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 photoelectrodes is not well understood. Using hematite as a prototype, we herein report that VO functions in a more complicated way in PEC process than previously reported. Through a comprehensive analysis of the key charge transfer and surface reaction steps in PEC processes on a hematite photoanode, we clarify that VO can facilitate surface electrocatalytic processes while leading to severe interfacial recombination at the semiconductor/electrolyte (S‐E) interface, in addition to the well‐reported improvements in bulk conductivity. The improved bulk conductivity and surface catalysis are beneficial for bulk charge transfer and surface charge consumption while interfacial charge transfer deteriorates because of recombination through VO‐induced trap states at the S‐E interface. Oxygen vacancies control the photoelectrochemical performance of metal oxide photoelectrodes by facilitating surface electrocatalytic processes and improving the bulk conductivity while inducing severe interfacial recombination at the semiconductor/electrolyte interface.