Undulated Ni(II)-Framework with In Situ-Grafted Open-Metal and Basic Sites for High-Performance Electrochemical Water Oxidation and Flexible Composite-Driven Size-Exclusive Autotandem Catalysis
Nilanjan Seal, Arun Karmakar, Subrata Kundu, Subhadip Neogi
Abstract
Purpose-driven pore functionality engineering in metal–organic frameworks (MOFs) manifests the most attractive approach to pursue electrochemical water oxidation as a renewable energy source, whereas the MOF-composite-driven atom-economic reaction confers an eco-friendly attribute in the modern scientific era. We report an unprecedented integration of multiple active sites, including Lewis acid centers, free pyridine, and amine moiety, inside the pore wall of a thermochemically stable and undulated mixed-ligand Ni(II) framework. The plentiful accessible and divergent open-metal nodes containing activated MOFs display excellent oxygen evolution reaction (OER) in alkaline medium through the quasi-reversible Ni+2/Ni+3 couple and show electrocatalytic parameters ranging among the best-reported values. Apart from the low overpotential, the remarkable Tafel slope (35.4 mV/dec) outperforms those of benchmark electrocatalysts like RuO2, IrO2, and commercial Co3O4. Importantly, the threefold increased turnover frequency (0.696 s–1) compared to commercial NiO, 98% Faradaic efficiency, and sufficient durability after multiple OER cycles validate the high performance of the material. The trifunctionalized MOF further demonstrates mild-condition autotandem catalysis in alcohol oxidation-Knoevenagel condensation with broad substrate tolerance and multicyclic performance. The astutely designed control experiments confirm that highly synergistic acid–base tandem coupling transpires inside the microporous vessel, wherein the rarest molecular-dimension-mediated size selectivity is realized considering sterically encumbered alcohols. The in situ-grafted MOF inside melamine foam (MF) yielded MOF@MF as a reconfigurable smart composite that promotes this one-pot cascade reaction with comparable activity and reusability to that of the sole MOF, and demonstrates a paradigm shift toward futuristic sustainable catalysis over a real-life platform.