Recent advances in metal oxide reinforced polymer composites for efficient piezoelectric energy harvesting applications

In recent years, there has been a growing demand for miniaturized and multipurpose gadgets. Invention of wearable gadgets like smartwatches, rings, and IoT's helps people to understand physical activities and health conditions. On the other hand, the environmental problems surrounding fossil fuel consumption and the limited battery lifespan made the researchers to develop clean and green energy sources. Piezoelectric nanogenerators (PENGs) having inherent ability to convert mechanical strains to electrical energy seek remarkable attention for energy harvesting applications. Nowadays, more researchers focus on polymer-based PENGs due to their excellent flexibility and compatibility, but the poor piezoelectric coefficient limit them to produce feeble electrical output, insufficient for wearable devices. Metal oxides improve the piezoelectric characteristics of polymer composites due to intrinsic piezoelectric properties and their ability to bind with polymers enhances its electrical output, morphological, mechanical, and thermal properties. This review lays out an extensive overview of the latest advancements in metal oxide-reinforced polymer composites for efficient energy harvesting applications. Here, essential characteristics of the PENGs, their structural properties, and their energy harvesting mechanism are discussed in detail. Furthermore, the review discovers the potential applications of PENGs, including wireless sensors like tire pressure monitoring systems, health monitoring systems, and wearable devices.