Silver-Modulated Copper Dynamics Under Pulsed Tandem Electrochemical CO₂ Reduction

Pulsed electrolysis and Cu-Ag tandem catalysis are both promising strategies for electrochemical CO₂ reduction, yet their interplay remains unclear. Here, we show that pulsed operation does not preserve the as-prepared Cu-Ag catalyst and instead generates a dynamic bimetallic working state in situ. During prolonged electrolysis, the catalyst evolves toward a favorable selectivity profile with significantly increased CO formation, persistent ethylene production, and suppressed hydrogen, methane, and formate pathways. Correlative SEM/EDS, XPS, ToF-SIMS, ICP-MS, and STEM-EELS show that this behavior arises from Ag-modulated Cu dissolution and redeposition under pulsed conditions. The resulting catalyst develops near-surface Ag enrichment, a topmost catalytically relevant layer containing both Cu and Ag, persistent Cu loss to the electrolyte, and subsurface cavities. Comparison with pure Cu under identical pulsed conditions further shows that Ag redirects the restructuring pathway of Cu toward a distinct Ag-rich yet still Cu-active catalytic state. Under pulsed CO₂ reduction, Ag therefore acts as a tandem component for CO formation and as a regulator of catalyst evolution.