Boron-Doped Carbon Coatings Stabilize Cu⁺/Cu⁰ Interfaces to Promote Multicarbon Formation in CO₂ Electroreduction

The construction of a stable Cu⁺/Cu⁰ reaction interface is a promising yet challenging strategy for the electrosynthesis of multicarbon (C₂₊) products from CO₂ reduction. Herein, we report a dual-phase Cu₂O/Cu catalyst encapsulated by boron (B)-doped carbon coatings (BC), denoted as Cu₂O(Cu)@BC. In a flow cell system with 1 M KOH electrolyte, this catalyst delivers a maximum C₂₊ Faradaic efficiency of 83.4% at -0.7 V versus the reversible hydrogen electrode (RHE) and a partial C₂₊ current density of 460 mA cm^-2 at -0.9 V versus RHE, while maintaining stable operation for over 42 h. This performance surpasses that of its counterpart without the BC coatings and other Cu-based catalyst systems. Comprehensive experimental investigations reveal that the BC coatings facilitate the formation of Cu⁺ species with higher oxidation states and stabilize the Cu⁺/Cu⁰ interface under reductive conditions. The resulting abundant and stable interfacial sites significantly increase *CO intermediate surface coverage, facilitating carbon-carbon coupling and promoting the formation of the key *OCH₂CH₃ intermediate for C₂₊ production. This work offers an effective strategy to maintain a high density of Cu⁺/Cu⁰ interfacial active sites and provides deeper insights into the stabilization and degradation mechanisms of Cu-based catalysts for efficient electrochemical CO₂-to-C₂₊ conversion.