Electrochemical activation of Cu_2−x S triggers sulfur leaching and the formation of amorphous, Cu-rich structures that enhance selectivity toward formate. This strategy doubles the Faradaic efficiency up to 75% for CO₂ conversion, offering a scalable pathway for sustainable catalyst design.

Precise control over the dynamic transformations that electrocatalysts undergo under operating conditions offers a powerful strategy for tailoring catalytic selectivity. Herein, the electrochemical modification of Cu_2−x S-derived catalysts to generate selective active sites for the electroreduction of CO₂ to formate is investigated. Through a combination of in situ and ex situ characterization techniques, it is demonstrated that electrochemical cycling induces sulfur leaching, resulting in the formation of reduced, amorphous copper structures that exhibit enhanced selectivity toward formate production. Compared to the pristine material, the electrochemically modified catalyst achieves a twofold improvement in Faradaic efficiency, reaching values as high as 75% for CO₂-to-formate conversion. These findings not only establish a cost-effective and scalable platform for catalyst fabrication and activation, but also open new avenues for advancing sustainable CO₂ conversion technologies toward industrial implementation.