High-performance Asymmetric Supercapacitors Research Articles

Rational design of sucrose-derived graphitic carbon coated MnMoO4 for high performance asymmetric supercapacitor

The utilization of rich chemistry originating from redox activity of manganese-based compounds has spurred an increasing interest into energy storage technologies including supercapacitors and rechargeable batteries. Engineering manganese molybdate would offer peculiar electronic properties, significantly amplify intrinsic electrochemical properties. Herein, graphitic carbon layers successfully coated around MnMoO4 via one-pot hydrothermal approach to form crystalline microcube-shaped structure embedded carbon matrix (su-GC@MnMoO4). Electrochemical measurements reveal, su-GC@MnMoO4 electrode demonstrated specific capacitance of 528 F g−1 at 2 A g−1 and a cycling retention of 98.7 % of initial capacitance after 5000 cycles. In a two-electrode system of asymmetric supercapacitor with su-GC@MnMoO4 as cathode and activated carbon (AC) as anode, we achieved specific energy of 35.4 W h kg−1 at specific power of 223 W kg−1 and 96.7 % of initial capacitance was retained after consecutive 10,000 cycles. These profound capacitive properties are ascribed to synergy between Mn redox strength and electronic-mechanical properties of sucrose derived carbon.

Facial design and synthesis of Ce doped Co-Ni oxide nanocages with cubic structure for high-performance asymmetric supercapacitors

From the perspective of nano science and nanotechnology, it is very interesting and important to develop a reasonable and practical synthesis route of nanomaterials for production and life. Here, we develop a strategy of hollow cubic metal oxide nanocages. The method was inspired by Pearson’s Hard-Soft-Acid-Base (HSAB) theory, and nanocages with excellent performance were prepared by coordination etching and optimization of reaction conditions. Firstly, Cu2O nanocubes were prepared by redox reaction at room temperature. Then, the hollow cubic NiCo2Ox/CeOy nanocages were obtained by HSAB theory and cerium doping. The nanomaterial has a specific capacitance of up to 1976 F/g at the current density of 1 A/g. In addition, the asymmetric supercapacitor (ASC) prepared with hollow cubic NiCo2Ox/CeOy nanocage as cathode and active carbon as anode exhibits an energy density as high as 37.1 Wh kg−1 at the power density of 375 W kg−1. The capacitance retention rate of the device is 91.5 % after 10,000 cycles. The device can be charged to light up LED lights. These excellent electrochemical properties, due to their unique structure and synergistic effect between materials, indicate the potential application value of hollow cubic NiCo2Ox/CeOy nanocages in high-performance supercapacitors.

Deoxyribonucleic acid scaffold assisted structural engineering to tune the intrinsic to extrinsic capacitive behavior in spinel structured MnCo2O4.5 for high-performance asymmetric supercapacitor application

The spinel structured materials (e.g., MnCo2O4.5) are good aspirants for supercapacitor electrode application due to their outstanding pseudocapacitor performance. However, due to the collapsing of the crystal and morphological structures during electrochemical analysis, inferior cyclic stability and low energy density problems are inevitable when the materials are used as supercapacitor electrodes. Alteration of intrinsic (diffusion-controlled) to extrinsic (surface-controlled) capacitive behavior is the effective solution to overcome these issues. Herein, the intrinsic capacitor behavior of the MnCo2O4.5 material was altered into an extrinsic mechanism through the precipitation process with the aid of a deoxyribonucleic acid (DNA)-based structural engineering process. The MnCo2O4.5 coated on nickel foam current collector delivered the specific capacity of 649C g−1 at 1 A g−1 and retained 97 % of its initial capacity after 5000 cycles at 20 A g−1 in three-electrode configurations. Additionally, the MnCo2O4.5//Activated carbon asymmetric device showed a specific capacity of 93.8C g−1 at 1 A g−1 with energy and power densities of 33.4 Wh Kg−1 and 681 W Kg−1 at 1 A g−1, respectively. DNA-based structural engineering demonstrates the tuning of intrinsic to extrinsic capacitive behavior resulting in better supercapacitor properties in MnCo2O4.5 material.

Carbon quantum dot-induced robust ε-MnO2 electrode by synergistic engineering of oxygen vacancy and low crystallinity for high-performance flexible asymmetric supercapacitor

Developing high-capacitance and robust electrode materials for robust flexible supercapacitors is an ongoing challenge. To fabricate such energy storage devices, flexible electrodes with desired electrochemical and mechanical performances are crucial. Composition and structure tailoring of electrode materials play a significant role in exploiting high-performance flexible supercapacitors. Herein, CQDs-modified ε-MnO2 nanosheets with abundant oxygen vacancies and low crystallinity was uniformly grown on the skeletons of carbon cloth by a facile one-step electrodeposition strategy. Benefiting from the structural features and intrinsic defects, the obtained CQDs/ε-MnO2 electrode delivered outstanding mechanical property with tensile strength of 87 MPa and excellent electrochemical activity with high specific capacitance of 334.5 F g−1 at 1 A g−1 and remarkable rate capability as well as good cycling stability with 90% of capacitance retention after 6000 cycles at 5 A g−1, which was much better than pristine ε-MnO2 electrode. In addition, the assembled aqueous asymmetric supercapacitor (ASC) with good flexibility based on the CQDs/ε-MnO2 electrode could provide an energy density of 68.2 Wh kg−1 with power density of 990 W kg−1 at 5 A g−1 and long-term stability, outperforming most currently available flexible supercapacitors.

Ni3S2 thin-layer nanosheets coupled with Co9S8 nanoparticles anchored on 3D cross-linking composite structure CNT@MXene for high-performance asymmetric supercapacitor

Supercapacitors attract tremendous research attention due to the cost-effectiveness, high power capacity and environment-friendly in the field of energy storage. In this work, Ni3S2 thin-layer nanosheets coupled with Co9S8 nanoparticles anchored on 3D cross-linking composite structure 5 mLCNT@MXene matrix (Ni/Co@C5M) was successfully synthesized via two-step hydrothermal and subsequent annealing treatment, possessing excellent electrochemical performance in terms of high rate capability, superior reversible capacity and outstanding durability. The electrode materials have distinct 3D cross-linking composite structure characteristics, which can significantly boost capacitive storage performance due to the introduction of CNT cross-linking conductive bridges and sulfides. Meanwhile, CNT can also prevent re-stacking of MXene layers and improve the electrical conductivity. As expected, the specific capacitance of Ni/Co@C5M electrode is 1827.5 F g−1 at 1 A g−1, which retains 88.57% after 10,000 cycles at a high current density of 30 A g−1 in cycling stability. Notably, an asymmetric supercapacitor (Ni/Co@C5M as the negative electrode and AC as the positive electrode, Ni/Co@C5M // AC) has exceptionally high energy density up to 78.4 Wh kg−1 at a power density of 699.3 W kg−1 and long capacitance retention of 86.67% at 20 A g−1 for 10,000 cycles. The designed Ni/Co@C5M // AC asymmetric supercapacitor in this work holds a promising future for the upgrading new high-performance energy storage device.

Three-Dimensional α-Fe2O3/Graphene Hydrogel Composites as Anode Materials for High-Performance Asymmetric Supercapacitors

Three-Dimensional α-Fe2O3/Graphene Hydrogel Composites as Anode Materials for High-Performance Asymmetric Supercapacitors

Three-dimensional binder-free electrodes with high loading of electroactive material for high performance asymmetric supercapacitors

ZnCo bimetallic LDH is successfully grown on 3D Co 3 O 4 scaffolds on nickel foam as a stable hierarchical core-shell heterostructural electrode. Benefiting from the fine ion/electron transport within Co 3 O 4 @Zn 1 Co 2 -LDH electrode, the prepared Co 3 O 4 @Zn 1 Co 2 -LDH//ZiF-8 DC asymmetric supercapacitor exhibits a high energy density of 1.1 mWh cm -2 at a power density of 4.0 mW cm -2 , which is superior to the values of previous reports. • Three-dimensional binder-free electrodes are constructed with a core-shell heterostructure. • The electrode material can achieve a high quality loading of 13∼15 mg cm -2 . • The electrode achieves high areal capacitance of 10.5 F cm -2 at 5 mA cm -2 and high long durability. • The ASC device delivers a high energy density of 1.1 mWh cm -2 at a power density of 4.0 mW cm -2 . • The ASC device shows 82.0% of capacitance retention after 10000 cycles at 30 mA cm -2 . Rational design of electrode material structure is a key factor to improve high energy density/power density and long lifetime of supercapacitors. Here, a simple two-step hydrothermal strategy was used to synthesize Co 3 O 4 on nickel foam (NF), and a core-shell heterostructure was constructed by growing ZnCo bimetallic layered double hydroxides (LDH) on Co 3 O 4 scaffolds. Because of its unique heterogeneous structure and optimization of different components, the electrochemical performance of the active components was maximized because of the synergistic effect. The electrode material can achieve a high- quality loading of 13∼15 mg cm -2 . The binder-free electrode material Co 3 O 4 @Zn 1 Co 2 -OH grown directly on NF can achieve a high areal capacitance of 10.5 F cm -2 at 5 mA cm -2 and rate performance (82.9% retention at 30 mA cm -2 ) and long durability (62.3% capacitance retention at 30 mA cm -2 ). Additionally, a Co 3 O 4 @Zn 1 Co 2 -LDH//ZiF-8 DC (ZiF-8 Derived Carbon) asymmetric supercapacitor (ASC) is assembled with an operating voltage of 1.5 V. The ASC device delivers a maximum energy density of 1.1 mWh cm -2 (33.7 Wh kg -1 ) at a power density of 4.0 mW cm -2 (19.6 W kg -1 ) and exceptional cycling stability (82.0% of capacitance retention after 10000 cycles at 30 mA cm -2 ). This work demonstrates that hierarchical core-shell heterostructures show great potential in development of next-generation electrochemical energy storage devices.

Coordination-derived nickel cobalt sulfide solid microspheres with surface defects for high-performance asymmetric supercapacitors

Bimetallic sulfides are effective cathode materials for asymmetric supercapacitors because of their excellent electrochemical properties. However, both the low utilization ratio of the electrode material and the low energy storage capacity have restricted further development. In this work, Ni and Co were reacted with terephthalic acid (H2BDC) and isonicotinic acid (Ina) under hydrothermal conditions, followed by hydrolysis in 1 M KOH and vulcanization in thiourea to yield nickel cobalt sulfide (CoNi2S4) solid microspheres (NiCoS) with surface defects consisting of bumps and holes. These structural and morphological features compensate for the shortcomings of bimetallic sulfide electrodes, enhance their energy storage capacity, and improve their capacitance performance. The specific capacitance of the asymmetric supercapacitor assembled with NiCoS and a self-made carbon electrode reached 168.0 and 101.6 F/g at specific currents of 1 and 20 A/g, respectively. An increase in the specific current by a factor of 20 corresponded to an increase in capacitance retention rate to 60.5%, improving the rate performance. When the specific power increased to 800 and 16 000 W/kg, the specific energy reached 59.7 and 36.2 Wh/kg, respectively. Following 5,000 charge/discharge cycles, the capacitance retention rate was 96.78%. Such excellent comprehensive electrochemical performance greatly increases the competitiveness of the NiCoS electrode in the field of electrochemical energy storage.

Size-controllable synthesis of covalently interconnected few-shelled Fe3O4@onion-like carbons for high-performance asymmetric supercapacitors

Fe3O4 is considered as an appealing anode material for constructing high-energy-density asymmetric supercapacitors owing to its high theoretical capacitance, large potential window, natural abundance and eco-friendliness. However, the dilemma of inadequate practical capacitance, low rate performance and unsatisfactory cycling stability of Fe3O4-based electrode materials significantly plagues their progress in supercapacitor applications. To well utilize the advantage of Fe3O4, herein, Fe3O4@onion-like carbons (OLCs) with covalently interconnected and few-shelled graphitic coatings were synthesized in a size-controllable manner from uniform-sized monodispersed nanoparticles of Fe3O4@oleic acid ligands. The ultrasmall-sized Fe3O4 nanoparticles with a good size uniformity enable a high electrochemical activity and a pseudocapacitive-dominated electrochemical behavior. Meanwhile, the efficient ion/electron transportations are facilitated by the structural advantages including covalently interconnected graphitic layers, conformal and seamless graphitic coating with ultrathin thickness, and hierarchical pores. As a result of the synergistic cooperation of these merits, the Fe3O4@OLCs hybrid structure exhibits a high specific capacitance of 686.1 F g−1 at 1 A g−1 and a high rate capability with 71.3% capacitance retention at 10 A g−1, superior to most of the reported Fe3O4-based electrode materials. An asymmetric supercapacitor device assembled based on Fe3O4@ OLCs shows a high energy density of up to 63.1 Wh kg−1, which is still maintained as high as 39.1 Wh kg−1 at a high power density of 1.49 kW kg−1. Moreover, a high cycling stability (more than 80% of initial capacitance remained after 10,000 cycles) is obtained. This study offers a novel strategy for preparing high-performance Fe3O4/carbon hybrid structures for asymmetric supercapacitor applications.

Three-Dimensional Graphene-TiO2-SnO2 Ternary Nanocomposites for High-Performance Asymmetric Supercapacitors.

Ternary nanocomposites synergistically combine the material characteristics of three materials, altering the desired charge storage properties such as electrical conductivity, redox states, and surface area. Therefore, to improve the energy synergistic of SnO2, TiO2, and three-dimensional graphene, herein, we report a facile hydrothermal technique to synthesize a ternary nanocomposite of three-dimensional graphene-tin oxide-titanium dioxide (3DG-SnO2-TiO2). The synthesized ternary nanocomposite was characterized using material characterization techniques such as XRD, Raman spectroscopy, FTIR spectroscopy, FESEM, and EDXS. The surface area and porosity of the material were studied using Brunauer-Emmett-Teller (BET) studies. XRD studies showed the crystalline nature of the characteristic peaks of the individual materials, and FESEM studies revealed the deposition of SnO2-TiO2 on 3DG. The BET results show that incorporating 3DG into the SnO2-TiO2 binary nanocomposite increased its surface area compared to the binary composite. A three-electrode system compared the electrochemical performances of both the binary and ternary composites as a battery-type supercapacitor electrode in different molar KOH (1, 3, and 6 M) electrolytes. It was determined that the ternary nanocomposite electrode in 6 M KOH delivered a maximum specific capacitance of 232.7 C g-1 at 1 A g-1. An asymmetric supercapacitor (ASC) was fabricated based on 3DG-SnO2-TiO2 as a positive electrode and commercial activated carbon as a negative electrode (3DG-SnO2-TiO2//AC). The ASC delivered a maximum energy density of 28.6 Wh kg-1 at a power density of 367.7 W kg-1. Furthermore, the device delivered a superior cycling stability of ∼97% after 5000 cycles, showing its prospects as a commercial ASC electrode.

Ultra-fast electro-reduction and activation of graphene for high energy density wearable supercapacitor asymmetrically designed with MXene

Controlled perforation of graphene is vital to surpass the performance of supercapacitors that rely on their pristine form. However, their practical utilization has been halted by energy-inefficient and lengthy processing. Here, we are reporting a pulse Joule heating strategy for on-site reduction and activation to realize a multimodal porous framework made of perforated graphene using millisecond current pulses. The multimodal porosity and surface functionalities of graphene were regulated at an ultrafast rate by passing a transient current. As-developed ready-to-use electrode composed of nano-to-macro multimodal porosity displays high areal capacitance of 380.2 mF cm−2 in symmetric two-electrode configuration, which is nearly 1.6 times higher than the non-electro activated counterpart. Furthermore, a high-performance wearable asymmetric supercapacitor with an areal energy density of 107.8 μWh cm−2 was realized using this multimodal porous graphene in combination with suitable negative electrodes made of MXene. High energy density, together with stable and repeatable performance of the wearable device for 10000 cycles of charge-discharge and 5000 cycles of bending, signifies the importance of the as-developed device for practical wearable applications. Direct, simple processing of electrodes and orders of magnitude lower cost–and–processing–time can make the process appealing for practical wearable and other energy storage applications.

Improving capacity of nickel phosphate Versailles Santa Barbara-5 with calcination for high-performance asymmetric supercapacitors

Versailles Santa Barbara-5 (VSB-5) is a prominent example of nanoporous nickel-based materials for energy storage applications due to their high theoretical specific capacitance, thermal and chemical stability, and ease of synthesis. Yet, improving the electrochemical properties of VSB-5 for high-performance supercapacitors remains in high interest to exceed the current state-of-the-art. This work demonstrates the effect of different calcination temperatures of nickel phosphate (NiP) VSB-5 on its structure, morphology, and electrochemical performances. NiP VSB-5 was synthesized via hydrothermal technique followed by calcination at 300 °C (NiP-300), 400 °C (NiP-400), 500 °C (NiP-500), 600 °C (NiP-600), 700 °C (NiP-700), and 800 °C (NiP-800). Interestingly, the calcination temperatures induce the crystal-amorphous phase change and affect the diameter size of the NiP VSB-5 rod structure. The NiP-600 delivers the highest specific capacity of 516 C g−1 at 0.62 A g−1 compared to as-synthesized VSB-5 (31.4 C g−1), NiP-300 (103 C g−1), NiP-400 (189 C g−1), NiP-500 (279 C g−1), NiP-700 (396 C g−1), and NiP-800 (0.97 C g−1). The high specific capacity of NiP-600 is triggered by the amorphous phase and smaller particle diameter size, which provide abundant active sites for redox reactions. Furthermore, we assembled the best performing NiP-600 as the cathode and activated carbon (AC) as the anode into an asymmetric supercapacitor (SC). The NiP-600//AC-based supercapacitors achieved a remarkable energy density of 52 Wh kg−1 at a power density of 434 W kg−1, which is superior to several reported nickel phosphate-based SC. The SC can maintain 71 % of original capacitance after 2000 cycles at a scan rate of 100 mV s−1. This study provides insight into the effect of calcination temperature to generate the best-performing NiP VSB-5 electrode for high-performance supercapacitor.

High-performance solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/VS2 cathode and Fe3O4@rGO hydrogel anode

Herein, we report the synthesis of MXene/VS2 composites for asymmetric supercapacitors using a hydrothermal method. Impressively, the resulting MXene/VS2 electrode shows an outstanding specific capacity of 895.7 C g−1 (1791.4 F g−1) at 1 A g−1, rate capability (587.5 C g−1 (1175.0 F g−1) at 20 A g−1), and cycle performance (90.6% capacity retention after 10,000 cycles), owing to its specific microstructures with connected nanosheets and enhanced electrochemical conductivity arising from the synergistic effect of VS2 and conductive MXene. To achieve higher energy density in the solid-state asymmetric supercapacitor (ASC) device, Fe3O4 nanoparticles uniformly dispersed and encapsulated into the rGO sheets (Fe3O4@rGO) as a negative electrode is also designed. The obtained MXene/VS2 was used as a cathode and Fe3O4@rGO acted as a anode. Further, an assembled MXene/VS2//Fe3O4@rGO ASC device delivered an impressive specific capacitance of 365.4 C g−1 (228.4 F g−1) at 1 A g−1, in addition, the device yielded the specific energy of up to 73.9 Wh kg−1 at the corresponding specific power of 728.2 W kg−1 with superior cycling performance (90.7% capacity retention after 10,000 cycles at 8 A g−1), demonstrating its high potential for applications in high-porformance energy storage devices.

Wood-derived scaffolds decorating with nickel cobalt phosphate nanosheets and carbon nanotubes used as monolithic electrodes for assembling high-performance asymmetric supercapacitor

Lightweight carbonized wood (CW) loaded with pseudocapacitive materials has demonstrated excellent energy density. However, the direct loading of active materials usually results in poor rate performance and cycling stability. Herein, we fabricated a CW electrode with high loading of active materials and conductivity through chemical vapor deposition (CVD) and electrodeposition to sequentially incorporate carbon nanotubes (CNTs) and nickel–cobalt phosphate (NiCo-P) nanosheets. This integrated NiCo-P/CNT/CW electrode exhibited a promising areal capacitance of 11.2F cm−2 at a current density of 10 mA cm−2, and a notable capacitance retention rate of 86.6 % at 60 mA cm−2. The asymmetric supercapacitor (ASC) device assembled with the prepared electrode as anode and the self-activated carbonized wood (SCW) electrode as cathode delivers outstanding energy density of 5.74 mWh cm−3 (12.1 Wh kg−1) at power density of 18.75 mW cm−3 (39.5 W kg−1) while maintaining a high capacitance retention of 92.4 % after 10,000 charge–discharge cycles. This work provides an advanced approach for constructing supercapacitors with remarkable energy density and rate performance from the natural wood derived electrodes.

One-pot synthesis of flower-like Ni-Co/reduced graphene oxide layered double hydroxide nanocomposites as advanced electrodes for high-performance asymmetric supercapacitors

Novel electrode materials with appropriate architectures are always desired to increase the energy density of supercapacitors. Here, the design and fabrication of NiCo-layered double hydroxides (NC-LDH) in composition with reduced graphene oxide (rGO) were prepared as high-performance electrodes for supercapacitors. In particular, a facile and one-pot scheme was designed for the growth of NC/rGO-LDH composites, which exhibited a high specific surface area of 204 m2/g. The compositional features of the composites, i.e., a two-dimensional flower-like layered architecture and conductive rGO, contributed to their highly impressive specific capacitance (1913.5 F/g at 1 A/g) and excellent cyclic performance. Furthermore, an asymmetric supercapacitor was designed using NC/rGO-LDH composites as the positive electrode and activated carbon as the negative electrode, which displayed a high energy density of 59.2 Wh/kg at a power density of 750 W/kg.

Unveiling the role of surface functional groups for the design of nickel manganese/reduced graphene oxide based composite electrode material for high performance asymmetric supercapacitor

Development of additive-free electrode material on conductive substrates is a cost-effective strategy and is essential for the fabrication of high-performance supercapacitor. Herein, the effect of transition metal ions on the preparation of bimetallic (Ni & Mn)/reduced graphene oxide (RGO) composites through multi-step electrodeposition technique was extensively analysed. Two different composites; nickel manganese oxide/RGO (NiMn-G/NF) and manganese nickel oxyhydroxide/RGO (MnNi-G/NF) were synthesized through step-wise electrodeposition technique. The NiMn-G/NF and MnNi-G/NF were prepared through interchanging the source of host transition metal ions (Ni and Mn). Various physicochemical characterization techniques confirmed that the crystal structure as well as the morphology and electrochemical performance of the composites were largely dependent on the host metal ions. The formation of surface functional groups may play a key role in the electrochemical performance of supercapacitors. The MnNi-G/NF electrode showed high specific capacitance of ~1525 F g−1 at 1.5 A g−1 current density compared to NiMn-G/NF (~1312.5 F g−1) and other synthesized electrode materials. An asymmetric supercapacitor (ASC) device was fabricated using MnNi-G/NF as positive and thermally-RGO as negative electrode materials. The fabricated device exhibited highest specific capacitance of ~173.3 F g−1 at 2 A g−1 current density and maximum energy density of ~54.1 Wh kg−1 and power density of 9 kW kg−1.

Fabrication of robust Fe2O3@NiCo2O4 core-shell composite with spikey surface for high-performance asymmetric solid-state supercapacitor

The need for a cost-effective and efficient energy storage system instigates researchers to develop emerging electrode materials for energy storage devices. The α-Fe2O3-based electrode material for supercapacitor application has received interest due to its good electrochemical performance, high mechanical strength, corrosion resistance, low cost, and abundant availability. This work develops a cost-effective, robust Fe2O3@NiCo2O4 core-shell composite with spikey surface via a facile hydrothermal strategy for high-performance electrode material for supercapacitors. The spikes of Fe2O3 are developed on NiCo2O4 to collaborate in a more accessible surface area, with robust morphological stability throughout electrochemical performances. The Fe2O3@NiCo2O4 core-shell composite exhibits a high specific capacity of 364 C g−1 at the scan rate of 5 mV s−1 and 81% cycling stability up to 10,000 successive charge-discharge cycles at the current density of 15 A g−1. Moreover, an asymmetric solid-state supercapacitor (ASSC) device was fabricated using Fe2O3@NiCo2O4 composite as a positive electrode and commercially purchased activated carbon as a negative electrode assembled via PVA/KOH gel electrolyte. The fabricated device offers a significant energy density of 31.7 W h Kg−1 at a power density of 700 W Kg−1. The ASSC exhibits excellent capacitance retention of 90% with ultra-high coulombic efficiency of 99.7% up to 10,000 GCD cycles. The ASSC can illuminate the red and yellow LED light. This work indicates that a robust Fe2O3@NiCo2O4 core-shell composite can be an economic strategy for fabricating high-performance practical supercapacitor applications.

Construction of high-performance asymmetric supercapacitor based on FeCo-LDH@C3N4 composite electrode material with penetrating structure

The layered structure of layered double hydroxides (LDH) is the key to its use as an electrode material, however, the lack of efficient charge exchange between layered structures severely limits the application of LDH in supercapacitors. In this work, FeCo-LDH was composited with C3N4 by hydrothermal method, and a penetrating structure was built using the layered structure of the two materials. The penetrating structure provides a channel for charge transfer between FeCo-LDH layers and also solves the self-stacking problem of C3N4. The structure of the composites was explored by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM), and the results showed that FeCo-LDH composited with C3N4 and formed a penetrating structure. In addition, the electrochemical behavior of the electrode material was evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Electrochemical test results show that it has a high specific capacity (593 C g−1) at 1 A g−1. Furthermore, in order to study the energy storage properties of the composites, the optimal composites were designed as positive electrode as asymmetric supercapacitors, and the designed asymmetric supercapacitor still has a retention rate of 83.72 % after 10,000 cycles. This attractive performance reveals that FeCo-LDH@C3N4 could as an electrode material for high-performance supercapacitors.

Preparation of rGO/MXene@NiCo-P and rGO/MXene@Fe2O3 positive and negative composite electrodes for high-performance asymmetric supercapacitors

In this study, reduced graphene oxide/MXene-based composite electrodes combined with Fe2O3 and NiCo-P as the negative and positive electrodes are prepared by a facile in-situ solvothermal route. Both rGO/MXene@Fe2O3 and rGO/MXene@NiCo-P have an interconnected nanostructure with the specific surface areas at 17.1 and 131.9 m2·g−1. The specific capacitance of the as-prepared rGO/MXene@Fe2O3 and rGO/MXene@NiCo-P composite electrodes are 248.13 and 214.66 mAh·g−1 under current density at 1 A·g−1. An asymmetric supercapacitor (ASC) is further assembled using rGO/MXene@Fe2O3 and rGO/MXene@NiCo-P as the negative and positive electrodes, respectively. The maximum energy density of the assembled ASC is 29.46 Wh·kg−1 at a power density of 700.34 W·kg−1. After 10,000 cycles, 70.87 % of the capacity can be retained. These results demonstrate the potential application of composite electrode materials for supercapacitors.

Phosphate ion-functionalized nickel-cobalt layered double hydroxide nanosheets derived from metal-organic framework compounds for high-performance asymmetric supercapacitors

The modification by functionalized ions (surface modification or doping) presents facile and efficient access to enhance the electrochemical performance of electrode materials. However, the effect of functionalized ions on the structure-performance relationship of electrode materials is not yet apparent. Herein, we develop a novel phosphate ion-functionalized nickel-cobalt layered double hydroxide nanosheet (Ni-Co-P80) derived from metal-organic framework compounds prepared as anode material for supercapacitors. The obtained Ni-Co-P80 not only remains characterized by high specific surface area and porosity, but also possesses more active sites and higher electrical conductivity with phosphate modification, thus improving the charge transfer kinetics. The electrochemical test results show that the highest specific capacitance of Ni-Co-P80 modified with phosphate ions increases by 49.7% compared to pure phase LDH. More impressively, the assembled asymmetric supercapacitor exhibits an excellent energy density of 64.89 Wh kg-1 at a power density of 1600 W kg-1 with an ultralong cyclic performance of 77.78% capacitance retention after 5000 cycles. This study explicitly demonstrates the remarkable enhancement of specific capacitance of layered double hydroxide following modification with phosphate ions. It brings a prospective pathway toward the rational design of LDH-based high-performance asymmetric supercapacitors.