Effect of PEFC operating conditions on the durability of sulfonated poly(arylene ether sulfone ketone) multiblock membranes

► Current densityaffects the durability of multiblockcopolymer membranes in PEFCs. ► Lower current densities (LCD) accelerated the degradation of the membranes. ► The amounts of sulfate ions in the drain water were an indicator of the degradation. ► LCD operation accelerated catalyst binder degradation. ► LCDaccelerated catalyst poisoning, resulting in decreased catalytic mass activity. The durability of a membrane-electrode assembly based on a sulfonated poly(arylene ether sulfone ketone) (SPESK) multiblock copolymer membrane having highly sulfonated hydrophilic blocks was evaluated at various cell currents in a polymer electrolyte fuel cell. The electrochemical properties and drain water collected from the anode and cathode were monitored during the test, followed by post-test analyses of the membrane. With a lower current test, the percentage remaining of the original weight-averaged molecular weight ( M w) orig of the SPESK membranes after the test decreased, and the sulfate ion release rate increased. In addition, the mass activity, evaluated from the current–potential ( I– E) curves and oxide formation charge current ( Q oxide) determined from cyclic voltammograms on the cathode were found to decrease with the lower current test. Fluoride ions originating from the catalyst layer were also detected in the drain water. There were greater amounts of fluoride ion with the lower current tests, similar to the case for the sulfate anion. Thus, it was concluded that the electrolyte binder in the catalyst layer was degraded. The effect of low current density may be associated with high cathode potential.