CN116207278A - Carbon-coated platinum alloy nano material and preparation method and application thereof - Google Patents

Abstract

The invention relates to the field of electrocatalysis, and discloses a carbon-coated platinum alloy nanomaterial and a preparation method and application thereof. The method comprises the following steps: (1) precursor preparation: removing the solvent in a homogeneous solution containing a metal precursor, a carbon source and a solvent to obtain a precursor material, wherein the metal precursor comprises a platinum source and a nickel source, and the carbon source is an acidic organic reducing agent; (2) roasting: carrying out high-temperature pyrolysis on the precursor material obtained in the step (1) in a reducing atmosphere to obtain a pyrolysis product, wherein the temperature of the high-temperature pyrolysis is 400-1100 ℃; (3) acid washing: and (3) carrying out contact reaction on the pyrolysis product obtained in the step (2) and an acid solution, and then sequentially carrying out solid-liquid separation, washing and drying. The preparation method has the advantages of simple process, low cost and wide raw material selection range, and the obtained nano material has good electrochemical performance.

Description

Carbon-coated platinum alloy nano material and preparation method and application thereof

Technical Field

The invention relates to the field of electrocatalysis, in particular to a carbon-coated platinum alloy nanomaterial and a preparation method thereof, a catalyst and a preparation method thereof, and application of the carbon-coated platinum alloy nanomaterial and the catalyst in fuel cells.

Background

The fuel cell is a device for directly converting chemical energy of fuel into electric energy through electrochemical reaction, and is considered as an ideal clean energy technology because of the advantages of high energy conversion efficiency, high energy density, quick start, small pollution and the like. The fuel cell mainly comprises the following reactions: anodic oxidation reactions (e.g. hydrogen oxidation of HOR, H ₂ →2H ⁺ +2e ^- Methanol oxidation MOR, etc.) and cathodic oxygen reduction reactions (ORR, O) ₂ ⁺ 4H ⁺ +4e ^- →2H ₂ O). Since cathodic oxygen reduction involves multiple electrons, the kinetic reaction rate is slower than that of anodic oxidation. Thus, the rate of the cathodic oxygen reduction reaction is a critical factor affecting the performance of the fuel cell. Currently, high efficiency cathode catalysts rely on the precious metal platinum, but platinum is expensive, such that the catalyst cost is about 40% of the total fuel cell cost; in addition, during the long circulation process, the electrochemical active area of platinum is obviously reduced with time due to the agglomeration and dissolution of platinum, and the service life of the fuel cell is influenced.

At present, one of the research directions of the cathode catalyst is to adopt carbon to coat platinum alloy nano materials, on one hand, the platinum alloy catalyst can improve the intrinsic activity and the utilization rate of platinum, and reduce the dosage of noble metal platinum; on the other hand, the carbon cage coating can inhibit agglomeration and dissolution of metals during long cycles, thereby improving stability. Zou Shouzhong et al (ACS appl. Energy Mater.2019,2, 2769-2778) report that 2-methylimidazole is used as an organic ligand and a carbon source, a 2-methylimidazole-Pt-Ni composite material with a MOF-like structure is formed by a solvothermal method first, and then a thermal annealing treatment is carried out, so that a carbon-coated platinum-nickel nanomaterial is prepared. CN112467155a reports that the liquid phase reduction method is adopted to synthesize oleylamine coated platinum nanoparticles, then the platinum nanoparticles are mixed with ketjen black, and the carbon coated platinum catalyst is prepared through high-temperature pre-crosslinking, carbonization and activation, and the preparation process is still complicated. Therefore, there is a need to develop a simple process and low cost method for preparing carbon-coated platinum alloy catalysts.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provide a carbon-coated platinum alloy nanomaterial, a preparation method thereof, a catalyst and a preparation method thereof, and application of the carbon-coated platinum alloy nanomaterial and the catalyst in a fuel cell.

In order to achieve the above object, the present invention provides a method for preparing a carbon-coated platinum alloy nanomaterial, the method comprising the steps of:

(1) Precursor preparation: removing the solvent in a homogeneous solution containing a metal precursor, a carbon source and a solvent to obtain a precursor material, wherein the metal precursor comprises a platinum source and a nickel source, and the carbon source is an acidic organic reducing agent;

(2) Roasting: carrying out high-temperature pyrolysis on the precursor material obtained in the step (1) in a reducing atmosphere to obtain a pyrolysis product, wherein the temperature of the high-temperature pyrolysis is 400-1100 ℃;

(3) Acid washing: and (3) carrying out contact reaction on the pyrolysis product obtained in the step (2) and an acid solution, and then sequentially carrying out solid-liquid separation, washing and drying.

Preferably, in step (1), the carbon source is one or more of citric acid, ascorbic acid, ethylenediamine tetraacetic acid, 2, 5-pyridinedicarboxylic acid, benzoic acid, and terephthalic acid.

Preferably, in the step (1), the platinum source is one or more of chloroplatinic acid, tetraamineplatinum acetate, platinum acetylacetonate and platinum chloride.

Preferably, in the step (1), the nickel source is one or more of nickel acetate, nickel dichloride hexahydrate, nickel acetylacetonate, basic nickel carbonate and nickel sulfate.

Preferably, in step (1), the molar ratio of the metal precursor to the carbon source in terms of metal element is 1:0.5-5.

Preferably, in step (1), the molar ratio of the platinum source in terms of platinum to the nickel source in terms of nickel is 1:0.5-20, preferably 1:1-10.

Preferably, in step (1), the metal precursor further comprises a cobalt source and/or a molybdenum source; preferably, the cobalt source is one or more of cobalt sulfate, cobalt carbonate and cobalt oxalate; preferably, the molybdenum source is one or more of ammonium molybdate, sodium molybdate and potassium molybdate.

Preferably, in step (1), the molar ratio of the platinum source in terms of platinum to the cobalt source in terms of cobalt is 1:0-0.1, the molar ratio of the platinum source in terms of platinum to the molybdenum source in terms of molybdenum being 1:0-0.1.

Preferably, in step (1), the solvent is one or more of water, an alcoholic solvent and N, N-dimethylformamide.

Preferably, in step (1), the alcohol solvent is ethanol.

Preferably, in step (2), the reducing atmosphere includes hydrogen or carbon monoxide, preferably a mixed atmosphere of hydrogen or carbon monoxide and an inert gas, and more preferably a mixed atmosphere of hydrogen and nitrogen.

Preferably, in step (2), the hydrogen or carbon monoxide comprises 5 to 30% by volume of the total gas.

Preferably, in the step (2), the heating rate of the pyrolysis is 2-10 ℃/min.

Preferably, in the step (2), the constant temperature time of the pyrolysis is 1-6h.

Preferably, in step (3), the acid solution is one or more of sulfuric acid solution, nitric acid solution and hydrochloric acid solution.

Preferably, in the step (3), the acid solution is used in an amount of H based on 1mol of nickel element in the pyrolysis product obtained in the step (2) ⁺ The content is more than 2 mol.

Preferably, in the step (3), when the acid solution is sulfuric acid solution, the acid concentration is 0.5-2mol/L, and the temperature of the contact reaction is 25-90 ℃; when the acid solution is nitric acid solution, the acid concentration is 0.5-15mol/L, and the contact reaction temperature is 25-60 ℃; when the acid solution is hydrochloric acid solution, the acid concentration is 0.5-2mol/L, and the contact reaction temperature is 25-90 ℃.

Preferably, in step (3), the contact reaction time is 3 to 50 hours, preferably 3 to 24 hours.

The second aspect of the present invention provides a carbon-coated platinum alloy nanomaterial obtained by the above-described preparation method of the first aspect of the present invention.

Preferably, in the nanomaterial, the carbon content is 10-50 wt%, the platinum content is 10-70 wt%, the nickel content is 5-70 wt%, the cobalt content is 0-5 wt%, the molybdenum content is 0-5 wt%, the hydrogen content is 0.1-3 wt%, and the oxygen content is 0.5-20 wt%.

Preferably, the carbon-coated platinum alloy nanomaterial has a core-shell structure with platinum alloy particles as an inner core and a carbon layer as a shell layer.

Preferably, the platinum alloy particles have a particle size of 3-100nm.

The third aspect of the present invention provides a catalyst comprising the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention described above and conductive carbon black.

Preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5.

In a fourth aspect, the present invention provides a process for the preparation of the catalyst of the present invention, which comprises: after mixing the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention described above with conductive carbon black in the presence of a solvent, the solvent in the resulting mixture is removed and dried.

Preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5.

Preferably, the mixing comprises one or more of ultrasound, mechanical agitation and milling, preferably for a period of time of from 0.5 to 2 hours, preferably for a period of time of from 8 to 24 hours, preferably the milling conditions comprise: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

In a fifth aspect, the present invention provides another process for preparing the catalyst of the present invention, which comprises: the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention described above is solid-phase mixed with conductive carbon black.

Preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5.

Preferably, the conditions of the solid phase mixing include: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

A sixth aspect of the present invention provides the use of the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention, the catalyst of the third aspect, or the catalyst obtained by the production method of the fourth or fifth aspect in a fuel cell.

The invention provides a novel material containing carbon-coated platinum nano particle core-shell structure through the technical scheme.

According to the technical scheme, the preparation method provided by the invention takes the acidic organic reducing agent as a carbon source, the catalyst precursor is pyrolyzed in a reducing atmosphere, and the nickel salt is used as a template and a catalyst of a carbon cage in the process of being reduced to generate the coated carbon cage in situ, so that the carbon-coated platinum alloy nanomaterial is prepared by a one-step method.

The carbon-coated cage can inhibit agglomeration and dissolution of metal in the electrochemical long-cycle process, and the obtained carbon-coated platinum alloy nanomaterial has good stability of electrochemical active area (ECSA). The carbon-coated platinum alloy nano material has good electrocatalytic activity, can be directly used as an oxygen reduction catalyst, or can be used as an oxygen reduction catalyst of a fuel cell after being uniformly mixed with conductive carbon black in proportion, and the electrochemical activity area change rate is not higher than 20% after 5000 electrochemical cycle scans.

The preparation method of the invention has the following advantages: firstly, the preparation process is simple, the cost is low, and the raw material selection range is wide; and secondly, when catalyzing the oxygen reduction reaction, the electrochemical active area (ECSA) of the catalyst has good stability.

Drawings

FIG. 1 is a TEM image of the carbon-coated platinum alloy nanomaterial obtained in example 1;

FIG. 2 is an XRD pattern of the carbon-coated platinum alloy nanomaterial obtained in example 1;

FIG. 3 is an XPS survey spectrum of the carbon-coated platinum alloy nanomaterial obtained in example 1;

FIG. 4 is a LSV graph of the carbon-coated platinum alloy catalyst obtained in example 1A before and after 5000 cycles of cyclic scanning as an ORR catalyst;

FIG. 5 is an ECSA graph of the carbon-coated platinum alloy catalyst obtained in example 1A before and after 5000 cycles of cyclic scanning as ORR catalyst;

FIG. 6 is a LSV graph of the carbon supported platinum nickel alloy catalyst obtained in comparative example 1 before and after 5000 cycles of cyclic scanning as ORR catalyst;

FIG. 7 is an ECSA graph of the carbon supported platinum nickel alloy catalyst obtained in comparative example 1 before and after 5000 cycles of cyclic scanning as ORR catalyst;

FIG. 8 is a LSV comparison of the carbon coated platinum alloy catalysts obtained in example 2A and comparative example 2A for use as ORR catalysts;

fig. 9 is a graph comparing ECSA for the carbon-coated platinum alloy catalysts obtained in example 2A and comparative example 2A as ORR catalysts.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

The invention provides a preparation method of a carbon-coated platinum alloy nanomaterial, which comprises the following steps:

(1) Precursor preparation: removing the solvent in a homogeneous solution containing a metal precursor, a carbon source and a solvent to obtain a precursor material, wherein the metal precursor comprises a platinum source and a nickel source, and the carbon source is an acidic organic reducing agent;

(2) Roasting: carrying out high-temperature pyrolysis on the precursor material obtained in the step (1) in a reducing atmosphere to obtain a pyrolysis product, wherein the temperature of the high-temperature pyrolysis is 400-1100 ℃;

(3) Acid washing: and (3) carrying out contact reaction on the pyrolysis product obtained in the step (2) and an acid solution, and then sequentially carrying out solid-liquid separation, washing and drying.

In the preparation method of the carbon-coated platinum alloy nanomaterial, an acidic organic reducing agent is used as a carbon source, a catalyst precursor is pyrolyzed in a reducing atmosphere, nickel salt is used as a template and a catalyst of a carbon cage in the process of being reduced, and the coated carbon cage is generated in situ, so that the carbon-coated platinum alloy nanomaterial is prepared by a one-step method.

According to the present invention, in the step (1), the carbon source may be used as the reducing agent at the same time, and may be any acidic organic compound having a reducing property, preferably a reducing organic acid, a reducing polyhydroxy compound, or the like, and specifically, one or more of citric acid, ascorbic acid, ethylenediamine tetraacetic acid, 2, 5-pyridinedicarboxylic acid, benzoic acid, and terephthalic acid may be used.

According to the present invention, in the step (1), the platinum source may be any platinum-containing compound soluble in the solvent, and may be, for example, an inorganic acid salt, or an organic acid salt containing platinum, and may be, for example, one or more of chloroplatinic acid, tetraamineplatinum acetate, platinum acetylacetonate, chloroplatinic acid salt, and platinum chloride, and preferably chloroplatinic acid, tetraamineplatinum acetate, and the like.

According to the present invention, in the step (1), the nickel source may be any nickel-containing compound soluble in the solvent, and may be, for example, an inorganic acid salt or an organic acid salt containing nickel, and may be, for example, one or more of nickel acetate, nickel dichloride hexahydrate, nickel acetylacetonate, basic nickel carbonate, and nickel sulfate.

According to the present invention, preferably, in the step (1), the molar ratio of the metal precursor to the carbon source in terms of metal element may be 1:0.5 to 5, preferably 1:0.5-3.

According to the present invention, the platinum source and the nickel source may be appropriately adjusted according to the desired platinum alloy composition, and preferably, the molar ratio of the platinum source in terms of platinum to the nickel source in terms of nickel is 1:0.5-20, preferably 1:1-10, preferably 1:2-4, for example, may be 1:1. 1:1.2, 1: 2. 1: 3. 1:4.5, 1: 5. 1: 6. 1:7.5, 1: 8. 1:9 or 1:10, etc.

According to a preferred embodiment of the present invention, the platinum alloy may further contain other metal components, such as cobalt, molybdenum, etc., as needed. In this case, in step (1), the metal precursor preferably further includes a cobalt source, a molybdenum source, and the like. As the cobalt source, for example, one or more of cobalt sulfate, cobalt carbonate, cobalt oxalate, and cobalt chloride may be used. As the molybdenum source, for example, one or more of ammonium molybdate, sodium molybdate, and potassium molybdate may be used. In addition, preferably, the molar ratio of the platinum source in terms of platinum to the cobalt source in terms of cobalt is 1:0-0.1, preferably 1:0-0.05, the molar ratio of the platinum source in terms of platinum to the molybdenum source in terms of molybdenum being 1:0-0.1, preferably 1:0-0.05.

In the production method of the present invention, other metal sources than the above-mentioned platinum source, nickel source, cobalt source and molybdenum source are preferably not used; more preferably, no other metal source is used in addition to the platinum source and nickel source described above. The other metal source may be other metal salts, such as alkali metal salts or alkaline earth metal salts.

According to the present invention, in the step (1), the precursor material is obtained by dissolving a metal precursor and a carbon source in a solvent to form a homogeneous solution, and then removing the solvent from the homogeneous solution. The kind of the solvent is not particularly limited as long as it can form a homogeneous solution, and it is preferable that the solvent is one or more of water, an alcoholic solvent such as ethanol, and N, N-Dimethylformamide (DMF), and it is more preferable that the solvent is water or a mixture of ethanol and water (the volume ratio of ethanol and water may be, for example, 0.1 to 10:1, and preferably 1 to 5:1). The amount of the solvent used in the present invention is not particularly limited, and is also sufficient to form a homogeneous solution.

The method of forming the homogeneous solution is not particularly limited in the present invention, and the homogeneous solution may be formed, for example, by stirring. The stirring rate and time are not particularly limited in the present invention, and the homogeneous solution can be formed. In addition, in order to form the homogeneous solution, the dissolution may be further accelerated by heating.

As a method for removing the solvent in the homogeneous solution, the solvent in the homogeneous solution may be removed by evaporation at a temperature and by a process well known to those skilled in the art, for example, by spin evaporation or oil bath heating evaporation. According to a specific embodiment of the present invention, the solvent in the homogeneous solution may be removed by drying in a vacuum oven at 60-120 ℃ for 12-24 hours.

According to the present invention, the catalyst precursor material is preferably suitably ground to obtain a catalyst precursor powder prior to performing the high temperature pyrolysis of step (2), in order to facilitate the pyrolysis. The manner and degree of grinding may be appropriately selected.

According to the present invention, preferably, in the step (2), pyrolysis is performed by high temperature pyrolysis under a reducing atmosphere to obtain a pyrolysis product. The reducing atmosphere preferably comprises hydrogen or carbon monoxide, preferably hydrogen or a mixed atmosphere of carbon monoxide and an inert gas, wherein the inert atmosphere can be nitrogen and/or argon and the like, and particularly can be a mixed atmosphere of hydrogen and nitrogen. Preferably, the hydrogen or carbon monoxide comprises 5-30% by volume of the total gas. Pyrolysis may be carried out in any apparatus that provides the pyrolysis conditions described above, for example in a tube furnace.

As conditions for pyrolysis, preferably, the temperature of the pyrolysis may be 400 to 1100 ℃, preferably 500 to 900 ℃, and the constant temperature time may be 1 to 6 hours, preferably 2 to 4 hours. The rate of heating up of the pyrolysis may be 2-10 c/min, preferably 2-5 c/min.

After the pyrolysis, the pyrolysis product is preferably naturally cooled in a reducing atmosphere, and then is continuously purged with the inert gas, preferably, after being properly ground as needed, and then subjected to subsequent acid washing.

According to the present invention, in the step (3), the acid solution may be an acid conventionally used in the art, as long as it is capable of properly removing nickel element in the pyrolysis product, which is not tightly coated with the carbon layer. Preferably, the acid is one or more of sulfuric acid solution, nitric acid solution and hydrochloric acid solution, and more preferably sulfuric acid solution; preferably, the concentration of the acid solution is 0.5-2moL/L.

According to the present invention, preferably, the acid solution is used in an amount of H based on 1mol of nickel element in the pyrolysis product obtained in the step (2) ⁺ It is preferably not less than 2mol, more preferably 4 to 20mol. In the present invention, the excessive acid solution means 1mol relative to nickel element in the pyrolysis product obtained in the step (2), and the acid solution is used in an amount of H ⁺ The content is more than 2 mol.

According to a preferred embodiment of the invention, when the acid solution is sulfuric acid solution, the acid concentration is 0.5-2mol/L, and the contact reaction temperature is 25-90 ℃; when the acid solution is nitric acid solution, the acid concentration is 0.5-15mol/L, and the contact reaction temperature is 25-60 ℃; when the acid solution is hydrochloric acid solution, the acid concentration is 0.5-2mol/L, and the contact reaction temperature is 25-90 ℃.

According to the invention, the pyrolysis product is preferably contacted with the acid solution for a period of 3 to 50 hours, preferably 3 to 24 hours.

According to the present invention, the washing is used to remove acid remaining on the pyrolysis product caused by the acid washing process, and thus, various water washing methods capable of washing the pyrolysis product to neutrality are applicable to the present invention. Preferably, the washing is performed with ultrapure water until the pH of the washing solution is neutral, and more preferably, the washing is performed with suction filtration.

According to the invention, the drying is used to remove water from the acid-washed product. The drying may be carried out under normal pressure or reduced pressure, and preferably vacuum drying is carried out. The drying conditions may include: the temperature is 60-80 ℃ and the time is 4-12h.

The second aspect of the present invention provides a carbon-coated platinum alloy nanomaterial obtained by the above-described preparation method of the first aspect of the present invention.

In the nanomaterial, preferably, the carbon content is 10 to 50 wt%, the platinum content is 10 to 70 wt%, the nickel content is 5 to 70 wt%, the cobalt content is 0 to 5 wt%, and the molybdenum content is 0 to 5 wt%. In addition, small amounts of hydrogen and oxygen (e.g., 0.1-3 wt% hydrogen and 0.5-20 wt% oxygen) are present in the nanomaterial. More preferably, the carbon content is 10-40 wt%, the platinum content is 30-60 wt%, the nickel content is 10-40 wt%, the cobalt content is 0-5 wt%, and the molybdenum content is 0-5 wt%.

The carbon-coated platinum alloy nano material obtained by the preparation method disclosed by the invention has a core-shell structure with platinum alloy particles as the inner core and a carbon layer as the shell. The carbon layer may be a carbon cage structure.

According to the present invention, the platinum alloy particles may preferably have a particle size of 3 to 100nm, preferably 5 to 50nm.

The third aspect of the present invention provides a catalyst comprising the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention described above and conductive carbon black.

In a fourth aspect, the present invention provides a process for preparing a catalyst, the process comprising: after mixing the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention with conductive carbon black in the presence of a solvent, the solvent in the resulting mixture is removed and dried.

In a fifth aspect, the present invention provides another method for preparing a catalyst, the method comprising: the carbon-coated platinum alloy nanomaterial of the second aspect of the present invention is solid phase mixed with conductive carbon black.

According to the catalyst and the preparation method of the catalyst, the carbon-coated platinum alloy nanomaterial can be used for catalyzing the cathode oxygen reduction reaction of a fuel cell after being mixed with conductive carbon black. The method of mixing is not particularly limited, and may be liquid phase mixing or solid phase mixing as long as they can be sufficiently and uniformly mixed.

According to the present invention, the conductive carbon black is not particularly limited as long as it can be used for the cathode oxygen reduction reaction of a fuel cell, and for example, ketjen black (for example, ECT-600 JD), cabot black (for example, vulcan XC 72), and the like can be used.

According to a preferred embodiment of the present invention, preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black may be 1:0.1 to 5, preferably 1:0.2-2. In addition, the content of the conductive carbon black in the catalyst is preferably 10 to 80% by weight, and more preferably 15 to 65% by weight.

As a method of liquid phase mixing, as described in the fourth aspect above, the carbon-coated platinum alloy nanomaterial may be mixed with the conductive carbon black in the presence of a solvent, and then the solvent in the resultant mixture may be removed and dried. Preferably, the mixing comprises one or more of ultrasound, mechanical agitation and grinding, preferably ultrasonic followed by agitation mixing. The conditions of the ultrasonic, mechanical agitation and grinding may be appropriately selected, preferably ultrasonic for 0.5 to 2 hours, preferably mechanical agitation for 8 to 24 hours, and preferably grinding conditions include: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

As a method of solid phase mixing, as described in the fifth aspect above, the carbon-coated platinum alloy nanomaterial may be directly solid phase mixed with the conductive carbon black to obtain a catalyst. The method and conditions of solid phase mixing are not particularly limited, and preferably, the conditions of solid phase mixing include: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

A sixth aspect of the invention provides the use of the carbon-coated platinum alloy nanomaterial of the second aspect of the invention, the catalyst of the third aspect of the invention, or the catalyst obtained by the preparation method of the fourth or fifth aspect of the invention in a fuel cell.

As described above, the carbon-coated platinum alloy nanomaterial of the present invention can be directly used as a catalyst for the cathode oxygen reduction reaction of a fuel cell, or can be mixed with conductive carbon black to prepare a catalyst for the cathode oxygen reduction reaction of a fuel cell.

The present invention will be described in detail by examples. Unless otherwise specified, all reagents used in the present invention are analytically pure and commercially available.

The surface morphology of the material was characterized by high resolution transmission electron microscopy (HRTEM, JEM-2100, manufactured by Japanese electronics Co., ltd.) and the acceleration voltage was 200kV.

The crystal structure of the material was characterized by X-ray diffraction (XRD, empyrean sharp shadow, malvern, netherlands).

The content and valence state of each element on the surface of the material were determined by X-ray photoelectron spectroscopy (XPS, thermo Scientific, ESCALab model 250).

The specific surface area of the material was determined by the Brunauer-Emmett-Taller method (BET, quantachrome AS-6B type analyzer).

The resistivity of the material was measured by a powder resistivity tester (semiconductor powder resistivity tester of the sozhou lattice, ST-2722 type).

The content test of carbon, hydrogen, oxygen and nitrogen elements is carried out on a Elementar Vario EL Cube element analyzer, and the specific operation method is as follows: the sample is weighed about 5mg in a tin cup, put into an automatic sample feeding disc, enter a combustion tube through a ball valve for combustion, and have a combustion temperature of 1000 ℃ (for eliminating atmospheric interference during sample feeding, helium is adopted for blowing), and C, H, N in the sample is respectively converted into carbon dioxide, water and nitrogen after copper reduction. And separating the mixed gas by a chromatographic column, and finally detecting by a thermal conductivity cell. When oxygen element is measured, the sample is cracked in a high-temperature cracking tube filled with carbon powder, oxygen in the sample is converted into carbon monoxide, carrier gas carries the cracked product into a series scrubber to remove acid gas and water vapor, and finally the obtained product enters an infrared detector for detection.

The content of platinum and nickel is measured by inductively coupled plasma emission spectrometry (ICP-OES), and the specific method is as follows: (1) nitrolysis: 10mg of catalyst sample is measured and placed in a flask, 16mL of fresh aqua regia is added, a magnetic stirrer is added, the flask is placed in an oil bath, the temperature of 120 ℃ is condensed and refluxed for 12 hours, after cooling to room temperature, a glass syringe is used for sucking the solution, a disposable filter head with the aperture of 0.22 mu m is used for filtering, the filtrate is added into a 500mL volumetric flask, and ultrapure water is added for volume fixing. (2) content test: 10mL of the solution with the fixed volume is taken, and an instrument Agilent 5110 is adopted for metal content testing.

Electrochemical testing method: (1) preparation of an electrode: weighing a certain weight of catalyst sample, dispersing into a mixed solution of water, ethanol/isopropanol and perfluorosulfonic acid (nafion), performing ultrasonic treatment in ice water for 1 hour to form uniform ink, sucking a certain amount of ink by a pipette gun, dripping the ink onto a glassy carbon electrode, naturally drying, and then using the solution for electrochemical testing, wherein the Pt loading amount is controlled to be 10-30 mu g/cm ² . (2) preparation of electrolyte: using 0.1M HClO ₄ As electrolyte, one half hour of aeration was performed prior to the test to obtain an oxygen-saturated or argon-saturated electrolyte, which was used for LSV testing and an argon-saturated electrolyte was used for CV testing to determine the electrochemically active area. (3) electrochemical testing: the saturated calomel electrode is used as a reference electrode, the carbon rod is used as a counter electrode, the potential range is selected to be 0.03-1.12Vvs RHE during LSV test, the rotating speed of the working electrode is 1600rpm, and the sweeping speed is 10mV/s; during CV test, the rotation speed of the working electrode is 0, and the sweeping speed is 50mV/s; the 5000-circle electrochemical cyclic scanning condition is that the rotating speed of the working electrode is 0, the potential range is from 0.6V to 1.0V, and the scanning speed is 50mV/s under the oxygen saturation state. The electrochemical activity was calculated using the corresponding current density at 0.9V.

Example 1

153.7g of 8 wt% chloroplatinic acid aqueous solution, 22.4g nickel acetate tetrahydrate and 23.1g anhydrous citric acid are mixed, 200mL deionized water is added, magnetic stirring is carried out for 1h, the mixture is distilled off until the solvent is evaporated to dryness, and the mixture is dried in a vacuum oven at 60 ℃ for 12h. After grinding the catalyst precursor powder, in H ₂ And N ₂ Atmosphere (H) ₂ 20% of total gas flow rate) is heated to 700 ℃ at a heating rate of 5 ℃/min, and is naturally cooled to room temperature after heat preservation for 4 hours, and nitrogen is usedAnd taking out after purging for 6 hours. After grinding, 1g of pyrolysis product is pickled for 12 hours at 25 ℃ by 80mL of 1mol/L dilute nitric acid, filtered, washed by deionized water until the pH value of the solution is neutral, placed into a vacuum oven at 60 ℃ for 8 hours, and dried to obtain the carbon-coated platinum alloy nanomaterial.

The specific surface area of the material measured by BET method is 161.7m ² And/g, wherein the resistivity of the material measured by the powder resistivity tester is 0.23 omega-m.

Example 1A

Measuring 20mg of the carbon-coated platinum alloy nanomaterial of example 1, adding 10mL of a mixed solvent of ethanol/water (V/V=3/1), and performing ultrasonic treatment for 1h; simultaneously, 8mg Keqin black (ECT-600 JD) is measured, 4mL of mixed solvent of ethanol/water (V/V=3/1) is added, and ultrasonic treatment is carried out for 1h; mixing the two solutions, performing ultrasonic treatment for 1h, mechanically stirring for 24h at the rotating speed of 800rpm, performing suction filtration, and drying in a vacuum oven at the temperature of 60 ℃ for 6h to obtain the carbon-coated platinum alloy catalyst.

Example 2

2.6g of chloroplatinic acid hexahydrate, 2.2g basic nickel carbonate (Ni content: 40.33% by weight) and 3.8g anhydrous citric acid were mixed, 200mL of deionized water was added, magnetically stirred for 1 hour to dissolve completely, heated and stirred in an oil bath at 80 ℃ until the solvent was evaporated, and then dried in a vacuum oven at 120 ℃ for 12 hours. After grinding the catalyst precursor powder, in H ₂ And N ₂ Atmosphere (H) ₂ 30% of the total flow of the gas) is heated to 500 ℃ at a heating rate of 5 ℃/min, is naturally cooled to room temperature after being kept warm for 4 hours, is purged for 6 hours by nitrogen, and is taken out. After grinding, 1g of pyrolysis product is washed with 80mL of 0.5mol/L dilute sulfuric acid at 90 ℃ for 12h, filtered, washed with deionized water until the pH value of the solution is neutral, and put into a vacuum oven at 60 ℃ for 8h to be dried, thus obtaining the carbon-coated platinum alloy nanomaterial.

Example 2A

The carbon-coated platinum alloy nanomaterial of example 2 was combined with ketjen black (ECY-600 JD) in a ratio of 5:2, and placing the mixture into a ball milling tank for ball milling for 4 hours at a speed of 200rpm under the protection of nitrogen atmosphere (after ball milling for 5min for each cycle, stopping for 2 min), thereby obtaining the carbon-coated platinum alloy catalyst.

Example 3

2.0g of tetraamineplatinum acetate, 2.5g of nickel dichloride hexahydrate and 2.8g of ascorbic acid are mixed, 150mL of deionized water is added for dissolution, magnetic stirring is carried out for 1h, then rotary evaporation is carried out, and the mixture is dried in a vacuum oven at 60 ℃ for 12h. After grinding the catalyst precursor powder, in H ₂ And N ₂ Atmosphere (H) ₂ 20% of the total flow of the gas) is heated to 400 ℃ at a heating rate of 2 ℃/min, is naturally cooled to room temperature after being kept warm for 2 hours, and is taken out after being purged for 6 hours by nitrogen. After grinding, 1g of pyrolysis product is washed with 80mL of 0.5mol/L dilute sulfuric acid at 90 ℃ for 12h, filtered, washed by deionized water until the pH value of the solution is neutral, and put into a vacuum oven for drying at 60 ℃ to obtain the carbon-coated platinum alloy nanomaterial.

Example 3A

A carbon-coated platinum alloy catalyst was prepared according to the method of example 1A, except that the carbon-coated platinum alloy nanomaterial of example 3 was used.

Comparative example 1

The molar ratio of chloroplatinic acid to nickel chloride is 1:1, adding deionized water into the mixture, stirring to dissolve completely, adding the aqueous solution dropwise into conductive carbon black Vulcan XC72, ultrasonic dispersing to mix uniformly, placing into a vacuum oven at 120deg.C for 12 hr to thoroughly dry, grinding, placing the precursor powder into a tube furnace, and adding into H ₂ /N ₂ In atmosphere (H) ₂ 20% of total gas flow rate) is heated to 400 ℃ at a heating rate of 5 ℃/min, the temperature is kept for 3 hours, the mixture is naturally cooled to room temperature, nitrogen is purged for 6 hours and then taken out, the water washing-suction filtration process is repeated for 3 times, and after the mixture is dried in a vacuum oven at 60 ℃ for 6 hours, the carbon-supported platinum-nickel alloy catalyst (PtNi/C) is obtained (the Pt content is 20 weight percent).

Comparative example 2

Carbon-coated platinum alloy nanomaterials were prepared according to the method of example 2, except that after grinding the catalyst precursor powder, the catalyst precursor powder was mixed with a catalyst precursor powder in a solvent such as N ₂ High temperature pyrolysis is carried out in the atmosphere.

Comparative example 2A

A carbon-coated platinum alloy catalyst was prepared in the same manner as in example 2A using the carbon-coated platinum alloy nanomaterial of comparative example 2.

Test example 1

The TEM and XRD patterns of the carbon-coated platinum alloy nanomaterial obtained in example 1 are shown in fig. 1 and 2. As can be seen from FIG. 1, the carbon-coated platinum alloy nanomaterial has a spheroid-like morphology, the core particles have a porous structure, and the diameter is 20-40nm. As can be seen from fig. 2, the material contains two sets of alloy peaks, one set of alloy peaks biased towards the Pt unimodal and one set of alloy peaks biased towards the Ni unimodal.

The TEM and XRD patterns of the carbon-coated platinum alloy nanomaterials obtained in examples 2 to 3 were also determined, which are similar to fig. 1 and 2, respectively.

Test example 2

The metal contents of the nano materials of examples 1-2 and comparative example 2 were measured by the ICP-OES method, and the contents of carbon, hydrogen, oxygen, and nitrogen elements in the materials were measured by an elemental analyzer, and the results are shown in table 1. In addition, fig. 3 shows an XPS spectrogram of the carbon-coated platinum alloy nanomaterial obtained in example 1. As can be seen from fig. 3, the carbon-coated platinum alloy nanomaterial prepared in example 1 contains Pt, ni, C, O element on the surface, and thus, the nitrogen element content of 0.21% measured by the elemental analyzer is an instrument error.

TABLE 1

Test example 3

The electrochemical activities of the nanomaterial and catalyst prepared in the above examples and comparative examples were measured, and the results are shown in table 2. The LSV curve and ECSA curve of the carbon-coated platinum alloy catalyst obtained in example 1A for catalyzing the oxygen reduction reaction are shown in fig. 4 and 5, respectively, the LSV curve and ECSA curve of the carbon-supported platinum nickel alloy catalyst (PtNi/C) obtained in comparative example 1 for catalyzing the oxygen reduction reaction are shown in fig. 6 and 7, respectively, and the LSV curve and ECSA curve of the carbon-coated platinum alloy catalyst obtained in example 2A and comparative example 2A for catalyzing the ORR catalyst are shown in fig. 8 and 9, respectively.

TABLE 2

From the above results, it can be seen that the nanomaterial and catalyst of the present invention have good ORR catalytic activity. Specifically, ptNi alloy prepared in comparative example 1 was directly supported on conductive carbon black, and ORR activity was severely reduced after 5000 cycles of cyclic scanning in an acid electrolyte, half-wave potential was reduced from initial 0.85V to 0.79V, and mass specific activity was reduced from initial 0.086A/mg _Pt Down to 0.041A/mg _Pt ECSA is defined by initial 50.95m ² /g _Pt Down to 35.91m ² /g _Pt ECSA retention was only 70%; while example 1A is a catalyst prepared by uniformly mixing PtNi alloy coated by a carbon cage and conductive carbon black, the catalyst has good stability after being circularly scanned for 5000 circles in an acid electrolyte, the half-wave potential is reduced from 0.89V to 0.88V, and the mass specific activity is reduced from 0.22A/mg _Pt Down to 0.17A/mg _Pt The ECSA slightly increased after the cyclic scan from the initial 27.90m ² /g _Pt Rising to 33.70m ² /g _Pt The retention was 120%.

As can be seen from comparing the results of comparative example 2A and example 2A, the half-wave potential of comparative example 2A was 0.85V and the weight specific activity was 0.15A/mg _Pt Whereas the half-wave potential of example 2A was 0.89V, the weight specific activity was 0.20A/mg _Pt Are all higher than comparative example 2A. The above comparison shows that example 2A calcined in a reducing atmosphere at 500 ℃ using the present invention has better ORR catalytic activity than comparative example 2A calcined in an inert atmosphere under the same conditions.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims (17)

1. The preparation method of the carbon-coated platinum alloy nano material is characterized by comprising the following steps of:

(1) Precursor preparation: removing the solvent in a homogeneous solution containing a metal precursor, a carbon source and a solvent to obtain a precursor material, wherein the metal precursor comprises a platinum source and a nickel source, and the carbon source is an acidic organic reducing agent;

(2) Roasting: carrying out high-temperature pyrolysis on the precursor material obtained in the step (1) in a reducing atmosphere to obtain a pyrolysis product, wherein the temperature of the high-temperature pyrolysis is 400-1100 ℃;

(3) Acid washing: and (3) carrying out contact reaction on the pyrolysis product obtained in the step (2) and an acid solution, and then sequentially carrying out solid-liquid separation, washing and drying.

2. The production method according to claim 1, wherein in the step (1), the carbon source is one or more of citric acid, ascorbic acid, ethylenediamine tetraacetic acid, 2, 5-pyridinedicarboxylic acid, benzoic acid, and terephthalic acid.

3. The production method according to claim 1 or 2, wherein in the step (1), the platinum source is one or more of chloroplatinic acid, tetraamineplatinum acetate, platinum acetylacetonate, chloroplatinate, and platinum chloride;

preferably, the nickel source is one or more of nickel acetate, nickel dichloride hexahydrate, nickel acetylacetonate, basic nickel carbonate, nickel carbonate and nickel sulfate.

4. The production method according to any one of claims 1 to 3, wherein in the step (1), a molar ratio of the metal precursor to the carbon source in terms of metal element is 1:0.5-5;

preferably, the molar ratio of the platinum source in terms of platinum to the nickel source in terms of nickel is 1:0.5-20, preferably 1:1-10.

5. The production method according to any one of claims 1 to 4, wherein in step (1), the metal precursor further comprises a cobalt source and/or a molybdenum source; preferably, the cobalt source is one or more of cobalt sulfate, cobalt carbonate, cobalt oxalate and cobalt chloride; preferably, the molybdenum source is one or more of ammonium molybdate, sodium molybdate and potassium molybdate;

preferably, the molar ratio of the platinum source in terms of platinum to the cobalt source in terms of cobalt is 1:0-0.1, the molar ratio of the platinum source in terms of platinum to the molybdenum source in terms of molybdenum being 1:0-0.1.

6. The production process according to any one of claims 1 to 5, wherein in the step (1), the solvent is one or more of water, an alcoholic solvent and N, N-dimethylformamide;

preferably, the alcoholic solvent is ethanol.

7. The production method according to any one of claims 1 to 6, wherein in step (2), the reducing atmosphere comprises hydrogen or carbon monoxide, preferably a mixed atmosphere of hydrogen or carbon monoxide and an inert gas, more preferably a mixed atmosphere of hydrogen and nitrogen;

preferably, the hydrogen or carbon monoxide comprises 5-30% by volume of the total gas.

8. The production method according to any one of claims 1 to 7, wherein in the step (2), the temperature rise rate of the high-temperature pyrolysis is 2 to 10 ℃/min;

preferably, the pyrolysis is carried out for a constant temperature of 1 to 6 hours.

9. The production method according to any one of claims 1 to 8, wherein in the step (3), the acid solution is one or more of a sulfuric acid solution, a nitric acid solution and a hydrochloric acid solution;

preferably, the acid solution is used in an amount of H based on 1mol of nickel element in the pyrolysis product obtained in the step (2) ⁺ Counting more than 2 mol;

preferably, when the acid solution is sulfuric acid solution, the acid concentration is 0.5-2mol/L, and the temperature of the contact reaction is 25-90 ℃; when the acid solution is nitric acid solution, the acid concentration is 0.5-15mol/L, and the contact reaction temperature is 25-60 ℃; when the acid solution is hydrochloric acid solution, the acid concentration is 0.5-2mol/L, and the contact reaction temperature is 25-90 ℃.

10. The process according to any one of claims 1 to 9, wherein in step (3), the contact reaction is carried out for a period of 3 to 50 hours, preferably 3 to 24 hours.

11. A carbon-coated platinum alloy nanomaterial obtained by the production method according to any one of claims 1 to 10.

12. The carbon-coated platinum alloy nanomaterial of claim 11, wherein the nanomaterial comprises 10-50 wt% carbon, 10-70 wt% platinum, 5-70 wt% nickel, 0-5 wt% cobalt, 0-5 wt% molybdenum, 0.1-3 wt% hydrogen, and 0.5-20 wt% oxygen.

13. The carbon-coated platinum alloy nanomaterial according to claim 11 or 12, wherein the carbon-coated platinum alloy nanomaterial has a core-shell structure in which platinum alloy particles are used as a core and a carbon layer is used as a shell layer;

preferably, the platinum alloy particles have a particle size of 3-100nm.

14. A catalyst comprising the carbon-coated platinum alloy nanomaterial of any of claims 11-13 and a conductive carbon black;

preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5.

15. A method for preparing a catalyst, comprising: mixing the carbon-coated platinum alloy nanomaterial of any one of claims 11 to 13 with conductive carbon black in the presence of a solvent, and removing the solvent from the resulting mixture and drying;

preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5;

preferably, the mixing comprises one or more of ultrasound, mechanical agitation and milling, preferably for a period of time of from 0.5 to 2 hours, preferably for a period of time of from 8 to 24 hours, preferably the milling conditions comprise: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

16. A method for preparing a catalyst, comprising: solid phase mixing the carbon-coated platinum alloy nanomaterial of any of claims 11-13 with conductive carbon black;

preferably, the weight ratio of the carbon-coated platinum alloy nanomaterial to the conductive carbon black is 1:0.1-5;

preferably, the conditions of the solid phase mixing include: ball milling is carried out in inert atmosphere at the rotating speed of 100-500rpm for 2-24h.

17. Use of the carbon-coated platinum alloy nanomaterial according to any of claims 11 to 13, the catalyst according to claim 14, or the catalyst obtained by the preparation method according to claim 15 or 16 in a fuel cell.

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