1成果简介

　　二维（2D）MXene因其巨大的比表面积和高导电性，成为湿度传感器的理想材料。然而，其层间距的限制使得实现高灵敏度湿度传感器变得困难。本文，北京理工大学丁洁 副教授、范绪阁 教授、中北大学 张文栋 教授等在《ACS Appl. Electron. Mater》期刊发表名为“Highly Sensitive Flexible Humidity Sensor Based on Bacterial Cellulose/MXene/Graphene Oxide Composite Film”的论文，研究通过采用细菌纤维素（BC）/MXene/氧化石墨烯（GO）复合薄膜，成功开发出高灵敏度柔性湿度传感器：其中BC构建用于固定MXene的网络结构，而GO则用于增强其吸湿性。
　　基于BC/MXene/GO复合材料制备的湿度传感器表现出高达217%的响应度、24.2秒的响应时间、11%至98%相对湿度（RH）的宽测量范围及优异的重复性。其湿度传感机制归因于膨胀效应与格罗特赫斯链式反应，且该效应随复合材料中氧化石墨烯含量的增加而增强。基于BC/MXene/GO复合材料制备的湿度传感器成功应用于呼吸监测与指尖非接触开关。这些成果为基于MXene及相关二维材料的柔性湿度传感器快速发展提供了重要支撑。
　　2图文导读 

 　　图1. Schematic of preparation processes of MXene, BC/MXene/GO composite material, and flexible humidity sensors based on BC/MXene/GO.

　　图2. (a–c) SEM images of BC, MXene and GO; (d) SEM image of BC/MXene/GO composite; (e–g) EDS images of BC/MXene/GO with C, O, and Ti; (h) XRD patterns of MXene, GO, BC, and BMG2, respectively; (i, j) XPS spectral images of humidity sensor based on BC/MXene/GO in C 1s and O 1s.

　　图3. (a) Humidity response performance of different devices (BMG0-BMG5) as the relative humidity changed between 11 and 98% RH, respectively. (b) Response/recovery time of BMG2 as the relative humidity changed between 11 and 98% RH. (c) Cyclic response curve of BMG2 as the relative humidity changed between 11 and 98% RH. (d) Hysteresis measurement of BMG2. (e) Dynamic humidity response performance of BMG2. (f) Fitting plot of humidity response data of BMG2. (g) Resistance response of BMG2 as it was gradually bended. (h) Variation of the base resistance of BMG2 with time. The device was measured at humidity environment of 11% RH for 3 min every 2 days. (i) Responsivity changes of BMG2 at various humidity levels with time (the initial relative humidity: 11%RH).

　　图4. Schematic diagram of humidity sensing mechanism (swelling effect) of the prepared flexible humidity sensors based on a BC/MXene/GO composite with low GO content.

　　图5. (a) Respiratory monitoring experiment of BMG2 in rapid and slow breathing modes, respectively. (b) Finger proximity experiment of BMG2 with different distances between the finger and the top surface of BMG2. (c) Fitting plot of the relative resistance change of BMG2 versus finger distance. (d, e) Gesture recognition experiment of four humidity sensor samples (BMG2) that work as four contactless switches.
　　3小结
　　本研究采用简易的层涂覆法，实现了基于不同氧化石墨烯含量的BC/MXene/GO复合材料的电阻式柔性湿度传感器。基于BMG2的柔性湿度传感器展现出最佳响应性能：灵敏度达217%（是纯MXene的16倍），响应时间仅24.2秒，恢复时间14.6秒，且具有良好的重复性和可靠性。此外，BMG2在高湿度与低湿度区间均表现出优异线性特性。本文探讨了制备湿度传感器的吸湿机理，包括膨胀效应和格罗特赫斯链式反应，其作用机制取决于BC/MXene/GO复合材料中的氧化石墨烯含量。基于BMG2的柔性湿度传感器成功应用于人体呼吸监测和非接触式指纹检测，并进一步验证了BMG2实现简单手势识别的功能。
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