Unveiling dual-linkage 3D hexaiminobenzene metal–organic frameworks towards long-lasting advanced reversible Zn–air batteries

Abstract

Advanced Zn–air batteries (ZABs) with ultrahigh cycle life, which also harness energy with bifunctional electrochemical reactions, are significantly challenging for the commercialization of hybrid/electric vehicles and wearable electronics. Herein, we demonstrated robust aqueous and flexible ZABs with novel three-dimensional dual-linked hexaiminobenzene metal–organic framework (Mn/Fe-HIB-MOF)-based bifunctional oxygen electrocatalysts and superionic functionalized bio-cellulose electrolytes (64 mS cm⁻¹). The well-defined quintet-shelled hollow sphere MOFs possess a hierarchical porous structure, excellent packing density with a surface area of 2298 m² g⁻¹, and chemical stability as compared to conventional MOFs. Mn/Fe-HIB-MOF exhibited superior bifunctional oxygen electrocatalytic activity (0.627 V) with half-wave potential (0.883 V) for oxygen reduction and overpotential (280 mV@10 mA cm⁻²) for oxygen evolution reactions, outperforming commercial Pt/C and RuO₂. Their favorable oxygen reactions and surface electronic structures were confirmed by density functional theory. Significantly, the Mn/Fe-HIB-MOF cathode demonstrated the highest lifetimes reported to date for rechargeable ZABs, namely 1000 h (0.75 V voltage gap@10 mA cm⁻²) over 6000 cycles and 600 h (efficiency ∼65.24%@25 mA cm⁻²) over 3600 cycles with excellent flexibility for liquid and all-solid-state flexible ZABs, respectively. These promising results illustrate the great potential of these novel hexaiminobenzene MOFs and superionic bio-cellulose membranes for the commercial implementation of rechargeable ZABs.