Near room temperature CH4 sensing and role of oxidation states for phase pure Wadsley VnO2n+1 nanostructures

Abstract

Metal-oxide based gas sensors with structural integrity during sensing hazardous gases near room temperature are of potential requirement. Methane (CH4) sensing by phase-pure Wadsley VnO2n+1 nanoparticles and the role of oxidation state in sensing are reported at a low operating temperature of 40 °C, which is very close to room temperature for the lowest concentration of 50 ppm. As VOx is extremely susceptible to change its oxidation state forming various metastable phases in the presence of air even close to room temperature, a systematic study of methane sensing behavior was performed with in-situ oxidation for the whole sensing-temperature range. The phases of the Wadsley nanoparticles were confirmed by Raman spectroscopic measurements. VO2 is particularly attractive among the Wadsley phases because of its first-order metal to insulator phase transition (MIT) near room temperature (340 K). A brief comparison of CH4 sensing of the phase-pure VnO2n+1 nanoparticles is provided for 50–500 ppm CH4 and the most suitable phase is identified on the basis of sensing response.