Poly(vinylidene fluoride) Copolymers for Hybrid Piezoelectric and Triboelectric Energy Harvesting

Converting environmentally wasted energy into electrical energy to supply low-power devices is a relevant objective for achieving clean energy management to support the Internet of Things and Industry 4.0 paradigms. Flexible poly(vinylidene fluoride) (PVDF) polymers are widely used to generate electrical energy from mechanical stimuli. This can be achieved by exploiting their piezoelectricity in piezoelectric nanogenerators (PENGs) and their high electron affinity in triboelectric nanogenerators (TENGs). The two working principles can also be combined into hybrid mechanical energy harvesters (piezo-tribo nanogenerators, PTENGs). This study reports on the energy harvesting performance of PVDF-based polymers with varying chemical compositions, triboelectrification properties, crystalline phase content, and dielectric responses. We investigated the electromechanical performance of TENGs and hybrid PTENGs based on the PVDF homopolymer and its copolymers, which include monomer units with varying hydrogen, fluorine, and chlorine atoms. Poled PVDF presented the highest PTENG electrical output, achieving a peak voltage of ≈50 V and a peak power density of 30 μW/cm2. Both poled PVDF and electrospun fibers produced a voltage output of 1 V in the piezoelectric mode, while the hybrid PTENG reached voltages of nearly 25 and 52 V, respectively. This demonstrates the significant influence of the triboelectric effect on hybrid systems. Triboelectrification between two dielectric materials was theoretically modeled using charge transfer principles, resulting in a representation that aligns well with experimental data. The maximum power output was found to increase with both the sample area and frequency.