Influence of the Molecular Structure on the Properties and Fuel Cell Performance of High Temperature Polymer Electrolyte Membranes

Aromatic polysulfones containing 2,5-bis(4-hydroxyphenyl) pyridine, or tetramethyl-biphenyl-diol units or 2,5-bis(4-methyl phenyl)-hydroquinone have been synthesised employing various comonomers' ratios. The resulting soluble high molecular weight copolymers were thoroughly investigated as potential electrolytes for high temperature PEM fuel cells. Excellent film forming properties, mechanical integrity, as well as high thermal and oxidative stability were confirmed for all the polymeric materials. The above characteristics, in combination with the high phosphoric acid doping level which results in conductivities in the range of 10-2 S cm-1, enabled the use of these poylelctrolytes as the proton conducting membranes in fuel cells operating at temperatures up to 200°C. A discussion on the effect of the chemical structure on the membranes' properties and fuel cell performance is herein presented.