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

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.