Electrolyte‐Induced Cu ⁺ Preservation Results in a Selectivity Switch of Electrocatalytic CO ₂ Reduction at a Copper‐Organic Framework as Electrocatalyst

We introduce a copper‐nicotinate (Cu‐NA) framework as a halogenide‐stabilized Cu + /Cu 0 pre‐catalyst for electrocatalytic CO 2 reduction with high C 2+ selectivity in a “neutral” electrolyte. Alkaline electrolytes (1 M KOH) primarily lead to H 2 and CH 4 formation due to rapid catalyst restructuring and carbonate precipitation, causing flooding of the gas‐diffusion electrode. Replacing the electrolyte with 1 M KCl induces a severe change in selectivity. Cu‐NA in KCl delivers >70% Faradaic efficiency for C 2+ products at a current density of 500 mA cm −2 with a C 2+ /C 1 ratio exceeding 14. Operando Raman spectroscopy detected strong CO ads accumulation and time‐dependent CO ads band shifts characteristic of high CO ads coverage conducive to C‐C coupling. Scanning electrochemical microscopy (SECM) measurements confirm that the local pH converges to highly alkaline values at high current densities in both electrolytes, ruling out pH as the origin of the selectivity switch. Post‐reaction XPS and XRD show that KCl preserves a Cu + ‐rich Cu/Cu 2 O surface and introduces surface‐bound chloride that suppresses HER, mitigates Cu dissolution/redeposition, and stabilizes the Cu + /Cu 0 interface essential for C 2+ formation. Anions can be used as active regulators of catalyst speciation and selectivity, offering a simple yet powerful design principle for CO 2 to C 2+ conversion at high current densities.