Self-Assembled Liquid Crystal Interphase Enabling Long-Life All-Iron Redox Flow Batteries

Aqueous all-iron redox flow batteries (AIRFBs) are an attractive avenue for large-scale energy storage due to the safety and cost-effectiveness of iron. However, the performance and durability of AIRFBs are limited by nonuniform Fe plating, hydrogen evolution and corrosion reactions at the anodes. Herein, a non-ionic surfactant, polyethylene glycol cetyl ether (Brij 56), is introduced into the electrolyte for stabilizing the anode, which can self-assemble on the iron surface to form a dynamic liquid crystal interphase. This oriented interfacial layer not only inhibits H₂O-induced side reactions by efficient Fe²⁺ ion desolvation at the anode interface, but also modulates Fe²⁺ ion transport owing to its anisotropic properties, acting as a soft template for the uniform iron deposition. Consequently, the liquid crystal interphase increases the anode reversibility of the AIRFB, achieving a high Coulombic efficiency (CE) of 99.4% and an energy efficiency of 74.5% over 300 h (230 cycles) at 20 mA cm^-2. Furthermore, the AIRFB with liquid crystal interphase retained a CE of 98.2% at a high current density of 60 mA cm^-2 and delivered a high capacity of 26 mAh cm^-2. These findings highlight the potential of interfacial engineering to promote performance for the next-generation energy storage technologies.