Crystal facet regulation of tin for electrochemical carbon dioxide reduction to formate.

The electrochemical CO2 reduction reaction (CO2RR) to formate represents a promising route for high-value CO2 utilization, which helps address environmental issues and enables energy storage. Tin (Sn)-based catalysts are widely used in CO2RR for formate production, yet the impact of crystal facets remains unreported. Here, we revealed the effect of Sn facets on CO2RR to formate. Sn electrodes with different facet preferences were obtained by controlling the electroreduction rate. The Sn-3 electrode with preferential (101) facet exposure achieved 87.8 % Faradaic efficiency (FE) for formate with a large partial current density (j), which is higher than that with abundant (200) facet (Sn-1) and a mixture of (200) and (101) facets (Sn-2). In membrane electrode assembly (MEA), the FEHCOOH of 88.5 % was obtained at the large current density of 500 mA cm-2 on Sn-3. Theoretical calculations and comprehensive experimental investigations revealed that the Sn(101) facet is conducive to the adsorption of *OCHO, thereby reducing the reaction energy barrier and enhancing formate generation during CO2RR. This work provides an understanding of Sn crystal facets for efficient CO2RR to formate.