Operando Three-Electrode Analysis of Nafion-Based Polymer Electrolyte Membrane Water Electrolyzers – Thermodynamic Relations

Polymer electrolyte membrane water electrolyzers (PEMWEs) offer clean hydrogen production when coupled to renewables, requiring minimal overvoltages for efficient operation. This study adapts and improves upon a three-electrode configuration utilized in fuel cell and electrolyzer technologies for comprehensive in operando thermodynamic analyses of PEMWE operation by accounting for the impact of catalyst layer dimensions and alignment. Catalyst-coated membrane Nafion N117-based cells with precise dimensions were developed, with design tolerances determined using finite-element simulations and verified by microscopic imaging. An external membrane strip connected to a Ag/AgCl reference electrode in acid solution enabled three-electrode electrochemical analyses of model platinum on Vulcan carbon and IrO2 catalysts in PEMWEs with minimal artifacts. This design enabled thermodynamic analysis and indicated cathodic and anodic contributions to the cell voltage. Under 1 atm hydrogen, liquid-fed conditions, the cathode exhibited non-negligible voltage contributions attributed to hydrogen transport processes, while charge transport in the anode accounted for ca. 15% of the series resistance. Above 1 A cm–2, the cathode became the main polarization resistance while the anode exhibited a low frequency inductive response. This work provides critical insights into PEMWE operation and methods for in operando analyses.