SMOX Gas Sensor Characterization of Classical Polycrystalline SnO2 Materials at Room Temperature and Spectroscopic Analysis of Their Time Dependent Performance Degradation

Abstract

This work examines a specific aspect of gas sensing with metal oxide semiconductor materials – namely, their operation at temperatures well below the conventional 200°C – 400°C range. The benefits of an ideally unheated sensor are clear: minimal power consumption, elimination of the heating element (enabling further miniaturization), and reduced costs. Known drawbacks of an unheated sensor that must be addressed include slow response and recovery times, often lower signal strength, and long term stability issues. The metal oxides investigated are tin dioxide variants prepared at different calcination temperatures and functionalized with palladium and platinum. The methods employed include DC resistance measurements for sensor characterization, as well as “operando” techniques like infrared spectroscopy of the sensor surface. A progressive degradation of initially strong sensor responses to hydrogen and carbon monoxide was observed following the final thermal treatment. Spectroscopic measurements reveal rapid onset of water condensation on the surface and a long term transformation of the oxides into less reactive molecular species. Experiments using temperature modulated operating modes demonstrate the potential and advantages of operating a sensor below the typical 300 °C threshold, while mitigating degradation through regular heating phases.