Ferrate(VI) Redox Chemistry for Energy Storage and Water Purification: A Cross-Domain Review

Abstract Ferrate(VI), an iron-based compound in the rare +6 oxidation state, has emerged as a multifaceted functional material for energy storage and environmental remediation. Its appeal stems from a high redox potential, a multielectron transfer capability, and the formation of iron(III) reduction products that are generally benign in most water matrices, however, in halide-containing waters, precautions are needed as bromate or iodate formation may occur. This Review provides a comprehensive overview of the fundamental properties, synthesis methods, and most critically, the stability challenges that hinder the practical application of Fe(VI) materials. We detail its application progress in two distinct fields: as a high-capacity cathode material in Superiron batteries, where we examine the three-electron reduction mechanism, interfacial instability, Fe(III) passivation, and shuttle effects that limit practical performance; and as a multifunctional reagent in water treatment, where the stepwise generation of reactive Fe(V)/Fe(IV) intermediates via oxygen-atom transfer, single-electron transfer, and radical pathways enables concurrent oxidation, disinfection, and coagulation. A central theme of this Review is the analysis of shared interfacial stability and reaction pathway regulation challenges across these domains. Finally, we highlight cross-domain synergy opportunities, proposing that strategies developed in one field can inform solutions in the other. This work aims to provide a foundational reference and forward-looking perspective for accelerating the development and deployment of Fe(VI)-based technologies.