Cheap Catalyst Could
Turn Sunlight, Water Into Fuel
By Alexis Madrigal
Wired Science
July 31, 2008
A new catalyst makes it feasible to split water with solar
power.
MIT chemists say the catalyst, used in conjunction with
cheap photovoltaic solar panels, could lead to inexpensive, simple systems that
use water to store the energy from sunlight.
In the process, the scientists may have cleared the major
roadblock on the long road to fossil fuel independence: Reducing the on-again,
off-again nature of many renewable power sources.
The catalyst enables the electrolysis system to function
efficiently at room temperature and at ordinary pressure. Like a reverse fuel
cell, it splits water into oxygen and hydrogen. By recombining the molecules
with a standard fuel cell, the O2 and H2 could then be used to generate energy
on demand.
"You've made your house into a fuel station,"
Daniel Nocera, a chemistry professor at MIT said.
"I've gotten rid of all the goddamn grids."
Solar energy currently makes less than one percent of the
world's electricity. The main drawback of the technology, preventing wider
adoption, is that solar systems only make power while the sun is shining. At
night or on cloudy days, those in need of power must look elsewhere. So storage
of electrical energy has been a long-sought after technological advance.
Batteries work but they're too big and expensive. Fuels, fossil or renewable,
are different: They act as their own storage, allowing for easy transport and
usage. That's one reason that coal and oil have such a dominant hold on the
world's energy market.
The MIT discovery could help transform electricity generated
through solar energy into a fuel, making it more competitive with fossil fuels.
That could prove to be a major milestone in clean technology.
"I think it's a very interesting discovery," said
Tom Mallouk, a chemistry professor at
The key advancement in Nocera's
Science paper is the development of an oxygen-producing catalyst made of cobalt
and phosphate. Splitting water requires two half-reactions, one to create
oxygen gas and the next to create hydrogen. For decades, Mallouk
said, scientists have been trying to reduce the cost of the oxygen part of the
reaction, with little success.
"The hydrogen side of the cell is only two electrons
per molecule. The oxygen side is four electrons per molecule," Mallouk said. "There is a rule in electrochemistry that
the more electrons you have the more complicated the process is."
It's important to note that Nocera's
breakthrough is in making it cheaper and simpler to split water by
electrolysis. Expensive machines have long been able to do the same thing, but
only by using iridium alloys or exotic nanoparticles.
The new catalyst is remarkable because its
made of common materials and can operate at room temperature and normal
pressure. Without the need to heat and pressurize the water, the energy needs
and cost of running the process overall are much lower. And that could make a
standard solar array on a home a viable source of electricity for creating all
the hydrogen a household would need.
The joke in clean tech circles about hydrogen is that
"hydrogen is the fuel of the future and always will be." But that's
in large part because producing hydrogen has been so expensive and
energy-intensive to produce. Most of the power in the world comes from fossil fuel, too, so making hydrogen generated tons of greenhouse
gases.
"It's never an issue in energy of whether you can do it
or not," Nocera said. "It's whether you can
do it cheaply."
And whether or not the setup will prove
cost-effective remains to be seen. It still uses a platinum catalyst to
produce hydrogen, for example.
Erik Straser, a leading clean
technology investor with the venture capital firm, Mohr-Davidow,
termed the technology "promising," but said the new paper didn't shed
light on its economic viability.
"I think that having operation at room temp and
standard pressure is a key innovation," he wrote in an e-mail to
Wired.com. "What is not there are any of the metrics that would let you
determine whether this made economic sense (a huge issue in these energy
technologies)."
Other scientists are, however, hard at work trying to find
cheaper hydrogen producing catalysts, including a group of scientists led by
Bjorn Winther-Jensen who published work on a
carbon-based catalyst in the same issue of Science this week.
Nocera himself admits that he hasn't
"driven down the whole road" on what the setup could cost. And, solar
panels remain very expensive on a per-kilowatt basis, even as innovation in the
field continues to drive costs down for consumers.
Still, despite the questions about the commercial viability
of the technology, Nocera said that the Bob
Metcalfe-run venture capital firm, Polaris, had "swooped in" on the
technology and was filing for patent protections.
Though Nocera doesn't expect retail
systems to be available for the better part of a decade, the questions about
the viability of his idea should begin to be answered soon, as prototype
designs attempt to deliver on his big promises.
"Within two years, you'll start seeing module designs,"
Nocera said. "A lot of my MIT colleagues are
raring to go and work on this and they are all engineers and they're pretty
damn good."
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