Influence of operating conditions on the degradation mechanism in high-temperature polymer electrolyte fuel cells

Abstract

The purpose of this study is to compare the degradation phenomena in high-temperature polymer electrolyte fuel cells (HT-PEFCs) under various operating conditions and investigate the degradation mechanism by using accelerated stress tests. Five stressors (i.e., high temperature, thermal cycling, open circuit voltage, high load cycling, and low load cycling) are applied to identical HT-PEFCs and compared to the standard operating condition. Extensive characterizations of the aged HT-PEFCs are then performed using techniques that include focused ion beam/scanning electron microscopy, inductively coupled plasma-mass spectrometry, energy dispersive X-ray mapping/line-scan analysis, polarization curves, electrochemical impedance spectroscopy and cyclic voltammetry. The results present a negligible amount of phosphoric acid leaching and notable degradation of the Pt/C catalyst. On the anode side, slight Pt corrosion is only visualized under open circuit conditions, while on the cathode side, evident Pt agglomeration in the catalyst layer and different Pt precipitation behaviors in the membrane are observed under all the conditions. The highest amount of Pt precipitation occurs in the cells held at open circuit voltage and cycled at low loads, which also exhibit the most pronounced performance degradation. In addition, the PA redistribution between the membrane and electrodes contributes to the cells’ resistance and performance differences.