Sulfide-derived-tin sites enable highly active electrochemical reduction of CO2 to formate

Electrochemical reduction of carbon dioxide (CO2RR) to formate provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks powered using renewable electricity. Unfortunately, high selectivity in formate electrosynthesis has thus far only been achieved at the expense of low current density, yielding impractically low partial current densities (jCHOO-). We hypothesized that the presence of sulfur atoms in the catalyst surface could promote under-coordinated sites, and thereby improve the electrochemical reduction of CO2 to formate. We explored, using density functional theory, how the incorporation of sulfur into tin may favour formate generation. We used atomic layer deposition of SnSx followed by a reduction process to synthesize sulfur-promoted-tin (Sn(S)) catalysts. X-ray absorption near-edge structure (XANES) studies reveal higher oxidation states in Sn(S) compared to the oxidation state of tin in Sn nanoparticles. Sn(S)/Au accelerates CO2RR at record geometric current densities of 55 mA cm−2 at −0.75 V vs. RHE with a faradaic efficiency of 93%. Furthermore, the partial current density for formate on Sn(S)/Au – normalized by electrochemically active surface area –is in between 1.2 and 3 times higher than that of Sn NPs/Au at all potentials. Sn(S) catalysts show excellent stability without deactivation (