The electrochemical behavlour of nickel oxide was mvestlgated using, as a model system, nickel-supported hydrous oxide films produced by potential cycling m base The potentlal/pH response of such electrodes was examined under cychc voltammetry and open-circuit condltlons m a range of buffer solutions (pH 7 0 -13 5) As outlined previously, the cychc voltammetry data indicated the presence of both anhydrous and hydrous components m the layer -the former glvmg a potentlal/pH response of ca 59 mV/pH unit and the latter ca 88.5 mV/pH unit. Under open-crrcult condltlons, with relatively thick films m the half-charged state, z.e , [Nl(II)] = [Nr(III)] , the observed potentlal/pH response was cu 75 mV/pH unit. With cathodlcally deposited layers the change from a hydrous to an anhydrous potentlal/pH response was accompanied by a levellmg off of the charge storage capacitysuggesting that the hydrous material 1s more active with regard to charge acceptance Along with a thermodynamic interpretation of the unusual potentlal/pH behavlour of the hydrous material, and relating this to the known structures of these matenals, the mvolvement of hydrous oxide sites m electrocatalytlc processes at nickel oxide electrodes was demonstrated.