Effects of Cathode Inlet Relative Humidity on PEMFC Durability during Startup-Shutdown Cycling II. Diagnostic Study

Abstract

This paper uses a variety of physicochemical methods to elucidate the mechanism by which cathode inlet relative humidity (RH) degrades a proton exchange membrane fuel cell (PEMFC) during startup-shutdown cycling. The results revealed that the pronounced Pt coarsening (agglomeration)/oxidation/dissolution (detachment) and migration were observed along with corrosion of the carbon support at the majority of cathode catalyst layers when PEMFCs were exposed to a higher cathode inlet RH during 1500 startup-shutdown cycles. These changes contributed to the significant loss of Pt mass available for electrochemical reactions and an active Pt surface area at the cathode, thus decaying the performance of the fuel cell. In addition, the rate of these multiple processes was RH-dependent. However, the degradation at the anode and membrane was not as severe as those observed at the cathode and did not show any dependence on the cathode inlet RH. Based on these results, a modified mechanism for the degradation of the cathode catalyst layer during startup-shutdown cycling of PEMFCs is proposed to explain the effects of RH on fuel cell performance and durability.