Understanding the structural and chemical changes that reactive metal–organic frameworks (MOFs) undergo is crucial for the development of new efficient catalysts for electrochemical reduction of CO₂. Here, we describe three Bi(III) materials, MFM-220, MFM-221 and MFM-222, which are constructed from the same ligand (biphenyl-3,3′,5,5′-tetracarboxylic acid) but which show distinct porosity with solvent-accessible voids of 49.6%, 33.6% and 0%, respectively. We report the first study of the impact of porosity of MOFs on their evolution as electrocatalysts. A Faradaic efficiency of 90.4% at −1.1 V vs. RHE (reversible hydrogen electrode) is observed for formate production over an electrode decorated with MFM-220-p, formed from MFM-220 on application of an external potential in the presence of 0.1 M KHCO₃ electrolyte. In situ electron paramagnetic resonance spectroscopy confirms the presence of ·COOH radicals as a reaction intermediate, with an observed stable and consistent Faradaic efficiency and current density for production of formate by electrolysis over 5 h. This study emphasises the significant role of porosity of MOFs as they react and evolve during electroreduction of CO₂ to generate value-added chemicals.

中文翻译：

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用于高效电还原 CO2 的铋基金属有机框架的演变

了解反应性金属有机框架 (MOF) 所经历的结构和化学变化对于开发用于电化学还原 CO ₂的新型高效催化剂至关重要。在这里，我们描述了三种 Bi( III ) 材料，MFM-220、MFM-221 和 MFM-222，它们由相同的配体（联苯-3,3',5,5'-四羧酸）构成，但表现出不同孔隙率分别为 49.6%、33.6% 和 0%。我们首次研究了 MOF 的孔隙率对其作为电催化剂的演变的影响。-1.1 V 时的法拉第效率为 90.4 %在用 MFM-220-p 装饰的电极上，在 0.1 M KHCO ₃电解质存在下施加外部电位时，观察到 RHE（可逆氢电极）用于甲酸盐的生产，该电极由 MFM-220 形成。原位电子顺磁共振光谱证实了 ·COOH 自由基作为反应中间体的存在，在 5 小时内通过电解生产甲酸盐具有稳定且一致的法拉第效率和电流密度。本研究强调了 MOF 孔隙率的重要作用，因为它们在 CO ₂电还原过程中反应和演化以产生增值化学品。