Oxidation/metallic state conversion of metal element in target gas: Endowing Ag2O-based sensor with trace-level CO detection ability

Metal oxide semiconductor (MOS)-based carbon monoxide (CO) gas sensors are confronted with the problem of poor response at low temperature (<100°C) due to the insufficient activation energy for the reaction between gas molecules and adsorbed oxygen. Inspired by the excellent catalytic ability of silver oxide (Ag 2 O) in the oxidation of CO to carbon dioxide (CO 2 ) at low temperature and the good conductivity of metallic Ag, Ag 2 O-based sensor was rationally designed for trace-level CO detection. The as-prepared CO sensor exhibited a detection range of 0–50 ppm with a low detection limit of 0.2 ppm at 80°C. Note that an abnormal decrease trend of resistance toward CO but increase trend of resistance toward other reducing gases (such as NH 3 , H 2 S and SO 2 , etc.) was observed in the as-prepared sensor, proving the good selectivity of CO toward other common reducing gases. The primary CO sensing mechanism of the transition of Ag element from the oxidation state to the metallic state was confirmed by the ex-situ X-ray photoelectron spectroscopy. This work confirms the influence of metal element’s oxidation/metallic states conversion on the gas sensing performances from the microscopic perspective, providing new ideas for the design of CO gas sensor working at low temperature.