Phosphonic Acid-Anchored Tungsten Oxide Nanowire with Boosted Activity and Stability for Ammonia Sensing

Highly active and stable sensing surfaces are critical for the integration of catalysis-based electrical gas molecular sensors. However, achieving both high sensitivity and durability remains a persistent challenge due to continuous exposure to target molecules often results in surface deactivation and sensing performance degradation. Herein, we demonstrate a robust surface functionalization strategy to simultaneously enhance sensitivity and long-term stability for ammonia (NH3) detection by modifying hexagonal tungsten oxide (h-WO3) nanowires with methylphosphonic acid (MPA). Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations reveal that phosphate groups in MPA selectively bind to the Lewis acid sites (undercoordinated W6+) on h-WO3 nanowires, effectively passivating the surface and mitigating degradation. Concurrently, the electron-rich P=O moiety facilitates strong interaction with NH3 molecules, leading to enhanced chemisorption and signal transduction. As a result, MPA-functionalized h-WO3 nanowire sensors exhibit a nearly tenfold increase in NH3 sensitivity compared to the unmodified h-WO3 sensors and maintain stable performance over 300 days of continuous operation. As a proof of concept for applied scenarios, we integrate the modified sensors into a microelectromechanical system (MEMS)-based smart ventilation system, enabling real-time NH3 monitoring and control in livestock environments. This work presents a viable route for designing high-performance, durable gas sensors through targeted molecular surface engineering.