Metal‐organic framework (MOF) thickness control for carbon dioxide electroreduction to formate

Abstract Decreasing particle size (like thickness) is a common strategy to enhance the activities of catalysts. In this work, we have synthesized two coppers, which are bismuth‐based metal‐organic framework (CuBi‐MOF) catalysts with different thicknesses (134.8 and 2.0 nm). In contrast to common expectations, large thickness CuBi‐MOF has exhibited superior activities as a comparison to its small‐thickness counterpart in terms of carbon dioxide electroreduction to produce formate, characteristic of high selectivity (Faraday efficiency > 90%), a wide window of potential (−0.6 to −1.6 V vs. reversible hydrogen electrode), and large current densities (up to −380 mA cm−2). The mechanism study has been performed by using density functional theory calculations, which highlight the strong synergic effect between Cu and Bi sites in large‐thickness CuBi‐MOF for activating CO2 molecules. Consequently, large‐thickness CuBi‐MOF could show smaller Gibbs free energies compared to its small counterpart for binding with reaction intermediate (*COOH, 1.1 vs. 1.8 eV). The result of this work could provide new insights into catalyst design toward a number of electrochemical systems.