Study On Sol-gel Flux Phase And Mass Transmission Process In Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) was considered to be the most potential mobile power sources of the automobile and other vehicles due to its outstanding advantages. However, methanol crossover from the anode to the cathode through the proton exchange membrane is one of the most critical barriers to the commercialization of DMFC, and this caused the waste of the fuel and the decline of the cell performance. For this problem, scholars at home and abroad had focused their research priority on it.Aimed at the methanol crossover in liquid feed DMFC, the paper proposed to change the fuel form that use the sol-gel methods to prepare the sol-gel flux phase to replace the traditional liquid flux phase.The preparation technics of sol-gel flux phase were studied in the paper, and the flux phase was prepared successfully for the first time. The proton conductivity of sol-gel flux phase and liquid flux phase were measured, and the conductivity of sol-gel flux phase equivalent to liquid flux phase. The methanol permeabilities of sol-gel flux phase and liquid flux phase were tested, the results showed that the methanol permeabilities of sol-gel flux phase was declined about 90% than liquid flux phase, this indicated that using sol-gel flux phase can prevent the methanol crossover effectively.For the high viscosity, the fluidity of the sol-gel flux phase was very poor, it can’t apply in the traditional planar type DMFC with the complicated narrow flow channels, so a group of tubular special-shaped direct methanol fuel cells (SDMFC) were prepared and the cell performances using sol-gel flux phase were studied. The impedance of sol-gel flux phase SDMFCs were tested, because of the special structure, their impedances were bigger than planar type DMFC which date was reported in documents. The effects of bube wall thickness, working temperature, flow rate of oxygen, loading of the diffusion layer and viscosity of the sol-gel flux phase on cell performance were studied by polarization curves and power density curves, and got the best numerical value of these parameter, and the highest power density of the sol-gel flux phase SDMFC was about 11.5mW/cm2 in this study. The discharge stability of the sol-gel flux phase SDMFC was researched, the cell potential keep steady after 10 hours discharge.After the methanol, water, proton and electron transfer process in flux phase were researched, a single dimension model perpendicular to MEA was established. Methanol and water transfer process were described, include methanol diffuse in flux phase, anode diffusion layer, anode catalyst layer and Nafion membrane, water diffuse in catalyst layer and Nafion membrane, methanol electrochemical oxidation in catalyst layer, and proton and electron transfer process.