The Direct Methanol Fuel Cell Stability Study

Direct methanol fuel cell (DMFC) is gaining more and more attention due to its advantages of high power density, mild operating condition, convenience of fuel storage and environment friendly. It becomes an ideal candidate for portable power sources, such as in personal digital assistant devices, cellular phones and notebook computers. In this paper, the lifetime of DMFC was investigated to understand the correlation between the structure of catalysts/membrane and cell performance versus time. Forthurmore, the method for restoring the performance loss during lifetime test was explored. Therefore, the works in this paper have great meaning in prolonging the cell lifetime, decreasing the cell cost and promoting the cell commercialization.Electrochemical impedance spectroscopy (EIS) has been widely used in fuel cells impedance analysis. However, for ohmic resistance (RΩ), EIS has the disadvantages such as long test period, complex data analysis with equivalent circuit. Therefore, the current interruption method was firstly explored to measure the RΩof direct methanol fuel cell (DMFC) at different temperature and current density. This RΩvia the current interruption is consistent with that via EIS and the deviation between them is small. It can be concluded that the current interruption method, for its advantages of much shorter test period and more straightforward data analysis, is a more suitable method to measure ohmic resistance in DMFC.The lifetime is one of the main problems which hinder the commercialization of DMFC. In the study, the reasons of performance loss were thoroughly analysed. Amony the analysis, the electrochemical methods (polarization curves, EIS, current interruption method) and physicochemical methods (X-ray Diffraction, Transmission Electron Microscope, ATR-IR, Energy Dispersive X-ray Detector and scanning electron microscope) were adopted. The results revealed that after the DMFC lifetime test, there were significant performance degradation; the particle size of electrocatalysts increased both in anode and cathode, and the degree was higher in cathode; Dissolution of Ru was found after lifetime test. Furthermore, the degradation of membrane was analysed by combining current interruption method and ATR-IR.In the end of the paper, cyclic voltammetry (CV) was conducted to oxidize CO, absorbed on catalysts in a direct methanol fuel cell (DMFC), for mitigating performance loss. The results show that after the scanning of cathode and anode with CV, the performance of DMFC is improved considerably.