Abstract: Optimization of direct methanol fuel cell(DMFC) temperature and flow rate can effectively prevent cathode “flooding”, reduce the adverse effects of methanol crossover on cathode reaction, therefore, it is critical to improve the performance of DMFC. In this paper, we reduced the cathode catalyst loading to strengthen electrochemical polarization of DMFC cathode oxygen reduction reaction, and measured polarization curves and electrochemical impedance under different operating conditions. Moreover, an improved equivalent circuit model LR(CR)(QR(LR)) is built to fit the measured spectrum to analyze the effect of operating parameters such as temperature, air flow rate, methanol flow rate on the cathode electrochemical reaction and mass transfer polarization process of DMFC under the full cell conditions. The results show that: increasing temperature will lead to more methanol to permeate to the cathode, and increase the charge transfer resistance of cathodic oxygen reduction reaction; and only using the high air flow can effectively prevent cathode flooding, and improve oxygen mass transfer to the catalyst; appropriately increasing the flow of methanol can promote the electrochemical reaction of DMFC, but the excessive flow of methanol may lower electrode surface temperature, increase penetration of methanol, therefore adversely affect oxygen reduction reaction.

Key words: Direct methanol fuel cell(DMFC), Low loading catalyst, Electrochemical impedance spectroscopy(EIS), Polarization, Oxygen reduction reaction(ORR)