Surface-engineered WO₃ thin films for efficient NO₂ sensing

Nitrogen dioxide (NO₂), mostly produced from exhaust fumes of cars and factories, has been labelled by the World Health Organization as one of the most hazardous air pollutants. Although metal oxide-based thin films have been employed to detect NO₂ earlier, significant challenges remain to be addressed particularly at low detection limits. This is presumably undermined by the low surface area and the high resistivity of metal oxide thin films. Herein, an attempt has been made to overcome these challenges by producing WO₃ thin films in the form of nanowires, introducing oxygen vacancies, and immobilizing platinum (Pt) onto the surface of tungsten oxide nanowires. The as-fabricated sensor is highly sensitive, selective and capable of detecting NO₂ at 500 ppb level. Furthermore, the sensing response of the as-fabricated sensor can be modulated by tuning the concentration of oxygen vacancy as well as the thickness of the Pt layers. While oxygen vacancy and catalytic properties of Pt are predominant, better electrical conductivity, improved specific surface area of one-dimensional WO₃ and the work functions between Pt and WO₃ also contribute. A plausible mechanism is proposed for the superior sensing properties of the as-fabricated Pt/WO₃ sensor.