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
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
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
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
Family Foundation. It was presented at the 241st National Meeting of
the American Chemical Society(ACS).
II. Connecting the Quantum Dots
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
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
The results were published in a paper [abstract] in
the peer-reviewed journal ACS Nano.
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