An ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, its preparation method and application

Abstract

The present invention relates to an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, a preparation method thereof and an application. In the catalyst preparation method, ethylene glycol is used as a solvent and a reducing agent, platinum nanoparticles supported on carbon black are prepared as seeds, and an oxygen reduction catalyst with an ordered platinum-cobalt intermetallic compound structure supported on carbon black is obtained by means of impregnation and heat treatment. The prepared catalyst is a black solid powder, and the nanoparticle size of the ordered platinum-cobalt intermetallic compound catalyst is 5-30 nm. The preparation method involved in the present invention is easy to implement, controllable and highly operable, and can be extended to the field of preparation of other intermetallic compounds. The catalyst involved in the present invention has better performance such as oxygen reduction catalytic activity and stability under acidic conditions than commercial catalysts, and can be widely applied to fields such as proton exchange membrane fuel cells and metal-air fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the energy crisis and environmental deterioration, clean energy is extremely urgent. Fuel cells have many advantages such as low pollution, environmental protection, and high power density. However, the oxygen reduction reaction process at the cathode has a problem of slow reaction kinetics, which directly affects the reaction efficiency of the entire fuel cell energy device and has become a key factor restricting the large-scale commercial development of fuel cells. At present, platinum-carbon catalysts are still the most commonly used catalysts to improve the efficiency of the oxygen reduction reaction. However, during the catalytic process, the activity of platinum-carbon catalysts often decreases over time, and the activity needs to be further improved, thus restricting large-scale applications. Therefore, developing catalysts with both high efficiency and high stability for the oxygen reduction reaction is an urgent problem to be solved. The ordered platinum-cobalt intermetallic compound with a face-centered tetragonal structure has atoms bonded together through d strong orbital interactions and is arranged in long-range order in a specific lattice direction, making it have high stability thermodynamically, and thus showing better stability than the corresponding disordered solid solution alloy materials in the oxygen reduction catalytic reaction. However, during the synthesis process, due to the need for precise atomic ratios and a certain amount of energy to break the energy barrier for the disorder-to-order transformation, the synthesis is extremely difficult. Therefore, it is of great significance to research and develop a simple, effective, and controllable synthesis method for a platinum-cobalt intermetallic compound oxygen reduction catalyst with high stability and high activity. Summary of the Invention

[0003] The purpose of the present invention is to solve problems such as the poor durability of platinum-carbon catalysts in the oxygen reduction reaction, while ensuring high activity of the catalyst and solving the problem of difficult synthesis of ordered platinum-cobalt intermetallic compounds. The present invention provides an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, a preparation method thereof, and an application thereof. By using the seed-mediated method, it is beneficial to control the metal ratio. By using the impregnation and heat treatment methods, the operation is simple and controllable. After impregnating a cobalt source and a phosphorus source with platinum nanoseeds, the dried sample is placed in an inert gas atmosphere to first generate a second phase, and then the transformation of the ordered intermetallic compound is realized, obtaining a platinum-cobalt catalyst with an ordered intermetallic compound structure. This intermetallic compound structure catalyst promotes the improvement of catalytic activity and stability. This method is simple, feasible, and controllable, with strong operability, and can promote the ordered structure transformation and the improvement of catalyst activity and stability.

[0004] To achieve the above object, the present invention adopts the following technical solution: An ordered platinum-cobalt intermetallic compound oxygen reduction catalyst is a black solid powder, and the nanoparticle size of the ordered platinum-cobalt intermetallic compound catalyst is 5 - 30 nm.

[0005] In a preferred embodiment of the present invention, the mass ratio of platinum to cobalt is 2:1 to 10:1; the nanoparticle size of the ordered platinum-cobalt intermetallic compound catalyst is 5 to 10 nm.

[0006] The present invention also protects a method for preparing an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, comprising the following steps:

[0007] (1) Implementing a seed-mediated method using platinum-carbon as nano-seeds;

[0008] (2) Performing an impregnation treatment using a cobalt source;

[0009] (3) Performing an impregnation treatment using a phosphorus source;

[0010] (4) Drying the product obtained by impregnation and then performing an annealing treatment to achieve the transformation of the ordered intermetallic compound.

[0011] In a preferred embodiment of the present invention, in step (1), the platinum-carbon is commercial JohnsonMatthey-PtC, TANAKA-Pt / C, Shanghai Hesen Pt / C or self-made platinum-carbon; more preferably, using ethylene glycol as a solvent and reducing agent, the platinum nanoparticles supported on carbon black are used as nano-seeds.

[0012] In a preferred embodiment of the present invention, in step (1), the mass fraction of platinum in the platinum-carbon is 10% to 80%.

[0013] In a preferred embodiment of the present invention, in step (2), the cobalt source is an aqueous solution of cobalt chloride, the concentration of the aqueous solution of cobalt chloride is 0.05 to 10 mol / L, and the mass ratio of platinum to cobalt is 2:1 to 10:1.

[0014] In a preferred embodiment of the present invention, in step (3), the phosphorus source is an aqueous solution of sodium hypophosphite, the concentration of the aqueous solution of sodium hypophosphite is 0.1 to 20 mol / L, and the mass ratio of phosphorus to cobalt is 1:1 to 10:1.

[0015] In a preferred embodiment of the present invention, the annealing treatment is that first, a second phase is formed under an inert gas, and then an induced structural phase change of this second phase occurs to achieve the transformation of the ordered intermetallic compound.

[0016] In a preferred embodiment of the present invention, in step (4), the drying is carried out at 50 - 80 °C for at least 10 h until completely dry to obtain a dried product; the annealing treatment is to grind the obtained dried product, and then heat it to 400 - 1000 °C at a rate of 5 - 10 °C / min under an inert atmosphere, keep it for less than 10 h, cool it to room temperature, and then grind it to obtain an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst.

[0017] The present invention also protects the application of the catalyst having an ordered platinum-cobalt intermetallic compound structure as an oxygen reduction catalyst.

[0018] Compared with the prior art, the present invention first prepares platinum nanoseeds using ethylene glycol as a solvent and a reducing agent, then impregnates the required cobalt source and phosphorus source. The impregnated and dried sample is subjected to annealing treatment to first generate a second phase, and then a second-phase structure-induced phase transformation occurs to achieve the transformation of an ordered intermetallic compound, obtaining an ordered platinum-cobalt intermetallic compound with a face-centered tetragonal structure. The prepared catalyst is a black solid powder, and the nanoparticle size of the ordered platinum-cobalt intermetallic compound catalyst is 5 - 30 nm. The coordination and strain effects generated by this face-centered tetragonal structure of the ordered platinum-cobalt intermetallic compound effectively regulate the electronic structure on the material surface, improving the activity of the catalyst. At the same time, the thermodynamically stable intermetallic compound further promotes the improvement of the catalyst stability. The preparation method involved in the present invention is easy to implement and controllable, with strong operability, and can be extended to other fields of intermetallic compound preparation. The catalyst involved in the present invention has better performance in terms of oxygen reduction catalytic activity and stability under acidic conditions than commercial catalysts, and can be widely applied to fields such as proton exchange membrane fuel cells and metal-air fuel cells. Brief Description of the Drawings

[0019] The following further describes the present invention with reference to the accompanying drawings.

[0020] Figure 1 It is a transmission electron microscope photograph of the ordered platinum-cobalt intermetallic compound oxygen reduction catalyst prepared in Example 1.

[0021] Figure 2 It is an X-ray diffraction pattern of the ordered platinum-cobalt intermetallic compound oxygen reduction catalyst prepared in Example 1.

[0022] Figure 3 It is a rotating disk curve graph of the stability test of the ordered platinum-cobalt intermetallic compound oxygen reduction catalyst prepared in Example 1. Detailed Description of the Embodiments

[0023] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Example 1

[0024] 0.08 g of Vulcan XC-72 was added to 30 mL of ethylene glycol solution, and after stirring, it was ultrasonicated for about 1.0 h until evenly dispersed to obtain a black suspension.

[0025] 1 mL of ethylene glycol solution of 1 mol / L chloroplatinic acid was added, and ultrasonic treatment was continued until evenly dispersed. Then, 0.1 mol / L sodium hydroxide solution was added to adjust the pH value to 9, and the solution was poured into a microwave hydrothermal reaction kettle. It was heated by microwave at 190 °C for 0.4 h. After the reaction ended, the obtained solution was filtered, washed and dried to obtain a black solid powder, that is, self-made platinum-carbon was used as the seed.

[0026] The platinum-carbon seed obtained by microwave hydrothermal reduction of ethylene glycol was put into a beaker, and impregnated with 0.1 mol / L cobalt chloride aqueous solution, and ultrasonicated until evenly dispersed to form a black paste.

[0027] 1.0 mol / L sodium hypophosphite aqueous solution was continuously added for impregnation, and after ultrasonicating until evenly dispersed, it was dried to obtain a dried product.

[0028] The dried product was ground with an agate mortar. After grinding evenly, it was put into a tubular furnace. Under an inert gas atmosphere, it was heated to 700 °C at a heating rate of 10 °C / min and held for 2 h, and then cooled to room temperature. After grinding, an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst was obtained. Example 2

[0029] Commercial Johnson Matthey platinum-carbon was taken as the seed and put into a beaker, and impregnated with 1.0 mol / L cobalt chloride aqueous solution, and ultrasonicated until evenly dispersed to form a black paste.

[0030] 1.0 mol / L sodium hypophosphite aqueous solution was continuously added for impregnation, and after ultrasonicating until evenly dispersed, it was dried to obtain a dried product.

[0031] The dried product was ground with an agate mortar. After grinding evenly, it was put into a tubular furnace. Under an inert gas atmosphere, it was heated to 900 °C at a heating rate of 5 °C / min and held for 6 h, and then cooled to room temperature. After grinding, an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst was obtained. Example 3

[0032] Take commercial TANAKA platinum-carbon as the seed, with a platinum mass fraction of 60%, put it into a beaker, and impregnate it with 0.5 mol / L cobalt chloride aqueous solution, and ultrasonicate until it is evenly dispersed to form a black paste;

[0033] Continue to impregnate with 1.0 mol / L sodium hypophosphite aqueous solution, ultrasonicate until evenly dispersed and then dry to obtain a dried product;

[0034] Grind the dried product in an agate mortar. After grinding evenly, put it into a tube furnace. Under an inert gas atmosphere, heat it at a heating rate of 8 °C / min to 800 °C, and keep it warm for 1 h. Then cool it to room temperature. After grinding, an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst is obtained.

[0035] Characterize and analyze the product prepared in Example 1. From Figure 1 As shown in the transmission electron microscope photograph of the ordered platinum-cobalt intermetallic compound oxygen reduction catalyst prepared in Example 1, it can be seen that the catalyst is evenly dispersed on the surface of the carbon support. From Figure 2 It can be seen that the catalyst simultaneously has the characteristic peaks of the face-centered cubic structure platinum-cobalt intermetallic compound, proving the formation of an ordered platinum-cobalt intermetallic compound. From Figure 3 It can be seen that the prepared ordered platinum-cobalt intermetallic compound oxygen reduction catalyst still maintains a high half-wave potential after 10,000 cycles and 30,000 cycles of testing, and has very excellent stability.

[0036] The above specific implementation manners describe the basic principles and main features of the present invention. Those skilled in the art of this industry should understand that the protection scope of the present invention is not limited by the above embodiments. Any changes or substitutions that can be thought of without creative labor should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope defined by the claims.

Claims

1. An ordered platinum-cobalt intermetallic compound oxygen reduction catalyst, characterized in that, it is a black solid powder, and the mass ratio of platinum to cobalt is 2:1 - 10:1; the nanoparticle size of the ordered platinum-cobalt intermetallic compound catalyst is 5 - 10 nm; its preparation method includes the following steps: (1) Using platinum-carbon prepared by microwave hydrothermal method as nano-seeds to achieve the seed-mediated method; (2) Impregnation treatment with a cobalt source; (3) Impregnation treatment with a phosphorus source; (4) Drying the impregnated product, and then annealing treatment to achieve the transformation of the ordered intermetallic compound; In step (1), ethylene glycol is used as the solvent and reducing agent, and carbon black supported platinum nanoparticles are prepared as nano-seeds. In the platinum-carbon, the mass fraction of platinum is 10% - 80%; In step (2), the cobalt source is an aqueous solution of cobalt chloride, the concentration of the aqueous solution of cobalt chloride is 0.05 - 10 mol / L, and the mass ratio of platinum to cobalt is 2:1 - 10:1; In step (3), the phosphorus source is an aqueous solution of sodium hypophosphite, the concentration of the aqueous solution of sodium hypophosphite is 0.1 - 20 mol / L, and the mass ratio of phosphorus to cobalt is 1:1 - 10:1; In step (4), the annealing treatment is that first, a second phase is formed under an inert gas, and then an induced structural phase change of this second phase occurs to achieve the transformation of the ordered intermetallic compound; the annealing treatment is to grind the obtained dried product, heat it to 400 - 1000 °C at a rate of 5 - 10 °C / min under an inert atmosphere, keep the temperature for less than 10 h, cool it to room temperature, and grind it to obtain an ordered platinum-cobalt intermetallic compound oxygen reduction catalyst.

2. The catalyst according to claim 1, characterized in that, in step (4), the drying is carried out at 50 - 80 °C for at least 10 h until completely dry to obtain a dried product.

3. Use of the catalyst according to any one of claims 1 - 2 as an oxygen reduction catalyst.

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