Atmosphere-directed reconstruction of Cu-based metal-organic frameworks toward efficient CO₂ electroreduction

The electrochemical reconstruction of metal-organic frameworks (MOFs) offers a promising approach for in situ fabrication of high-performance electrocatalysts. However, this innovation is often hindered by unpredictable structural transformations due to the complex thermodynamic and kinetic interplay of such multiple electrochemical and chemical processes. Herein, the reaction-atmosphere (Ar or CO₂) guided reconstruction of Cu-based MOFs to Cu nanoparticles with mixed-valence surfaces/interfaces was investigated for the first time to unravel the kinetic contribution made by intermediate chemisorption. As shown, Cu-1,3,5-benzenetricarboxylate (HKUST-1) with frangible Cu-O₄ nodes undergoes thermodynamically favored reduction quickly upon applying cathodic potentials, followed by varied surface changes kinetically governed by the intermediates of the hydrogen evolution reaction or CO₂ reduction reaction (HER or CO₂RR). Under an Ar atmosphere, the predominant HER increases the [OH^-] in the microenvironment near the cathode and thereby boosts the re-oxidation of in situ formed Cu toward Cu/Cu₂O interfaces. Conversely, the CO₂RR facilitates the strong adsorption of *CO on Cu surfaces, effectively preserving Cu(0) species. Thanks to the rich Cu/Cu₂O interfaces with a lowered energy barrier for *CO-*CO coupling during the subsequent CO₂RR test, the electrocatalysts restructured under Ar afford the obviously improved CO₂-to-C₂H₄ conversion as compared with their counterparts restructured under CO₂. Such an atmosphere-controlled reconstruction strategy is further validated using CuBDC (BDC = 1,4-benzenedicarboxylate) with labile Cu-O₄ nodes, while CuPz₂ (Pz = pyrazole), with robust Cu-N₄ coordination, remains stable, highlighting the framework-dependent nature. These findings establish atmosphere-controlled reconstruction of metastable MOFs as a powerful tool for rational electrocatalyst design.