Non−noble metal catalyst embedded WO3 microspheres for enhancement of NO2 gas sensing

Nitrogen dioxide (NO₂) is a toxic gas that critically affects air pollution and human health. Although semiconductor-based gas sensors are highly promising for detecting toxic gases, their performance is often limited by low sensitivity and slow recovery times. Noble metal catalysts have been widely employed to overcome these limitations by promoting oxygen spill-over from NO₂ to the semiconductor surface, thereby enhancing sensor response. In this work, we fabricated a high-performance NO₂ gas sensor using sulfur, which is non-noble metal catalyst, supported on WO₃ microspheres via a two-step hydrothermal synthesis. The incorporation of sulfur did not alter the crystallinity or morphology of the WO₃, but it introduced additional oxygen vacancies and facilitated the spill-over effect, resulting in a sensing response more than 100 times higher than that of bare WO₃. At an operating temperature of 150°C, the sulfur-loaded WO₃ exhibited a response of nearly 500–5 ppm of NO₂, with a detection limit as low as 50 ppb. This study suggests a viable approach to replacing noble metal catalysts and presents a simple fabrication strategy for developing highly sensitive gas sensors.