Composite Electrocatalysts For Oxygen Reduction Of Cobalt - Polypyrrole - Carbon (Co-of PPy / C)

Direct methanol fuel cells (DMFCs) are one of the nearly commercialized fuel cells at present. Electrocatalysts are required to enhance the efficiency because of low temperature cell operation. Pt based catalysts supported on carbon are commonly used for low temperature fuel cells. However, the scarce and expensive Pt metal hinders the commercialization of fuel cells. Therefore, it's of great significance to develop low-cost non-precious metals as catalysts for fuel cell application.In recent years, conducting polymers(CPs) have attracted much attention as the high-performance non-platinum electrocatalysts or catalyst supports because of their high specific surface area, high electron conductivity as well as high stability. The non-precious metal cathode catalysts such as Co supported on CPs and carbon have demonstrated excellent activities and stability with promising prospect for practical application.In this thesis, cobalt-polypyrrole-carbon (Co-PPy/C) catalysts have been prepared for oxygen reduction reaction (ORR) in DMFCs. The effect of preparation parameters, such as polymerization temperature, oxidant catalyst and its usage and modified agent on the catalytic activity of ORR has been investigated. The results showed that the optimum preparation conditions are as follows: reaction temperature of 0℃, hydrogen peroxide as the oxidant catalyst, and CH₃COOH as the modified agent. The maximum peak current and peak potential of ORR over the optimum Co-PPy/C catalyst in O₂-saturated 0.5 mol·L^-1 H₂SO₄ solution are 2.563×10^-4 A and 0.1168 V, respectively.The effect of the loading contents of PPy and Co on the catalytic activities of Co-PPy/C catalysts has also been studied. The catalytic activity increased as the loading content of PPy increased until the PPy/C mole ratio reached 0.5, and then decreased. As for the loading content of Co, the best catalytic activity was obtained at a Co/N mole ratio of 0.4.The home-made Co-PPy/C and commercial PtRu/C catalyst were used as the cathode catalyst and the anode catalyst, respectively, to prepare MEAs and a single DMFC. The results of cell polarization testing showed that the current density at 0.4 V cell potential and the maximum power density were 80 mA·cm^-2 and 58.92 mW·cm^-2, respectively at the following operating conditions: methanol concentration of 2 M, methanol flow rate of 1mL·min^-1, oxygen flow rate of 100 mL·min^-1 and cell temperature of 60℃.