Tailoring the ethanol selectivity of SnO2-based MEMS gas sensors via WO3-loading in double-pulse-driven mode.

This work demonstrates a strategy to tailor the ethanol selectivity of SnO2-based MEMS gas sensors by combining WO3 loading with a pulse-driven heating mode. This dynamic operating mode separates the sensing signal, allowing for the distinction between an initial transient response in the target gas atmosphere (S p) and a total response (S i). WO3-loaded SnO2 nanoparticles (NPs) were synthesized via hydrothermal treatment and impregnation methods. The optimal 1.5 mol% WO3-loaded SnO2 (1.5-W-Sn) exhibited highly dispersed WO3 species and an enhanced specific surface area. At measurement temperature of 350 °C, the 1.5-W-Sn sensor showed selectivity toward 10 ppm ethanol with an S p value significantly higher than those for other VOCs. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements confirmed that the 1.5-W-Sn sample enhanced ethanol adsorption at low-temperature. More critically, results of the temperature programmed reaction after ethanol adsorption confirmed that WO3 loading altered the ethanol reaction pathway, which was evidenced by ethylene desorption. This altered pathway, coupled with the rapid combustion of its byproducts during the measurement step is responsible for the high S p value. The combination of pre-adsorption and an altered reaction pathway, enables the sensor's marked selectivity to ethanol. These findings underscore a powerful design strategy, where material properties and dynamic operation modes are tailored the selective detection.