Pulsed Electrocatalysis on SnO2 Electrodes for Boosting Formate Selectivity and Activity during CO2 Electroreduction

Abstract

Tin oxide (SnO₂) is considered a candidate catalyst for the electrocatalytic CO₂ reduction (CO₂R) to formate conversion. However, the self-reduction of SnO₂ to metallic Sn at high current densities leads to an unavoidable sharp decrease in formate selectivity. Herein, a SnO₂-based catalyst (Pul-SnO₂) is synthesized via pulsed electrocatalysis of SnO₂ precursors. Due to the ability to maintain the high oxidation valence states and promote the formation of oxygen vacancies, Pul-SnO₂ exhibited a high formate selectivity of 90% at a high current density of 600 mA cm⁻², significantly higher than that of a conventional Sn-based catalyst (81% and 100 mA cm⁻²) obtained via constant potential electrocatalysis. The in situ Raman spectra, kinetic isotope effect, cyclic voltammetry, and theoretical calculations demonstrated that the high oxidation states of SnO₂ promote CO₂ molecules activation and the oxygen vacancies enhance water dissociation, thereby accelerating the proton-coupled electron transfer process to reduce the free energy of *OCHO intermediate generation. Moreover, the identified adsorbed hydroxyls (*OH) with suitable coverage during CO₂R also promote the *OCHO formation and further make the formation of *OCHO more energy-favorable. As a result, the Pul-SnO₂ catalyst showed a super selectivity in CO₂R to formate, while maintaining excellent activity and stability.