Synthesis of Novel Organic Ni (II) N-isonicotinoylhydrazine-Carbothioamide Complexes and their Application in the Oxygen Evolution Reactions

The five novel nickel organic complexes featuring different electron-rich and electron-deficient groups were synthesized as electrocatalysts by using N-(aryl/alkyl)-2-isonicotinoylhydrazine-1-carbothioamide compounds in coordination with nickel acetate tetrahydrate and 1,10-phenanthroline. These Ni-complexes were characterized using infrared and Raman spectroscopy and were subsequently employed for the oxygen evolution reaction (OER) in water splitting under alkaline conditions. The overpotential and Tafel slope for Ni-based complex Ni-1 were as low as 454 mV and 111.90 mV dec-1, respectively, at a current density of 10 mA cm-2, indicating excellent electrochemical performance. Furthermore, Ni-1 demonstrated good electrochemical stability, with only minor voltage fluctuations observed during the continuous bubble generation over a 40 hours electrolysis period and nickel maintains a +2 oxidation state (Ni2+) in the complex both before and after the OER test via characterization of N2p spectra by X-ray photoelectron spectroscopy (XPS) measurements. This study confirms the electronic effect of substituent groups on the water-splitting ability of Ni-complexes bearing the two different organic ligands, showing that the overpotential and Tafel slope increase with a decrease in the electron-donating capacity of the substituent groups.