Progresses and Perspectives of All-Iron Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) are a promising option for long-duration energy storage (LDES) due to their stability, scalability, and potential reversibility. However, solid-state and non-aqueous flow batteries have low safety and low conductivity, while aqueous systems using vanadium and zinc are expensive and have low power and energy densities, limiting their industrial application. An approach to lower capital cost and improve scalability is to utilize cheap Earth-abundant metals such as iron (Fe). Nevertheless, all-iron RFBs have many complications, involving voltage loss from ohmic resistance, side reactions such as hydrogen evolution, oxidation, and most significantly electrode plating, and dendrite growth. To address these issues, researchers have begun to examine the effects of various alterations to all-iron RFBs, such as adding organic ligands to form Fe complexes and using a slurry electrode instead of common materials such as graphite or platinum rods. Overall, progress in improving aqueous all-iron RFBs is at its infant stage, and new strategies must be introduced, such as the utilization of nanoparticles, which can limit dendrite growth while increasing storage capacity. This review provides an in-depth overview of current research and offers perspectives on how to design the next generation of all-iron aqueous RFBs.