Mechanism of CO and O3 sensing on WO3 surfaces: First principle study

The microscopic mechanism of O3 and CO sensing on WO3 surfaces is clarified by a first principle study. It is shown that ozone reduces to O2 on the (0 0 1) surface of WO3 decreasing in such a way the number of oxygen vacancies and the conductivity (since oxygen vacancies act as donors in WO3). The mechanism of CO sensing is just the opposite: the CO molecule is oxidized to CO2 on the WO3 surface increasing the number of oxygen vacancies and the conductivity. The reaction enthalpy for the reduction process of O3 is found to be −2.54 eV in local density approximation (LDA) and −2.86 in generalized gradient approximation (GGA). The corresponding values for CO are −1.73 eV (LDA) and −1.52 eV (GGA). The adsorptions of O3 and CO without reduction or oxidation are also calculated but the related energies are much smaller.