New Energy Times

Let Water Power Your Mobile Phone
Journal of Micromechanics and Microengineering

A new way of generating electricity from flowing water could mean that in the future you will never have to charge up your mobile phone again. Instead of a normal battery, mobile phones could be fitted with a battery that uses water - you just need to pressurise it regularly.

Research published today by the Institute of Physics journal, Journal of Micromechanics and Microengineering reveals a new method of generating electric power by harnessing the natural electrokinetic properties of a liquid such as ordinary tap water when it is pumped through tiny microchannels. The research team from the University of Alberta, Edmonton, Canada, have created a new source of clean non-polluting electric power with a variety of possible uses, ranging from powering small electronic devices to contributing to a national power grid.

The research was led by Professor Daniel Kwok and Professor Larry Kostiuk from the University of Alberta. Professor Kostiuk said: “This discovery has a huge number of possible applications. It’s possible that it could be a new alternative energy source to rival wind and solar power, but this would need huge bodies of water to work on a commercial scale. Hydrocarbon fuels are still the best source of energy but they’re fast running out and so new options like this one could be vital in the future”.

“The applications in electronics and microelectronic devices are very exciting. 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”.

The key to electrical power generation is to create a sustainable electrical charge separation. The physical phenomenon involved in this research is the charge separation that occurs at solid-liquid interfaces due to the dissociation of the solid. As a result, the surface becomes charged and opposite-charged ions in the liquid are attracted to it; while like-charged ions are repelled, resulting in a thin liquid layer with a net charge. This region, known as the Electric Double Layer (EDL), ranges from several nanometers to a few micrometers thick, but is the primary mechanism for charge separation.

The research team constructed a solid-liquid interface as a channel with a diameter similar to the EDL and forced the liquid through this channel, the net charges in the EDL are transported downstream. This preferential transport of one type of ion will create a current, and hence voltage difference across the ends of the channel if the solid is non-conducting.

When an external electric circuit is added by placing electrodes at the ends of the channel, then electrical energy is extracted as current flows between the electrodes. The source of that energy is the work done to push the liquid through the channel. Although the power generated from a single channel is extremely small, millions of parallel channels can be used to increase the power output.

Abstract. Pressure-driven flow in a microchannel induces a streaming current due to the presence of an electrical double layer in the interface between the electrolyte solution and channel wall. As the streaming current is of the order of a nano-amphere and is additive, we propose here a method to develop an electrokinetic battery consisting of an array of microchannels that converts the hydrostatic pressure of a liquid into electrical work. We have given oscillating analytical solutions by means of an electrical circuit analysis to model the multi-microchannel battery. Using superposition of the appropriate Fourier series, the derived analytical solutions are useful to predict the current when there is more general time-dependent flow through a microchannel array. To illustrate the idea, we have studied steady-state pressure-driven flow in micropore porous glass filter and compared the results with those predicted from our model. From a 30 cm hydrostatic pressure drop, an external current of 1–2 µA was obtained by means of water passing through the micropore porous glass filter. A larger current can be obtained by simply using a solution with higher salt concentration. This results in a new and potentially useful method of energy conversion by means of an array of microchannels.

Print publication: Issue 6 (November 2003)
Received 23 April 2003, in final form 25 June 2003
Published 20 October 2003

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