CH4 activation and sensing on hexagonal WO3 (001) and (110) surfaces

Abstract

The gas sensing activity of metal oxides is determined by the nature of the surface exposed to ambient gas. In this work, density functional theory (DFT) has been used to investigate the CH4 sensing mechanism on hexagonal WO3 (001) and (110) surfaces. It is found that the spatial geometrical structure of the (110) surface plays an important role in the activation of the CH bond of the inert CH4 gas. The calculated results indicate that the flat (001) surface is nearly not sensitive to CH4 gas. However, on the ridge-like (110) surface, large transfers occur on both four-fold coordinated W4c and hole2, the side bridge site between W4c and O1c, with charge transfers of up to 0.286e and 0.266e, respectively. Allowing the CH4 molecule to be as close as possible (2.317 Å or so) to the surface due to the open and cuspidated surface structure should be the intrinsic reason for the high activity of the (110) surface. A 4-fold improvement in sensing ability is obtained. In addition, the nature of the physical adsorption creates potential for the material to be reused. Therefore, the presence of a highly active (110) surface solves the insensitivity issue of pure WO3 and makes it a promising material for methane detection.