Scalable Copper–Silver Foam Electrocatalysts with Tunable Porosity for Selective CO ₂ Reduction to CO

Silver-based catalysts are widely recognized as benchmark materials for the electrochemical reduction of CO2 to CO due to their high selectivity and favorable reaction kinetics; however, their high cost limits large-scale deployment. A viable strategy to overcome this challenge is to dilute Ag with earth-abundant Cu, although Cu alone typically suffers from lower CO selectivity, higher overpotentials, competing reaction pathways, and structural instability during long-term operation. Herein, we report a scalable and controllable strategy to integrate Cu with Ag into a three-dimensional porous bimetallic foam architecture using a Hydrogen Bubble Dynamic Template (HBDT)-assisted electrodeposition method. By systematically optimizing the acetic acid concentration (bubble stabilizer) in the precursor electrolyte, copper–silver (Cu–Ag) foams with tailored pore sizes and compositions were obtained. The optimized CuAg-0.10 foam exhibits superior CO2 to CO performance, achieving a high Faradaic efficiency (FE) of 90.2% at −0.99 V vs RHE, outperforming both monometallic Cu and Ag foams. The porous CuAg network enables CO formation at significantly lower overpotentials, reflecting a strong synergistic interaction between Cu and Ag on the reconstructed dendritic pore walls. Enhanced activity is attributed to the increased electrochemically active surface area, improved mass transport through interconnected pores, and weakened adsorption of the key *CO intermediates at Cu–Ag interfaces. Electrochemical impedance spectroscopy confirms reduced charge-transfer resistance, while Ultramicroelectrode (UME)-based fast-scan cyclic voltammetry (FSCV) verifies formation of stable *CO intermediate. Overall, this work demonstrates that the porous CuAg foam structure offers an efficient, durable, and scalable electrocatalyst for selective CO2 to CO conversion.