Operando Three-Electrode\nAnalysis of Nafion-Based\nPolymer Electrolyte Membrane Water Electrolyzers – Thermodynamic\nRelations

Polymer electrolyte membrane water electrolyzers (PEMWEs)\noffer\nclean hydrogen production when coupled to renewables, requiring minimal\novervoltages for efficient operation. This study adapts and improves\nupon a three-electrode configuration utilized in fuel cell and electrolyzer\ntechnologies for comprehensive <i>in operando</i> thermodynamic\nanalyses of PEMWE operation by accounting for the impact of catalyst\nlayer dimensions and alignment. Catalyst-coated membrane Nafion N117-based\ncells with precise dimensions were developed, with design tolerances\ndetermined using finite-element simulations and verified by microscopic\nimaging. An external membrane strip connected to a Ag/AgCl reference\nelectrode in acid solution enabled three-electrode electrochemical\nanalyses of model platinum on Vulcan carbon and IrO<sub>2</sub> catalysts\nin PEMWEs with minimal artifacts. This design enabled thermodynamic\nanalysis and indicated cathodic and anodic contributions to the cell\nvoltage. Under 1 atm hydrogen, liquid-fed conditions, the cathode\nexhibited non-negligible voltage contributions attributed to hydrogen\ntransport processes, while charge transport in the anode accounted\nfor ca. 15% of the series resistance. Above 1 A cm<sup>–2</sup>, the cathode became the main polarization resistance while the anode\nexhibited a low frequency inductive response. This work provides critical\ninsights into PEMWE operation and methods for <i>in operando</i> analyses.