Two-Dimensional MOF Modulated Fiber Nanogenerator for Effective Acoustoelectric Conversion and Human Motion Detection

The real-time application of piezoelectric nanogenerators (PNGs) under a harsh environment remains a challenge due to lower output performance and poor durability. Thus, the development of flexible, sensitive, and stable PNGs became a topic of interest to capture different human motions including gesture monitoring to speech recognition. Herein, a scalable approach is adapted where naphthylamine bridging a [Cd­(II)-μ-I4] two-dimensional (2D) metal–organic framework (MOF)-reinforced poly­(vinylidene fluoride) (PVDF) composite nanofibers mat is prepared to fabricate a flexible and sensitive composite piezoelectric nanogenerator (C-PNG). The needle-shaped MOF was successfully synthesized by the layering and diffusion of two different solutions. The incorporation of single-crystalline 2D MOF ensures a large content of electroactive phases (98%) with a resultant high-magnitude piezoelectric coefficient of 41 pC/N in a composite nanofibers mat due to the interfacial specific interaction with −CH2–/–CF2– dipoles of PVDF. As an outcome, C-PNG generates high electrical output (open-circuit voltage of 22 V and maximum power density of 24 μW/cm2) with a very fast response time (tr ≈ 5 ms) under periodic pressure imparting stimuli. Benefiting from bending and twisting functionality, C-PNG is capable of scavenging biomechanical energy by mimicking complex musculoskeletal motions that broaden its application in wearable electronics and fabric integrated medical devices. In addition, C-PNG also demonstrates an efficient acoustic vibration to electric energy conversion capability with an improved power density and acoustic sensitivity of 6.25 μW and 0.95 V/Pa, respectively. The overall energy conversion efficiency is sufficient to operate several consumer electronics without any energy storage unit. This acoustic observation is further validated by the finite element method-based theoretical simulation. Overall, the 2D MOF-based device design strategy opens up a new possibility to develop a human-motion compatible energy generator and a self-powered acoustic sensor to power up electronic gadgets as well as low-frequency noise detection.严苛环境下压电纳米发电机（piezoelectric nanogenerators, PNGs）的实际应用仍面临输出性能偏低、耐久性较差的挑战。因此，开发柔性、高灵敏且稳定的压电纳米发电机成为研究热点，可用于捕捉包括手势监测、语音识别在内的多种人体运动信号。 本文采用可规模化制备方法，通过萘胺桥联[Cd(II)-μ-I4]二维金属有机框架（metal–organic framework, MOF）增强聚偏氟乙烯（poly(vinylidene fluoride), PVDF）复合纳米纤维膜，制备得到柔性高灵敏复合压电纳米发电机（C-PNG）。 通过两种溶液的分层扩散法成功合成了针状金属有机框架。由于与PVDF的−CH2–/–CF2–偶极子存在界面特异性相互作用，引入单晶二维金属有机框架可使复合纳米纤维膜的电活性晶相占比高达98%，并获得41 pC/N的高压电系数。 实验结果表明，在周期性压力刺激下，该复合压电纳米发电机可产生高电输出（开路电压22 V，最大功率密度24 μW/cm²），且响应速度极快（tr≈5 ms）。 得益于优异的弯曲与扭转性能，该复合压电纳米发电机可通过模拟复杂肌肉骨骼运动收集生物机械能，拓展了其在可穿戴电子设备及织物集成医疗器件中的应用场景。此外，该器件还具备高效的声振-电能转换能力，最大功率密度达6.25 μW，声敏灵敏度为0.95 V/Pa。 其整体能量转换效率足以在无需储能单元的情况下驱动多款消费电子设备。该声学性能通过基于有限元法（finite element method）的理论模拟得到了进一步验证。 综上，基于二维金属有机框架的器件设计策略为开发适配人体运动的能量发电机及自供电声传感器提供了新的可能，可用于驱动电子小器件及实现低频噪声检测。