Decomposition mechanism of perfluorosulfonic acid electrolyte in polymer electrolyte fuel cells

Decomposition behavior of perfluorosulfonic acid (PFSA) electrolytes caused by the crossover of H2 or O2 in PEFCs was evaluated at 80 °C with a newly proposed method. Two gas-diffusion electrodes, consisting of Pt catalysts supported on carbon black and Nafion® ionomer, were mounted in a fuel cell housing with and without Nafion® membrane. Mixed gas of H2 and air with a constant composition was supplied to the cell, simulating crossover to an anode or a cathode. The F− emission rates increased with increasing the relative humidity in both H2-rich and O2-rich conditions, probably due to the enhanced penetration of H2O2, and/or the relating radical in swollen electrolyte. It was found that an appreciable fraction of H2O2 or OH radical was easily scavenged at Pt particles in the catalyst layer or in the Pt-dispersed Nafion®, resulting in the suppressed F− emission rates. Degradation mechanism of PFSA electrolytes was discussed.