Based on the above results, the gas sensor based on the SnO2-Pd-Pt-In2O3 composite exhibits low operating temperature (160◦C),ultra-high response to a range of concentrations of methanol(5 ppm–100 ppm), excellent selectivity, remarkable repeat ability and long-term stability. The results indicate that the as-prepared SnO2-Pd-Pt-In2O3 composite is a promising gas-sensing material for methanol detection. SnO2 and In2O3 are typical n-type oxide semiconductor mate-rials. Their response mechanism involves the interaction between the detected gases and chemisorbed oxygen ions on the surface of the materials, leading to the resistance change of the sensor [46].In order to clarify the gas sensing performance of the as-prepared SnO2-Pd-Pt-In2O3composite gas sensor, a possible reaction mechanism is proposed, as presented in Fig. 10(a). In air, the oxygen molecules could adsorb onto the sample of the outer surface and capture free electrons from the sample, and will create absorbed Ox−ions (O2(ads)−, O(ads)−, O(ads)2−) at grain boundaries, and a thick space charge layer will be formed. The presence of the nega-tive surface charges will generate a higher surface potential barrier,and lead to a high electrical resistance. This process may be, shown as follows [20]: