First-principles study of absorption mechanism of hydrogen on W20O58 (010) surface

Abstract

With the development of modern industrial technology, tungsten products prepared from traditional tungsten powder cannot meet the demands of industry. However, the properties of tungsten products produced from ultra-fine tungsten powder have been greatly improved:they have high strength, high toughness, and low metal plasticity-brittle transition temperature. Hence, it is necessary to carry out theoretical research of the micro-adsorption dynamics during hydrogen reduction of W20O58, which is beneficial to synthetizing ultra-fine tungsten powder. In this article, to comprehend the crystal characteristics of W20O58 (010) surface and provide the theoretical reaction law for hydrogen reduction on W20O58 (010) surface, the absorption mechanism of H2 molecule on W20O58 (010) surface is studied by the first-principles calculation based on density functional theory in a plane wave pseudo-potential framework. The results show that the indirect band gap of W20O58 is 0.8 eV, indicating that it has metallic characteristic. The W20O58 (010) surface has different terminations, i.e., WO-terminated (010) surface and O-terminated (010) surface. After the geometrical optimization of the two surfaces, the W–O bond length and bond angle of W–O–W are both changed. In addition, six absorption configurations of H2 on W20O58 (010) surface, including WO-L-O1c, WO-V-O1c, WO-L-O2c, WO-V-O2c, O-L-O1c and O-V-O1c, are chosen to be investigated. The calculation results show that the WO-L-O1c, WO-V-O1c and WO-L-O2c absorption system are unstable, while the WO-V-O2c, O-L-O1c and O-V-O1c absorption configuration are stable. When H2 molecule is dissociated into two H atoms, the absorption energies of the three stable configurations are-1.164 eV,-1.021 eV and-3.11 eV, respectively. It is obvious that the O-V-O1c absorption configuration is the most stable one. The analysis of density of states reveals that the 1s state of H atom interacts with the 2p and 2s states of O atom. The outermost O1c atom of O-terminated (010) surface contains an unsaturated bond, which results in the formation of bonding between two H atoms and O1c atom. As a result, an H2O molecule is formed and an oxygen vacancy on the surface is generated after absorption reaction. By combining experimental observations with simulation calculations, the mechanism of hydrogen reduction of W20O58 can be revealed from a microscopic view.