Effect of ambient oxygen partial pressure on the hydrogen response of SnO₂ semiconductor gas sensors

In this study, the influence of the oxygen partial pressures (PO2) on the sensor response to H₂ of SnO₂ resistive-type gas sensors was evaluated under various humid atmospheres. SnO₂ nanoparticles of 8–15 nm in diameter were synthesized using a hydrothermal technique followed by calcination at 600°C. Additionally, a large amount of pores with diameters greater than 10 nm was confirmed in the nanoparticles. The electrical resistance at 350°C was decreased with decreasing the P_O2, and the electrical resistance in the presence of 10 ppm H₂ was much smaller than that in the absence of H₂ in both dry and humid atmospheres regardless of the P_O2. Furthermore, the sensor response to 10 ppm H₂ at 350°C increased with decreasing P_O2 in both dry and humid atmospheres. Thus, decreasing the amount of oxygen adsorption enhanced the effect of rooted hydroxyl formation on the SnO₂ surface through a combustion reaction between H₂ and adsorbed oxygen and improved the sensor response to H₂. These results are important for understanding the fundamental mechanisms of gas detection and for the material surface design of highly sensitive resistive-type semiconductor gas sensors.