Pd and Pd-Cu Alloy Deposited Nafion Membranes for Reduction of Methanol Crossover in Direct Methanol Fuel Cells

To reduce methanol crossover in direct methanol fuel cells (DMFCs), Nafion 115 membrane was modified by sputtering a thin layer of Pd or a thin layer of Pd-Cu (60:40) alloy. The sputtered membranes were characterized by using a scanning electron microscope, an energy-dispersive X-ray spectrometer, and X-ray diffraction analysis. At room temperature, the modified membranes showed significant improvements in both the open-circuit voltage (OCV) and cell performance as compared with the bare Nafion 115 membrane; and Pd-sputtered membrane performed better than the Pd-Cu-sputtered membrane in OCV and cell performance. The methanol permeation rate studied by the voltammetric method in a DMFC configuration under the open-circuit condition indicated that the improvements in the cell performance occurred because the methanol crossover was lower with the modified membranes than with the bare membrane. At a higher cell operating temperature (70°C), the Pd-sputtered membrane showed higher OCV and higher performance only at low current densities, but the performance was found to decline at high current densities. It was also found that at this higher temperature operation, the Pd-Cu-sputtered membrane at high current densities exhibited a better performance than the bare Nafion 115 membrane did.