Electrochemical characterization of Pemion®-based PEM electrolyzer with low precious group metal loadings

Membrane-electrode-assemblies (MEAs) designed with hydrocarbon membranes and ultra-low PGM loadings in the catalyst layers (CLs) are essential to improve the cost efficiency of incumbent proton exchange membrane water electrolyzers (PEMWEs). In this work, we investigated the influence of anode and cathode PGM loadings on the electrochemical performance of single-cell MEAs fabricated with a hydrocarbon Pemion® membrane. Cell performance was evaluated using polarization and electrochemical impedance spectroscopy measurements under steady-state electrolysis conditions. Potentiostatic and galvanostatic impedance measurements were analyzed with an equivalent circuit model (ECM) and distribution of relaxation times (DRT) to identify and deconvolute the resistance contributions. Increasing iridium loading at the anode catalyst layer improved the PEMWE cell performance through enhanced oxygen evolution reaction (OER) kinetics. At the cathode catalyst layer, platinum loading was varied using two configurations: (i) fixed Pt/C ratio, which resulted in varying CL thickness, and (ii) variable Pt/C ratio, achieved by dilution with a high surface area Ketjen Black, to maintain a constant CL thickness. Cathodes with variable thickness exhibited increased resistive losses as platinum loading was reduced, dominated by interfacial contact and mass transport losses. However, when the cathode CL thickness was maintained, cell performance was largely insensitive to platinum loading. This work provides insights into the electrochemical response of fluorine-free hydrocarbon PEMs to variations in the anode and cathode catalyst loadings and highlights that optimization of the catalyst layer structure can enable ultra-low PGM loadings in the cathode CL without compromising PEMWE performance.