The role of titanium at the interface of hematite photoanode in multisite mechanism: Reactive site or cocatalyst site?

Hematite (α-Fe₂O₃) constitutes one of the most promising photoanode materials for oxygen evolution reaction (OER). Recent research on Fe₂O₃ have found a fast OER rate dependence on surface hole density, suggesting a multisite reaction pathway. However, the effect of heteroatom in Fe₂O₃ on the multisite mechanism is still poorly understood. Herein we synthesized Fe₂O₃ on Ti substrates (Fe₂O₃/Ti) to study the oxygen intermediates of OER by light-dark electrochemical scans. We identified the Fe-OH species disappeared and Ti-OH intermediates appeared on Fe₂O₃/Ti when pH = 11−14, which significantly improved the OER performance of Fe₂O₃/Ti. Combined with the density functional theory calculations, we propose that Ti atom acts as cocatalyst site and captures proton from neighboring Fe-OH species under highly alkaline condition, thereby promoting the coupling of Fe=O and reducing the energy barrier of the non-electrochemical step. Our work provides a new insight into the role of heteroatom in OER multisite mechanism based on clarifying the reaction intermediates.