Oxygen-Vacancy-Dominated Cocatalyst/Hematite Interface for Boosting Solar Water Splitting.

Surface suppression is one of critical issues for semiconductors in photoelectrochemical (PEC) water splitting. Deposition of oxygen evolution cocatalysts on photoanodes can improve the oxygen evolution rate, but still it has some limits in some cases. In this work, we propose a new and simple precipitation approach to transform the surface of hematite into iron phosphate (Fe-Pi). Further, Ar-plasma treatment on Fe-Pi/FeO introduces oxygen vacancies on the phosphorous and photoanode. A surface phosphate treatment accelerates the transfer of holes from the bulk to the surface. Besides, creating oxygen vacancy defects on Fe-Pi/FeO can significantly increase the reactivity of active sites, leading to the remarkable enhancement in oxygen evolution reaction activity and PEC performance. The resulting photoanode has a current density of 2.71 mA cm at 1.23 V and 3.5 mA cm at 1.50 V under simulated solar light condition. The reduced surface recombination by Fe-Pi layer and Ar-plasma treatment is confirmed by electrochemical analysis. These findings give a great potential of the use of a combination strategy for cocatalyst deposition and optimizing the performance of hematite.