The CO and H2 gas selectivity of CuO-doped SnO2–ZnO composite gas sensor

For the selective detection of reducing gases (CO gas against H2 gas, or vice versa), SnO2–ZnO composites were fabricated and the surface was coated with CuO. The electrical conductivity and the CO and the H2 gas sensing properties of CuO-coated SnO2–ZnO composites were examined between 80 and 450 °C. O, coated and thus doped to SnO2, apparently acted as a catalyst and thus lowered the sensing temperature and slightly increased the sensitivity values for both CO and H2 gases. The ZnO addition into CuO-doped SnO2 increased the sensitivity to CO gas at low temperature and the sensitivity to H2 gas at high temperature due to the combined effect of the microstructure and the composition. As a result, the high selectivity for CO gas was obtained between 150 and 250 °C while the high selectivity for H2 gas was shown between 310 and 400 °C, depending upon the ZnO content. As the content of ZnO increases above 3 mol%, both the CO and the H2 selectivities decreased.