Converting CO2 into everyday materials

A team of researchers has developed an electrochemical system that can turn carbon dioxide into valuable carbon-based products like ethylene and ethanol – which can be used in a range of materials, from plastic to lycra.

As the world continues to pump carbon into the atmosphere, it is increasingly important to not only cease emissions but also work out ways to pull CO2 back out of the atmosphere.

But carbon capture and storage technologies don’t tend to make much money, so there’s little incentive for companies to invest in them.

PhD candidate, Ms Shuzhen Zhang, who contributed to this project, samples the outlet stream from the electrochemical reactor for product analysis. Credit: University of Sydney

This study, involving scientists from the University of Sydney and the University of Toronto, may start to change the game. It has developed a way to turn CO2 into something usable – and economically valuable.

The new electrochemical system, described in a paper in Science, relies on specially designed electrolysers that use electricity to convert CO2 and water into the building blocks of common materials.

“Our research differs to previous approaches,” explains Fengwang Li, co-author from the University of Sydney’s School of Chemical and Biomolecular Engineering. “Instead of choosing between an efficient use of electricity or efficient use of carbon, we do both.”

The system can create high-value products such as ethanol and ethylene, which are organic chemical compounds used across a range of industries. Ethylene, for example, is used in the manufacture of medical devices, metal fabrication and plastic production; it’s the most-produced organic compound in the world.

This system may therefore help create a market for captured carbon, using the resulting carbon-based products in industry.

This system has been designed to run under acidic conditions, which is an advantage over others because it improves efficiency by reducing unwanted reactions.

“Previous systems operated in alkaline or neutral conditions, meaning most of the CO2 was wasted, and would be converted into carbonate instead,” says Li. “By contrast, our process, using high acidity, retains CO2 at rates of up to 70 percent.”

Running the machine in acidic conditions does, however, mean hydrogen ions are converted to hydrogen gas, leaving few electrons to combine with CO2. The team tried to solve this problem by increasing the electrical current through the solid catalyst that the CO2 flows over. This flooded the reactor with electrons.

“In effect, we’re creating a reactor that is acidic throughout, except for a tiny layer within less than 50 micrometres of the catalyst surface,” explains co-author and University of Toronto researcher, Haoming Erick Huang. “In that specific region, it is not acidic, in fact it’s slightly alkaline. There, CO2 can get reduced to ethylene by those electrons.”

They also added a positively charged ion to the reaction, creating an electric field in the region around the catalyst to help CO2 become absorbed preferentially to the hydrogen ions.

The combination of two techniques allows the system to utilise 77% of available CO2, with about 50% being converted into valuable products.

But there’s still a way to go before this technology can be scaled up to capture and convert carbon at industrial scales.

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