Room-temperature selective NO2 sensing using porous TiO2 nanorods via a humidity-mediated conduction

Abstract

The development of room-temperature (RT) NO₂ gas sensors with high sensitivity and selectivity is essential for real-time environmental monitoring. Here, we demonstrate an ionic-mediated sensing strategy using highly porous TiO₂ nanorods (NRs). The vertically aligned architecture enhances hydroxyl coverage and enables proton hopping pathways under humid conditions, leading to a transition from electronic hopping conduction in dry air to proton-dominated conduction in humid environments. The TiO₂ NR sensors achieve ultrafast detection at RT, with response and recovery times of approximately 5 s and 7 s toward 2 ppm NO₂. A high response of approximately 670 and a theoretical detection limit of 505 ppt are obtained at 40% relative humidity. Comparable responses at 20% RH under higher bias demonstrate a broadened operational humidity window. The sensors exhibit excellent repeatability with a coefficient of variation of 3.87% and strong selectivity with negligible responses to reducing gases. These results highlight ionic-mediated TiO₂ NRs as a practical platform for low-power, NO₂ sensing at RT with bias-tunable humidity adaptability.