The application of a nickel( ii ) Schiff base complex in water oxidation: the importance of nanosized materials

Herein, the role of Ni oxide in the electrocatalytic water oxidation of a nickel( ii ) Schiff base ( N , N ′-bis (salicylidene)ethylenediamino nickel( ii )) is investigated using scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, nuclear magnetic resonance spectroscopy, extended X-ray absorption fine structure, X-ray absorption near edge structure, chronoamperometry, electrochemical methods and theoretical calculations. Although Ni oxide does not have a pure, simple and crystalline structure, the experiments showed that Ni oxide at a pH of 11 is a water-oxidizing catalyst on the surface of a fluorine-doped tin oxide electrode. At pH 3 or 7, no clear water oxidation or NiO x formation was detected. Below this low pH, a solid with high carbon content was detected, which is not a water-oxidizing catalyst. A metal oxide-based mechanism for water oxidation in the presence of a metal complex has not been considered using theoretical calculations. Herein, our theoretical calculations indicated that after the oxidation of the Ni( ii ) complex, all Ni equatorial bonds in the oxidation state of III were weakened. This effect may cause the decomposition of the intermediate to NiO x . This study could be very promising for the design and synthesis of new, efficient and stable catalysts.