Facile Fabrication of Ag Electrodes for CO<sub>2</sub>-to-CO Conversion with Near-Unity Selectivity and High Mass Activity
Nicolò B. D. Monti, Marco Fontana, Adriano Sacco, Angelica Chiodoni, Andrea Lamberti, Candido Fabrizio Pirri, Juqin Zeng
Abstract
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.