Self-Poled Poly(vinylidene fluoride)/MXene Piezoelectric Energy Harvester with Boosted Power Generation Ability and the Roles of Crystalline Orientation and Polarized Interfaces

Micropiezoelectric devices have become one of the most competitive candidates for use in self-powered flexible and portable electronic products because of their instant response and mechanic-electric conversion ability. However, achievement of high output performance of micropiezoelectric devices is still a significant and challenging task. In this study, a poly(vinylidene fluoride) (PVDF)/MXene piezoelectric microdevice was fabricated through a microinjection molding process. The synergistic effect of both an intense shear rate (>10⁴ s^-1) as well as numerous polar C-F functional groups in MXene flakes promoted the formation of β-form crystals of PVDF in which the crystallinity of β-form could reach as high as 59.9%. Moreover, the shear-induced shish-kebab crystal structure with a high orientation degree (f_h = ∼0.9) and the stacked MXene acted as the driving force for the dipoles to regularly arrange and produce a self-polarizing effect. Without further polarization, the fabricated piezoelectric microdevices exhibited an open-circuit voltage of 15.2 V and a short-circuit current of 497.3 nA, under optimal conditions (400 mm s^-1 and 1 wt % MXene). Impressively, such piezoelectric microdevices can be used for energy storage and for sensing body motion to monitor exercise, and this may have a positive impact on next-generation smart sports equipment.