Microscopic Nature of Gas Adsorption on WO3 Surfaces: Electron Interaction and Localization.

Even though WO3 has been used in gas-sensors for many years, little is known about the gas-sensing mechanism. Using first-principles density functional theory and experimental methods, we study the adsorption of CO, H2, NH3, and NO2 on the surface of WO3 (001). The results indicate that the surface undergoes reconstruction after gas adsorption, which inevitably causes the localization of surface electrons and a change of the electric (sensing) signal. Through the analysis of atomic orbital and molecular orbital, the adsorption mechanism can be effectively predicted. The above analysis confirms that the resistance change is only related to the electronic behavior of the surface and the gas. We corrected problems associated with adsorption energy to characterize the adsorption strength of a gas on a surface, and we investigated the effect of the test temperature and test environment on both electronic interaction and the final electric sensing signal.