Synthesis and analysis of Ag2FeO4 Fe(VI) ferrate super-iron cathodes

The first IR spectra of Ag2FeO4 are presented, and compared to spectra of K2FeO4 and Ag2O. Ag2FeO4 is synthesized by dissolving K2FeO4 in aqueous Ag(I), and isolation of the precipitate. ICP analysis provides evidence of over 99% conversion from potassium to the silver salt, although chromite analysis indicates a 13% Fe(III) impurity in the Ag2FeO4 product. Ag2FeO4 is less stable than K2FeO4 or BaFeO4, at 0 °C falling in purity from 87% to 83% over a period of 1 week, and to 73% at 25 °C, although this instability may be an artifact of the higher Fe(III) impurity in the synthesized salt. Alkaline Zn anode/cathode cells are discharged. The measured Ag2FeO4 coulombic efficiency is less than that of other Fe(VI) cathodes, related to inhibition of charge transfer due to the Fe(III) impurity sites interspersed in the cathode.