Understanding the Roles of Oxygen Vacancies in Hematite-Based Photoelectrochemical Processes

Oxygen vacancy (VO) engineering is an effective method to tune the photoelectrochemical (PEC) performance, but the influence of Vo on photoelectrode is not well understood. Using hematite as a prototype, here we report that VO functions in a more complicate way in PEC process than previously reported. By comprehensive analysis of the key charge transfer and surface reaction steps in PEC process on hematite photoanode, we clarify that VO can facilitate surface electrocatalytic process but meanwhile leads to severe interfacial recombination at the semiconductor/electrolyte (S-E) interface, in addition to the well-reported bulk conductivity improvement. The improved bulk conductivity and surface catalysis are beneficial for bulk charge transfer and surface charge consumption, however the interfacial charge transfer is deteriorated due to the recombination via VO induced trap states at the S-E interface.