Hydrogen oxidation on graphene-covered Pt(111) electrodes

Membrane-coated electrocatalysts offer a promising solution for current challenges in electrocatalysis, such as the susceptibility of the hydrogen oxidation reaction (HOR) to impurities. However, the understanding of how such coatings influence electrochemical processes remains limited. In this study, we present graphene-covered Pt(111) as a model system to investigate these effects. Graphene, known for its chemical stability and tunability, serves as a representative membrane, while Pt(111) is a well-known HOR catalyst that provides a useful comparison. The defect density in the graphene was systematically varied electrochemically and quantified using a proton-permeation resistance, measured with electrochemical impedance spectroscopy. We found that significant HOR activity is only obtained beyond a critical defect density. This suggests that molecular hydrogen permeation requires larger defect structures compared to atomic-scale defects that facilitate proton transport. Beyond this critical defect density the limitation of H 2 mass transport is also observed. We also show evidence that multi-layer graphene structures do not allow for effective HOR. Additionally, we observed a potential-dependent change in catalytic performance: cycling below 1.0 V led to a decrease in HOR current, while cycling to more positive potentials led to an increase. We attribute this behavior to potential-induced structural changes in the graphene layer. This study thereby highlights the importance of understanding the dynamic behavior of catalyst coatings in relation to their catalytic performance.