Effects of Gas Adsorption Properties of an Au-Loaded Porous In2O3 Sensor on NO2-Sensing Properties

Gas adsorption properties of semiconductor-type gas sensors using porous (pr-) In2O3 powders loaded with and without 0.5 wt % Au (Au/pr-In2O3 and pr-In2O3 sensors, respectively) at 100 °C were examined by using diffuse reflectance infrared Fourier transform spectroscopy, and the effect of the Au loading onto pr-In2O3 on the NO2-sensing properties were discussed in this study. We found the following: the resistance of the Au/pr-In2O3 sensor in dry air is lower than that of the pr-In2O3 sensor; the DRIFT spectra of both the sensors show a broad positive band between 1600 and 1000 cm-1 in dry air (reference: in dry N2 at 100 °C), which mainly originates from oxygen adsorbates and/or lattice oxygen, and that this band is much larger for the Au/pr-In2O3 sensor than for the pr-In2O3 sensor; the Au loading also increases the adsorption amount of H2O and the reactivity of NO2 on the pr-In2O3 surface; and the NO2 response of the Au/pr-In2O3 sensor in dry air is marginally higher than that of the pr-In2O3 sensor in the examined concentration range of NO2 (0.6-5 ppm) in dry air. The obtained results strongly support the enhancement of the NO2 adsorption onto the pr-In2O3 surface by Au loading, which contributed to the improvement of the NO2-sensing properties.