Ni(II)-Based Coordination Polymer with Pi-Conjugated Organic Linker as Catalyst for Oxygen Evolution Reaction Activity

Coordination polymers (CPs) based on transition metals have immense importance as electrocatalysts due to their diverse chemical structures coupled with redox-active metal centers. Among the earth-abundant transition metals, Ni(II) has huge importance as oxygen evolution reaction (OER) electrocatalyst owing to its high electrical conductivities, low cost, and most importantly, ability to exist in multiple oxidation states. In this report, a new Ni(II)-based CP [Ni(MCA)(bipy)(H2O)2]n denoted as CP 1 (H2MCA = mesaconic acid, bipy = 4,4′-bipyridine) was prepared by a solvothermal method. The crystal structure analysis revealed that CP 1 has a two-dimensional structure having 8 Å × 12 Å rectangular channels. For comparison purposes, we have also synthesized another CP formulated as {[Ni(bipy)3(H2O)2]·(bipy)·(ClO4)2} CP 2 and tried to clarify the role of the coordinated mesaconate linker in OER. The developed CPs were directly utilized as OER catalysts in alkaline solution. The bi-linker CP 1 shows a higher OER activity compared to mono-linker CP 2 and requires an overpotential of 530 mV at a current density of 10 mA cm–2. This indicates that the additional pi-conjugated organic linker mesaconic acid in CP 1 eases the formation of NiOOH species, which enhances the OER activity.