Approaches and technical challenges to high temperature operation of proton exchange membrane fuel cells

Water loss and the coincident increase in membrane resistance to proton conduction are significant barriers to high performance operation of traditional proton exchange membrane fuel cells at elevated temperatures where the relative humidity may be reduced. We report here approaches to the development of high temperature membranes for proton exchange membrane fuel cells; composite perfluorinated sulfonic acid membranes were prepared to improve water retention, and non-aqueous proton conducting membranes were prepared to circumvent the loss of water. Experimental results of composite membranes of Nafion and zirconium phosphate show improved operation at elevated temperatures. Imidazole impregnated membranes poisoned the electrocatalysts. Cesium hydrogen sulfate membranes were not able to produce appreciable current. A brief analysis of temperature requirements for CO tolerance and a framework for understanding water loss from fuel cell membranes are presented.