Dr. ETUSUKO FUJITA
Examines "Artificial Photosynthesis" to Produce Clean Green Fuels

COVER PHOTO CREDIT Miranda Gatewood

Dr. Jim Muckerman, senior chemist; Dr. Etsuko Fujita, senior chemist;
Dr. David Grills, associate chemist; and Dr. Dmitry Polyansky, assistant chemist at the Brookhaven National Lab’s Chemistry Department

 

Green plants have been doing it for eons…using energy from the sun to convert carbon dioxide and water into oxygen and carbohydrates by way of the nebulous green substance, chlorophyll. Called photosynthesis, the process makes air breathable and provides fuel for plants to survive and feed the entire food chain.

Scientists at the U.S. Department of Energy’s prestigious Brookhaven National Laboratory on Long Island, led by senior chemist Dr. Etsuko Fujita, are taking a cue from nature in an attempt to solve 21st-century man’s insatiable need for energy. They hope to find a way to combine the energy of light with simple substances like water and carbon dioxide and, with the help of a “catalyst,” produce raw materials for the chemical industry and inexpensive fuels through a process researchers call “artificial photosynthesis.”

Fujita, who received a B.S. from Ochanomizu University in Japan and a Ph.D. from the Georgia Institute of Technology, developed the research program and has assembled a core team within the Chemistry Department to advance the research. Her team includes Jim Muckerman, a Brookhaven lab scientist for more than 35 years; associate chemist David Grills, who holds B.S. and Ph.D. degrees from the University of Nottingham in the UK; and assistant chemist Dmitry Polyansky, who received his B.S. and M.S. degrees from Mendelyeyev University of Chemical Technology of Russia, in Moscow, and a Ph.D. from Bowling Green State University in Ohio.
“Artificial photosynthesis is very complicated chemistry,” remarks Fujita, who, as a Brookhaven Lab postdoctoral research associate in the 1970s, became interested in solar energy during the “first” energy crisis. In 1986, when she moved to the Chemistry Department, her interests expanded to photochemistry, the process in which the absorption of light by a chemical substance produces a photochemical reaction. In other words, small molecules are energized to undergo change.

Senior chemist Jim Muckerman points out, however: “We can’t just put water and carbon dioxide in a bulb and shine light on it.” Instead, the scientists are trying to find a catalyst that will serve as the “mediator” and bring about the chemical reaction. Muckerman says that the catalyst must fulfill the functions of a photocatalyst to absorb light to create separated positive and negative charges, and a catalyst to use those charges—“to do the chemistry on these starting molecules,” he adds—to produce a useful chemical compound, in this case, potential fuels like ethanol or methanol.

“We are trying to bring fundamental knowledge into the field,” adds Polyansky. “And, if we can explain well how these interactions work, then other people can use this knowledge to actually make a device.”

With energy needs expected to double by the year 2050, and double again by the end of the century, Fujita says, “We believe biomass, nuclear, wind and geothermal, leading renewable energy resources, may not be enough to supply the energy gap.” Muckerman adds, “The amount of solar energy that is potentially usable is more than enough to make up all the energy needs that we have.”

Most importantly, Muckerman notes that the scientists are addressing “the real environmental problem”: the impact of carbon dioxide (CO2) in the atmosphere. “It’s a real threat and a global problem,” Fujita remarks. “Our environment has changed quite a lot. Glaciers and permafrost are melting. In the artificial photosynthesis process, we are recycling CO2.” Grills notes that the researchers hope to make it possible to “capture CO2 from industrial emissions, rather than releasing it, and make use of it to produce fuels.”

Birth of a field
Over 30 years ago, the Japanese chemists Fujishima and Honda experimented with light energy and the catalyst titanium dioxide, using the charges generated to “split” water into hydrogen and oxygen. “This was a big breakthrough,” remarks Fujita, saying that it showed the possibilities of using solar energy to make fuel.

The key is the catalyst, which drives the conversion of very stable molecules, like water and carbon dioxide, into more energy-rich molecules. Fujita notes the inefficiency of titanium dioxide, which is white in color and absorbs only 3% of solar light. “Scientists have learned that the catalyst should be a colored material, such as black lead.”

Grills explains that in the laboratory, the Brookhaven scientists use lasers as their light source because lasers can produce intense visible light for investigating the pathways for producing hydrogen from water through the action of catalysts. “Once you have hydrogen,” notes Muckerman, “you can actually react the hydrogen with carbon dioxide to make liquid fuels.” In order to keep the process clean and green, he adds, “you would have to make the hydrogen out of a renewable energy source, and solar is probably the way to go.”
Special techniques with lasers allow the scientists to understand how the catalysts work by viewing the multi-step process on a fast time scale, like a billion steps a second. Polyansky says, “We are trying to understand the concept of how the system works. By looking at the individual paths independently, we can solve the puzzle piece by piece.”
Grills is concentrating on experimenting with different solvents, which provide the important phase of the process where the chemical reactions actually take place. Catalysts capable of converting CO2 into carbon monoxide, a powerful source of fuel, already exist; however, Grills says, “The catalysts are slow and inefficient—nowhere near efficient enough to use in a practical application.” In addition to investigation with organic solvents, Grills is dissolving the catalyst in high-pressure CO2, called “supercritical CO2,” whereby the chemical, a gas under normal conditions, takes on some of the properties of a liquid and can act as a good solvent. He looks for supercritical CO2 to speed up the reactions dramatically and make the artificial photosynthesis process more efficient. Fujita adds that supercritical CO2 has a concentration one hundred times higher than in conventional solvents.

“We want to accomplish the same functions of natural photosynthesis by a different route,” says Grills. “One that is stable, faster and cheaper,” adds Muckerman.

Solar energy conversion to fuels could bring advantages. Muckerman points out that solar photovoltaic cells, while widely used, cannot store the energy they produce, and while solar energy plants can be built in the sun-drenched desert, the technology for efficient transport of the electricity generated does not exist. Yet, he notes, “We are proposing the production of fuels that can be stored and transported to the end user.”

Popular science
“This field is getting really hot,” says Fujita, because of the heightened awareness of global energy problems. Artificial photosynthesis is being explored at the Institute for Molecular Science in Japan, the Institute for Artificial Photosynthesis in Sweden and in multiple locations in the United States. Fujita and the scientists in the Chemistry Department are working with the theory group at Brookhaven’s Center for Functional Nanomaterials and Stony Brook University’s Physics and Astronomy Departments, and have collaborations with scientists at the Institute for Molecular Science, the University of Houston and the California Institute of Technology.
In an effort to bring their scientific research to the public, the Brookhaven team gives talks in the Lab’s Chemistry Department, participates in conferences, and presents their work at scientific meetings locally and across the country.
“I guess we’re on the map of people who are active in the field,” Muckerman points out. Grills notes that they work with high school students in the summer program, giving demonstrations in photochemistry and the properties of CO2. Brookhaven Lab sponsors a public lecture series where Muckerman recently presented the group’s work, and the team has written extensively technical papers and articles presenting an overview of their research.

“Dr. Fujita is a pioneer,” remarks Muckerman. “She’s recognized as one of the world’s leaders in the field.” Fujita’s work was acknowledged by Brookhaven National Lab, which presented her with its highest accolade, The Science and Technology Award. Earlier this year, she was honored for her accomplishments by the Town of Brookhaven at its annual Women’s Recognition Night.

Fujita is quick to add that all of her colleagues “contribute” their research. Muckerman’s work on theory is closely integrated into the ongoing experiments, explaining what is being observed in the lab and what can be done next. Fujita is delighted to be working with Grills and Polyansky, who bring their knowledge of physical and inorganic chemistry and use of lasers in catalysis.

Speaking for his colleagues, Muckerman says they all have “a passion” for their work. He recalls: people would ask him what he does as a scientist, and he’d reply that he makes up problems and tries to solve them. They would answer: They pay you to do that?” He adds, “Now I can say I’m working on the energy problem, the most important problem of the 21st century.”