Observation on\nSwitching Properties of WO<sub>3</sub>‑Based H<sub>2</sub> Sensor\nRegulated by Temperature and Gas\nConcentration

Transition metal oxide semiconductors have great potential\nfor\nuse in H<sub>2</sub> sensors, but in recent years, the strange phenomena\nabout gas-sensitive performance associated with their special properties\nhave been more widely discussed in research. In some cases, the resistance\nof transition metal oxide gas sensors will emerge with some changes\ncontrary to their intrinsic semiconductor characteristics, especially\nin gas sensor research of WO<sub>3</sub>. Based on the hydrothermal\nsynthesis of WO<sub>3</sub>, our work focuses on the abnormal change\nof tungsten oxide resistance to different gases at low temperature\n(80–200 °C) and high temperature (above 200 °C).\nThrough in situ FT-IR and in situ XPS, combined with density functional\ntheory calculations, a new reasonable explanation of WO<sub>3</sub> is proposed for the abnormal resistance change caused by temperature\nand the strange response due to gas concentration. The occurrence\nof these findings can be attributed to the synergistic effect resulting\nfrom the presence of two contributing factors. One of them is attributed\nto the alteration in the surface valence state of WO<sub>3</sub> induced\nby gas, resulting in the reduction of W<sup>6+</sup>. The other one\nis due to the reaction between gas and adsorbed oxygen on the surface\nof WO<sub>3</sub>. This work presents a novel and rational concept\nfor addressing the reaction mechanism between gas and transition metal\noxide semiconductors, thereby paving the way for the development of\nhighly efficient gas sensors based on transition metal oxide semiconductors.