WHAT IF WE COULD WRING LIQUID FUEL FROM SUNLIGHT?
What if chemists could capture energy from our nearly inexhaustible star and store it in the chemical bonds of hydrocarbon
fuels, like gasoline?
Plants have been doing something like this for billions of years
through photosynthesis. Plants harvest solar energy and use
it to power a chemical chain reaction that makes sugars, or in
other words, their “fuel.”
Inspired by those leafy green powerhouses, UC San Diego
scientists are working to develop a system they call “artificial
photosynthesis.” The process will likewise use sunlight to
create a chemical reaction that creates energy, only instead of
plant-powering sugars, the product will be high-density fuel.
The effort is led by Cliff Kubiak, UC San Diego distinguished
professor of chemistry and biochemistry, and a member of the
Joint Center for Artificial Photosynthesis, a multi-university
innovation hub funded by the Department of Energy to create
Kubiak and colleagues are working on ways to loosen the
tenacious bonds in carbon dioxide molecules so that the atoms
therein can be reassembled into liquid fuels. Plants do this
naturally via enzymes, yet these enzymes are high-maintenance
proteins that must continually be replenished—not so easy to
Kubiak and colleagues are developing a more efficient system
that replaces those unwieldy proteins with chemical structures
that serve like scaffolding. Kubiak likens these “metal-organic
frameworks,” or MOFs, to the mix-and-match children’s building kits we all know as Tinkertoys.
“They’re modular—we can put whatever catalyst we want in
there and then it’s nailed down into this robust, solid-state
structure,” he says. “We decided to use the MOF as a platform
for making things that are like enzymes but aren’t floppy
peptides that can degrade.”
Along with Seth Cohen, another chemistry professor at
UC San Diego, the team created an MOF that allowed them to
infuse the “scaffolding” struts with a photosensitive chemical,
akin to chlorophyll and other pigments that nature uses for
photosynthesis. When light shines on the setup, the electrons
shuffle and carbon dioxide molecules recombine with hydrogen
to form nascent molecules of fuel.
This particular MOF is just one possibility in the progress
toward achieving viable products that create fuel via artificial
photosynthesis. “There’s going to be a lot more,” Kubiak says.
“We’re doing such new things that there are still broad strokes
Taking cues from plants to produce fuel for the future.
A TANKFUL OF
BY SUSAN BROWN