Role of Co ion in ionic covalent organic networks for boosting the electrocatalytic oxygen evolution reaction

The development of efficient and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for advancing sustainable energy conversion technologies. Herein, we report the design and synthesis of two novel hydrazide-linked ionic covalent organic networks, ABP-1 and ABP-2, constructed from a pyridinium-functionalized tri-carbohydrazide building block and bromo-methylated aromatic linkers. Post-synthetic metalation with Co(II) afforded Co-ABP-1 and Co-ABP-2, wherein the hydrazide moieties effectively chelate cobalt ions, ensuring stable immobilization within the porous ionic framework. Comprehensive structural characterization confirmed successful network formation, cobalt incorporation, and preservation of meso-porosity after metalation. Electrochemical investigations in alkaline medium (1.0 M KOH) revealed that cobalt incorporation significantly enhances OER performance compared to the pristine networks. Both Co-ABP-1 and Co-ABP-2 achieved a benchmark current density of 10 mA cm^-2 at an overpotential of ∼430 mV, accompanied by favourable Tafel slopes of 68 and 67 mV dec^-1, respectively, indicating improved charge-transfer kinetics. The enhanced activity is attributed to the synergistic interplay between redox-active Co(II) centers and the ionic porous architecture, which facilitates electrolyte diffusion, increases electrochemically active surface area, and promotes efficient electron transport. Notably, Co-ABP-2 exhibited higher double-layer capacitance and electrochemically active surface area, correlating with its superior catalytic performance. Furthermore, long-term electrolysis demonstrated good durability and appreciable faradaic efficiency under strongly alkaline conditions.