Enhanced Biomechanical Energy Harvesting and Gesture Monitoring: Superhydrophobic, High-Performance Hybrid Piezo-Triboelectric Nanogenerator Using Flexible Nanofibers

The burgeoning field of nanogenerators presents ongoing challenges in elevating performance through innovative strategies and architectures. This study addresses these challenges by synergistically combining the distinct properties of piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG). It harnesses the bulk polarization effect inherent in PENG and the contact electrification and electrostatic induction in TENG, thereby leveraging their combined strengths. Our focus is the development of a novel hybrid piezo-triboelectric nanogenerator (HPTENG), which employs a multi-layered nanofiber architecture, showing significant promise for applications in flexible electronics and electronic skins. This work introduces composite nanofibers composed of polyvinylidene fluoride (PVDF)-MoS2-MXene (PMMX), capitalizing on the superior piezoelectric effect of MoS2-PVDF and the two-dimensional structure and abundant dangling bonds of MoS2-MXenes. We synthesized MXene (Ti3C2) via chemical etching and MoS2 using the hydrothermal method. The resulting TENG, employing PMMX nanofibers as the negative triboelectric layer and Nylon 6,6 nanofibers as the positive layer, exhibited an open-circuit voltage (Voc) of 25 V and short-circuit current (Isc) of 1.2 µA. The PENG displayed a Voc of 10 V and Isc of 2.0 µA. Notably, the HPTENG demonstrated enhanced performance with a Voc of 100 V and Isc of 6.0 µA. This amplification can be attributed to the synergistic Piezoelectric-Triboelectric (TE-PE) effect, facilitating the conversion of random, low-frequency mechanical energy into electricity by altering the charge density in electrodes under external forces. Our study further emphasizes the necessity of augmenting the electrical performance of PENGs and TENGs to improve energy harvesting efficiency and signal-to-noise ratio. The practicality of HPTENG was validated by attaching it to various human joints, including fingers, elbows, palms, and knees, effectively monitoring real-time motion during activities like bending, running, and walking. Additionally, the need for hydrophobicity in wearable devices, to mitigate the influence of sweat, is addressed through contact angle studies of electrospun PMMX fibers, which demonstrated a significant angle of 117.5 degree, confirming their hydrophobic nature. The promising results of this study highlight the potential of HPTENG as an effective system for human gesture monitoring. The unique material composition and straightforward fabrication strategy presented here pave the way for novel solutions in the realm of advanced energy harvesting.