal catalyst, which comprises a carbon carrier with metal nanoparticles distributed and loaded thereon, and the surface of the metal nanoparticles is coated with a carbon layer.

[0027] The carbon carrier is one of solid nanoparticles or porous continuous structure, and the particle size of the solid nanoparticles is 1nm-300μm.

[0028] The particle size of the metal nanoparticles is 1-20nm.

[0029] The pore structure in the carbon layer is one of loose porous, trace porous or closed non-porous.

[0030] The coating is one of no coating, partial coating or full coating.

[0031] The thickness of the carbon layer is 0.001nm-50nm.

[0032] The number of layers of the carbon layer is 0-50 layers.

[0033] Beneficial effects: By using platinum and acetylacetone salt of transition metal, and after uniform impregnation, the platinum-based intermetallic compound nanoparticles wrapped by controllable carbon layer can be prepared by directly annealing in air atmosphere, and then by two-step gas phase reduction in hydrogen-argon atmosphere, which can effectively prevent particle agglomeration, and the carbon-supported metal catalyst with high ordered degree, small and uniform distribution of catalyst particles and excellent activity can be prepared. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1aA particle distribution electron micrograph of the graphitized carbon supported metal catalyst of Example 1 of the present application.

[0035] Figure 1b An electron micrograph of the particles of the graphitized carbon supported metal catalyst of Example 1 of the present application.

[0036] Figure 2 XRD test results of the graphitized carbon supported metal catalyst of Example 1 of the present application.

[0037] Figure 3 A TGA curve of the precursor of Example 1 of the present application obtained by heating at 5°C / min in air.

[0038] Figure 4a A particle distribution electron micrograph of the graphitized carbon supported metal catalyst of Example 2 of the present application annealed in air at 152°C.

[0039] Figure 4b A particle distribution electron micrograph of the graphitized carbon supported metal catalyst of Example 2 of the present application annealed in air at 164°C.

[0040] Figure 4c A particle distribution electron micrograph of the graphitized carbon supported metal catalyst of Example 2 of the present application annealed in air at 188°C.

[0041] Figure 4d ORR polarization curves of the graphitized carbon supported metal catalyst of Examples 1 and 2 of the present application annealed in air at 152°C, 164°C, 176°C, and 188°C, respectively.

[0042] Figure 5 XRD test results of the graphitized carbon supported metal catalyst of Example 2 of the present application annealed in air at 152°C, 164°C, and 188°C, respectively.

[0043] Figure 6 A particle distribution electron micrograph of the graphitized carbon supported metal catalyst of Example 3 of the present application.

[0044] Figure 7 XRD test results of the graphitized carbon supported metal catalyst of Example 3 of the present application.

[0045] Figure 8 A particle distribution electron micrograph of the KB600 supported platinum-based intermetallic compound catalyst of Example 4 of the present application.

[0046] Figure 9 XRD test results of the KB600 supported platinum-based intermetallic compound catalyst of Example 4 of the present application.

[0047] Figure 10aThe electron microscope image of the catalyst particle of the present application Comparative Example 1.

[0048] Figure 10b The electron microscope image of the catalyst particle of the present application Comparative Example 1.

[0049] Figure 11 The XRD test result of the catalyst of the present application Comparative Example 1.

[0050] Figure 12 The ORR polarization curve graph of the graphitized carbon supported metal catalyst of the present application Example 1 and the commercial platinum carbon catalyst of Comparative Example 2.

[0051] Figure 13 The ORR polarization curve graph of the KB600 supported platinum metal intermetallic compound catalyst of the present application Example 4 and the commercial platinum carbon catalyst of Comparative Example 2.

[0052] Figure 14 The ORR polarization curve graph of the graphitized carbon supported metal catalyst of the present application Example 1 and the graphitized carbon supported catalyst of Comparative Example 1.

[0053] Figure 15 The specific activity numerical column contrast graph of the present application Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0054] The present application provides a carbon supported metal catalyst and a preparation method thereof, in order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0055] At present, platinum metal intermetallic compound catalysts generally need to be annealed at high temperature to obtain higher order degree, and the order degree of platinum metal intermetallic compound catalyst is positively correlated with its catalytic performance, but high temperature annealing will inevitably accelerate metal sintering, produce larger crystallites, cause the nanometer particles of platinum metal intermetallic compound catalyst to agglomerate, reduce the specific surface area and mass specific activity, thereby greatly reducing the activity and stability of the catalyst.

[0056] In view of this problem, the present application provides a preparation method of a carbon supported metal catalyst, which comprises the following steps:

[0057] S1, dispersing platinum acetylacetone, acetylacetone salt of transition metal and carbon material in solvent, drying to remove solvent to obtain a precursor, and then first annealing to obtain a mixture;

[0058] S2, the mixture is annealed for the second time under hydrogen argon atmosphere, after cooling, acid washing, washing and drying, and annealing for the third time under hydrogen argon atmosphere to obtain carbon supported metal catalyst.

[0059] The present application can prepare platinum-based intermetallic compound nanoparticles wrapped by controllable carbon layers by using platinum and acetylacetone salt of transition metal, directly annealing through air atmosphere after uniform impregnation, and then carrying out two-step gas phase reduction under hydrogen argon atmosphere, can effectively prevent particle agglomeration, and can prepare carbon supported metal catalyst with high order degree, small and uniform distribution of catalyst particles and excellent activity.

[0060] The ratio of platinum to transition metal is 1:0.1-10, preferably 1:1-1.2.

[0061] Specifically, in the present application, by directly using platinum and acetylacetone salt of transition metal, the acetylacetone group therein is directly used as a carbon layer raw material, and the acetylacetone group can limit the occurrence of agglomeration by decomposing and recombining to form a carbon layer to wrap platinum-based intermetallic compound nanoparticles, thereby obtaining a catalyst material with uniform distribution of nanoparticles and high activity.

[0062] In step S1, after the acetylacetone platinum, acetylacetone salt of transition metal and graphitized carbon are dispersed in the solvent, they can be uniformly mixed by ultrasonic mixing, and then dried by rotary evaporation.

[0063] Further, the carbon material includes graphitized carbon or commercial carbon material. The graphitized carbon is prepared by heating amorphous carbon material to 1200-3000°C for 10 min-6h in an inert atmosphere or nitrogen atmosphere, and then naturally cooling to room temperature. Specifically, the graphitized carbon can also be replaced by commonly used commercial carbon materials on the market, such as one of Vulcan XC72, KB300 (Ketjen Black 300), KB600 (Ketjen Black 600), BP 2000 or Toray carbon. The carbon material is preferably graphitized carbon, which has better corrosion resistance than other carbon materials in a high-temperature acidic environment, but at the same time, the graphitized carbon has fewer surface defect sites and cannot effectively load metal nanoparticles, so traditional chloroplatinic acid impregnation will cause the particles to easily agglomerate, and through the adjustment of the present application, the problem of particle agglomeration can be effectively solved.

[0064] In step S1, the solvent can be specifically acetone, and the amount of acetone is 6-10 ml, which can be selected according to different carbon materials, and the specific standard can be 150 mg of carbon material corresponding to 6-10 ml of acetone, because different carbon materials have different volumes after being soaked in the solvent, so it is required that the acetone can immerse the carbon material, so as to be dispersed. In this application, the acetylacetone salt and the carbon material are uniformly dispersed in the acetone to obtain a uniform solution, so as to uniformly distribute the nanoparticles on the carbon carrier by subsequent gas phase reduction.

[0065] wherein the acetone is removed by rotary drying. The acetone acts as a dispersing agent as a precursor solvent and does not participate in the synthesis of the material. If it is not removed, it will cause uneven dispersion of the precursor, thereby causing agglomeration of the particles.

[0066] Further, the first annealing condition is annealing in an air atmosphere at a temperature of 100-500℃ for 5-500 min. At present, the general method of introducing a carbon layer through an organic ligand needs to add other substances, which may introduce other impurities, and the steps are more complicated and the cost is increased. In this application, the acetylacetone salt is used as an organic metal salt of the target metal, and the composition is relatively simple, and the carbon layer formed by the acetylacetone group is simpler and purer.

[0067] Preferably, the first annealing condition is annealing in an air atmosphere at a temperature of 176℃ for 20-40 min. Specifically, the platinum-based intermetallic compound nanoparticles are wrapped by the carbon layer to prevent agglomeration under high-temperature annealing conditions, but the wrapped carbon layer cannot be too thick, otherwise it will affect the catalytic effect of the catalyst. In this application, the control of the first annealing temperature at 176℃ is proposed for the acetylacetone group. The pre-oxidation intervention in the air atmosphere at 176℃ can regulate the subsequent decomposition and recombination of the acetylacetone group, optimize the carbon layer formed, and the catalyst wrapped by the carbon layer can be uniformly distributed on the graphitized carbon carrier, which is beneficial to prepare a carbon-loaded metal catalyst with excellent oxygen reduction reaction performance.

[0068] Further, the weight loss rate of the mixture before and after the first annealing is 1-50%wt. Wherein, the weight loss rate can be controlled according to the annealing time and temperature. Carbon will react at high temperature, and generally the longer the time or the higher the temperature, the less carbon is left, and the higher the weight loss rate. More specifically, annealing in an air atmosphere will oxidize part of the acetylacetone group, affecting the content of the carbon layer on the surface. The weight loss rate of the mixture before and after the first annealing will affect the performance of the carbon layer. Too low weight loss will result in a thicker carbon layer, and the exposed active sites will be fewer. Increasing the weight loss rate will cause the carbon layer to become thinner or even unable to form, which will cause the particles to agglomerate and the performance to decrease.

[0069] More preferably, the weight loss rate of the mixture before and after the first annealing is not higher than 30%wt. When the weight loss rate exceeds 30%wt, the particles are prone to grow larger, which is more likely to affect the catalytic performance. By controlling the weight loss rate within a suitable range, the active sites and the thickness of the carbon layer can be well balanced.

[0070] Further, the second annealing is performed at 400-1100℃ for 10min-8h, and more preferably at 700℃ for 6h. In the present application, by performing high-temperature annealing in a hydrogen-argon atmosphere, the platinum acetylacetonate and the transition metal acetylacetonate salt in the mixture can be reduced in situ into nano metal particles. Then, at high temperature, the acetylacetonate groups are decomposed and recombined. After that, by continuously maintaining high temperature and continuously flowing the hydrogen-argon atmosphere, the decomposed acetylacetonate groups are decomposed into small molecular fragments at high temperature, and at the same time, the carbon layer is formed to wrap the nano metal particles, thereby limiting the growth of the particles and effectively preventing the agglomeration or sintering of the particles. At the same time, the reduced nano metal particles can also obtain high order degree at high temperature, thereby obtaining a catalyst material with uniform particle distribution and high activity. The operation is simple, no other impurities and elements are introduced, the order degree of the alloy is higher, the stability and performance are improved, the particles are smaller, and the performance is better.

[0071] Further, the acid pickling is performed in sulfuric acid with a concentration of 0.1-1mol / L, and more preferably with a concentration of 0.25mol / L, at 60℃ for 12h. In the present application, by acid pickling, the extra transition metal atoms on the surface of the metal particles are removed, which is beneficial to improve the stability.

[0072] Further, the third annealing is performed at 100-500℃ for 10min-6h, and more preferably at 200℃ for 1.5h. In the present application, by performing the third annealing, the metal structure strength between platinum and transition metal can be stabilized, thereby improving the stability.

[0073] In the second and third annealings, the argon-hydrogen ratio in the hydrogen-argon atmosphere can be maintained within a safe range of 99:1-80:20.

[0074] Further, the transition metal acetylacetonate salt is one or more of acetylacetonate iron, acetylacetonate nickel, acetylacetonate molybdenum, acetylacetonate vanadium, acetylacetonate copper, acetylacetonate manganese, acetylacetonate zinc, acetylacetonate titanium, acetylacetonate tungsten, acetylacetonate chromium and acetylacetonate zirconium. Preferably, the transition metal acetylacetonate salt is preferably acetylacetonate cobalt. Platinum-cobalt alloy has higher performance among the currently reported platinum-based alloys, and is also a commonly used alloy selection for alloy catalysts. By using platinum-cobalt alloy, the performance of the catalyst can be improved.

[0075] Specifically, chloroplatinic acid is used as the platinum source, and decomposition at high temperature will produce agglomeration. Currently, the metal particles are generally reduced at low temperature first, and then some substances are added to limit the agglomeration of the particles before high-temperature treatment. These added substances will also have residues after high-temperature annealing, so further treatment is often required, and the performance of the carbon layer formed will be affected in the process, which will affect the diffusion of the solution on the surface of the catalyst during use and affect the catalytic effect. In the present application, acetylacetone salt is used as the metal source, and the acetone used is extremely volatile and will not volatilize. Through high-temperature treatment with graphitized carbon, the acetylacetone salt will be decomposed at high temperature, and the decomposed substances will form a carbon layer to wrap and limit the agglomeration of the particles. Compared with the existing preparation method, the preparation can be completed in a shorter operation step, the synthesis is simple, and the cost is lower.

[0076] Further, the platinum loading in the carbon-supported metal catalyst is 1-60 wt%, and more preferably 5-60 wt%.

[0077] The present application also provides a carbon-supported metal catalyst, which comprises a carbon carrier with metal nanoparticles distributed and loaded thereon, and the surface of the metal nanoparticles is coated with a carbon layer.

[0078] Specifically, in the provided carbon-supported metal catalyst, the metal nanoparticles are uniformly distributed on the carbon carrier, and each metal particle on the carbon carrier is wrapped by a carbon layer.

[0079] Further, the carbon carrier can be one of a solid nanoparticle or a porous continuous structure, and the particle size of the solid nanoparticle is 1 nm-300 μm. The carbon carrier of the solid nanoparticle or the porous continuous structure includes commercial carbon materials and graphitized carbon.

[0080] Further, the particle size of the metal nanoparticles is 1-20 nm, and preferably 3-5 nm. Specifically, the metal nanoparticles can be one of platinum, iron, nickel, molybdenum, vanadium, copper, manganese, zinc, titanium, tungsten, chromium, zirconium, or an intermetallic compound of two or more metals, and more preferably platinum nanoparticles and platinum-based intermetallic compound nanoparticles. The particle size of the metal nanoparticles can be measured by observing the STEM image or the XRD test result of the carbon-supported metal catalyst.

[0081] Further, the pore structure in the carbon layer can be one of loose porous, trace porous, or closed non-porous. Further, the pore structure in the carbon layer is preferably loose porous, which has a larger electrochemical contact area and is beneficial to improve the electrochemical performance.

[0082] Specifically, the wrapped carbon layer can be observed for the distribution of pores through the STEM image of the carbon-supported metal catalyst, or can be judged according to electrochemical data. The loose porous structure has a good electrochemical contact area, so the excellent electrochemical performance indicates that the wrapped carbon layer has a loose porous structure.

[0083] Further, the coating can be none, partial or full coating, preferably full coating. The degree of coating of the carbon layer can be observed by STEM image of the carbon supported metal catalyst.

[0084] Further, the thickness of the carbon layer is 0.001-50 nm, preferably 0.01 nm-3 nm. The thickness of the carbon layer can be observed by STEM image of the carbon supported metal catalyst.

[0085] Further, the number of layers of the carbon layer is 0-50 layers, preferably 1-2 layers. The number of layers of the carbon layer can be observed by STEM image of the carbon supported metal catalyst.

[0086] Preferably, the provided carbon supported metal catalyst can also be prepared by the preparation method of the carbon supported metal catalyst as described above. By the preparation method provided in the present application, the structure and properties of the carbon support can be maintained, and the preparation can be performed on the required carbon support as needed. The prepared carbon supported metal catalyst has loose and porous carbon layer fully coated on the metal nanoparticles, the thickness of the carbon layer is less than 3 nm, the number of layers of the carbon layer is less than 2 layers, the thickness and the number of layers of the carbon layer formed by acetylacetonyl group can be controlled by controlling the annealing conditions, and the particle size of the metal nanoparticles is 1-20 nm. The carbon supported metal catalyst has good catalytic performance, high stability and high cycle performance.

[0087] The following is further illustrated by specific examples.

[0088] Example 1

[0089] The graphitized carbon supported platinum cobalt intermetallic compound of Example 1 includes the following steps:

[0090] The platinum acetylacetone, cobalt acetylacetone and 150 mg of graphitized carbon are dispersed in 7 ml of acetone and uniformly ultrasonicated; the platinum loading is controlled to be 30 wt%, and the cobalt loading is controlled to be 30 wt%, dried by rotary evaporation, and the precursor of Example 1 is obtained after the acetone is removed by drying, and then the first annealing is performed at 176°C under air atmosphere, and the mixture is obtained after annealing for 20 min;

[0091] The mixture is annealed for the second time at 700°C for 6 hours under hydrogen argon atmosphere, cooled, put into 0.25 mol / L sulfuric acid, acid washed at 60°C for 12 h, washed with deionized water after acid washing, and then dried in a vacuum oven at 65 degrees, and the third annealing is performed at 200°C for 1.5 h under hydrogen argon atmosphere after drying, and the graphitized carbon supported platinum cobalt intermetallic compound catalyst of Example 1 is obtained.

[0092] The graphite carbon used in Example 1 was prepared by heating the amorphous carbon material at 1800°C for 75 minutes in an argon atmosphere, and then naturally cooling to room temperature.

[0093] The STEM images of the particle distribution and the electron microscope images of the graphite carbon supported platinum-cobalt intermetallic compound catalyst of Example 1 are shown in Figure 1a and Figure 1b respectively. It can be observed that the particles are uniformly distributed on the surface of the graphite carbon, and the carbon support carries the platinum-cobalt intermetallic compound particles, which are thinly and completely coated with a carbon layer on the surface of the particles, and the thickness of the carbon layer is less than 2.5 nm. The XRD test of Example 1 is shown in Figure 2 , which shows that Pt1Co1(platinum-cobalt intermetallic compound with a platinum-cobalt atomic ratio of 1 / 1) is successfully prepared. It can be concluded from the observation of the electron microscope images and the XRD test results that the particle size of the platinum-cobalt intermetallic compound particles coated with the carbon layer is 4-5 nm. The TGA curve of the precursor containing acetylacetone salt and graphite carbon in Example 1 is shown in Figure 3 obtained by heating at 5°C / min in air.

[0094] Example 2

[0095] The preparation method of the graphite carbon supported platinum-cobalt intermetallic compound catalyst of Example 2 is basically the same as that of Example 1, except that three sets of precursors are provided in Example 2, and the first annealing temperature is set to 152°C, 164°C and 188°C respectively, and are respectively designated as Example 2a, Example 2b and Example 2c. The graphite carbon supported platinum-cobalt intermetallic compound catalyst prepared in Example 2 is subjected to STEM test and XRD test. The particle distribution of the STEM images is shown in Figure 4a , Figure 4b and Figure 4c respectively. It can be observed that the particles are uniformly distributed on the surface of the graphite carbon, and the carbon support carries the platinum-cobalt intermetallic compound particles, which are thinly and completely coated with a carbon layer on the surface of the particles, and the performance of the carbon layer is slightly different. The graphite carbon supported platinum-cobalt intermetallic compound catalysts prepared in Example 1 and Example 2 are subjected to activity test, and the oxygen reduction reaction test is carried out in an electrochemical cell in an oxygen-saturated 0.1M perchloric acid solution, and the scanning rate is 20mV s -1 . The ORR performance test of Example 1 and Example 2 is shown in Figure 4d . It can be found that the ORR performance of Example 1 annealed at 176°C is relatively good. The XRD test is shown in Figure 5The observation can find that the particle becomes larger with the temperature rising, and the main peak shows the peak of solid solution. The small bifurcation of the peak can be the result of the incomplete combination of the particles. It can be seen that the first annealing temperature also affects the combination effect of platinum-based metal. With the temperature rising, the effect of carbon layer on the particle growth decreases, resulting in the particle becoming larger.

[0096] Example 3

[0097] The preparation method of the graphitized carbon supported platinum-cobalt intermetallic compound catalyst of Example 3 is basically the same as that of Example 1, and the difference lies in that the second annealing condition of Example 3 is in a hydrogen-argon atmosphere and at 700°C for 2h. The STEM test and XRD test are performed on the prepared graphitized carbon supported platinum-cobalt intermetallic compound catalyst of Example 3. The particle distribution of the STEM test is as shown in Figure 6 The observation can find that the particle distribution on the surface of the graphitized carbon is slightly poor, and the carbon carrier loads the platinum-cobalt intermetallic compound particles, which are fully coated with a carbon layer on the surface of the particles. The XRD test is as shown in Figure 7 The electron microscope shows that the particles are uniformly distributed, but the XRD test shows the peak of solid solution. It can be seen that the order degree is low because the annealing time is only two hours, which is slightly insufficient compared with Example 1.

[0098] Example 4

[0099] The preparation method of the carbon supported platinum-cobalt intermetallic compound catalyst of Example 4 is basically the same as that of Example 1, and the difference lies in that the graphitized carbon used for loading in Example 4 is replaced by porous KB600. The STEM test and XRD test are performed on the prepared KB600 supported platinum-cobalt intermetallic compound catalyst of Example 4. The test results of the STEM test are as shown in Figure 8 The observation can find that the particles are uniformly distributed on the surface of the graphitized carbon, and the carbon carrier loads the platinum-cobalt intermetallic compound particles, which are thinly and fully coated with a carbon layer on the surface of the particles. The XRD test is as shown in Figure 9 The electron microscope shows that the particles are uniformly distributed, but the order degree is slightly lower than that of Example 1 using graphitized carbon.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] The preparation method of the graphitized carbon supported catalyst of Comparative Example 1 includes the following steps:

[0103] The platinum acetylacetonate, cobalt acetylacetonate and graphitized carbon are dispersed in 7ml of acetone and ultrasonically mixed uniformly. The platinum loading is controlled to be 30wt%, and the drying is performed by rotary evaporation. After the acetone is removed by drying, the precursor of Comparative Example 1 is obtained;

[0104] The precursor was annealed in a hydrogen-argon atmosphere at 700°C for 6 hours, after cooling, it was put into 0.25 mol / L sulfuric acid, and acid washed at 60°C for 12 hours. After acid washing, the catalyst was washed with deionized water, and then dried in a vacuum oven at 65 degrees. After drying, the catalyst was annealed in a hydrogen-argon atmosphere at 200°C for 1.5 hours, to obtain the graphitized carbon supported platinum-cobalt intermetallic compound catalyst of Comparative Example 1.

[0105] The raw materials and preparation method of Comparative Example 1 were basically the same as those of Example 1, except that the precursor of Comparative Example 1 was not subjected to the first annealing treatment in an air atmosphere. The graphitized carbon supported catalyst prepared in Comparative Example 1 was subjected to STEM testing and XRD testing. The particle distribution and electron microscope image taken by STEM are shown in Figure 10a and Figure 10b It can be seen from the STEM that the particles are uniformly distributed, and a carbon layer is fully coated on the surface of the particles. Compared with the carbon layer of Example 1, the thickness of the carbon layer is increased to more than 5 nm. The XRD test results are shown in Figure 11 It can be found that the order degree of the material of the sample without annealing is lower, thereby resulting in that the activity is far lower than that of Example 1 subjected to air annealing.

[0106] Comparative Example 2

[0107] A commercially available platinum supported catalyst with a platinum loading of 40wt% was used as the raw material, and the loading of the catalyst was 20.0 μg Pt / cm 2 .

[0108] The graphitized carbon supported platinum-cobalt intermetallic compound catalyst of Example 1 and the commercial Pt / C catalyst of Comparative Example 2 were subjected to the same activity test as Example 2, and the activity test results are shown in Figure 12 It can be found by comparing the polarization curves of the graphitized carbon supported platinum-cobalt intermetallic compound catalyst and the commercial Pt / C catalyst that the MA of the catalyst of Example 1 subjected to the annealing pretreatment in air is as high as 3162 mA / mg Pt, while the MA of the commercial Pt / C catalyst is 430 mA / mg Pt. It can be found from the comparison results that the MA of the graphitized carbon supported platinum-cobalt intermetallic compound of Example 1 is 7-8 times that of the commercial platinum-carbon catalyst. The platinum-based intermetallic compound catalyst prepared by the preparation method of the present application has a significant activity advantage.

[0109] The KB600 supported platinum-cobalt intermetallic compound catalyst of Example 4 and the commercial Pt / C catalyst of Comparative Example 2 were subjected to the same activity test as Example 2, and the activity test results are shown in Figure 13As shown in the figure, by comparing the polarization curves of the KB600 loaded platinum-cobalt intermetallic compound catalyst and the commercial Pt / C catalyst, it can be found that the MA of the catalyst pretreated by annealing in air in Example 4 is up to 2030 mA / mg Pt, while the MA of the commercial Pt / C catalyst is 400 mA / mg Pt. It can be found by comparison that the activity is still much higher than that of the commercial platinum-carbon catalyst. The platinum-based intermetallic compound catalyst prepared by the method of the application has a significant activity advantage.

[0110] The graphitized carbon loaded platinum-cobalt intermetallic compound catalyst of Example 1 and the graphitized carbon loaded catalyst of Comparative Example 1 were subjected to the same activity test as Example 2, and the activity test results are shown in the figure. Figure 14 It can be found that the specific MA of Comparative Example 1 without annealing is 882 mA / mg Pt, which is lower than that of Example 1. The electrochemical performance of Comparative Example 1 with a thicker carbon layer is lower than that of Example 1. It can be seen that the nature of the carbon layer affects the electrochemical activity, and the degree of pore-free of the carbon layer of Comparative Example 1 is lower than that of Example 1, which also shows that the treatment of pre-oxidation in air provided by the application can improve the activity of the catalyst. The columnar comparison graph of the specific activity values of Example 1, Comparative Examples 1 and 2 is shown in the figure. Figure 15 It can be found that the electrochemical performance of Example 1 is good, and the loose and porous carbon layer has a good electrochemically accessible area. The preparation method provided by the application can effectively improve the activity of the catalyst.

[0111] It should be understood that the application of the application is not limited to the above examples. Those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the application.

Claims

1. A method for preparing a carbon-supported metal catalyst, characterized in that, Includes the following steps: Platinum acetylacetonate, acetylacetonate salts of transition metals and carbon materials are dispersed in a solvent, and the precursor is obtained by drying to remove the solvent. After a first annealing in air atmosphere, a mixture is obtained. The mixture was annealed a second time under a hydrogen-argon atmosphere, cooled, acid-washed, washed, and dried, and then annealed a third time under a hydrogen-argon atmosphere to obtain the carbon-supported metal catalyst. The temperature of the first annealing is 100-188℃, and the annealing time is 5-500 min; The weight loss of the mixture before and after the first annealing is 1-50% wt; The conditions for the second annealing are annealing at 400-1100℃ for 10 min-8 h; The conditions for the third annealing are annealing at 100-500℃ for 10 min-6 h.

2. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The temperature of the first annealing is 176℃, and the annealing time is 20-40 min; The weight loss of the mixture before and after the first annealing is 1-30% wt.

3. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The pickling conditions are as follows: pickling in sulfuric acid with a concentration of 0.1-1 mol / L at 60°C for 12 hours.

4. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The carbon material includes graphitized carbon or commercial carbon materials; The graphitized carbon is prepared by heating amorphous carbon materials at 1200-3000℃ for 10 min-6 h in an inert or nitrogen atmosphere, and then naturally cooling to room temperature. The commercially available carbon material is one of Vulcan XC72, KB300, KB600, BP 2000, or Toray carbon.

5. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The transition metal acetylacetone salt is one or more of the following: iron acetylacetone, nickel acetylacetone, molybdenum acetylacetone, vanadium acetylacetone, copper acetylacetone, manganese acetylacetone, zinc acetylacetone, titanium acetylacetone, tungsten acetylacetone, chromium acetylacetone, and zirconium acetylacetone.

6. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The platinum loading in the carbon-supported metal catalyst is 1-60 wt%.

7. A carbon-supported metal catalyst prepared by the method for preparing a carbon-supported metal catalyst according to any one of claims 1-6, characterized in that, Including carbon supports loaded with metal nanoparticles, the metal nanoparticles having a carbon layer coated on their surface; The carbon support is either a solid nanoparticle or a porous continuous structure, and the particle size of the solid nanoparticle is 1 nm-300 μm. The particle size of the metal nanoparticles is 1-20 nm; The pore structure in the carbon layer is one of loose porous, microporous, or closed non-porous; The coating can be either partial or full coating. The thickness of the carbon layer is 0.01-3 nm; The carbon layer has 1-2 layers.

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