Aqueous iron-based redox flow batteries for large-scale energy storage.

The rapid advancement of flow batteries offers a promising pathway to addressing global energy and environmental challenges. Among them, iron-based aqueous redox flow batteries (ARFBs) are a compelling choice for future energy storage systems due to their excellent safety, cost-effectiveness and scalability. However, the advancement of various types of iron-based ARFBs is hindered by several critical challenges, including hydrogen evolution, inferior reversibility of metal deposition and stripping, and undesirable dendrite formation in hybrid flow systems with metal plating/stripping on the negative electrode. Additionally, all-soluble iron-based ARFBs face limitations in redox species solubility and electrolyte stability. To address these issues, various strategies have been developed, such as modifications to electrolytes, electrodes and separators, as well as flow stack optimization. This review provides a comprehensive overview of iron-based ARFBs, categorizing them into dissolution-deposition and all-soluble flow battery systems. It highlights recent advancements in the field and explores future prospects, focusing on four key areas: materials innovation and mechanistic understanding; flow battery system design and engineering; new electrochemistry explorations; and interdisciplinary strategies. By offering insights into these emerging directions, this review aims to support the continued research and development of iron-based flow batteries for large-scale energy storage applications.