Cu-S Planes in a Metal-Organic Framework for Selective Electrochemical Conversion of CO2 to Formate

The electrochemical reduction of CO2 into value-added chemicals is pivotal for advancing toward carbon neutrality and sustainable energy sources. However, achieving high selectivity for specific products remains challenging due to numerous potential reaction pathways. In this work, we present an innovative copper-sulfur planar structure, Cu-S-BDC, within a metal-organic framework (MOF) catalyst, which demonstrates remarkable selectivity towards formate as the sole carbon product. Notably, it achieves a 59% Faradaic efficiency (FE) for formate at -0.4 V vs. the reversible hydrogen electrode (RHE) in a 1 M KOH electrolyte. The reaction mechanism uncovers that the Cu-S catalytic sites within the MOF stabilize the HCOO* intermediate, thereby facilitating selective formate production. Additionally, we elucidate the electronic properties of the MOF, revealing a narrow band gap of 1.203 eV, which enhances the charge transfer within the quasi-2D inorganic building unit structure of the MOF and consequently increases the electrochemical reaction current density. This study highlights the potential of engineering the metal coordination environment within MOFs to enhance both product selectivity and conductivity in electrochemical CO2 reduction.