Framework Excavation of UiO‐66 for In Situ Confined Cu 3 Cluster Assembly Toward Nitrite Electroreduction

ABSTRACT Heterogenizing molecular catalysts requires the simultaneous preservation of structural precision, active‐site accessibility, and long‐term stability. To address the limited capacity of robust small‐pore frameworks for molecular clusters and the susceptibility of large‐pore hosts to guest leaching and structural degradation, we propose a “Framework Excavation” strategy. This strategy selectively creates local enlargements within the microporous framework to generate sufficient space for the in situ formation of metal clusters, while the retained narrow channels kinetically confine the as‐formed clusters and allow substrates to pass through the pores to fully access the highly exposed cluster sites. As a demonstration, chemically stable UiO‐66 was engineered with missing‐Zr 6 ‐node defects and employed as a host for the ship‐in‐a‐bottle assembly of Cu 3 molecular clusters, yielding Cu 3 @UiO‐66‐Exc. In electrocatalytic nitrite reduction, Cu 3 @UiO‐66‐Exc achieves an NH 3 Faradaic efficiency of 98.7% and a yield rate of 19.21 mg cm −2 h −1 , with stable performance over 300 h of cumulative electrolysis. Mechanistic studies, including DMPO‐H spin‐trapping, in situ infrared spectroscopy and theoretical computations, reveal that the confined Cu 3 architecture promotes active‐hydrogen generation and successive hydrogenation of nitrogen‐containing intermediates. This work establishes a catalyst support design principle that enables the in situ generation, long‐term retention, and high site accessibility of molecular clusters within a robust microporous framework.