Spatially Resolved Electrochemical Impedance Spectroscopy of Automotive PEM Fuel Cells

Fuel cell electric vehicles (FCEVs), which use polymer electrolyte membrane fuel cells (PEMFCs), provide a prospect to add to a future of harmful-emission-free mobility. However, an in-depth understanding of degradation mechanisms and contributions to performance losses is needed to commercialize FCEVs further. Most previous PEMFC degradation research has focused on global indicators of the cell condition. Still, failure occurs typically due to inhomogeneities in production or operation, leading to localized regions of high degradation rates. Despite simulations indicating that local degradation effects are significantly more pronounced at larger scales, experimental studies only exist for small-sized laboratory fuel cells so far. Here, we present the results of a comprehensive study of spatial distributions of essential PEMFC parameters using electrochemical impedance spectroscopy across the cell surface of automotive-size fuel cells with an active area of 285 cm². In particular, the results reveal increasing mass transport problems with increasing distance from the air inlet and a tendency of lower proton resistances in the center of the cell. One hundred twenty realistic freeze-start cycles degenerated the cell performance drastically. The outer cell regions, subject to the lowest temperatures, showed the most substantial degradation rates, partly compensated by central cell regions with slightly higher temperatures. These findings bridge the gap between simulation and experiment and provide valuable insights for future fuel cell design and operating strategies.