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MIT Professor Daniel Nocera claims to have invented the first affordable solar cell capable of mimicking nature and performing photosynthesis -- splitting water.  (Source: Christopher Harting/MIT)

Another study examined how quantum dots may be able to perform "Multiple Exciton Generation" an unusual phenomena that sees an excited quantum dot electron (blue, left) transfer energy to multiple electrons in another quantum dot (green, right)  (Source: Mark T. Lusk, Department of Physics, Colorado School of Mines)
"Her green plastic watering can/For her fake Chinese (silicon) plant/In the fake (silicon) earth."

One of the most promising sources of future energy is solar power.  We're currently only harvesting a minuscule fraction of the estimated 12.2 billion kilowatt-hours of solar energy that hits the Earth every day [source].  While nuclear fission and fusion power also will be critical to the future of man, solar power may be usable on planetoids that lack fissile fuels like uranium and fussile fuels like deuterium.

Before we can get to such ambitious terrestrial or interplanetary objectives, much work needs to be done.  A pair of new studies published by the Massachusetts Institute of Technology and the Colorado School of Mines offer intriguing tools that could one day be applied to making solar power more efficient.

I. Growing a Solar "Tree"

Scientists often find that nature has produced designs that rival any that mankind has cooked up.  A perfect example of that is the tree.  

A dominant plant species across much of the world, trees have solved much of the problems that have puzzled alternative energy scientists.  They not only store collected solar energy in polysaccharides, but also manage an immensely large solar collecting surface via their multipurpose evolutionary invention, the leaf.

Using the chemical model of the leaf, researchers at MIT created a poker card-sized silicon cell, doped with special catalysts and controlling electronics.  The team reports that the device is capable of producing an abundantly positive energy balance by splitting water into hydrogen and oxygen.  The reactions it carries out are similar to those that occur inside chloroplasts in photosynthetic plant cells.

The emitted gases could be harvested and stored for use powering a fuel cell.  Daniel Nocera, Ph.D. [profile], who led the team, describes [press release], "A practical artificial leaf has been one of the Holy Grails of science for decades. We believe we have done it. The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. Our goal is to make each home its own power station.  One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology."

Professor Nocera reports that his leaf actually beats nature's design in efficiency by a factor of 10, and may be even more efficient in the future.  Of course it lacks natural leafy plants' ability to heal from damage, self-replicate, and self-generate from ground resources.  Nonetheless, the efficiency mark is an impressive achievement.

The key to that success is special nickel-cobalt catalyst that Professor Nocera cooked up.  Much like photosynthetic pigments that use metal ions as their active center, these catalysts use the harvest solar energy to perform chemical reactions.

John Turner of the U.S. National Renewable Energy Laboratory in Boulder, Colorado created a similar "solar leaf" a decade ago, but it relied on expensive rare metal catalysts.  Since then, many other researchers have created new solar leaf designs, but most of their designs remained quite expensive or lacked efficiency.

By contrast Professor Nocera's design is far cheaper, while maintaining a respectable efficiency.

The key obstacle now to this technology being practically suited for mass production is the lack of availability of cheap, durable fuel cells.  Currently fuel cells capable of producing enough energy to power a modern house remain quite expensive, costing tens, if not hundreds of thousands of dollars.  Still, it is reasonable to hope that similar breakthroughs will one day be able to drop the cost of fuel cells enough that the entire system will become feasible for mass deployment.

MIT's research was funded by The National Science Foundation (NSF) and the Chesonis Family Foundation.  It was presented at the 241st National Meeting of the American Chemical Society(ACS).

II. Connecting the Quantum Dots

Quantum dots are outlandish human-constructed atoms that confine electrons to a three dimensional space in a crystal-like motif.  The electrons are capable of absorbing photons to form excitons and the properties of quantum dots themselves are somewhat like bulk semiconductors, making them an attractive target for photodetectors or solar cells.

Scientists are still struggling to understand the complex structures they've created, though.  The dots operate on quantum physics rules far different from those observed on a macroscopic scale.

New research at the Colorado School of Mines offers evidence in support of a controversial theory called multiple exciton generation (MEG), which suggests that a quantum dot's electron that has absorbed light energy from a single photon can transfer that energy to multiple other electrons.

Previous studies have been remarkably inconsistent on the possible relationship between quantum dot size and MEG events, thus it was an attractive target for simulation, says the research team.  

Using a computer cluster funded by a NSF grant the team revealed that each size of quantum dot is capable of performing MEG for a select slice of the solar spectrum.  Smaller dots have the highest efficiency of electricity generation from their spectrum-dependent MEG events.

The team's leader, Professor Mark Lusk [profile], says that the results indicate that using a mix of quantum dots could produce superior electricity generation capabilities in future solar cells.  He states [press release], "We can now design nanostructured materials that generate more than one exciton from a single photon of light, putting to good use a large portion of the energy that would otherwise just heat up a solar cell."

The results were published in a paper [abstract] in the peer-reviewed journal ACS Nano.

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By Paj on 3/30/2011 7:54:02 AM , Rating: 2
Evolutionary theory did not cause the Holocaust or eugenics - xenophobia and social prejudices did. They existed long before evolution, and will exist for some time yet.

Darwin himself did much to dismiss the perceived differences between races at the time, highlighting what they had in common.

Evolution is biology. It is descriptive, not prescriptive - yet it has been blamed for many things, from pre-martial sex to communism. Which makes your comment...

The sad thing about people is they can never separate their own personal issues, their prejudices, and own world view and actually do objectionable science.

...all the more ironic.

By hawwah on 3/30/2011 8:49:04 PM , Rating: 2
To say that evolution is biology implies that evolution = biology or that evolution = science; when in fact biology can as a science only provide evidence to help prove or disprove a given theory. For evolution to occur there would have to be a natural mechanism, a scientific fact, by which genetic information or DNA could be created. There is no biological mechanism, or mechanism in any field of science which allows this.
As far a eugenics and the holocaust are concerned, as I said, these were events and actions taken by scientists, doctors, nurses and many others; whose belief in evolution gave them cause and justification for those actions. Evolution from its inception, has always been exceedingly adept at introducing egocentric believes into a persons worldview. And of course as part of ones worldview evolution will inherently degrade all concept of morality.
It is extremely difficult for anyone to separate their worldview entirely, as it provides the basis for how we think and understand the world. The core beliefs that make up our worldview will either aid or discourage things like racism or religious racism, as far as they are able. Evolution largely supports and promotes an atheistic belief system, something that people like Richard Dawkins have admitted; prior to the theory no atheist in the world was considered intellectual because they had no basis on which to support their beliefs. Today however evolution is still the only support the atheist religion has to justify their perspective, which is why they defend it so ferociously even without any scientific mechanism. And as a religion, it is the only one, which by its own nature requires the believer to admit all other religions and their beliefs in part or as a whole are wrong and incorrect. Its just to bad that most people have never taken the time to step back from what they believe, ask ‘why do i believe this’, and follow the implications of their beliefs to there logical conclusion. (assuming you can reach that conclusion without having your worldview distort it)

"The whole principle [of censorship] is wrong. It's like demanding that grown men live on skim milk because the baby can't have steak." -- Robert Heinlein

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