Numerical modeling of the degradation rate for membrane electrode assemblies in high temperature proton exchange membrane fuel cells and analyzing operational effects of the degradation

Abstract

The numerical model of the degradation rate in high temperature proton exchange membrane fuel cells (HT-PEMFC) using phosphoric acid (PA) doped polybenzimidazole (PBI) membranes is developed and expressed as a semi-empirical relationship. The model accounts for the degradation factors in terms of activation, ohmic, and concentration over-potentials and the subsequent degradation rate for high temperature membrane electrode assemblies (MEAs). Furthermore, the model considers the operating temperature effects on the degradation rate, because the degradation rate is highly dependent on the operating temperature. The developed model is validated with HT-PEMFC polarization curves obtained by ourselves and with degradation data after long-term operations reported in the literature. The agreement between the model predictions and the experimental data is good. The model is used to investigate the effects of operating temperature, PA doping level, and inlet gas pressure on the HT-PEMFC initial performance and its degradation rate. The analysis suggests that the predicted lifetime and average performance for high temperature MEAs exhibit a trade-off by changing the operating temperature. In particular, the performance of an HT-PEMFC operated at higher temperature shows a slight degradation at first but a fast degradation rate later. The degradation at higher temperature is mainly caused by activation over-potential.