Role of oxygen vacancy in metal oxide based photoelectrochemical water splitting

Photoelectrochemial (PEC) water splitting relies on the optoelectric property of the photoelectrodes. Oxygen vacancy (V-O) has attracted increasing attention in tailoring photoelectrodes in the following three aspects: light harvest, charge separation and transfer, and surface reaction kinetics. Even though the V-O may increase the recombination as a kind of defects in metal oxide based photoelectrode, a number of recent researches have revealed the beneficial feature of V-O in PEC, which is controversial to the former understanding. Thus, a comprehensive analysis about the oxygen vacancy in the metal oxide photoelectrodes will be important for applying V-O in achieving high PEC performance. Herein, we contribute a critical review on the role of oxygen vacancy including its formation mechanism, characterization methods, and the influence on the semiconductor and surface catalytic properties. The knowledge will help to clarify the effect of V-O in terms of the structure-performance relationship in the PEC process.