Berkeley Lab Researchers Use Solar Energy and Renewable
Hydrogen to Produce Methane
(August 25, 2015) A
team of researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley
National Laboratory (Berkeley Lab) developing a bioinorganic hybrid approach to
artificial photosynthesis have achieved another milestone. Having generated
quite a buzz with their hybrid system of semiconducting nanowires and bacteria
that used electrons to synthesize carbon dioxide into acetate, the team has now
developed a hybrid system that produces renewable molecular hydrogen and uses
it to synthesize carbon dioxide into methane, the primary constituent of
natural gas.
“This study represents another key breakthrough in
solar-to-chemical energy conversion efficiency and artificial photosynthesis,”
says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division
and one of the leaders of this study. “By generating renewable hydrogen and
feeding it to microbes for the production of methane, we can now expect an
electrical-to-chemical efficiency of better than 50 percent and a
solar-to-chemical energy conversion efficiency of 10-percent if our system is
coupled with state-of-art solar panel and electrolyzer.”
(From left)
Peidong Yang, Christopher Chang and Michelle Chang led the development
of an artificial
photosynthesis system that can convert CO2 into valuable chemical
products using
only water and sunlight. (Photo by Roy Kaltschmidt)
Yang, who also holds appointments with UC Berkeley and the
Kavli Energy NanoScience Institute (Kavli-ENSI) at Berkeley, is one of three
corresponding authors of a paper describing this research in the Proceedings of
the National Academy of Sciences (PNAS). The paper is titled “A hybrid bioinorganic
approach to solar-to-chemical conversion.” The other corresponding authors are
Michelle Chang and Christopher Chang. Both also hold joint appointments with
Berkeley Lab and UC Berkeley. In addition, Chris Chang is a Howard Hughes
Medical Institute (HHMI) investigator. (See below for a full list of the
paper’s authors.)
Photosynthesis is the process by which nature harvests the
energy in sunlight and uses it to synthesize carbohydrates from carbon dioxide
and water. Carbohyrates are biomolecules that store the chemical energy used by
living cells. In the original hybrid artificial photosynthesis system developed
by the Berkeley Lab team, an array of silicon and titanium oxide nanowires
collected solar energy and delivered electrons to microbes which used them to
reduce carbon dioxide into a variety of value-added chemical products. In the
new system, solar energy is used to split the water molecule into molecular
oxygen and hydrogen. The hydrogen is then transported to microbes that use it
to reduce carbon dioxide into one specific chemical product, methane.
A major advance in
artificial photosynthesis poses win/win for the environment
– removing CO2
from the atmosphere and using it for green chemistry,
including
renewable fuel production. (Photo by Caitlin Givens)
“In our latest work, we’ve demonstrated two key advances,”
says Chris Chang. “First, our use of renewable hydrogen for carbon dioxide
fixation opens up the possibility of using hydrogen that comes from any
sustainable energy source, including wind, hydrothermal and nuclear. Second,
having demonstrated one promising organism for using renewable hydrogen, we can
now, through synthetic biology, expand to other organisms and other value-added
chemical products.”
The concept in the two studies is essentially the same – a
membrane of semiconductor nanowires that can harness solar energy is populated
with bacterium that can feed off this energy and use it to produce a targeted
carbon-based chemical. In the new study, the membrane consisted of indium
phosphide photocathodes and titanium dioxide photoanodes. Whereas in the first
study, the team worked with Sporomusa ovata, an anaerobic bacterium that
readily accepts electrons from the surrounding environment to reduce carbon
dioxide, in the new study the team populated the membrane with Methanosarcina
barkeri, an anaerobic archaeon that reduces carbon dioxide using hydrogen rather
than electrons.