Origin of highly efficient photocatalyst NiO/SrTiO3 for overall water splitting: Insights from density functional theory calculations

SrTiO3 loaded with NiO cocatalyst is one of representative photocatalysts for overall water splitting, which have attracted considerable attention. However, the function of NiO particles in the photocatalytic system is still under debate. In this work, we present a theoretical investigation based on density functional theory calculations to reveal the origin of the high photocatalytic performance achieved by loading NiO onto SrTiO3 surface. By considering two terminations of SrTiO3 (001), the interfacial geometries, electronic structures, charge densities and optical absorptions of NiO(001)/SrTiO3 (001) have been calculated. The interface including SrO-termination connecting with NiO(001) (NiO/SrO) has a stronger covalent interaction than the one including TiO2-termination connecting with NiO(001) (NiO/TiO2). The analyses on electronic properties and charge redistributions indicate that the formation of interfacial structures reduces the effective masses of photoinduced carriers and results in a type-II band alignment, which is conducive to separate the photogenerated carriers into two components of the interface. The electrons gathering on SrTiO3 side will take part in the hydrogen evolution reaction, while the holes accumulating on NiO side will participate in the oxygen evolution reaction. It is found that the geometrical reconstruction around the interface has no influence on the extension of absorption edge due to the characteristics of heterostructures with indirect band gap. This study reveals that NiO functions as the water oxidation cocatalyst to suppress the recombination of photoinduced electron and hole pairs, which leads to the enhancement of photocatalytic activity in SrTiO3 system.