Neutral Zinc-Iron Flow Batteries: Advances and Challenges

Zinc-iron flow batteries (ZIFBs) emerge as promising candidates for large-scale energy storage owing to their abundant raw materials, low cost, and environmental benignity. Among them, neutral zinc-iron flow batteries (NZIFBs) offer additional advantages such as environmental friendliness and non-corrosive operation, which draw significant attention. Nevertheless, the development of NZIFBs faces several critical challenges, including zinc dendrite formation and hydrogen evolution reaction (HER) on the anode side, as well as ferric ion hydrolysis and the limited solubility of active species on the cathode side. In addition, ion crossover presents further obstacles to membrane selection. In recent years, researchers have addressed these issues through advances in electrolyte, membrane, and electrode engineering, leading to a series of technological breakthroughs and notable progress in NZIFBs. However, comprehensive reviews focusing exclusively on NZIFBs remain scarce. Therefore, this work provides a concise overview of the background and key challenges associated with NZIFBs, followed by a systematic summary of the latest research progress in electrolytes, ion-exchange membranes, and electrode materials. Finally, based on this, an appropriate outlook is provided for the future development and large-scale commercialization of NZIFBs.