“…Due to the advantages of low cost, high sensitivity, stable performance, being easy to fabricate and compatibility with modern electronic devices, metal oxide semiconductors (MOSs) have been widely used for the detection of various gases, including H 2 S, 16–19 NO 2 , 20 NH 3 , 21,22 CO, 23 H 2 , 24 C 2 H 5 OH, 25 formaldehyde, 26 NO 2 , 27 and other volatile vapors. 28 Metal oxides for gas-sensing were mainly focused on binary compounds like SnO 2 , 29–31 ZnO, 32–35 CuO, 36,37 TiO 2 , 38,39 NiO, 40,41 and so on. As very promising sensing materials, multi-element metal oxides have attracted increasing attention due to their rich multi-valence state cations, unique crystal structure characteristics, and controllable composition in recent years.…”