Selective CO Gas Detection of Zn2SnO4 Gas Sensor

The ability of semiconductor gas sensors to differentiate between gases is essential but difficult to obtain. In this study, Zn₂SnO₄ was made to be CO selective and the possible mechanism for the selectivity was studied.The electrical and the gas-sensing properties of uncoated and CuO-coated Zn₂SnO₄ were investigated. In order to obtain an ohmic contact to Zn₂SnO₄, a ZnO layer was stacked on top of Zn₂SnO₄ and co-fired. CuO was coated by immersing the sintered sample in Cu-containing solution. Both uncoated and CuO-coated samples showed the higher sensitivity to 200 ppm CO gas than to 200 ppm H₂ gas. However, the CuO-coated Zn₂SnO₄ showed much enhanced sensitivity and thus good selectivity for CO gas (S_CO/S_H2 6) compared to the uncoated sample. The excellent selectivity of Zn₂SnO₄-based materials for CO gas was explained by the difference in the mechanisms of CO and H₂ oxidation.