The mechanism of semiconductor to metal transition in the hydrogenation of VO2: a density functional theory study

Abstract

VO₂ is a glamorous material with specific metal–semiconductor-transition (MST). The hydrogenation of VO₂ could make it a promising material for application in an ambient environment. In this work, we reveal the hydrogenation of VO₂ by modulating the hydrogen content and monitoring interaction models, adsorption energies, the density of states, electron density, and charge transfer between hydrogen and the VO₂ surface. The monoclinic VO₂(020) surface shows a distinct electronic polarization, and the majority spin band gap is larger than the minority spin band gap. The energy gap of the monoclinic VO₂ surface is highly dependent on the majority spin band. The interaction between hydrogen and oxygen in the first layer of the VO₂ surface is stronger than those in other layers. The energy gap on the surface of VO₂ decreases gradually with increasing hydrogen content, and when twelve hydrogen atoms are adsorbed on the surface, an energy gap of 0 eV eventually appears, suggesting that monoclinic VO₂ turns into a metallic conductor from a semiconductor. In the process of VO₂ hydrogenation, the electron transfer only occurs between hydrogen and its connected oxygen atoms on the VO₂ surface, and vanadium atoms just play an intermediary role.