Carbon dioxide reduction: Copper plus

Nature Commun. 7, 12123 (2016)

Electrochemical reduction of CO₂ not only reduces its emission into the atmosphere but also generates useful fuels such as methane, ethylene and other compounds. Cu-based catalysts have been shown to be active for the reaction but applications have been plagued by the relatively high voltages that are required during operation. Furthermore, fundamental understanding of the Cu redox chemistry that governs the conversion of CO₂ is elusive, as most studies are based on ex situ techniques. Beatriz Roldan Cuenya and colleagues in Germany and USA have now reported plasma-activated Cu catalysts with high selectivity (60%) towards ethylene formation and employed in operando techniques to analyse the activity and selectivity of the catalysts in their working state.

The researchers used a plasma activation method to synthesize oxidized Cu catalysts, which exhibit roughened nanostructured surface layers with CuO at the top and Cu₂O in the interlayer above the crystalline Cu. During the early period of the CO₂ reduction reaction, the surface layers reconstruct, becoming somewhat depleted in oxygen and rich in Cu⁺. Importantly, following these initial changes, the Cu₂O species were found to be relatively stable in the surface layer while the activity and selectivity remained almost unchanged, suggesting the significant role of Cu⁺ in the reaction. This result challenges the conventional view that metallic Cu is the only active species.