Macro- and Nano-Porous Ag Electrodes Enable Selective and Stable Aqueous CO Reduction.

Electrochemical carbon dioxide (CO) reduction from aqueous solutions offers a promising strategy to overcome flooding and salt precipitation in gas diffusion electrodes used in gas-phase CO electrolysis. However, liquid-phase CO electrolysis often exhibits low CO reduction rates because of limited CO availability. Here, a macroporous Ag mesh is employed and activated to achieve selective CO conversion to CO with high rates from an aqueous bicarbonate solution. It is found that activation of Ag surface using oxidation/reduction cycles produces nanoporous surfaces that favor CO-to-CO conversion. Notably, it is found that a combination of dissolved CO in bicarbonate solution with CO generated in situ from bicarbonate ions enables increased CO availability and a CO-to-CO conversion rate over 100 mA cm. By optimizing the oxidation/reduction cycles to fine-tune the structure of Ag surface, CO-to-CO conversion is reported from a bicarbonate solution with CO Faradaic efficiency of over 85% at current density of 100 mA cm, high concentration of 24.7% at outlet gas stream and stability of over 100 h with maintaining CO FE over 85% during whole reaction time.