Selectivity sensing response of ZnO-xCo3O4 based sensor to CO against CH4

Abstract

Semiconductor based composites gas sensors are low-cost, high sensitivity and fast response-recovery speed. However, the selectivity of this kind of sensor to homogeneous gases is unfortunately poor. Thus far, few metal oxide semiconductor-based sensors with ultra-high selectivity to homogeneous gases have been prepared. In this paper, the ZnO-xCo3O4 composite was fabricated and their gas sensing selectivity, crystal structure, morphology, and chemical element state have been measured. The results show that the gas sensing behavior is seriously influenced by the respective concentrations of both n- and p-type materials in the ZnO-0.269Co3O4 composite as the optimized sensing materials. This ZnO-0.269Co3O4 composite, which is the crucial material for the p-n transformation, demonstrates a high selectivity value of 24.2 to CO against CH4 when roasted at 550 °C and working at 350 °C. The obtained gas sensing results show a significant breakthrough in solving the poor selectivity of ZnO-based sensors. Moreover, the repeatability and stability of 28 days was tested in this paper. And, the band theory has been proposed to explain the high selectivity of the ZnO-0.269Co3O4 sensor to CO against CH4 according to the experimentally observed gas sensing and other compositional results. The strategy employed in this paper offers a promising way to solve the poor selectivity of the metal oxide semiconductor sensors to homogeneous gases, in this case, reduced gases.