Polyoxometalate-derived cubic/orthorhombic WO3 heterophase junction: High sensitivity for detecting ppb-level NO2

WO 3 is a representative metal oxide semiconductor gas sensing material with good selectivity and high sensitivity. However, high electron-hole recombination is a common drawback of WO 3 -based gas sensors. Here, we used silicotungstic acid (SiW 12 ), a classical Keggin-type polyoxometalate (POM) as precursor. After oxidation, WO 3 with cubic/orthorhombic mixed-phase were in-situ formed. Gas sensing performances of the WO 3 to ppb-level NO 2 gas were tested to explore whether the POM-derived WO 3 has advantage for gas sensor applications. Surprisingly, the c/o-WO 3 calcined at 800 °C exhibit a response value of 5.239 to 500 ppb NO 2 with very high selectivity, good long-term stability, repeatability and humidity resistance. By mechanism analysis, the bandgap positions of o-WO 3 and c-WO 3 are staggered, forming an internal electric field that favours electron-hole separation and improves the gas sensing performance. This work transforms POMs into two-phase mixed WO 3 , providing a new idea for the application of POMs as precursors in gas sensors.