Molten-Salt-Assisted Synthesis of Bismuth Catalysts with Rich Grain Boundaries for Efficient CO<sub>2</sub> Conversion to High-Purity Formic Acid.

Luo, Laihao; Gao, Qinlong; Wang, Haoyuan; Liu, Chunxiao; Ji, Yuan; Li, Xu; Jiang, Qiu; Zheng, Tingting et al. · Nano Lett · 2025

basic_science · Level V

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Abstract

Electrochemical CO<sub>2</sub> 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 CO<sub>2</sub>RR 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 CO<sub>2</sub> 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.