Stabilized Alkaline Fe(VI) Charge Transfer

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 K 2 FeO 4 and Cs 2 FeO 4 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 ZrCl 4 through an organic medium by the conversion of ZrCl 4 to ZrO 2 . 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 BaFeO 2 , 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.