Electrocatalytic Oxygen reduction properties of a trinuclear Cobalt complex with a Pyridine-based pincer ligand: Synthesis, structural characterization, and mechanistic insights

Abstract

Clean energy systems like fuel cells and metal–air batteries require efficient, earth-abundant oxygen reduction reaction (ORR) catalysts. Platinum (Pt) alloys are effective yet expensive and scarce, prompting the hunt for alternatives. Molecular complexes, especially those incorporating 3d transition metals, are interesting due to their well-understood structures and controllable characteristics. This work examines the coordination chemistry of a novel pentadentate ligand, 2,2′-[{(1E,1′E)-pyridine-2,6-diyl-bis(methaneylylidene)bis(azaneylylidene)} diphenol (LH2), with cobalt perchlorate (Co(ClO4)2·XH2O) in acetonitrile. The trinuclear coordination complex [Co3(L)2(CH3CN)5]·2ClO4 (1) was described by single crystal X-ray diffraction, revealing a monoclinic system and deformed trigonal bipyramidal geometry around cobalt(II) centers. Complex 1 has strong electrocatalytic activity for ORR, with an onset potential of 0.52 V and a Tafel slope of 136 mV dec⁻¹. This electrocatalytic process was explained using density functional theory (DFT) calculations, which showed a multi-step reaction pathway begun by oxygen adsorption. The results show that electrical and geometric parameters improve catalytic efficiency, providing essential insights for developing improved materials for electrochemical applications. This work goes beyond fundamental coordination chemistry to create more efficient catalysts that improve energy conversion and storage reaction kinetics and stability.