To Battle Climate Change, Scientists Tap into Carbon-Hungry Microorganisms for Clues

by Theresa Duque (Lawrence Berkeley National Laboratory) New technique could fast-track future carbon-free solar fuels -- Berkeley Lab scientists have developed a nature-inspired technique for converting carbon dioxide into solar fuels.

Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a new technique, modeled after a metabolic process found in some bacteria, for converting carbon dioxide (CO2) into liquid acetate, a key ingredient in “liquid sunlight” or solar fuels produced through artificial photosynthesis.

The new approach, reported in Nature Catalysis, could help advance carbon-free alternatives to fossil fuels linked to global warming and climate change.

The work is also the first demonstration of a device that mimics how these bacteria naturally synthesize acetate from electrons and CO2.

“What’s amazing is that we learned how to selectively convert carbon dioxide into acetate by mimicking how these little microorganisms do it naturally,” said senior author Peidong Yang, who holds titles of senior faculty scientist in Berkeley Lab’s Materials Sciences Division and professor of chemistry and materials science and engineering at UC Berkeley.

For decades, researchers have known that a metabolic pathway in some bacteria allows them to digest electrons and CO2 to produce acetate, a reaction driven by the electrons. The pathway breaks CO2 molecules down into two different or “asymmetric” chemical groups: a carbonyl group (CO) or a methyl group (CH3). Enzymes in this reaction pathway enable the carbons in CO and CH3 to bond or “couple,” which then triggers another catalytic reaction that produces acetate as the final product.

Researchers in the field of artificial photosynthesis have wanted to develop devices that mimic the pathway’s chemistry – called asymmetric carbon-carbon coupling – but finding synthetic electrocatalysts that work as efficiently as bacteria’s natural enzymatic catalysts has been challenging.

Copper’s talent for converting carbon into various useful products was first discovered in the 1970s. Based on those previous studies, Yang and his team reasoned that artificial photosynthesis devices equipped with a copper catalyst should be able to convert CO2 and water into methyl and carbonyl groups, and then turn these products into acetate.

Chemical analytical experiments conducted in Yang’s UC Berkeley lab revealed that copper’s pairing of carbonyl and methyl groups produced not only acetate but other valuable liquids, including ethanol and acetone. The isotopic tracking allowed the researchers to confirm that the acetate was formed through the combination of the CO and CH3.

In 2015, Yang co-led a study that demonstrated an artificial photosynthesis system comprised of semiconducting nanowires and bacteria using the energy in sunlight to produce acetate from carbon dioxide and water. The finding had significant implications for a growing field in which researchers have spent decades looking for the best chemical reactions to produce high yields of liquid products from CO2.

The new study advances this earlier work by demonstrating a synthetic electrocatalyst – the copper-silver nanoparticles – that “clearly mimics what bacteria do to produce liquid products from CO2,” Yang said. “We still have a lot of work to do to improve it, but we’re excited by its potential to advance artificial photosynthesis.”

The Molecular Foundry is a DOE Office of Science user facility at Berkeley Lab. READ MORE