Amorphization and High-Entropy (Ni/Fe/Cu/Zn) Tuning over MIL-88(Co) Enable In Situ Irreversible Transformation of an Active CoOOH Layer toward Super Alkaline OER Efficiency

Conventional crystalline metal–organic frameworks (MOFs) have rigid, ordered frameworks that hinder structural reconstruction under OER conditions, resulting in limited exposure of active sites. To address these challenges, we develop an amorphous, high-entropy Co-based MOF (aHE-MOF) by atomically dispersing Fe, Ni, Cu, and Zn into MIL-88(Co) with the assistance of 2-methylimidazole (2-MeIM). The synergistic interactions of amorphous and high-entropy materials could tune the electronic structure and provide abundant defect sites, thereby inducing the uniform formation of catalytically active CoOOH phases to accelerate the OER kinetics. In situ studies reveal that the aHE-MOF irreversibly transforms into a CoOOH/aHE-MOF heterostructure under OER conditions, optimizing the d-band center of Co and intermediate adsorption. The reconstructed catalyst exhibits excellent OER activity in alkaline and simulated seawater electrolytes, achieving low overpotentials of 191 mV@10 mA·cm –2 and 333 mV@100 mA·cm –2 in alkaline freshwater, respectively, and remarkable long-term stability (∼100 h) with minimal performance decay. Operando Raman spectroscopy and DFT calculations confirm that the irreversible phase reconstruction and associated electronic modulation drive the enhanced OER performance.