Determination of Oxygen Adsorption Species on SnO2: Exact Analysis of Gas Sensing Properties Using a Sample Gas Pretreatment System

Oxygen adsorption plays key roles in resistive-type SnO2 gas sensors that can very sensitively detect combustible gases such as CO and hydrocarbons. Thus, exact evaluation of the electric resistance of SnO2 in response to oxygen is important to understand the oxygen adsorption mechanism. However, infinitesimal impurities contained in even high-grade commercial oxygen cylinders impose great effect on the sensitivity of SnO2. In this study, we designed an experimental system, which composed of gas pretreatment chambers including a Pt/Al2O3 combustion catalyst and a zeolite adsorbent, for exact analysis of gas sensing properties. Our experimental system allowed for the accurate determination of the dependence of the electrical resistance (R) on oxygen partial pressure (PO2) by removing impurities in sample gases. According to the linear correlation between R versus PO21/4, we concluded that oxygen adsorbed on the SnO2 surface in the form of O2- at 350 and 450 degrees C in extremely dry conditions that was achieved using the experimental system. The competitive adsorption on the SnO2 surface in the form of O- and O2- was suggested at 300 degrees C. (C) 2014 The Electrochemical Society. All rights reserved.