Abstract Subjecting a rhodium surface in base to repetitive triangular potential sweeps over the range 0 to 1.55 V (HE) resulted in the formation of a thick oxide film. The formation of this film occurred only in solutions of high pH and the rate of increase per cycle was observed to depend on such factors as hydroxide ion concentration, sweep limits, sweep rate, temperature, and the amount of oxide already present. Appreciable charge storage effects at about 1.37 V are attributed to a bulk redox process involving proton transfer within the oxide layer. The enhancement effect is discussed in terms of the formation of a non-protective, poorly adherent, oxide layer. A brief comparison is made between these results for rhodium in base and those reported earlier for iridium in acid.