Electrocatalytic C─C Coupling of Dimethyl Oxalate to C₄ Dicarboxylate on Cu

Electrocatalytic conversion of CO to value-added multi-carbon chemicals enables carbon resource recycling and emission reduction. Building on the industrial process of dimethyl oxalate (DMO) production from CO and methanol, we report in this work a selective electrochemical pathway to convert DMO to dimethyl tartarate (DMT), a precursor to multiple C₄-dicarboxylic acids. On a Cu_α catalyst dominated by Cu(111)-like sites, Faradaic efficiency and partial current density for DMT reach 74.7% and 152 mA/cm^{- 2}, respectively, which significantly outperforms Cu_β dominated with Cu(100)/(110)-like sites. Facet dependence of the C─C coupling is confirmed via reactivity tests on single-crystal Cu surfaces and CO-poison experiments. In situ Raman spectroscopy reveals that DMO adopts distinct adsorption configurations on different Cu facets-planar on Cu(111) and upright on Cu(100)/(110)-accounting for the selectivity difference of DMT. Mechanistic studies indicate a surface-mediated nonradical pathway, with the initial electron transfer to adsorbed DMO as the rate-determining step for DMT formation. Our work enables the production of C₄-dicarboxylic acids via cascade reactions with CO as the initial feedstock.