Electrochemical Impedance Spectroscopy-based Screening of Membrane Effects via Gas Diffusion Electrode Half-Cells for PEMFC Performance Optimization

Abstract

The widespread commercialization of polymer electrolyte membrane fuel cells (PEMFCs) is constrained by the performance and durability of the polymer electrolyte membrane, a critical bottleneck for gigawatt-scale technology. Although membrane thickness must be optimized to balance resistance and stability, conventional single-cell testing of full membrane electrode assemblies (MEAs) cannot isolate the membrane’s intrinsic contribution to overall cell resistance from complex electrode and interfacial effects. To overcome these limitations, this study employed a gas diffusion electrode (GDE) half-cell setup combined with electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis to directly resolve membrane-related resistivity. This methodology enables the separation and quantification of ohmic resistance (Rohm), charge-transfer resistance (Rct), and mass transport resistance (Rmt), providing a reproducible route to probe the membrane’s individual role under well-defined conditions. By comparing a GDE without membrane (true zero-thickness) as baseline to the extrapolated zero-thickness data, we quantify for the first time how membrane insertion itself reconfigures the catalyst layer (CL)/membrane interface, introducing a significant and fundamental baseline resistance. While our results confirm the established principle that total resistance (Rtotal) increases with membrane thickness, the initial membrane insertion - rather than thickness alone - is the primary driver of Rohm. Conversely, membrane thickness is the key factor governing Rct, whereas Rmt is fundamentally dictated by polymer chemistry and operating conditions. Beyond demonstrating the well-established GDE half-cell concept, this study establishes a quantitative, thickness-resolved framework for isolating and characterising membrane-induced resistances, offering mechanistic insights to guide rational membrane and electrode design for advanced PEMFCs.