Electrocatalytic Oxidation of Methanol, Ethanol, and Glycerol on Ni(OH)₂Nanoparticles Encapsulated with Poly[Ni(salen)] Film

This study describes a systematic investigation of the electrocatalytic activity of poly[Ni(salen)] films, as catalysts for the electro-oxidation of Cn alcohols (Cn = methanol, ethanol, and glycerol) in alkaline medium. The [Ni(salen)] complex was electropolymerized on a glassy carbon surface and electrochemically activated in NaOH solution by cyclic voltammetry. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy results indicate that during the activation step the polymeric film hydrolyzes, leading to the formation of β-Ni(OH)2 spherical nanoparticles, with an average size of 2.4 ± 0.5 nm, encapsulated with the poly[Ni(salen)] film. Electrochemical results obtained together with the in situ Fourier transform infrared spectroscopy confirm that the electro-oxidation of methanol, ethanol, and glycerol occurs by involving a cycling oxidation of β-Ni(OH)2 with the formation of β-NiOOH species, followed by the charge transfer to the alcohols, which regenerates β-Ni(OH)2. Analyses of the oxidation products at low potentials indicate that the major product obtained during the oxidation of methanol and glycerol is the formate, while the oxidation of ethanol leads to the formation of acetate. On the other hand, at high potentials (E = 0.6 V), there is evidence that the oxidation of Cn alcohols leads to carbonate ions as an important product.