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Harvesting the Sun's Energy
updated: Feb 25, 2013, 3:00 PM

Source: UCSB

A new method of harvesting the Sun's energy is emerging, thanks to scientists at UC Santa Barbara's Departments of Chemistry, Chemical Engineering, and Materials. Though still in its infancy, the research promises to convert sunlight into energy using a process based on metals that are more robust than many of the semiconductors used in conventional methods. The researchers' findings are published in the latest issue of the journal Nature Nanotechnology. "It is the first radically new and potentially workable alternative to semiconductor-based solar conversion devices to be developed in the past 70 years or so," said Martin Moskovits, professor of chemistry at UCSB.

In conventional photoprocesses, a technology developed and used over the last century, sunlight hits the surface of semiconductor material, one side of which is electron-rich, while the other side is not. The photon, or light particle, excites the electrons, causing them to leave their postions, and create positively-charged "holes." The result is a current of charged particles that can be captured and delivered for various uses, including powering lightbulbs, charging batteries, or facilitating chemical reactions.

"For example, the electrons might cause hydrogen ions in water to be converted into hydrogen, a fuel, while the holes produce oxygen," said Moskovits.

In the technology developed by Moskovits and his team, it is not semiconductor materials that provide the electrons and venue for the conversion of solar energy, but nanostructured metals -- a "forest" of gold nanorods, to be specific.

For this experiment, gold nanorods were capped with a layer of crystalline titanium dioxide decorated with platinum nanoparticles, and set in water. A cobalt-based oxidation catalyst was deposited on the lower portion of the array.

"When nanostructures, such as nanorods, of certain metals are exposed to visible light, the conduction electrons of the metal can be caused to oscillate collectively, absorbing a great deal of the light," said Moskovits. "This excitation is called a surface plasmon."

As the "hot" electrons in these plasmonic waves are excited by light particles, some travel up the nanorod, through a filter layer of crystalline titanium dioxide, and are captured by platinum particles. This causes the reaction that splits hydrogen ions from the bond that forms water. Meanwhile, the holes left behind by the excited electrons head toward the cobalt-based catalyst on the lower part of the rod to form oxygen.

According to the study, hydrogen production was clearly observable after about two hours. Additionally, the nanorods were not subject to the photocorrosion that often causes traditional semiconductor material to fail in minutes.

"The device operated with no hint of failure for many weeks," Moskovits said.

The plasmonic method of splitting water is currently less efficient and more costly than conventional photoprocesses, but if the last century of photovoltaic technology has shown anything, it is that continued research will improve on the cost and efficiency of this new method -- and likely in far less time than it took for the semiconductor-based technology, said Moskovits.

"Despite the recentness of the discovery, we have already attained ‘respectable' efficiencies. More importantly, we can imagine achievable strategies for improving the efficiencies radically," he said.

Research in this study was also performed by postdoctoral researchers Syed Mubeen and Joun Lee; grad student Nirala Singh; materials engineer Stephan Kraemer; and chemistry professor Galen Stucky.

Comments in order of when they were received | (reverse order)

 EZ2 agree helpful negative off topic

2013-02-25 03:02 PM

Sounds very promising


 COMMENT 378592 agree helpful negative off topic

2013-02-25 04:09 PM

Exciting is right! What are the next steps?


 COMMENT 378622 agree helpful negative off topic

2013-02-25 05:19 PM

The Nano Revolution is just beginning. This is going to be the next huge thing that everyone will be talking about.


 COMMENT 378632 agree helpful negative off topic

2013-02-25 05:31 PM

Especially all those suckers who spent thousands on Solar!


 COMMENT 378636 agree helpful negative off topic

2013-02-25 05:37 PM

Go Team UCSB!


 COMMENT 378699 agree helpful negative off topic

2013-02-25 09:45 PM

Man, would I love to work on that!


 COMMENT 378729 agree helpful negative off topic

2013-02-26 07:07 AM

How much gold does it take to generate 100 W? Efficiency AND economics are the big questions.


 COMMENT 378752 agree helpful negative off topic

2013-02-26 08:13 AM

Titanium, Platinum, and gold, AND nanotechnology? I'm sorry guys, at what point will this be economically feasible? At what point will gold and platinum ever going to be cheap? I don't see a lot of massive deflation in our future.

Unless there's some kind of massive energy density in this technology's future (and it doesn't sound like there is yet), or a better set of metals for use, this seems like an exercise in futility.


 COMMENT 378795 agree helpful negative off topic

2013-02-26 09:24 AM

Nanotechnology is using materials on an atomic or molecular scale, so maybe so little of this material will be needed that it will be economically feasible?


 RICHYRICH agree helpful negative off topic

2013-02-26 09:55 AM

Those people who put in solar panels are not suckers. I have done well over a hundred installs in Santa Barbara, and a good chunk of those folks have already attained a 100% recoup of thier investment, with manymore years of life left in the system. And as electric rates rise, they are laughing all the way to the bank. Also, due to the pioneers that chose to invest in PV technology, panels prices have fallen from over $4/watt wholesale in 2006 to less than $1/watt today.

Thank you to UCSB for continuing to push the edge.


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