New electrical generator harvest energy from droplets

A charge trapping‐based electricity generator.

Global warming is expected to have far-reaching, long-lasting, and, in many cases, devastating consequences for planet Earth. With an increasing threat, it demands the use of renewable energy sources.

Strategies toward harvesting energy from water movements are proposed in recent years. Earlier attempts to harvest this energy using various techniques were either limited in efficiency or stability or required an external voltage.

In a new attempt, scientists from the University of Twente and South China Normal University have proposed an electrical generator that can harvest energy from impacting droplets and other sources of mechanical energy.

This charge trapping‐based electricity generator (CTEG) can also be said as an electret. It composed of hydrophobic fluoropolymer films that are pre‐charged by a homogeneous electrowetting‐assisted charge injection (h‐EWCI) method, allowing an ultrahigh negative charge density of 1.8 mC m−2.

Scientists used a dedicated designed circuit to connect the bottom electrode and top electrode of a platinum wire. The resultant instantaneous currents were beyond two mA, power density above 160 W m−2, and energy harvesting efficiency over 11% is achieved from continuously falling water droplets.

Scientists injected charges into an insulating layer of this capacitor by employing a novel charging method based on electrowetting – the modification of the ability of liquids to maintain contact with a solid surface with an electric field. An electrical current is generated upon the impact of a droplet when the induced counter-charges on the capacitor are redistributed.

By using composite samples with high strength, scientists were able to increase the number of injected charges significantly. The smart design of the electrodes allowed the charge redistribution in their generator to occur most efficiently.

Niels Mendel, one of the authors says“Our method can also be considered for other applications where mechanical energy needs to be converted into electrical energy, for example in wearables, from tidal waves, or for sensing. More research is needed to design a generator that can harvest energy from rain efficiently enough.”

Journal References:
  1. Hao Wu et al. Charge Trapping‐Based Electricity Generator (CTEG): An Ultrarobust and High-Efficiency Nanogenerator for Energy Harvesting from Water Droplets, Advanced Materials. DOI: 10.1002/adma.202001699
  2. Hao Wu, et al. Energy harvesting from drops impacting onto charged surfaces, Physical Review Letters

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