Supramolecular Metal-Organic Framework Electrocatalysts with Hydration-Adaptive Gallery Expansion and Linker-Mediated Distal Ni-Co Cooperation Enable Framework-Retentive Oxygen Evolution

Atomic‑level tailoring of electronic communication between spatially separated metal sites offers a route to accelerate multielectron electrocatalysis. We report Ni-TPTC, Co-TPTC, and heterobimetallic Ni-Co-TPTC supramolecular metal-organic frameworks (SMOFs) for the oxygen evolution reaction (OER) built from a terphenyl‑tetracarboxylate (TPTC) linker. Single‑crystal X‑ray diffraction of Ni-TPTC reveals trans‑bis‑aqua octahedral chains assembled into a π‑stacked, hydrogen‑bonded lattice, and powder X‑ray diffraction shows that the Co and Ni/Co analogues are isostructural. In 1.0 M KOH, Ni-Co-TPTC reaches 20 mA cm−2 at 350 mV overpotential and maintains operation at ~60 mA cm−2 for 45 h with modest decay to ~85% of the initial current. Time‑dependent ex-situ diffraction shows dominant framework reflections with low‑angle shifts consistent with gallery dilation (d‑spacing ~7.7 → ~9.2 Å) at early times, while Co K‑edge X‑ray absorption and microscopy reveal Co‑rich oxide/oxyhydroxide‑like domains at longer times that correlate with decay. X‑ray photoelectron spectroscopy, quantified by the Remote Binding‑Energy Differential, tracks composition‑dependent Ni-Co polarization, and DFT free‑energy analysis suggests that a model Ni-Co environment lowers the Co‑centered potential‑limiting step by ~0.24 eV relative to the Co‑only framework. These results suggest that framework‑retentive expansion and distal Ni-Co coupling can drive OER activity before gradual deligation and oxide formation mark longer‑time degradation.