Macro‐ and Nano‐Porous Ag Electrodes Enable Selective and Stable Aqueous CO 2 Reduction

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Electrochemical carbon dioxide (CO 2 ) reduction from aqueous solutions offers a promising strategy to overcome flooding and salt precipitation in gas diffusion electrodes used in gas‐phase CO 2 electrolysis. However, liquid‐phase CO 2 electrolysis often exhibits low CO 2 reduction rates because of limited CO 2 availability. Here, a macroporous Ag mesh is employed and activated to achieve selective CO 2 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 2 ‐to‐CO conversion. Notably, it is found that a combination of dissolved CO 2 in bicarbonate solution with CO 2 generated in situ from bicarbonate ions enables increased CO 2 availability and a CO 2 ‐to‐CO conversion rate over 100 mA cm −2 . By optimizing the oxidation/reduction cycles to fine‐tune the structure of Ag surface, CO 2 ‐to‐CO conversion is reported from a bicarbonate solution with CO Faradaic efficiency of over 85% at current density of 100 mA cm −2 , 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.