Antimony-Doped Tin Dioxide Gas Sensors Exhibiting High Stability in the Sensitivity to Humidity Changes

The type and amounts of oxygen adsorption species at various atmospheric humidity levels are important factors in improving the sensitivity to combustible gases and stability to humidity changes of SnO₂-based resistive-type gas sensors. We investigated the effect of antimony (Sb) doping of SnO₂ nanoparticles on the stability of the sensitivity to humidity changes and oxygen adsorption species under humid atmosphere. No significant degradation of the sensitivity to hydrogen of Sb-SnO₂ sensors was observed between 16 and 96 RH%, while an undoped SnO₂ sensor showed gradually decreasing responses with increasing humidity. An evaluation of oxygen adsorption species under humid atmosphere showed a transition from O^2- to O^- with increasing humidity from 16 to 96 RH%. However, the O^2- adsorption sites were maintained on the surfaces of the Sb-SnO₂, even as the humidity increased. Moreover, the extent of oxygen adsorption on the Sb-SnO₂ was not obviously changed with increasing humidity. These results indicate that Sb atoms function as hydroxyl absorbers and also generate O^2- adsorption sites in their vicinity. Additionally, Pd loading on the Sb-SnO₂ further enhanced the sensor response under humid atmosphere, while maintaining the stability to humidity changes. Therefore, we successfully imparted stability to the sensitivity of SnO₂ nanoparticles during humidity changes, representing an important improvement with applications to the development of high performance, practical, resistive-type gas sensors.