The quantum size and spin–orbit coupling effects in BiVO4 with several atomic layers studied by density functional theory

Abstract

The quantum size and spin–orbit coupling (SOC) effects play an important role in the electronic structure of photocatalytic materials with heavy elements such as Bi, Pb, Ir, Te, Sb, Sn, etc. How these two effects affect the conduction band (CB) or the valence band (VB) edge of a photocatalyst is not well understood. In this work, we investigated the quantum size and SOC effects on the CB and VB edges of BiVO₄ (BVO) with a thickness of several atomic layers. The BVO is a good water oxidation photocatalyst but doesn’t have the hydrogen reduction ability. We find that when the thickness of a BVO layer is smaller than 0.64 nm, the CB edge upshifts significantly because of the quantum size effect. But after including the SOC effect, the CB edge remains almost unchanged. The CB edge of BVO upshifts above the equilibrium redox potentials for H₂/H₂O with a thickness of ∼0.64 to 1.28 nm. Within this thickness, only the quantum size effect dominates and the SOC effect is very weak. Both the quantum size and SOC effects are insignificant as the thickness of the BVO layers increases to be larger than 1.28 nm. The results presented here provide an essential step toward the understanding and rational design of photocatalysts from both the quantum size and SOC effects.