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Polyoxometalates (POMs), as multinuclear metal oxide clusters, possess natural multi-electron redox properties and high electrical conductivity. However, their susceptibility to leaching and agglomeration limits their application in energy storage. MOF materials provide a solution to the limitation of POMs due to their controllable pore sizes, big surface areas and strong adsorption properties. The synergistic effect between the two components greatly improves the electrochemical properties of the composites. In view of this, PMo 12 is encapsulated in ZIF-67 to form PMo 12 @ZIF-67 by in situ self-assembly, and benefitted from this unique precursor, MoSe 2 /(Ni, Co)Se 2 hollow structures assembled by nanoparticles are synthesized though Ni2+ etching and selenization process. At the same time, the PMo 12 content is optimized to get the best performance of 60-MoSe 2 /(Ni, Co)Se 2. In the three-electrode test, the developed 60-MoSe 2 /(Ni, Co)Se 2 electrode material exhibits an excellent specific capacity of 359.9 mA h g−1 at a current density of 1 A g−1, and a capacitance retention rate of 83.7 % after 10,000 cycles. In addition, the asymmetric supercapacitor (ASC) assembled with a positive electrode of 60-MoSe 2 /(Ni, Co)Se 2 and a negative electrode of activated carbon exhibits an excellent energy density of 40.3 W h kg−1 at a power density of 800.9 W kg−1. These superior electrochemical properties are attributed to the unique electronic structure of PMo 12 , which further demonstrates the feasibility of constructing hollow multicomponent selenides as energy storage materials using PMo 12 -ZIF-67 as a precursor. [Display omitted] • Successful construction of hollow MoSe 2 /(Ni, Co)Se 2 nanomaterial by in situ self-assembly. • 60-MoSe 2 /(Ni,Co)Se 2 exhibits a high specific capacitance of 359.9 mA h g−1 at 1 A g−1. • The ASC device displays a high energy density of 40.3 Wh kg−1 at 800.9 W kg−1. • The assembled ASC device keeps 89.6 % of its initial capacity after 10,000 cycles. [ABSTRACT FROM AUTHOR]

In this article, a trimesic acid-mediating control synthesis strategy was proposed for preparing the NiCo-MOF composition structure of microsphere and nanosheet by substituting 1,4-dicarboxybenzene with trimesic acid. Then the pre-synthesized MOF, as a precursor and template, was further vulcanized by a facile hydrothermal method to obtain hollow microsphere and nanosheet interleaved nickel and cobalt bimetallic sulfide materials (NiCo-S) while these microspheres and nanosheets were composed of smaller nanoparticles. This unique structure endowed quick electron/ion transport and electrolyte penetration as well as abundant redox active sites, significantly facilitating electrochemical performance. The obtained NiCo-S-2 showed higher specific capacitance (1790.4 F g−1) than its precursor NiCo-MOF-2 and other molar ratios of counterparts. Using it as an positive electrode and activated carbon (AC) as negative electrode, the assembled asymmetric supercapacitor NiCo-S-2//AC also delivered a high specific capacitance of 114.4 F g−1 and big specific energy of 35.5 Wh kg−1 at 799.99 W kg−1. • A ligand mediated control synthesis strategy was used for NiCo-MOF preparation. • Hollow microsphere and nanosheet interleaved structural NiCo-S had high specific capacitance (1790.4 F g−1). • NiCo-S-2//AC ASC delivered a high energy density of 35.5 Wh kg−1 at at 799.99 W kg−1. [ABSTRACT FROM AUTHOR]

Considering the high electrical conductivity of carbon dots (CDs) and good oxidation-reduction property of polyoxometalates (POMs), a novel CDs coated POMs /metal organic frameworks (POMOFs) composition structure, CDs@PMo 12 /Ni-MOF, was prepared by hydrothermal reaction in this work. PMo 12 was encapsulated in the Ni-MOF framework to form the POMOF composite material, which realized the fixation of water-soluble [PMo 12 O 40 ]3- (PMo 12). A comparison study on the cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) of the resulting CDs@PMo 12 /Ni-MOF with different compositions revealed that 6CDs@PMo 12 /Ni-MOF was better formulation in terms of specific capacity (748.8 C·g−1 at 1 A·g−1) and rate performance (75.93 % at 10 A·g−1). Furthermore, a hybrid supercapacitor device was assembled using 6CDs@PMo 12 /Ni-MOF as positive electrode and activated carbon (AC) as negative electrode, which showed an high energy density of 39.22 Wh·kg−1 under 749.9 W·kg−1 and excellent cyclic stability (98.4 % for 20000 cycles at 5 A·g−1). [Display omitted] • Fixation of water-soluble PMo 12 was realized to form POMOF composite material. • CDs@PMo 12 /Ni-MOF has excellent rate performance and cycle stability. • 6CDs@PMo 12 /Ni-MOF exhibits high specific capacitance and energy density. [ABSTRACT FROM AUTHOR]

Due to the insufficient performance, it is still a challenge to combine conventionally synthesized metal-organic framework (MOF-74) with other materials to fabricate composite electrodes for high-performance supercapacitors. Herein, we synthesized a series of NiCo-MOF-74 composite materials with different amounts of polypyrrole nanotubes (T-PPy) denoted as NiCo-MOF-74/T-PPy-m (m = 2.5, 5, 10, 15 and 20) through in situ growth of the bimetallic MOF around the PPy nanotubes by a simple solvothermal method. By comparison, the NiCo-MOF-74(1)/T-PPy-10 composite, with a Ni/Co molar ratio of 1:1 obtained in the presence of 10 mg of T-PPy, possessed the highest specific capacitance of 849 C·g−1 at 1 A·g−1 and excellent cyclic stability with a capacitance retention rate of 90.0% after 10,000 cycles as well as good rate performance. Moreover, the assembled asymmetric supercapacitor respectively using NiCo-MOF-74(1)/T-PPy-10 and active carbon as positive electrode and negative electrode achieved a superior energy density of 58.4 Wh kg−1 at the power density of 747.6 W kg−1 and high cyclic lifespan (91.4% capacitance retention after 10,000 cycles). The mechanism of capacitance increase was studied in detail, influences of metal molar ratios, morphology and addition amounts of PPy on electrochemical performances of the formed composition materials were systematically discussed, and it was found that the interpenetrating network structure assembled by "string of candied haws"-like T-PPy-interweaved NiCo-MOF-74(1) polyhedrons possessed the best capacitive performance for enhanced conductivity of the resulted composite, improved dispersity of the bimetallic MOF and more exposed active sites. And the interwoven structure alleviated the stress change-induced structure or phase variation caused by repeated volumetric swelling and shrinking during charge/discharge cycle and enhanced the rate capability and cycling stability. Interpenetrating network structure assembled by "string of candied haws"-like T-PPY-interweaved NiCo-MOF-74(1) polyhedrons [Display omitted] • Interpenetrating networks assembled by PPY nanotube-interweaved NiCo-MOF-74 were constructed. • The structure delivered good conductivity, high specific capactitance and long cyclic lifespan as supercapacitor electrode. • NiCo-MOF-74 in situ grown around the PPY tubes was directly used as electrode without carbonization and heteroatom doping. [ABSTRACT FROM AUTHOR]

The caCTF-1 derived from CTF-1 by carbonization is introduced into the multi-step heat treatment carbon repaired pC-C 3 N 4 to form a 3D interconnected nitrogen-rich carbon structure (caC@pC). Through carbon repairing process, the obtained pC-C 3 N 4 has an extended π-conjugate plane and it is closely interconnected with the nitrogen-rich caCTF-1, thereby accelerating charge transfer, improving energy storage, and exhibiting high specific capacitance (535.8 F·g−1 under 1 A·g−1) and good rate performance. In addition, by employing MOF with diphenyl semicarbazide structural unit as a precursor, NiCoTe 2 is prepared by a simple hydrothermal process, which exhibits high redox activity with a high specific capacitance of 2006.0 F·g−1 at 1 A·g−1 and good cycle stability. The hybrid supercapacitor NiCoTe 2 //caC@pC HSC is assembled with caC@pC as the negative electrode and NiCoTe 2 as the positive electrode. When the power density is 790.05 W·kg−1, it exhibits a high energy density of 50.84 Wh·kg−1 and high cycle stability. After 25,000 cycles, the capacitance retention rate is 87.88%. • A three-dimensional cross-linked nitrogen-rich carbon material caCTF-1 @pC-C 3 N 4 was constructed. The 3D cross-linked structure facilitates the rapid penetration of electrolyte ions. The introduction of nitrogen source into the carbon material can enhance the surface charge mobility of carbon. The material exhibits high specific capacitance (535.8 F·g−1 under 1 A·g−1) and good rate performance (the specific capacitance still remains 85.67% at 10 A·g−1) in the three-electrode test. • caCTF-1 is derived from CTF-1. This material has a high nitrogen content and was first used in supercapacitors, showing better application potential. • The carbon self-repairing pC-C 3 N 4 can be combined with ethanol to introduce carbon units into g-C 3 N 4 through the hydrothermal method, which improves the slow charge transfer due to the limitation of bridge nitrogen atoms. Multi-step heat treatment also makes it have more pores. Thereby improving electrochemical performance. • NiCoTe 2 with broccoli structure provides fast Faraday reaction active sites, ensures high utilization of electrode materials, and enables electrode active materials to exhibit ultra-high specific capacitance (2006 F/g at 1 A/g), rate performance and good cycle stability (when assembled into a supercapacitor, the capacitance retention rate after 20,000 cycles is 96.15%). • The assembled asymmetric supercapacitor NiCoTe 2 //caC@pC has a large potential window (0–1.6 V) and high energy density (when the power density is 790.05 W/kg, the energy density is 50.84 Wh/ kg), and good cycle stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • MoS 2 @Ni-MOF was prepared and alkalized to obtain MoS 2 /Ni(OH) 2. • MoS 2 /Ni(OH) 2 has high specific capacitance and long cycling life for supercapacitor. • MoS 2 /Ni(OH) 2 was used to construct electrochemical sensor for HQ and CC. A nickel-based metal-organic framework (Ni-MOF) layer was in situ grown on the surface of the sheet MoS 2 to synthesize MoS 2 @Ni-MOF as a precursor. In order to improve the properties of the precursor material, the final MoS 2 /Ni(OH) 2 material was obtained by alkalizing the precursor material. Supercapacitors and electrochemical sensors were prepared by MoS 2 /Ni(OH) 2 composite material. The test indicates that alkaline treatment of Ni-MOF materials is helpful to improve electrochemical performance. MoS 2 /Ni(OH) 2 material used as supercapacitor electrode has a high specific capacitance of 2192 F g−1 and excellent cyclic stability (the capacitance retention rate remains 85.19% after 10,000 charge/discharge cycles). The hybrid supercapacitor (HSC) was assembled with MoS 2 /Ni(OH) 2 as the positive electrode and activated carbon as the negative electrode. The MoS 2 /Ni(OH) 2 //AC HSC device shows an excellent energy density of 50.58 Wh kg−1 at the power density of 800 W·Kg−1. In addition, the MoS 2 /Ni(OH) 2 modified GCE electrode is an excellent electrochemical sensor for the simultaneous determination of hydroquinone (HQ) and catechol (CC). The modified electrode provides wide linear ranges of 1 ∼ 500 and 2 ∼ 400 μM and low detection limits of 0.43 and 0.48 μM for HQ and CC, respectively (S/N=3). The MoS 2 /Ni(OH) 2 material can be applied to supercapacitors and electrochemical sensors, indicating that the material has great potential application value in energy storage and biosensing. [ABSTRACT FROM AUTHOR]