Water oxidation through electrocatalytic process using cobalt and nickel complexes of thiazole Schiff-base ligands.

Ni(OAc) 2.4H 2 O and CoCl 2.6H 2 O reacted with thiazole ligands, HL and HL' (where HL= (E)-2-(((4-phenylthiazol-2-yl)imino)methyl)phenol and HL'= (Z)-2-(2-benzylidenehydrazinyl)-4-phenylthiazole, in ethanol to create new mononuclear Co(II) and Ni(II) complexes, CoL 2 , NiL 2 , CoL' 2 , and NiL' 2 (1 - 4). X-ray diffraction analysis, spectroscopic, and electrochemical methods were used to study the complexes. A carbon paste electrode that had been modified by complexes 1 - 4 was used as the working electrode in a three-electrode setup to test the complexes' ability in water oxidation reaction at pH 13. The linear sweep voltammetry (LSV) curves showed that complexes 3 and 2 have much greater activity and only require the overpotential of 570 and 690 mV ʋs. RHE at a current density of 10 mA/cm2 with Tafel slopes of 86.92 and 94.19 mVdec−1 respectively in an alkaline solution. In addition, the amperometry tests exhibited brilliant stability for water oxidation by CPE-complex 3 and CPE-complex 2 under electrochemical conditions at pH 13. Although X-ray diffraction patterns did not display a crystalline structure, the scanning electron microscopy images displayed that cobalt oxide and nickel oxide in an alkaline condition are proper catalysts for water oxidation reaction on the surface of the modified electrode. • We synthesized new thiazole Schiff base complexes of Co(II) and Ni(II). • These complexes can catalyze the oxidation of water in alkaline solution electrochemicaly. • Two of the complexes showed significantly higher activity by lowering Tafel slopes and overpotentials. • The surfaces of working electrodes modified by complexes are confirmed to have amorphous cobalt and nickel oxides by EDX and XRD analysis. [ABSTRACT FROM AUTHOR]