Oxygen evolution reaction on Pt supported maghemite surfaces

Maghemite surfaces have recently emerged as promising materials for (electro)photo-catalytic applications, particularly in the context of the oxygen evolution reaction (OER). In this study, density functional theory (DFT) is applied to explore the mechanistic details of OER and its fundamental steps on the most stable maghemite layers grown on a Pt substrate. Our investigation reveals that the Pt substrate significantly influences the surface energetics, through both geometric and electronic effects. On the (001) surface, the geometry of Pt negatively affects the OER energetics. On the contrary, the inclusion of electronic effects facilitates the evolution of oxygen, however, energetics remains less favorable than on the free standing surface. A comparative analysis of the (001) and (111) maghemite surfaces demonstrates that both surfaces present a similar reactivity towards OER, when grown on a Pt substrate. In particular, an overpotential ( η ) of 1.28 V is calculated on the (111) surface, a value similar to that on (001) ( η = 1 . 30 V ). Despite a similar global reactivity, distinct potential limiting steps are identified. Specifically, on the (111) surface, the formation of the *OH intermediate is identified as the potential limiting step, while the *O formation is limiting on the (001) surface, as commonly observed on other iron oxides. These findings offer atomic-level insights about the reactivity of maghemite surfaces over OER process. They also clearly evidence the influence of surface structure on mechanisms and that of substrate on global efficiency. • Ability of maghemite for oxygen evolution reaction. • Determining role of Pt substrate for maghemite efficiency in OER. • Similar overpotentials for cubic and tetragonal maghemite. • Influence of maghemite model on the nature of determining steps.