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, SnO2-x/In2O3-y heterostructures, 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 SnO2-x/In2O3-y heterostructures 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 SnO2-x/In2O3-y heterostructures synthesized in ultra-high vacuum (UHV) system compared to SnO2-x/In2O3-y heterostructures formed in a low vacuum furnace. The observed 25~30% higher hydrogen production efficiency in SnO2-x/In2O3-y heterostructures formed in UHV comparing with SnO2-x/In2O3-y heterostructures 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.