Researchers developed a new way to convert CO2 into sustainable fuel, crucially without any unwanted products or waste, according to a study published in Nature Chemistry (1).
The team from the University of Cambridge, UK, already knew that biological enzymes can produce fuels using renewable energy sources, but this mechanism is not very efficient. Now, they managed to improve fuel production about 18 times in a lab setting, showing that CO2 emissions can be converted into green fuels without wasting any energy.
Most methods developed so far for converting CO2 into fuel also produce a series of other by-products. It’s possible to limit their production, but this also reduces the efficiency of CO2 conversion. This means it’s possible to produce clean fuel, but at a very high cost.
The new method shows that some enzymes found in bacteria can convert CO2 into fuel in a process called electrolysis. These enzymes are much more efficient than chemical catalysts, like gold, but they’re also more sensitive to their local chemical environment. If the conditions aren’t exactly right, the enzymes struggle, and the chemical reaction is slow. To avoid this problem, the Cambridge team, in collaboration with a team from the Universidade Nova in Lisbon, Portugal, created a method to ensure the enzymes always have the perfect conditions.
“Enzymes have evolved over millions of years to be extremely efficient and selective, and they’re great for fuel-production because there aren’t any unwanted by-products,” said Dr. Esther Edwardes Moore from Cambridge’s Yusuf Hamied Department of Chemistry. “However, enzyme sensitivity throws up a different set of challenges. Our method accounts for this sensitivity so that the local environment is adjusted to match the enzyme’s ideal working conditions.”
In simple terms, this new method relies on the cooperation between two enzymes: one producing fuel and the other controlling the environment. This way, it’s possible to speed up reactions and increase efficiency at the same time.
“We ended up with just the fuel we wanted, with no side-products and only marginal energy losses, producing clean fuels at maximum efficiency,” said first author Dr. Sam Cobb. “By taking our inspiration from biology, it will help us develop better synthetic catalyst systems, which is what we’ll need if we’re going to deploy CO2 electrolysis at a large scale.”
“Electrolysis has a big part to play in reducing carbon emissions,” added Professor Erwin Reisner, who led the research. “Instead of capturing and storing CO2, which is incredibly energy-intensive, we have demonstrated a new concept to capture carbon and make something useful from it in an energy-efficient way.”
For the authors, the trick was to use natural enzymes instead of synthetic catalysts. There has been significant improvement in the development of synthetic catalysts, but they’re still not as good as enzymes. The authors suggest that once the technology with catalysts catches up, the same principle can be used.
“Once you manage to make better catalysts, many of the problems with CO2 electrolysis just disappear,” concluded Dr. Cobb. “We’re showing the scientific community that once we can produce catalysts of the future, we’ll be able to do away with many of the compromises currently being made since what we learn from enzymes can be transferred to synthetic catalysts.”
(1) Cobb, S.J., Badiani, V.M., Dharani, A.M. et al. Fast CO2 hydration kinetics impair heterogeneous but improve enzymatic CO2 reduction catalysis. Nat. Chem. (2022). https://doi.org/10.1038/s41557-021-00880-2