Activity and Selectivity Control in CO₂ Electroreduction to Multicarbon Products over CuO_x Catalysts via Electrolyte Design

The CO₂ electroreduction reaction (CO₂RR) to chemicals and fuels is of both fundamental and practical significance, since it would lead to a more efficient storage of renewable energy while closing the carbon cycle. Here we report enhanced activity and selectivity for the CO₂RR to multicarbon hydrocarbons and alcohols (∼69% Faradaic efficiency and -45.5 mA cm^-2 partial current density for C₂₊ at -1.0 V vs RHE) over O₂-plasma-activated Cu catalysts via electrolyte design. Increasing the size of the alkali-metal cations in the electrolyte, in combination with the presence of subsurface oxygen species which favor their adsorption, significantly improved C-C coupling on CuO_x electrodes. The coexistence of Cs⁺ and I^- induced drastic restructuring of the CuO_x surface, the formation of shaped particles containing stable CuI species, and a more favorable stabilization of the reaction intermediates and concomitant high C₂₊ selectivity. This work, combining both experiment and density functional theory, provides insights into the active sites and reaction mechanism of oxide-derived Cu catalysts for the CO₂RR.