Theoretical insights into interfacial and electronic structures of NiOx/SrTiO3 photocatalyst for overall water splitting

SrTiO3 is a promising candidate photocatalyst for overall water splitting. Loading suitable co-catalysts, such as NiOx, the mixture of Ni and NiOx remarkably improve the photocatalytic activity. However, spatial locations and functions of components in NiOx/SrTiO3 are under debate. Here, using first-principles density functional theory (DFT) calculations, we investigate the initial growth of Ni-n (n = 1-4) and (NiO)(n) (n = 1, 2 and 4) clusters on stoichiometric (100) surfaces of SrTiO3, and explore interfacial and electronic structures of composite photocatalysts. It is found that Ni-n clusters are easier to undergo aggregation on SrO-termination than on TiO2-termination. The adsorption of Ni-n cluster on (100) surfaces elevates the Fermi level towards the conduction band, which may benefit the occurrence of hydrogen evolution reaction. The structural similarity between (NiO), cluster and surface has an essential effect on the most stable adsorption configuration. For (NiO)(n)/SrTiO3 systems, the occupied states of (NiO)(n) cluster well overlap with those of (100) surfaces in the valence band maximum, which is in favor of the separation of photogenerated electrons and holes to SrTiO3 support and (NiO), cluster, respectively. The detailed DFT analysis provides important insights into the growth of NiOn on surfaces of SrTiO3 and presents an explanation on the different models of NiOx/SrTiO3 photocatalyst proposed by experimental groups. Our calculations build a basis for further investigations on the mechanism of photocatalytic water-splitting reaction in NiOx/SrTiO3 composite system. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.