How to recycle CO2 from flue gases

Extracting and reusing CO2 from flue gases is a challenging task, particularly because carbon dioxide typically constitutes only a small percentage of these gas mixtures. Achieving this under realistic conditions requires catalytic processes that can function effectively at low CO2 concentrations, enabling its transformation into valuable materials.

Addressing Competitive Reactions

"Our problem is the competitive reactions that take place at the catalyst," explained Wolfgang Schuhmann. "The fewer CO2 molecules there are to convert, the more likely it is that hydrogen will be produced during catalysis instead of the desired product." Adjusting the electrolyte by making the solution more alkaline can help mitigate this issue, but it creates another challenge: CO2 is converted into carbonate, rendering it unavailable for the intended reactions.

To date, catalytic processes for CO2 reduction have been demonstrated to work effectively at CO2 concentrations as low as 10 to 20 percent. However, researchers have aimed to push these boundaries even further. "By using a superactive catalyst based on nickel-copper, we were able to successfully catalyze the reduction down to a CO2 content of five percent," stated Adib Mahbub, the study's first author.

Innovations at Ultra-Low CO2 Levels

When the CO2 concentration dropped below five percent, the researchers employed additional strategies. By fine-tuning electrical potentials and adjusting the electrolyte, they managed to carry out the reduction process with a gas mixture containing just two percent CO2. Schuhmann commented, "Although this means a loss of energy, clever process control allows us to access sources for the first time that we were previously unable to use for CO2 reduction."

The team's work highlights the potential for utilizing extremely low-concentration CO2 sources, a crucial step toward developing methods for capturing and reducing atmospheric CO2, where concentrations are even lower. "Future generations will have to build on such concepts if they want to extract CO2 from the atmosphere," Schuhmann added.

Research Report:Towards the use of low-concentration CO2 sources by direct selective electrocatalytic reduction