Advances in ferrofluid-based triboelectric nanogenerators: Design, performance, and prospects for energy harvesting applications

Small-scale electronic devices need self-powering technology, and one way to do that is to use mechanical energy harvesters. These devices can turn ambient mechanical energy into electricity. Triboelectric nanogenerators (TENGs) are the best choice for converting mechanical energy into electrical energy, but they have a problem in converting ultra-low vibrations in the environment. Traditional TENGs with solid frictional layers are not wellsuited for this purpose. To address this limitation, liquid-solid (L-S) TENGs have emerged, which can capture ultra-low vibrational frequencies due to their fluidic nature. Despite this advantage, L-S TENGs exhibit lower energy conversion efficiency than their solid counterparts, and they cannot be used in hybrid energy harvesting. New research has started using ferrofluids in TENGs to address these issues. The resulting ferrofluid-solid based (FF-S) TENGs have showcased a promising outcome by replacing the liquid component with ferrofluids. These systems have demonstrated their capability to capture ultra-low vibrational frequencies effectively and are also used for hybrid energy harvesting. In the current review, we present a comprehensive overview of diverse designs, operational mechanisms, and applications of FF-S TENGs. Furthermore, we delve into the potential opportunities and prospects for integrating FF-S TENGs into practical applications.