Engineering Stable CO ₂ -to-Formic Acid Electrocatalysis: Individual Ultrathin Bismuth-Assembled Nanosheets for Long-Term Operation in Solid-Electrolyte Electrolyzers

Developing electrocatalysts that combine high efficiency with long-term stability for CO2 reduction to formic acid remains a significant challenge, especially at industrial-scale current densities. Here, we report individual ultrathin bismuth-assembled nanosheets (Bi-INS) synthesized via a triethanolamine (TEA)-directed solvothermal method. The coordinating role of TEA guides the two-dimensional assembly of a basic bismuth carbonate precursor, effectively suppressing nanosheet stacking. This unique architecture provides abundant accessible active sites and accelerates interfacial charge transfer and intermediates adsorption. Consequently, Bi-INS achieves a peak formate Faradaic efficiency (FE) of 90% and maintains an FE above 80% over a broad potential range. In a solid-electrolyte membrane electrode assembly electrolyzer, the catalyst demonstrates exceptional durability for producing formic acid solution, operating stably for 300 h at 100 mA·cm−2 with an average FE of 82.6%. This work demonstrates that surfactant-assisted structural regulation is a robust strategy for designing scalable and durable catalysts for industrial CO2 electrolysis.