Suspension Plasma Sprayed ZnO Coatings for CO2 Gas Detection

Hollow spherical ZnO, prepared by hydrothermal synthesis method with a soft template, was dispersed in deionized water to form a uniform suspension. The micromorphology, phase composition and UV absorbance of ZnO powder were analyzed by SEM, EDS, XRD and UV–Vis. The ZnO coatings were deposited on Al 2 O 3 substrates equipped with Pt electrodes to fabricate gas sensors by suspension plasma spraying. The effects of CO 2 concentration and relative humidity (RH) on the gas sensing properties of the ZnO coatings at room temperature (~ 25 °C) were studied, and the gas sensing mechanism was discussed. The experimental results elucidate two results: First, the response value rises with the increase of CO 2 concentration under the condition of constant RH; second, the responses for concentrations of 3, 4, 5% CO 2 rise with RH increasing from 0-60%. Under the condition of 400 ppm CO 2 , the response rises from 6.87-57.92, with an increase of RH from 20-80%.