Pre-Organized Active Sites Strategy Steering a Bismuth-Based MOF Nanosheet for High-Efficiency Acidic CO2 Electroreduction.

Electrochemical reduction of CO2 to formic acid in acidic media offers a promising route to mitigate carbon loss, yet it remains challenging to design catalysts that effectively suppress the competing hydrogen evolution reaction and achieve industrial-level current densities under acidic conditions. Here, we demonstrate exfoliating a densely packed 3D pillar-layered bismuth-based metal-organic framework into ultrathin nanosheets, enabling efficient CO2-to-formic acid conversion. Remarkably, the removal of 1,4‑benzenedicarboxylate linkers during exfoliation leads to the exposure of the underlying dinuclear bismuth sites, which retain the original coordination site geometry. Mechanistic studies reveal that these exposed dinuclear sites exhibit intrinsic geometric compatibility with key intermediates (*CO2 or *OCHO), resembling the native carboxylate binding mode, thereby significantly lowering the Gibbs free energy barrier for intermediate formation. Concurrently, the modified electronic structure results in a reduced work function that facilitates electron transfer. As a result, the optimized catalyst achieves an industrial-relevant current density of 500 mA cm-2 with a formic acid Faradaic efficiency of 95%, doubling the performance of the bulk MOF and surpassing most reported catalysts. This work highlights a precise structural evolution strategy for creating geometrically optimized active sites, offering new insights into the design of efficient electrocatalysts for acidic CO2 reduction.