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 H-2 gas. However, the CuO- coated Zn2SnO4 showed much enhanced sensitivity and thus good selectivity for CO gas (S-CO/S-H2 similar to 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 H-2 oxidation.