Electrochemical reduction of CO 2 into valuable chemicals is considered a promising approach to achieve a carbonneutral circular economy. This work aims at CO 2 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 CO 2 electrolysis, a relatively low Ag loading of 151.3 μg cm −2 approaches 100% CO selectivity in both KHCO 3 and KOH electrolytes. In a KHCO 3 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 g Ag −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 CO 2 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 g Ag −1 . In addition, excellent CO selectivity (>90%) is obtained in a wide potential range from −0.3 to −1.2 V vs RHE.
The electrocatalytic reduction of CO2 into useful fuels, exploiting rationally designed, inexpensive, active, and selective catalysts, produced through easy, quick, and scalable routes, represents a promising approach to face today’s climate challenges and energy crisis. This work presents a facile strategy for the preparation of doped SnO2 as an efficient electrocatalyst for the CO2 reduction reaction to formic acid and carbon monoxide. Zn or Ti doping was introduced into a mesoporous SnO2 matrix via wet impregnation and atomic layer deposition. It was found that doping of SnO2 generates an increased amount of oxygen vacancies, which are believed to contribute to the CO2 conversion efficiency, and among others, Zn wet impregnation resulted the most efficient process, as confirmed by X-ray photoelectron spectroscopy analysis. Electrochemical characterization and active surface area evaluation show an increase of availability of surface active sites. In particular, the introduction of Zn elemental doping results in enhanced performance for formic acid formation, in comparison to un-doped SnO2 and other doped SnO2 catalysts. At −0.99 V versus reversible hydrogen electrode, the total faradaic efficiency for CO2 conversion reaches 80%, while the partial current density is 10.3 mA cm−2. These represent a 10% and a threefold increases for faradaic efficiency and current density, respectively, with respect to the reference un-doped sample. The enhancement of these characteristics relates to the improved charge transfer and conductivity with respect to bare SnO2.
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