Ultraselective Dual Detection of Hydrogen and Ammonia Using Pd-W₁₈O₄₉ Nanowire MEMS Chemoresistive Gas Sensor

Gas sensor technologies have attracted considerable attention owing to their diverse applications, including indoor air quality monitoring, disease diagnosis, and food quality assessment. Metal oxide semiconductor (MOS) chemiresistive gas sensors have been suggested as a reliable platform for gas detection due to their high sensitivity, rapid response, small size, and cost-effectiveness. Nevertheless, their simple sensing mechanism, based on charge transfer between target gases and the sensing material, often limits their selectivity. In this study, we propose two promising strategies to enhance target gas selectivity – chemical affinity control and temperature modulation. W₁₈O₄₉ nanowires were synthesized using a solvothermal reaction and subsequently decorated with Pd nanoparticles via a wet impregnation process. The Pd-decorated W₁₈O₄₉ nanowire (Pd-W₁₈O₄₉ NWs) sensor exhibited high sensitivity, outstanding selectivity, and ppb-level detection limits for hydrogen and ammonia at operating temperatures of 125 °C and 225 °C, respectively. The improved sensing performance is attributed to the strong chemical affinity between the gases and the sensing materials, as well as the oxidative catalytic properties of Pd. Furthermore, the distinct temperatures required to oxidize the gases enable selective detection via simple temperature modulation. To optimize power efficiency, the dual-functional Pd-W₁₈O₄₉ NWs was integrated into a micro-electromechanical systems (MEMS) platform, and its sensing performance was evaluated. The Pd-W₁₈O₄₉ NWs MEMS sensor, with its dual functionalities, paves the way for the development of selective, miniaturized, and low-power gas sensors.