Co3O4-A systematic investigation of catalytic and gas sensing performance under variation of temperature, humidity, test gas and test gas concentration

A “new” gas sensing material; Co3O4, which is mainly known as a good catalyst for CO combustion, was investigated by means of resistance and catalytic conversion measurements. A systematic screen of sensors with sensitive layers of undoped, 0.2 wt% Pd- and Pt-doped Co3O4 was done by variation in temperature, humidity, test gas, and test gas concentration. It was found that all three kinds of materials show best response to EtOH (sensor signals up to 28,000 @ 100 °C, 0% r.h., 90 ppm), good response to CO (sensor signals up to 100 @ 100 °C, 0% r.h., 50 ppm), but only a marginal response to CH4 exposure, in particular at 50% r.h. The occurrence of maxima in sensor signals at 50% r.h. indicates a change in the surface reaction mechanism for both EtOH (175-200 °C) and CO exposure (125-150 °C). The 0.2 wt% Pt-doped sensors display superior gas sensing properties concerning recovery times and sensor signal height as well as a higher overall catalytic conversion. Additionally, at 0% r.h. and under exposure to CO a comparison with the benchmark material SnO2 @ 300 °C reveals even higher sensor signals for Co3O4 @ 100 °C.