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Researchers Show New Piezeoelectrochemical Effect Can Scavenge Energy Wastes Such as Noise or Vibration to Generate Hydrogen Via Water Splitting

Hong
H2 and O2 are produced by deforming a ZnO fiber or BaTiO3 dendrite in water via oxidation-reduction reactions. Credit: ACS, Hong et al. Click to enlarge.

Materials scientists at the University of Wisconsin-Madison have discovered a phenomenon—the direct conversion of mechanical energy to chemical energy—which they termed the piezoelectrochemical (PZEC) effect. They then applied the PZEC effect to generate hydrogen and oxygen via direct water splitting.

Their study, they write in a paper published online 2 March in ACS’ Journal of Physical Chemistry Letters, provides a simple and cost-effective technology that may generate hydrogen fuels by scavenging energy wastes such as noise or stray vibrations from the environment.

The mechanism of the water decomposition via the PZEC effect relies on the piezoelectric properties of the materials. Although the piezoelectric effect has been known for over 100 years and has been demonstrated in many fields, little work has been done to address its application in wet conditions (such as in solution) and particularly in the direct conversion of mechanical energy to chemical energy.

...conditions. In this study, we use microfibers of ZnO and dendritic BaTiO3 to initiate a phenomenon and drive a nonspontaneous redox reaction, the formation of H2 and O2 gases from water, by using mechanical energy. Here, we show the capabilities of these materials for scavenging energy waste from the environment, such as noise and vibration, to generate hydrogen and oxygen gases.

—Hong et al.

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

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

When the fibers bend, asymmetries in their crystal structures generate positive and negative charges and create an electrical potential. Smaller fibers bend more easily than larger crystals and therefore also produce electric charges easily. So far, the researchers have achieved an 18% efficiency with the nanocrystals, higher than most experimental energy sources.

The physics and chemistry of generating hydrogen and oxygen gases from pure water arise from the combination of piezoelectric properties of ZnO fibers and BaTiO3 dendrites and the redox reaction of water. Both ZnO and BaTiO3 are well-characterized piezoelectric materials...Specific morphological aspects of ZnO and BaTiO3 such as fibers and dendrites will acquire electric potentials on their surfaces if an external mechanical energy is applied that results in a bending (deformation) of the fibers or dendrites. The strain induced electric potential formed on the fiber or dendritic surface in wet conditions (i.e., in pure water) is available for the reduction and oxidation reaction via charge transfer to species such as water molecules adsorbed on the surface.

Note that the developed potential must be greater than the standard redox potential of water (1.23 eV) to make electrons available to initiate the redox reaction in this experiment. Residual charges or potentials lower than 1.23 eV will not participate in reactions to form H2 and O2 from water.

—Hong et al.

In addition, they noted, in the PZEC effect, the catalyst—i.e., the zinc oxide and barium titanate—participated in the direct water splitting reaction by donating strain-induced electrons and holes without being oxidized, reduced, or decomposed. TEM and XRD observations showed that no metal species or other extra phases appeared in our experiment samples before and after the reactions.

Because the fiber and plate sizes can be tuned, said Xu, even small amounts of mechanical noise—such as a vibration or water flowing—could bend the fibers and plates. 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.

Using fibrous ZnO and dendritic BaTiO3 catalysts with piezoelectric properties, we have demonstrated the PZEC effect for generating H2 and O2 from water. We have successfully verified a direct conversion of mechanical energy to chemical energy. Finding an optimum fiber length and introducing the resonance frequency of ZnO and BaTiO3 for the direct water splitting process, it may be possible to obtain a much greater H2 and O2 production rate.

Utilizing the piezoelectric fibrous samples, the phenomena demonstrated could usher in a new era in the field of recycling environmental energy wastes. Vibrational energy waste generated in the environment from noise, wind power, running water, or water wave action can be scavenged or harvested as a driving force for direct water splitting, thereby forming H2 and O2 by means of PZEC fiber arrays implanted on a substrate. The fiber arrays can also be used to harvest artificial energy wastes such as traffic noise and vibrations and convert them into hydrogen and other chemical energies.

The principle of the PZEC effect using these fibers could be a very important step forward in nanotechnology that recycles the energy wastes from the environment into precious alternative chemical energy. This work will open a new field of study on hydrogen generation, redox reactions, and energy recycling.

—Hong et al.

The new paper is co-authored by graduate student Kuang-Sheng Hong, research scientist Hiromi Konishi and mechanical engineering professor Xiaochun Li, all at UW-Madison. Xu’s research is supported by grants from the UW-Madison Graduate School, National Science Foundation, NASA Astrobiology Institute and the US Department of Energy.

Resources

  • Kuang-Sheng Hong, Huifang Xu, Hiromi Konishi and Xiaochun Li (2010) Direct Water Splitting Through Vibrating Piezoelectric Microfibers in Water. J. Phys. Chem. Lett., Article ASAP doi: 10.1021/jz100027t

Comments

David Caldine

What would the hydrogen be used for?

ToppaTom

I hesitate to accept that such imaginative and cutting edge ideas have near term (or any) promise when those promoting it apparently do not have a lot of common sense (or assume we do not).

At the very least, their assumption that there may be useful power to be extracted from walking, breezes or traffic noise (via the generation of H & O, no less) implies they have come across a very interesting phenomenon/invention that, if it has a valuable use, they don’t know what it might be.

As an apparently new technology, this IS interesting.

JMartin

If this could be economically incorporated in a sound abatement system around highways, I would find it interesting.

Chad Snyder

Toppa-

Are you suggesting these scientists lack "common sense"?

Such an assertion, if it is yours, lacks common sense and flies in the face of how most great scientific breakthroughs usually evolve.

Ultimately, if theoretically cost-effective, I have no doubts there will be numerous other scientists and industrialists that will figure out ways to capitalize on the PZEC effect. Even if cost-ineffective, such a scientific finding could still be the key finding for another scientist's research.

DaveD

The obvious question is what is the efficiency of this reaction?

If you use the same mechanical energy with straight pizoelectrics and produce electricity to be used directly, that would almost certainly be more efficient than producing hydrogen from a pizoelectrochemical effect which would then have to be fed into a ~50% efficient fuel cell to produce electricity.

So either the pizoelectrochemical is more than twice as efficient as pizoelectrical...or you just added another step that reduces the total energy output.

Interesting discovery....but does it pass the common sense test for usage in the real world?

David Caldine

It would be nice if this new phenomenon could be used to break down CO2 into CO and O2.

BaTiO3 rings a bell. I'm happy to know somebody besides EESTOR has found a practical use for it.

Matthew

Speaking of EESTOR, have we seen anything tangible out of them yet?

kelly

"..New Piezeoelectrochemical Effect Can Scavenge Energy Wastes Such as Noise or Vibration to Generate Hydrogen Via Water Splitting" at what energy rate per what unit of Noise or Vibration?

Treehugger

I read that the VC Perkin Kleimer took distances with EESTOR, but who knows what's going on

GdB

So sounds PZEC like squeezing the hydrogen out of water. They should call it the Water to hydrogen juicer!

SJC

They could put rows of these down the center and sides of the interstate. The traffic noise should be enough to power the street lamps...use some imagination.

sulleny

I would imagine if installed in the stands of a major sports arena, the energy of stomping feet AND screaming fans could power the lighting system. IF the competition failed to stimulate enough enthusiasm - the lights go out.

Thus encouragement for event directors to keep games exciting!

ToppaTom

If they put rows of these down the center and sides of the interstate and harnessed the traffic noise at 100% efficiency (fat chance), the power would be orders of magnitude too low to power any street lights.

Sports arenas probably can have many times the dB level of highways but, likewise, are no source of significant power.

Use some common sense; ask yourself how an old battery powered “ghetto blaster” could provide seemingly endless, ear splittingly loud noise - And answering "It takes rather little power (even with low efficiency speakers) to create a LOT of noise - thus; noise contains little power.”


SJC

There was an article about piezo walk tiles that produced enough on a busy walkway to light store fronts. This is an interesting application and I think it should be seen as such.

ToppaTom

Piezo walk tiles are not PZEC.
Piezoelectric power can provide some power, but it is a far cry from PZEC.

The Tokyo station walk had sufficient energy, from 400,000 people per day, to light up only electronic signboards.

Wonder why the people who use soft ear plugs in high noise locations keep from burning their ears?
No power.

DaveD

For deployment, it has to reach a certain level of practicalality. If a city spends XX million dollars to deploy PZEC (or even PZE) on a sidewalk to take advantage of noise and vibrations, it has to be balanced against the idea of deploying XX million dollars worth of solar panels or wind turbines instead. Which one produces more energy in that particular geography per dollar spent? (I'm trying to compare only clean energies here for apples to apples.)

It's great to brainstorm all the things we could do with something, but it still has to be practical when it's time to deploy it. This sounds more like an interesting experiment that may apply in some special application where you simply need hydrogen and no other energy source will do.
If you need to produce electricity to light up stores then there are probably better pay backs that don't involve the extra step of going to chemical and back again.
But if I'm wrong and this is more cost effective then it should obviously get it's shot.

SJC

"Piezo walk tiles are not PZEC"

I never said that they were, you really need to read more carefully.

sulleny

"Here, we show the capabilities of these materials for scavenging energy waste from the environment, such as noise and vibration, to generate hydrogen and oxygen gases."

My suggestion, do a demo at a World Cup soccer event (involving Latin teams) - encourage controversy in refereeing which raises emotional levels (and crowd noise, vibration). If not convert H2 to e-lighting, at least build an "EmotoTorch" in the outfield that flames modulate with crowd emotion.

Emotion = energy. Remember "Monsters Inc."

SJC

Kewl idea :)

Arnold

Hell,
I knew my involvement with breeding big noisy GM crickets was going come home.
Well not exactly my involvement, I got some other crickets in on that act!

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