Scavenging energy waste to turn water into hydrogen fuel

Mar 11, 2010 by Jill Sakai

(PhysOrg.com) -- Materials scientists at the University of Wisconsin-Madison have designed a way to harvest small amounts of waste energy and harness them to turn water into usable hydrogen fuel.

The process is simple, efficient and recycles otherwise-wasted energy into a useable form.

"This study provides a simple and cost-effective technology for direct water splitting that may generate hydrogen fuels by scavenging energy wastes such as noise or stray vibrations from the environment," the authors write in a new paper, published March 2 in the Letters. "This new discovery may have potential implications in solving the challenging energy and environmental issues that we are facing today and in the future."

The researchers, led by UW-Madison geologist and crystal specialist Huifang Xu, grew nanocrystals of two common crystals, and barium titanate, and placed them in water. When pulsed with ultrasonic vibrations, the flexed and catalyzed a chemical reaction to split the into hydrogen and oxygen.

When the fibers bend, asymmetries in their crystal structures generate positive and negative charges and create an electrical potential. This phenomenon, called the piezoelectric effect, has been well known in certain crystals for more than a century and is the driving force behind quartz clocks and other applications.

Xu and his colleagues applied the same idea to the nanocrystal fibers. "The bulk materials are brittle, but at the nanoscale they are flexible," he says, like the difference between fiberglass and a pane of glass.

Smaller fibers bend more easily than larger crystals and therefore also produce electric charges easily. So far, the researchers have achieved an impressive 18 percent efficiency with the nanocrystals, higher than most experimental energy sources.

In addition, Xu says, "because we can tune the fiber and plate sizes, we can use even small amounts of [mechanical] noise — like a vibration or water flowing — to bend the fibers and plates. With this kind of technology, we can scavenge energy waste and convert it into useful chemical energy."

Rather than harvest this electrical energy directly, the scientists took a novel approach and used the energy to break the chemical bonds in and produce oxygen and hydrogen gas.

"This is a new phenomenon, converting mechanical energy directly to chemical energy," Xu says, calling it a piezoelectrochemical (PZEC) effect.

The chemical energy of is more stable than the electric charge, he explains. It is relatively easy to store and will not lose potency over time.

With the right technology, Xu envisions this method being useful for generating small amounts of power from a multitude of small sources — for example, walking could charge a cell phone or music player and breezes could power streetlights.

"We have limited areas to collect large energy differences, like a waterfall or a big dam," he says. "But we have lots of places with small energies. If we can harvest that , it would be tremendous."

Explore further: New molecule puts scientists a step closer to understanding hydrogen storage

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User comments : 3

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Caliban
1 / 5 (1) Mar 11, 2010
I can't seem to visualize this in a working example. How is the H2 converted back into electrical energy to power the cell phone, for instance? I can see larger-scale applications, but some of the small scale things don't make any sense to me.
Anyone shed some light?
Skepticus
not rated yet Mar 11, 2010
All well and good, while zillions of fossil-fueled power plants still discharging large amount of "waste heat". Too often, one hears that the heat recovery for useful work is "uneconomical". I guess what the operators and policy makers means is that as long as we can be "legally" wasteful and make a buck while burning fuel, why worry about the technology available, and the rest of the foul-smelling rabble's troubles? It's just statistics.
localcooling
not rated yet Mar 12, 2010
Well, an application could maybe be a hydrogen fuel cell fed with water, which then is converted to hydrogen, using said mechanism. Maybe in a closed/semi-closed loop. H2O -> 2H + O -> H2O ???
Slick
Mar 12, 2010
This comment has been removed by a moderator.