Acid-Stable Cu Cluster\nPrecatalysts Enable High Energy\nand Carbon Efficiency in CO<sub>2</sub> Electroreduction

The electrochemical reduction of CO<sub>2</sub> in acidic\nmedia\noffers the advantage of high carbon utilization, but achieving high\nselectivity to C<sub>2+</sub> products at a low overpotential remains\na challenge. We identified the chemical instability of oxide-derived\nCu catalysts as a reason that advances in neutral/alkaline electrolysis\ndo not translate to acidic conditions. In acid, Cu ions leach from\nCu oxides, leading to the deactivation of the C<sub>2+</sub>-active\nsites of Cu nanoparticles. This prompted us to design acid-stable\nCu cluster precatalysts that are reduced in situ to active Cu nanoparticles\nin strong acid. Operando Raman and X-ray spectroscopy indicated that\nthe bonding between the Cu cluster precatalyst ligand and in situ\nformed Cu nanoparticles preserves a high density of undercoordinated\nCu sites, resulting in a C<sub>2</sub>H<sub>4</sub> Faradaic efficiency\nof 62% at a low overpotential. The result is a 1.4-fold increase in\nenergy efficiency compared with previous acidic CO<sub>2</sub>-to-C<sub>2+</sub> electrocatalytic systems.