Engineering researchers generate an electrical current with pressurized water

by Phoebe Dey and Roland Lines

What started as a simple conversation between two engineering professors has led to the development of a new way to harness electricity—from pressurized tap water.

A team of researchers and students from the Department of Mechanical Engineering, led by Daniel Kwok and Larry Kostiuk, ’85 MSc, found a way to exploit the natural electrical properties of a liquid, such as ordinary tap water, as it flows across a surface. The scientists are calling their creation an electrokinetic microchannel battery.

“This effect is only possible for microfluidics,” says Kostiuk. “You have to use very small channels to get a streaming current to flow. Each channel contributes less than a nonoamp, but you can gang together as many as you need.”

The team’s discovery, published in the Journal of Micromechanics and Microengineering in October, made headlines around the world. The electric current the device generated was extremely small, but it attracted a lot of attention because it is the first time since 1839 that a new electric principle has been used to generate a current.

Most modern electrical generation employs electromagnetic induction, which was discovered and demonstrated by Michael Faraday in 1831. For example, a nuclear power plant doesn’t generate electricity directly from the fission reaction; instead, the nuclear energy is used to heat water, which then drives a turbine that creates electricity through electromagnetic induction.

Kwok and Kostiuk’s battery is being promoted by observers as a safe, non-polluting, completely renewable method of producing electric power.

“This new technology could provide an alternative energy source to rival wind and solar power,” says Kostiuk, “although this would need huge bodies of water to work on a commercial scale.”

Another application that is generating interest is for batteries in devices such as mobile phones or calculators, which could be charged up by pumping water to high pressure.

Kostiuk says a more immediate use of the new technology might be found in a place where large amounts of water are already being filtered daily—water-purification plants. If the mechanics of electrokinetic electricity can be improved, water plants could use the technology to meet some of their own electricity needs, or even generate electricity for others.

David Lynch, dean of the Faculty of Engineering, praised the mechanical engineering team for its rigour and creativity. “The discovery of an entirely new way of producing power is an incredible fundamental research breakthrough,” he said. “It has been more than 160 years since the last such fundamental discoveries that have now led to the current applications associated with solar cells and fuel cells. This groundbreaking discovery of an electrokinetic effect that can generate electricity could be equally revolutionary. It will earn these engineering researchers and the University of Alberta a place of prominence in scientific journals and textbooks for decades to come and electrokinetic cells may find significant applications in numerous commercial areas.”

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The successful, collaborative project started soon after Kostiuk was appointed chair of the Department of Mechanical Engineering. When Kostiuk made his rounds to learn what his colleagues were studying, he listened to Kwok describe his work with electrokinetics, which is the science of electrical charges in moving substances, such as water.

In that meeting, Kwok explained how, when water travels over a surface, the ions that it is made up of “rub” against the solid, leaving the surface slightly charged.

“Then Larry said to me, ‘Well, that sounds like a battery to me,’ and I just paused and then realized what he said,” recalls Kwok. “It shows the importance of interdisciplinary work—sometimes we focus so much on our research that we aren’t able to take a step back and see what others can see.”

Scientists have known about the electrokinetic effect for decades, and it has been used in many industrial applications, such as electro-osmosis for the treatment of hazardous wastes and electrophoresis for electroplating. The current generated by standard electrokinetics is so small, however, that no one thought it had any realistic potential for generating electricity.

Indeed, the U of A team’s initial efforts at tapping the potential of the phenomenon generated such a minute amount of energy that the task was thought impossible, said Jun Yang, a graduate student working towards his PhD in mechanical engineering who designed the experiment at Kwok’s request.

But Yang, who came to the U of A from the Beijing Institute of Technology two years ago, says he wanted to try again. After three days, he says, it occurred to him that the current might be enlarged if many thousands of microchannels were added together.

Yang and Kwok exchanged ideas on ways to increase the number of channels they forced water through. It would have been extremely expensive and time-consuming to build a microchannel array through nanofabrication, but then they hit upon the solution of using a naturally porous material, such as glass.

The team, which also includes graduate student Fuzhi Lu, has since been able to improve on the results detailed in their research paper, generating 20 times as much energy and illuminating LED lights.

“Our demonstration was just to prove the principle, not to generate a lot of power,” says Kostiuk, “but we did show that you can convert hydrostatic pressure directly into electrical work.”

The potential environmental benefit of clean energy conversion using safe, renewable materials is motivating the team to explore how their prototypical device may be developed into a battery for eventual commercial use. The inventors are working with the U of A’s Technology Transfer Group to develop a commercialization strategy for the groundbreaking work. A patent application has been filed by the University to obtain broad, early protection of the invention.

How the electrokinetic microchannel battery works

The underlying principle behind Kwok and Kostiuk’s battery is something called the electrokinetic effect. At the point of contact between a solid and a fluid, some of the atoms in the solid disassociate, forming positive ions and free, negative electrons. Depending on the material of the solid, either the electrons or the positive ions will flow into the fluid, giving the solid a net charge.

If the solid is non-conductive, the charge remains localized at its surface, attracting oppositely charged ions and repelling similarly charged ions in the fluid. As a result, a thin, charged layer, known as the electric double layer (EDL), forms along the interface of the fluid and the solid.

By forcing the fluid through channels with a diameter similar to the EDL—only 13 microns across (about one tenth the diameter of a human hair)—only the attracted type of fluid ion is able to move through the channel with ease; fluid ions with the same charge as the surface of the solid are repelled from the channel. This flow leads to a separation of fluid charges on either side of the channel, which creates an electrical potential (voltage) between the two ends.

Although the current generated from a single microchannel is extremely small—less than one billionth of an amp—Kwok and Kostiuk’s battery used a disc containing hundreds of thousands of parallel microchannels to increase the power output to useful levels.

The missing link in the electrokinetic chain of research

Although it was unknown to Kwok and Kostiuk when they were first developing their battery, the U of A team was not the first to investigate harnessing electrokinetics to generate a current: J. Fletcher Osterle, a professor at Carnegie Mellon University, published a paper titled “Electrokinetic energy conversion” in the Journal of Applied Mechanics in 1964. Osterle’s paper addressed the broad concepts of the phenomenon, but not its applications, and Kwok and Kostiuk only learned about Osterle’s work after publicizing their independent discovery of the electrokinetic microchannel battery.

“Probably the reason no one carried on Osterle’s work is that he concludes the efficiency can never be better than .04 percent,” says Kostiuk. “We haven’t done much better than that so far, but we do think that we can do much better—we have much better technologies today … than they did in the 1960s.”

Some milestones in electrical science

Although the “strange effect” of static electricity was observed by the Greeks in 600 BC, scientific research into the nature of electricity didn’t really start until William Gilbert, court physician to Queen Elizabeth, investigated the connection between static electricity and magnetism in 1600.

For more than 100 years, static electricity was the only type known. It wasn’t until 1729 that Stephen Gray demonstrated that electricity could be transferred from place to place with conducting wires, although he still relied on electrostatic machines to generate the electricity.

The first big step in electrical generation came in 1800, when Allesandro Volta discovered the electrochemical effect, showing that electricity is created when moisture comes between two different metals. Volta then built the first electric battery, called the voltaic pile.

In 1822, Thomas Seebeck discovered the thermoelectric effect by showing that an electrical current will flow in a circuit of dissimilar metals if the metals are at different temperatures.

Michael Faraday’s 1831 discovery of electromagnetic induction—the principle that a changing magnetic field will create a current in a conducting wire—led to the first generation of electrical current on a practical scale by rotating a magnet within a wire coil. Almost all modern electrical generation employs electromagnetic induction; what varies is the method of powering the turbine that turns the magnet.

The year 1839 saw the discovery of two more methods of producing electrical currents. In England, William Grove discovered proton exchange membranes, using them to combine hydrogen and oxygen to produce electricity and water in what he called a “gas voltaic battery,” the forerunner of modern fuel cells. In France, Alexandre Edmond Becquerel discovered the photoelectric effect—that light shining on a metal surface causes the release of electrons—which is used to create an electrical current in solar cells.

In 2002, Daniel Kwok and Larry Kostiuk successfully harnessed the electrokinetic effect—the separation of charges along a solid/fluid interface—to create their electrokinetic microchannel battery.