Highly Sensitive, Temperature-Independent Oxygen Gas Sensor Based on Anatase TiO₂ Nanoparticle Grafted, 2D Mixed Valent VO_x Nanoflakelets

Herein, we report a facile approach for the synthesis of TiO₂ nanoparticles tethered on 2D mixed valent vanadium oxide (VO_x/TiO₂) nanoflakelets using a thermal decomposition assisted hydrothermal method and investigation of its temperature-independent performance enhancement in oxygen-sensing properties. The material was structurally characterized using XRD, TEM, Raman, DSC, and XPS analysis. The presence of mixed valent states, such as V₂O₅ and VO₂ in VO_x, and the metastable properties of VO₂ have been found to play crucial roles in the temperature-independent electrical conductivity of VO_x/TiO₂ nanoflakelets. Though pristine VO_x exhibited characteristic semiconductor-to-metal transition of monoclinic VO₂, pure VO_x nanoflakelets exhibited poor sensitivity toward sensing oxygen. VO_x/TiO₂ nanoflakelets showed a very low temperature coefficient of resistance above 150 °C with improved sensitivity (35 times higher than VO_x for 100 ppm) toward oxygen gas. VO_x/TiO₂ nanoflakelets exhibited much higher response, faster adsorption and desorption toward oxygen as compared to pristine VO_x beyond 100 °C, which endowed the sensor with excellent temperature-independent sensor properties within 150–500 °C. The faster adsorption and desorption after 100 °C led to shorter response time (3–5 s) and recovery time (7–9 s). The results suggest that 2D VO_x/TiO₂ can be a promising candidate for temperature-independent oxygen sensor applications.