Vacancy-Engineered Tungsten Nitride for Self-Powered NO₂ Sensing

Fuel cell-type electrochemical gas sensors provide an attractive platform for self-powered air-quality monitoring but are traditionally limited by reliance on platinum catalysts. Here, we report a platinum-free NO₂ sensor based on vacancy-engineered tungsten nitride (WN) that operates efficiently at room temperature. Deliberate introduction of nitrogen vacancies activates WN by enhancing NO₂ adsorption and accelerating interfacial charge transfer. The resulting sensor delivers a high sensitivity of 0.247 μA·ppm^-1, a current response of 11.8 μA at 50 ppm NO₂, ultrafast response and recovery (9.6/11.6 s), and excellent long-term stability exceeding 150 days. Integrated into a compact platform, the device demonstrates the feasibility of tracking dynamic NO₂ fluctuations in vehicle exhaust. This work establishes defect-engineered metal nitrides as viable noble-metal alternatives for low-cost, durable, and decentralized air-quality sensing technologies.