A catalyst for oxygen reduction reaction and its preparation method and application

Abstract

The present application relates to the field of fuel cell technology, and discloses an oxygen reduction reaction catalyst and its preparation method and application, including the following steps: adding graphyne powder to water, ultrasonically dispersing until the graphyne powder is completely and evenly dispersed in the water to obtain a graphyne solution; mixing the graphyne solution with a chloroplatinic acid solution, adding a dilute formic acid solution under stirring, and reacting under stirring; filtering, washing the solid phase, and drying to obtain the oxygen reduction reaction catalyst. The present application prepares the oxygen reduction reaction catalyst by adopting an optimized liquid phase reduction method, and the steps are simple, and the platinum nanoparticles of the prepared oxygen reduction reaction catalyst grow uniformly in size and uniformly distributed on the surface of graphyne, and have excellent ORR activity and stability, and have performance superior to commercial catalysts.

Description

Technical Field

[0001] The present application relates to the field of fuel cell technology, and mainly to an oxygen reduction reaction catalyst and a preparation method and application thereof. Background Art

[0002] The cathode oxygen reduction reaction (ORR) of fuel cells is a slow kinetic process and usually uses efficient precious metal catalysts. In actual fuel cell applications, platinum-carbon catalysts with high platinum loading (40-50 wt%) can meet the application requirements: (1) High loading can reduce the thickness of the catalyst layer in the membrane electrode and effectively reduce mass transfer losses under high current density; (2) Platinum-carbon catalysts with appropriate particle size (usually considered to be 3-5 nm) and uniform dispersion can show good catalytic activity and stability in the half-cell and membrane electrode. However, platinum-carbon catalysts, especially those with high platinum loading, still face severe challenges brought by metal particle agglomeration and electrochemical stability during the preparation process. The realization of high-loading electrocatalysts through the functionalization of carbon carriers is of great significance to solving problems such as low platinum utilization, activity and stability.

[0003] On the one hand, there are many new carbon carrier materials that can be used as ORR electrocatalysts, including carbon nanotubes, graphene, carbon quantum dots, carbon nanobelts, carbon cages, and carbon materials derived from metal organic frameworks (MOFs), which have aroused widespread interest in various research fields. By exploring the regulation mechanism of carbon carriers on ORR activity, designing and developing new carbon carriers, and designing and regulating the active centers of catalysts based on carbon carriers, it is conducive to the development of efficient and durable ORR catalysts. The problem with carbon carriers is that it is difficult to disperse platinum nanoparticles on highly graphitized carriers, and high specific surface area carbon carriers have poor stability. Therefore, it is urgent to explore new carbon carriers to achieve uniform dispersion of platinum nanoparticles while providing good stability.

[0004] On the other hand, the main preparation methods for commercial platinum-carbon catalysts are impregnation reduction and liquid phase reduction. Among them, the impregnation reduction method is simple to operate and easy to scale up, but the uniformity of platinum nanoparticles and the position of platinum nanoparticles on the carbon carrier are difficult to control. When using a high specific surface area carbon carrier, it is very easy to deposit into the micropores of the carbon carrier and cannot be used. The liquid phase reduction method mainly uses sodium borohydride as a reducing agent, which is dangerous and easy to cause boron contamination in the sample, affecting performance. In addition, sodium borohydride has strong reducing properties and poor control over the size of platinum nanoparticles; if ethylene glycol with weaker reducing properties is used as a solvent and reducing agent, the size of the platinum nanoparticles can be better controlled, but the cost is higher.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide an oxygen reduction reaction catalyst and a preparation method and application thereof. The oxygen reduction reaction catalyst uses graphyne as a carrier and loads platinum nanoparticles, aiming to solve the problem that the existing carbon carrier cannot simultaneously achieve uniform dispersion of platinum nanoparticles and provide good stability.

[0007] The technical solution of this application is as follows:

[0008] A method for preparing an oxygen reduction reaction catalyst, comprising the following steps:

[0009] Adding graphyne powder into water and dispersing by ultrasonication until the graphyne powder is completely and evenly dispersed in the water to obtain a graphyne solution;

[0010] The Graphene Oxygen Dioxide solution is mixed with a chloroplatinic acid solution, and a dilute formic acid solution is added under stirring, and the mixture is reacted under stirring;

[0011] The solid phase is filtered, cleaned and dried to obtain the oxygen reduction reaction catalyst.

[0012] The oxygen reduction reaction catalyst is prepared by adopting an optimized liquid phase reduction method with simple steps.

[0013] The method for preparing the oxygen reduction reaction catalyst, wherein the concentration of the graphyne solution is 0.5-5 mg / mL, and the concentration of the chloroplatinic acid solution is 0.02-0.08 M.

[0014] By combining the graphyne solution and the chloroplatinic acid solution within the above concentration range, platinum nanoparticles can be grown on the surface of graphyne with uniform size and uniform distribution.

[0015] The method for preparing the oxygen reduction reaction catalyst, wherein after the Graphene Oxygen Dioxide Solution is mixed with the Chloroplatinic Acid Solution, the method further comprises the following steps:

[0016] The mixed solution of the Graphene Oxygen Dioxide Solution and the Chloroplatinic Acid Solution is allowed to stand for 3 hours or more.

[0017] The method for preparing the oxygen reduction reaction catalyst, wherein the step of reacting under stirring is specifically reacting in a 50-70° C. water bath under stirring for 0.5-3 h.

[0018] The method for preparing the oxygen reduction reaction catalyst, wherein, in the step of mixing the graphyne solution with the chloroplatinic acid solution, the mixing mass ratio of graphyne to platinum atoms is in the range of 8:2 to 5:5.

[0019] The method for preparing the oxygen reduction reaction catalyst, wherein the volume fraction of the dilute formic acid solution is 3-5%, and 0.2-1.0 mL of pure formic acid is added for every 10 mg of platinum atom.

[0020] The preparation method of the oxygen reduction reaction catalyst comprises adding 0.3-0.5 mL of pure formic acid for every 10 mg of platinum atom.

[0021] The method for preparing the oxygen reduction reaction catalyst, wherein the ultrasonic dispersion time is 30-60 minutes.

[0022] An oxygen reduction reaction catalyst, wherein the oxygen reduction reaction catalyst is prepared by the above-mentioned preparation method of the oxygen reduction reaction catalyst, the oxygen reduction reaction catalyst uses the graphene as a carbon carrier, and the surface of the graphene is loaded with platinum nanoparticles;

[0023] The oxygen reduction reaction catalyst, wherein the loading amount of the platinum nanoparticles ranges from 20wt% to 50wt%, and the particle size range of the platinum nanoparticles is from 2 to 5 nm.

[0024] An application of the oxygen reduction reaction catalyst as described above, wherein the oxygen reduction reaction catalyst is used as a catalyst for cathode oxygen reduction reaction of a fuel cell.

[0025] Beneficial effects: The oxygen reduction reaction catalyst of the present application uses graphyne as a carrier and loads platinum nanoparticles. The oxygen reduction reaction catalyst is prepared by adopting an optimized liquid phase reduction method. The steps are simple, and the platinum nanoparticles of the prepared oxygen reduction reaction catalyst grow on the surface of graphyne with uniform size and uniform distribution, have excellent ORR activity and stability, and have performance superior to commercial catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a transmission electron microscopy image of the oxygen reduction reaction catalyst in Example 1 of the present application (scale is 50 nm).

[0027] Figure 2 This is a transmission electron microscopy image of the oxygen reduction reaction catalyst in Example 1 of the present application (scale is 20 nm).

[0028] Figure 3 This is a transmission electron microscopy image of the oxygen reduction reaction catalyst in Example 1 of the present application (scale is 20 nm).

[0029] Figure 4 This is a comparison diagram of polarization curves of the oxygen reduction reaction catalyst in Example 1 of the present application before and after 10,000 cycles under O2 in the electrochemical test.

[0030] Figure 5This is a comparison chart of the CV graphs of the oxygen reduction reaction catalyst in Example 1 of the present application before and after 10,000 cycles of electrochemical testing. DETAILED DESCRIPTION

[0031] The present application provides an oxygen reduction reaction catalyst and its preparation method and application. In order to make the purpose, technical solution and effect of the present application clearer and more specific, 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 are not used to limit the present application.

[0032] Graphdiyne (GDY) is a new type of two-dimensional carbon allotrope with independent intellectual property rights in my country, and is a research field led by Chinese scientists internationally. As a two-dimensional all-carbon material containing both sp and sp2 hybridized carbon atoms, Graphdiyne has many unique properties that traditional carbon materials do not have, such as rich carbon chemical bonds, natural ultra-large pore structure, adjustable band gap, excellent electron / ion transport capacity, high stability, high intrinsic activity, and controllable growth on any substrate surface. Graphdiyne has demonstrated unique advantages and advancements in synthesis, preparation, directional modification, performance regulation, device design, etc., and is very consistent with the needs of catalysis, energy conversion, energy storage and other fields. Before the date of this application, there was no related research on the use of Graphdiyne as a carbon carrier to prepare oxygen reduction reaction catalysts.

[0033] Specifically, the oxygen reduction reaction catalyst provided in the present application uses graphyne as a carbon carrier and loads platinum nanoparticles on the surface of graphyne; wherein the loading amount of the platinum nanoparticles ranges from 20wt% to 50wt%, and the particle size range of the platinum nanoparticles is 2 to 5 nm.

[0034] The unique electronic structure and two-dimensional network of graphyne are conducive to the adsorption and anchoring of precursor metal ions, achieving atomic-level dispersion and anchoring, and also facilitating the uniform dispersion and growth of metal clusters. At the same time, the ordered crystalline structure of graphyne itself is much more stable than that of amorphous carbon carriers. Therefore, using graphyne as a carbon carrier can simultaneously achieve uniform dispersion of platinum nanoparticles and provide good stability.

[0035] The oxygen reduction reaction catalyst provided in the present application can be prepared by electrochemical deposition, hydrothermal / solvothermal, liquid phase reduction method and other methods, and can realize the anchoring and dispersion of metal clusters, size control, crystal surface growth, etc. on the surface of graphyne, and has flexible adjustability. Preferably, the liquid phase reduction method is used in the present application to prepare the oxygen reduction reaction catalyst, and the step parameters of the liquid phase reduction method are optimized to make the steps simple, the production time short, and the production efficiency high. The platinum nanoparticles of the prepared oxygen reduction reaction catalyst grow on the surface of graphyne with uniform size and uniform distribution, and have excellent ORR activity and stability, and have performance superior to commercial catalysts. The application of the above-mentioned oxygen reduction reaction catalyst is also provided in the present application, and the above-mentioned oxygen reduction reaction catalyst is used as a catalyst for the cathode oxygen reduction reaction of a fuel cell.

[0036] Specifically, the preparation method of the oxygen reduction reaction catalyst provided in the present application comprises the following steps:

[0037] (i) Adding gyrene powder into water and dispersing it by ultrasonication until the gyrene powder is completely and evenly dispersed in the water to obtain a gyrene solution.

[0038] The ultrasonic dispersion time can be 30-60 minutes. During the ultrasonic dispersion process, it is preferably carried out in an ice water bath. The temperature is controlled by the ice water bath to avoid uncontrollable factors caused by the increase of water temperature.

[0039] The concentration of graphyne in the graphyne solution is 0.5-5 mg / mL, which is mainly coordinated with the concentration of the Pt precursor salt, so that platinum nanoparticles can grow on the surface of graphyne with uniform size and uniform distribution.

[0040] (ii) Mix the Graphene Olefin Solution and the Chloroplatinic Acid Solution, add the dilute formic acid solution while stirring, and then transfer to a 50-70°C water bath and keep stirring for 0.5-3h.

[0041] In the present application, the Pt precursor salt is chloroplatinic acid, and the concentration of the chloroplatinic acid solution can be 0.02-0.08 M. At this concentration, in combination with a specific concentration of Graphene solution, Pt nanoparticles can grow on the surface of Graphene with uniform size and uniform distribution. The concentration of the chloroplatinic acid solution will affect the size growth of the Pt particles. If the concentration is too high, the Pt nanoparticles may agglomerate and become too large. If the concentration is too low, Pt may be reduced in the solution and cannot be loaded on the carrier surface, affecting the loading capacity. In the embodiment of the present application, the concentration of the chloroplatinic acid solution used is 0.06 M.

[0042] When the graphyne solution is mixed with the chloroplatinic acid solution, the mixing mass ratio of graphyne to platinum atoms can range from 8:2 to 5:5.

[0043] In the present application scheme, by using dilute formic acid in a certain concentration range as a reducing agent, it is safe and pollution-free, and the growth size of Pt nanoparticles can be well controlled. Specifically, the volume fraction of the dilute formic acid solution can be 3-5%, and the concentration of the dilute formic acid solution will also affect the growth of the Pt particle size. If the concentration is too high, Pt may be reduced in the solution and cannot be loaded on the carrier surface, affecting the loading amount. If the concentration is too low, the reaction time will be extended and the size or loading amount of the Pt nanoparticles may also be affected. Further, 0.2-1.0mL of pure formic acid is added to each 10mg of platinum atoms, and preferably, 0.3-0.5mL of pure formic acid is added to each 10mg of platinum atoms. Using the preparation method provided by the present application, the amount of reducing agent is very low. Even if it is enlarged to the preparation of 100g of catalyst, the amount of pure formic acid used is only about 1000mL, and the waste liquid produced at the end contains very little formic acid, which not only greatly reduces the production cost, but also reduces the cost of waste liquid treatment.

[0044] In the present application, a dilute formic acid solution is added at room temperature, and a reaction will begin after the addition. If Pt nanoparticles are left standing at room temperature, they can grow in the form of nanowires. Therefore, in the present application, a dilute formic acid solution needs to be added under stirring conditions, and appropriate stirring can transform the nanowire morphology into a dispersed nanoparticle morphology, which is conducive to the uniform distribution of Pt nanoparticles on the surface of graphyne and uniform size. In the embodiment of the present application, the stirring speed is preferably 400-800 rmp.

[0045] In the present application, in order to reduce the reaction time, the reaction temperature is also optimized. By using an appropriate heating temperature, the reaction time is shortened to 0.5-3 hours, greatly improving the productivity. If the reaction is carried out at room temperature, it may take more than 48-72 hours to completely reduce the chloroplatinic acid.

[0046] Preferably, in step (ii), after the graphyne solution and the chloroplatinic acid solution are mixed and before the dilute formic acid solution is added, the mixed solution of the graphyne solution and the chloroplatinic acid solution is allowed to stand for 3 hours or more, so that the platinum atoms can be pre-anchored on the surface of the graphyne and the loading effect can be improved.

[0047] (iii) filtering, washing and drying the solid phase to obtain an oxygen reduction reaction catalyst.

[0048] Among them, the cleaning is to use ultrapure water to clean the solid phase. There is no special requirement for the drying temperature, just dry the water without high temperature treatment.

[0049] The present application is further described below through specific embodiments.

[0050] Example 1

[0051] (1) Prepare a 10 mg / mL chloroplatinic acid solution and a 5% volume fraction dilute formic acid solution.

[0052] (2) Take a 100 mL vial, weigh 22.5 mg of graphyne powder, add 11.5 mL of water, and ultrasonically disperse for about 30 min until the graphyne powder is completely and evenly dispersed in the water.

[0053] (3) Calculate the volume of chloroplatinic acid solution to be added based on a platinum loading of 40 wt%, i.e., the mass ratio of graphyne to platinum is 6:4. Add 1.5 mL of chloroplatinic acid solution and continue to disperse until uniform.

[0054] (4) While stirring, add 11 mL of the prepared dilute formic acid solution, then transfer to a 60°C water bath and keep stirring for 1 h.

[0055] (5) After the reaction is completed, filter and wash with ultrapure water several times, and then dry.

[0056] The prepared oxygen reduction reaction catalyst Pt / GDY was characterized by transmission electron microscopy. Figure 1~Figure 3 As shown, Figure 1 This is a transmission electron microscope image of the oxygen reduction reaction catalyst Pt / GDY (scale is 50nm). Figure 2 This is a transmission electron microscopy image of a part of the oxygen reduction reaction catalyst Pt / GDY (scale is 20 nm). Figure 3 This is a transmission electron microscopy image of a part of the oxygen reduction reaction catalyst Pt / GDY (scale is 20 nm). Figure 1~Figure 3 It can be seen that the platinum nanoparticles are evenly dispersed on the surface of graphyne.

[0057] The ORR catalytic activity and stability of the prepared oxygen reduction reaction catalyst Pt / GDY were tested:

[0058] (1) Experimental preparation

[0059] Cleaning of test instruments: The electrolytic cell, counter electrode, gas duct, salt bridge and other components are heated and boiled with ultrapure water; the glassy carbon electrode is polished and cleaned with polishing powder and rinsed with ultrapure water.

[0060] Ink dispersion solvent preparation: ethanol: water: Nafion = 1000:1000:0.75 (volume ratio).

[0061] Electrolyte preparation: 0.1 M HClO4 solution is diluted with 70% perchloric acid (99.999%).

[0062] Others: The air duct, weighing sample bottle and cleaned test parts must be kept clean and free of contamination.

[0063] (2) Experimental steps:

[0064] ① Accurately weigh 2-3 mg of sample and record the weight in grams.

[0065] ② Add the ink dispersion solvent to the weighed sample to prepare 1.0 mg / mL ink.

[0066] ③Ultrasonicate the ink for 3-4 min, drop 10 μL of ink on the glassy carbon electrode, and let it stand until it is completely dry.

[0067] ④ After the glassy carbon electrode is dried, soak the surface of the glassy carbon electrode with ultrapure water and install it into the rotating disk electrode test system.

[0068] ⑤ High-purity Ar and O2 were introduced into the electrolyte for about 20 minutes respectively for testing different electrochemical processes.

[0069] The half-cell (RDE) test results are as follows:

[0070] The initial activity test results of the oxygen reduction reaction catalyst Pt / GDY in the embodiment of the present application are as follows: mass specific activity (MA): 369.5 mA / mg, electrochemical active area (ECSA): 55.6 m 2 / g.

[0071] The results of the 10,000-cycle stability test of the oxygen reduction reaction catalyst Pt / GDY in the embodiment of the present application are as follows: MA decays to 321.9 mA / mg, with a decay rate of 12%; ECSA: 53.3 m 2 / g, attenuation ratio 4.2%. Figure 4 Polarization curves of the electrochemical test of oxygen reduction reaction catalyst Pt / GDY under O2, before and after 10,000 cycles. Pt / GDY initial is the polarization curve before the cycle, and 10,000 Cycles is the polarization curve after 10,000 cycles. Figure 5 The electrochemical test CV diagram of the oxygen reduction reaction catalyst Pt / GDY is shown in Figure 1. The scan rate is 20 mV / s, and the comparison is made before and after 10,000 cycles. Initial is the CV diagram before the cycle, and 10,000Cycles is the CV diagram after 10,000 cycles. According to this test result, it can be seen that the oxygen reduction reaction catalyst Pt / GDY in the embodiment of the present application has excellent stability.

[0072] A commercial catalyst (brand: Johnson Matthey 40% PtC catalyst) was purchased as a comparative example, and its catalytic activity and stability were tested under the same test conditions. The results are as follows:

[0073] Initial activity: MA: 298 mA / mg, ECSA: 54 m 2 / g;

[0074] After 10,000 cycles of AST testing: MA: 270 mA / mg, attenuation 10%; ECSA: 51 m 2 / g, attenuation 6%.

[0075] It should be understood that the application of the present application is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made according to the above description, and all these improvements and changes should fall within the scope of protection of the present application.

Claims

1. A method for preparing an oxygen reduction reaction catalyst, characterized in that: The following steps are involved: Adding gypsum powder to water and dispersing by ultrasonication until the gypsum powder is completely and evenly dispersed in the water to obtain a gypsum solution; the concentration of the gypsum solution is 0.5-5 mg / mL; The gydne solution is mixed with a chloroplatinic acid solution, wherein the mixing mass ratio of gydne to platinum atoms is in the range of 8:2 to 5:5, and a dilute formic acid solution is added under stirring, wherein 0.2 to 1.0 mL of pure formic acid is added for every 10 mg of platinum atoms, and the mixture is reacted in a 50 to 70° C. water bath under stirring for 0.5 to 3 h; the concentration of the chloroplatinic acid solution is 0.02 to 0.08 M; and the volume fraction of the dilute formic acid solution is 3 to 5%; The solid phase is filtered, cleaned and dried to obtain the oxygen reduction reaction catalyst.

2. The method for preparing an oxygen reduction reaction catalyst according to claim 1, characterized in that: After the Graphene Oxygen Solution is mixed with the Chloroplatinic Acid Solution, the following steps are also included: The mixed solution of the Graphene Oxygen Dioxide Solution and the Chloroplatinic Acid Solution is allowed to stand for more than 3 hours.

3. The method for preparing an oxygen reduction reaction catalyst according to claim 1, characterized in that: For every 10 mg of platinum atom, 0.3-0.5 mL of pure formic acid was added.

4. The method for preparing an oxygen reduction reaction catalyst according to claim 1, characterized in that: The ultrasonic dispersion time is 30-60 min.

5. An oxygen reduction reaction catalyst, characterized in that The oxygen reduction reaction catalyst is prepared by the preparation method of any one of claims 1 to 4, wherein the oxygen reduction reaction catalyst uses the graphene as a carbon carrier, and the surface of the graphene is loaded with platinum nanoparticles.

6. The oxygen reduction reaction catalyst according to claim 5, characterized in that The loading amount of the platinum nanoparticles ranges from 20wt% to 50wt%, and the particle size of the platinum nanoparticles ranges from 2 to 5 nm.

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