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

Abstract In this work, all-printed tungsten oxide (WO 3 ) sensors were fabricated from nanoparticle-based screen-printable inks, where the WO 3 nanopowders were hydrothermally synthesized with various HCl concentrations to give enhanced room-temperature detection of ammonia (NH 3 ) gas. The monoclinic phase of WC powders (calcined WO 3 ) with square nanoplate-like morphology and porosities was identified from x-ray diffraction, field-emission scanning electron microscopy and Brunauer–Emmett–Teller surface area analysis. The silver precursor ink-derived interdigitated electrodes were found to be crystalline with an average finger width and Ag film thickness of 1 ± 0.4 mm and 3.8 ± 0.5 µ m, respectively. The formulated WO 3 inks with hydroxyethyl cellulose showed a thixotropic fluid-like behavior and exhibited a viscosity of ∼9 × 10 4 mPa s, which is a key requirement for screen printing. Rheological study of the formulated WC inks revealed a thixotropic nature, with all WC inks showing a viscosity of 85 ± 3 Pa s and a recovery rate of 80% in the recovery stage. This work explains the role of pH in hydrothermally synthesis of WO 3 by correlating the gas-sensing characteristics of the screen-printed sensors fabricated from formulated inks, where the WC-15 gas sensor showed a maximum gas response of ∼340 towards 100 ppm of NH 3 gas. This facile and cost-effective method for fabricating chemiresistive gas sensors could pave the way for the development of flexible and printable devices for ppb-level detection of NH 3 gas and its monitoring.