Significantly enhanced performance of direct methanol fuel cells at elevated temperatures

The performance of direct methanol fuel cells (DMFCs) is constrained by the sluggish kinetics of methanol oxidation reaction. Increasing the temperature can effectively increase the methanol oxidation kinetics, offering new opportunities to achieve high performance. Here we studied the performance of DMFCs based on the newly developed silica impregnated phosphoric acid doped polybenzimidazole (PA/PBI/SiO2) composite membrane. The composite membrane shows a proton conductivity of 2.9-4.1 x 10(-2) S cm(-1) at temperatures between 200 and 250 degrees C and is stable at high temperatures. The cells using the composite membrane successfully delivered a peak power density of 136 mW cm(-2) and 237 mW cm(-2) at 260 degrees C using the Pt/C and PtRu/C as the anode catalysts, respectively. The cells with the PA/PBI/SiO2 composite membrane show a much higher power output than that with conventional PA/PSI membranes. Most importantly, the results demonstrate that there exists a distinct transition temperature around 205 degrees C for the performance of DMFCs. Above this transition temperature, the increase in power density with temperature is 208 mWcm(-2)/100 degrees C, which is more than 4 times higher than 50 mWcm(-2)/100 degrees C obtained at temperatures below 205 degrees C. The presence of such transition temperature for DMFCs is most likely due to the significantly enhanced kinetics of the methanol oxidation reaction at elevated temperatures. Operation at elevated temperatures, i.e., above 205 degrees C, is most effective to significantly enhance the power performance of DMFCs.