2D Borophene Oxide Substrate for C₂₊ Products Synthesis via CO₂ Electroreduction at Industrial Current Densities

The industrialization of electrochemical CO₂ reduction reaction for multi-carbon products synthesis is limited by HER competition, sluggish C─C coupling kinetics, and carbonate deposition. Through rational computational screening, we identify β-rhombohedral borophene oxide (β-rh. BO) as an ideal two-dimensional substrate to simultaneously overcome these bottlenecks. Evaluated in a flow cell with 1 M KOH electrolyte, the β-rh. BO-supported Cu (BO-Cu) demonstrates outstanding performance across an industrially relevant current density range of -700 to -1500 mA cm^-2, achieving a peak C₂₊ Faradaic efficiency (FE) of 85.9% and a partial current density exceeding -1082 mA cm^-2. Mechanistic studies reveal that β-rh. BO serves a role beyond an electron donor. Specifically, it redistributes hydrated K⁺ and alters the interfacial water structure, which not only suppresses HER by diverting proton transfer toward *CO hydrogenation rather than H₂ evolution, but also enables the transformation of symmetric C─C coupling to asymmetric C─C coupling via modulating the charge distribution of intermediates. Furthermore, the introduction of β-rh. BO drastically reduces carbonate deposition. This work presents a novel multifunctional substrate that synergistically modulates the electronic structure, tailors interfacial water structure, and suppresses carbonate deposition, offering a new paradigm for the design of electrocatalysts for industrial CO₂RR applications.