Enhancement of Water Splitting by Controlling the Amount of Vacancies with Varying Vacuum Level in the Synthesis System of SnO 2-x /In 2 O 3-y Heterostructure as Photocatalyst

Abstract Photocatalyic water splitting with metal oxide heterostructure as photocatalysts has been a valuable and efficient hydrogen production method in recent years. Previous studies have shown that oxygen vacancies formed in photoelectrochemical reactions play an important part in the efficiency enhancement. However, the relation between the oxygen vacancy formation and the vacuum level of synthesis system has not been investigated. In this work, SnO 2-x /In 2 O 3-y heterostructures (SIH), as water splitting photocatalysts, were prepared in the synthesis systems with different vacuum levels. A series of in situ transmission electron microscope (TEM) observation had been carried out, observing the detailed changes during SIH formation, basically following the thermodynamic rules. X-ray photoelectron spectroscopy, photoluminescence measurements and in situ TEM observations indicate that the amount of oxygen vacancies increase in SIH synthesized in ultra-high vacuum (UHV) system compared to SIH formed in a low vacuum furnace. The observed 60% higher hydrogen production efficiency in SIH formed in UHV compared with SIH formed in furnace ambient is attributed to presence of the more abundant oxygen vacancies. The results indicate that an optimized heterostructured photocatalyst can be designed by controlling the vacuum level in the synthesis process.