Electrospun poly(vinylidene fluoride) nanofibers: a review on its utilization in energy harvesting devices

This review provides a comprehensive exploration of small-scale energy harvesting (EH) for low-power devices, covering various ambient energy sources such as human activities, solar, thermal, mechanical vibration, radio frequency (RF), magnetism, and temperature differentials. It explains the use of conversion mechanisms like piezoelectric, thermoelectric, pyroelectric, and triboelectric. The focus is on piezoelectric materials, particularly pyroelectric materials, delving into the fundamental principles and equations governing their operation. The mechanisms of piezoelectric and pyroelectric effects under mechanical loadings and temperature changes are also explained. The review addresses material selection for small-scale EH, discussing both inorganic and organic piezoelectric materials. It justifies the preference for lead-free materials like poly(vinylidene fluoride) (PVDF) due to its biocompatibility, mechanical flexibility, ease of thin film production, and cost-effective implementation, replacing toxic lead-based materials. The various polymorphs within PVDF are explained, emphasizing the β-phase as the one responsible for its highest piezoelectric property. Different methods to enhance β-phase content in PVDF are reviewed, with electrospinning highlighted as a one-step process eliminating the need for post-treatment steps. The research effort to fabricate PVDF-based EH devices with various techniques, dimensions, mechanical loadings, and excitations is thoroughly examined. Recent advancements in the Internet of Things and low-power devices have driven interest in device miniaturization and complex circuit module fabrication using microelectromechanical systems (MEMS) technologies. The review explores approaches for fabricating PVDF-based EH devices using MEMS techniques and discusses hybrid systems combining piezoelectric and pyroelectric effects, with PVDF as the conversion medium.