Enhanced Fe(VI) cathode conductance and charge transfer: effects on the superiron battery

Cathodes comprising Fe(VI) salts are capable of three-electron reduction, and are useful for the formation of energetic `super-ironʹ batteries. Material additions to the Fe(VI) cathode can be used to enhance the conductance and the efficiency of charge transfer to the cathode, and control the characteristics of the electrochemical storage. Whereas several common carbons are ineffective as conductive matrices for Fe(VI) reduction, several others such as small particle (1 mu m) graphite, compressed carbon black, and fluorinated polymer graphites support efficient Fe(VI) 3e- reduction. Several inorganic salts also sustain Fe(VI) reduction, but at lower current densities. Titanates and other salts added to a K2FeO4 cathode improve the faradaic efficiency of Fe(VI) reduction at higher (~3 mA cm-2) discharge current densities. Fluorinated polymer graphites provide an unusual additive to the Fe(VI) cathode mix, and at a low level (10 wt.%) addition can support efficient Fe(VI) reduction.