Researchers Develop Efficient Concept to Convert CO2 into Clean Fuels Without any Undesirable By-Products

Scientists have formulated an efficient concept to convert carbon dioxide (CO₂) into clean, sustainable fuels, without any waste or undesirable by-products. University of Cambridge scientists have earlier demonstrated that biological catalysts, or enzymes, can create fuels cleanly using renewable energy sources, however, at low efficiency.

Their most recent research has enhanced fuel production efficiency by 18 times in a laboratory scenario, showing that polluting carbon emissions can be converted into green fuels efficiently without energy being wasted. The results are reported in two interrelated articles in Nature Chemistry and Proceedings of the National Academy of Sciences.

The majority of approaches for turning CO₂ into fuel also generate undesirable by-products such as hydrogen. Researchers can change the chemical conditions to lessen hydrogen formation, but this also decreases the performance for CO₂ conversion: so cleaner fuel can be made, but by compromising efficiency.

The Cambridge-developed proof-of-concept depends on enzymes derived from bacteria to drive the chemical reactions which turn CO₂ into fuel, a process known as electrolysis. Enzymes are more efficient than other catalysts, such as gold, but they are extremely sensitive to their local chemical surroundings. If the local environment is not precisely right, the enzymes break down and the chemical reactions are sluggish.

The Cambridge scientists, collaborating with a team from the Universidade Nova de Lisboa in Portugal, have formulated a technique to enhance the efficiency of electrolysis by tweaking the solution conditions to modify the local surrounding of the enzymes.

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. 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.

Dr. Esther Edwardes Moore, First Author of PNAS Paper, Yusuf Hamied Department of Chemistry, Cambridge University

The scientists used computational approaches to engineer a system to enhance the electrolysis of CO₂. Employing the enzyme-based system, the level of fuel production grew by 18 times compared to the existing benchmark solution.

To enhance the local environment further, the scientists demonstrated how two enzymes can combine together, one creating fuel and the other regulating the environment. They discovered that incorporating another enzyme, accelerated the reactions, both boosting efficiency and decreasing undesirable by-products.

“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 Dr Sam Cobb, first author of the Nature Chemistry paper. “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. 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.

Professor Erwin Reisner, Study Lead and Fellow of St John’s College, Cambridge University

The scientists state that the secret to more resourceful CO₂ electrolysis depends on the catalysts. There have been major enhancements in the creation of synthetic catalysts in the last few years, but they still fall behind the enzymes used in this study.

“Once you manage to make better catalysts, many of the problems with CO₂ electrolysis just disappear,” said 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.”

Once we designed the concept, the improvement in performance was startling. I was worried we’d spend years trying to understand what was going on at the molecular level, but once we truly appreciated the influence of the local environment, it evolved really quickly.

Dr. Esther Edwardes Moore, First Author of PNAS Paper, Yusuf Hamied Department of Chemistry, Cambridge University

“In future, we want to use what we have learned to tackle some challenging problems that the current state-of-the-art catalysts struggle with, such as using CO₂ straight from air as these are conditions where the properties of enzymes as ideal catalysts can really shine,” said Cobb.

Erwin Reisner is a Fellow of St John’s College, Cambridge. Esther Edwardes Moore finished her PhD with Corpus Christi College, Cambridge. Sam Cobb is a Research Fellow of Darwin College, Cambridge.

The study was partly supported by the European Research Council, the Leverhulme Trust, and the Engineering and Physical Sciences Research Council.

Journal References:

• Moore, E.E., et al. (2022) Understanding the local chemical environment of bioelectrocatalysis. Proceedings of the National Academy of Sciences. doi.org/10.1073/pnas.2114097119.
• Cobb, S.J., et al. (2022) Fast CO₂ hydration kinetics impair heterogeneous but improve enzymatic CO₂ reduction catalysis. Nature Chemistry. doi.org/10.1038/s41557-021-00880-2.