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

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.