The irreversible R-T curves of metal oxide gas sensor under programmed temperature cycle

Metal oxide used as resistive gas sensor has been known for a long time and the resistance variation is related to the gas around sensor. This behavior can be rationalized by the model of oxygen ionization, which has relation to the oxygen adsorption. One special phenomenon that the irreversible R-T curves of metal oxide gas sensor under programmed temperature cycle appears repeatedly in previous reports. However the classical adsorption isobar cannot explain it perfectly. Herein a series of experiments were designed to reveal the laws of the irreversible R-T curves. Moreover the proper adsorption potential energy curves and the adsorption isobar for oxygen adsorption were proposed to better illustrate the mechanisms. Based on the above theory, we found a way to obtain the surface state filled with abundant chemisorbed oxygen. For pure SnO2, it can maintain at least 27 min within the 5% decrease of resistance. Simultaneously the gas sensing behavior was investigated at room temperature. It will contribute to more thoroughly understand the characteristic of metal oxide gas sensor.