Unlocking Pathway-Selective OER in a Self-Adaptive MOF-on-MOF Heterostructure toward Industrial-Level Alkaline Water Electrolysis

Understanding the intricate relationship between dynamic active site evolution and the pathway-selective oxygen evolution reaction (OER) is essential, yet it remains elusive. Herein, molecular-level integration of Ni-BDC (BDC = 1,4-benzenedicarboxylic acid) and Co-BPDC (BPDC = 4,4′-biphenyldicarboxylic acid) on Ni foam (NF) affords a self-adaptive bimetallic metal–organic framework (MOF)-on-MOF platform that enables dynamically responsive reconstruction into OER-active NiCoOOH/NF via real-time modulation of the coordination geometry at Ni–Co dual sites. Theoretical calculations and in situ spectroscopy uncover densely packed Ni–Co dual sites with shortened interatomic spacing in reconstructed NiCoOOH/NF, which facilitates the switching of the OER pathway from the adsorbate evolution mechanism (AEM) to the oxide pathway mechanism (OPM), thereby enabling spin-aligned O* intermediate formation and direct O–O* coupling for accelerated reaction kinetics. The resulting NiCoOOH/NF catalyst delivers an ultralow overpotential of 301 mV at 1 A cm–2 and maintains continuous operation beyond 1000 h. Upon integration into anion exchange membrane water electrolyzers (AEMWEs), it sustains a cell voltage of 1.77 V at 1 A cm–2 for durations exceeding 240 h. This work highlights a distinctive perspective on the fundamental mechanistic understanding of reconstructed catalysts.