By James Pearce 10/11/03
Canadian scientists have developed a method of generating electricity from water for use in small devices, paving the way for devices such as water-powered mobile phones.
The technology is based on the interaction between liquids and solids on a very small scale. The surface of the solid receives a small charge, and this attracts opposite-charged ions in the liquid, while like-charged ions are repelled. The process creates an Electric Double Layer (EDL) – a thin liquid layer with a net charge that ranges from several nanometres to a few micrometres thick.
Professor Daniel Kwok and Professor Larry Kostiuk from the University of Alberta created channels similar in size to the EDL and forced liquid through the channels, resulting in a movement of net charges downstream. Because the ions that are repelled by the surface move faster than the ions that are attracted to the surface a current is generated, and leads to a voltage difference across the ends of the channel if the solid is a non-conducting material.
The power generated from a single channel is extremely small – a 30 cm column of water will produce one-two microamps – but the researchers envisage millions of parallel channels being used to increase the power output to a level sufficient to power electrical devices such as mobile phones and calculators.
The system needs to have energy inputted, in the form of applying pressure to the liquid in the channels. Mobiles powered by this method would not be plugged into power mains to recharge, but would require pumping.
"The applications in electronics and microelectronic devices are very exciting," said Kostiuk. "This technology could provide a new power source for devices such as mobile phones or calculators which could be charged up by pumping water to high pressure. What we have achieved so far is to show that electrical power can be directly generated from flowing liquids in microchannels."