Study On Hydrogen Sensitivity Characteristics Of WO 3 / Carbon Nanotube Composites

With the wide application of hydrogen in our daily lives, it is very important for us to research the hydrogen sensor. There are a lot of researches about the traditional resistance hydrogen sensor based on the metal oxide semiconductor, which develops very quickly, having the advantages of simple structure, small volume and low cost. But it also has certain limitations, such as large bulk resistance, low sensitivity and poor selectivity. Introducing multi-walled carbon nanotubes?MWCNTs?, this paper is based on the material of WO₃ and use its good conductive performance to reduce the body resistance of material so as to enhance the sensitivity of the material. As Pd has a strong adsorption for hydrogen, so it can enhance the selectivity of hydrogen that doping with Pd in the sensitive materialsIn this paper, sol-gel method is adopted for the composite material of Pd-WO₃/MWCNTs. We adopt the way of coating the film twice. First, the WO₃/MWCNTs film is prepared, then Pd doped WO₃ film is made up on it so that carbon nanotubes can be completely covered under the film, avoiding the contact with the water vapor, which can make it fully in charge of transport, thus reduce the body resistance of material.The initial current of WO₃ thin films, Pd doped WO₃ thin film and composite material of Pd-WO₃/MWCNTs are measured and we find that initial resistance has been greatly reduced after adding MWCNTs. We got the optimum operating temperature is about 250? through analyzing the gas sensing properties of Pd-WO₃/MWCNTs films. The optimum operating temperature was decreased compared with no doping MWCNTs. At this temperature, the sensitivity can reach 221.6 of Pd-WO₃/MWCNTs composite material to 1200 ppm hydrogen. And the selectivity of the films to hydrogen is very good after mixing with Pd, and the sensitivity of some other reducing gases are very low.