Water oxidation by a nickel complex: New challenges and an alternative mechanism

Water splitting toward hydrogen production is a promising way for energy storage. The catalytic role of the metal hydroxides formed by the decomposition of molecular catalysts toward oxygen-evolution reaction (OER) is a challenge in water-splitting systems. Recently, [Ni(TMC)(CH3CN)](NO3)2 (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, complex 1), was reported to be the most efficient nickel-based complex at neutral pH. In this study, the role of the formed Ni hydroxide-like nanosized species in the presence of this complex under oxygen-evolution reaction (OER) is studied by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectrometry, and electrochemical method. A new method for detecting trace Ni hydroxide-like nanosized species on the surface of an electrode is also reported, which is promising for the detection of heterogeneous nickel-based catalysts on the surface of an electrode. The experiments suggest that Ni hydroxide-like nanosized species formed during reaction is an alternative catalyst for OER.