Electrocatalytic Water Oxidation by Ni(II) Complexes of Tridentate Differently Substituted Hydrazine-1-carbothioamides: Synthesis and Structural Characterizations

Herein, we reports the synthesis of 2-benzoylpyridine-derived ligands with two different substituents, namely, N-(4-chlorophenyl)-2-(phenyl(pyridin-2-yl)methylene)hydrazine-1-carbothioamide (HClPhBHCT) and N-(4-methylphenyl)-2-(phenyl(pyridin-2-yl)methylene)hydrazine-1-carbothioamide (HMPhBHCT) and their corresponding Ni(II) complexes [Ni(ClPhB)Cl] and [Ni(MePhB)Cl], respectively. They are characterized using spectroscopic methods, single-crystal X-ray diffraction, and cyclic voltammetry. Subsequently, these nickel complexes were employed for the oxygen evolution reaction (OER) under alkaline conditions. Among the two complexes, [Ni(MePhB)Cl] delivers a current density of 10 mA cm^–2 at the lowest overpotential of 330 mV with a Tafel slope of 71 mV dec^–1. The complex undergoes electrochemical anodic activation to form a [Ni(MePhB)Cl]/Ni(O)OH interface acting as an active catalyst, as established by the spectroscopic and electrochemical characterizations. The vast electrochemically active surface area and, consequently, large number of active sites of [Ni(MePhB)Cl] may be responsible for its remarkable performance. In addition to its strong OER activity, [Ni(MePhB)Cl] showed outstanding long-term stability on continuous operation, supporting its potential use in commercial systems.