Pressure-crystallized piezopolymer/ionomer/graphene quantum dot composites: A novel poling-free dynamic hybrid electret with enhanced energy harvesting properties

We report the design and fabrication of a novel self-powered poling-free dynamic electret by hybridizing a piezocomposite with graphene quantum dots (GQDs). The polymeric hybrid piezoelectret was prepared through the solution casting of a ternary poly (vinylidene fluoride) (PVDF)/Nafion/GQD composite followed by pressure crystallization. During the fabrication, Nafion ionomer filled PVDF cells, resulting in the formation of artificial macroscopic dipoles, and GQDs induced the self-assembly of macromolecular chains in PVDF cell walls, leading to the growth of piezoelectric nanowires. The synergistic action of the man-made macroscale dipoles of Nafion and the inherent molecular dipoles of PVDF cells, together with the deformation and relaxation of the in situ formed polar crystalline polymeric nanowires, enabled the PVDF/Nafion/GQD composites to convert kinetic mechanical energy into electricity with remarkably enhanced efficiency. Compared with its PVDF/Nafion counterpart, the electrical output of a developed PVDF/Nafion/GQD nanogenerator, without any treatment of electrical poling, achieved considerable increase in both short-circuit current and open-circuit voltage, and showed better stable and durable performance for more than 20000 continuous working cycles. Particularly, the PVDF/Nafion/GQD composite also exhibited more improved mechanical-to-electrical conversion even if it has endured a long-term brine disposal. The study presented herein may open a new avenue for the manufacturing of a new class of electret-transducer materials that permit applications in powering autonomous micro-/nano-systems with high operational and environmental stability.