Electric sea creature sparks China’s nanogenerator innovation

Chinese researchers say their tiny device can generate 3,000 volts by copying the way a ray uses electricity as a weapon without harming itself. Lead researcher Song Qunliang said the design is simple and robust enough to be assembled at home with a pair of scissors. — SCMP

Chinese scientists say they have designed the most powerful droplet-based nanogenerator so far, with an output of 3,000 volts.

A single discharge of the tiny device – inspired by the electric ray fish – can light up more than 1,260 LED bulbs, each rated above three volts, said the team, in a paper published by the peer-reviewed journal Energy & Environmental Science.

The previous record set by a droplet-based nanogenerator was 237 volts, while a device using an alternative energy source achieved 1,600 volts, the researchers said.

The research was led by Song Qunliang, from Southwest University’s Institute for Clean Energy and Advanced Materials, and Guo Hengyu, from Chongqing University’s State Key Laboratory of Power Transmission Equipment and System Security and New Technology.

Nanogenerators are small electronic chips that convert mechanical signals – such as small physical movements or falling rain drops – into electricity. They are typically based on solid-liquid contact electrification, the natural phenomenon which generates static electricity and lightning.

Conventional nanogenerators use displacement current – a virtual phenomenon associated with the generation of magnetic fields by time-varying electric fields – to produce an alternating current (AC).

The Chinese team’s total current triboelectric nanogenerator (TC-TENG), uses both displacement current and actual conduction current as its driving forces, significantly increasing the extracted energy.

Song said the TC-TENG’s design was inspired by the way electric rays use electricity as a weapon to stun and kill other marine creatures without harming themselves.

“Every micro-drop (in the TC-TENG) corresponds to a cell in the electrical organ of a ray. The power generated by a single cell is relatively low, which is not sufficient for an electric ray to stun prey or defend itself,” he said.

“However, when more than 1,000 power generation units form an ordered columnar array and then the power stored in the array is released simultaneously via neural control, a transient hefty electric discharge is generated.”

Song said the team built a water charge shuttle architecture to carry the micro-drops between the device’s electrodes, delivering negative and positive charges sequentially through precise modulation of its own hydrodynamics.

The charges are delivered continuously until the voltage reaches a threshold, when a neural-like controller triggers the discharge process, just like the nervous system of an electric ray.

When the voltage across the TC-TENG drops, the controller switches off and another round of energy accumulation and power release starts.

The bionic design integrates power generation, conversion and storage in an all-in-one device. The TC-TENG features a compact array architecture, high-voltage direct current (DC) output and controllable energy release, the paper said.

“TC-TENG has an ultra-high output voltage, with unparalleled capability for harvesting high-entropy water energy,” Song said in the paper.

In the 20 years since the invention of the nanogenerator, China has become the international leader in the field, but they are unlikely to become a viable power source yet, despite the latest progress.

However, because nanogenerators convert mechanical signals into electricity, they could be used to identify acid and alkali leaks in chemical plants.

“Using nanogenerators as a power source is still unrealistic, because the energy carried by droplets is limited. But we have more than enough for sensing applications,” Song said.

The device could also be used to detect liquids, as well as for energy collection. The team will build on its current research to further explore the TC-TENG’s potential in energy harvesting devices, Song said.

Meanwhile, its simple structure and low price make the TC-TENG suitable for practical applications, according to the paper. The device is made of polytetrafluoroethylene (PTFE) plates, commercially available copper electrodes, plus platinum and copper wires.

“Fabrication of TC-TENG is simple and robust. The assembly work could be done at home with scissors,” Song said. – South China Morning Post

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