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. In traditional PEMFC setups with thin, reinforced membranes, the experimentally measured ohmic resistance (R_ohm) typically comprises contributions from contact resistances and high-frequency transport processes. Consequently, membrane thickness cannot be directly obtained as an independent resistance parameter in full-cell measurements. However, 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 assess the membrane-related resistance. Under well-defined and reproducible conditions, this approach enables the separation and quantification of membrane- and interface-related contributions to ohmic, charge-transfer, and mass transport contributions. 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 (R_total) increases with membrane thickness, the initial membrane insertion – rather than thickness alone – is the primary driver of R_ohm. Conversely, membrane thickness is the key factor governing charge-transfer resistance (R_ct), whereas mass-transport resistance (R_mt) 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.