2D Borophene Oxide Substrate for C ₂₊ Products Synthesis via CO ₂ Electroreduction at Industrial Current Densities

ABSTRACT

The industrialization of electrochemical CO ₂ 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 C ₂₊ 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 H ₂ 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 CO ₂ RR applications.