Coordinatively Unsaturated Sites in Nanostructured Ni/Co Coordination Polymers for Alkaline Oxygen Evolution Reaction

Coordination polymers (COPs) have emerged as promising electrocatalysts owing to their well-dispersed metal active sites and the ability to modulate their catalytic activity through various activation strategies. This work reports the synthesis of two one-dimensional coordination polymers, namely, [Ni(L1)(4,4′-bpy)(H2O)2]n·L1 and[Co(L1)(4,4′-bpy)(H2O)2]n·L1, where L1 is 2-amino-5-nitrobenzoic acid and 4,4′-bpy is 4,4′-bipyridine, using a facile hydrothermal method. The molecular and crystal structures of the synthesized coordination polymers were determined by using single-crystal X-ray diffraction. The fully coordinated Ni and Co-COPs were investigated for the electrocatalytic oxygen evolution reaction (OER). To further enhance the electrocatalytic activity, a simple microwave-induced plasma etching process is applied to the synthesized COP, generating coordinatively unsaturated metal sites (CUMSs) without altering its phase or composition. The plasma-engineered COP reserves the bulk structure compared to pristine COP. The lattice-strained, noble metal-free Co-COP demonstrated superior electrocatalytic OER activity compared to RuO2 and Ni-COP, exhibiting a lower overpotential of 450 mV at 50 mA cm–2 (η50) and enhanced kinetics with a remarkably low Tafel slope of 56.5 mV dec–1. The development of lattice strain in the COP can inspire further microstructure tuning of COP for various applications.