Cathodic degradation mechanisms of pure Sn electrocatalyst in a nitrogen atmosphere

The application of electrocatalysts used at high cathodic overpotentials for the electrochemical reduction of pollutant species such as CO₂ has revealed a lack of understanding of the cathodic degradation mechanisms of those materials. Pure Sn is one of the most relevant candidate materials mainly because of its high selectivity for the reduction of CO₂ to formic acid and formate salts. Degradation of the electrocatalyst can arise from a combination of cathodic polarization and induced changes to the surface by CO₂ reduction products. In this study, the cathodic degradation mechanisms of pure Sn were studied as a function of rotation rate, time, current density, electrolyte concentration, grain size, and orientation in a nitrogen-saturated atmosphere using a rotating disk electrode. Several degradation morphologies were observed, but three were dominant. In the first type, electrochemical alterations of grains with specific orientations produced substantial weight changes, both losses and gains. The second type resulted in an alkali-rich deposit that had a high coverage but produced small weight changes. The third type consisted of carbon-rich stains that typically had a small coverage.