Algae Turned Into High-Temperature Hydrogen Source

This image shows the process by which Photosystem I in thermophilic blue-green algae can be catalyzed by platinum to produce a sustainable source of hydrogen.

(Credit: Barry D. Bruce/University of Tennessee, Knoxville)

--------------------------------------------------------------------------------------------------

In the quest to make hydrogen as a clean alternative fuel source, researchers have been stymied about how to create usable hydrogen that is clean and sustainable without relying on an intensive, high-energy process that outweighs the benefits of not using petroleum to power vehicles.

New findings from a team of researchers from the University of Tennessee, Knoxville, and Oak Ridge National Laboratory, however, show that photosynthesis – the process by which plants regenerate using energy from the sun – may function as that clean, sustainable source of hydrogen.

The team, led by Barry Bruce, a professor of biochemistry and cellular and molecular biology at UT Knoxville, found that the inner machinery of photosynthesis can be isolated from certain algae and, when coupled with a platinum catalyst, is able to produce a steady supply of hydrogen when exposed to light.

The findings are outlined in a recent issue of the journal Nature Nanotechnology.

Bruce, who serves as the associate director for UT Knoxville's Sustainable Energy and Education Research Center, notes that we already get most of our energy from photosynthesis, albeit indirectly.

The fossil fuels of today were once, millions of years ago, energy-rich plant matter whose growth also was supported by the sun via the process of photosynthesis. There have been efforts to shorten this process, namely through the creation of biomass fuels that harvest plants and covert their hydrocarbons into ethanol or biodiesel.

"Biofuel as many people think of it now -- harvesting plants and converting their woody material into sugars which get distilled into combustible liquids -- probably cannot replace gasoline as a major source of fuel," said Bruce. "We found that our process is more direct and has the potential to create a much larger quantity of fuel using much less energy, which has a wide range of benefits."

A major benefit of Bruce's method is that it cuts out two key middlemen in the process of using plants' solar conversion abilities. The first middle man is the time required for a plant to capture solar energy, grow and reproduce, then die and eventually become fossil fuel. The second middle man is energy, in this case the substantial amount of energy required to cultivate, harvest and process plant material into biofuel. Bypassing these two options and directly using the plant or algae's built-in solar system to create clean fuel can be a major step forward.

Other scientists have studied the possibility of using photosynthesis as a hydrogen source, but have not yet found a way to make the reaction occur efficiently at the high temperatures that would exist in a large system designed to harness sunlight.

Bruce and his colleagues found that by starting with a thermophilic blue-green algae, which favors warmer temperatures, they could sustain the reaction at temperatures as high as 55 degrees C, or 131 degrees F. That is roughly the temperature in arid deserts with high solar irradiation, where the process would be most productive. They also found the process was more than 10 times more efficient as the temperature increased.

"As both a dean and a chemist, I am very impressed with this recent work by Professor Bruce and his colleagues," said Bruce Bursten, dean of UT Knoxville's College of Arts and Sciences. "Hydrogen has the potential to be the cleanest fuel alternative to petroleum, with no greenhouse gas production, and we need new innovations that allow for hydrogen to be readily produced from non-hydrocarbon sources. Professor Bruce and his team have provided a superb example of how excellence in basic research can contribute significantly to technological and societal advances."

Co-authors on the paper along with Bruce include Infeyinwa Iwuchukwu, a UT Knoxville graduate student in chemical and biomolecular engineering; Michael Vaughn, a research technician; Natalie Myers, a UT Knoxville graduate student in microbiology; Hugh O'Neill, a UT Knoxville-ORNL research professor and Paul Frymier, a UT Knoxville professor of chemical and biomolecular engineering.

For Future Superconductors, A Little Bit Of Lithium May Do Hydrogen A Lot Of Good

Ball-and-stick image of hypothetical metallic crystal cells composed of one lithium, or Li, atom and six hydrogen, or H, atoms. The lithium-hydrogen compound is predicted to form under approximately 1 million atmospheres, which is one-fourth the amount of pressure required to metalize pure hydrogen. The pressure at sea level is one atmosphere and the pressure at the center of the Earth is around 3.5 million atmospheres. Li atoms are green and H atoms are white.
-----------------------------------------------------------------------------------------------------------------------------------------
Scientists have a long and unsuccessful history of attempting to convert hydrogen to a metal by squeezing it under incredibly high and steady pressures.

Metallic hydrogen is predicted to be a high-temperature superconductor. A superconductor is a state of matter where electrons, and thus electricity, can flow indefinitely and without resistance.

In a paper published this week in the online edition of the Proceedings of the National Academy of Sciences, a team of scientists from Cornell University and the State University of New York at Stony Brook announce a theoretical study that predicts the metallization of hydrogen-rich mixtures at significantly lower pressures.

By adding small amounts of lithium to hydrogen, the study calculates that the resulting system may be metalized at around one-fourth the pressure required to metalize pure hydrogen. Funding for the project was provided by the National Science Foundation (NSF).

Hydrogen and lithium are the first and third lightest elements in the universe, respectively. Under the temperature and pressures found on Earth, hydrogen is a gas and lithium is a metal. In hydrogen gas, the atoms are robustly bonded together in pairs and each hydrogen atom contributes one electron to the bonding. In chemistry shorthand, hydrogen is called H2.

Hydrogen and lithium normally react with each other to form a stable compound. This lithium-hydrogen compound, or LiH, is not metallic.

Metallic hydrogen is thought to be present in the interiors of planets like Jupiter and Saturn because of the intense gravitational forces and pressures that are found there.

On Earth, researchers have tried to pry loose hydrogen's electron by squeezing it between the facets of a diamond anvil cell under pressures up to 3.4 million atmospheres. The pressure at sea level is one atmosphere. The pressure at the center of the Earth is around 3.5 million atmospheres. Scientists have not been successful with this method of steady pressures. They have been, however, with shock-wave methods.

To get around hydrogen's decidedly fixed stance of not becoming a metal under currently accessible laboratory pressures, the research team used sophisticated computer programs.

The programs theoretically calculate if hydrogen can be metalized by combining a lithium atom with varying numbers of hydrogen atoms. The programs also compute if metallic hydrogen can be made under pressures achievable in a laboratory.

The lithium and hydrogen combinations predicted by the study currently do not exist on Earth.

One of the combinations predicted by the team contains one lithium atom for every six hydrogen atoms or LiH6 (see top right image). The complex calculations predict that in the hypothetical compound the Li atom is triggered to release its lone outer electron, which is then distributed over the three H2 molecules.

Under pressure, the hypothetical reaction forms a stable and metallic hydrogen compound.

The calculations also predict that LiH6 could be a metal at normal pressures. However, under these conditions it is not stable and would decompose to form LiH and H2.

"The stable and metallic LiH6 compound is predicted to form around 1 million atmospheres, which is around 25 percent of the pressure required to metalize hydrogen by itself," said Eva Zurek, lead author of the paper and an assistant professor of chemistry at The State University of New York, Buffalo.

"Interestingly, between approximately 1 and 1.6 million atmospheres, all the LiH combinations studied were stable or metastable and all were metallic," said Roald Hoffmann, co-author, recipient of the 1981 Nobel Prize in chemistry and Cornell's Frank H.T. Rhodes Professor of Humane Letters, Emeritus.

Another one of the hypothetical compounds studied by the team was composed of one lithium atom and two hydrogen atoms or LiH2 (see bottom right image).

"The theoretical study opens the exciting possibility that non-traditional combinations of light elements under high pressure can produce metallic hydrogen under experimentally accessible pressures and lead to the discovery of new materials and new states of matter," said Daryl Hess, a program director in the NSF Division of Materials Research.

"Once again, these researchers have taken chemistry to a new frontier," said Carol Bessel, a program director in the NSF Division of Chemistry. "They have described, through their theories and calculations, molecules that test our fundamental assumptions about atoms, molecules and structures. In doing so, they challenge the experimentalists to make what they have imagined in their minds a reality to be held in the hand."

The team members believe the information gleaned from the study suggests that one may combine large amounts of hydrogen with other elements. The information may also some day assist with the design of a metallic hydrogen-based superconductor.

"We have already been in touch with laboratory experimentalists about how LiH6 might be fabricated, starting perhaps with very finely divided forms of the common LiH compound along with extra hydrogen," said Neil W. Ashcroft, co-author, and Cornell's Horace White Professor of Physics, Emeritus.

Additional authors include Artem R. Oganov, an associate professor, and Andriy O. Lyakhov, a post doctoral research associate, of the State University of New York at Stony Brook, Department of GeoSciences. Zurek was a postdoctoral associate in Hoffmann's research group when the studies were completed.

Funding for the study was provided by the NSF Divisions of Chemistry and Materials Research. The research was also supported in part by NSF through TeraGrid resources provided by the National Center for Supercomputing Applications.

---

Adapted from materials provided by National Science Foundation.