In-situ Transformed Binuclear Co(II) and Ni(II) Complexes as the Electro-catalysts for Water Oxidation Reaction

Abstract

The metals (Co and Ni) coordinated three cationic complexes from transformed ligand, namely N, N-(amino(methoxy)(pyrimidin-2-yl)methyl)pyrimidine-2-carboxamide, which is produced from 2-cyanopyrimidine and hydroxyl-amine hydrochloride in in situ conditions under 3d metal mediation, that are the first report as dimeric water oxidation catalysts (WOC). From the single crystal X-ray data, both cobalt complex (1) and nickel complex (3) are homologous dinuclear cationic complexes with octahedral geometries with two chloride counter anions, but the cobalt complex (2) has a similar dimeric cationic complex structure with monomeric tetrahedral [CoCl4]2- anionic counterpart for balancing the overall charge of the complex (2). Electrochemical studies have been done for the three complexes, and comparisons have been made. However, Ni-analogue (3) has a specific activity of 104.4 mA/cm² at 1.60 V (vs. RHE), which is much greater than that of Co-analogues; 2 (54.79 mA/cm²) and 1 (37.95 mA/cm²). Meanwhile, mass activity of 3 at 1.6 V (vs RHE) is 74.73 mA/cm2, which is higher than that of 2 (32.7 mA/cm2) and 1 (17.81 mA/cm2). It is also established that the Ni analogue (3) exhibits superior oxygen evolution reaction (OER) activity compared to its Co analogues, with lower overpotential, smaller charge-transfer resistance, higher electrochemically active surface area, higher turnover frequency, and superior Faradaic efficiency.