Isomorphous Cobalt Coordination Frameworks: Enhancing Electrocatalytic Oxygen Evolution Reaction through Coordinated Solvent Variations

Abstract

Oxygen evolution reaction (OER) is a key electrochemical redox reaction involved in metal–air batteries and water-splitting devices. Reducing the energy barrier of these reactions accentuates the necessity in designing competent electrocatalysts. There is an urgent demand for affordable and durable catalysts utilizing non-noble metals, specifically Ni, Co, and Fe, for the OER. In this context, three following cobalt(II) coordination frameworks based on a pyridyl carboxylic acid ligand were synthesized: [Co₃(μ₃-OH)(PCA)₄(DMF)₂(H₂O)](NO₃)·DMF·3H₂O (1), [Co₃(μ₃-OH)(PCA)₄(EtOH)₃](NO₃)·3EtOH·3H₂O (2), and [Co₃(μ₃-OH)(PCA)₄(DMA)₂(H₂O)] (ClO₄)·DMA·H₂O) (3) using a solvothermal method. The single-crystal diffraction studies confirm the similarity in the three-center cobalt secondary building unit (SBU) and the final 3D topology. These frameworks are investigated as potential catalysts for the OER under alkaline (1 M KOH) conditions. Compound 1 shows extraordinary OER activity demonstrating an overpotential value of 0.37 V at 10 mA cm^–2 and a Tafel slope of 78.9 mV. The alternation in the coordination sphere resulting from the difference in coordinated solvent emerges as an intriguing reason contributing to the exceptional activity of a coordination network. The effective electronic modulation within the cobalt trinuclear center induced by the changes in the coordination sphere has lowered the free energy barrier for the desorption of the oxygen produced. This work emphasizes the significant influence and effect of the coordination environment in catalytic activity, serving as a template for designing advanced electrocatalysts that are free from noble metals.