Nanocrystalline In2O3-based H2S sensors operable at low temperatures

Nanocrystalline In2O3-based solid solutions, with different concentration of Co, with cubic structure were successfully prepared by a simple route. The as-prepared materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The indirect heating structure sensors based on pure and doped In2O3 as sensitive materials were fabricated on an alumna tube with Au electrodes and gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The results showed that In2O3 had high response towards H2S gas at an operating temperature 150 °C, while 2.5 wt.% Co-doped In2O3 sensor exhibited enhance response and selectivity to H2S at rather lower operating temperature. Incorporation of platinum further improved the response, selectivity and response time towards H2S. Platinum incorporated 2.5 wt.% Co-doped In2O3 (Pt: 0.5 wt.%) was able to detect 10–100 ppm of H2S in air at an operating temperature of 100 °C. The selectivity of the sensor elements for H2S against liquefied petroleum gas (LPG), NH3 and H2 gases was studied. The improved gas-sensing properties can mainly be attributed to the selectivity to oxidation of H2S and noble metal additive sensitization.