Advances in Triboelectric Energy Harvesting at Liquid–Liquid Interfaces

The rapid development of energy harvesting devices, driven by the need for sustainable energy, has led to innovative solutions in nanotechnology. Triboelectric nanogenerators (TENGs) stand out for their ability to convert mechanical energy from various environmental sources into electrical power. This review delves into the recent advancements in TENGs, particularly those focusing on liquid–liquid interfaces. Liquid–liquid charge exchange (L-LCE) TENGs, an emerging innovation, offer several advantages over traditional solid-based TENGs, including enhanced adaptability and efficiency under variable environmental conditions. The triboelectric effect and electrostatic induction, essential to TENGs, enable energy harvesting from familiar sources, such as human motion, wind, ocean waves, and vibrations. The review explores the charge transfer mechanisms between immiscible liquids, such as deionized water and transformer oil, focusing on the electric double layer (EDL) formation at the liquid–liquid interface. Factors such as ion concentration and chemical composition influencing the EDL are analyzed. Liquid–liquid interactions allow for higher surface charge densities and a superior energy harvesting efficiency. This makes L-LCE TENGs particularly promising for small-scale applications such as wearable electronics and medical devices as well as large-scale systems. The potential of liquid–liquid TENGs in remote, off-grid environments is also discussed, where traditional power sources may not be viable. This review covers current mechanisms, applications, and the future of liquid–liquid TENGs, highlighting their transformative role in energy harvesting technologies.