Ultra-Wide Voltage Aqueous Superbatteries Enabled by Iron and Zinc Zeolitic Frameworks.

Extensive research on supercapacitor-battery hybrid devices has bridged the gap between conventional batteries and supercapacitors. However, several challenges persist, including limited capacitance in the negative potential range, restricted rate capability, and a narrow potential window (<1.23 V) in aqueous electrolytes. Drawing inspiration from the notable benefits of bottom-up synthesis, which allows tailoring of structure and functionality through the selection of molecular components, we successfully synthesized an Fe-incorporated zeolitic imidazolate framework-8 (composed of Zn nodes and 2-methylimidazole linkers). Subsequently, the metal-organic framework was hydrothermally composited with graphene oxide in the presence of urea to prepare a dual metal oxide/N-doped reduced graphene oxide (DMO-NrGO) nanocomposite. Benefiting from the high hydrogen evolution overpotential of zinc-based compounds and the promising negative potential range activity of iron-based species, the lower potential limit of the X-ray confirmed crystalline-amorphous heterophase DMO-NrGO nanocomposite extends up to -1.45 V. It exhibits a specific capacity (capacitance) of 119 mA h g^-1 (378 F g^-1) at 1.0 A g^-1 in 3.0 M KOH. Interestingly, the symmetric DMO-NrGO based superbattery device demonstrates an ultrawide voltage window of 1.95 V, with a superior specific energy of 28 W h kg^-1 and an outstanding specific power of 29 kW kg^-1 at 3.0 A g^-1. The outstanding electrochemical performance can be attributed to the heterophase structure of the nanocomposite, which accommodates more active sites, provides additional ion transport channels, reduces phase-transformation resistance, and facilitates smooth electron transfer between metal oxides and graphene. This innovative synthetic strategy opens opportunities for developing high-performance aqueous energy storage devices.