Dual-functional Fe3O4-decorated porous carbon nanosheets for kinetics-enhanced aqueous zinc–iodine batteries

Aqueous rechargeable zinc–iodine batteries (ARZIBs) have been highlighted as a favorable solution for energy storage, in view of their sustainability, cost-effectiveness, and safety. Nonetheless, the practical implementation of ARZIBs is challenged by the sluggish iodine-reduction-reaction kinetics as well as the shuttling behavior of the soluble polyiodide substances. Herein, Fe3O4 nanoparticles embedded in porous carbon nanosheets (Fe3O4 NPs@PCNs) with a large specific surface area (1407.8 m2 g−1) are proposed as an iodine host for ARZIBs. This structure not only enhances iodine adsorption but also supports the electrocatalytic reversible conversion of iodine. Both experimental evidence and theoretical analyses highlight that the presence of the Fe3O4 nanoparticles can effectively accelerate the iodine-reduction-reaction reversibly, while mitigating the shuttling effect of polyiodide ions. The resultant ARZIBs exhibit a specific capacity of 269.8 mAh g−1 at 0.5 A g−1, with 85% of this capacity being contributed by the discharge platform. Additionally, they demonstrate high rate capabilities, delivering 211.1 mAh g−1 at 20 A g−1, minimal self-discharge, and cycling stability for 15,000 cycles. This performance is attributed to the synergistic effect of the catalytic activity of Fe3O4 nanoparticles and physical confinement provided by the carbon framework. The findings of this study illuminate the critical effect of Fe3O4 in transforming a nonpolar carbon material into an efficient iodine host, paving the way for the realization of reversible ARZIBs.