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Solar energy-harvesting “nanotrees” could produce hydrogen fuel on a mass scale

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March 8, 2012

Electronic microscopic image of a 'nanoforest,' with green tint added for contrast (Imge: ...

Electronic microscopic image of a 'nanoforest,' with green tint added for contrast (Imge: Wang Research Group, UC San Diego Jacobs School of Engineering)

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While hydrogen is considered a "clean" fuel because the only waste product it generates is water, the conventional way to produce it relies on electricity, which is usually produced through the burning of fossil fuels. Researchers at the University of California, San Diego (UCSD), have now developed a "3D branched nanowire array" that they claim could cheaply and cleanly deliver hydrogen fuel on a mass scale.

The nanowires, which are made from abundant natural materials such as silicon and zinc oxide, mimic the structure of a forest of trees, with individual vertical "trees" sprouting hundreds of nano-sized "branches." Like forests, this structure maximizes the amount of solar energy that can be captured, with the vertical structures trapping and absorbing the light, while the flat surfaces reflect it.

Using this nanotree structure, the researchers were able to maximize the amount of solar energy captured for use in producing hydrogen in a process called photoelectrochemical water-splitting. This process usually uses planar solar cells to produce hydrogen in a process similar to the electrolysis of water, but the UCSD team says their nanowire arrays produce more hydrogen fuel efficiently.

The light trapping effect in nanowire arrays sees photons bounced between single nanowires...

Ke Sun, a PhD student in electrical engineering who led the project, says the vertical nanotree structure also allows very small gas bubbles of hydrogen to be extracted much faster to maximize the hydrogen gas output. Additionally, the surface area for chemical reactions has been enhanced by at least 400,000 times in the nanotree structure compared to its planar counterparts.

While the team says its nanotrees provide a cheap way to produce hydrogen fuel on a mass scale, they are aiming to go further. Like other research teams, they are looking to use the nanotree structure to mimic photosynthesis in a device that not only harnesses the power of the sun to produce hydrogen fuel, but also captures CO2 from the atmosphere to reduce carbon emissions at the same time.

"We are trying to mimic what the plant does to convert sunlight to energy," said Sun. "We are hoping in the near future our 'nanotree' structure can eventually be part of an efficient device that functions like a real tree for photosynthesis."

The team is also looking at alternatives to zinc oxide which, although it absorbs the sun's ultraviolet light, has stability issues that affect the nanotree structure over time.

The team's research appears in the journal Nanoscale

Source: UCSD

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
18 Comments

Hydrogen is a lousy motor fuel because it migrates through everything and has a low energy density even when liquified or highly compressed. I would prefer to use liquid ammonia as a fuel.

Slowburn
9th March, 2012 @ 12:28 am PST

Slowburn - Haven't you heard that graphene is completely impervious to any type of gas? so solutions are possible. If you think that this new idea to harvest H2 is not noteworthy and that you'd prefer to use liquid ammonia, just go out there and get it done yourself!

AussieJohn
9th March, 2012 @ 02:29 am PST

The water level is rising and the forests are shrinking. Theese things...i don't know if ere good.

Iosif Eugen Olimpiu
9th March, 2012 @ 03:36 am PST

Slowburn. What a delicious non sequitur. You are very handsome.

Russ Pinney
9th March, 2012 @ 03:56 am PST

Hydrogen Fuel Cells produce electricity ... why on earth would you burn it?

Jeff Rosati
9th March, 2012 @ 07:23 am PST

I'm always happy in advances like these but I'd be happier if any of this stuff actually made it out of the Lab- not that it never happens- the super strong, scratch resistant glass used in Iphones and the like was invented by Corning in a Lab- in the 60s

billybob222
9th March, 2012 @ 09:34 am PST

The scratch resistant screen!?! You do realize that every single component in the iPhone was in the lab at some point, a lot of it more recently than the 1960's. These projects almost always go somewhere, when they don't lead to directly marketable applications the lessons learned serve a useful purpose in another lab.

This work is brilliant!

Jeff- One of the main reasons you may want to burn it instead of feed it to a fuel cell is because sometimes the transition to electrical potential is just to slow for the application. There are also tech reasons. Example: You can feed an unlimited supply of H2 into a fuel cell indefinitely but even all of that electrical energy isn't going to put a rocket into space without a magnetic linear accelerator or some similar intermediary that doesn't currently exist. Burning a Hydrogen based fuel can.

There are a lot of reasons to burn it.

Adam Thomas Flynn
9th March, 2012 @ 11:57 am PST

re; Jeff Rosati

Hydrogen Fuel Cells produce electricity by burning it in a very controlled manner.

Besides an ICE engine costs less and has a longer life expectancy.

.............................................................................................................................

re; AussieJohn

Please demonstrate a tank that is sealed by a single sheet of graphene without joints, and a valve that seals as well for hydrogen as I can expect for ammonia.

Slowburn
9th March, 2012 @ 12:34 pm PST

They shouldn't sit on this until it fits their own definition of "perfect." If it can really create hydrogen as efficiently and inexpensively as they claim and this can be mass produced, they should begin releasing this for sale to companies now. Then later, once they've fixed the degradation issue and found a way to efficiently absorb carbon dioxide, release "nanotree 2.0" and continue from there.

Don't sit on this "nanotree 1.0 just because you don't have the new and improved version ready yet. Bring it to market and then make it even better for future versions, just like every other product on the market.

Dave Andrews
9th March, 2012 @ 12:38 pm PST

Interesting:) I thought Hydrogen engins at the end of the day, is more about zero emissions, not how it is made or pedantic lab work.

And ammonia made on a scale to power and replace the car, sounds like that idea should be on the back burner not the slow burner:)

Paul Perkins
10th March, 2012 @ 12:14 am PST

This would require ultra pure water, otherwise at the nano scale, the nano substances would be easily contaminated,polluted, damaged or surface area rapidly reduced, degraded. Now to produce ultra pure water requires energy.

Dawar Saify
10th March, 2012 @ 04:36 am PST

re; Paul Perkins

Combining hydrogen and nitrogen to make ammonia is a widely used industrial process, and it also can be done on an energy available basis.

Slowburn
10th March, 2012 @ 06:58 am PST

Excellent. I've dreamed of this.

Please get these people in touch with the solar cell engineers so that we can skip the detour over hydrogen to get electricity.

Conny Söre
10th March, 2012 @ 02:55 pm PST

Much effort is being done in looking for new materials that store hydrogen in a cheap, efficient way w/o compromising too much on energy density. Solid hydrogen hydride complexes are in its n-th generation of development and seem promising. Hydrogen at a glance doesn't seem to be a practical carrier of energy given its low energy per volume ratio, but if you look at its energy per weight ratio it's higher than gasoline. It's more attractive if you can build a storage device that doesn't weigh too much and isn't too bulky.

I like the approach the scientists in these articles go. Producing hydrogen fuel from solar energy is the way to go to fill in the gap electricity does not fill very well.

I'm not a fan of auto vehicles that uses unpractical, heavy lithium batteries to go about. Their electricity is by no means clean as it was just generated in a nearby power plant that uses fossil fuels.

Fretting Freddy the Ferret pressing the Fret
10th March, 2012 @ 03:51 pm PST

re; Conny Söre

This is for providing power to places you can not reach with an extension cord.

Slowburn
10th March, 2012 @ 06:39 pm PST

Anything that gets us away from the "prehistoric Otto Motor" can only be good. Saves pollution and the independance of oil states like Iran.

The hydrogen motor is available -just need a clean process to produce hydrogen.

If this is a way forward then by all means.

Good work!!

Didgeman
12th March, 2012 @ 08:00 am PDT

Don't get too excided yet, just another lab experiment. there are others...

http://www.gizmag.com/ornl-photosynthesis-hydrogen-fuel/17780/

http://www.gizmag.com/breakthrough-in-using-sunlight-to-split-water/14833/

It still has to be build on commercial scale at competitive cost.

tswift
22nd March, 2012 @ 11:19 am PDT

The volume issue is severe. You can extract more hydrogen from a given volume of methane than you can from the same volume of pure liquid hydrogen.

And leave the g-dang CO2 in the atmosphere alone. It's crucial, harmless, the rootstock of all life, and doubling or quadrupling it would be great. It has actually very little effect on temperature; that's a minor twitch in the atmosphere's system of counter-balanced negative feedbacks. Which, actually, is rather unfortunate as we're in far more danger of cooling. Which you REALLY don't want to experience.

Brian Hall
28th March, 2012 @ 04:50 am PDT
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