Electrode-free piezoelectric nanogenerator based on carbon black/polyvinylidene fluoride–hexafluoropropylene composite achieved via interface polarization effect

[Display omitted] •Development of electrode-free piezoelectric nanogenerator.•Polyvinylidene fluoride–hexafluoropropylene as matrix and carbon black as filler.•Electrode-free signal transmission via interface polarization effect.•CB particles as both inner electrode and piezoelectric enhancer.•Facile repair via re-spraying due to self-polarization-based preparation. Flexible piezoelectric nanogenerators (PENGs) with high sensitivity, easy deformability, anti-corrosion features, and facile fabrication are highly advantageous for biological tissue sensing/monitoring applications in complex environments. The large-scale and low-cost preparation of flexible piezoelectric polymers requires additional electrode layers for charge collection, compromising the flexibility and corrosion resistance of the PENGs while increasing their fabrication difficulty and cost. In this study, we developed an electrode-free PENG based on a composite film composed of polyvinylidene fluoride–hexafluoropropylene (PVDF-HFP) as the matrix, and carbon black (CB) as the filler. With an appropriate content of approximately 5 wt%, and under the interface polarization effect, the CB particles in the composite film acted as both the inner electrode and the piezoelectric enhancer, thus realizing a sensing functionality without the use of an additional electrode. The effects of the positions of CB particles in the PVDF matrix on the potential distribution, and the functions of CB polarization in the inner electrode and piezoelectric enhancer were simulated using COMSOL Multiphysics software. An excellent piezoelectric performance was achieved, including a current of 0.66 μA, voltage of 17.6 V, and charge of 4.7 nC. Further, electrode-free PENGs, with the multi-self-polarization PVDF-HFP matrix exhibit a promising application as sensors for effectively monitoring human activities and complex environments and can be effectively repaired (up to 80 %) via a facile spray-coating process.