Examination of Humidity Impact during 160˚C Catalyst Accelerated Stress Test for High-Temperature Ion-Pair Polymer-Based Fuel Cells

Abstract A catalyst accelerated stress test (AST) was conducted on high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs)at 160˚C to investigate the effects of humidification on platinum catalyst degradation in phosphoric acid-rich environments. Progression of Pt degradation was evaluated by quantifying relative changes in electrochemical surface area (ECSA), based on hydrogen adsorption and desorption peaks. Distribution of relaxation times (DRT) analysis was performed to monitor the evolution of phenomena-specific resistances. The results suggest that under dry conditions, phosphoric acid anhydride formation leads to reduced electrode proton conductivity and decreased catalytic active site accessibility. After 90,000 cycles, under both dry and 11% RH feed gas conditions, DRT peak analysis revealed increasing impedance centered around 100 Hz, which could be attributed to cathodic charge transfer resistance (CTR). However, only the dry condition also showed an increase in impedance in the 250 Hz region, which could be attributed to anodic CTR. DRT peak analysis revealed increased anodic and cathodic charge transfer resistance (CTR) after 90,000 cycles in dry conditions, whereas feed gas humidification at 11% relative humidity resulted in increased cathodic CTR only. Overall, larger voltage loss was observed for humidified cell vs. dry cell after 90,000 cycles, as well as higher ECSA loss indicating that humidified AST introduces larger stressors on the MEA during HT-PEMFC AST operation