CN101814607A - Preparation method of platinum/graphen catalyst for proton exchange membrane fuel cell - Google Patents

Abstract

The invention discloses a preparation method of a platinum/graphen catalyst for a proton exchange membrane fuel cell. The platinum/graphen catalyst for the proton exchange membrane fuel cell is prepared by adopting graphen as a carrier, taking sodium borohydride or ethylene glycol as a reducing agent, and reducing oxidized graphite and chloroplatinic acid together, and the platinum loading capacity of the catalyst is between 10 and 60 weight percent. The catalyst has the initial electrochemical activity superficial area of 4.75 m<2>/g, and the performance attenuation of 18.4 percent in 3,000 times of cyclic volt-ampere tests. Compared with the conventional commercial catalyst platinum/XC-72 (having the attenuation of 44.5 percent) of E-TEK Company, the catalyst shows higher electrochemical stability.

Description

A kind of preparation method of platinum/graphene catalyst for proton exchange membrane fuel cell

technical field

The invention relates to a method for preparing a catalyst for a fuel cell, in particular to a method for preparing a platinum/graphene catalyst for a proton exchange membrane fuel cell.

Background technique

Proton exchange membrane fuel cell (PEMFC) has the advantages of simple structure and short start-up time, and has shown good application prospects in recent years. However, in order to achieve real commercial application of PEMFC, problems such as catalyst cost and stability need to be solved. Improving the structure of the catalyst support is beneficial to the stability of the catalyst. Various conductive carbon materials, such as carbon microspheres, multi-walled carbon nanotubes, and single-walled carbon nanotubes, have been used as electrocatalyst supports in order to improve their stability.

At present, the most widely used commercial conductive carbon black is XC-72. For example, in U.S. Patent No. 3,857,737, the impregnation method is used to load platinum ammonium complex ions on XC-72. Platinum oxygen gel is loaded on XC-72 by the method, and Chinese patent CN1915521A adopts solid-phase method to load platinum on XC-72, find out from the report, the platinum/XC-72 catalyst that is loaded on this carrier has relatively Good electrocatalytic performance, but the stability of the Pt/XC-72 catalyst was not reported. Journal of Power Sources magazine 2007, volume 172, page 145, reported the current status of the stability of platinum/carbon catalysts, discussed XC-72, carbon nanotubes and other carrier materials, and believed that the stability of the carrier has a great impact on the stability of the catalyst , the article pointed out that in the fuel cell operating environment (greater than 0.6 volts, room temperature and above operating temperature) the carbon carrier will be significantly lost, this is because the carbon carrier will generate carbon dioxide or carbon monoxide under this condition, accompanied by the agglomeration of metal particles , The catalyst activity will show a large attenuation. After 170 hours, the activity of the platinum/carbon catalyst based on XC-72 is 80%, and the activity of the platinum/carbon catalyst based on carbon nanotubes is 30%. Therefore, in order to improve the stability of the catalyst, it is necessary to select a more stable carrier.

Geim pointed out in Science magazine 2009, volume 324, page 1530, that graphene is a carbon material with less than 10 layers of graphite molecular layered structure, and has a relatively high specific surface area (the theoretical specific surface area of single-layer graphene can reach 2620m ² /g), which can Provide more command load bits. At the same time, graphene exhibits a strong quantum effect and has good electron conductivity. Through first-principle calculations, it is found that platinum clusters can be stably supported on graphene, while the adsorption energy of carbon monoxide or hydrogen on platinum particles will be reduced due to the presence of graphene, which is more conducive to the reaction in fuel cells. Therefore, graphene can serve as a good carbon support.

At present, the initial activity and preparation method of the platinum/graphene catalyst prepared by using sodium borohydride or ethylene glycol as the reducing agent has not yet been investigated. There is also no relevant content about the preparation of platinum/graphene catalysts in the patent.

The Journal of Physical Chemistry C, 2009, volume 113, page 7990, reported a preparation method of a platinum/graphene catalyst. The researchers carried out reduction at pH=2 to obtain a 50wt% platinum/graphene catalyst.

The platinum/graphene catalyst reported in Electrochemistry Communications magazine 2009, volume 11, page 846 needs to be reduced at pH=10 for 24 hours, and dried at 40°C to obtain a 45wt% platinum/graphene catalyst.

The Journal of Physical Chemistry C magazine, 2008, volume 112, page 19841, reported a method for preparing a platinum/graphene catalyst by reducing the ethylene glycol method for methanol electrooxidation.

The platinum/graphene catalyst reported on page 954 of Volume 11 of Electrochemistry Communications in 2009 was prepared with high-temperature hydrogen as a reducing agent. After the cyclic voltammetry test, the catalyst performance decayed to 37.6%, showing better stability than commercial catalysts.

Contents of the invention

The purpose of the present invention is to prepare a platinum/graphene catalyst for proton exchange membrane fuel cells, wherein the platinum loading is 10wt%-60wt%. This catalyst uses graphene as a carrier, and utilizes the unique quantum effect and two-dimensional ductility of graphene to improve the stability of the catalyst. By blending chloroplatinic acid and graphite oxide, using sodium borohydride or ethylene glycol as a reducing agent for co-reduction, and controlling the activity of the catalyst by adjusting the reduction time, a proton exchange membrane fuel with higher stability is prepared battery catalyst.

A kind of preparation method of platinum/graphene catalyst for proton exchange membrane fuel cell of the present invention is as follows, and the following all represent with mass parts:

A. Sodium borohydride reduction method: Ultrasonically disperse graphite oxide in deionized water to form 1000-20000 parts of graphite oxide dispersion of 0.05wt%-1wt%, add 2.66-15.93 parts of chloroplatinic acid and mix evenly to make platinum in platinum/ The loading in the graphene catalyst is 10wt%-60wt%, adjust the pH value to 9-13 with 0.5M-4M potassium hydroxide aqueous solution, add 160-640 parts of sodium borohydride and 5000-10000 parts of deionized water, and reduce 1- 18 hours, then suction-filtered, washed with deionized water, and dried at 60-100° C. for 6-24 hours to obtain a platinum/graphene catalyst for proton exchange membrane fuel cells;

Or B. Ethylene glycol reduction method: Get graphite oxide and ultrasonically disperse it in ethylene glycol to form 1000-20000 parts of graphite oxide dispersion liquid of 0.05wt%-1wt%, add 2.66-15.93 parts of chloroplatinic acid and mix evenly, make platinum in The loading of the platinum/graphene catalyst is 10wt%-60wt%, and the pH value is adjusted to 9-13 with 0.5M-4M potassium hydroxide ethylene glycol solution, reduced at 90-150°C for 3-12 hours, and then suction filtered, and washing with deionized water, and drying the product at 60-100° C. for 6-24 hours to obtain a platinum/graphene catalyst for proton exchange membrane fuel cells.

The raw material graphite oxide in the present invention is prepared according to the literature report on page 771 of volume 11 of Chemistry of Materials magazine in 1999. The specific preparation method is as follows: 1 part of graphite is stirred and dispersed in 80 parts of 98wt% concentrated sulfuric acid, and 4.5 After reacting for 5 days, add deionized water and 10 parts of 30wt% aqueous hydrogen peroxide solution to terminate the reaction, then centrifuge, wash 16 times with deionized water, and dry at 80°C for 24 hours to obtain graphite oxide.

In the preparation method of a platinum/graphene catalyst for a proton exchange membrane fuel cell of the present invention, graphene is used as a carrier, and the unique quantum effect of graphene is used to form an electronegative center on the surface of graphene, and platinum particles are adsorbed in the catalyst preparation process , so that the platinum particles can be more stably loaded on the surface of the carrier and are not easy to migrate; at the same time, due to the large specific surface area of graphene, the supported platinum particles are not easy to contact and agglomerate, which can better maintain the catalytic activity of the catalyst. A kind of platinum/graphene catalyst for proton exchange membrane fuel cell prepared in the present invention is 18.4% after 3000 cycles of cyclic voltammetry tests, and the catalyst performance decay is 18.4%, which is shown by the commercial catalyst platinum/XC-72 of E-TEK Company 44.5% has better stability.

Description of drawings

1 is a cyclic voltammogram of a platinum/graphene catalyst and a platinum/XC-72 catalyst for a proton exchange membrane fuel cell obtained in Example 3 and Comparative Example 1.

Fig. 2 is a performance decay comparison of a platinum/graphene catalyst for a proton exchange membrane fuel cell and a platinum/XC-72 catalyst obtained in Example 3 and Comparative Example 1.

Detailed ways

The following examples help to further illustrate the present invention in detail, but should not be construed as limiting the scope of the present invention.

(Du Pont公司)溶液，超声分散于1ml去离子水中。移取6μl滴于玻碳电极表面，室温干燥。测试前先在浸入三电极的硫酸体系中通入氩气半小时，以50mV/s的扫描速率在-0.2V到0.8V(SCE)区间内进行多次循环伏安扫描，直至曲线稳定，并将其转化为相对于标准氢电极(SHE)的数值。电化学稳定性测试也在该三电极体系中完成。对体系进行扫描至稳定，以50mV/s的速率扫描3000次。对每次循环伏安数据计算得到相应的电化学活性表面积。The method for detecting the electrochemically active surface area and stability of a platinum/graphene catalyst used in a proton exchange membrane fuel cell obtained in the present invention is completed by performing a cyclic voltammetry test in a standard three-electrode system. A platinum wire was used as the counter electrode, a saturated calomel electrode (SCE) was used as the reference electrode, a glassy carbon electrode with a diameter of 3 mm was used as the working electrode, and the electrolyte was 0.5 mol/L sulfuric acid solution. The test is carried out on the CH50A (Shanghai Chenhua Company) system. The specific operation process is: accurately weigh 5mg of catalyst powder, add 50μl of 5wt%

(Du Pont Company) solution, ultrasonically dispersed in 1 ml deionized water. Pipette 6 μl drops on the surface of the glassy carbon electrode and dry at room temperature. Before the test, argon gas was passed through the sulfuric acid system immersed in the three electrodes for half an hour, and multiple cyclic voltammetry scans were performed in the range of -0.2V to 0.8V (SCE) at a scan rate of 50mV/s until the curve was stable, and This is converted to a value relative to a standard hydrogen electrode (SHE). Electrochemical stability tests were also done in this three-electrode system. Scan the system until it is stable, and scan 3000 times at a rate of 50mV/s. The corresponding electrochemically active surface area was calculated for each cyclic voltammetry data.

Embodiment 1. sodium borohydride reduction method

Get graphite oxide and ultrasonically disperse it in deionized water to form 2g of 0.45wt% graphite oxide dispersion, add 2.66mg of chloroplatinic acid and mix evenly, so that the loading of platinum in the platinum/graphene catalyst is 10wt%. Adjust the pH value to 9 with 0.5M potassium hydroxide aqueous solution, add 0.16g sodium borohydride and 5g deionized water, reduce for 1 hour, then filter with suction, wash with deionized water, and dry at 100°C for 6 hours to obtain a proton exchange Platinum/graphene catalysts for membrane fuel cells. The electrochemically active surface area results are listed in Table 1.

Embodiment 2. Sodium borohydride reduction method

Graphite oxide was ultrasonically dispersed in deionized water to form 16g of a 0.05wt% graphite oxide dispersion, and 5.31mg of chloroplatinic acid was added and mixed uniformly so that the loading of platinum in the platinum/graphene catalyst was 20wt%. Adjust the pH value of the mixture to 10 with 4M potassium hydroxide aqueous solution, add 0.64g sodium borohydride and 10g deionized water, reduce for 2 hours, then filter with suction, wash with deionized water, and dry at 60°C for 24 hours to obtain a proton Platinum/graphene catalysts for exchange membrane fuel cells. The electrochemically active surface area results are listed in Table 1.

Embodiment 3. Sodium borohydride reduction method

Graphite oxide was ultrasonically dispersed in deionized water to form 10 g of a 0.08 wt % graphite oxide dispersion, and 5.31 mg of chloroplatinic acid was added and mixed uniformly so that the loading of platinum in the platinum/graphene catalyst was 20 wt %. Adjust the pH value to 10 with 1M potassium hydroxide aqueous solution, add 0.4g sodium borohydride and 5g deionized water, reduce for 4 hours, then filter with suction, wash with deionized water, and dry at 80°C for 12 hours to obtain a proton exchange membrane Platinum/graphene catalysts for fuel cells. The results of the electrochemically active surface area are listed in Table 1, the cyclic voltammetry test results of the initial electrochemical activity and electrochemical activity after cycling are shown in Figure 1, and the performance decay of the catalyst is shown in Figure 2.

Table 1 and Figure 1 illustrate the initial electrochemical activity of the platinum/XC-72 catalyst and the platinum/graphene catalyst and the electrochemical activity after 3000 cycles, wherein the initial value of the electrochemically active surface area of the platinum/XC-72 catalyst is 54.94 m ² /g, 30.26m ² /g after circulation, the initial value of the electrochemically active surface area of the platinum/graphene catalyst is 47.54m ² /g, and 38.8m ² /g after circulation, it can be seen that the platinum/graphene catalyst is in circulation with higher electrochemical activity.

Fig. 2 illustrates that although the initial electrochemically active surface area of the platinum/graphene catalyst prepared by the present invention is smaller than the platinum/XC-72 catalyst, it has higher stability in 3000 cyclic voltammetric test operations, platinum/graphene The catalyst meter decays by 18.4%, while the platinum/XC-72 catalyst performance decays by 44.5%, indicating that the platinum/graphene catalyst is more suitable for proton exchange membrane fuel cells.

Embodiment 4. sodium borohydride reduction method

Graphite oxide was ultrasonically dispersed in deionized water to form 12g of a 0.05wt% graphite oxide dispersion, and 10.62mg of chloroplatinic acid was added to mix evenly, so that the loading of platinum in the platinum/graphene catalyst was 40wt%. Adjust the pH value to 13 with 1M potassium hydroxide aqueous solution, add 0.64g sodium borohydride and 5g deionized water, reduce for 18 hours, then filter with suction, wash with deionized water, and dry at 80°C for 12 hours to obtain a proton exchange membrane Platinum/graphene catalysts for fuel cells. The electrochemically active surface area results are listed in Table 1.

Embodiment 5. sodium borohydride reduction method

Get graphite oxide and ultrasonically disperse it in deionized water to form 4g of 0.1wt% graphite oxide dispersion, add 15.93mg of chloroplatinic acid and mix evenly, so that the loading of platinum in the platinum/graphene catalyst is 60wt%. Adjust the pH value to 10 with 4M potassium hydroxide aqueous solution, add 0.64g sodium borohydride and 7.5g deionized water, reduce for 4 hours, then filter with suction, wash with deionized water, and dry at 80°C for 18 hours to obtain a proton exchange Platinum/graphene catalysts for membrane fuel cells. The electrochemically active surface area results are listed in Table 1.

Embodiment 6. Ethylene glycol reduction method

Graphite oxide was ultrasonically dispersed in ethylene glycol to form 16g of a 0.05wt% graphite oxide dispersion, and 5.31mg of chloroplatinic acid was added to mix evenly, so that the loading of platinum in the platinum/graphene catalyst was 20wt%. Adjust the pH value to 9 with 0.5M potassium hydroxide ethylene glycol solution, reduce at 90°C for 3 hours, then filter with suction, wash with deionized water, and dry the product at 100°C for 6 hours to obtain a proton exchange membrane fuel cell. platinum/graphene catalyst. The electrochemically active surface area results are listed in Table 1.

Embodiment 7. Ethylene glycol reduction method

Get graphite oxide and ultrasonically disperse it in ethylene glycol to form 1g of 0.4wt% graphite oxide dispersion, add 15.93mg of chloroplatinic acid and mix evenly, so that the loading of platinum in the platinum/graphene catalyst is 60%. Adjust the pH value to 13 with 4M potassium hydroxide ethylene glycol solution, reduce at 150°C for 12 hours, then suction filter, wash with deionized water, and dry the product at 80°C for 24 hours to obtain a proton exchange membrane fuel cell. Platinum/graphene catalyst. The electrochemically active surface area results are listed in Table 1.

Comparative example 1

The catalyst used in the comparative example is the commercial platinum/carbon catalyst of E-TEK Company, and its carrier is XC-72, and the platinum loading is 20wt%. The cyclic voltammetry test results of chemical activity and electrochemical activity after cycling are shown in Figure 1, and the performance decay of the catalyst is shown in Figure 2.

Table 1

Example carrier Platinum loading (wt%) reducing agent PH value Recovery time (h) Electrochemical active surface area (m ² /g) 1 Graphene 10 Sodium borohydride 9 1 7.6 2 Graphene 20 Sodium borohydride 10 2 11.8

Example carrier Platinum loading (wt%) reducing agent PH value Recovery time (h) Electrochemical active surface area (m ² /g) 3 Graphene 20 Sodium borohydride 10 4 47.5 4 Graphene 40 Sodium borohydride 13 18 50.8 5 Graphene 60 Sodium borohydride 10 4 62.4 6 Graphene 20 Ethylene glycol 9 3 13.8 7 Graphene 40 Ethylene glycol 13 12 45.3 Comparative example 1 XC-72 20 - - - 54.5

Claims (1)

1. a kind of preparation method of platinum/graphene catalyst for proton exchange membrane fuel cell, it is characterized in that preparation method is as follows, below all represent with mass parts: A. Sodium borohydride reduction method: Ultrasonically disperse graphite oxide in deionized water to form 1000-20000 parts of graphite oxide dispersion of 0.05wt%-1wt%, add 2.66-15.93 parts of chloroplatinic acid and mix evenly to make platinum in platinum/ The loading in the graphene catalyst is 10wt%-60wt%, adjust the pH value to 9-13 with 0.5M-4M potassium hydroxide aqueous solution, add 160-640 parts of sodium borohydride and 5000-10000 parts of deionized water, and reduce 1- 18 hours, then suction filtered, washed with deionized water, and dried at 60-100°C for 6-24 hours to obtain a platinum/graphene catalyst for proton exchange membrane fuel cells; Or B. ethylene glycol reduction method: get graphite oxide and ultrasonically disperse it in ethylene glycol to form 1000-20000 parts of graphite oxide dispersion liquid of 0.05wt%-1wt%, add 2.66-15.93 parts of chloroplatinic acid and mix evenly, make platinum in The loading of the platinum/graphene catalyst is 10wt%-60wt%, and the pH value is adjusted to 9-13 with 0.5M-4M potassium hydroxide ethylene glycol solution, reduced at 90-150°C for 3-12 hours, and then suction filtered, and washing with deionized water, and drying the product at 60-100° C. for 6-24 hours to obtain a platinum/graphene catalyst for proton exchange membrane fuel cells.

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