Selective, Stable and Humidity-Robust NO₂ Sensing at Room Temperature with Porous WS₂ Films

Nitrogen dioxide (NO₂) is a hazardous air pollutant with a lowered annual mean exposure limit from 40 to 10 μg/m³ (∼5 parts-per-billion by volume, ppb) by the World Health Organization in 2021. This motivates the exploration of low-power and cost-efficient sensors that can detect such low concentrations of NO₂, exhibit high selectivity against interfering analytes and resilience to humidity fluctuations. Here, a selective, stable and humidity-robust sensor for NO₂ sensing at room temperature is presented. Flame-aerosol deposition followed by dry sulfidation results in highly porous (98%) and nanostructured WS₂ films. These films exhibit a 5-fold increase in response and over an order-of-magnitude reduction in response time, compared to conventional spin-coated films. Remarkable sensing performance down to 1 ppb of NO₂ (with a signal-to-noise ratio of 12.9) is achieved with high selectivity (>164) toward environmental interferents including NH₃, NO, acetone, H₂S, benzene, CO, ethanol, methanol, N₂O and toluene. We also reveal high robustness (response change ± 18%) against varying relative humidity (0-90%) and response stability over more than 6 months (±10%). This sensor outperforms previously reported NO₂ sensors operating at room temperature, making it well-suited for integration into devices for environmental monitoring or wearables for personal exposure assessment.