The Role of Surfaces on the NO₂ Gas Sensing Performance of WO₃ Nanorods— Experimental and Theoretical Insights

Metal semiconducting oxides (MOXs) have stood out due to their functional properties. Among the various applications, the MOXs have been widely used as resistive gas sensors due to their sensitivity and fair stability. Tungsten trioxide (WO₃) is an n-type wide band-gap semiconductor applied as an active layer. Multiple factors behind gas-sensing properties have been considered responsible for improving sensing performance, however, an important aspect to consider is the relationship between sensing performance and MOX exposed facets/surfaces. The nature of surfaces exposed to the target gas becomes a key factor in enhancing the material sensing activity, as some facets exhibit higher reactivity to certain analytes than other surfaces. In this sense, we conducted an experimental and theoretical investigation regarding the nitrogen dioxide (NO₂) gas-sensing properties of WO₃ rod-like shape structures obtained via aerosol-assisted chemical vapor deposition. Electrical measurements showed the sensitivity of the nanorods towards NO₂ gas ranging from 0.1 to 1 ppm (parts-per-million), operating at room temperature under blue-light stimulation. Density Functional Theory calculations revealed that the surfaces play an important role in the NO₂ adsorption/desorption processes. Moreover, it was observed that the NO₂ adsorption energies followed the order (110) > (010) > (001) > (101), as well as indicating a physical adsorption mechanism with long-range W-O interactions. These results revealed the relationship between the NO₂ adsorption and the distinct WO3 facets, providing a better understanding of the morphological changes and the sensing performance of the rod-like structures.