The Effect of Cathode Catalyst Layer Composition on Hydrogen Crossover and Performance in Anion Exchange Membrane Water Electrolysis

Abstract

A major challenge in AEM electrolysis is the undesired hydrogen permeation from the cathode to the anode—the so-called hydrogen crossover. Although this process has been thoroughly examined in proton exchange membrane (PEM) systems, the effect of the cathode catalyst layer composition on H2 crossover has not yet been systematically investigated in AEM systems. In this study, gas diffusion electrodes with cathode catalyst layer variations in platinum loading (0.3 vs 0.8 mgPt cm–2), the Pt content in Pt/C (20 vs 50 wt % Pt), and ionomer content (5–24 wt % PiperION) were tested to assess their effects. Varying the Pt/C content and loading in the cathode catalyst layer while keeping the ionomer content constant revealed a linear increase of the H2 crossover at 3 A cm–2 with increasing platinum loading density (Pt loading divided by the catalyst layer volume). Additionally, a 24 wt % PiperION ionomer binder provided the lowest HFR, Tafel slope, and H2 crossover, along with improved long-term stability. Increasing the PiperION ionomer content consistently reduces H2 crossover despite a decrease in void volume and porosity, which is attributed to the increased hydrophobicity of the cathode catalyst layer. Overall, the results indicate that a more hydrophobic cathode catalyst layer effectively suppresses the H2 crossover in AEM water electrolysis. Finally, the combination of 20 wt % Pt with 0.3 mgPt/cm2 and a high ionomer binder content (24 wt %) resulted in the lowest H2 crossover, demonstrating that cathode catalyst layer composition is a key lever for decreasing H2 crossover.