Re: The Future Navy Will Be Nuclear

On Oct 17, 2:37 pm, Roman J. Rohleder <rjrohle...@xxxxxx> wrote:
Juergen Nieveler <juergen.nieveler.nos...@xxxxxxxx> schrieb:


Producinghydrogenthrough photosynthesis with bacteria for example is
one way, when it comes down to it the sun is the only reliable power
source on this planet (when it runs out, we're in trouble anyway).

Hydrogenis not the answer to our needs - currently it is expensive to
produce and and difficult to store.



November/December 2008
Sun + Water = Fuel
With catalysts created by an MIT chemist, sunlight can turn water into
hydrogen. If the process can scale up, it could make solar power a
dominant source of energy.
By Kevin Bullis

"I'm going to show you something I haven't showed anybody yet," said
Daniel Nocera, a professor of chemistry at MIT, speaking this May to
an auditorium filled with scientists and U.S. government energy
officials. He asked the house manager to lower the lights. Then he
started a video. "Can you see that?" he asked excitedly, pointing to
the bubbles rising from a strip of material immersed in water. "Oxygen
is pouring off of this electrode." Then he added, somewhat
cryptically, "This is the future. We've got the leaf."

What Nocera was demonstrating was a reaction that generates oxygen
from water much as green plants do during photosynthesis--an
achievement that could have profound implications for the energy
debate. Carried out with the help of a catalyst he developed, the
reaction is the first and most difficult step in splitting water to
make hydrogen gas. And efficiently generating hydrogen from water,
Nocera believes, will help surmount one of the main obstacles
preventing solar power from becoming a dominant source of electricity:
there's no cost-effective way to store the energy collected by solar
panels so that it can be used at night or during cloudy days.

Solar power has a unique potential to generate vast amounts of clean
energy that doesn't contribute to global warming. But without a cheap
means to store this energy, solar power can't replace fossil fuels on
a large scale. In Nocera's scenario, sunlight would split water to
produce versatile, easy-to-store hydrogen fuel that could later be
burned in an internal-combustion generator or recombined with oxygen
in a fuel cell. Even more ambitious, the reaction could be used to
split seawater; in that case, running the hydrogen through a fuel cell
would yield fresh water as well as electricity.

Storing energy from the sun by mimicking photosynthesis is something
scientists have been trying to do since the early 1970s. In
particular, they have tried to replicate the way green plants break
down water. Chemists, of course, can already split water. But the
process has required high temperatures, harsh alkaline solutions, or
rare and expensive catalysts such as platinum. What Nocera has devised
is an inexpensive catalyst that produces oxygen from water at room
temperature and without caustic chemicals--the same benign conditions
found in plants. Several other promising catalysts, including another
that Nocera developed, could be used to complete the process and
produce hydrogen gas.

Nocera sees two ways to take advantage of his breakthrough. In the
first, a conventional solar panel would capture sunlight to produce
electricity; in turn, that electricity would power a device called an
electrolyzer, which would use his catalysts to split water. The second
approach would employ a system that more closely mimics the structure
of a leaf. The catalysts would be deployed side by side with special
dye molecules designed to absorb sunlight; the energy captured by the
dyes would drive the water-splitting reaction. Either way, solar
energy would be converted into hydrogen fuel that could be easily
stored and used at night--or whenever it's needed.

Nocera's audacious claims for the importance of his advance are the
kind that academic chemists are usually loath to make in front of
their peers. Indeed, a number of experts have questioned how well his
system can be scaled up and how economical it will be. But Nocera
shows no signs of backing down. "With this discovery, I totally change
the dialogue," he told the audience in May. "All of the old arguments
go out the window."

The Dark Side of Solar
Sunlight is the world's largest potential source of renewable energy,
but that potential could easily go unrealized. Not only do solar
panels not work at night, but daytime production waxes and wanes as
clouds pass overhead. That's why today most solar panels--both those
in solar farms built by utilities and those mounted on the roofs of
houses and businesses--are connected to the electrical grid. During
sunny days, when solar panels are operating at peak capacity,
homeowners and companies can sell their excess power to utilities. But
they generally have to rely on the grid at night, or when clouds shade
the panels.

This system works only because solar power makes such a tiny
contribution to overall electricity production: it meets a small
fraction of 1 percent of total demand in the United States. As the
contribution of solar power grows, its unreliability will become an
increasingly serious problem.

If solar power grows enough to provide as little as 10 percent of
total electricity, utilities will need to decide what to do when
clouds move in during times of peak demand, says Ryan Wiser, a
research scientist who studies electricity markets at Lawrence
Berkeley National Laboratory in Berkeley, CA. Either utilities will
need to operate extra natural-gas plants that can quickly ramp up to
compensate for the lost power, or they'll need to invest in energy
storage. The first option is currently cheaper, Wiser says:
"Electrical storage is just too expensive."

But if we count on solar energy for more than about 20 percent of
total electricity, he says, it will start to contribute to what's
called base load power, the amount of power necessary to meet minimum
demand. And base load power (which is now supplied mostly by coal-
fired plants) must be provided at a relatively constant rate. Solar
energy can't be harnessed for this purpose unless it can be stored on
a large scale for use 24 hours a day, in good weather and bad.

In short, for solar to become a primary source of electricity, vast
amounts of affordable storage will be needed. And today's options for
storing electricity just aren't practical on a large enough scale,
says Nathan Lewis, a professor of chemistry at Caltech. Take one of
the least expensive methods: using electricity to pump water uphill
and then running the water through a turbine to generate elec­tricity
later on. One kilogram of water pumped up 100 meters stores about a
kilojoule of energy. In comparison, a kilogram of gasoline stores
about 45,000 kilojoules. Storing enough energy this way would require
massive dams and huge reservoirs that would be emptied and filled
every day. And try finding enough water for that in places such as
Arizona and Nevada, where sunlight is particularly abundant.

Batteries, meanwhile, are expensive: they could add $10,000 to the
cost of a typical home solar system. And although they're improving,
they still store far less energy than fuels such as gasoline and
hydrogen store in the form of chemical bonds. The best batteries store
about 300 watt-hours of energy per kilogram, Lewis says, while
gasoline stores 13,000 watt-hours per kilogram. "The numbers make it
obvious that chemical fuels are the only energy-dense way to obtain
massive energy storage," Lewis says. Of those fuels, not only is
hydrogen potentially cleaner than gasoline, but by weight it stores
much more energy--about three times as much, though it takes up more
space because it's a gas.

The challenge lies in using energy from the sun to make such fuels
cheaply and efficiently. This is where Nocera's efforts to mimic
photosynthesis come in.

Imitating Plants
In real photosynthesis, green plants use chlorophyll to capture energy
from sunlight and then use that energy to drive a series of complex
chemical reactions that turn water and carbon dioxide into energy-rich
carbohydrates such as starch and sugar. But what primarily interests
many researchers is an early step in the process, in which a
combination of proteins and inorganic catalysts helps break water
efficiently into oxygen and hydrogen ions.

The field of artificial photosynthesis got off to a quick start. In
the early 1970s, a graduate student at the University of Tokyo, Akira
Fujishima, and his thesis advisor, Kenichi Honda, showed that
electrodes made from titanium dioxide--a component of white paint--
would slowly split water when exposed to light from a bright, 500-watt
xenon lamp. The finding established that light could be used to split
water outside of plants. In 1974, Thomas Meyer, a professor of
chemistry at the University of North Caro­lina, Chapel Hill, showed
that a ruthenium-based dye, when exposed to light, underwent chemical
changes that gave it the potential to oxidize water, or pull electrons
from it--the key first step in water splitting.

Ultimately, neither technique proved practical. The titanium dioxide
couldn't absorb enough sunlight, and the light-induced chemical state
in Meyer's dye was too transient to be useful. But the advances stimu­
lated the imaginations of scientists. "You could look ahead and see
where to go and, at least in principle, put the pieces together,"
Meyer says.

Over the next few decades, scientists studied the structures and
materials in plants that absorb sunlight and store its energy. They
found that plants carefully choreograph the movement of water
molecules, electrons, and hydrogen ions--that is, protons. But much
about the precise mechanisms involved remained unknown. Then, in 2004,
researchers at Imperial College London identified the structure of a
group of proteins and metals that is crucial for freeing oxygen from
water in plants. They showed that the heart of this catalytic complex
was a collection of proteins, oxygen atoms, and manganese and calcium
ions that interact in specific ways.

"As soon as we saw this, we could start designing systems," says
Nocera, who had been trying to fully understand the chemistry behind
photosynthesis since 1984. Reading this "road map," he says, his group
set out to manage protons and electrons somewhat the way plants do--
but using only inorganic materials, which are more robust and stable
than proteins.

Initially, Nocera didn't tackle the biggest challenge, pulling oxygen
out from water. Rather, "to get our training wheels," he began with
the reverse reaction: combining oxygen with protons and electrons to
form water. He found that certain complex compounds based on cobalt
were good catalysts for this reaction. So when it came time to try
splitting water, he decided to use similar cobalt compounds.

Nocera knew that working with these compounds in water could be a
problem, since cobalt can dissolve. Not surprisingly, he says, "within
days we realized that cobalt was falling out of this elaborate
compound that we made." With his initial attempts foiled, he decided
to take a different approach. Instead of using a complex compound, he
tested the catalytic activity of dissolved cobalt, with some phosphate
added to the water to help the reaction. "We said, let's forget all
the elaborate stuff and just use cobalt directly," he says.

The experiment worked better than Nocera and his colleagues had
expected. When a current was applied to an electrode immersed in the
solution, cobalt and phosphate accumulated on it in a thin film, and a
dense layer of bubbles started forming in just a few minutes. Further
tests confirmed that the bubbles were oxygen released by splitting the
water. "Here's the luck," Nocera says. "There was no reason for us to
expect that just plain cobalt with phosphate, versus cobalt being tied
up in one of our complexes, would work this well. I couldn't have
predicted it. The stuff that was falling out of the compounds turned
out to be what we needed.

"Now we want to understand it," he continues. "I want to know why the
hell cobalt in this thin film is so active. I may be able to improve
it or use a different metal that's better." At the same time, he wants
to start working with engineers to optimize the process and make an
efficient water-splitting cell, one that incorporates catalysts for
generating both oxygen and hydrogen. "We were really interested in the
basic science. Can we make a catalyst that works efficiently under the
conditions of photosynthesis?" he says. "The answer now is yes, we can
do that. Now we've really got to get to the technology of designing a
cell."

Catalyzing a Debate
Nocera's discovery has garnered a lot of attention, and not all of it
has been flattering. Many chemists find his claims overstated; they
don't dispute his findings, but they doubt that they will have the
consequences he imagines. "The claim that this is the answer for
artificial photosynthesis is crazy," says Thomas Meyer, who has been a
mentor to Nocera. He says that while Nocera's catalysts "could prove
technologically important," the advance is "a research finding," and
there's "no guarantee that it can be scaled up or even made
practical."

Many critics' objections revolve around the inability of ­Nocera's lab
setup to split water nearly as rapidly as commercial electrolyzers do.
The faster the system, the smaller a commercial unit that produced a
given amount of hydrogen and oxygen would be. And smaller systems, in
general, are cheaper.

The way to compare different catalysts is to look at their "current
density"--that is, electrical current per square centimeter--when
they're at their most efficient. The higher the current, the faster
the catalyst can produce oxygen. Nocera reported results of 1 milliamp
per square centimeter, although he says he's achieved 10 milliamps
since then. Commercial electrolyzers typically run at about 1,000
milliamps per square centimeter. "At least what he's published so far
would never work for a commercial electrolyzer, where the current
density is 800 times to 2,000 times greater," says John Turner, a
research fellow at the National Renewable Energy Laboratory in Golden,
CO.

Other experts question the whole principle of converting sunlight into
electricity, then into a chemical fuel, and then back into electricity
again. They suggest that while batteries store far less energy than
chemical fuels, they are nevertheless far more efficient, because
using electricity to make fuels and then using the fuels to generate
electricity wastes energy at every step. It would be better, they say,
to focus on improving battery technology or other similar forms of
electrical storage, rather than on developing water splitters and fuel
cells. As Ryan Wiser puts it, "Electrolysis is [currently]
inefficient, so why would you do it?"

The Artificial Leaf
Michael Grätzel, however, may have a clever way to turn Nocera's
discovery to practical use. A professor of chemistry and chemical
engineering at the École Polytechnique Fédérale in Lausanne,
Switzerland, he was one of the first people Nocera told about his new
catalyst. "He was so excited," Grätzel says. "He took me to a
restaurant and bought a tremendously expensive bottle of wine."

In 1991, Grätzel invented a promising new type of solar cell. It uses
a dye containing ruthenium, which acts much like the chlorophyll in a
plant, absorbing light and releasing electrons. In ­Grätzel's solar
cell, however, the electrons don't set off a water-splitting reaction.
Instead, they're collected by a film of titanium dioxide and directed
through an external circuit, generating electricity. Grätzel now
thinks that he can integrate his solar cell and ­Nocera's catalyst
into a single device that captures the energy from sunlight and uses
it to split water.

If he's right, it would be a significant step toward making a device
that, in many ways, truly resembles a leaf. The idea is that Grätzel's
dye would take the place of the electrode on which the catalyst forms
in Nocera's system. The dye itself, when exposed to light, can
generate the voltage needed to assemble the catalyst. "The dye acts
like a molecular wire that conducts charges away," Grätzel says. The
catalyst then assembles where it's needed, right on the dye. Once the
catalyst is formed, the sunlight absorbed by the dye drives the
reactions that split water. Grätzel says that the device could be more
efficient and cheaper than using a separate solar panel and
electrolyzer.

Another possibility that Nocera is investigating is whether his
catalyst can be used to split seawater. In initial tests, it performs
well in the presence of salt, and he is now testing it to see how it
handles other compounds found in the sea. If it works, Nocera's system
could address more than just the energy crisis; it could help solve
the world's growing shortage of fresh water as well.

Artificial leaves and fuel-producing desalination systems might sound
like grandiose promises. But to many scientists, such possibilities
seem maddeningly close; chemists seeking new energy technologies have
been taunted for decades by the fact that plants easily use sunlight
to turn abundant materials into energy-rich molecules. "We see it
going on all around us, but it's something we can't really do," says
Paul Alivisatos, a professor of chemistry and materials science at the
University of California, Berkeley, who is leading an effort at
Lawrence Berkeley National Laboratory to imitate photosynthesis by
chemical means.

But soon, using nature's own blueprint, human beings could be using
the sun "to make fuels from a glass of water," as Nocera puts it. That
idea has an elegance that any chemist can appreciate--and
possibilities that everyone should find hopeful.

Kevin Bullis is Technology Review's Energy Editor.
http://www.technologyreview.com/printer_friendly_article.aspx?id=21536&channel=energy&section=
.

Relevant Pages

  • Re: Stupid "free energy" idea
    ... use up in require additional energy to the truck. ... Actually it is impossible to generate more power than you use. ... as by utilizing vehicle traffic on roadways. ... Energy sources useful for the generation of electricity include wind, ...
    (rec.martial-arts)
  • Re: Defining Chi with Judo Terms thread
    ... contraceptives in the drinking water or in the food supply? ... The real long pole in the tent is energy. ... Pilot plants of Ocean Thermal power systems have been built and ... the technology for Ocean Thermal Plants is there. ...
    (rec.martial-arts)
  • Re: Free electricity is not cheap
    ... He certainly did not know about fusion energy, this was not worked out until ... These "Teslas" are said to be under development by the Tesla company, ... "Free" Electricity ... hidden power of the Universe. ...
    (sci.physics.fusion)
  • Turning Power Plant Challenges into Clean Technology Opportunities
    ... Turning Power Plant Challenges into Clean Technology Opportunities ... Looks at Water and Renewable Energy ...
    (misc.invest.stocks)
  • Re: On the slow verge of a civil war in the USA, satellite TV in vans
    ... less than current heating energy) produces a gallon of water a minite, ... cooling, electric power for the big flat-screen TV, fridge, microwave ... 500 kilowatts and filled up in 10 minutes with electricity at a power ...
    (sci.astro)