Preparation And Activity Test Of The Cathodic Catalyst In Proton Exchange Membrane Fuel Cell

Energy crisis becomes more serious with the development of industry, therefore, many new kinds of energy sources have been studied recently. Proton exchange membrane fuel cell (PEMFC) is a new kind of energy device being widely researched due to its many advantages, such as high energy density, high energy conversion efficiency and low emission of pollutant. It can be used as power source in the transports or the portable electronic devices. While it can not be used widely due to the addition of noble metal in the PEMFC. The studies on PEMFC catalysts with low cost, high efficiency and high stability become focus by researches.Oxygen reduction reaction (ORR) occurs at the cathode of PEMFC. The catalyst for ORR is used on the cathode of PEMFC. Pt, as the most active pure metal catalyst for ORR, its catalytic activity can be much improved by the addition of another transition metal. In this paper, Green Synthesis preparation of alloy nanoparticles of Pt and Pd is made using glucose as reducing agent and starch as dispersing agent. The as-prepared Pt-Pd nanoparticles are loaded on the surface of active carbon to obtain the Pt-Pd/C catalyst used for ORR.UV-Vis spectrum is used to study the change of metal ion in the reaction solution for the synthesis of metal nanoparticles. The time needed to finish the experiment of synthesizing metal nanoparticles is determined by the UV-Vis spectrum curves. The influence of Glucose solution with different concentration on the metal nanoparticles is discussed in the paper. The finding indicates that the larger the concentration, the faster the reaction rate is. Two kinds of starches are used to synthesize nanoparticles. The dispersing effect of No.l starch with higher relative molecular mass is better than No.2 starch. Provided that the starches meet the need of the minimum concentration to realize the dispersing nanoparticles, the lower the concentration, the better the dispersing effect is.High-resolution transmission electron microscope (HRTEM) images show that Pt-Pd nanoparticles prepared using No.1 starch disperse uniformly on the carbon, while Pt-Pd nanoparticles prepared using No.2 starch aggregate obviously on the carbon. The metal mass ratio in the catalyst is determined by thermogravimetric analysis (TGA). The highest metal mass ratio in the catalyst reaches to about 30%. The real metal mass ratio is nearly 20% measured by TGA for the catalysts with theory metal mass ratio of 20%. Pt-Pd nanoparticles have the same face centered cubic crystal structure as Pt.Cyclic votammetry is used to measure the catalytic activity for ORR of the catalysts prepared by the Green Synthesis. The comparison between half-wave potentials on the ORR curves of the as-prepared catalysts and commercial Pt/C with the same metal loading on the electrode shows that the catalytic activity for ORR of the catalyst with Pt:Pd=3:1 is slightly higher than that of commercial Pt/C, and the catalytic activity for ORR of the catalyst with Pt:Pd=1:1 is lower than that of commercial Pt/C. At 0.9 V (vs.RHE) on the ORR curves, both catalysts with Pt:Pd= 3:1 and Pt:Pd=1:1 have higher electrochemical surface area (ECSA) specific kinetic current density than commercial Pt/C, and both catalysts with Pt:Pd=3:1 and Pt:Pd=1:1 have higher Pt mass specific kinetic current density than commercial Pt/C. The catalyst with Pt:Pd=1:1 shows better ORR catalytic activity than that of commercial Pt/C in the presence of methanol. It means that the catalyst with Pt:Pd=1:1 is more suitable to be used as a cathode catalyst in direct methanol fuel cell. The results of this paper show that the cost of PEMFC can be decreased by the application of cathode catalyst of Pt-Pd/C nanoparticles.