A Redox-Active 1D Co(II) Coordination Polymer and Its Ni-Composite: Structure, Surface Characterization, and Application in the Water Splitting Reaction

Energy is at the heart of a sustainable society; with increasing focus on noncarbon (non-C) energy sources, hydrogen (H₂) fuel is the center of attraction as a clean alternative. Among emerging technologies, electrocatalytic water splitting, especially the oxygen evolution reaction (OER), plays a crucial role in sustainable H₂ production. In line with Sustainable Development Goals (SDGs), coordination polymers (CPs) have attracted consideration due to their flexible porosity, high surface area, redox-active metal centers, and structural stability, making them promising OER catalysts. Herein, we report a redox-active Co(II)-based coordination polymer (Co-CP), synthesized using the unsymmetrical bridging ligand (<i>E</i>)-<i>N</i>-(pyridin-4-ylmethylene)-4H-1,2,4-triazol-4-amine (<b>pmta</b>) and terminal carboxylate ligand 2,5-thiophenedicarboxylate (<b>tda</b>^<b>2</b>^-). The Co-CP exhibits electrocatalytic OER activity in an alkaline medium. To check the performance of OER activity, Ni²⁺ has been incorporated into the Co-CP framework, to form Ni@Co-CP composites. Optimized OER efficiency is observed for Ni-2@Co-CP, which shows stability of the crystalline framework upon nickel incorporation even under strenuous experimental conditions and exhibits an overpotential of 290 mV at 10 mA cm^-2, a Tafel slope of 35 mV dec^-1, and a charge transfer resistance of 6.97 Ω. The strategic incorporation of extraneous metal ions into CP frameworks offers a versatile approach for designing advanced electrocatalysts. Such materials not only show great promise for OER but also hold potential for broader energy conversion and storage applications.