Resistive CO gas sensors based on In2O3 and InSnOx nanopowders synthesized via starch-aided sol-gel process for automotive applications

Pure and Sn-doped In2O3 nanopowders have been synthesized by a starch-aided sol–gel process. A detailed characterization by means of TEM and HRTEM, TG–MS, XRD and 119Sn solid-state NMR analysis has been carried out. It has shown that the grains of the samples as-synthesized and dried at 120◦C are in the nanometer range. Moreover, on the Sn-doped In2O3 sample, the homogeneous distribution of the dopant with no segregation phase effects has been demonstrated. The thermal treatment at 550◦C induced an increase of grain size up to about 30 nm and of crystallinity. The behaviour of the resistive gas sensors based on the synthesized nanopowders in the monitoring of carbon monoxide for automotive applications has been evaluated. Electrical and sensing tests have been performed on the sensor devices in a thick film configuration depositing pure and Sn-doped In2O3 nanopowders by screen-printing over a ceramic substrate. The results have been discussed in relation to the chemical and microstructural properties of the synthesized nanopowders. The good sensing behaviour of these samples has been associated with their special features such as very small grains and high oxygen vacancies due to the peculiar reductive character of starch pyrolysis.