Achieving satisfactory multi-carbon (C₂₊) products selectivity and current density under acidic condition is a key issue for practical application of electrochemical CO₂ reduction reaction (CO₂RR), but is challenging. Herein, we demonstrate that combining microenvironment modulation by porous channel structure and intrinsic catalytic activity enhancement via doping effect could promote efficient CO₂RR toward C₂₊ products in acidic electrolyte (pH ≤ 1). The La-doped Cu hollow sphere with channels exhibits a C₂₊ products Faradaic efficiency (FE) of 86.2% with a partial current density of −775.8 mA cm⁻². CO₂ single-pass conversion efficiency for C₂₊ products can reach 52.8% at −900 mA cm⁻². Moreover, the catalyst still maintains a high C₂₊ FE of 81.3% at −1 A cm⁻². The channel structure plays a crucial role in accumulating K⁺ and OH^- species near the catalyst surface and within the channels, which effectively suppresses the undesired hydrogen evolution and promotes C–C coupling. Additionally, the La doping enhances the generation of *CO intermediate, and also facilitates C₂₊ products formation.

The optimal Cu oxidation state during CO ₂ reduction is stabilized and identified by applying a pulsed potential, which shows a C ₂₊ FE of 70.3% with a current density of 24.1 mA cm ⁻² in an H-type cell.

The electrocatalytic reaction pathway is highly dependent on the intrinsic structure of the catalyst. CO₂/CO electroreduction has recently emerged as a potential approach for obtaining C₂₊ products, but it is challenging to achieve high selectivity for a single C₂₊ product. Herein, we develop a Cu atomic ensemble that satisfies the appropriate site distance and coordination environment required for electrocatalytic CO-to-acetate conversion, which shows outstanding overall performance with an acetate Faradaic efficiency of 70.2% with a partial current density of 225 mA cm^-2 and a formation rate of 2.1 mmol h^-1 cm^-2. Moreover, a single-pass CO conversion rate of 91% and remarkable stability can be also obtained. Detailed experimental and theoretical investigations confirm the significant advantages of the Cu atomic ensembles in optimizing C-C coupling, stabilizing key ketene intermediate (*CCO), and inhibiting the *HOCCOH intermediate, which can switch the CO reduction pathway from the ethanol/ethylene on the conventional metallic Cu site to the acetate on the Cu atomic ensembles.