Engineering Bifunctional Carbon Hosts with Rich ─OH and ─C═O for Synergistic Confinement and Redox Kinetics in Zn-I₂ Batteries

Aqueous zinc-iodine (Zn-I₂) batteries have attracted extensive attention as next-generation energy storage systems due to their inherent safety, environmental benignity, and theoretical high capacity (211 mAh g^-1). Nevertheless, their practical application is still hampered by the dissolution and shuttling of soluble polyiodides, leading to rapid capacity decay and inferior cycling stability. Although porous carbon-based host materials physically confine iodine species, thereby improving electrochemical performance, the crucial role of surface functional groups on carbon (─OH, ─C═O, and ─COOH) in regulating the electrochemical behavior has been neglected. Herein, we designed and synthesized hierarchical micro-mesoporous carbon (MMC) nanospheres rich with hydroxyl (─OH) and carbonyl (─C═O) groups as iodine hosts. The multiscale porous structure facilitates high iodine loading, while ─OH groups remarkably enhance the chemical adsorption of iodine species via O─H∙∙∙I bond, thereby suppress the shuttle effect. Additionally, ─C═O groups actively participate in additional Faradaic redox reactions. Consequently, the prepared I₂/MMC-Rich electrode delivers outstanding electrochemical performance: it provides an initial capacity of 160.87 mAh g^-1 at 10 A g^-1 and maintains 135.58 mAh g^-1 after 25 000 cycles, with a capacity retention rate of 84%. This work offers a rational strategy for developing functional carbon materials toward high-performance and long-life Zn-I₂ batteries.