Amorphous BiSn _x O _y for Efficient CO ₂ Electroreduction to Formate via In Situ Doping

The practical implementation of electrochemical CO₂ reduction to formate has been limited by persistent issues concerning product selectivity, operational current density, and long-term stability. To address these challenges, we developed an amorphous BiSn_xO_y precatalyst capable of overcoming conventional activity-stability compromises, enabling efficient and durable formate production at industrially relevant current densities. The amorphous structure exhibits significantly reduced oxygen vacancy formation energy compared to its crystalline counterpart, facilitating rapid structural transformation under electrocatalytic conditions. Remarkably, this catalyst demonstrates exceptional performance, achieving a Faradaic efficiency (FE_Formate) of 95.6% at 800 mA cm^-2 in a flow cell, maintaining stable operation at 500 mA cm^-2 in a membrane electrode assembly (MEA) electrolyzers, and delivering an FE of 92.3% for over 160 h at 200 mA cm^-2. We further validated the practical applicability by integrating the catalyst into a solar-powered MEA system for sustainable formate generation. Through comprehensive in situ spectroscopic characterization and density functional theory (DFT) calculations incorporating crystal orbital Hamilton population (COHP) analysis, we elucidate that Sn incorporation tailors the electronic configuration of Bi sites, optimizing the binding of the crucial *OCHO intermediate for selective formate formation. This work establishes a dynamic catalyst paradigm that transcends classical activity-stability tradeoffs, charting an atom-efficient pathway for industrial CO₂ valorization using renewable energy.