Spatially Resolved Current Density and Electrochemical Impedance Spectroscopy in PEM Fuel Cells

ABSTRACT The durability and efficiency of proton exchange membrane fuel cells (PEMFC) are crucial for their deployment in heavy‐duty applications. The membrane‐electrode assembly (MEA) of a PEMFC plays a central role and can be characterized using in situ methods like polarization curves, current density mapping, and electrochemical impedance spectroscopy (EIS). In medium‐sized to large cells, inhomogeneous conditions often occur across the active area. Segmented current‐density measurement boards enable spatially resolved analysis of current density and temperature, and with additional electronics, also spatially resolved EIS. This allows detailed investigation of membrane resistance, diffusion, charge transfer, and proton transport across the cell surface. In this study, current‐density distribution under various operating conditions and spatially resolved EIS measurements were performed on an automotive‐sized PEMFC. The results show a significant influence of the membrane humidification state on the local performance. Higher humidity, pressure, and stoichiometry improve the homogeneity of the current density distribution. The spatially resolved EIS reveals increasing impedance values from the cathode inlet to the outlet. Equivalent circuit fitting enabled assigning resistances to physical processes and mapping their distributions across the active area. These findings are crucial for a deeper understanding of local operating phenomena in automotive‐sized fuel cells.