Constructing a bilayer structure has not been reported as a method to mitigate the adverse effect of water poisoning on oxide chemiresistors while simultaneously enhancing gas selectivity and sensitivity. To address this challenge, pyrochlore-Bi₂Sn₂O₇ has been first utilized as an overlayer on a ZnO sensing layer for constructing a bilayer acetone chemiresistor, leading to remarkable improvement in the performance for trace-level (500 p-p-b) acetone detection under high humidity (80% relative humidity). In addition, owing to the catalytic predecompositions of ethanol across the overlayer, an outstanding acetone gas selectivity (S_acetone/S_ethanol = 2.9) has been achieved, with a more than 4-fold improvement compared with monolayer ZnO chemiresistor (S_acetone/S_ethanol = 0.7). More significantly, comprehensive experiments coupled with in situ characterizations have verified the generation of hydroxyl radicals (•OH) on the Bi₂Sn₂O₇ overlayer. These radicals are capable of enhancing the kinetics between •OH and acetone, reducing the activation energy required for the gas sensing reaction, and thus leading to an unexpected phenomenon of enhanced acetone sensitivity under high humid conditions (S_{acetone at 80% RH} > S_{acetone at 5% RH}). These demonstrations offer crucial insight into the precise design of highly efficient overlayers for breath sensing.

中文翻译：

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Bi2Sn2O7 外层有助于双层化学电阻器对呼气丙酮进行不受湿度影响且高度选择性的检测


构建双层结构尚未被报道为减轻水中毒对氧化物化学电阻器的不利影响，同时提高气体选择性和灵敏度的方法。为了应对这一挑战，焦绿石-Bi₂Sn₂O₇ 首先被用作 ZnO 传感层上的覆盖层，用于构建双层丙酮化学电阻器，从而显著提高了高湿度（80% 相对湿度）下痕量 （500 p-p-b） 丙酮检测的性能。此外，由于乙醇在外层上的催化预分解，实现了出色的丙酮气体选择性（S_丙酮/S_乙醇 = 2.9），与单层 ZnO 化学电阻器（S_丙酮/S_乙醇= 0.7）。更重要的是，综合实验与原位表征相结合，验证了 Bi₂Sn₂O₇ 外层上羟基自由基 （•OH） 的产生。这些自由基能够增强 •OH 和丙酮之间的动力学，降低气体传感反应所需的活化能，从而导致在高湿度条件下丙酮敏感性增强的意外现象（80_{% RH 时的 S 丙酮} > > S_{丙酮 在 5% RH 时} ）。这些演示为用于呼吸传感的高效外层的精确设计提供了重要的见解。