Density functional theory study of the interaction of H2 with pure and Ti-doped WO3 (002) surfaces

Density functional theory (DFT) calculations are conducted to explore the interaction of H2 with pure and Ti-doped WO3 (002) surfaces. Four top adsorption models of H2 on pure and Ti-doped WO3 (002) surfaces are investigated respectively, they are adsorption on bridging oxygen O1c, absorption on plane oxygen O2c, absorption on 5-fold W5c (Ti), and absorption on 6-fold W6c. The most stable and H2 possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O2c site, while the favourable adsorption sites for H2 in a Ti-doped surface is not only an O2c site but also a W6c site. The adsorption energy, the Fermi energy level EF, and the electronic population are investigated and the H2-sensing mechanism of a pure-doped WO3 (002) surface is revealed theoretically: the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H2. It can be predicted that the method of Ti-doped into a WO3 thin film is an effective way to improve WO3 sensor sensitivity to H2 gas.