Mechanism of CO adsorption on hexagonal WO3 (0 0 1) surface for gas sensing: A DFT study

In this work, the adsorption of CO on O-terminated and WO-terminated hexagonal WO3 (0 0 1) surfaces was studied systematically by density functional theory (DFT) calculation. The results indicate that both of the two surfaces have considerable reactivity to CO, with the O-terminated (0 0 1) surface being more active than WO-terminated (0 0 1) surface. On the WO-terminated (0 0 1) surface, CO exhibits physical adsorption, with moderate adsorption energy and charge transfer from CO molecule to the surface. While on the O-terminated (0 0 1) surface, chemical adsorption occurred. Where CO is oxidized into CO2 leaving an oxygen vacancy on the surface, and resulting in larger charge transfer from CO molecule to the surface. The resistance in both cases has been decreased obviously. Our results confirm that h-WO3 can be a good sensor material for CO detection.