Facile Fabrication of Ag Electrodes for CO₂-to-CO Conversion with Near-Unity Selectivity and High Mass Activity

Electrochemical reduction of CO2 into valuable chemicals is considered a promising approach to achieve a carbon-neutral circular economy. This work aims at CO2 conversion to CO with high efficiency at silver (Ag) electrodes with low catalyst loadings. The free-standing electrodes were simply prepared via sputtering deposition, achieving an easy control of the Ag loading. In CO2 electrolysis, a relatively low Ag loading of 151.3 μg cm–2 approaches 100% CO selectivity in both KHCO3 and KOH electrolytes. In a KHCO3 electrolyte, this electrode achieves current densities as high as 26.6 and 56.5 mA cm–2 at −1.0 and −1.2 V vs reversible hydrogen electrode (RHE), respectively, corresponding to mass activities of 175.8 and 373.4 A gAg–1. Moreover, it also demonstrates high stability during a 15 h test at −1.2 V vs RHE, showing high retention in both the CO selectivity and geometric current density. By optimizing the operation conditions, a single-pass CO2 to CO conversion of about 22% is achieved, and such a high value is maintained for 14 h. When changing to the KOH electrolyte, the electrode shows an impressive increase in current density, achieving 240.0 and 365.0 mA cm–2 at −1.0 and −1.2 V vs RHE, respectively, corresponding to a high mass activity of 1586.3 and 2412.5 A gAg–1. In addition, excellent CO selectivity (>90%) is obtained in a wide potential range from −0.3 to −1.2 V vs RHE.