Cationic Cu Species Tracked via Operando X-Ray Microscopy during CO₂ Electrocatalysis and Their Role in Boosting C-C Coupling Activity

Unraveling and guiding the dynamic evolution of active species in efficient electrochemical CO2 reduction (ECR) catalysts remains a challenge. Through observing the chemical and morphological changes of high-performance ECR catalysts in action, we pinpointed the essential intermediate species that lead to highly active surfaces and notably improved C–C coupling activity. Operando scanning transmission soft X-ray microscopy, a method that illustrates the nanoscale chemical composition distribution of Cu-based catalysts during ECR, showed that the emergence of partial Cu+ phases and surface Cu2+ phases are key to the dynamic dissolution-redeposition mechanism and heightened C–C coupling activity, respectively. We further established that this dissolution-redeposition process is electrochemical formation Cu²⁺ phases, even at elevated cathodic potentials. Our correlative microscopy and electrochemical analysis strengthen the substantial contribution of Cu2+ phases toward C-C coupling. In addition, DFT calculations corroborated that Cu2+ phases amplifies C–C coupling activity.