Gold nanorods provide whole new way of harvesting energy from the sun

Feb 24, 2013

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 .

"For example, the electrons might cause 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 , but nanostructured metals—a "forest" of nanorods, to be specific.

For this experiment, gold nanorods were capped with a layer of crystalline decorated with platinum , 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 , 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 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.

Explore further: A promising light source for optoelectronic chips can be tuned to different frequencies

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grondilu
5 / 5 (4) Feb 24, 2013
I want to hope this is not yet another ground-breaking announce in solar energy that we will never hear about again.
ValeriaT
5 / 5 (5) Feb 24, 2013
Is it really a new idea? (1, 2, ...) - and I'm not even asking if it's economically viable and durable from long-term perspective.
Steven_Anderson
2.6 / 5 (5) Feb 24, 2013
When you are close to a developing technology such as solar, or phones for instance, it's hard to see the impact of breaking developments. If however you step back and look where the technology has come from and where it's going, a pattern emerges that shows a stead state progression toward higher efficiency and lower cost over time. http://en.wikiped...ar_cell.

http://rawcell.com
antialias_physorg
3.7 / 5 (3) Feb 25, 2013
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.

Gold, cobalt, platinum? Does seem a bit expensive if one were to scale it up. I'm thinking that replacing these materials with less costly ones might impact the efficiency/stability in a negative way.

Still. It's certainly something to follow up on.
VendicarE
5 / 5 (1) Feb 25, 2013
Odd how the efficiencies are almost never mentioned in these articles.
VendicarE
not rated yet Feb 25, 2013
Don't worry, there will be plenty of these elements once Martini and Rossi figure out how to get their E-Cat device to work.

"Gold, cobalt, platinum?" - Antialias
PPihkala
1 / 5 (1) Feb 25, 2013
But of course when there will be E-cats, then demand for solar tech will diminish.