Single-Electrode Gas Sensors Based on an In2O3–Graphene Composite

Indium oxide–graphene (In2O3/Gr) composites (2.0 and 4.0 wt % graphene) have been prepared by sol–gel synthesis and the microstructure and gas-sensing properties of the composites (in the composition of single-electrode ceramic sensors) have been studied. The composites have the form of heterogeneous systems formed by the In2O3 phase ranging in crystallite size from 7 to 12 nm and the graphene phase. The microstructure of the composites has been shown to depend on the fabrication process. The In2O3/Gr-based sensors have higher sensitivity to reducing (CH4) and oxidizing (NO2) gases than do In2O3-based sensors and shorter response and recovery times. Possible causes of their better gas sensitivity are the formation of spatially separated positively and negatively charged regions, which leads to electron concentration redistribution in individual phases; the increased defect density in the indium oxide and graphene phases in the composite; and the large specific surface area of graphene.