A new strategy for humidity independent oxide chemiresistors: Dynamic self-refreshing of In₂O₃ sensing surface assisted by layer-by-layer coated CeO₂ nanoclusters

The humidity dependence of the gas sensing characteristics of metal oxide semiconductors has been one of the greatest obstacles for gas sensor applications during the last five decades because ambient humidity dynamically changes with the environmental conditions. Herein, a new and novel strategy is reported to eliminate the humidity dependence of the gas sensing characteristics of oxide chemiresistors via dynamic self-refreshing of the sensing surface affected by water vapor chemisorption. The sensor resistance and gas response of pure In₂O3 hollow spheres significantly change and deteriorate in humid atmospheres. In contrast, the humidity dependence becomes negligible when an optimal concentration of CeO₂ nanoclusters is uniformly loaded onto In₂O₃ hollow spheres via layer-by-layer (LBL) assembly. Moreover, In₂O₃ sensors LBL-coated with CeO₂ nanoclusters show fast response/ recovery, low detection limit (500 ppb), and high selectivity to acetone even in highly humid conditions (relative humidity 80%). The mechanism underlying the dynamic refreshing of the In₂O₃ sensing surfaces regardless of humidity variation is investigated in relation to the role of CeO₂ and the chemical interaction among CeO₂, In₂O3, and water vapor. This strategy can be widely used to design high performance gas sensors including disease diagnosis via breath analysis and pollutant monitoring.