Floating Electricity Generator for Omnidirectional Droplet Vibration Harvesting

Earth Sciences Nanoscience Energy Engineering Electrical Engineering Ocean Engineering Energy Chemistry Chemistry Materials Science Engineering
floating generator droplet vibration omnidirectional energy harvesting capacitor ocean energy

Floating Generator for Omnidirectional Droplet Vibration Harvesting

Floating Omnidirectional Droplet Vibration Generator: Breakthrough Research

Academic Background

With the widespread application of Internet of Things (IoT) devices in marine environmental monitoring, how to provide stable power to these devices without relying on the power grid has become an urgent issue. Traditional renewable energy sources such as wind and solar power have limitations in marine environments, while triboelectric nanogenerators (TENGs) are considered a potential solution due to their high efficiency in mechanical energy conversion. However, most existing TENG devices rely on solid-solid interface friction, which leads to wear and tear, limiting their long-term use. Additionally, many droplet-based TENGs can only harvest energy in a single direction, making them unsuitable for the unpredictable multidirectional waves in marine environments.

To address these issues, the research team proposed a Floating Droplet-based Electricity Generator (FDEG) designed to efficiently and sustainably harvest ocean wave energy through an asymmetric capacitance design between the droplet and electrodes, significantly improving electrical output and achieving multidirectional energy collection.

Paper Source

This study was conducted by Jiaming Zhou, Xiaoting Ma, Zihao Deng, Jingyi Gao, Eunjong Kim, Hongjian Zhou, and Dong-Myeong Shin from The University of Hong Kong. It was published on April 18, 2025, in the journal Device, titled Floating Electricity Generator for Omnidirectional Droplet Vibration Harvesting. The paper is open access and can be accessed via the DOI link.

Research Process

1. Device Design and Fabrication

The core structure of the FDEG consists of two main parts: an inner power generation layer and an outer supporting layer. The inner layer includes a thin fluorinated ethylene propylene (FEP) film with ring and circular copper electrodes arranged on it. The outer layer is a hemispherical acrylic bowl that keeps the device afloat and drives the inner layer’s movement through water waves. A droplet (deionized water) is embedded on top of the FEP layer, triggering charge flow between the electrodes as it rolls.

Key Design Features:

  • Asymmetric Electrode Design: The ring electrode is located on the top of the FEP layer, directly contacting the droplet, while the circular electrode is placed underneath the FEP layer to avoid direct contact with the droplet.
  • Closed-Loop Circuit: The droplet momentarily connects the ring and circular electrodes during rolling, forming a closed loop and thereby enhancing current output.

2. Working Mechanism Study

The working mechanism of the FDEG is based on the triboelectric effect between the droplet and the electrodes. When the droplet comes into contact with the FEP layer or the ring electrode, the surface of the FEP layer or the ring electrode accepts negative charges from the droplet. The process is divided into four stages: 1. Stage I: The droplet contacts the ring electrode, closing the circuit, and then separates. 2. Stage II: The droplet slides toward the center of the FEP layer, reducing the contact area, and the circuit is disconnected again. 3. Stage III and IV: The above process is repeated, transferring charges through an external load.

3. Parameter Optimization

To optimize the output performance of the FDEG, the research team adjusted parameters such as droplet volume and electrode spacing. Experiments showed that when the droplet volume matched the electrode spacing, the current output reached its maximum. Additionally, computational fluid dynamics (CFD) simulations were used to study the device’s response to different wave amplitudes and frequencies, validating its applicability in real marine environments.

4. Salinity Impact Study

To expand its application scope, the research team tested the effects of different salinities and salt types on the FDEG’s output. The results indicated that low-concentration salt solutions significantly increased the peak current, while high-concentration salt solutions reduced the output. This finding provides theoretical support for the application of the FDEG in different water environments.

Main Results

  1. High Current Output: With a droplet volume of 2.4 mL, the FDEG achieved an instantaneous current output of 22.80 ± 1.68 mA, 20 times higher than single-electrode configurations.
  2. High Power Density: When using a 0.5 mM Na₂SO₄ solution, the FDEG achieved a power density of 1,190.6 W/m³, setting a new record for droplet-based TENGs.
  3. Omnidirectional Performance: The device can operate stably in multidirectional wave environments, making it suitable for unpredictable marine conditions.
  4. Salinity Optimization: Low-concentration salt solutions (1 mM NaCl and 0.5 mM Na₂SO₄) significantly increased the peak current.

Conclusion and Value

This study pioneers a droplet-based omnidirectional vibration generator, significantly enhancing electrical output through asymmetric electrode design and instantaneous switching of a closed-loop circuit. The device not only boasts high power density and charge density but also demonstrates potential for extensive energy harvesting from natural vibrations, including ocean waves, pendulum swings, and cantilever oscillations. With further refinement and scalability, the FDEG could pave the way for commercial-scale power generation, offering a cost-effective and sustainable energy solution for marine IoT devices and beyond.