Layered nickel metal–organic framework for high performance alkaline battery-supercapacitor hybrid devices

Abstract

Alkaline battery-supercapacitor hybrid devices (ABSHDs) are attracting considerable attention because they combine the advantages of both alkaline batteries and supercapacitors. Herein, a nickel metal–organic framework (Ni-MOF) was demonstrated to have a high specific capacity and could further improve energy storage through a novel strategy: “synergistic effect between Ni-MOF and Fe(CN)₆⁴⁻/Fe(CN)₆³⁻”. The unique 2D-layered crystal structure of the Ni-MOF could provide enough space for Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ storage and diffusion and Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ could act as an electron relay during charge–discharge processes by coupling Ni(II)/Ni(III) in the Ni-MOF electrode. Moreover, we assembled an Ni-MOF//CNTs-COOH ABSHD in 3 M KOH and 0.1 M K₄Fe(CN)₆ mixed electrolyte with an extended voltage window of 1.4 V, which resulted in a high energy density (55.8 W h kg⁻¹) and power density (7000 W kg⁻¹) simultaneously. Hence, the results in this study could broaden the applications of MOFs in energy storage devices and provide insightful guidelines for developing other redox additives.