All-printed WO3 films on Ag-interdigitated electrode derived from aqueous screen-printable inks for room-temperature ammonia gas detection

Abstract In this work, all-printed tungsten oxide (WO3) sensors were fabricated from nanoparticle-based screen-printable inks, where the WO3 nanoparticles were hydrothermally synthesized with varied HCl concentrations towards enhanced room-temperature detection of ammonia gas. The monoclinic phase of calcined WO3 powders with square nanoplate-like morphology and porosities identified from XRD, FESEM micrographs and BET surface area analysis, respectively. The silver-precursor ink derived interdigitated electrodes (Ag-IDEs) were found to be crystalline with an average finger-width and Ag-film thickness of 1 ± 0.4 mm and ~3.8 µm, respectively. The rheological behaviour of the formulated WO3 inks using hydroxyethyl cellulose depicted a thixotropic fluid-like behaviour and exhibited a viscosity of ~ 9×104 mPa-s, which is a key requirement for screen-printing. The rheological study of the formulated WC-inks revealed thixotropic nature with all WC-inks showing viscosity of 85 ± 3 Pa-S, with a recovery rate of 80% in the recovery stage. This work explains the role of pH on hydrothermally synthesized WO3, and by correlating the gas sensing characteristics of fabricated screen-printed sensors from formulated inks, where WC-15 gas-sensor showed maximum gas response of ~340 towards 100 ppm of ammonia gas. This facile, and cost-efficient method of fabricating chemiresistive gas-sensors paved a way for development of flexible and printable devices towards ppb-level detection of NH3 gas and its monitoring.