Pt/C catalyst degradation in proton exchange membrane fuel cells due to high-frequency potential cycling induced by switching power converters

Abstract

Proton exchange membrane fuel cells are operated using switching power converters that produce high-frequency ripple currents. These ripples cause high-frequency potential cycling of cells, which is believed to lead premature deterioration in the electrochemical surface area (ECA) of Pt/C catalysts. The qualitative relationship between ECA losses and the frequency of potential cycling was investigated in the range of 1 Hz to 1 kHz. For frequencies higher than 100 Hz, ECA losses were comparable with those at the potential hold condition. However, for lower frequencies, ECA decreased significantly with decreasing frequency. TEM observations showed that there was marked Pt particle growth for the 1-Hz cycling condition, whereas particle size distributions at 100 Hz and potential hold conditions were comparable. The currents associated with Pt oxidation and reduction during potential cycling were also investigated at various potentials and frequencies, and the charges associated with Pt loss (Δ Q) were determined by integrating the measured current. A correlation between the ECA trend and Δ Q was observed. The results obtained in this study are considered informative for electrical engineering research, because it relates to the design of switching power converters that do not negatively influence the Pt/C catalyst durability.