Pd-induced polarized Cu⁰-Cu⁺ sites for electrocatalytic CO₂-to-C₂₊ conversion in acidic medium

The acidic CO₂ reduction reaction (CO₂RR) offers a promising approach to mitigate CO₂ reactant loss and carbonate deposition, which are challenging issues in alkaline or neutral electrolytes. However, the hydrogen evolution reaction (HER) competes in the proton-rich environment near the catalyst surface as a side reaction, reducing the energy efficiency of generating multi-carbon (C₂₊) products. In this work, we proposed a palladium (Pd) doping strategy in a copper (Cu)-based catalyst to stabilize polarized Cu⁰-Cu⁺ sites, thus enhancing the CC coupling step during the CO₂RR while suppressing HER. At an optimal doping ratio of 6%, the Pd dopants were well dispersed as single atoms without aggregation, allowing for the stabilization of subsurface oxygen (O_Sub), preserving the polarized Cu⁰-Cu⁺ active sites, and reducing the energy barrier of CC coupling. The Pd-doped Cu/Cu₂O catalyst exhibited a peak Faradaic efficiency (FE) of 64.0% for C₂₊ products with a corresponding C₂₊ partial current density of 407.1 mA∙cm^-2 at -2.18 V versus a reversible hydrogen electrode, a high CO₂ single-pass conversion efficiency (SPCE) of 73.2%, as well as a high electrochemical stability of ∼ 150 h at industrially relevant current densities, thus suggesting a potential approach for tuning the electrocatalytic CO₂ performances in acidic environments with higher carbon conversion efficiencies.