Ligand-tuning copper in coordination polymers for efficient electrochemical C-C coupling.

Cu catalyses electrochemical CO 2 reduction to valuable multicarbon products but understanding the structure-function relationship has remained elusive due to the active Cu sites being heterogenized and under dynamic re-construction during electrolysis. We herein coordinate Cu with six phenyl-1H-1,2,3-triazole derivatives to form stable coordination polymer catalysts with homogenized, single-site Cu active sites. Electronic structure modelling, X-ray absorption spectroscopy, and ultraviolet-visible spectroscopy show a widely tuneable Cu electronics by modulating the highest occupied molecular orbital energy of ligands. Using CO diffuse reflectance Fourier transform infrared spectroscopy, in-situ Raman spectroscopy, and density functional theory calculations, we find that the binding strength of *CO intermediate is positively correlated to highest occupied molecular orbital energies of the ligands. As a result, we enable a tuning of C-C coupling efficiency-a parameter we define to evaluate the efficiency of C 2 production-in a broad range of 0.26 to 0.86. This work establishes a molecular platform that allows for studying structure-function relationships in CO 2 electrolysis and devises new catalyst design strategies appliable to other electrocatalysis.