Aqueous Zinc Batteries with Ultra-Fast Redox Kinetics and High Iodine Utilization Enabled by Iron Single Atom Catalysts

Rechargeable aqueous zinc iodine (ZnǀǀI₂) batteries have been promising energy storage technologies due to low-cost position and constitutional safety of zinc anode, iodine cathode and aqueous electrolytes. Whereas, on one hand, the low-fraction utilization of electrochemically inert host causes severe shuttle of soluble polyiodides, deficient iodine utilization and sluggish reaction kinetics. On the other hand, the usage of high mass polar electrocatalysts occupies mass and volume of electrode materials and sacrifices device-level energy density. Here, we propose a “confinement-catalysis” host composed of Fe single atom catalyst embedding inside ordered mesoporous carbon host, which can effectively confine and catalytically convert I₂/I⁻ couple and polyiodide intermediates. Consequently, the cathode enables the high capacity of 188.2 mAh g⁻¹ at 0.3 A g⁻¹, excellent rate capability with a capacity of 139.6 mAh g⁻¹ delivered at high current density of 15 A g⁻¹ and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Furthermore, the electrocatalytic host can also accelerate the I+↔I2 conversion. The greatly improved electrochemical performance originates from the modulation of physicochemical confinement and the decrease of energy barrier for reversible I⁻/I₂ and I₂/I⁺ couples, and polyiodide intermediates conversions.[Figure not available: see fulltext.]