Electrochemically Driven Cation Exchange Enables the Rational Design of Active CO₂ Reduction Electrocatalysts

Metal oxides or sulfides are considered to be one of the most promising CO₂ reduction reaction (CO₂ RR) precatalysts, owing to their electrochemical conversion in situ into highly active electrocatalytic species. However, further improvement of the performance requires new tools to gain fine control over the composition of the active species and its structural features [e.g., grain boundaries (GBs) and undercoordinated sites (USs)], directly from a predesigned template material. Herein, we describe a novel electrochemically driven cation exchange (ED-CE) method that enables the conversion of a predesigned CoS₂ template into a CO₂ RR catalyst, Cu₂ S. By means of ED-CE, the final Cu₂ S catalyst inherits the original 3 D morphology of CoS₂ , and preserves its high density of GBs. Additionally, the catalyst's phase structure, composition, and density of USs were precisely tuned, thus enabling rational design of active CO₂ RR sites. The obtained Cu₂ S catalyst achieved a CO₂ -to-formate Faradaic efficiency of over 87 % and a record high activity (among reported Cu-based catalysts). Hence, this study opens the way for utilization of ED-CE reactions to design advanced electrocatalysts.