Acid-Stable Cu Cluster Precatalysts Enable High Energy and Carbon Efficiency in CO₂ Electroreduction

The electrochemical reduction of CO₂ in acidic media offers the advantage of high carbon utilization, but achieving high selectivity to C₂₊ products at a low overpotential remains a challenge. We identified the chemical instability of oxide-derived Cu catalysts as a reason that advances in neutral/alkaline electrolysis do not translate to acidic conditions. In acid, Cu ions leach from Cu oxides, leading to the deactivation of the C₂₊-active sites of Cu nanoparticles. This prompted us to design acid-stable Cu cluster precatalysts that are reduced in situ to active Cu nanoparticles in strong acid. Operando Raman and X-ray spectroscopy indicated that the bonding between the Cu cluster precatalyst ligand and in situ formed Cu nanoparticles preserves a high density of undercoordinated Cu sites, resulting in a C₂H₄ Faradaic efficiency of 62% at a low overpotential. The result is a 1.4-fold increase in energy efficiency compared with previous acidic CO₂-to-C₂₊ electrocatalytic systems.