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

The electrochemical reconstruction of metal-organic frameworks (MOFs) offers a promising approach for 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 CO) 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-O 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 CO reduction reaction (HER or CORR). Under an Ar atmosphere, the predominant HER increases the [OH] in the microenvironment near the cathode and thereby boosts the re-oxidation of formed Cu toward Cu/CuO interfaces. Conversely, the CORR facilitates the strong adsorption of *CO on Cu surfaces, effectively preserving Cu(0) species. Thanks to the rich Cu/CuO interfaces with a lowered energy barrier for *CO-*CO coupling during the subsequent CORR test, the electrocatalysts restructured under Ar afford the obviously improved CO-to-CH conversion as compared with their counterparts restructured under CO. Such an atmosphere-controlled reconstruction strategy is further validated using CuBDC (BDC = 1,4-benzenedicarboxylate) with labile Cu-O nodes, while CuPz (Pz = pyrazole), with robust Cu-N 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.