'Impurity' in copper catalyst found to boost CO2 reduction efficiency

South Korean researchers have uncovered the operating mechanism of a copper catalyst that could improve the efficiency of carbon dioxide reduction technology, which converts CO2 into industrial raw materials.

The National Research Foundation of Korea announced Tuesday that a joint research team led by Choi Chang-hyuk, a professor at Pohang University of Science and Technology, along with Kim Se-ho of Korea University and Shin Hye-young of Kyung Hee University, established that sodium ion impurities entering a copper catalyst stabilize its highly active sites, thereby enhancing CO2 conversion performance.

CO2 reduction technology — which converts carbon dioxide into compounds such as carbon monoxide and ethylene — is considered a next-generation technology for achieving carbon neutrality and storing renewable energy. Oxide-derived copper catalysts excel at reduction reactions, but their complex structural and compositional changes during the reaction had made it difficult to identify the causes of performance improvements.

The research team focused not only on the catalyst itself but also on the role of electrolyte ions. They confirmed that sodium ions derived from the electrolyte — previously dismissed as mere impurities inside the catalyst — actually stabilize key active sites and enhance CO2 reduction performance.

Impurities are typically regarded as something to be removed, but in materials science, small amounts of impurities often alter a material's properties for the better. Classic examples include adding trace carbon to pure iron to produce steel, and doping silicon with minute quantities of elements to control its electrical properties in semiconductors. This study similarly shows that trace sodium ions inside a copper catalyst act as hidden regulators that boost catalytic performance.

Using cryogenic atom probe tomography, the team confirmed that when copper oxide is reduced, impurity sodium ions from the electrolyte are trapped in nanoscale defects inside the catalyst, forming a fine microstructure.

The sodium ions were found to penetrate not just the catalyst surface but to depths of tens of nanometers or more into the interior. This shows that trace amounts of sodium ions from the electrolyte can migrate inside the catalyst as copper oxide undergoes electrochemical reduction and its structure is rearranged.

The findings suggest that designing high-performance electrocatalysts requires consideration not only of the catalyst material itself but also of electrolyte ions and voltage operating conditions. The team expects the approach to be applicable beyond CO2 electrolysis to a range of electrochemical systems involving dynamic structural changes in catalysts, including water electrolysis and fuel cells.

"This study is significant in that it elucidates, at the atomic level, the role of sodium ions that have penetrated the catalyst in stabilizing active sites," Choi said. "We plan to expand our research into various electrocatalytic systems, including water electrolysis and nitrogen reduction, by investigating the relationship between electrolyte composition and the internal microstructure of catalysts."

The research, supported by the Ministry of Science and ICT and the National Research Foundation of Korea, was published Monday in Nature Catalysis, an international journal in the field of catalysis.