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Metal–organic frameworks (MOFs) have found wide applications in the field of supercapacitors due to their highly controllable porous structure, big specific surface area, and abundant chemical functional groups. MOF-on-MOF hybrids not only enhance the composition of MOFs (such as ligands and/or metal centers) but also provide greater structural diversity. By utilizing MOFs as precursors for preparing sulfides, the unique characteristics and inherent structure of MOFs are preserved but their conductivity and capacitance are enhanced. This study successfully synthesized hollow-structured Ni3S4@Co3S4 derived from an Ni-MOF@ZIF-67 hybrid structure, where the Ni-MOF serves as the core and ZIF-67 as the satellite. The Ni3S4@Co3S4 electrode demonstrated a specific capacity as high as 747.3 C g−1 at 1 A g−1, and it could still maintain 77% of its initial capacity at 10 A g−1. Furthermore, the assembled Ni3S4@Co3S4//AC hybrid supercapacitor (HSC) device achieved a maximum energy density of 30.8 W h kg−1 when the power density was 750 W kg−1. The device exhibited remarkable cycling durability, retaining 85.4% of its initial capacitance after 5000 cycles. Therefore, the derived functional materials based on MOF-on-MOF provide a more scalable and promising approach for the preparation of efficient electrode materials. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) are battery-type supercapacitor electrode materials with application potential due to their abundant active metal sites and surface functional groups. The traditional LDH structure easily aggregates and collapses. In this work, a stable cobalt zeolite imidazole framework (Co-ZIF) was used as the derived template to grow LDH nanosheets in situ to increase the contact area with the electrolyte, and polyaniline (PANI) acted as a conductive bridge to provide a rapid charge transfer pathway. The fabricated NiCo-LDH@PANI hollow structure demonstrated a specific capacity of 1315 C g−1 at 1 A g−1 and achieved a rate capacity of 951 C g−1 at 20 A g−1. Furthermore, the battery–supercapacitor hybrid device (NiCo-LDH@PANI//AC) exhibited an high energy density of 66.2 W h kg−1 at a power density of 800 W kg−1 with 95.5% capacitance retention after 20 000 cycles. [ABSTRACT FROM AUTHOR]

A novel tetrahydroxy-anthraquinone zeolitic framework (TZM) with a Viburnum blossom-like structure is synthesized via a simple solvothermal method by using tetrahydroxy-anthraquinone to substitute imidazolate without carbonization at high temperature. Considering the excellent electrochemical performance of the TZM, including a high specific capacitance of 2030 F g−1 at a current density of 1 A g−1, and good cycling stability with a capacitance retention of 94% of the initial capacitance after 1000 cycling charge/discharge measurements, an aqueous TZM//AC asymmetric supercapacitor (ASC) in 1 M KOH electrolyte is successfully fabricated by using the resultant TZM as the positive electrode and activated carbon nanosheets (ACS) as the negative electrode, respectively. The as-assembled aqueous ASC delivers a high energy density of 47.7 W h kg−1 at a power density of 750 W kg−1 with a high potential window of 0–1.5 V. Moreover, for the purpose of exploring the practical application of the active materials, an all-solid-state ASC TZM//ACS device with PVA-KOH gel electrolyte and separator is assembled and connected, which can light up a red light-emitting diode (LED). Its good performance demonstrates that the TZM//ACS ASC is a promising energy-storage system. [ABSTRACT FROM AUTHOR]