Splitting Water for Renewable Energy Simpler Than First Thought?

Their findings, developed with the assistance of researchers at UC Davis in the USA and using the facilities at the Australian Synchrotron, was published in the journalNature Chemistryon May 15, 2011.

Professor Leone Spiccia from the School of Chemistry at Monash University said the ultimate goal of researchers in this area is to create a cheap, efficient way to split water, powered by sunlight, which would open up production of hydrogen as a clean fuel, and leading to long-term solutions for our renewable energy crisis.

To achieve this, they have been studying complex catalysts designed to mimic the catalysts plants use to split water with sunlight. But the new study shows that there might be much simpler alternatives to hand.

"The hardest part about turning water into fuel is splitting water into hydrogen and oxygen, but the team at Monash seems to have uncovered the process, developing a water-splitting cell based on a manganese-based catalyst," Professor Spiccia said.

"Birnessite, it turns out, is what does the work. Like other elements in the middle of the Periodic Table, manganese can exist in a number of what chemists call oxidation states. These correspond to the number of oxygen atoms with which a metal atom could be combined," Professor Spiccia said.

"When an electrical voltage is applied to the cell, it splits water into hydrogen and oxygen and when the researchers carefully examined the catalyst as it was working, using advanced spectroscopic methods they found that it had decomposed into a much simpler material called birnessite, well-known to geologists as a black stain on many rocks."

The manganese in the catalyst cycles between two oxidation states. First, the voltage is applied to oxidize from the manganese-II state to manganese-IV state in birnessite. Then in sunlight, birnessite goes back to the manganese-II State.

This cycling process is responsible for the oxidation of water to produce oxygen gas, protons and electrons.

Co-author on the research paper was Dr Rosalie Hocking, Research Fellow in the Australian Centre for Electromaterials Science who explained that what was interesting was the operation of the catalyst, which follows closely natures biogeochemical cycling of manganese in the oceans.

"This may provide important insights into the evolution of Nature's water splitting catalyst found in all plants which uses manganese centres," Dr Hocking said.

"Scientists have put huge efforts into making very complicated manganese molecules to copy plants, but it turns out that they convert to a very common material found in the Earth, a material sufficiently robust to survive tough use."

The reaction has two steps. First, two molecules of water are oxidized to form one molecule of oxygen gas (O₂), four positively-charged hydrogen nuclei (protons) and four electrons. Second, the protons and electrons combine to form two molecules of hydrogen gas (H₂).

The experimental work was conducted using state-of-the art equipment at three major facilities including the Australian Synchrotron, the Australian National Beam-line Facility in Japan and the Monash Centre for Electron Microscopy, and involved collaboration with Professor Bill Casey, a geochemist at UC Davis.

"The research highlights the insight obtainable from the synchrotron based spectroscopic techniques -- without them the important discovery linking common earth materials to water oxidation catalysts would not have been made," Dr Hocking said.

It is hoped the research will ultimately lead to the development of cheaper devices, which produce hydrogen.

The work was primarily funded by the U.S. National Science Foundation and the U.S. Department of Energy Monash University, the Australian Research Council through the Australian Centre of Excellence for Electromaterials Science, and the Australian Synchrotron.

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New Green Technology for Hydrogen Production

Hydrogen is a valuable feedstock for the petrochemical industry and it may play a big role in the energy supply of the future, as a green, non-polluting, and efficient energy carrier. If it is burnt, only water is formed. However, the conventional technology for hydrogen production from natural gas ('steam reforming') is a highly energy intensive process, operated at high pressures (up to 25 bar) and high temperature (850^oC), with multistage subsequent separation and purification units. Moreover, huge amounts of CO₂have to be handled in post-processing steps.

TU Eindhoven has now developed a new and improved technology called"sorption enhanced catalytic reforming of methane," using novel catalyst/sorbent materials. Halabi, working in collaboration with the Energy Research Centre of the Netherlands (ECN), has demonstrated the feasibility of producing hydrogen through such a process at much lower temperatures (400 to 500 degrees Celsius).

The process is performed in a packed bed reactor using a Rhodium-based catalyst and a Hydrotalcite-based sorbent as a new system of materials. Hydrogen is produced on the active catalyst and the cogenerated CO₂is effectively adsorbed on the sorbent, hence preventing any CO₂emissions to the atmosphere.

Halabi:"Direct production of high purity hydrogen and fuel conversion greater than 99.5% is experimentally achieved at low temperature range of (400 -- 500^oC) and at a pressure of 4.5 bar with a low level of carbon oxides impurities: less than 100 ppm." The enormous reduction of the reactor size, material loading, catalyst/sorbent ratio, and energy requirements are beneficial key factors for the success of the concept over the conventional technologies. Small size hydrogen generation plants for residential or industrial application operated at a relatively low pressure, of less than 4.5 bar, seem to be feasible.

Dr. Mohamed Halabi received his PhD on May 9, 2011, at TU Eindhoven based on his dissertation"Sorption Enhanced Catalytic Reforming of Methane for Pure Hydrogen Production -- Experimental and Modeling." He conducted his research at the laboratory of Chemical Reactor Engineering, under the supervision of Prof. Jaap Schouten.

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Improving Photosynthesis? Solar Cells Beat Plants at Harvesting Sun's Energy, for Now

Plants are less efficient at capturing the energy in sunlight than solar cells mostly because they have too much evolutionary baggage. Plants have to power a living thing, whereas solar cells only have to send electricity down a wire. This is a big difference because if photosynthesis makes a mistake, it makes toxic byproducts that kill the organism. Photosynthesis has to be conservative to avoid killing the organisms it powers.

"This is critical since it's the process that powers all of life in our ecosystem," said Kramer, a Hannah Distinguished Professor of Photosynthesis and Bioenergetics."The efficiency of photosynthesis, and our ability to improve it, is critical to whether the entire biofuels industry is viable."

The annually averaged efficiency of photovoltaic electrolysis based on silicon semiconductors to produce fuel in the form of hydrogen is about 10 percent, while a plant's annually averaged efficiency using photosynthesis to form biomass for fuel is about 1 or 2 percent.

Plants, following the path of evolution, are primarily interested in reproducing and repairing themselves. The efficiency at which they produce stored solar energy in biomass is secondary.

Still, things can change.

Just as early Native Americans manipulated skinny, non-nutritious Teosinte into fat, juicy kernel corn, today's plants can be manipulated to become much better sources of energy.

Researcher Arthur J.Nozik, a NREL senior research fellow, and Senior Scientist Mark Hanna working at DOE's National Renewable Energy Laboratory (NREL), recently demonstrated how a multi-junction, tandem solar cell for water splitting to produce hydrogen can provide higher efficiency -- more than 40 percent -- by using multiple semiconductors and/or special photoactive organic molecules with different band gaps arranged in a tandem structure.

The coupling of different materials with different gaps means photons can be absorbed and converted to energy over a wider range of the solar spectrum.

"In photovoltaics, we know that to increase power conversion efficiency you have to have different band gaps (i.e., colors) in a tandem arrangement so they can more efficiently use different regions of the solar spectrum," Nozik said."If you had the same gap, they would compete with each other and both would absorb the same photon energies and not enhance the solar conversion efficiency."

Photosynthesis does use two gaps based on chlorophyll molecules to provide enough energy to drive the photosynthesis reaction. But the two gaps have the same energy value, which means they don't help each other to produce energy over a wider stretch of the spectrum of solar light and enhance conversion efficiency.

Furthermore, most plants do use the full intensity of sunlight but divert some of it to protect the plant from damage. Whereas photovoltaics use the second material to gain that photoconversion edge, plants do not, Nozik noted.

One of NREL's roles at the DOE workshop was to help make it clear how the efficiency of photosynthesis could be improved by re-engineering the structure of plants through modern synthetic biology and genetic manipulation based on the principles of high efficiency photovoltaic cells, Nozik said. In synthetic biology plants can be built from scratch, starting with amino acid building blocks, allowing the formation of optimum biological band gaps.

The newly engineered plants would be darker, incorporating some biological pigments in certain of nature's flora that would be able to absorb photons in the red and infrared regions of the solar spectrum.

As plants store more solar energy efficiently, they potentially could play a greater role as alternative renewable fuel sources. The food that plants provide also would get a boost. And that would mean less land would be required to grow an equivalent amount of food.

The new information in theSciencemanuscript will help direct the development of new plants that have a better propensity for reducing carbon dioxide to biomass. This could spur exploration of blue algae, which not only comprise about one quarter of all plant life, but are ideal candidates for being genetically engineered into feedstock, because they absorb light from an entirely different part of the spectrum compared to most other plants.

"It would be the biological equivalent of a tandem photovoltaic cell," said Robert Blankenship, one of the lead authors in theSciencepaper who studies photosynthesis at Washington University in St. Louis."And those can have very high efficiencies."

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Forklift Trucks That Run on a Green Charge

Risavika harbour just outside Stavanger is among the candidates for trials of ten of the 30 forklift trucks, says SINTEF's Steffen Møller-Holst.

SINTEF is a participant in the project's development phase, which will bring the green European truck to its final goal. Under its bodywork, the truck houses a miniature power station in the shape of a fuel cell that runs on hydrogen, and which delivers power to its electric motor. All that the truck emits in operation is water vapour!

The best of both worlds

"A hydrogen-driven forklift truck running on fuel cells combines the advantages of diesel and battery-driven vehicles. The hydrogen-based technology means rapid refuelling, just like diesel, while it is also energy-efficient and every bit as environmentally friendly as a battery truck," says Møller-Holst.

The SINTEF scientist points out that a forklift truck fitted with fuel cells and operating two eight-hour shifts a day reduces CO₂emissions by the equivalent of eight private cars.

Developed under the European Union's auspices

The truck's power system has been developed in the course of a joint European effort run by the European Union.

SINTEF is to perform laboratory tests that will explore how much fuel cell performance falls by over time. At the same time, SINTEF will systematise and analyse feedback from the trials of the 30 demonstration trucks. The knowledge gained in this process will be used to improve the control system and optimise operation, which will ensure that the fuel cell will have a life-cycle that meets the commercial requirements of the market.

Danish projects

The Danish company H2 Logic AS has been responsible for developing the trucks' fuel-cell technology. The solution is a development of a fuel cell that the company had previous developed with Scandinavian backing; its partners included SINTEF and Statoil.

These large forklift trucks in the joint European project have been designed to carry heavy loads. They are manufactured by the Danish company Dantruck, which is showing them off this week at the enormous CeMAT trade fair in Hanover.

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A Renewable Twist on Fossil Fuels

Such a feat could help reduce the rising CO₂levels implicated in global warming and also offer a new method of renewable energy production.

Oak Ridge Associated Universities (ORAU), a consortium of 98 Ph.D.-granting universities, of which UD is a member, has selected Rosenthal to receive the Ralph E. Powe Junior Faculty Enhancement Award to pursue the novel research. Rosenthal is one of 30 award winners nationwide.

The competitive award, which provides$5,000 in seed funding from ORAU and$5,000 in matching funding from the faculty member's university, is intended to enrich the research and educational growth of young faculty and serve as a springboard to new funding opportunities.

Rosenthal and his team are designing electrocatalysts from metals such as nickel and palladium that will freely give away electrons when they react with carbon dioxide, thus chemically reducing this greenhouse gas into energy-rich carbon monoxide or methanol.

Besides its use in making plastics, solvents, carpet and other products, methanol fuels race cars in the United States and currently is being researched as a hydrogen carrier for fuel cell vehicles.

Carbon monoxide is an important precursor to liquid hydrocarbons in the energy arena, in addition to its applications as an industrial chemical for producing plastics to detergents to the acetic acid used in food preservation, drug manufacturing and other fields.

"The catalytic reduction of carbon dioxide to carbon monoxide is an important transformation that would allow for the mitigation of atmospheric CO₂levels, while producing an energy-rich substrate that forms a basis for fuels production," Rosenthal says.

"The chemistry we're doing is energetically uphill -- it's an energy-storing process rather than a downhill, energy-liberating process," he notes."And our goal is to make liquid fuel renewably from wind and solar sources, not from typical fossil fuel bases."

As early as junior high, Rosenthal said, he realized that basic life processes are linked to molecular energy conversion. Then his undergraduate and graduate research took off on renewables.

He earned his undergraduate degree in organic chemistry from New York University and his doctorate in inorganic chemistry at MIT while studying how metals catalyze various energy conversion processes. His doctoral adviser at MIT was Dan Nocera, a leading scientist in renewable energy research.

The strong reputation of the chemistry and biochemistry department lured Rosenthal, a New York City native, to UD. He joined the UD faculty this past fall and already has a research group of eight focusing on the project -- one postdoctoral researcher, four graduate students and three undergraduates.

"The CO₂problem is very important, and people have to tackle it," Rosenthal says."It's my hope to be able to map out the molecular design principles for efficient CO₂conversion into fuels. Then you can think about doing this on a commercially relevant scale."

Conservative estimates predict that by 2050, the rate of global energy consumption will roughly double the rate recorded at the end of the 20th century. Most scientists believe that rising carbon dioxide levels are leading to global climate change.

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Portable Tech Might Provide Drinking Water, Power to Villages

Such a technology might be used to provide power and drinking water to villages and also for military operations, said Jerry Woodall, a Purdue University distinguished professor of electrical and computer engineering.

The alloy contains aluminum, gallium, indium and tin. Immersing the alloy in freshwater or saltwater causes a spontaneous reaction, splitting the water into hydrogen and oxygen molecules. The hydrogen could then be fed to a fuel cell to generate electricity, producing water in the form of steam as a byproduct, he said.

"The steam would kill any bacteria contained in the water, and then it would condense to purified water," Woodall said."So, you are converting undrinkable water to drinking water."

Because the technology works with saltwater, it might have marine applications, such as powering boats and robotic underwater vehicles. The technology also might be used to desalinate water, said Woodall, who is working with doctoral student Go Choi.

A patent on the design is pending.

Woodall envisions a new portable technology for regions that aren't connected to a power grid, such as villages in Africa and other remote areas.

"There is a big need for this sort of technology in places lacking connectivity to a power grid and where potable water is in short supply," he said."Because aluminum is a low-cost, non-hazardous metal that is the third-most abundant metal on Earth, this technology promises to enable a global-scale potable water and power technology, especially for off-grid and remote locations."

The potable water could be produced for about$1 per gallon, and electricity could be generated for about 35 cents per kilowatt hour of energy.

"There is no other technology to compare it against, economically, but it's obvious that 34 cents per kilowatt hour is cheap compared to building a power plant and installing power lines, especially in remote areas," Woodall said.

The unit, including the alloy, the reactor and fuel cell might weigh less than 100 pounds.

"You could drop the alloy, a small reaction vessel and a fuel cell into a remote area via parachute," Woodall said."Then the reactor could be assembled along with the fuel cell. The polluted water or the seawater would be added to the reactor and the reaction converts the aluminum and water into aluminum hydroxide, heat and hydrogen gas on demand."

The aluminum hydroxide waste is non-toxic and could be disposed of in a landfill.

The researchers have a design but haven't built a prototype.

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Hydrogen Fuel Tech Gets Boost from Low-Cost, Efficient Catalyst

The discovery is an important development in the worldwide effort to mimic the way plants make fuel from sunlight, a key step in creating a green energy economy. It was reported inNature Materialsby theorist Jens Nørskov of the Department of Energy's SLAC National Accelerator Laboratory and Stanford University and a team of colleagues led by Ib Chorkendorff and Søren Dahl at the Technical University of Denmark (DTU).

Hydrogen is an energy dense and clean fuel, which upon combustion releases only water. Today, most hydrogen is produced from natural gas which results in large CO₂-emissions. An alternative, clean method is to make hydrogen fuel from sunlight and water. The process is called photo-electrochemical, or PEC, water splitting. When sun hits the PEC cell, the solar energy is absorbed and used for splitting water molecules into its components, hydrogen and oxygen.

Progress has so far been limited in part by a lack of cheap catalysts that can speed up the generation of hydrogen and oxygen. A vital part of the American-Danish effort was combining theory and advanced computation with synthesis and testing to accelerate the process of identifying new catalysts. This is a new development in a field that has historically relied on trial and error."If we can find new ways of rationally designing catalysts, we can speed up the development of new catalytic materials enormously," Nørskov said.

The team first tackled the hydrogen half of the problem. The DTU researchers created a device to harvest the energy from part of the solar spectrum and used it to power the conversion of single hydrogen ions into hydrogen gas. However, the process requires a catalyst to facilitate the reaction. Platinum is already known as an efficient catalyst, but platinum is too rare and too expensive for widespread use. So the collaborators turned to nature for inspiration.

They investigated hydrogen producing enzymes -- natural catalysts -- from certain organisms, using a theoretical approach Nørskov's group has been developing to describe catalyst behavior."We did the calculations," Nørskov explained,"and found out why these enzymes work as well as they do." These studies led them to related compounds, which eventually took them to molybdenum sulfide."Molybdenum is an inexpensive solution" for catalyzing hydrogen production, Chorkendorff said.

The team also optimized parts of the device, introducing a"chemical solar cell" designed to capture as much solar energy as possible. The experimental researchers at DTU designed light absorbers that consist of silicon arranged in closely packed pillars, and dotted the pillars with tiny clusters of the molybdenum sulfide. When they exposed the pillars to light, hydrogen gas bubbled up -- as quickly as if they'd used costly platinum.

The hydrogen gas-generating device is only half of a full photo-electrochemical cell. The other half of the PEC would generate oxygen gas from the water; though hydrogen gas is the goal, without the simultaneous generation of oxygen, the whole PEC cell shuts down. Many groups -- including Chorkendorff, Dahl and Nørskov and their colleagues -- are working on finding catalysts and sunlight absorbers to do this well."This is the most difficult half of the problem, and we are attacking this in the same way as we attacked the hydrogen side," Dahl said.

Nørskov looks forward to solving that problem as well."A sustainable energy choice that no one can afford is not sustainable at all," he said."I hope this approach will enable us to choose a truly sustainable fuel."

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