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

Abstract

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.