The open-circuit, cathodic reduction and anodic charging characteristics of oxide films on both electropolished and electropolished + HNOS etched nickel electrodes have been studied in aqueous Na,SO, solutions. While the oxide film thicknesses are approximately the same, the film on etched nickel dissolves much more rapidly than that on elcctro&ishcd nickel. To ualvanostatically passivate etched nickel at charging rates in the range 2&200 fi cm" in pH 2.8 Na,SO,ythe rate ofoxide &emical dissolution has to be substantially dccrcascd and this is achieved by lowering the electrol$te temperalure from 25" C 10 S'C. The transient anodic passivation charge thus observed for etched nickel is -2x larger than that for eicctropolished nickel. With either pretreatment, the current efficiency for oxide formation is low ( --20%), the majority of the transient charge (-SO-/d accounted for by Ni'+ in solution. Chemical dissolution of the oxide alone cannot expKi the observed charging differences between etched and elcctropolished nickel since the individual charges and oxide formation eurrent efliciencies are not influenced by ano& charging rate or solution aggressiveness. The rcaulte are best explained in tcms of a continual breakdown and repair of the oxide film at defect areas during anodic charging, with most of the charge consumed by ine&icnt film repair. The influence of the oxide defects and the reason for the differences in behaviour between clectropolishcd and etched niclcel are discussed.