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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]

Among a large variety of energy storage technologies, supercapacitors possess special advantages such as rapid charge/discharge, high power density, safety, and environmental friendliness to meet the requirement of specific applications. The common electrode materials of supercapacitors, including porous carbon, conductive polymers, and metal oxides/hydroxides, have their own benefits and drawbacks in energy density and stability. Owing to the big surface area and controllable porosity, the metal-organic frameworks (MOFs) have been explored as important candidates for supercapacitor applications. This mini-review focuses on the recent advances of MOF-based materials including pristine MOFs, MOFs composite materials, and MOF-derived materials in the development of long cycling life supercapacitors. The devices discussed here mean those with capacitive retention rates of more than 90% after 10,000 cycles and high energy density. In addition, we also describe the fundamental knowledge of supercapacitors, highlight the stabilization mechanism of MOFs, and propose the strategies to enhance the stability of MOF-based supercapacitor electrodes. • The fundamental knowledge of supercapacitor is illustrated. • The fundamental mechanisms of MOFs stabilization are emphasized. • Recent advances of MOF-based long cycling stability supercapacitors are reviewed. • The strategies to enhance the stability of MOF-based supercapacitors are proposed. [ABSTRACT FROM AUTHOR]

Currently, people are attempting to replace vehicles powered by fossil fuels with electric vehicles in an effort to reduce energy problems and air pollution. However, up to now this attempt has not been successful owing to safety deficiencies, short cruising ranges, and inconvenience. In this study, we have developed a safe, convenient, and refillable bi-electrolyte fuel cell to serve as a generator for electric vehicles and to supply auxiliary power to the vehicles. In terms of power, we have designed a new range-extending, charging-driving mechanism, which is a simple mechanical device that can also increase the cruising range, torque, and speed of electric vehicles and can charge while driving. After mixing 3-9 μm of zinc powder with 40 wt% KOH electrolyte and setting the open circuit voltage to 1.4 V, we use a constant voltage method to test with a current density of 70 mA/cm2, a power density of 0.53 W, a constant voltage of 0.3 V, and a reaction area of 25 cm2. [ABSTRACT FROM AUTHOR]

[Display omitted] • FNCS@NVL multi-metal hollow heterostructure was constructed. • FNCS@NVL exhibits a high specific capacitance of 1964.4F·g−1 at 1 A·g−1. • FNCS@NVL//AC delivers an ultrahigh energy density of 71.9 Wh·kg−1 at 800.01 W·kg−1. Metal-organic framework (MOF) derivatives as supercapacitor electrodes are limited by their poor conductivity and capacitance properties. Therefore, it is crucial to improve the performance by constructing a rational structure. Here, MIL-88A is converted into a unique hollow heterostructure FeNiCoSe@NiV layered double hydroxide (FeNiCoSe@NiV-LDH, simplified as FNCS@NVL) by a simple ion-exchange combined with co-precipitation technique. The Ni-Co ratio is modulated by an intermediate optimization strategy. Owing to the multi-metal sites and the unique structure, the designed FNCS@NVL shows excellent electrochemical properties as expected. It exhibits excellent specific capacity (1964.4 F·g−1 at 1 A·g−1) and capacitance retention (82.1 % at 10,000 cycles) at three-electrode setup. In addition, the hybrid supercapacitor (HSC) assembled by FNCS@NVL as the positive electrode and activated carbon as the negative electrode also exhibits a high energy density of 71.9 W h·kg−1 at a power density of 800.01 W·kg−1. These results demonstrate that the designed FNCS@NVL complex is an excellent energy storage material and further validate the great potential of polymetallic materials in energy storage. It provides a unique idea for constructing supercapacitors with high energy density and power density. [ABSTRACT FROM AUTHOR]

The application of MOF materials in supercapacitors has been greatly restricted due to the poor conductivity and structural stability. Given that, this work improves the conductivity and stability of Ni-MOF by self-assembled strategy. We report here the Mo-doped Ni-MOF nanosheets (M-NMN), in which the Mo-based clusters are encapsulated in the holes of the Ni-MOF frame structure by self-assembly. The results show that the M-NMN-1 material with a Mi/Mo molar ratio of 1: 1 exhibits an excellent electrochemical performance. Furthermore, the nanosheet structure of the M-NMN-1 materials acts as a "superhigh way" for charge transport to accelerate charge transfer rate and enhance the conductivity of the electrode materials. As-prepared M-NMN-1 electrode material exhibits high specific capacity of 802 C g−1 at 1 A g−1. Furthermore, assembled battery-supercapacitor hybrid device exhibits an excellent energy density of 59 Wh kg−1 at a power density of 802 W kg−1, and superior cycle retention of 93% after 20,000 cycles. Image 1 • Design and fabrication of self-assembled Mo-doped Ni-MOF nanosheets (M-NMN-1). • The M-NMN-1 material exhibits the improved the conductivity and stability. • The ultrahigh specific capacity of 802 C g-1 at 1 A g-1 in three electrode system. • High energy density of 59 Wh kg-1 at power density of 802 W kg-1 in hybrid device. [ABSTRACT FROM AUTHOR]

We created a simple electrodeposition method of preparing Ni 3 S 2 nanosheets deposited on 3D hemp-activated carbon supported by a Ni foam. We selected three optimized deposition cycles because of high capacitances of 3D hemp-activated carbon/Ni 3 S 2 electrodes (2,797.43 F g−1 at 1 A g−1) in a 6 M KOH solution. Meanwhile, the capacitances' retention rate is 82.13%, indicating an excellent cyclic stability. To evaluate the further performance of 3D hemp-activated carbon/Ni 3 S 2 electrodes materials in a full cell, the self-assembled all-solid-state supercapacitors device 3D hemp-activated carbon//3D hemp-activated carbon-Ni 3 S 2 have the energy density of 55.32 Wh kg−1 at a current density of 1 A g−1, and a great cycle ability (it retain approximately 83.47% of the initial capacitance after 10,000 charge/discharge cycles). Image 1 • Agricultural wastes hemp bast is used to preparation porous activated carbon. • Ni 3 S 2 decorated on 3DHAC supported by binder-free Ni foam has high capacitance performance. • HAC//HAC-Ni 3 S 2 delivers an energy density of 55.32 Wh kg−1 at a power density of 1,053.71 Wkg−1. • Capacitance retention of HAC//HAC-Ni 3 S 2 electrode after 10000 charge-discharge cycles is 83.47%. [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]

• Ni-MOF on MXene is vulcanized to sandwiched p-MXene/Ni 3 S 4 /CuS in the presence of copper. • p-MXene/Ni 3 S 4 /CuS show the remarkable specific capacitance. • The p-MXene/Ni 3 S 4 /CuS//AC has a high energy density and ultrahigh cyclic stability. [Display omitted] Metal-organic frameworks (MOFs) have ordered porous structure and intriguing properties for supercapacitors, however, poor conductivity and cycle stability limits their application. To solve these problems, hence, a simple strategy is proposed, by which MOFs are in-situ grown in the porous conductive p-MXene substrate. And then, along with the introduction of CuS, the grown Ni-MOF is derived to Ni 3 S 4 , which is more stable and more electrochemically active. Due to higher contact area, excellent synergistic effect and more exposed active sites, the prepared sandwiched p-MXene@Ni 3 S 4 /CuS nanostructure displays a big specific capacitance (1917 F·g−1) and superior cycling performance (91.2%@30000). What's more, the assembled p-MXene@Ni 3 S 4 /CuS//AC asymmetric device delivers a high energy density of 87.62 Wh·Kg−1 at the power density of 775.02 W·Kg−1, suggesting that this material provides a brilliant candidate for energy storage. [ABSTRACT FROM AUTHOR]

• Design and fabrication of self-assembled Ni-doped ZIF-67 (NiCo-ZIF-67). • Sandwich MXene/NiCoZDHis used for supercapacitor for the first time. • The specific capacitance of MXene/NiCoZDH is greater than that of MXene and ZIF-67. • Excellent cyclic stability of MXene/NiCoZDH (90.9%@30,000). Zeolite-imidazole frameworks (ZIFs) are the promising materials for supercapacitors (SC), however, the shortcomings of easy agglomeration, low conductivity and low stability limit the further improvement of their electrochemical properties. Hence, in order to produce high-performance SC, ZIFs are usually grown directly on some conductive substrates or post-treated. In this paper, MXene was explored as the substrate and Ni-doped ZIF-67 (denoted as NiCo-ZIF-67) was in situ anchored on negatively charged MXene surface via chemical bonds to supply more available active sites for the enhancement of capacitance. At the same time, the surface functional groups in MXene can also enhance the chemical connection between NiCo-ZIF-67 and MXene to attain higher ion diffusion and charge transfer rates. The size of the NiCoZDH (ZIFs-derived double hydroxide denoted as ZDH) obtained by the alkali treatment of NiCo-ZIF-67 is smaller, which is good for increasing specific surface area. The prepared composite MXene/NiCoZDH electrode shows a larger specific capacitance (877 F g-1) than MXene/NiCo-ZIF-67 (460 F·g-1), NiCoZDH (354 F g-1), NiCo-ZIF-67 (130 F g-1) and MXene (15 F g-1), and superior cycling stability with a capacitance retention of 90.9% after 30000 cycles. Additionally, the assembled asymmetric supercapacitor delivers an energy density of 34 Wh kg-1 at the power density of 748 W kg-1 and maintains 93.3% of the initial capacitance after 30,000 cycles. [ABSTRACT FROM AUTHOR]

• A simple ultrasound-assisted method was used to synthesize nitrogen-containing p - π conjugated-organic ligands. • Nitrogen-containing conjugated organic ligands have good conductivity. • Carbon-enriched MOFs and derived porous carbon have excellent electrochemical performance. • The change law of electrochemical performance was explored with gradient temperature. • The MOF-B-600//AC ASC device exhibits a high energy density of 63.62 Wh·kg−1 at power density of 400 W·kg−1. [Display omitted] This article aims to use nitrogen-doped metal p - π conjugated-organic frameworks and derived carbon-rich electrode materials for high-performance electrode materials. Nitrogen-doped contributes to the energy storage performance, and the p-π conjugated-organic ligands of the conjugated system can not only improve the stability of the structure, but increase the conductivity of the material. Gradient carbonization can explore the maximum electrochemical potential of MOF-B, from which the previous 1271.0 increased to 2727.5 F·g−1 at a current density of 1.0 A·g−1. The excellent capacitance retention rate is 86.67% of the initial value at a high current density after 20,000 cycles. Besides, the MOF-B-600//AC also shows a high energy density of 63.62 Wh·kg−1 at a power density of 400 W·kg−1 and good coulomb efficiency of 90.7%. As a result, the excellent electrochemical performance of the nitrogen-doped and carbon-enriched MOF-B-600 has potential application prospects in energy storage devices. [ABSTRACT FROM AUTHOR]

The transition metal selenides have aroused wide concern due to their potential characteristics in the energy storage and conversion. The formation of multivariate MOFs attracts much research attention and provides the essential guarantee for multivariate mixed-metal selenides. Herein, a series of isostructural MOF-74 materials with different divalent metals were prepared by changing the molar ratios of nickel to cobalt. After selenizing, CoSe 2 , NiSe 2 and three kinds of mixed-metal selenides were easily obtained, prompting us to systematically research the effect of different metal species and molar ratios on the electrochemical performance of the mixed-metal selenides. It is found that mixed-metal selenides derived from MOF-74 display much better performance than single metal selenides, and NiCoSe-4 with a Ni/Co molar ratio of 4:1 demonstrates a high specific capacity of 211 mAh g−1 at a current density of 1 A g−1. What's more, the assembled asymmetric supercapacitor NiCoSe-4//AC shows a high energy density of 61.24 Wh kg−1 at power density of 800 W kg−1, which suggests that NiCoSe-4 as a promising electrode material possesses further research value and potential for practical applications in energy storage fields. Image 1 • CoSe 2 , NiSe 2 and three kinds of mixed-metal selenides were easily obtained by selenizing different isostructural MOF-74 materials. • Mixed-metal selenides of electrochemical performance derived from MOF-74 display much better than single metal selenides, and NiCoSe-4 demonstrates a high specific capacity of 211 mAh g−1 at a current density of 1 A g−1. • The assembled NiCoSe-4//AC exhibits high energy density of 61.24 Wh kg−1 at power density of 800 W kg−1. The capacitance retention and Faradic efficiency of the NiCoSe-4//AC are 91% and 89% after 12,000 cycles at a current density of 10 A g−1. [ABSTRACT FROM AUTHOR]

A new two-dimensional covalent organic framework (DBT-MA-COF) is designed and synthesized via Carbon–Nitrogen coupling reaction by using 2,5-dibromothiophene (DBT) and melamine (MA) as the monomers. The C−Hˑ N intralayer hydrogen bonding exists in the structure of DBT-MA-COF so that a plane rigid structure can be maintained. The material exhibits a quasi-reversible redox process caused by triazine units and the transformation of the quinone and aromatic structures to make the DBT-MA-COF possess pseudocapacitive characteristics. DBT-MA-COF has high heteroatom content for the existence of triazine and thiophene units, which can accelerate the transfer of electrolyte ions on the surface of DBT-MA-COF electrode and improve the solution conductivity of the material. The assembled asymmetric supercapacitor DBT-MA-COF//C-CTS ASC has a high energy density of 32.1 W h kg−1 with the power density of 800 W kg−1. The cycle life of the device is excellent which can reach 83% even after 30,000 continuous galvanostatic charge-discharge cycles. The strategy in this work provides a line of thinking to design and prepare new COFs used as long life and pseudocapacitive supercapacitor materials. Image 1 • A novel covalent organic framework(DBT-MA-COF) is synthesized via Carbon-Nitrogen coupling reaction. • C-H...N intralayer hydrogen bonding existed in DBT-MA-COF leads to a plane rigid structure. • The COF has pseudocapacitive characteristics for a transformation of quinone and aromatic structures in triazine unit. • The existence of triazine and thiophene units improves the conductivity of the resulting material. • Assembled asymmetric supercapacitor shows a high energy density of 32.1Wh kg-1 and the long life of 83% after 30000 cycles. [ABSTRACT FROM AUTHOR]

A facile alkaline treatment stripping precursor strategy is developed for preparing MOF derived double hydroxide. The bimetallic MOFs material provides multi-type of redox reaction centres, and the hydroxide nanonanoflower obtained by alkali stripping Ni-MOF@Co-MOF effectively expands the "active area (circumference)" of the redox reaction. The exfoliated sheets expose more active sites, which are more favorable for effective contact with the electrolyte and facilitate the occurrence of redox reactions. The MOF derived double hydroxide maintains the structural and performance advantage of the MOF precursor as well as overcomes the disadvantages of poor conductivity and serious agglomeration of common hydroxide. As-synthesized electrode exhibited high specific capacity of 1088 C g−1 at 1 A g−1 and cycle retention of 94% after 12,000 cycles. Furthermore, assembled battery-supercapacitor hybrid device exhibits a maximum energy density of 66.5 Wh kg−1 at a power density of 825 W kg−1, and superior cycle retention and coulombic efficiency of 86% and 95% after 18,000 cycles, which shows that Ni-MOF@Co-MOF derived double hydroxide has good potential application value. [ABSTRACT FROM AUTHOR]

In this present paper, a novel layered multi-metal sulphide was reported as a positive electrode material with abundant electroactive sites and redox reaction centres. Molybdenum and sulfur elements were introduced into the metal-organic frameworks (M-MOF: M = Ni, Co and Ni/Co) to synthesize layered MMoS x by a hydrothermal method. The electrochemical performance comparison of MOFs and six electrode materials demonstrated that NiCoMoS x electrode materials had the best electrochemical performance and the highest specific capacitance. The highest specific capacitance could reach 2595 F g−1 at a current density of 1 A g−1. The NiCoMoS x electrode material also had an excellent cycle stability with a retention rate of 90.8% after 10,000 charge and discharge cycles. In addition, the as-assembled NiCoMoS x //AC assymmetric supercapacitor (ASC) device exhibited a maximum energy density of 48.2 Wh·kg−1 at a power density of 807.2 W kg−1, and the capacity retention rate after 10,000 charge and discharge cycles was 91.6%. This electrochemical performance indicated that this kind of material had a good market development prospect. • Six kinds of materials were synthesized by hydrothermal method to make working electrodes, and electrochemical properties were tested and compared. • It is proved that cobalt-nickel composite has higher specific capacitance and better electrochemical performance after molybdenum-doped vulcanization with MOF as precursor. • NiCoMoS x electrode material has good electrochemical properties and excellent cycling stability. • The assembled asymmetric supercapacitor has good energy storage and can light up red LED. [ABSTRACT FROM AUTHOR]

Nitrogen sulfur co-doped bimetal nanocomposites (NS-BNs) are prepared through vulcanization and annealing using bimetallic Ni/Co-MOF as a precursor. The nitrogen sulfur co-doped bimetal nanocomposites have abundant electroactive sites and redox reaction centres, which exhibit remarkable electrochemical performance as electrode materials for supercapacitor. The specific capacitance could reach 1529 F g−1 at a current density of 1 A g−1 and excellent cycle stability (retention rate of 89.29% after 10000 cycles). After the current density is expanded ten times, the specific capacitance can still reach 1069 F g−1, indicating superior rate performance. Furthermore, the assembled asymmetric supercapacitor displayed a high energy density of 41.04 Wh kg−1 at power density of 750 W kg−1. As a result, non-metal doped nanocomposites material has promised applications for electrochemical supercapacitors. Image 1 • Advanced asymmetric supercapacitor device assembled by nitrogen sulfur co-doped bimetal nanocomposites. • Outstanding electrochemical behaviour and ultrahigh specific capacitance of 1529 F g−1 at 1 A g−1. • High energy density of 41.04 Wh kg−1 at power density of 750 W kg−1. • Remarkable long term cycle stability with 90% after 10000 charge-discharge cycles. [ABSTRACT FROM AUTHOR]