Waste CO2 transformed into high-value chemicals

Addressing the challenge posed by escalating carbon dioxide (CO₂) emissions and their impact on climate change, researchers from the National University of Singapore (NUS) have developed a novel technique that advances the conversion of waste CO₂ into value-added chemicals and fuels.

Led by Assistant Professor Lum Yanwei, the research team’s innovation enables the direct conversion of CO₂ from treated flue gas, a common by-product of industrial processes, into high-value multi-carbon (C₂₊) products such as ethylene and ethanol — essential raw materials for the production of various everyday compounds such as plastics, polymers and detergents. This not only circumvents the need for high-purity CO₂ but also efficiently repurposes a prevalent waste product.

Carbon capture, utilisation and storage is a fundamental process to a sustainable future, relying on a suite of technologies among which the electrochemical reduction of CO₂ is vital. The process, which transforms CO₂ into a range of valuable feedstocks for chemicals and fuels, traditionally demands high-purity CO₂, leading to significant costs due to the energy-intensive purification of the compound from sources like flue gases. Furthermore, the presence of oxygen impurities in flue gas results in undesired side reactions, which significantly reduces the efficiency of the CO₂ reduction process.

Lum’s team aimed to sidestep these challenges by integrating catalyst design with electrolyte selection. In a study which was published in the journal Nature Communications, the researchers first introduced a new method to design catalysts with greatly enhanced efficiencies for the electrochemical conversion of CO₂. Utilising this approach, they designed a nickel catalyst boasting exceptional performance for CO₂ reduction, achieving an efficiency rate exceeding 99%. The team later designed a composite system by sequentially layering this nickel catalyst onto a copper surface.

“We found that integrating acidic electrolytes with this composite system significantly suppresses the undesired side reactions from oxygen impurities in flue gas,” Lum said. This system, which was also described in Nature Communications, demonstrated comparable performance with systems that utilise pure CO₂ as feedstock.

Lum highlighted the potential economic impact of the team’s research, stating, “The cost of purifying CO₂ can amount to about US$70 to $100 per ton, which can constitute about 30% of the costs involved in converting CO₂ to feedstocks such as ethylene through electrochemical means.

“Our novel technique demonstrates a potential pathway for the development of efficient electrolysers for the direct conversion of CO₂ in flue gas, using simple yet effective electrolyte and catalyst design strategies to advance integrated sustainability solutions,” he said.

The potential implications of this research extend beyond the production of ethylene and ethanol. By adjusting the catalyst system, the new technique could be applied to synthesise other valuable chemicals such as acetate and propanol, which are used in the production of everyday products such as adhesives and disinfectants respectively. This versatility offers a broad platform for converting waste CO₂ into a diverse range of chemicals, underscoring the technique’s adaptability to different industrial needs.

“We are seeing strong interest from the industry and are currently in talks with some companies to further advance this research,” Lum said. “Our goal is to enhance the energy efficiency and scalability of our system, moving beyond laboratory-scale experiments towards developing prototype reactors that can be applied in industrial settings.”

Image caption: The NUS team designed a nickel-based composite catalyst that facilitates the direct conversion of carbon dioxide from flue gas into multi-carbon products with remarkable efficiency.