An Ultra-Selective and Humidity-Resistant Room-Temperature-Operated NO₂ Sensor Based on Black TiO₂

As a common gas-sensing material, TiO₂ is limited by poor gas selectivity and humidity immunity like many other metal oxides. Here, an ultra-selective and humidity-resistant room temperature-operated NO₂ sensor is developed using black TiO₂ for the first time. Compared with conventional white TiO₂, black TiO₂ significantly enhances NO₂ selectivity and humidity resistance by enhancing the NO₂ response for ≥10 times while simultaneously suppressing responses to 7 common interfering gases and H₂O adsorption. A wireless portable equipment is developed that exhibits the capabilities of identifying NO₂ from a mixed atmosphere and recognizing environmental differences in practical scenarios. These improvements and different response types are attributed to the regulation of H₂O adsorption: H₂O layers are formed on white TiO₂, leading to dominant ion-proton conductivity and blocked gas-solid interactions, while H₂O adsorption is suppressed and hydroxyl groups are formed on black TiO₂, enhancing NO₂ response. This study not only promotes a significant advancement and proves the feasibility of using common metal oxides for high-performance NO₂ detection at room temperature in a mixed environment irrespective of ambient humidity, but also offers valuable insights into the sensing mechanisms.