Multi-electron transfer electrode materials for high-energy-density flow batteries

Flow batteries (FBs) have emerged as a promising technology for practical energy storage, mainly due to their outstanding characteristics of ultralong lifespan, safety, and scalability. Despite these attractive features, current FB technologies remain relatively expensive and have low energy density, limiting their widespread implementation. The multi-electron transfer FB systems are one of the most promising strategies to reduce the cost and enhance energy density. In this review, we give a comprehensive overview of the progress on multi-electron reaction materials, including the inorganic halogen-based, transition metal-based, and heteropoly acid-based materials and organic molecules (viologen derivatives, quinone derivatives, and heterocyclic aromatic compound derivatives). Finally, the challenge and perspective on the exploration of multi-electron materials for high-performance FBs are also provided.