Electrical and CO gas sensing properties of layered ZnO–CuO sensor

The electrical conductivity and the CO gas-sensing characteristics of ZnO–CuO-layered samples were studied and compared with those of ZnO samples modified with various dopants. Layered ZnO–CuO samples were fabricated by sequentially pressing ZnO and CuO powders in a die followed by co-firing at 800°C for 3 h. The control of porosity of both ZnO and CuO enabled a stable contact between ZnO and CuO. The addition of SnO2 into ZnO prevented the densification of ZnO and further addition of Al2O3 and CuO, respectively, increased and decreased the electrical conductivity of porous ZnO without further changing the microstructure. All layered samples showed the electrical conductivity mostly determined by the heterocontact interface. The layered sample with Al-doped ZnO showed the highest CO gas sensitivity among all samples.