An experimental and numerical study of spatial and temporal catalyst degradation during start-up and shut-down of PEM fuel cells

Degradation during start-up and shut-down (SUSD) of proton exchange membrane (PEM) fuel cells is investigated both experimentally and numerically. In order to understand spatial degradation, the local cell voltage and electrochemical surface area (ECSA) during SUSD are measured using a segmented cell. Novel phenomena such as undegraded inlet segments and a gradual rise in resting potential at the start of the test are hence observed. To further interpret the experimental data, an advanced SUSD model is developed, which accurately reproduces detailed experimental phenomena. The local potential is calculated independently based on the mixture gas concentration and kinetics, without imposing an artificial hydrogen/air interface, allowing for a more realistic transition of the membrane phase potential. The study shows that hydrogen has a greater influence on local membrane phase potential than air due to its faster reaction kinetics and residual hydrogen in inlet gas during SD can safeguard the inlet segments against degradation.