Unidirectional porous PVDF Piezoelectrets fabricated via gradient ice-templating for enhanced energy harvesting performance

Next-generation energy systems require a device that can deliver flexibility and high piezoelectric efficiency. Polyvinylidene fluoride (PVDF) polymer offers excellent flexibility but suffers from limited piezoelectric performance. In this work, hierarchically porous PVDF structures with vertically aligned pores were fabricated via an eco-friendly ice-templating method with gradient cooling, by varying the PVDF concentration from 3 to 15 wt% to overcome these limitations. The calculated electroactive β-phase fraction of the piezoelectret with 15 wt% was 86.77%, which is significantly higher than the 72.63% value of the flat and dense PVDF sample. The piezoelectret PVDF device with 15 wt% generated a maximum electrical output of 35 V and a peak current of 1.1 μA under a constant force, which is significantly higher than that of a dense PVDF-based device. The electromechanical mechanism and the influence of internal porosity on the PVDF device were investigated using multiphysics simulations. The simulation results are in good agreement with the experimentally observed output trends, confirming that the porous piezoelectret structure consistently outperforms the dense PVDF structure. In addition, the unidirectionally grown porous piezoelectret-based device can capture electrical signals under ambient conditions through the impact of falling water droplets, while also reducing organic residues in seawater and rainwater. This dual capability highlights the device as a promising candidate for self-sustained systems that unite energy harvesting with water purification, and points to its potential use in portable purification, field deployable monitoring, and other environmentally relevant applications.