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

The microscopic mechanism of O-3 and CO sensing on WO3 surfaces is clarified by a first principle study. It is shown that ozone reduces to O-2 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 O-3 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 O-3 and CO without reduction or oxidation are also calculated but the related energies are much smaller. (C) 2011 Elsevier B.V. All rights reserved.