Theoretical investigation of loading Ni clusters on the α-Ga2O3 surfaces for photocatalytic hydrogen evolution

Abstract

Abstract In the semiconductor-based photocatalysts for overall water splitting, loading proper cocatalysts play a crucial role in enhancing the photocatalytic activity. In this work, we have chosen Nin/α-Ga2O3 as a model and provided detailed density functional theory calculations to investigate the function of cocatalysts in hydrogen evolution reaction (HER). We have studied the formation and stability of Nin (n = 1–4) cluster on two stable surfaces of α-Ga2O3 (001) and (012). In a Nin/α-Ga2O3 system, as the Ni 3d states well overlap with O and Ga states, the excited electrons transferred from Ga to Ni may participate in HER. We theoretically predict that introduction of Nin cluster on (012) surface can elevate the Fermi level toward the conduction band, which is favorable for the occurrence of HER. Electrochemical computations are used to explore the mechanism of HER. It is found that, in most of Nin/α-Ga2O3 systems, the active sites of HER are on Nin clusters. Loading Nin clusters not only importantly reduces the Gibbs free energy of HER but also improves the reaction activity of surface O and Ga sites in HER. Our calculations reasonably explain the experimental observation on significant enhancement of activity for generating hydrogen after loading nickel oxide cocatalysts.