Among various forms of energy, ocean blue energy has become one of the most promising sources due to its vast coverage and large total amount. However, the lack of economically efficient harvesting technologies has long restricted the extraction and development of blue energy. The emerging triboelectric nanogenerator (TENG) excels at collecting mechanical energy from the surrounding environment. Based on electrostatic induction and the triboelectric effect, it differs from traditional electromagnetic generators by being lightweight and low-cost, making it particularly suitable for collecting low-frequency mechanical energy from the surface of seawater. In recent years, the push towards blue energy has become an important development direction for triboelectric nanogenerators, attracting more and more research institutions and personnel to engage in this field. However, there is still a long way to go to achieve the efficiency and stability required for the industrialization of TENG arrays.
Recently, Academician Zhonglin Wang from Georgia Tech collaborated with Professor Chenguo Hu from Chongqing University to propose the oblate spheroidal triboelectric nanogenerator for the first time. This device contains two original generator units designed for two different sea conditions, representing a new strategy for collecting all-weather ocean blue energy. As shown on the left, the upper generator consists of three arched units made of spring steel and a disc on top. The arched steel pieces serve as both springs and electrodes, perfectly supporting the weight of the disc, eliminating the need for additional components like springs, resulting in a compact and low-cost design. The lower generator consists of two radially arranged films and steel balls, where the rolling of the steel balls allows the two copper-coated films to make and break contact, generating electrical energy.
To highlight the advantages of the oblate spheroidal shell compared to a spherical shell, the researchers calculated the distance the steel balls deviate from the center at different tilt angles, as well as the bottom area they can cover. As shown on the right, the blue lines and shaded areas represent the data for the spherical shell, while other colors represent the data for the oblate spheroidal shell at different heights. At the same tilt angle, the arc length deviated from the center by the steel balls inside the oblate spheroidal shell is longer, resulting in more significant movement and a more sensitive response. At the same tilt angle, the area of the surface covered by the steel balls around the axis during one complete rotation is also larger. Thus, under the impact of small waves, the movement of objects within the oblate spheroidal shell is more pronounced, allowing more friction layers to make contact and separate, leading to higher output performance of the generator, thereby more effectively utilizing small wave energy. For larger waves, the oblate spheroidal generator relies on the specially designed upper generator, which has high output characteristics, clearly defining the roles of each component, each excelling in their respective areas.
For the oblate spheroidal shell, after deflection, its center of gravity can form a restoring torque with the help of its curved surface, driving the shell back to its initial horizontal position, thus possessing unparalleled self-recovery stability compared to other shapes, saving fixed materials. Additionally, the use of the oblate spheroidal shell also endows the lower generator with high responsiveness. The researchers explored the working principles and output performance of the two-layer generator, achieving a maximum open-circuit voltage of 281 V, a short-circuit current of 76 µA, and a half-cycle transfer charge of 270 nC. Furthermore, they tested the output performance on water, which was generally consistent with experimental data, successfully charging a capacitor. The proposed oblate spheroidal shell and dual-layer generator strategy provides a new structure and new ideas for future triboelectric nanogenerators to collect all-weather blue energy, promising to become an important choice in the design of future blue energy generators.
The related work was published in Advanced Energy Materials . Doctoral students Guanlin Liu, Hengyu Guo, and Sixing Xu are co-first authors, while Academician Zhonglin Wang from the Beijing Institute of Nanoenergy and Nanosystems and Professor Chenguo Hu from the School of Physics at Chongqing University are co-corresponding authors.
Original text (scan or long press the QR code to access the original page):
Oblate Spheroidal Triboelectric Nanogenerator for All-Weather Blue Energy Harvesting
Guanlin Liu, Hengyu Guo, Sixing Xu, Chenguo Hu, Zhong Lin Wang
Adv. Energy Mater., 2019, 9, 1900801, DOI: 10.1002/aenm.201900801
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