Integrating hydrovoltaic device with triboelectric nanogenerator to achieve simultaneous energy harvesting from water droplet and vapor

Extensive efforts have been made to collect energy from water to generate electricity. However, producing a high density of electrical power for small mobile electronics is challenging. Triboelectric nanogenerator (TENG), which can convert droplet water into electricity, provides sustainable electrical power for small electronics. In addition, hydrovoltaic device (HD) can harvest energy from water evaporation into electricity for small electronics. Herein, an integrated device aimed at collecting energy from both impinging water droplets and evaporation is proposed by combining a TENG with an HD. An architecture that comprises a fluorinated ethylene propylene (FEP) film as a triboelectric layer with an aluminum electrode is used to collect energy from impinging water droplets. A silicon-based HD with an asymmetrical structure where nanostructured silicon plus hierarchical nanofabric carbon electrode is used to harvest energy from vaporizing water droplets. Silver is used as a mutual electrode to integrate the TENG and the HD to generate electricity by fully using falling water droplet energy. The microstructure is built on the FEP film surface to enlarge the contact area between the droplets and FEP, greatly boosting the output of the TENG with an open-circuit voltage of 200 V and a short circuit current of 60 μA in pulsed mode, respectively. Meanwhile, the HD device yields a consistent open-circuit voltage of 550 mV and a short circuit current density of 30 μA/cm2. This integrated device provides a smart strategy to generate electricity by fully collecting energy from impinging water droplets and evaporation, paving an alternative way to efficiently harvest water energy.