Enhanced electroactive β-phase of the sonication-process-derived PVDF-activated carbon composite film for efficient energy conversion and a battery-free acceleration sensor

Abstract

A flexible, lightweight, and highly efficient poly(vinylidene fluoride)-activated carbon (C-PVDF-AC) composite film in 30 V/V% concentration was derived using the sonication process, followed by heat treatment, and studied for unconventional energy conversion and active sensing purposes (without battery energy). The use of the sonication process originates the high electroactive β-phase of PVDF without the requirement for an additional electrical poling process. The substitution of AC fillers in PVDF stabilized and improved the electroactive β-phase of PVDF and also acted as electrical conduction paths between –CH₂–/–CF₂– electric dipoles of PVDF. The frequency-dependent dielectric constant and electrical conductivity of the sonication-process-derived PVDF and composite films showed a better response, which was due to the improvement in the electric dipole–dipole interactions and interfacial interactions between the AC fillers and PVDF molecular chains. An unpoled PVDF nanogenerator (P-NG) and composite nanogenerator (C-NG) generated high peak-to-peak V_OC and I_SC values of 37.77 V and 299 nA and 37.87 V and 0.831 μA, respectively, under 6.6 kPa pressure. No electrical poling effect was observed in P-NG output, whereas C-NG (30 V/V%)'s output showed a significant voltage increment (≈30%) and current increment (≈96%). The obtained instantaneous power density ≈63.07 mW m⁻² of C-NG was sufficient to drive low-power electronic devices such as LEDs and displays. It was experimentally verified that the C-NG device itself can act as a self-powered acceleration sensor (SAS) and the output voltage showed a linear behavior between the input accelerations from 0.5 to 5 m s⁻² and the shaft load.