Multi-Mode Water-Tube-Based Triboelectric Nanogenerator Designed for Low-Frequency Energy Harvesting with Ultrahigh Volumetric Charge Density

Vast renewable energies are contained in mechanical motions in nature such as ocean waves. However, it is challenging to effectively harness these energy sources due to their low frequency and irregularity. Triboelectric nanogenerators (TENGs) are a promising technology for renewable energy conversion, but conventional TENGs suffer from challenges including single-mode operation, low contact intimacy, and material abrasion. Here, by encapsulating deionized DI water into a fluorinated ethylene-propylene tube, a versatile and high-performance water-tube-based TENG (WT-TENG) is developed. Benefiting from the high flexibility of the water, the WT-TENG can work at various operation modes and generate power from multiple mechanical energy sources. With the intimate water/solid contact, the WT-TENG achieves an ultrahigh volumetric output charge density of 9 mC m⁻³ at a frequency of 0.25 Hz, beyond all previous reports. Moreover, multiple finger-sized WT-TENG units can be easily integrated as one device and realize multiplied outputs. A wearable body motion energy harvester and a water wave energy harvester are demonstrated as examples of the WT-TENG applications. The proposed WT-TENG can be regarded as a new brick for the TENG mansion, and numerous applications could be built up based on the WT-TENG units.