The chemistry of the Fe(VI) compound, K2FeO4, was investigated in aqueous potassium hydroxide electrolyte for its potential use in secondary storage systems. High charge storage K2FeO4 material was synthesized using alkaline hypochlorite oxidation of ferric nitrate and characterized by in situ X-ray diffraction and Mossbauer spectroscopy. The discharge-charge profile of the cathode, measured vs. a zinc anode, was semiquantitatively correlated with changes in Fe6+/Fe3+ ratio and the nature of structural transformation at each stage by in situ Mossbauer and in situ synchrotron X-ray diffraction spectroscopy. The data in conjunction with the charge-discharge profile clearly indicates the rechargeability of K2FeO4 with a charge efficiency of about 36% of the total current passed under the prevailing experimental conditions. These results are potentially important to the design of Fe6+ compound analogs for use in secondary energy storage systems. (C) 2003 The Electrochemical Society.