A recent development by researchers at the University of Cambridge and the Universidade Nova de Lisboa has led to an 18-time increase in the efficiency of clean fuel production from CO2.
The new proof of concept relies on enzymes isolated from bacteria to power the chemical reactions which convert carbon dioxide into fuel, a process called electrolysis.
In two papers published in the journals Nature Chemistry and Proceedings of the National Academy of Sciences, the scientists explain that enzymes are more efficient than other catalysts, such as gold, but they are highly sensitive to their local chemical environment. If the local environment isn’t exactly right, the enzymes fall apart and the chemical reactions are slow.
To address this issue, the Britain and Portugal-based researchers have developed a method to improve the efficiency of electrolysis by fine-tuning the solution conditions to alter the local environment 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,” Esther Edwardes Moore, first author of the PNAS paper, said in a media statement. “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.”
The researchers used computational methods to design a system to improve the electrolysis of CO2. Using the enzyme-based system, the level of fuel production increased by 18 times compared to the current benchmark solution.
Edwardes Moore explained that to improve the local environment further, she and her team made two enzymes work together, one producing fuel and the other controlling the environment. They found that adding another enzyme sped up the reactions, both increasing efficiency and reducing unwanted 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,” Sam Cobb, first author of the Nature Chemistry paper, said. “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.”
Normally, methods for converting CO2 into fuel also produce unwanted by-products such as hydrogen. Scientists have tried before to alter the chemical conditions to minimize hydrogen production, but this also reduces the performance for CO2 conversion; so cleaner fuel has been produced but at the cost of efficiency.
“Electrolysis has a big part to play in reducing carbon emissions,” Erwin Reisner, the Cambridge professor who led the research, said. “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.”
The researchers are convinced that the secret to more efficient CO2 electrolysis lies in the catalysts. There have been big improvements in the development of synthetic catalysts in recent years, but they still fall short of the enzymes used in this work.
“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,” Cobb said.
“In the 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.”