High-temperature humidity sensors based on WO3-SnO2 composite hollow nanospheres

Three kinds of humidity sensors were fabricated from WO3-SnO2 composite hollow nanospheres (WO3-SnO2 HNS), WO3 nanoparticles (WO3 NPs) and SnO2 nanoparticles (SnO2 NPs). WO3-SnO2 HNS were prepared by a facile hydrothermal process with a diameter and thickness of about 550 nm and 30 nm, respectively. Temperature-dependent properties of as-prepared humidity sensors were investigated at various values of relative humidity and temperature. It was found that the WO3-SnO2 HNS humidity sensor showed good performance at 80 degrees C. The response time, recovery time and sensitivity were evaluated while switching the humidity between 35% RH and 98% RH. The response time decreased from 289 to 29 s, the recovery time reduced from 22 to 8 s, and the sensitivity changed from 16.2 to 11.4 as the work temperature was raised from 24 to 80 degrees C. An opposite humidity sensing phenomenon was observed between WO3 NPs and SnO2 NPs at a high temperature, which might explain the temperature-dependent properties of the WO3-SnO2 HNS humidity sensor. This work could stimulate a right approach to design practical humidity sensors with high sensitivity, long stability and fast response.