Unveiling the acetone sensing mechanism by WO3 chemiresistors through a joint theory-experiment approach

The acetone sensing mechanism by WO_3 was investigated through a combined experimental and theoretical approach. The gamma-monoclinic WO_3 powder was synthesized by a template-mediated sol-gel method and characterized on structural, surface, morphological and optical points of view. A thin film of WO_3 was deposited on interdigitated Au electrodes by hot-spray method and tested at 300 oC (while applying a bias of 1.0 V) for acetone gas sensing, both in presence and absence of oxygen in the gas carrier. Interestingly, the absence of oxygen had no significant effect on the sensor response intensity but it dramatically increased the recovery times (from 120 s to 2700 s). In order to explain these experimental results, by means of ab initio density functional theory calculations, we modeled a defective gamma-WO_3 surface structure and simulated the adsorption of acetone and oxygen molecules on top of it. We unprecedentedly evidenced that, in presence of surface oxygen vacancies, both acetone adsorption and its oxidation reaction can occur. However, their contribution to the sensor response strictly depends on the inert/oxidative atmosphere present in the sensing chamber, which in turn strongly affects the surface oxygen population. Our findings can either be the guidelines for future studies aimed at delineating the possible reaction products or pave the way for the engineering of tailored nanomaterials having specific surface features and enhanced sensing properties.