Planar [Cu–S]–Organic Framework for Selective and Low-Overpotential CO2–to–Formate Reduction

The development of advanced catalysts with innovative nanoarchitectures is critical for addressing energy and environmental challenges such as the electrochemical CO2 reduction reaction (CO2RR). In this work, we present the synthesis of an innovative copper-sulfur planar structure, Cu-S-BDC, within a metal-organic framework (MOF) catalyst, which demonstrates 100% selectivity towards formate as the sole carbon product. Structural analysis and surface characterizations reveal that Cu-S-BDC exhibits quasi-two-dimensional inorganic building units, with Cu bonded to two S-CH3 groups and one BDC linker, while carboxylate groups adopt a bridging coordination mode. This unique arrangement not only imparts remarkable structural stability but also enhances the electronic properties of the MOF, as evidenced by a narrow band gap of 1.203 eV that facilitates efficient charge transfer and increased electrochemical current density in CO2RR. Notably, it offers a Faradaic efficiency (FE) of 92% for formate at an overpotential as low as -0.4 V vs. the reversible hydrogen electrode (RHE) in an aqueous electrolyte of 1 M KOH, as well as a current density of -25.8 mA/cm2 at -0.9 V vs. RHE, averaged over 24 hours of electrolysis. This study highlights a fresh perspective in the field of MOF electrocatalysts by demonstrating that engineering the metal coordination environment can significantly enhance the electronic properties and consequently improve the electrocatalytic performance of these materials.