High-performance Droplet-based Electricity Generator


Student thesis: Doctoral Thesis

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Award date29 Jun 2020


Blue energy using water as a carrier, such as tidal energy, wave kinetic energy, thermal differential energy, etc., has huge application prospects due to its huge reserves and no pollution. For the development of this ideal energy source, the traditional method is to use bulky hydraulic power generation equipment to generate electricity. Although this manner can effectively harvest the large-scale kinetic energy stored in the continuous water flow, the collection of relatively low-frequency water energy becomes inefficient. In recent years, triboelectric nanogenerators (TENG), involving the coupling effect of the contact electrification and electrostatic induction, and hydrovoltaic technology have attracted worldwide attention due to their simple design and diverse material selection. However, at present, these low-frequency water energy harvesting technologies still face the dilemma of poor weather resistance, low charge density, and small peak power density, which greatly limits their practical application. In this thesis, on the basis of understanding the electrical phenomena of the water-solid interface, we focus on the droplet energy harvesting, aiming to develop the high-performance droplet electricity generators by designing new materials and electrode structures, allowing for the electric output with strong weather resistance, high power density, and energy conversion efficiency.

First, this thesis summarizes the recent progress in the basic research of two kinds of electric effects at the water-solid interface: electrohydrodynamic effect and hydroelectric effect, which lays a theoretical foundation for the understanding and design of droplet electricity generator.

Second, inspired by hierarchical structures on the peristome of the Nepenthes pitcher, we report a design of a novel slippery lubricant-impregnated porous surface (SLIPS) based TENG, referred to as SLIPS-TENG, for droplet energy harvesting. The slippery and configurable lubricant layer not only serves as a unique substrate for liquid-droplet transport and optical transmission but also for efficient charge transfer. Moreover, we showed that there exists a critical thickness in the liquid layer, below which the triboelectric effect is almost identical to that without the presence of such a lubricant film. In addition to electricity generation stability at low temperatures, the new droplet-based TENG offers many unique advantages in practical applications, such as optical transparency, configurability, self-cleaning, and flexibility.

Third, inspired by the unique set of structures similar to a field-effect transistor, we developed a new transistor-like impinging droplet-based electricity generator architecture (TIDE-G), in which polytetrafluoroethylene (PTFE)/Indium Tin Oxide (ITO), Al electrode and water droplet are in analogy to the source, drain, and gate, respectively. In particular, continuous droplet impinging on the PTFE electret imparts sufficient surface charges and robust stability, rendering it possible to leverage this ideal source for efficient charge transfer even in harsh environments. We also showed that the spreading of the soft, configurable droplet bridges the originally disconnected components in the device into a closed, electrical system, transforming the conventional interfacial effect into a desirable bulk effect. Such a unique design allows for the reversible and efficient transfer of charges between the source and drain, resulting in the enhancement of power density by several orders of magnitude over its counterparts imposed by the interfacial effect.

In summary, this thesis systemically investigated the high-performance droplet-based electricity generators. The marriage of SLIPS and TENG provides a paradigm shift for the design of robust and versatile energy devices that can be used as a clean and longer-lifetime alternative in various working environments. Furthermore, the droplet energy generator with transistor-like architecture that fundamentally overcomes the physical limitation inherent in the traditional approaches which are imposed by the undesirable interfacial effect and achieve the highest energy conversion efficiency. We believe that our work on the high-performance droplet-based electricity generator will yield important insights to the fundamental understanding of interfacial electrical phenomena and therefore spur a wide range of applications.

    Research areas

  • Water-solid interface, Slippery surface, Bulk effect, Water energy harvesting, Droplet-based electricity generator