Liquid–Liquid Triboelectric Nanogenerator for Harvesting Distributed Energy

Abstract As one of the most widely distributed water resources, rainwater contains tremendous energy that cannot be effectively utilized by the conventional electromagnetic generators. Triboelectric nanogenerators (TENGs) represent a distributed method to convert trivial mechanical energy into electricity based on contact electrification. Benefiting from the large and replenishable contact interfaces in liquid–liquid systems, liquid–liquid TENG further promises efficient charge transfer. However, the limited understanding of liquid–liquid contact electrification has restricted its development. In this study, the mechanisms of contact electrification in various liquid–liquid systems is comprehensively investigated and thus a liquid–liquid TENG with optimized materials and structures to harvest energy from rainwater is demonstrated. The proposed liquid–liquid TENG generates a high charge density (3.63 µC L −1 ) with high output stability (crest factor ≈1.1) and long effective contact electrification time. Based on the direct current characteristics, energy harvested from rainwater can be fed directly to electronic devices and a self‐powered rainfall sensor can also be implemented. This study highlights the promise of all‐liquid systems in distributed green energy and passive sensors, offering a new perspective on self‐powered devices.