The influence of material dispersion on the redox behaviour of nickel oxide electrodes

The electrochemical behaviour of nickel oxide was investigated using, as a model system, nickel-supported hydrous oxide films produced by potential cycling in base. The potential/pH response of such electrodes was examined under cyclic voltammetry and open-circuit conditions in a range of buffer solutions (pH 7.0 – 13.5). As outlined previously, the cyclic voltammetry data indicated the presence of both anhydrous and hydrous components in the layer—the former giving a potential/pH response of ca. 59 mV/pH unit and the latter ca. 88.5 mV/pH unit. Under open-circuit conditions, with relatively thick films in the half-charged state, i.e., [Ni(II)] = [Ni(III)], the observed potential/pH response was ca. 75 mV/pH unit. With cathodically deposited layers the change from a hydrous to an anhydrous potential/pH response was accompanied by a levelling off of the charge storage capacity—suggesting that the hydrous material is more active with regard to charge acceptance. Along with a thermodynamic interpretation of the unusual potential/pH behaviour of the hydrous material, and relating this to the known structures of these materials, the involvement of hydrous oxide sites in electrocatalytic processes at nickel oxide electrodes was demonstrated.