Effect of Humidity on the Sensitivity of an Ion-Doped TiO2 Nanotube-Based Gas Sensor to H2S and Its Mechanism via Density Functional Theory

We analyzed the effects of humidity on the H2S sensing ability of the undoped, Zn-doped, and Fe-doped TiO2 nanotube (TiNT)-based gas sensors. The 0.1 M Zn-doped TiNT-based gas sensor had more stable responses to 50 ppm H2S at 300 degrees C compared to the undoped TiNT when the relative humidity (RH) ranged from 3 to 85%RH. For the 0.1 M Fe-doped TiNT sensor, the response reached the highest value (34.19-50 ppm H2S) at 70%RH. The Fe-doped TiNT sensors maintained relatively high responses when the relative humidity was below 60%RH. To determine the relationship between the sensing mechanism and TiO2 band structures and to determine the effect of water on the sensing mechanism, the systematic density functional theory (DFT) calculations for adsorption modes were performed. We found that metal ion doping was effective in improving the performance of H2S TiNT film-based gas sensors under different relative humidities. We also demonstrated the value of metal-doped TiNT gas sensors in practical environments.