A palladium-alloy deposited Nafion membrane for direct methanol fuel cells

The problem of methanol crossover through Nafion membranes is one of the challenges in the application of direct methanol fuel cells (DMFCs). In order to reduce methanol crossover, the Nafion membrane is modified by sputtering a thin layer of Pt/Pd–Ag/Pt on its surface in the present study. The modified membrane was characterized using scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD), and time-of-flight secondary ion mass spectroscope system (TOF-SIMS). The characterization indicates that sputtering over the surface of Nafion polymer can successfully form an alloy layer of Pt/Pd–Ag/Pt although it is not crack-free. In applying the modified membrane (Pt/Pd–Ag/Pt/Nafion) to a 5 cm2 single cell of DMFC, it is found that this new membrane is effective in reducing methanol crossover in the cell and gives a higher cell performance than that of a single Nafion membrane. Among the three modified Nafion 117 membranes having 0.1, 0.2, and 1 μm of sputtering Pd–Ag film, the 1 μm thick film gives the highest performance. The results also show that the performance of the fuel cell with 1 μm sputtering Pd–Ag film on the Nafion membrane is higher than that of cell with Nafion membrane having catalyst loading twice as high.