Gas sensing behavior of palladium oxide for carbon monoxide at low working temperature

To explore the potential of late transition metal oxides as gas-sensing material, the mechanism and sensing performance of palladium oxide at low working temperature (<100 °C) were studied. The temperature-dependent response of as-synthesized PdO exhibited excellent sensitivity to different CO concentrations at different operating temperatures from 25 °C to 100 °C which is possibly due to the different amount of adsorption of CO at different temperatures. The oscillatory response to CO was observed in oxygen-free environment at 100 °C that might be the oscillation between adsorption and desorption of CO on PdO surface. The oxygen deficient PdOx synthesized by calcinations the sample in reducing environment was compared to well-crystalline PdO on the sensing behavior to CO in different oxygen atmosphere. In rich oxygen condition, both types of PdO maintain the long-term stability to the CO sensing. However, in pure nitrogen, lattice oxygen from well-crystalline and deficient PdO has different activity in gas sensing. Based on the correlation between rate of catalytic reaction and rate of response of sensor, the reactivity of different oxygen species, which are chemisorbed oxygen, lattice oxygen from PdO and PdOx, was compared and analyzed. The results indicated that the possible order of reactivity in CO oxidation from high to low was: PdOx (x < 1) > chemisorbed oxygen > PdO.