Tailoring CO2 Adsorption Configuration with Spatial Confinement Switches Electroreduction Product from Formate to Acetate

Abstract

Multi-proton-coupled electron transfer, multitudinous intermediates, and unavoidable competing hydrogen evolution reaction during CO₂ electroreduction make it tricky to control high selectivity for specific products. Here, we present spatial confinement of Fe single atoms (FeN₂S₂) by adjacent FeS clusters (Fe₄S₄) to orientate the transition of CO₂ adsorption configuration from C,O-side to O-end, which triggers a shift of activated CO₂ from first-step protonation to C–C coupling, thus switching the target product from HCOOH in high Faraday efficiency (FE: 90.6%) on FeN₂S₂ to CH₃COOH (FE: 82.3%) on Fe₄S₄/FeN₂S₂. The adsorption strength of *OCHO upon the solitary FeN₂S₂ site is linearly related to the coordination number of Fe–S, with HCOOH predominantly produced over single-atom FeN₂S₂ (ortho-substituted S atoms). Fe₄S₄ cluster functions as a switch for a specific reduction product, which can not only optimize the spatial and electronic structure of the neighboring FeN₂S₂ but also impel complete reduction of CO₂ to the hydrocarbon intermediate *CH₃, followed by coupling of CO₂* and *CH₃ via the single-atom cluster synergistic catalysis of Fe₄S₄/FeN₂S₂. This spatial confinement strategy provides a new avenue to modulate the reactant adsorption model for desirable reaction pathways, with potential applications in diverse multistep electrochemical processes of controlled selectivity.