Performance of sputter-deposited platinum cathodes with Nafion and carbon loading for direct methanol fuel cells

One of the difficulties for a direct methanol fuel cell (DMFC) is low catalyst utilization efficiency because a certain amount of Pt loading is inactive as the catalyst. Sputter-deposited Pt electrodes are expected to improve mass activities for oxygen reduction reaction (ORR) compared with those prepared by a conventional method. Meanwhile, mass activities of sputter-deposited Pt cathodes for the ORR decreased with an increase in amount of Pt loading. In this study, the loading of protonic and electronic conductors to improve mass activities of sputter-deposited Pt electrode were investigated as cathodes for DMFCs. Cathodes prepared by spreading the mixture of Nafion, carbon and butyl acetate (NCB) solution on sputter-deposited Pt showed an increase in current densities and mass activities for the ORR. These may suggest an increase in catalyst active sites. Moreover, results of AC impedance analysis showed a decrease in charge transfer resistance and an increase in double layer capacitance for a sputter-deposited Pt cathode with NCB spread. Consequently, effects of NCB on cathodic polarization were explained by supplying protonic and electronic conduction paths to electrochemically inactive Pt with the oxygen diffusion path maintained. Mass activities were found about fifteen times higher than a Pt/C cathode prepared by a conventional method.