A General Solution to Mitigate Water Poisoning of Oxide Chemiresistors: Bilayer Sensors with Tb₄O₇ Overlayer

Water poisoning, the dependence of gas-sensing characteristics on moisture, in oxide chemiresistors remains a long-standing challenge. Various approaches are explored to mitigate water poisoning but they are often accompanied by significant deterioration of sensing capabilities such as gas response deterioration, gas selectivity alteration, and sensor resistance increase up to unmeasurable levels. Herein, a novel sensor design with a moisture-blocking Tb₄O₇ overlayer is suggested as a facile and universal strategy to remove moisture poisoning without sacrificing intrinsic sensing properties. A submicrometer-thick coating of Tb₄O₇ overlayer on In₂O₃ sensors effectively eliminates the humidity dependence of the gas-sensing characteristics without significantly altering the gas response, selectivity, and sensor resistance. Furthermore, the general validity of the water-blocking effect using the Tb₄O₇ overlayer is confirmed in diverse gas sensors using SnO₂, ZnO, and Pd/SnO₂. The negligible moisture interference of the bilayer sensor is explained in terms of the hydrophobic nature of the Tb₄O₇ overlayer and the prevention of formation of the -OH radical by the interaction between Tb₄O₇ and In₂O₃. A universal solution to design diverse humidity-independent gas sensors with different gas selectivities can open up new pathways toward building accurate and robust gas sensors with new functionalities and high-performance artificial olfaction.