Controllable and Scalable Fabrication of Superhydrophobic Hierarchical Structures for Water Energy Harvesting

Abstract

We report a controllable and scalable fabrication approach for the superhydrophobic hierarchical structures and demonstrate the excellent ability to harvest water energy when applied to water-solid contact triboelectric nanogenerator (TENG). A strategy combined with multiple photolithography and micromolding process was developed to accurately regulate the diameters and the center distances of the two-level micropillars. A variety of hierarchical structures were successfully fabricated and presented the advantages of structure control, large scale, high accuracy, and high consistency. The hydrophobic property characterizations were conducted, and the results indicated that the hierarchical structures showed a larger contact angle than the single-level structures and achieved superhydrophobicity. Then the hierarchical structures were applied to water-TENGs with flowing water continuously dripping on, and the effect of the structure parameter on the triboelectric output was analyzed. The hierarchical structures exhibited a superior ability to harvest water energy than the flat film and the single-level structures due to the enhanced friction area and superhydrophobic property. At a flowing velocity of 8 mL/s, the hierarchical structure generated the output voltage of approximately 34 V and the short-circuit current of around 5 μA. The water-TENG device exhibited a power density peak of 7.56 μW/cm2 with a resistive load of 16.6 MΩ at a flowing velocity of 10 mL/s. These findings shed light on the potential applications of the hierarchical structures-based water-TENGs to water energy harvesting and self-powered sensor devices.