Molten-Salt-Assisted Synthesis of Bismuth Catalysts with Rich Grain Boundaries for Efficient CO₂ Conversion to High-Purity Formic Acid

Electrochemical CO2 reduction to formic acid, powered by renewable electricity, enables a sustainable carbon cycle by providing a versatile chemical feedstock and energy carrier. Bismuth-based catalysts are known for their high formate selectivity but face challenges in balancing selectivity and stability at industrial current densities. In this study, we present a two-step approach that combines molten-salt synthesis with in situ reduction to fabricate polycrystalline bismuth catalysts with rich exposed grain boundaries (GB-Bi). The GB-Bi catalysts demonstrate exceptional CO2RR performance, achieving a Faradaic efficiency exceeding 90% toward formate at ampere-level current densities. Spectroscopic evidence combined with theoretical calculations validated the role of grain boundaries in promoting CO2 adsorption and activation, thereby enhancing the overall catalytic performance. Moreover, when deployed in a solid-state electrolyte reactor, GB-Bi demonstrated outstanding stability, continuously producing a high-purity formic acid solution at -200 mA for over 210 h.