Unraveling the Surface Chemistry of CO Sensing with In2O3 Based Gas Sensors

Abstract The effect of water vapor on the physical and chemical characteristics of semiconducting metal oxides (SMOX), as well as the resulting varying in sensing behavior is a highly researched field. Up to now, most investigations have been done on SnO2 and there is limited information on other interesting materials. In this work, we explored In2O3 based gas sensors using DC resistance measurements combined with diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS). The effect of water vapor and its influence on the CO detection was examined. Three different materials were chosen with varying levels of humidity cross interference humidity on the detection of this analytic. In the electrical measurements, humidity has different effects on the baseline resistance. This is related to the different initial level of surface hydroxylation, confirmed by infrared measurements through isotopic exchange experiments. The exposure to CO shows a decrease of the identified In-O bands indicating a reduction of the surface. The formation of carbonates is favored on highly hydroxylated surfaces. It is found that their formation is a subsequent reaction with formed CO2. Carbonates do not have a significant electrical impact and their formation is significantly hindered in wet conditions suggesting that H2O and CO2 have the same adsorption sites on the surface of In2O3. The measurements in nitrogen show that the sensing of CO involves the oxygen in the lattice.