Hydrogen Gas Sensing Mechanism in Zinc Oxide Nanowire and Nanotube: A Density Functional Theory Study

The application of solid-state sensors in the detection of hydrogen gas is a positive step to prevent safety issues created by hydrogen leakage. In this paper, the absorption of hydrogen molecules on the outside and inside of ZnO nanotube and ZnO nanowire has been investigated by employing density functional theory. Results demonstrate that hydrogen gas is physically absorbed at distances between 2.20 A and 2.26 A from the surface of ZnO nanotubes and ZnO nanowire, respectively. The hydrogen molecule has the same adsorption behavior on both the outside and the inside wall of ZnO nanotube; as a result, the effective surface of ZnO nanotube increases. On the other hand, the adsorption of hydrogen molecules leads to a shift of the Fermi level toward valence band edge. This shift is more pronounced in ZnO nanowires, which leads to a better sensitivity toward hydrogen molecules. However, ZnO nanotubes could provide more surface-to-volume ratio, which also increases the sensitivity of the nanostructure.