Modulating Oxygen Vacancies in Lead Chromate for Photoelectrocatalytic Water Splitting

Although modulating oxygen vacancies in semiconductors has attracted broad interest in photocatalysis and photoelectrocatalysis, identifying the intrinsic roles of oxygen vacancies on photoelectrocatalytic properties is often elusive. In this work, the oxygen vacancies in a typical semiconductor lead chromate (PbCrO₄ ) are regulated via controlling the oxygen chemical potentials of O-poor and O-rich post-annealing atmospheres. Oxygen vacancies identified in PbCrO₄ can introduce electronically shallow energy levels and deep energy levels owing to the symmetry difference of oxygen atoms in the structure. A higher population of deep energy levels created under O-poor atmosphere induces the formation of more surface trapped states, resulting in a higher photovoltage for charge separation. Meanwhile, the existence of surface trapped states can significantly improve the charge injection efficiency of the PbCrO₄ photoanode and enhance the water oxidation activity. By modulating oxygen vacancies in the PbCrO₄ photoanode, a photocurrent density of 3.43 mA cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) under simulated AM1.5G is acheived. Further passivation of surface trapped states and introducing the water oxidation cocatalyst CoPi lead to a record applied bias photon-to-current efficiency (ABPE) of 1.12%. This work provides a guide to understand the mechanism of oxygen vacancies in oxide-based semiconductor photocatalysis and photoelectrocatalysis.