Metal-Organic Frameworks and Their Derivatives-Based Nanostructure with Different Dimensionalities for Supercapacitors.

With the urgent demand for the achievement of carbon neutrality, novel nanomaterials, and environmentally friendly nanotechnologies are constantly being explored and continue to drive the sustainable development of energy storage and conversion installations. Among various candidate materials, metal-organic frameworks (MOFs) and their derivatives with unique nanostructures have attracted increasing attention and intensive investigation for the construction of next generation electrode materials, benefitting from their unique intrinsic characteristics such as large specific surface area, high porosity, and chemical tunability as well as the interconnected channels. Nevertheless, the poor electrochemical conductivity severely limits their application prospects, hence a variety of nanocomposites with multifarious structures have been designed and proposed from different dimensionalities. In this review, recent advances based on MOFs and their derivatives in different dimensionalities ranging from 1D nanopowders to 2D nanofilms and 3D aerogels, as well as 4D self-supporting electrodes for supercapacitors are summarized and highlighted. Furthermore, the key challenges and perspectives of MOFs and their derivatives-based materials for the practical and sustainable electrochemical energy conversion and storage applications are also briefly discussed, which may be served as a guideline for the design of next-generation electrode materials from different dimensionalities.

In Situ Generation of Vertically Crossed P-Cu3Se2 Ultrathin Nanosheets Derived from Cu2S Nanorod Arrays for High-Performance Supercapacitors.

Transition-metal selenides (TMSs) have great potential in the synthesis of supercapacitor electrode materials due to their rich content and high specific capacity. However, the aggregation phenomenon of TMS materials in the process of charging and discharging will cause capacity attenuation, which seriously affects the service life and practical applications. Therefore, it is of great practical significance to design simple and efficient synthesis strategies to overcome these shortcomings. Hence, P-doped Cu3Se2 nanosheets are loaded on vertically aligned Cu2S nanorod arrays to synthesize CF/Cu2S@Cu3Se2/P nanocomposites with a unique core-shell heterostructure. Notably, the Cu2S precursors can be rapidly converted into Cu3Se2 nanorod arrays in situ in just 30 min at room temperature. The unique core-shell heterostructure effectively avoids the aggregation phenomenon, and the doped P elements further enhance the electrochemical properties of the electrode materials. Therefore, the as-prepared CF/Cu2S@Cu3Se2/P electrode exhibits a high areal capacitance of 5054 mF cm-2 (1099 C g-1) at 3 mA cm-2 and still retains 90.2% capacitance after 10 000 galvanostatic charge-discharge (GCD) cycles. The asymmetric supercapacitor (ASC) device assembled from synthetic CF/Cu2S@Cu3Se2/P and activated carbon (AC) possesses an energy density of 41.1 Wh kg-1 at a power density of 480.4 W kg-1. This work shows that the designed CF/Cu2S@Cu3Se2/P electrode has broad application prospects in the field of electrochemical energy storage.

In situ construction of metal-organic frameworks on chitosan-derived nitrogen self-doped porous carbon for high-performance supercapacitors.

The intelligent use of regenerable and degradable biomass materials to substitute the synthetic materials can bring huge economic benefits and environmental improvements. In addition, metal-organic framework (MOF) based cathode materials are becoming a research hotspot for supercapacitors. Here, Co nanoparticle-modified nitrogen self-doped porous carbonized chitosan aerogel (CCA-Co) precursors were prepared by sol-gel, freeze-drying technique and carbonization process using biomass chitosan particles and cobalt compounds as raw materials. Then the layered composite (CCA-Co@MOF) was obtained by growing Co-doped Ni MOF (Co-Ni MOF) with CCA-Co precursor as the carrier. Notably, the presence of Co nanoparticles in carbonized chitosan aerogel (CCA) not only promotes the self-assembly of CCA and MOF, but also etched Co ions can participate in the growth of MOF, resulting in excellent electrochemical performance. Specifically, the specific capacitance of CCA-Co@MOF reaches 1877.2 F g-1, which is much superior to CCA-M@MOFs (M = Ni, Zn and Cu) and other contrast materials. Furthermore, the asymmetric supercapacitor (CCA-Co@MOF//AC ASC) assembled using CCA-Co@MOF and activated carbon (AC) electrodes, exhibits a high energy density (45.9 Wh kg-1 at 431.7 W kg-1). This work highlights the advantages of metal nanoparticle-modified and carbonized chitosan aerogels for MOF growth, demonstrating its great value in the field of electrochemical energy storage.

Embedding of conductive Ag nanoparticles among honeycomb-like NiMn layered double hydroxide nanosheet arrays for ultra-high performance flexible supercapacitors.

Layered double hydroxides are considered promising electrode materials for the preparation of high-energy-density supercapacitors owing to their suitable microstructure and significant electrochemical properties. In this study, honeycomb-like NiMn-layered double-hydroxide (NiMn-LDH) nanosheet arrays with numerous electron/ion channels, a large number of active sites, considerable redox reversibility, and significant electrical conductivity were synthesized by combining Co2(OH)2CO3 nanoneedle arrays with NiMn-LDH nanosheet arrays and Ag nanoparticles on a carbon cloth (CC) substrate through a hydrothermal strategy (CC@Co2CH/NM-LDH-Ag). The fabricated CC@Co2CH/NM-LDH-Ag binder-free electrode exhibited a high specific capacitance of 10,976 mF cm-2 (3092F/g, 1391.4C g-1) at 2 mA cm-2 (1 A/g), and a high capacitance retention of 93.2 % after 10,000 cycles at a current density of 20 mA cm-2. In addition, a solid-state asymmetric supercapacitor (ASC) device assembled using CC@Co2CH/NM-LDH-Ag as the cathode possessed an ultrahigh energy density of 68.85 Wh kg-1 at a power density of 722.6 W kg-1, and two fabricated ASC units in series were able to power a multifunctional display for more than 30 min. Therefore, this study provides a new approach for the design and synthesis of high-performance flexible electrodes.

Ternary NiCeCo-Layered Double Hydroxides Grown on CuBr2@ZIF-67 Nanowire Arrays for High-Performance Supercapacitors.

Ternary layered double-hydroxide-based active compounds are regarded as ideal electrode materials for supercapacitors because of their unique structural characteristics and excellent electrochemical properties. Herein, an NiCeCo-layered double hydroxide with a core-shell structure grown on copper bromide nanowire arrays (CuBr2@NCC-LDH/CF) has been synthesized through a hydrothermal strategy and calcination process and utilized to fabricate a binder-free electrode. Due to the unique top-tangled structure and the complex assembly of different active components, the prepared hierarchical CuBr2@NCC-LDH/CF binder-free electrode exhibits an outstanding electrochemical performance, including a remarkable areal capacitance of 5460 mF cm-2 at 2 mA cm-2 and a capacitance retention of 88% at 50 mA cm-2 as well as a low internal resistance of 0.163 Ω. Moreover, an all-solid-state asymmetric supercapacitor (ASC) installed with CuBr2@NCC-LDH/CF and activated carbon electrodes shows a high energy density of 118 Wh kg-1 at a power density of 1013 W kg-1. Three assembled ASCs connected in series can operate a multifunctional display for over three and a half hours. Therefore, this innovative work provides new inspiration for the preparation of electrode materials for supercapacitors.

Controllable synthesis of nickel doped hierarchical zinc MOF with tunable morphologies for enhanced supercapability.

Metal-organic frameworks (MOFs) are attracting tremendous research interest because of their rich redox sites and high specific area which are beneficial for the energy storage applications. Nevertheless, the poor conductivity, low mechanical strength and unsatisfactory capacity severely hinder their wide application. Hence, it is of practical significance to design highly efficient and facile strategy to solve these issues. Herein, vertically oriented ZnO nanorod arrays are applied as precursor to synthesize laminated scale-like and highly-oriented Ni/Zn-MOF/ZnO nanocomposite. Owing to the desirable conductivity resulting from the doping nickel ions and the interaction between ZnO and its relative MOF, the fabricated 0.3Ni/Zn-MOF/ZnO@CC electrode exhibits an electrochemical capacitance of 1693 mF cm-2 at 1 mA cm-2. Moreover, the electrochemical capacitance retention of 80.7 % after 2500 cycling numbers is obtained under the constant current density of 10 mA cm-2 and the low internal resistance Rs of 0.89 Ω is observed. For practical application, the as-synthesized laminated scale-like Ni/Zn-MOF/ZnO@CC nanocomposite is served as positive electrode to fabricate solid-state asymmetric supercapacitor device. Moreover, a 2.5 V indicator could be powered for 8 min when the prepared supercapacitor units are connected. This work demonstrates the promising potential of the synthesized scale-like Ni/Zn-MOF composites for electrochemical energy storage applications.

Origami and layered-shaped ZnNiFe-LDH synthesized on Cu(OH)2 nanorods array to enhance the energy storage capability.

The combination of layered nanorod arrays with unique core-shell structure and transition metal layered double hydroxide (LDH) is considered as a feasible solution to improve the electrochemical performances of capacitor electrode. In this study, layered ZnNiFe-LDH@Cu(OH)2/CF core-shell nanorod arrays, which consist of ultrathin ZnNiFe-LDHs nanosheet shells and ordered Cu(OH)2 nanorod inner cores, are successfully designed and fabricated by a typical hydrothermal way and a simple in situ oxidation reaction. The electrode prepared using ZnNiFe-LDH@Cu(OH)2/CF nanomaterial reveals an remarkable area capacitance of 6100 mF cm-2 at 3 mA cm-2 current density, which is excellently superior than those of ZnFe-LDH@Cu(OH)2/CF, NiFe-LDH@Cu(OH)2/CF, Cu(OH)2/CF and CF. Additionally, the capacitance retention remains as high as 83.4% after 5000 cycles and a very small Rs (0.567 Ω) can be observed. In addition, an asymmetric supercapacitor device is successfully fabricated employing ZnNiFe-LDH@Cu(OH)2/CF. Meanwhile, the ZnNiFe-LDH@Cu(OH)2/CF//AC device can achieve an energy density of 44 Wh kg-1 and a corresponding power density of 720 W kg-1 and possess the capability to light up a multi-function monitor for 33 min just using two ASC equipments connected in series. Therefore, the prepared ZnNiFe-LDH@Cu(OH)2/CF composite materials with unique structure has great application potential in energy storage devices.

In Situ Synthesis of CoCeSx Bimetallic Sulfide Nanoparticles on a Bi-Pyrene Terminated Molecular Wire Modified Graphene Surface for Supercapacitors.

The excellent electrical conductivity of graphene is due to its highly-conjugated structures. Manipulation of the electronic and mechanical properties of graphene can be achieved by controlling the destruction of its in-sheet conjugation system. Herein, we report the preparation of CoCeSx -SA@BPMW@RGO through π-π stacking interactions at the molecular level. In this study, sodium alginate was reacted with Co2+ and Ce3+ , and the composite was loaded onto a graphene surface. The graphene sheets were prepared using a bi-pyrene terminated molecular wire (BPMW) to avoid re-stacking of the grapheme sheets, thereby forming nanoscale spaces between sheets. The angle between the BPMW coplanar pyrene group and the phenyl group was 33.2°, and the graphene layer is supported in an oblique direction. Finally, a three-dimensional porous composite was obtained after annealing and vulcanization. The obtained CoCeSx -SA@BPMW@RGO exhibited excellent electrical conductivity and remarkable cycle stability. When the current density was 1 A g-1 , its specific capacitance was as high as 1004 F g-1 . BPMW modifies graphene through the synergistic effect of π-π stacking interaction and special structure to obtain excellent electrochemical performance. Moreover, a solid-state asymmetric supercapacitor device was fabricated based on the synthesized CoCeSx -SA@BPMW@RGO hybrid, which exhibited a power density of 979 W kg-1 at an energy density of 23.96 Wh kg-1 .