MOF-Derived Bi/Bi₂O₃ Heterostructure on N-Doped Carbon: Synergistic Catalysis for CO₂ Electroreduction to Formate

The electrochemical reduction of CO₂ to formate represents a promising route for sustainable chemical production and carbon utilization. However, developing catalysts that combine high selectivity, activity, and stability under industrially relevant conditions remains a challenge. In this work, we report a high-performance electrocatalyst, synthesized by controlled pyrolysis of a Bi-metal-organic framework, yielding Bi/Bi₂O₃ nanoparticles embedded in a nitrogen-doped carbon matrix (Bi/Bi₂O₃/NC). The optimal catalyst, Bi/Bi₂O₃/NC-600, exhibits exceptional performance for the CO₂ reduction reaction, achieving a formate Faradaic efficiency of 97% at −0.9 V vs. RHE, and demonstrates remarkable stability, maintaining high selectivity during prolonged operation under high current densities in flow-cell and membrane electrode assembly configurations. Combined in situ spectroscopic characterization and density functional theory calculations reveal that grain boundaries stabilize a mixed-phase Bi³⁺/Bi⁰ interface under cathodic potentials. This unique interface optimizes the local electronic structure, facilitating charge transfer to the critical *COOH intermediate and significantly lowering the energy barrier for the potential-determining step. This work provides a rational design principle, leveraging synergistic metal/oxide interfaces within conductive heteroatom-doped carbons, to advance efficient and durable electrocatalysts for practical CO₂ electroreduction.