Stabilization of iron(VI) ferrate cathode materials using nanoporous silica coatings

Ferrate salts containing Fe (VI) have received attention as cathode materials in recent years due to their theoretical ability to accept three electrons while being reduced to Fe (III). Unfortunately, ferrate salts are also somewhat unstable, particularly when stored at elevated temperatures or in the presence of an alkaline electrolyte. In this paper, we document the stability of solid barium and potassium ferrate salts under various environmental conditions and report on the use of SiO2 thin-film coatings to stabilize cathodes composed of solid barium ferrate. The nanoporous coatings are deposited from colloidal silica suspensions using sol-gel techniques. The enhanced stability of coated ferrates is demonstrated, and their discharge performance is characterized relative to uncoated materials. The coating technique employed may be applicable to other nanoparticulate metal oxide chemistries, thus presenting a possible method to modify ferrates and perhaps overcome their stability limitations. (C) 2006 The Electrochemical Society.