Unlocking Synergistic Ligand–Metal Interplay in Dual Redox-Active Metal–Organic Framework for High-Efficiency and Durable Overall Water Splitting

The development of bifunctional electrocatalysts that efficiently operate for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in a single electrolyte under high current density remains a critical challenge toward applied overall water splitting. Herein, we designed a robust and microporous Co(II)-based nonpenetrating metal–organic framework (MOF) via juxtaposition of redox-active naphthalenediimide linker and π-electron rich C 2 -symmetric dicarboxylate ligand that features in situ-generated [Co 2 (COO) 4 ] chain and exhibits high thermo-chemical stability. The efficient charge-mediating architecture upon interface engineering with conductive nickel foam (NF) delivers remarkable bifunctional water splitting activity in an alkaline medium (1 M KOH), achieving an industrially relevant current density of 100 mA·cm –2 with low overpotentials of 313 mV (OER) and 263 mV (HER). Importantly, rapid reaction kinetics, minimal charge-transfer resistance, and >95% Faradaic efficiency outperform the majority of contemporary as well as benchmark materials. The catalyst demonstrated excellent electrochemical durability in both water oxidation and reduction reactions for over 40 h and retains its structural and morphological attributes after prolonged chronoamperometric operation, demonstrating high-performance water splitting. Performance comparison with an isostructural Cd-MOF analogue confirms the essential contribution of ligand–metal synergism in the Co-MOF for much enhanced redox articulation and electrocatalysis. When deployed as both electrodes, the bifunctional MOF/NF system efficiently catalyzes overall water splitting with only 1.678 V cell voltage at 10 mA·cm –2, marking it among the leading MOF-based electrocatalysts. The findings highlight the pivotal role of ligand–metal cooperativity and hierarchical interface engineering in boosting the electrochemical efficacy of MOF catalysts and provide a promising strategy in designing next-generation bifunctional electrocatalysts for sustainable energy applications.