Superiron cathodes, consisting of unusual Fe(VI) particles, are substantially stabilized with a low-level zirconia coating, which improves the experimental energy storage capacity of alkaline superiron batteries. Fe(VI) cathodes sustain three-electron alkaline reduction at a single, energetic [0.60 V vs standard hydrogen electrode (SHE)] potential. Superiron cathode salts such as K2FeO4 and Cs2FeO4 are stable in the solid state but tend to be passivated in alkaline electrolyte due to the formation of an Fe (III) overlayer. A zirconia coating is derived from ZrCl4 through an organic medium by the conversion of ZrCl4 to ZrO2. The zirconia coating shuttles hydroxide through to the interior cathode material, sustains a high rate of alkaline cathode charge transfer in the redox reduction of Fe(VI) to Fe(III) redox reduction, and inhibits Fe(III) passivation. The zirconia coating effectively enhances the stability of these superiron cathodes. However, for an Fe(VI) salt, which is not stable in the solid state, such as BaFeO2, an applied zirconia coating is not observed to stabilize alkaline cathodic charge transfer. Small particle and solid KOH and AgO additives each are observed to improve Fe(VI) cathodic charge transfer and enhance accessible Fe(VI) gravimetric capacity. (c) 2007 The Electrochemical Society.