Electrochemical characteristics of acid electrolytes for fuel cells. Final report, January 1, 1989-June 30, 1991

The electrochemical evaluation of new perfluorinated fuel cell electrolytes provided by GRI contractors at Clemson and Iowa shows the kinetics for O2 reduction on Pt improves with these acids compared to with phosphoric acid. The improvement is mainly due to the lesser tendency of these acids to adsorb on Pt. Kinetics do not have a strong dependence on pH or O2 solubility when mass transport is not involved. Concentrated sulfonyl acids were usually found to wet Teflon resulting in the flooding of Teflon-bonded gas fed electrodes and poor performance at high current densities. These perfluorinated electrolytes were, however, found to be useful as performance enhancing additives to concentrated phosphoric acid in some cases. The alpha,omega-bis-phosphonic acid with a perfluoroethylene bridge gave superior performance compared to phosphoric acid at elevated temperatures (up to 200 degrees C) for 500 hours. Bis-phosphonic acids with higher CF2 to PO3H2 ratios dehydrated more readily at elevated temperatures, resulting in resistive voltage losses. New perfluorinated phosphonic acid containing olefins were found to be polymerizable. This suggests that with a reasonable synthetic effort, new kinds of ionomer membranes are attainable, and these may be superior to Nafion for fuel cell applications.