A joint research group led by team leader (at the time of research) Yo Tanaka of the RIKEN Center for Biosystems Dynamics Research, Visiting Researcher Yaxiaer Yalikun (Associate Professor at Nara Institute of Science and Technology), and Professor Norihiro Kamamichi of the School of Science and Technology for Future Life at Tokyo Denki University has developed a pressure-driven compact generator that uses the electrical interaction between water and glass. Their research was published in Scientific Reports. RIKEN has applied to patent their research as a power generation device and method.
Energy harvesting devices, which obtains power from heat, light, pressure, and other sources in the environment, are attracting attention as a means of supplying the vast number of information terminals and sensors associated with the spread of the IoT. Of these technologies, pressure can generate relatively large amounts of power, but the power generation efficiency is somewhat poor for slow, repetitive pressures (vibrations) such as walking.
From this background the research group conceived the idea of using the electrical interaction between water and glass filter channels to generate electricity by applying pressure flowing water in order to separate ions. They conducted a study to optimize the fabrication conditions and a demonstration experiment for use in a pressure-driven glass generator.
Water spontaneously separates into hydrogen and hydroxide ions. Glass is negatively charged in water due to the separation of hydrogen ions on its surface. Therefore, if a microfluidic channel is fabricated with glass and water flows through it under pressure, hydrogen ions can easily enter the channel, but hydroxide ions cannot, resulting in ion separation.
When the inlet and outlet of the flow path are connected by wires, hydrogen gas is produced at the outlet and oxygen gas at the inlet and an electric current flows. Since voltage is proportional to pressure and current is proportional to the number of channels, increasing the power, which is the product of the two, requires the integration of a large number of channels with high pressure resistance.
The research group fabricated a circular-shaped fine glass filter and attached rubber gaskets to it as a generator design to realize this. They incorporated it into a holder with high pressure resistance performance, attached mesh electrodes to the top and bottom of the filter and connected it by wires to an external measuring device to collect current from a large area.
They fabricated a glass filter to form a three-dimensional flow path by milling commercial glass powder in a mortar, placing it in a mold, and sintering it in a furnace.
By experimenting with various sintering temperatures and milling times, they found that the maximum power (27 V, 0.14 mA and an output power of 0.8 mW) was achieved at a temperature of 700°C and a milling time of five minutes. The power generation efficiency was 0.021%. Furthermore, when they created a foot-operated test device assuming a weight of 60 kg and conducted tests with it, the duration of power generation was proportional to the milling time, with a maximum energy output (18 V, current of 0.26%, and power of 4.8 mW) at a milling time of 10 minutes. The power generation efficiency was 0.017%.
In the demonstration test, they successfully operated LED lighting, a small fan, and wireless communicator. While ordinary piezoelectric devices last less than 0.1 second, the new generator can generate power continuously with long, relaxed vibrations for more than one second. It also provides more than 1,000 times the power than that of ion filtering generators using materials such as semiconductors, alloys, and wood.
Yalikun commented on the result, saying "We will continue research and development in the two prongs of integration and high output, and hope to apply the technology to health management devices within one year and sensors for the disabled within three to five years."
Publication: Scientific Reports
Title: A pressure driven electric energy generator exploiting a micro- to nano-scale glass porous filter with ion flow originating from water
This article has been translated by JST with permission from The Science News Ltd.(https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.