On the significance of hydroxide ion in the electro-oxidation of methanol on Ni

Electro-oxidation of methanol on Ni in NaOH solutions with the alkali concentration in the range of 0.05–0.5 M and in the presence of 0.5 M Na2SO4 supporting electrolyte is studied. All the mentioned species compete for adsorption on Ni and OH− is essential for the electro-oxidation process. The electro-oxidation seems to proceed through the electro-chemical reactions of adsorbed methanol and hydroxide species and the removal of the resulting intermediate by adsorbed hydroxyl groups. The mechanism is consistent with the cyclic voltammetry and impedance spectroscopy results and can semi-quantitatively account for the appearance of capacitive, inductive and negative resistance loops as well as Warburg lines in the Nyquist plots. No involvement of Ni2+/Ni3+ in the oxidation process at low and medium concentration of alkali was observed.