Degradation behavior of PEMFC MEA under load cycling and constant operation conditions

Abstract

Durability of automotive MEAs is usually studied using the FC-DLC protocol which corresponds to a test covering operation from OCV to high current densities. Hence, in such a test the impact of the different current density ranges on degradation is not distinguished. Therefore, in this study, individual degradation tests have been performed at low and high current density with and without additional cycling. The tests have been supported by current density distribution measurements to monitor local operation conditions and evaluate local degradation issues. Reversible as well as irreversible performance losses were studied by performing electrochemical analysis and subsequent ex-situ physico-chemical investigations. As degradation processes loss of proton conductivity and increase in charge transfer resistance was observed. ECSA losses were observed after all tests. Cycling at low current density leads to Pt dissolution and migration to the membrane. Interestingly, MEA areas exhibiting high local performance exhibit particularly high Pt concentration in the membrane. Under constant operation strong performance losses due to water management issues were observed associated to inhomogeneity of current density distribution along the flow field. Generally, cycling tests have shown lower degradation compared to constant current operation which is also linked to partial recovery of reversible degradation losses upon cycling conditions.