A Pt / C catalyst with ultra-low Pt loading and preparation method thereof

Abstract

The present invention belongs to the field of hydrogen energy technology, and discloses a Pt / C catalyst with ultra-low Pt loading and a preparation method thereof. The method comprises the following steps: adding a Pt precursor solution to an electrolyte solution to obtain a mixed solution, introducing an inert gas into the mixed solution, adding a carbon-based carrier, and treating the mixed solution with a double pulse electrochemical deposition method using a three-electrode system. After the deposition is completed, the carbon-based carrier is taken out, rinsed, and dried to obtain a Pt / C catalyst with ultra-low Pt loading; the carbon carrier is connected to a working electrode, the counter electrode is a Pt sheet, and the reference electrode is Ag / AgCl; the concentration of the Pt precursor in the mixed solution is 1 to 10 mmol / L. The size of the Pt nanoparticles prepared by the present invention is between 1nm-3nm, and is mainly distributed at the edge of the graphite layer and the defect position on the graphite layer. The prepared catalyst has a high active specific surface area, and is a highly active ultra-low Pt loading catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen energy, and particularly relates to a Pt / C catalyst with an ultra-low Pt loading and a preparation method thereof. Background Art

[0002] There are three main types of catalysts in hydrogen fuel cells: platinum-based catalysts, low-platinum catalysts and non-platinum catalysts. At present, the commonly used commercial catalyst in hydrogen fuel cells is platinum (Pt). Pt has good molecular adsorption and dissociation characteristics, so platinum catalysts have become the most ideal and currently the only commercial catalyst material. At present, the commercially commonly used catalyst is the supported catalyst Pt / C (Pt nanoparticles dispersed on a carbon powder carrier). Pt catalyst is one of the core materials of fuel cells, accounting for more than 40% of the cost of fuel cell stacks. In September 2020, the Ministry of Finance, the Ministry of Industry and Information Technology and other five departments jointly issued the "Notice on the Demonstration Application of Fuel Cell Vehicles", which clearly pointed out that it is necessary to focus on supporting the research and development breakthroughs of key materials and components such as catalysts. In order to improve performance and reduce dosage, small-particle Pt nano-dispersion preparation technology is generally adopted. However, the current problem is that small-size Pt particles will break free from the constraints of the carrier, migrate to larger particles, be merged and disappear, and large particles can survive and continue to grow; small-size Pt particles are more susceptible to oxidation reactions, diffuse to the surface of large-size platinum particles in the form of platinum ions and deposit, which leads to agglomeration. To this end, people doped carbon carriers with nitrogen, oxygen, boron and other impurity atoms to enhance the surface adhesion of Pt particles and various transition metals (such as Co, Ni, Mn, Fe, Cu, etc.), which not only improved the durability but also helped to enhance the anti-migration and agglomeration ability of Pt-containing catalysts. The Pt / Ir (Ta) catalyst developed by 3M Company in the United States based on ultra-thin film catalytic technology has achieved an average of as low as 0.09 mg / cm at the cathode and anode. 2 The amount of platinum used has reached 9.4kW / g (150kPa reaction pressure) and 11.6kW / g (250kPa reaction pressure). The PtCo / high surface area carbon (HSC) developed by Volkswagen Group of Germany has also made important progress, with the catalytic power density and heat dissipation capacity exceeding the planned target values ​​set by the US Department of Energy (2016-2020).

[0003] The platinum-based catalysts required for the preparation of hydrogen fuel cells have problems such as low activity, large dosage and high cost. Reducing the amount of platinum-based catalysts and optimizing the preparation of membrane electrodes based on this goal are important ways to reduce the commercial cost of hydrogen fuel cell systems. Summary of the invention

[0004] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a method for preparing a Pt / C catalyst with ultra-low Pt loading.

[0005] Another object of the present invention is to provide a Pt / C catalyst with ultra-low Pt loading prepared by the above method.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a Pt / C catalyst with an ultra-low Pt loading, comprising the following steps:

[0008] A Pt precursor solution is added to an electrolyte solution to obtain a mixed solution, an inert gas is introduced into the mixed solution, a carbon-based carrier is added, and the mixed solution is treated by a double-pulse electrochemical deposition method using a three-electrode system. After the deposition is completed, the carbon-based carrier is taken out, rinsed, and dried to obtain a Pt / C catalyst with an ultra-low Pt loading;

[0009] Among them, the carbon-based support is connected to the working electrode, the counter electrode is a Pt sheet, and the reference electrode is Ag / AgCl;

[0010] The concentration of the Pt precursor in the mixed solution is 1 mmol / L to 10 mmol / L.

[0011] Preferably, the double-pulse electrochemical deposition voltage is -0.1V to +0.6V, and the deposition time is 5s to 200s.

[0012] Preferably, the double-pulse electrochemical deposition is first deposited at a voltage of -0.1v to -0.02v for 10 to 50ms, and then deposited at a voltage of +0.58v to +0.6v for 5 to 200s.

[0013] Preferably, the Pt precursor is one of H2PtCl6, PtCl4, and K2PtCl6, the electrolyte solution is a perchloric acid solution or a sulfuric acid solution, and the concentration of the electrolyte solution is 0.1 to 0.5 mol / L.

[0014] Preferably, the working electrode potential is 0.86V.

[0015] Preferably, the carbon-based carrier is one or more of highly oriented pyrolytic graphite (HOPG), carbon nanotubes, carbon black, biochar, and activated carbon.

[0016] Preferably, the carbon-based carrier is highly oriented pyrolytic graphite (HOPG), which is pretreated to expose a new clean surface, has a square side length of 10 mm, and a thickness of 2 mm.

[0017] Preferably, the inert gas is one of helium, argon and nitrogen, and the flow rate is 0.05-0.1 mL / s.

[0018] A Pt / C catalyst with ultra-low Pt loading is prepared by the above method.

[0019] The technical solution of the present invention is based on electrochemical pulse deposition technology. H2PtCl6 is used as a Pt precursor, the electrolyte solution is a perchloric acid solution or a sulfuric acid solution, the pulse voltage is between -0.1V and 0.6V (relative to a standard reference electrode), and the nucleation and growth times are controlled at 10-50ms and 5-200s, respectively.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] (1) Catalyst materials in hydrogen fuel cells account for more than 40% of the entire fuel system. The ultra-low loading Pt / C catalyst prepared by the present invention can further reduce the Pt loading to 0.05 mg / cm 2 Compared with the technology of 3M Company in the United States, the amount of Pt catalyst used can be reduced by about 45%, the cost of the catalyst can be reduced by about 45%, the loading amount of the catalyst is reduced, and the activity per unit specific surface area is almost unchanged.

[0022] (2) The aqueous phase preparation method described in the present invention is simple to operate and has advantages in scale-up production.

[0023] (3) The stability of Pt nanoparticles is further improved. Compared with traditional Pt / C catalysts, the Pt nanoparticles prepared in the present invention have smaller particle sizes and are mostly formed at the defect sites of carbon-based materials. This design enables Pt nanoparticles to have a higher binding force with carbon-based carriers, inhibiting the particle agglomeration phenomenon caused by the migration of Pt nanoparticles on the surface.

[0024] (4) It has a higher active specific surface area. Since the particle size of the prepared Pt nanoparticles is only about 1 nm, compared with the traditional Pt / C catalyst, the unit mass of Pt has a higher active surface area. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the potential setting process of the double electrochemical pulse method and the corresponding current-time distribution diagram.

[0026] Figure 2 This is the atomic force microscopy image of the catalyst product obtained by electrochemical pulse deposition method and the Pt particle size analysis on its surface.

[0027] Figure 3 The performance comparison chart of commercial Pt / C catalyst and the catalyst developed by the present invention in 0.5M H2SO4 electrolyte at room temperature. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0029] Example 1

[0030] This scheme is based on electrochemical pulse deposition. The specific process is as follows:

[0031] (1) Prepare a carbon-based carrier. In this implementation case, highly oriented pyrolytic graphite (HOPG) is used. The square side length is 10 mm and the thickness is 2 mm. The exposed surface of one side of the HOPG is taped and then removed to expose a new clean surface. The treated HOPG is placed in a clean container for later use.

[0032] (2) Prepare 100 mL of 0.1 mol / L perchloric acid solution and add an appropriate amount of concentrated H2PtCl6 solution into the prepared 100 mL perchloric acid solution to make the H2PtCl6 concentration be 1 mmol / L.

[0033] (3) Take a clean four-necked flask, rinse it with deionized water three times, air-dry it, and pour the prepared H2PtCl6 perchloric acid solution into the four-necked flask.

[0034] (4) Take a clean Ag / AgCl standard reference electrode, rinse it three times with deionized water, and place it in a flask.

[0035] (5) Take a clean Pt counter electrode, rinse it three times with deionized water, and place it in a flask.

[0036] (6) Connect the HOPG carbon support to the working electrode and suspend it above the solution in the flask.

[0037] (7) Argon gas was introduced into the solution at a flow rate of 0.05 mL / s.

[0038] (8) After half an hour, the HOPG carbon support was placed in the solution. Figure 1 The working electrode potential was set to 0.86 V compared to the standard hydrogen electrode.

[0039] (9) Set the double pulse deposition time and potential. Use an electrochemical workstation (Metrohm PGSTAT302N) for deposition. Figure 1 As shown in the figure below, at room temperature, the nucleation potential of Pt nanoparticles is

[0040] -0.22v, nucleation time is 10ms, Pt nanoparticle growth potential is +0.58v, and growth time is 180s.

[0041] (10) After the deposition is completed, the HOPG carbon support is quickly removed, repeatedly rinsed with deionized water, and blown dry with gas to obtain a Pt / C catalyst with an ultra-low Pt loading.

[0042] (11) The prepared Pt / C catalyst was placed in a clean container for characterization.

[0043] (12) The surface morphology of the finished catalyst prepared in this case under atomic force microscopy is shown in the figure below: Figure 2 As shown in (c), the particle size of the Pt nanoparticles on its surface is Figure 2 As shown in red in (d), the particle size of Pt nanoparticles is smaller, only about 1 nm. Compared with traditional Pt / C catalysts, Pt has a higher active surface per unit mass, and the formation sites are mostly at the defect sites of carbon-based materials. This design makes the Pt nanoparticles have a higher binding force with the carbon-based carrier, inhibiting the particle agglomeration phenomenon caused by the migration of Pt nanoparticles on the surface.

[0044] Example 2

[0045] The same process as in Example 1 was used to change the nucleation and growth time of the Pt nanoparticles. The surface morphologies of the other two samples obtained under atomic force microscopy were as follows: Figure 2 As shown in (a) and (b), the nucleation time and growth time of the nanoparticles 2(a) and 2(b) are 10ms and 50s, and 10ms and 100s.

[0046] Example 3

[0047] Electrochemical activity test of Pt / C catalyst

[0048] The performance of commercial Pt / C catalyst and the catalyst prepared by the present invention are compared in 0.5M H2SO4 electrolyte at room temperature. Figure 3 , the catalyst loading amount decreased, the activity per unit specific surface area almost did not decrease, and the performance of the catalyst was slightly better than that of the commercial Pt / C catalyst.

[0049] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a Pt / C catalyst with ultra-low Pt loading, characterized in that: The following steps are involved: A Pt precursor solution is added to an electrolyte solution to obtain a mixed solution, an inert gas is introduced into the mixed solution, a carbon-based carrier is added, and the mixed solution is treated by a double-pulse electrochemical deposition method using a three-electrode system. After the deposition is completed, the carbon-based carrier is taken out, rinsed, and dried to obtain a Pt / C catalyst with an ultra-low Pt loading; Among them, the carbon-based support is connected to the working electrode, the counter electrode is a Pt sheet, and the reference electrode is Ag / AgCl; The Pt precursor is one of H2PtCl6, PtCl4, and K2PtCl6, and the concentration of the Pt precursor in the mixed solution is 1 mmol / L; The double pulse electrochemical deposition is first deposited at a voltage of -0.02V for 10 to 50ms, and then deposited at a voltage of +0.58V for 5 to 200s.

2. The method for preparing a Pt / C catalyst with an ultra-low Pt loading according to claim 1, characterized in that: The electrolyte solution is a perchloric acid solution or a sulfuric acid solution, and the concentration of the electrolyte solution is 0.1-0.5 mol / L.

3. The method for preparing a Pt / C catalyst with an ultra-low Pt loading according to claim 1 or 2, characterized in that: The working electrode potential is 0.86V.

4. The method for preparing a Pt / C catalyst with an ultra-low Pt loading according to claim 1, characterized in that: The carbon-based carrier is one or more of highly oriented pyrolytic graphite, carbon nanotubes, carbon black, biomass carbon, and activated carbon.

5. The method for preparing a Pt / C catalyst with an ultra-low Pt loading according to claim 4, characterized in that: The carbon-based carrier is highly oriented pyrolytic graphite, and the square side length of the highly oriented pyrolytic graphite is 10 mm and the thickness is 2 mm.

6. The method for preparing a Pt / C catalyst with an ultra-low Pt loading according to claim 1, characterized in that: The inert gas is one of helium, argon and nitrogen, and the flow rate is 0.05-0.1 mL / s.

7. A Pt / C catalyst with ultra-low Pt loading, characterized in that: The method is prepared by any one of claims 1 to 6.

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