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Hydrogen feasibility update - The search for water-splitting materials brightens up (forward below) - Cautionary Note: "... a necessary but insufficient condition" Perhaps our magnificent technological sophistication is searching in the wrong micro closets? Probable Causes:
- Brought on by extreme aversion and avoidance to interpret the scientifically linked, historical, treasure trove of data from humanities past
- Non recognition of an unmatched, world wide Icon of the past (mathematically translated), the circle and the sine wave - a visual broadcast of Nature's physical, primary Constant, revealing an expanded version of E=MC^2 - the Radius of Curvature of all Natural Law
- A Radius of Curvature Constant conclusively Illuminating
the engineering and electrochemical nature and ingredients for splitting water effortlessly, while paving the way to FTL (faster than light) and Field-Dependent Propulsion Systems - Back Burner Placement of a General Systems grasp, a micro to macro scientific consolidation view, which would also reveal the missing Illusion (light/vision related), simplistic principles of a Radius of Curvature Constant, permitting manipulation of natural laws in harmonic accordance, rather than costly and inefficient pitting of one natural law against another.
- "In the manipulation of Gravity and ZPE, the world would change. Nothing would ever be the same again. The physical, mental and spiritual sciences would unite under the same natural laws" - brings on FEAR by the populace to avoid at all costs; LOVE by those in Power to keep secret at all costs. Not surprising, NASA's "Breakthrough Propulsion Physics" lost its program funding.
THE CURRENT STATUS QUO IS SHAPED BEHAVIOR MODIFICATION - DELIBERATE CUES FOCUSING ON THE TRIVIA AND AVOIDANCE OF GESTALT / COMPREHENSION / UNDERSTANDING - akin to an absurd analogy of being forced to determine how a laboratory fingernail came into being without the slightest thought given, or permitted, to its origination, the fact that it was connected to the human body. A disconnected fingernail loses meaning when common sense is lost.
As they used to say in the destroyed wisdom circles of civilization's recorded history, "absolute power and greed corrupts absolutely, bringing about total madness and destruction". (NOTE MODERN PSYCHOLOGY'S COMPLETE FREUDIAN AVERSION TO ADDRESS THE CONCEPTS OF POWER, HUMAN DEVELOPMENT AND HUMAN EVOLUTIONARY NATURE - a causal factor of directional (ALL SCIENCE) university funding - the FREEDUMB of lost choice in democracy).
Will the Nature of the True Evil Beast be recognized prior to the analogy of "the dragon eating its own tail consumes itself entirely?
The immensity and destructive Power of "unregulated, non-living, law creating entities, that are privatizing every natural ingredient required for LIFE for the sole and ONLY goal of maximum profit, in the hands of a few.......................... will make WWII look like heaven in comparison.
http://fadingillusionviarealitycurve.blogspot.com/FWD:==================================
Solar Hydrogen: The search for water-splitting materials brightens up
http://www.sciencenews.org/articles/20041030/bob10.asp
Science News Online - Week of Oct. 30, 2004; Vol. 166, No. 18 - Alexandra Goho
In his 1874 science fiction tale The Mysterious Island, Jules Verne
predicted, "Water will be the coal of the future." It is a vision of
infinite clean energy available for people to use. More than 30 years
ago, Japanese scientists took a seminal step in that direction.
With a piece of titanium dioxide and some sunlight, they split water into
hydrogen and oxygen. Although researchers have tried to refine the
process over the years, nobody has come up with a system that is both
efficient and inexpensive enough to produce sufficient hydrogen for use as
a clean-burning fuel on the roads, in industry, and at home. Recently,
however, researchers have picked up the pace of their pursuit of the
ultimate water-splitting system.
With rising oil prices and the specter of climate change that's due to the
burning of fossil fuel, the vision of a hydrogen economy looms ever larger
in people's minds. After all, it's a fuel for which the only by-product
is water. And hydrogen packs more energy per unit mass than any fossil
fuel does.
But the main source of hydrogen today is natural gas, a non-renewable
resource. And the steam-based process for extracting hydrogen from the
gas generates carbon dioxideone of the primary global warming gases. To
circumvent these problems, scientists are exploring alternative
strategies. Among them are photosynthetic microbes that churn out
hydrogen (SN: 10/12/02, p. 235:
<http://www.sciencenews.org/articles/20021012/bob11.asp>) and
electromechanical systems that use the electricity from wind turbines to
make hydrogen from water (SN: 7/21/01, p. 45:
<http://www.sciencenews.org/articles/20010721/bob14.asp>).
However, many scientists contend that catalytic materials that use
sunlight to split water on the spot, a process known as direct
solar-hydrogen production, could be the most promising strategy.
In solar-hydrogen systems, when photons strike the catalytic material,
they excite electrons, which then roam about freely until they meet a
water molecule at the material's surface. The extra electrons strip the
two hydrogen atoms away from water's one oxygen atom, producing hydrogen
fuel. The oxygen atom simultaneously hooks up with another oxygen atom,
forming an oxygen molecule.
Not only is sunlight readily available, "you don't need a lot of water to
make hydrogen fuel," says John Turner of the Department of Energy's
National Renewable Energy Laboratory in Golden, Colo.
If all the 230 million cars and other light-duty vehicles in the United
States were running on hydrogen, 100 billion gallons of water per year
would be sufficient to supply the fuel, Turner says. The nation's
households collectively consume almost that much water in just a week of
drinking, cooking, and washing.
What's sorely missing, however, is a water-splitting material that's
simultaneously efficient, inexpensive, and stable. Whoever invents a
substance that meets all three criteria will add momentum toward a
hydrogen economy, revving up progress to highway speeds.
Mix it up
The most widely studied material for solar hydrogen is titanium dioxide,
the same stuff used to make white paint. Titanium dioxide is great at
splitting water, but it absorbs only ultraviolet (UV)
light, which constitutes a scant few percent of the solar energy reaching
Earth's surface. Researchers have tried with some success to increase
titanium dioxide's efficiency by spicing it with different elements.
Other chemists are instead layering different light-absorbing materials to
combine the best of each into one device that taps the broad band of
energy the sun offers.
Several years ago, Turner and his colleagues created such a layered device
by placing gallium indium phosphide, which absorbs ultraviolet and visible
light, on top of gallium arsenide, which absorbs infrared lights (SN:
4/18/98, p. 246). The resulting device could convert 12.5 percent of
sunlight's energy into the production of hydrogen.
This was a feat of efficiency, but "the materials are expensive and they
only last about 20 hours" before corroding, says Turner.
To speed up the discovery of suitable materials, chemical engineers at the
University of California, Santa Barbara have adapted a robotics-intensive
strategy known as combinatorial chemistry, the same approach that
pharmaceutical chemists take to synthesize and test new drugs. Led by
Eric McFarland, the group designed a system that can rapidly synthesize
120 different materials and test each one's water-splitting capacity, all
in a single day.
The system works in the following way. First, the researchers coat a
4-inch-square glass plate with titanium foil to serve as an electrode.
They next add a thick layer of Teflon perforated with 120 holes. The
researchers then fill the holes with different preformulated solutions
containing a dissolved semiconductor material mixed with various metals.
For instance, the base semiconductor might have zinc oxide or tungsten
oxide, and each sample would be doped with differing proportions of,
nickel, copper, or chromium.
In a process called electrodeposition, a robotic instrument dips an
electrode into each solution one by one, causing the dissolved materials
to form a thin solid film on the titanium-coated glass.
Peeling away the Teflon leaves behind 120 thin dots of material, each with
a different composition.
To test the water-splitting potential of the newly created films, a second
robotic instrument lowers a tiny chamber onto each dot and fills the
chamber with a conductive aqueous solution, or electrolyte.
The robot then shines light on the chamber and measures the current the
film generates. By repeating this quick test on each film, the robot
screens the entire array in a matter of hours.
The greater the current produced by a film when illuminated, the more
electrons it gives up, and therefore the greater its potential to split
water and generate hydrogen.
This technique amounts to an efficient form of trial-and-error. "We can
afford to try all sorts of wacky things," says Thomas Jaramillo, one of
the investigators working on the project. "That's the real power of this
technology."
It also enables the researchers to take inexpensive semiconductors such as
zinc oxide and tweak them to improve their properties.
Already, the Santa Barbara team has seen some promising results.
The researchers found that when they added cobalt to zinc oxide to create
a mixture that was 4.5 percent cobalt by weight, they boosted the zinc
oxide's current-generating capacity fourfold. The extra cobalt enables
the material to absorb a larger part of the solar spectrum and thereby
free up more electrons, explains Jaramillo.
In tandem
Changing a material's chemistry is just one way of devising new candidates
for use in solar-hydrogen production. With the advent of nanotechnology,
scientists have come to recognize that tweaking a material's fine
structure can have dramatic effects. Take the so-called tandem cell
invented by Michael Grtzel of the Swiss Federal Institute of Technology in
Lausanne, a leader in the field of photovoltaics.
The tandem cell consists of two separate but electrically connected
light-absorbing materials, one of which splits water. The water-splitting
material faces the sun and consists of a thin film of either tungsten
trioxide or iron oxide in front of a sheet of conducting glass. The back
material is a photovoltaic device known as a Grtzel cell (SN:
12/20&27/03, p. 398: Available to subscribers at
<http://www.sciencenews.org/articles/20031220/note18.asp>).
a5486_3625.jpg
BUBBLING WITH HYDROGEN. In this tandem cell, a nanostructured metal-oxide
film absorbs the sun's ultraviolet and blue light to split water.
Hydrogen Solar Ltd.
The nanoscale structure of the metal-oxide film is critical to its water
splitting capacity. The film is made of 50 to 100 loosely packed layers
of metal-oxide spheres, each about 20 nanometers in diameter. This
geometry provides a vast amount of surface1,000 times as great as its
two-dimensional area. The small spheres also make the material more
chemically reactive than it would be in bulk form.
When exposed to sunlight, the nanostructured film absorbs UV and blue
light. The rest of the spectrum passes through the material to be
absorbed by the Grtzel cell. That solar cell provides extra electrons
that make the water splitting more efficient.
In September, Hydrogen Solara British company that's working with Grtzel
to develop the technologyannounced that its tandem cell with the
nanostructured film had achieved 8 percent efficiency. This marked a
doubling of the performance of earlier devices without the nanostructured
film. The firm says it is close to reaching the U.
S. Department of Energy's efficiency goal of 10 percent, says David Auty,
chief executive of Hydrogen Solar, which is headquartered in Guilford,
England. That's the benchmark for commercial viability, says Auty.
Auty envisions installing arrays of tandem cells on the rooftops of home
garages. The cells would provide drivers with hydrogen for their fuel
cell vehicles. These vehicles would consume hydrogen and produce water,
essentially reversing the process that generated the hydrogen in the first
place.
A rooftop unit working with 10 percent efficiency in a sunny Southern
California location could generate enough hydrogen to drive 11,000 miles
per year in the small Mercedes-Benz fuel cell car that went on the market
in Germany in June, says Auty. To generate larger amounts of fuel, tandem
cells could cover the roofs of factories and even central fueling
stations, from which trucks would transport hydrogen across the country.
This scenario would still require practical solutions for the
transportation of this highly explosive gas.
With funding from the Department of Energy, Hydrogen Solar is
collaborating with the University of Nevada at Las Vegas to develop its
technology. The company plans to have a pilot fueling station up and
running near the campus in 3 years.
Auty concedes that hydrogen from tandem cells, at least in the near term,
will cost at least twice of much as hydrogen produced from natural gas.
But the price of natural gas fluctuates widely, he says. What's more,
unlike the method used to extract hydrogen from natural gas, the
tandem-cell technique doesn't generate carbon dioxide.
Like many people in the industry, Auty anticipates that regulations
eventually will dictate that oil and gas companies capture and sequester
the carbon dioxide they generate. "I don't think anyone knows just how
much extra it's going to cost, but it's certainly going to add to the
price of the fuel," he says.
And that, Auty adds, should help make solar hydrogen more economical.
Molecular machines
While Hydrogen Solar continues to refine its materials, other groups are
pursuing a different approach. These investigators are engineering
complex molecular machines that can split water using solar energy.
Consider the work of Karen Brewer of Virginia Polytechnic Institute and
State University in Blacksburg. She says the reason it's been so
difficult to make efficient solar hydrogen materials is that each water
molecule needs two additional electrons to strip off its hydrogen atoms.
Her lab is developing molecular structures that can deliver multiple
electrons simultaneously to a central reaction center, which then
catalyzes the splitting of water.
Many of the other solar-hydrogen materials are inefficient in gathering up
the two electrons needed to split water. Because the reaction is thus
energy intensive, materials such as titanium dioxide work only under
high-energy UV light. By designing materials at the molecular scale,
Brewer says she can build greater efficiency into the system. For
instance, she has designed molecular complexes that absorb visible light
and thereby tap into energy carried in a larger part of the solar spectrum.
The Virginia Tech team tested different combinations of components over
many years before it created successful supramolecular complexes.
"We figured it out through an awful lot of work and a lot of wrong choices
along the way," says Brewer. Her group presented its results in August at
the national meeting of the American Chemical Society in Philadelphia.
Brewer's molecular complexes mimic natural photosynthesis. The machine, a
combination of organic and metal-containing components, comprises three
main units. A chemical bridge connects each of the two light-absorbing
units to a catalytic central unit.
The light-absorbing units contain ruthenium atoms. As in a chlorophyll
molecule, a photon hitting a ruthenium atom excites one of its electrons.
The electron is then shuttled to the central unit, which contains a
rhodium atom. The rhodium collects electrons, two at a time, to perform
the reaction.
To ensure that the excited, mobilized electrons would gather in the
central unit, the researchers designed the complex's chemical bridges to
attract the electrons from the light-absorbing segments and shuttle them
in the right direction. Once the team got the bridges in order, the next
challenge was finding a metal for the central catalytic unit that would be
strong enough to pull the electrons.
"The problem initially was that the electrons would just sit there on the
bridges," says Brewer.
Eventually, the team found the answer in rhodium. "This has been a major
breakthrough for us," Brewer says. Not only is rhodium a strong electron
acceptor, but it's also reactive enough to split water and it's stable.
In short, it could be just right for making solar-hydrogen systems.
The researchers have done preliminary experiments in which they mixed the
molecular complexes with water in a glass vial and exposed the vial to
visible light. Soon thereafter, hydrogen began to bubble from the
system. These initial studies indicate that the efficiency of the system
is already "reasonable," Brewer says.
As the world begins to shift toward a hydrogen economy, other
hydrogen-generating technologies initially might win out over
solar-generated hydrogen. "Countries will use whatever source is cheapest
at the time," says Veziroglu. "It may be natural gas, coal, wind, or
hydropower, but eventually, it will be solar energy."
And if water and sunlight are all it takes, then Jules Verne's fantasy of
burning water like coal will have been realized.
If you have a comment on this article that you would like considered
for publication in Science News, send it to editors@....
Please include your name and location.
References:
Baeck, S.-H., T.F. Jaramillo . . . and E.W. McFarland. 2004. Parallel
synthesis and characterization of photoelectrochemically and
electrochromically active tungstenmolybdenum oxides. Chemical
Communication (4):390-91. Abstract available at
http://dx.doi.org/10.1039/b313924g.
Baeck, S.-H. . . . T.F. Jaramillo . . . and E.W. McFarland. 2003.
Enhancement of photocatalytic and electrochromic properties of
electrochemically fabricated mesoporous WO3 thin films. Advanced
Materials 15(Aug. 5):1269-1273. Abstract available at
http://dx.doi.org/10.1002/adma.200304669.
Baeck, S.-H., T.F. Jaramillo, C. Brndli, and E.W. McFarland. 2002.
Combinatorial electrochemical synthesis and characterization of
tungsten-based mixed-metal oxides. Journal of Combinatorial Chemistry
4(November):563-568. Available at http://pubs.acs.org/cgi-bin/sample.cgi/
jcchff/2002/4/i06/html/cc020014w.html.
Brewer, K.J., M. Elvington, and R. Miao. 2004. Photochemical
reactivity of mixed-metal supramolecular complexes: Applications
as photochemical molecular devices. 228th American Chemical Society
National Meeting. Aug. 21-26. Philadelphia.
Fujishima, A., and K. Honda. 1972. Electrochemical photolysis of
water at a semiconductor electrode. Nature 238(July 7):37-38.
Jaramillo, T.F. . . . and E.W. McFarland. 2004. Combinatorial
electrochemical synthesis and screening of mesoporous ZnO for
photocatalysis. Macromolecular Rapid Communications 25(January):297301.
Abstract available at http://dx.doi.org/10.1002/marc.200300187.
Khaselev, O., and J.A. Turner. 1998. A monolithic
photovoltaic-photoelectrochemical device for hydrogen production
via water splitting. Science 280(April 17):425-427. Available at
http://www.sciencemag.org/cgi/content/full/280/5362/425.
Miller, E.L., R.E. Rocheleau, and X.M. Deng. 2003. Design considerations
for a hybrid amorphous silicon/photoelectrochemical multijunction
cell for hydrogen production. International Journal of Hydrogen
Energy 28(June):615623. Abstract available at
http://dx.doi.org/10.1016/S0360-3199(02)00144-1.
Turner, J.A. 2004. Sustainable hydrogen production. Science 305(Aug.
13):972-974. Abstract available at
http://www.sciencemag.org/cgi/content/abstract/305/5686/972.
Verne, J. 1875. The Mysterious Island. New York: Scribner, Armstrong.
Further Readings:
Bak, T., et al. 2002. Photo-electrochemical hydrogen generation
from water using solar energy. Materials-related aspects. International
Journal of Hydrogen Energy 27(October):991-1022. Abstract available
at http://dx.doi.org/10.1016/S0360-3199(02)00022-8.
Goho, A. 2003. New materials take the heat. Science News 164(Dec.
20&27):398. Available to subscribers at
http://www.sciencenews.org/articles/20031220/note18.asp.
Gorman, J. 2003. An inexpensive catalyst generates hydrogen. Science
News 164(July 19):45. Available to subscribers at
http://www.sciencenews.org/articles/20030719/note12.asp.
______. 2002. Hydrogen: The next generation. Science News 162(Oct.
12):235-236. Available at
http://www.sciencenews.org/articles/20021012/bob11.asp.
Jaramillo . . . and E.W. McFarland. 2003. Catalytic activity of
supported Au nanoparticles deposited from block copolymer .icelles
Journal of the American Chemical Society 125(June 18):7148-7149.
Jiang, D.-L., et al. 2004. Photosensitized hydrogen evolution from
water using conjugated polymers wrapped in dendrimeric electrolytes.
Journal of the American Chemical Society 126(Sept. 29):12084-12089.
Lewis. N.S. 2001. Light work with water. Nature 414(Dec. 6):589-590.
Raloff, J. 2001. Power harvests. Science News 160(July 21):45-47.
Available at http://www.sciencenews.org/articles/20010721/bob14.asp.
Wu, C. 1998. Solar cell converts water into hydrogen. Science News
153(April 18):246.
Zou, Z., et al. 2001. Direct splitting of water under visible light
irradiation with an oxide semiconductor photocatalyst. Nature
414(Dec. 6):625-627. Abstract available at
http://dx.doi.org/10.1038/414625a.
Sources:
David Auty
Hydrogen Solar Ltd.
The Surrey Technology Center
40 Occam Road
Surrey Research Park
Guildford GU2 7YG
United Kingdom
Karen J. Brewer
1105 Hahn Hall
Chemistry Department
Virginia Tech
Blacksburg, VA 24061-0212
Michael Grdtzel
Laboratory for Photonics and Interfaces
Swiss Federal Institute of Technology
CH-1015 Lausanne
Switzerland
Thomas F. Jaramillo
Chemical Engineering Department
University of California, Santa Barbara
Santa Barbara, CA 93106-5080
Eric McFarland
Department of Chemical Engineering
Engineering II, Room 3331
University of California, Santa Barbara
Santa Barbara, CA 93106
Eric L. Miller
Hawaii Natural Energy Institute
University of Hawaii, Manoa
1680 East-West Road, Post 109
Honolulu, HI 96822
John A. Turner
National Renewable Energy Lab
Mailstop 1613
1617 Cole Boulevard
Golden, CO 80401-3393
T. Nejat Veziroglu
Mechanical Engineering
McArthur Engineering Building
Room 219
University of Miami
P.O. Box 248294
Coral Gables, FL 33124-0620
http://www.sciencenews.org/articles/20041030/bob10.asp
From Science News, Vol. 166, No. 18, Oct. 30, 2004, p. 282.
Copyright (c) 2004 Science Service. All rights reserved.
--
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/
http://www.sciencenews.org/articles/20041030/bob10.asp
Science News Online - Week of Oct. 30, 2004; Vol. 166, No. 18 - Alexandra Goho
In his 1874 science fiction tale The Mysterious Island, Jules Verne
predicted, "Water will be the coal of the future." It is a vision of
infinite clean energy available for people to use. More than 30 years
ago, Japanese scientists took a seminal step in that direction.
With a piece of titanium dioxide and some sunlight, they split water into
hydrogen and oxygen. Although researchers have tried to refine the
process over the years, nobody has come up with a system that is both
efficient and inexpensive enough to produce sufficient hydrogen for use as
a clean-burning fuel on the roads, in industry, and at home. Recently,
however, researchers have picked up the pace of their pursuit of the
ultimate water-splitting system.
With rising oil prices and the specter of climate change that's due to the
burning of fossil fuel, the vision of a hydrogen economy looms ever larger
in people's minds. After all, it's a fuel for which the only by-product
is water. And hydrogen packs more energy per unit mass than any fossil
fuel does.
But the main source of hydrogen today is natural gas, a non-renewable
resource. And the steam-based process for extracting hydrogen from the
gas generates carbon dioxideone of the primary global warming gases. To
circumvent these problems, scientists are exploring alternative
strategies. Among them are photosynthetic microbes that churn out
hydrogen (SN: 10/12/02, p. 235:
<http://www.sciencenews.org/articles/20021012/bob11.asp>) and
electromechanical systems that use the electricity from wind turbines to
make hydrogen from water (SN: 7/21/01, p. 45:
<http://www.sciencenews.org/articles/20010721/bob14.asp>).
However, many scientists contend that catalytic materials that use
sunlight to split water on the spot, a process known as direct
solar-hydrogen production, could be the most promising strategy.
In solar-hydrogen systems, when photons strike the catalytic material,
they excite electrons, which then roam about freely until they meet a
water molecule at the material's surface. The extra electrons strip the
two hydrogen atoms away from water's one oxygen atom, producing hydrogen
fuel. The oxygen atom simultaneously hooks up with another oxygen atom,
forming an oxygen molecule.
Not only is sunlight readily available, "you don't need a lot of water to
make hydrogen fuel," says John Turner of the Department of Energy's
National Renewable Energy Laboratory in Golden, Colo.
If all the 230 million cars and other light-duty vehicles in the United
States were running on hydrogen, 100 billion gallons of water per year
would be sufficient to supply the fuel, Turner says. The nation's
households collectively consume almost that much water in just a week of
drinking, cooking, and washing.
What's sorely missing, however, is a water-splitting material that's
simultaneously efficient, inexpensive, and stable. Whoever invents a
substance that meets all three criteria will add momentum toward a
hydrogen economy, revving up progress to highway speeds.
Mix it up
The most widely studied material for solar hydrogen is titanium dioxide,
the same stuff used to make white paint. Titanium dioxide is great at
splitting water, but it absorbs only ultraviolet (UV)
light, which constitutes a scant few percent of the solar energy reaching
Earth's surface. Researchers have tried with some success to increase
titanium dioxide's efficiency by spicing it with different elements.
Other chemists are instead layering different light-absorbing materials to
combine the best of each into one device that taps the broad band of
energy the sun offers.
Several years ago, Turner and his colleagues created such a layered device
by placing gallium indium phosphide, which absorbs ultraviolet and visible
light, on top of gallium arsenide, which absorbs infrared lights (SN:
4/18/98, p. 246). The resulting device could convert 12.5 percent of
sunlight's energy into the production of hydrogen.
This was a feat of efficiency, but "the materials are expensive and they
only last about 20 hours" before corroding, says Turner.
To speed up the discovery of suitable materials, chemical engineers at the
University of California, Santa Barbara have adapted a robotics-intensive
strategy known as combinatorial chemistry, the same approach that
pharmaceutical chemists take to synthesize and test new drugs. Led by
Eric McFarland, the group designed a system that can rapidly synthesize
120 different materials and test each one's water-splitting capacity, all
in a single day.
The system works in the following way. First, the researchers coat a
4-inch-square glass plate with titanium foil to serve as an electrode.
They next add a thick layer of Teflon perforated with 120 holes. The
researchers then fill the holes with different preformulated solutions
containing a dissolved semiconductor material mixed with various metals.
For instance, the base semiconductor might have zinc oxide or tungsten
oxide, and each sample would be doped with differing proportions of,
nickel, copper, or chromium.
In a process called electrodeposition, a robotic instrument dips an
electrode into each solution one by one, causing the dissolved materials
to form a thin solid film on the titanium-coated glass.
Peeling away the Teflon leaves behind 120 thin dots of material, each with
a different composition.
To test the water-splitting potential of the newly created films, a second
robotic instrument lowers a tiny chamber onto each dot and fills the
chamber with a conductive aqueous solution, or electrolyte.
The robot then shines light on the chamber and measures the current the
film generates. By repeating this quick test on each film, the robot
screens the entire array in a matter of hours.
The greater the current produced by a film when illuminated, the more
electrons it gives up, and therefore the greater its potential to split
water and generate hydrogen.
This technique amounts to an efficient form of trial-and-error. "We can
afford to try all sorts of wacky things," says Thomas Jaramillo, one of
the investigators working on the project. "That's the real power of this
technology."
It also enables the researchers to take inexpensive semiconductors such as
zinc oxide and tweak them to improve their properties.
Already, the Santa Barbara team has seen some promising results.
The researchers found that when they added cobalt to zinc oxide to create
a mixture that was 4.5 percent cobalt by weight, they boosted the zinc
oxide's current-generating capacity fourfold. The extra cobalt enables
the material to absorb a larger part of the solar spectrum and thereby
free up more electrons, explains Jaramillo.
In tandem
Changing a material's chemistry is just one way of devising new candidates
for use in solar-hydrogen production. With the advent of nanotechnology,
scientists have come to recognize that tweaking a material's fine
structure can have dramatic effects. Take the so-called tandem cell
invented by Michael Grtzel of the Swiss Federal Institute of Technology in
Lausanne, a leader in the field of photovoltaics.
The tandem cell consists of two separate but electrically connected
light-absorbing materials, one of which splits water. The water-splitting
material faces the sun and consists of a thin film of either tungsten
trioxide or iron oxide in front of a sheet of conducting glass. The back
material is a photovoltaic device known as a Grtzel cell (SN:
12/20&27/03, p. 398: Available to subscribers at
<http://www.sciencenews.org/articles/20031220/note18.asp>).
a5486_3625.jpg
BUBBLING WITH HYDROGEN. In this tandem cell, a nanostructured metal-oxide
film absorbs the sun's ultraviolet and blue light to split water.
Hydrogen Solar Ltd.
The nanoscale structure of the metal-oxide film is critical to its water
splitting capacity. The film is made of 50 to 100 loosely packed layers
of metal-oxide spheres, each about 20 nanometers in diameter. This
geometry provides a vast amount of surface1,000 times as great as its
two-dimensional area. The small spheres also make the material more
chemically reactive than it would be in bulk form.
When exposed to sunlight, the nanostructured film absorbs UV and blue
light. The rest of the spectrum passes through the material to be
absorbed by the Grtzel cell. That solar cell provides extra electrons
that make the water splitting more efficient.
In September, Hydrogen Solara British company that's working with Grtzel
to develop the technologyannounced that its tandem cell with the
nanostructured film had achieved 8 percent efficiency. This marked a
doubling of the performance of earlier devices without the nanostructured
film. The firm says it is close to reaching the U.
S. Department of Energy's efficiency goal of 10 percent, says David Auty,
chief executive of Hydrogen Solar, which is headquartered in Guilford,
England. That's the benchmark for commercial viability, says Auty.
Auty envisions installing arrays of tandem cells on the rooftops of home
garages. The cells would provide drivers with hydrogen for their fuel
cell vehicles. These vehicles would consume hydrogen and produce water,
essentially reversing the process that generated the hydrogen in the first
place.
A rooftop unit working with 10 percent efficiency in a sunny Southern
California location could generate enough hydrogen to drive 11,000 miles
per year in the small Mercedes-Benz fuel cell car that went on the market
in Germany in June, says Auty. To generate larger amounts of fuel, tandem
cells could cover the roofs of factories and even central fueling
stations, from which trucks would transport hydrogen across the country.
This scenario would still require practical solutions for the
transportation of this highly explosive gas.
With funding from the Department of Energy, Hydrogen Solar is
collaborating with the University of Nevada at Las Vegas to develop its
technology. The company plans to have a pilot fueling station up and
running near the campus in 3 years.
Auty concedes that hydrogen from tandem cells, at least in the near term,
will cost at least twice of much as hydrogen produced from natural gas.
But the price of natural gas fluctuates widely, he says. What's more,
unlike the method used to extract hydrogen from natural gas, the
tandem-cell technique doesn't generate carbon dioxide.
Like many people in the industry, Auty anticipates that regulations
eventually will dictate that oil and gas companies capture and sequester
the carbon dioxide they generate. "I don't think anyone knows just how
much extra it's going to cost, but it's certainly going to add to the
price of the fuel," he says.
And that, Auty adds, should help make solar hydrogen more economical.
Molecular machines
While Hydrogen Solar continues to refine its materials, other groups are
pursuing a different approach. These investigators are engineering
complex molecular machines that can split water using solar energy.
Consider the work of Karen Brewer of Virginia Polytechnic Institute and
State University in Blacksburg. She says the reason it's been so
difficult to make efficient solar hydrogen materials is that each water
molecule needs two additional electrons to strip off its hydrogen atoms.
Her lab is developing molecular structures that can deliver multiple
electrons simultaneously to a central reaction center, which then
catalyzes the splitting of water.
Many of the other solar-hydrogen materials are inefficient in gathering up
the two electrons needed to split water. Because the reaction is thus
energy intensive, materials such as titanium dioxide work only under
high-energy UV light. By designing materials at the molecular scale,
Brewer says she can build greater efficiency into the system. For
instance, she has designed molecular complexes that absorb visible light
and thereby tap into energy carried in a larger part of the solar spectrum.
The Virginia Tech team tested different combinations of components over
many years before it created successful supramolecular complexes.
"We figured it out through an awful lot of work and a lot of wrong choices
along the way," says Brewer. Her group presented its results in August at
the national meeting of the American Chemical Society in Philadelphia.
Brewer's molecular complexes mimic natural photosynthesis. The machine, a
combination of organic and metal-containing components, comprises three
main units. A chemical bridge connects each of the two light-absorbing
units to a catalytic central unit.
The light-absorbing units contain ruthenium atoms. As in a chlorophyll
molecule, a photon hitting a ruthenium atom excites one of its electrons.
The electron is then shuttled to the central unit, which contains a
rhodium atom. The rhodium collects electrons, two at a time, to perform
the reaction.
To ensure that the excited, mobilized electrons would gather in the
central unit, the researchers designed the complex's chemical bridges to
attract the electrons from the light-absorbing segments and shuttle them
in the right direction. Once the team got the bridges in order, the next
challenge was finding a metal for the central catalytic unit that would be
strong enough to pull the electrons.
"The problem initially was that the electrons would just sit there on the
bridges," says Brewer.
Eventually, the team found the answer in rhodium. "This has been a major
breakthrough for us," Brewer says. Not only is rhodium a strong electron
acceptor, but it's also reactive enough to split water and it's stable.
In short, it could be just right for making solar-hydrogen systems.
The researchers have done preliminary experiments in which they mixed the
molecular complexes with water in a glass vial and exposed the vial to
visible light. Soon thereafter, hydrogen began to bubble from the
system. These initial studies indicate that the efficiency of the system
is already "reasonable," Brewer says.
As the world begins to shift toward a hydrogen economy, other
hydrogen-generating technologies initially might win out over
solar-generated hydrogen. "Countries will use whatever source is cheapest
at the time," says Veziroglu. "It may be natural gas, coal, wind, or
hydropower, but eventually, it will be solar energy."
And if water and sunlight are all it takes, then Jules Verne's fantasy of
burning water like coal will have been realized.
If you have a comment on this article that you would like considered
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Further Readings:
Bak, T., et al. 2002. Photo-electrochemical hydrogen generation
from water using solar energy. Materials-related aspects. International
Journal of Hydrogen Energy 27(October):991-1022. Abstract available
at http://dx.doi.org/10.1016/S0360-3199(02)00022-8.
Goho, A. 2003. New materials take the heat. Science News 164(Dec.
20&27):398. Available to subscribers at
http://www.sciencenews.org/articles/20031220/note18.asp.
Gorman, J. 2003. An inexpensive catalyst generates hydrogen. Science
News 164(July 19):45. Available to subscribers at
http://www.sciencenews.org/articles/20030719/note12.asp.
______. 2002. Hydrogen: The next generation. Science News 162(Oct.
12):235-236. Available at
http://www.sciencenews.org/articles/20021012/bob11.asp.
Jaramillo . . . and E.W. McFarland. 2003. Catalytic activity of
supported Au nanoparticles deposited from block copolymer .icelles
Journal of the American Chemical Society 125(June 18):7148-7149.
Jiang, D.-L., et al. 2004. Photosensitized hydrogen evolution from
water using conjugated polymers wrapped in dendrimeric electrolytes.
Journal of the American Chemical Society 126(Sept. 29):12084-12089.
Lewis. N.S. 2001. Light work with water. Nature 414(Dec. 6):589-590.
Raloff, J. 2001. Power harvests. Science News 160(July 21):45-47.
Available at http://www.sciencenews.org/articles/20010721/bob14.asp.
Wu, C. 1998. Solar cell converts water into hydrogen. Science News
153(April 18):246.
Zou, Z., et al. 2001. Direct splitting of water under visible light
irradiation with an oxide semiconductor photocatalyst. Nature
414(Dec. 6):625-627. Abstract available at
http://dx.doi.org/10.1038/414625a.
Sources:
David Auty
Hydrogen Solar Ltd.
The Surrey Technology Center
40 Occam Road
Surrey Research Park
Guildford GU2 7YG
United Kingdom
Karen J. Brewer
1105 Hahn Hall
Chemistry Department
Virginia Tech
Blacksburg, VA 24061-0212
Michael Grdtzel
Laboratory for Photonics and Interfaces
Swiss Federal Institute of Technology
CH-1015 Lausanne
Switzerland
Thomas F. Jaramillo
Chemical Engineering Department
University of California, Santa Barbara
Santa Barbara, CA 93106-5080
Eric McFarland
Department of Chemical Engineering
Engineering II, Room 3331
University of California, Santa Barbara
Santa Barbara, CA 93106
Eric L. Miller
Hawaii Natural Energy Institute
University of Hawaii, Manoa
1680 East-West Road, Post 109
Honolulu, HI 96822
John A. Turner
National Renewable Energy Lab
Mailstop 1613
1617 Cole Boulevard
Golden, CO 80401-3393
T. Nejat Veziroglu
Mechanical Engineering
McArthur Engineering Building
Room 219
University of Miami
P.O. Box 248294
Coral Gables, FL 33124-0620
http://www.sciencenews.org/articles/20041030/bob10.asp
From Science News, Vol. 166, No. 18, Oct. 30, 2004, p. 282.
Copyright (c) 2004 Science Service. All rights reserved.
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