Team develops new water splitting technique that could produce hydrogen fuel

Aug 01, 2013
This is an artist's concept of a commercial hydrogen production plant that uses sunlight to split water in order to to produce clean hydrogen fuel. Credit: University of Colorado

A University of Colorado Boulder team has developed a radically new technique that uses the power of sunlight to efficiently split water into its components of hydrogen and oxygen, paving the way for the broad use of hydrogen as a clean, green fuel.

The CU-Boulder team has devised a solar-thermal system in which sunlight could be concentrated by a vast array of mirrors onto a single point atop a central tower up to several hundred feet tall. The tower would gather heat generated by the to roughly 2,500 degrees Fahrenheit (1,350 Celsius), then deliver it into a reactor containing known as metal oxides, said CU-Boulder Professor Alan Weimer, research group leader.

As a compound heats up, it releases oxygen atoms, changing its and causing the newly formed compound to seek out new , said Weimer. The team showed that the addition of steam to the system—which could be produced by boiling water in the reactor with the concentrated sunlight beamed to the tower—would cause oxygen from the to adhere to the surface of the metal oxide, freeing up for collection as gas.

"We have designed something here that is very different from other methods and frankly something that nobody thought was possible before," said Weimer of the chemical and biological engineering department. "Splitting water with sunlight is the Holy Grail of a sustainable hydrogen economy."

A paper on the subject was published in the Aug. 2 issue of Science. The team included co-lead authors Weimer and Associate Professor Charles Musgrave, first author and doctoral student Christopher Muhich, postdoctoral researcher Janna Martinek, undergraduate Kayla Weston, former CU graduate student Paul Lichty, former CU postdoctoral researcher Xinhua Liang and former CU researcher Brian Evanko.

One of the key differences between the CU method and other methods developed to split water is the ability to conduct two chemical reactions at the same temperature, said Musgrave, also of the chemical and biological engineering department. While there are no working models, conventional theory holds that producing hydrogen through the metal oxide process requires heating the reactor to a high temperature to remove oxygen, then cooling it to a low temperature before injecting steam to re-oxidize the compound in order to release hydrogen gas for collection.

"The more conventional approaches require the control of both the switching of the temperature in the reactor from a hot to a cool state and the introduction of steam into the system," said Musgrave. "One of the big innovations in our system is that there is no swing in the temperature. The whole process is driven by either turning a steam valve on or off."

"Just like you would use a magnifying glass to start a fire, we can concentrate sunlight until it is really hot and use it to drive these chemical reactions," said Muhich. "While we can easily heat it up to more than 1,350 degrees Celsius, we want to heat it to the lowest temperature possible for these chemical reactions to still occur. Hotter temperatures can cause rapid thermal expansion and contraction, potentially causing damage to both the chemical materials and to the reactors themselves."

In addition, the two-step conventional idea for water splitting also wastes both time and heat, said Weimer, also a faculty member at CU-Boulder's BioFrontiers Institute. "There are only so many hours of sunlight in a day," he said.

The research was supported by the National Science Foundation and by the U.S. Department of Energy.

With the new CU-Boulder method, the amount of hydrogen produced for fuel cells or for storage is entirely dependent on the amount of metal oxide—which is made up of a combination of iron, cobalt, aluminum and oxygen—and how much steam is introduced into the system. One of the designs proposed by the team is to build reactor tubes roughly a foot in diameter and several feet long, fill them with the metal oxide material and stack them on top of each other. A working system to produce a significant amount of would require a number of the tall towers to gather concentrated sunlight from several acres of mirrors surrounding each tower.

Weimer said the new design began percolating within the team about two years ago. "When we saw that we could use this simpler, more effective method, it required a change in our thinking," said Weimer. "We had to develop a theory to explain it and make it believable and understandable to other scientists and engineers."

Despite the discovery, the commercialization of such a solar-thermal reactor is likely years away. "With the price of natural gas so low, there is no incentive to burn clean energy," said Weimer, also the executive director of the Colorado Center for Biorefining and Biofuels, or C2B2. "There would have to be a substantial monetary penalty for putting carbon into the atmosphere, or the price of fossil fuels would have to go way up."

Explore further: The best of two worlds: Solar hydrogen production breakthrough

More information: "Efficient Generation of H2 by Splitting Water with an Isothermal Redox Cycle," by C.L. Muhich et al. Science, 2013.

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User comments : 18

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mzso
2.6 / 5 (15) Aug 01, 2013
Saying "efficiently split water" without providing efficiency numbers is valueless. How much of the solar energy would be converted?
How much money would it cost to produce a kWh of energy?
holoman
2 / 5 (18) Aug 01, 2013
Boy, took about alot of press releases to this me too already done stuff.

Still waiting for something unique and new.
lengould100
2.9 / 5 (8) Aug 02, 2013
I highly doubt that any system which hopes to have a solar collector heat up to 1350 C will have any useful efficiency. At that temperature, most of the incoming solar energy will simply be re-radiated back out. Kills system efficiency.
antialias_physorg
3.5 / 5 (4) Aug 02, 2013
Couple of numbers would have been nice. The abstracts for the article I found don't give anything interms of useful numbers (energy concentrated vs. hydrogen produced).

Gut feeling would indicate that heating something then cooling it down for transport is wasting a lot of energy compared to the catalytic forms of splitting water. But gut feeling is rarely a good indicator in these matters.
Urgelt
2.7 / 5 (7) Aug 02, 2013
lengould100 wrote, "I highly doubt that any system which hopes to have a solar collector heat up to 1350 C will have any useful efficiency. At that temperature, most of the incoming solar energy will simply be re-radiated back out. Kills system efficiency."

Yeah, what he said. Furthermore, the sticking point with hydrogen at this point isn't producing it so much as what to do with it once it's produced. Compression is horribly energy-intensive, and hydrogen is hard to confine without leakage. And once compressed and confined, there's a very good English word for what you've got.

A bomb.

Hydrogen as a transportation fuel sucks badly, and tweaking production efficiency - if this method even does that, which isn't clear from the article - doesn't fix that problem at all.
antialias_physorg
4.7 / 5 (6) Aug 02, 2013
Compression is horribly energy-intensive

Compression efficiency is, dependent on the type of compressor used 80-85% efficient. Which isn't that bad seeing as hydrogen storage would allow a lot of energy from renewable sources - and the energy grid in general - to be store which would otherwise be 100% lost.

And once compressed and confined, there's a very good English word for what you've got.

A bomb.

Which is true of any and every energy storage solution. A bomb is stored/concentrated energy. Be it a tank of gas or a tank of compressed hydrogen or whatever. You can always find a way to cause an accident that will release a lot of that energy quickly - and the results are never pretty.

Hydrogen as a transportation fuel sucks badly,

Then don't use compression. Use an metal-organic framework (MOF-177 has already exceeded the 2010 the volumetric requirements set by the DOE for hydrogen storage.
gracilism
2.6 / 5 (5) Aug 02, 2013
And how many square miles of mirrors would it take to replace our fossil fuel dependency? Put me in the nuclear power camp for energy solutions.
atrid3s
3 / 5 (2) Aug 02, 2013
It is a wise way to follow if you integrate stirling engine generators. At 1,350 degrees Celsius I am sure the output of this integration is more than sufficient and cost effective
lonewolfmtnz
1 / 5 (8) Aug 03, 2013
Oh great! Just imagine LA's 'freeways' clogged with a million plus mobile Hydrogen bombs - and/or everywhere else! Now there's a chain reaction I'd like to see. LOL. Dumb FKN Monkeys!
Neinsense99
1.4 / 5 (9) Aug 03, 2013
Oh great! Just imagine LA's 'freeways' clogged with a million plus mobile Hydrogen bombs - and/or everywhere else! Now there's a chain reaction I'd like to see. LOL. Dumb FKN Monkeys!

To the commenter who asked why ratings and the comment filter were implemented, I suggest we've found the answer.
Neinsense99
1.4 / 5 (10) Aug 03, 2013
And how many square miles of mirrors would it take to replace our fossil fuel dependency? Put me in the nuclear power camp for energy solutions.

Next time try making the decision AFTER getting the answer. That is, if you actually wanted an answer for a non-rhetorical question.
VendicarE
2.5 / 5 (2) Aug 03, 2013
"At that temperature, most of the incoming solar energy will simply be re-radiated back out. Kills system efficiency." - Lengould

An excellent point that was not immediately obvious to me.
Anonym
1.4 / 5 (9) Aug 04, 2013
"With the price of natural gas so low, there is no incentive to burn clean energy," said Weimer ... "There would have to be a substantial monetary penalty for putting carbon into the atmosphere..."

The fascist carbon tax raises its ugly head again.

We are in a virtuous cycle, although you'd never know that from the way "climate change" is being spun.

More people = more carbon = more food production.
More food = more wealth = slower population growth

Hydrogen technology needs to compete with so-called "fossil fuels" on its merits, which are legion. And why shouldn't it be cheaper to make energy from sunshine than from oil, which is expensive to extract, refine and transport. When hydrogen tech is truly ready for prime time, the use of hydrocarbons will simply wither away.
subfuzion
not rated yet Aug 04, 2013
Everyone complaining about system efficiency is missing the point. System efficiency is important, even of paramount importance when dealing with limited resources and harmful side effects and byproducts, but it's not the number one concern when it comes to harnessing the sun's energy to separate hydrogen from water. In the race to build more efficient commodity hydrogen fuel systems, we're still not even out of the starting blocks. To get the technology to the point where the cost of producing clean energy is even close to that of using our limited natural resources will be a major win.
VendicarE
3 / 5 (2) Aug 04, 2013
"More people = more carbon = more food production. " anonym

And yet grain stores are lower now than they were in the 1960's.

Around 60 days to global famine.

America's grain production belt is reverting to desert.
RealScience
4 / 5 (1) Aug 04, 2013
I highly doubt that any system which hopes to have a solar collector heat up to 1350 C will have any useful efficiency. At that temperature, most of the incoming solar energy will simply be re-radiated back out. Kills system efficiency.


@lengould100 - You are overlooking two factors: concentration, and selective emitters.
Black-body radiation at 1350C is 3.9 x 10^5 W/m2, which is ~390 times more than unconcentrated sunlight.
So at 1000 suns concentration (easily achievable with a large number of small heliostats), a black body would re-radiate ~39% of the incoming energy, which would indeed seriously impact efficiency.
However selective emitters can absorb ~90% of the incoming spectrum while having emissivity of ~20% in longer wavelengths that a 1350C source emits, reducing the re-radiated energy to below 10% of the incoming energy.
And concentrations of >1000x are also achievable.
DrNutrients
1.4 / 5 (9) Aug 06, 2013
The veiled argument for carbon tax by the lead scientist suggested that the Journal Science has become a mouth piece for the elite's political agenda. .

A real breakthrough in electrolysis came in 2009!

Urine electrolysis - 95 per cent less energy than water electrolysis
Fuel Cells, Sep 03 2009 (The Hydrogen Journal)
http://www.h2jour...wsID=270

You didn't see this in the Journal Science, because ANYONE can experiment with this approach in their backyard. We need to practice more empiricism without being inhibited by mathematical dogma.

"Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality." Nikola Tesla
Jaeherys
not rated yet Aug 07, 2013
So I glanced over the article and looked for efficiency rates but could not find any. The article gives rates of gas production and without a knowledge of the underlying accepted theory it is meaningless (I don't know what is good or bad) but here are the results.

Operating temperature conditions (Red/Ox, °C) || Total H2 generated (μmol g–1) || Peak H2 generation rate (μmol g–1 s–1)
Hercynite 1350/1000 || 31.4 ± 2.3 || 0.06 ± 0.04
Hercynite 1500/1200 || 93.7 ± 19.2 || 0.32 ± 0.01
Hercynite 1350/1350 || 102 ± 18 || 0.55 ± 0.16
Ceria 1350/1000 || 16.4 ± 3.6 || 0.14 ± 0.04

Graph compariing the different techniques http://www.scienc...arge.jpg Not sure if it will be viewable without a Yorku ID.