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Maintaining a high specific energy without losing cycling stability is the focus of the supercapacitor field. In this study, carbon nanofibers including europium oxide nanoparticles (CNF/Eu2O3) have been synthesized in the presence of thiourea via a simple approach and applied for the first time as an electrode for SCs. The CNF/Eu2O3-1 electrode doped with nitrogen and sulfur heteroatoms possessed a favorable specific capacitance of 183.2 F g−1, a specific energy of 9.15 W h kg−1, and an excellent capacitance retention of 94.8% even after 10 000 cycles at 1 A g−1. Such excellent performance is ascribed to the surface functionalities, high surface area, and good interaction of Eu2O3 with CNFs. This strategy will provide guidance for other rare element-based electrodes in the field of energy storage. [ABSTRACT FROM AUTHOR]

Herein, MnO2 nanoflowers are electrodeposited on a self-supported and electroconductive electrode in which 2D Ti3C2Tx nanosheets are encased in carbon nanofibers (MnO2@Ti3C2Tx/CNFs). This improves the conductivity and hydrophilicity of the MnO2 composite electrode. The asymmetric supercapacitor shows a high energy density of 46.4 W h kg−1 and a power density of 4 kW kg−1. [ABSTRACT FROM AUTHOR]

VN usually has poor rate performance and cycle stability. In this work, porous VN nanosheet arrays were prepared on carbon nanofibers embedded with Ti3C2Tx nanosheets by electrospinning and chemical vapor deposition. The 3D network accelerates the transfer of electrons and electrolyte ions, prevents the aggregation of VN and the self-stacking of MXene, and enhances cycle stability. The solid-state flexible device comprising Co3O4, MXCF@VN, and KOH/PVA exhibits exceptional energy densities of 83.95 W h kg−1 and robust cycling stability (82.8% retention after 20 000 cycles). [ABSTRACT FROM AUTHOR]

Transition metal sulfides (TMSs) are favorable as electrode materials for supercapacitors (SCs) because of their high theoretical capacity, low cost, fascinating redox reversibility, electronic conductivity, and reduced charge transfer resistance. However, TMS electrodes suffer from weak compatibility and combination at heterogeneous interfaces, resulting in TMS stripping and electrode capacity degradation during long-term charging/discharging processes. Herein, we used a convenient, feasible, cheap, and environmentally friendly hydrothermal method to grow S/CoS2/NiS2in situ on Pien Tze Huang-based porous carbon (PZH) to promote the poor electric conductivity and unsatisfactory cycling stability of TMSs. Furthermore, TMSs can be tightly embedded on the surface of PZH to prevent falling off or collapse during long-term processes and usage. The prepared S/CoS2/NiS2/PZH electrode possessed an excellent specific capacitance of 1159.2 F g−1 at 0.5 A g−1, and after 10 000 cycles at 5 A g−1, the capacitance retention was maintained over 84.6%. This in situ method is promising for the development of stable TMS-based electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

Carbon materials play an important role in supercapacitors due to their structural diversity, rich surface morphology, excellent chemical stability and highly active surfaces. Currently, there are many reports on the synthesis methods for carbon-based materials. The molten salt method stands out among the many methods for its advantages of economy, environmental protection, high efficiency, and maneuverability. Here, we focus on the different roles played by molten salts as templates, sealants, reaction media, and catalysts from the point of view of their functions. The properties and selection principles of the molten salts are discussed in depth, focusing on the morphology, structure, and capacitive properties of the carbon materials prepared using the molten salt strategy. Finally, the current research status of the preparation of carbon-based materials by the molten salt method is summarized, the shortcomings of existing technology are pointed out, and the prospects for its development are envisioned. It is hoped that this review can provide some basic knowledge for the preparation of carbon-based materials by the molten salt method and promote further research on molten salt technology. [ABSTRACT FROM AUTHOR]

Thin carbon nanofibers (TCNFs) hanging on branched carbon nanofibers (3D TCNF/CNF) with an N-doping level up to 8.7 at% for high-performance supercapacitors are designed and synthesized. TCNF/CNF shows a 3D hierarchical porous structure, a large surface area, abundant ionic-channels, and a great number of electrochemically active sites by N-doping. Because of the multiple synergistic effects of these features, the supercapacitors (SCs) based on TCNF/CNF show a remarkably excellent electrochemical behavior with a high specific capacitance of 224 F g−1. After 50 000 cycles of charge/discharge, 92% of the initial capacitance value is retained in 1.0 M H2SO4 electrolyte. Moreover, the TCNF/CNF-based SCs show low internal resistance, leading to a high power density with a relatively high energy density. [ABSTRACT FROM AUTHOR]

Highly graphitic porous carbon was derived from kelp biomass and prepared using KOH as the main activating agent with K2FeO4 as the assisting activated agent for supercapacitor applications. The optimum K2FeO4 mass in the total activating agent and temperature were investigated. The characterization results showed porous sheet carbon with a high specific surface area of 2868 m2 g−1 and a low ID/IG of 0.909. It delivered an excellent specific capacitance of 438 F g−1 at 0.5 A g−1. In addition, the assembled supercapacitor device reached the highest energy density of 19.9 W h kg−1 with a power density of 398 W kg−1. [ABSTRACT FROM AUTHOR]

The mesoporous carbon nanofiber arrays that stand on carbon–gold double-layer current collectors are synthesized by self-assembly of a PS-b-PEO copolymer and resol in AAO templates for a high-power micro-supercapacitor at high current densities. [ABSTRACT FROM AUTHOR]

In view of the problems surrounding the research and application of carbon materials, the process of choosing a carbon source is still not perfect. There are few studies concentrating on the establishment of structure–property relationships based on the choice of carbon source. In this regard, our present work contributes the design of an organic precursor that is expected to allow the controllable construction of the carbon material, thus regulating its functionality. A highly π-conjugated Schiff base moiety with alternating imine groups (C＝N) and benzene rings was incorporated into the main chain of a mesoporous polymer. For comparison, a bisphenol-A-type moiety was employed in the main chain of another mesoporous polymer. Using the mesoporous polymers as organic precursors for porous carbon sources, the formation of mesoporous carbon can be attributed to the presence of the highly π-conjugated Schiff base moiety due to its self-supporting effect and char-forming ability, which are absent in the bisphenol-A-type moiety. However, we are not only concerned with the contribution from the chemical structure of the designed precursor to the controllable construction of mesoporous carbon, but also concerned with its regulation of the electrochemical performance of the resulting material. Through characterization using cyclic voltammetry (CV), galvanostatic charge–discharge profiles, and electrochemical impedance spectroscopy (EIS), this kind of mesoporous carbon has been found to have excellent charge storage and transportation abilities and shows potential for application in the electrodes of electrochemical capacitors. [ABSTRACT FROM AUTHOR]

A novel N-doped MOF-based hierarchical carbon fiber (NPCF) towards supercapacitors was prepared by the pyrolysis of MOF nanofibers. Due to its unique 1D hollow structures, the NPCF exhibits better energy storage capacity than the other previously reported MOF-derived carbon materials. [ABSTRACT FROM AUTHOR]

Electrode materials play a vital role for supercapacitors. The development of an efficient and reproducible strategy for the fabrication of hollow mesoporous materials with specific morphologies and microstructures has attracted considerable research interest in recent years. Herein, NiCo2Se4 with a mesoporous surface and one-dimensional tubular hollow structure is synthesized using carbon nanofibers as the template for use as the positive electrode material in asymmetric supercapacitors. Because of the bimetallic selenide component and the unique structure, mesoporous NiCo2Se4 tubes demonstrate exceptional energy-storage performance. When evaluated as an electrode material for supercapacitors, these mesoporous NiCo2Se4 tubes show a specific capacitance of 209.1 mA h g−1 (1762.1 F g−1) at a current density of 1 A g−1, with a retention of 82% after 10 000 cycles at 5 A g−1. Even when the current density increased to 20 A g−1, 61% is still retained. Asymmetric supercapacitors are assembled by mesoporous NiCo2Se4 tubes and active carbon shows a high energy density of 24.03 W h kg−1 at a power density of 1.055 kW kg−1 as well as long-term cycle stability (94% retention of the initial specific capacitance after 10 000 cycles at 5 A g−1). All experimental results highlight that mesoporous NiCo2Se4 tubes will be a promising electrode material for practical supercapacitor applications. [ABSTRACT FROM AUTHOR]

The rational design of the morphological structure of electrode materials is considered as an important strategy to obtain high-performance supercapacitors. So, NiCoZnS materials with different Ni/Co/Zn molar ratios on Ni foam (NF) were synthesized, in which the Ni/Co/Zn molar ratio plays a key role in the morphological structure and electrochemical performances. Furthermore, the pre-prepared NiCoZnS materials act as substrates to guide the self-assembling of NiCoFe layered double hydroxide (LDH) nanosheets on the substrate surface to form core--shell electrode materials (NiCoZnS@NiCoFe-LDH) with a 3D mesoporous hierarchical network structure for further improving electrochemical performances. The unique interconnected coral-like NiCoZnS1@NiCoFe-LDH with a large specific surface area (93.1 m² g-1) and high specific capacitance is achieved at the Ni/Co/Zn molar ratio of 1 : 1 : 1. Benefiting from the unique structural feature and respective merits of the NiCoZnS and NiCoFe-LDH, the NiCoZnS1@NiCoFe-LDH demonstrates an ultrahigh specific capacitance of 1524.0 C g-1 (3386.7 F g-1) at 1.0 A g-1 and excellent 95.0% capacitance retention at 10 A g-1 after 5000 cycles. As for practical application, the assembled NiCoZnS1@NiCoFe-LDH//AC delivers a favorable energy density of 66.25 W h kg-1 at 1500 W kg-1 and a long-term cycling lifetime (86.04% retention at 5.0 A g-1 after 10 000 cycles), which suggests promising potential in energy storage and conversion. [ABSTRACT FROM AUTHOR]

Thick carbon nanofiber (CNF) films were uniformly grown on metal wires with the assistance of pre-deposited NiO nanowalls. The as-prepared wire-shaped composites that integrate the capacitance of CNFs and Ni particles were directly used as electrodes to construct high capacitive fiber supercapacitors for micro-power supplies. [ABSTRACT FROM AUTHOR]

We demonstrate a facile methodology to fabricate binder-free porous carbon nanofiber electrodes for room temperature ionic-liquid supercapacitors. The device provides an energy density of 80 W h kg−1 based on the mass of two electrodes while retaining the high rate capability of supercapacitors with near-ideal CV curves at a high scan rate of 200 mV s−1. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have emerged as promising electrode materials for supercapacitors (SCs) due to their highly porous structures, tunable chemical compositions, and diverse morphologies. However, their applications are hindered by low conductivity and poor cycling performance. A novel approach for resolving this issue involves the growth of layered double hydroxides (LDHs) using MOFs as efficient templates or precursors for electrode material preparation. This method effectively enhances the stability, electrical conductivity, and mass transport ability of MOFs. The MOF-derived LDH exhibits a well-defined porous micro-/nano-structure, facilitating the dispersion of active sites and preventing the aggregation of LDHs. Firstly, this paper introduces synthesis strategies for converting MOFs into LDHs. Subsequently, recent research progress in MOF-derived LDHs encompassing pristine LDH powders, LDH composites, and LDH-based arrays, along with their applications in SCs, is overviewed. Finally, the challenges associated with MOF-derived LDH electrode materials and potential solutions are discussed. [ABSTRACT FROM AUTHOR]

In order to quench the thirst for efficient energy storage devices, a novel praseodymium-based state-ofthe-art three-dimensional metal-organic framework (MOF), {[Pr(pdc)2]Me2NH2}n (YK-1), has been synthesized by using a simple solvothermal method employing a readily available ligand. YK-1 was characterised by single-crystal XRD and crystallographic analysis. The electrochemical measurements of YK-1 show that it exhibits a specific capacitance of 363.5 F g-1 at a current density of 1.5 A g-1 with 83.8% retention after 5000 cycles. In order to enhance its electrochemical performance for practical application, two composites of YK-1 with graphene oxide (GO) and functionalised multi-walled carbon nanotubes (FCNTs), namely YK-1@GO and YK-1@FCNT, were fabricated by employing a facile ultrasonication technique. The as-synthesized MOF and the composites were characterized by PXRD, FTIR, SEM, and TEM techniques. YK-1@GO and YK-1@FCNT offer enhanced specific capacitances of 488.2 F g-1 and 730.2 F g-1 at the same current density with 93.8% and 97.7% capacity retention after 5000 cycles, respectively (at 16 A g-1). Fascinated by the outstanding results shown by YK-1@FCNT, a symmetric supercapacitor device (SSC) based on it was fabricated. The assembled SSC achieved a remarkable energy density (87.6 W h kg-1) and power density (750.2 W kg-1) at a current density of 1 A g-1, along with very good cycling stability of 91.4% even after 5000 GCD cycles. The SSC device was able to power up several LED lights and even operated a DC brushless fan for a significant amount of time. To the best of our knowledge, the assembled SSC device exhibits the highest energy density among the MOF composite-based SSCs reported so far. [ABSTRACT FROM AUTHOR]

Supercapacitors are regarded as promising electrochemical energy storage solutions due to their multiple advantages. In this study, we report simple hydrothermal synthesis of nanostructured MnMoO4 (MMO) using CTAB and PVA as structure-directing agents, which is then employed as an electrode material in high-performance asymmetric supercapacitors. This resulted in the formation of morphologies analogous to nanoflakes (for CTAB; MMO-C), nanosheets (for PVA; MMO-P), and nanobundles (without a surfactant; MMO). MMO-C has a nanoflake-like structure with a large surface area, and an increasing number of electroactive surface sites and contact areas at the electrode–electrolyte interface. This results in a higher specific capacitance than other electrodes, measuring 919.6 F g−1 and 505 F g−1 at 1 A g−1 and 10 A g−1, respectively. It also exhibits extended cycling performance, with 94.1% retention after 10 000 cycles. The fabricated MMO-C//activated carbon (AC) asymmetric supercapacitor (ASC) device achieved a high specific capacitance of 111.9 F g−1 at 1 A g−1 in an operational potential window of 0–1.5 V. The ASC also has a high specific energy of 39.45 W h kg−1 at a specific power of 837.66 W kg−1 while retaining 90.3% of its initial capacitance after 10 000 cycles. A red LED was also turned on for 120 seconds when two ASCs were connected in series. [ABSTRACT FROM AUTHOR]

Hydrothermally synthesized micro-flower structure of ZnMoO4 and nano-flower structure of Ni(OH)2 were employed as an electrode materials for supercapacitors. Composites of ZnMoO4 anchored with Ni(OH)2 were prepared in different ratios (9 : 1, 8 : 2, 7 : 3) and their electrochemical performance was analyzed using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD) analysis, and stability studies. The Z/N-2 composite with a weight ratio of ZMO : NOH of 8 : 2, displayed a higher specific capacitance of 662 F g−1 at a current density of 1 A g−1. During the stability study, the composite (Z/N-2) exhibited a 73.4% retention of its capacitance at a current density of 5 A g−1, indicating its excellent stability at a high current density after 4000 cycles. The enhanced performance of the Z/N-2 composite, resulting from the good conductivity of ZnMoO4 and the battery-type charge-storage behavior of Ni(OH)2, paves way for its development as a robust electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

Transition metal sulfides have attracted much attention due to their excellent electrochemical properties. However, their preparation process often requires multiple steps to be completed, which poses difficulties for their application. In this paper, a NiCo2S4(NCS)@NiCo-LDH material was successfully prepared as the cathode material for the prepared supercapacitor by a one-step hydrothermal method using a MOF as a sacrificial template. The electrode material exhibits good electrochemical performance due to the regular microstructure with abundant active sites. The electrode material exhibits a specific capacitance as high as 4191.25 mF cm−2 in the three-electrode system at a current density of 2 mA cm−2. This is much higher than the sum of the capacitances of the NiCo2S4 and NiCo-LDH materials. To further validate its practical application, it was assembled with an activated carbon negative electrode to prepare a high-performance supercapacitor with a scalable voltage window of up to 1.6 V. The device was able to maintain 90% capacity retention after 5000 cycles and showed excellent performance. This work provides a new way to design and fabricate electrode materials with high performance and lifetime. [ABSTRACT FROM AUTHOR]

Grid-scale energy storage solutions are necessary for using renewable energy sources efficiently. A supercapattery (supercapacitor + battery) has recently been introduced as a new variety of hybrid devices that engage both capacitive and faradaic charge storage processes. Nano-chain architectures of Ni0.5Co0.5S electrode materials consisting of interconnected nano-spheres are rationally constructed by tailoring the surface structure. Nano-chains of the bimetallic sulfide Ni0.5Co0.5S are presented to have a superior charge storage capacity. The Ni0.5Co0.5S nano-chain electrode presents a capacitance of 2001.6 F g−1 at 1 mV s−1, with a specific capacity of 267 mA h g−1 (1920 F g−1) at 1 A g−1 in 4 M KOH aqueous electrolyte through the galvanostatic charge–discharge (GCD) method. The reason behind the high charge storage capacity of the materials is the predominant redox-mediated diffusion-controlled pseudocapacitive mechanism coupled with surface capacitance (electrosorption), as the surface (outer) and intercalative (inner) charges stored by the Ni0.5Co0.5S electrodes are close to 46.0% and 54.0%, respectively. Additionally, a Ni0.5Co0.5S//AC two electrode full cell operating in asymmetric supercapacitor cell (ASCs) mode in 4 M KOH electrolyte exhibits an impressive energy density equivalent to 257 W h kg−1 and a power density of 0.73 kW kg−1 at a current rate of 1 A g−1. [ABSTRACT FROM AUTHOR]

Although bimetallic oxide electrodes have excellent physical and chemical properties, as well as a high theoretical capacity, their low energy density and poor cycling stability restrict their application in supercapacitors (SCs). This study demonstrates an effective method for enhancing the conductivity and capacitance performance of NiMoO4 by inducing oxygen vacancies. The electrochemical performance of Ov-NiMoO4 nanoneedles soaked in NaBH4 solution was significantly superior to that of untreated NiMoO4 electrodes, exhibiting excellent electrochemical properties. Moreover, the density functional theory (DFT) calculations further indicate that the material possesses a higher electron transmission rate. An asymmetric supercapacitor (ASC) based on NiMoO4 was prepared, using Ov-NiMoO4@Ni foam (NF) as the positive electrode and activated carbon as the negative electrode. These findings could further expand the applications of transition metal-based materials and provide an effective approach for the study of ASCs. [ABSTRACT FROM AUTHOR]

MXenes have gained significant recognition due to their outstanding electrical conductivity, abundant surface functional groups, and distinctive two-dimensional layered structure. However, restacking of nanoflakes hinders the electrochemical performance of Ti3C2Tx-based supercapacitors. Herein, a Ti3C2Tx/VN composite is fabricated using a one-step in situ nitriding method. The presence of VN within the Ti3C2Tx nanoflakes results in an increased interlayer spacing, providing additional electrochemically active sites for charge storage. In addition, the Ti3C2Tx nanosheets form a continuous metallic skeleton that suppresses the formation of soluble salts from VN during charging and discharging resulting in better cycling stability. As the negative electrode in supercapacitors, Ti3C2Tx/VN demonstrates an outstanding specific capacity of 382.1 F g−1 at a current density of 1 A g−1 and exceptional cycling endurance, retaining 93.5% of its capacity after 5000 cycles. An asymmetric supercapacitor comprising Co3O4 and Ti3C2Tx/VN as the positive and negative electrodes, respectively, shows high energy and power densities of 69.1 W h kg−1 (1 A g−1) and 7.6 kW kg−1 (8 A g−1). The results reveal a promising strategy to design composite anodes with high energy and power densities for supercapacitors. [ABSTRACT FROM AUTHOR]

A manganese–cobalt asbolane material synthesized by low-temperature cationic exchange from birnessite in cobalt nitrate solution has been comprehensively characterized and tested for the first time as a massive (with high active mass loading) positive electrode material for to asymmetric aqueous supercapacitors. The structure of this Mn-rich material, which is homologous to the natural asbolanes well known by mineralogists, consists of MnO2-type slabs with partial substitution of Co3+ for Mn; the slabs alternate with Co(OH)2 islands located in the interlayer spacing. This structural arrangement was confirmed through in-depth electronic transmission microscopy analyses, which reveal two interlocking hexagonal sublattices with distinct a lattice-cell parameters but identical c parameters. The electrochemical performance of this geomimetic phase in alkaline electrolytes is highly promising, with specific capacitance of up to 180 F g−1 at moderate current densities and 94 F g−1 at 10 A g−1. Investigation into the charge storage mechanisms indicates effective synergy between the pseudocapacitive properties of the MnO2 slabs and the Co(OH)2 islands, in which protonic conduction is suspected to play a key role. Additionally, long-term cycling and calendar aging tests suggest that the interlayer cobalt gradually migrates to the metal oxide layer upon cycling while maintaining excellent energy storage performance. This study clearly underscores the value of exploring geomimetic minerals as potential electrode materials for energy storage applications. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) have drawn much attention owing to their unique superiorities. The selection of electrode materials is significantly crucial as it influences SC performance. Defects such as low specific capacitance and poor rate performance need to be settled urgently to achieve enhanced SC performance. Here, we have developed an effective and facile strategy to prepare a binder-free nitrogen-doped graphene hydrogel (NDGH) as an electrode material. The electrochemical performance of NDGH was measured in three different electrolytes (2 M KOH, 1 M Na2SO4 and 1 M H2SO4), and it showed superior performance in 2 M KOH. NDGH had an outstanding specific capacitance of 224.1 F g−1 at 1 A g−1 and retained 80.7% of the capacitance at 10 A g−1. Meanwhile, NDGH possessed good cycling stability, with 93% capacitance retention after 6000 cycles. The contributions of surface-controlled and diffusion-controlled processes to NDGH capacitance were analyzed in different electrolytes. Compared with 1 M Na2SO4 (52%) and 1 M H2SO4 (13%), superior surface-controlled contribution was observed in the 2 M KOH (73%) electrolyte at 10 mV s−1. The symmetric supercapacitor (SSC) consisting of NDGH delivered an energy density of 14.3 W h kg−1 at a power density of 582.8 W kg−1 in the KOH electrolyte. These excellent electrochemical performance parameters could be achieved due to the synergistic effect of the multistage pore structure, nitrogen doping and binder-free hydrogel, which allow abundant electrochemical reactions to take place at the interface between the electrode materials and the electrolyte. This strategy may be further broadened to prominently enhance the specific capacitance and rate performance of graphene oxide. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs), a new class of energy storage devices, have been widely investigated due to their high power density, long cycling stability and fast charging and discharging capabilities. Copper cobaltate nanomaterials have especially gained much attention as electrode materials for supercapacitors owing to their simple preparation, integration possibility, and high theoretical capacity. This review mainly focused on the latest achievements in applying copper cobaltate-based nanomaterials as supercapacitor electrodes. Notably, the impact of advantages of morphologies (nanowire, nanosheet, microflower, core–shell, etc.), supports (Ni foam, carbon materials and their derivatives, conductive polymers, MOFs and MXene), and heteroatomic dopants (S, P, Ni, Ag and Mn) on the electrochemical properties of copper cobaltate-based nanomaterials is systematically discussed. Finally, challenges and perspectives toward the future development of copper cobaltate-based nanomaterials for supercapacitors are presented. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) have been the subject of considerable interest because of their distinct advantages. The performance of SCs is directly affected by the electrode materials. Metal oxides derived from Prussian blue analogues (PBAs) are often used as electrode materials for SCs. Herein, we developed a multi-step strategy to fabricate ternary hollow metal oxide (CuO/NiO/Co3O4) heterostructures. The core–shell structured PBA (NiHCC@CuHCC) with Ni-based PBA (NiHCC) as the core and Cu-based PBA (CuHCC) as the shell was prepared by a crystal seed method. The ternary metal oxide (CuO/NiO/Co3O4) with a hollow structure was obtained by calcinating NiHCC@CuHCC. The prepared CuO/NiO/Co3O4 demonstrates an excellent specific capacitance of 262.5 F g−1 at 1 A g−1, which is 27.4% and 16.2% higher than those of CuO/Co3O4 and NiO/Co3O4, respectively. In addition, the material showed outstanding cycling stability with a capacitance retention of 107.9% after 3000 cycles. The two-electrode system constructed with CuO/NiO/Co3O4 and nitrogen-doped graphene hydrogel (NDGH) demonstrates a stable and high energy density of 27.1 W h kg−1 at a power density of 1037.5 W kg−1. The capacitance retention rate was 100.7% after 4000 cycles. The reason for the excellent electrochemical properties could be the synergistic effect of the introduced heterojunction of CuO/NiO, the hollow structure, and various metal oxides. This strategy can greatly inspire the construction of SC electrodes. [ABSTRACT FROM AUTHOR]

Regular nanoarrays are ideal structures for supercapacitors; however, they often require multiple operations during their preparation. Therefore, it is very important to obtain such structures easily and quickly. In addition, the synergy between elements is crucial for the composition design of electrode materials. In this study, NiCoSe2@CC electrode materials were successfully obtained by electrodeposition using flexible carbon cloth as a collector and having efficient synergy between the Ni and Co elements to meet the demand for flexible devices. The regular microstructure and highly efficient synergistic composition enabled the electrode material to exhibit a capacitance of 3150 mF cm−2 and to maintain 85% cycle retention after 2500 cycles. Furthermore, this was matched with an activated carbon (AC) electrode to prepare a flexible solid-state asymmetric supercapacitor. A specific capacitance of 78 F g−1 was exhibited at a current density of 0.25 A g−1, and this could be maintained at 85% at 30 mA cm−2 during 5000 cycles of testing, showing promising application potential. [ABSTRACT FROM AUTHOR]

Previous studies have found that high entropy oxides can be used as electrode materials for supercapacitors. However, there is still the problem of their low energy density. We tried to increase the energy density while increasing the specific capacitance of high entropy oxides from the potential window. Transition metal elements Fe, Co, Cr, Mn and Ni were selected for their electrochemical activity, and high entropy oxides were prepared by a sol–gel method under different calcination temperatures. The calcination temperature affects the structural morphology and crystallinity of the high entropy oxides and thus also affects the electrochemical performance. The spinel-phase (FeCoCrMnNi)3O4 with a high specific surface area of 63.1 m2 g−1 was prepared at a low calcination temperature of 450 °C. The specific capacitance is 332.2 F g−1 at a current density of 0.3 A g−1 in 1 M KOH electrolyte with a wide potential window of (−1, 0.6). An improved energy density of 103.8 W h kg−1 is reached via the designed microstructure of the high entropy oxide electrode. [ABSTRACT FROM AUTHOR]

The capacitance of electrode materials is directly influenced by their surface area. In this work, we synthesized three-dimensional interconnected honeycomb-like carbon nanosheets (RTK-3) utilizing a homemade phenolic resin along with KOH etching and in situ doping of thiourea. These nanosheets possess a large surface area (2277.71 m2 g−1) and are rich in heteroatoms, which results in outstanding electrochemical performance, with specific capacitances of 349 F g−1 at 0.5 A g−1 and 217 F g−1 at 10 A g−1. Additionally, the assembled symmetric supercapacitor (RTK-3//RTK-3) exhibits exceptional performance in different aqueous electrolytes. Specifically, it delivers an energy density of 6.11 W h kg−1 at a power density of 249.61 W kg−1 in alkaline electrolytes, while it achieved a preeminent energy density of 36.34 W h kg−1 at 810.11 W kg−1 in neutral electrolytes due to its larger potential window (0–1.8 V). The utilization of resin-based carbon materials to prepare high-performance supercapacitors represents a novel approach and could potentially lead to the application of other large surface area and heteroatom-doped materials in energy storage. [ABSTRACT FROM AUTHOR]

In the last few years, renewable, inexpensive, biocompatible, and biodegradable wood and lignocellulose materials have triggered considerable research interest for application in various functional devices. However, there is still a lack of a new perspective to deeply understand the structure–property–function relationships of micro-/nanostructures and components of natural wood, so as to explore the potential of wood assembly of nano-energy materials with different dimensions. Herein, the recent progresses in the design and construction of free-standing supercapacitor (SC) electrodes containing wood-derived materials are reviewed. We begin with an illustrated introduction to the hierarchical structure and characteristics of natural wood with a "top–down" view, which includes the cell walls, cellulose microfibers, nanocellulose, and cellulose supramolecules. Next, the fabrication, structure, and properties of lignocellulose are highlighted. We focus on the structure–property–function relationships between the hierarchical micro- and nanoscale structure of wood and electroactive materials. The focus then turns to a summary of the recent advances in wood-based free-standing SC electrodes with a unique point that is ever out of the spotlight, including one-dimensional integrated fibers, two-dimensional flexible films/papers, three-dimensional porous hydrogels/aerogels, and ultra-thick electrodes. Finally, we put forward our perspectives on the challenges to further promoting the development of this emerging field in the future. [ABSTRACT FROM AUTHOR]

In this study, economical porous biochar was prepared from an apricot shell and used as an electrode material for a supercapacitor, showing excellent capacitance, cycling stability and rate performance. KOH was used as the activator for preparing the biochar, and the effects of different activator concentrations on the specific surface area, pore volume, morphology and the electrochemical properties of the prepared biochar material were investigated. The results showed that increasing the KOH concentration from 0 mol L−1 to 4 mol L−1 changed the surface morphology of the prepared biochar from a smooth and non-porous structure to a porous honeycomb structure. The specific surface area and pore volume of the porous biochar increased first and then decreased and reached a maximum value (2452.7 m2 g−1, and 1.613 cm3 g−1) at a KOH concentration of 3 mol L−1. After assembling the supercapacitor with the prepared biochar, the specific capacitance (Cs) was 216 F g−1 at 0.5 A g−1 and the Cs could still reach a high capacity of 189 F g−1 at 20 A g−1, which was 87.5% of the Cs at 0.5 A g−1. Meanwhile, the assembled supercapacitor showed a high capacity retention rate of 99.5% after 10 000 cycles of charging and discharging at 5 A g−1 and a high energy density of 7.48 W h kg−1 at 125 W kg−1 power density. [ABSTRACT FROM AUTHOR]

A novel method, reduction followed by oxidation procedure, has been developed to fabricate efficient electrodes derived from metal–organic frameworks (MOFs), which were synthesized using terephthalic acid (TP) and 1,3,5-benzenetricarboxylic acid (BTC) as organic ligands. The copper-based composites, namely Cu/CuxO@C (x = 1 and 2), were obtained through two steps: first calcining the precursors at high temperature under a nitrogen atmosphere, and then calcining in air to increase the number of porous active sites. For a more convenient description, the calcined materials are denoted as 800-TP, 900-TP, 800-BTC and 900-BTC, respectively, according to the calcination temperature and the corresponding organic ligand. Their electrochemical performances in supercapacitors (SCs) suggest that a higher calcination temperature endows the as-resultant materials with a larger specific surface area, higher carbon content, higher electrical conductivity, and better ion transport ability. For example, the 900-BTC electrode delivers a specific capacity of 400 C g−1 at a current density of 3 A g−1 under a three-electrode configuration. Even under a double-electrode system, the corresponding 900-BTC//AC device (AC represents activated carbon) also achieves superior electrochemical performance with an energy density of 24.02 W h kg−1 at a power density of 825 W kg−1 and the specific capacitance retention rate for the device is maintained at 91.7% after 3000 unceasing loops, indicating its potential for practical applications. [ABSTRACT FROM AUTHOR]

In this work, polyoxometalate (POM) derived MoO3/CoMoO4 composites were prepared by a facile hydrothermal method and subsequent calcination process utilizing carbonized glucose as the template. Detailed characterization showed that Co and Mo species coated carbon spheres could be synthesized via the hydrothermal treatment of Co2Mo10 POM and glucose, which transformed into polyhedron MoO3/CoMoO4 particles after calcination. The electrochemical results indicated that the optimized MoO3/CoMoO4-40 could display the best electrochemical performances, including remarkable specific capacity (951.5 C g−1 at 1 A g−1) and outstanding cycle life (92.7% capacity retention after 5000 cycles). Furthermore, the MoO3/CoMoO4-40//AC asymmetric supercapacitor (ASC) fabricated by MoO3/CoMoO4-40 and activated carbon (AC) exhibited a high energy density of 54.7 W h kg−1 at a power density of 812.1 W kg−1, and capacitance retention of 93.5% at 8 A g−1 after 5000 charge/discharge cycles. These results demonstrated that the present method is a simple and efficient strategy for the construction of high performance supercapacitor materials. [ABSTRACT FROM AUTHOR]

Transition metal hybrid nanomaterials have attracted wide attention in the field of energy storage due to their rich redox activity and good conductivity and structural stability. In this work, low-crystalline Ni(OH)2·0.75H2O nanosheets embedded with NiMoO4 nanoparticles (NiMo-LDH) on nickel foam (NF) were synthesized by a simple urea-assisted hydrothermal method. By optimizing the Ni/Mo molar ratio and urea concentration in the initial reaction solution, the composition of NiMo-LDH was effectively controlled, which was found to have a crucial impact on the electrochemical performance of the NiMo-LDH electrode. The NiMo-LDH (Ni2Mo1–urea0.2 M) electrode shows porous ultra-thin two-dimensional characteristics and NiMoO4 nanoparticles (3–5 nm) embedded in nickel hydroxide nanosheets can provide more exposed active sites, accelerate electron transport and enhance the faradaic reaction. The Ni2Mo1–urea0.2 M electrode exhibits an extremely high capacitance of 4.4 F cm−2 (2001 F g−1) at 4 mA cm−2 (1.8 A g−1), with 63% capacitance retention observed at 48 mA cm−2 (21.8 A g−1). More importantly, the asymmetric supercapacitor (ASC) assembled using Ni2Mo1–urea0.2 M as the positive electrode presents an energy density value of 70.76 W h kg−1 at 318.84 W kg−1 and 26.24 W h kg−1 even at 7680 W kg−1 along with good stability of 82% over 5000 cycles at 100 mV s−1. [ABSTRACT FROM AUTHOR]

The conversion of bio-waste rich in heteroatoms into useful porous carbons with good chemical properties is a feasible approach contributing to electrode materials for supercapacitors. In this work, rapeseed meal rich in crude protein is used as the precursor to synthesize N,S self-codoped porous carbons. The carbon sample obtained via pre-carbonization followed by KOH activation (RM@HTC) exhibits a developed micro-mesoporous interconnected carbon structure with a large specific surface area of up to 3283.2 m−2 g−1. The N and S atoms are well retained with a N content of 1.49% for RM@HTC. In a three-electrode system, the RM@HTC-based electrode reaches a high specific capacitance of 303.4 F g−1 at a current density of 1 A g−1, and the specific capacitance is retained at 210.0 F g−1 at 10 A g−1. In a two-electrode system, the energy density reaches 9.0 W h kg−1 at a power density of 625.0 W kg−1. RM@HTC also exhibits excellent cycle stability with a capacity retention rate of 92.9% after 10 000 charge–discharge cycles at 10 A g−1. [ABSTRACT FROM AUTHOR]

Since the industrial revolution, modern society has experienced rapid technological development, which has greatly increased the demand for energy, and cheap energy for production will be more and more difficult to obtain. In the past decades, energy depletion and environmental pollution have attracted people's attention, and prompted people to explore advanced and green energy storage and conversion technologies. Supercapacitors have attracted extensive attention due to their great potential to meet the requirements of high energy density and high power density, but their excellent performance largely depends on the development of advanced electrode materials. Carbon materials are widely used in supercapacitors, but the preparation of high-performance carbon materials still needs harsh conditions. Therefore, there is an urgent need to develop effective methods to produce high-performance carbon materials with limited environmental impact by using renewable resources. Biomass is an important precursor of carbon materials due to its unique structure, abundant resources, biodegradability and low cost. Porous carbons transformed from biomass as a new type of high-performance sustainable material have attracted extensive attention due to the advantages, such as good porosity, large specific surface area, good graphitization degree, etc. Although there have been many studies and summaries on porous carbon materials transformed from biomass, improvements and additions are still needed. This paper further summarizes the latest progress of biomass-derived porous carbon materials in the field of supercapacitors, and the preparation methods of biomass-based porous carbon materials are newly classified from the perspective of the preparation process. Secondly, the design methods and strategies of high-performance biomass-based porous carbon materials are analyzed in detail. The application of biomass-based porous carbon materials in advanced supercapacitors is reviewed. Finally, the challenges and prospects for the future development of biomass-based carbon materials are discussed. This review shows the great potential of high-performance biomass-based porous carbon materials, provides good design ideas for their application in the field of high-performance supercapacitors, and is expected to stimulate new discoveries and promote the practical application of biomass-based porous carbon materials in the field of more energy storage and conversion. [ABSTRACT FROM AUTHOR]

With the aim of addressing the global warming issue and fossil energy shortage, eco-friendly and sustainable renewable energy technologies are urgently needed. In comparison to energy conversion, studies on energy storage fall behind and remain largely to be explored. By storing energy from electrochemical processes at the electrode surface, supercapacitors (SCs) bridge the performance gap between electrostatic double-layer capacitors and batteries. Organic electrode materials have drawn extensive attention because of their special power density, good round trip efficiency and excellent cycle stability. Porous organic polymers (POPs) have drawn extensive attention as attractive electrode materials in SCs. In this review, we present and discuss recent advancements and design principles of POPs as efficient electrode materials for SCs from the perspectives of synthetic strategies and the structure–performance relationships of POPs. Finally, we put forward the outlook and prospects of POPs for SCs. [ABSTRACT FROM AUTHOR]

Transition metal sulfides (TMSs) have been widely explored as electrode materials for supercapacitors (SCs). Nevertheless, the application of TMSs alone is limited due to their lattice expansion and dissolution in an alkaline electrolyte. To overcome these challenges, in this study, hierarchical core–shell hollow Co3S4@NiCo2O4 nanosheet arrays have been constructed on reduced graphene oxide/nickel foam (rGO/NF) through a metal–organic framework (MOF)-engaged strategy. The MOF-derived two-dimensional (2D) hollow Co3S4 nanosheets can offer rich electroactive sites and rapid charge transport paths. The 2D NiCo2O4 nanosheets with high electrochemical activity and a stable lattice can overcome the intrinsic defects of Co3S4 by coating on its surface. Besides, the binder-free configuration ensures good electronic conductivity and mechanical stability. Thus, the Co3S4@NiCo2O4/rGO/NF exhibits a significantly improved specific capacitance (6.34 F cm−2 at 2 A cm−2), rate capability (57.9% at 50 mA cm−2) and cycling durability (70.9%, after 5000 cycles), compared with Co3S4/rGO/NF. Moreover, the Co3S4@NiCo2O4/rGO/NF and an activated carbon (AC) electrode have been constructed into an asymmetric supercapacitor (ASC), which exhibits an excellent energy density (35.7 W h kg−1 at a power density of 799.3 W kg−1) and an outstanding cycling stability (85.7% capacitance retention after 10 000 cycles) and a high coulombic efficiency (95%). Two solid-state ASCs can power four green light emitting diode (LED) bulbs for 4 min, demonstrating the great potential of the Co3S4@NiCo2O4/rGO/NF electrode in practical applications. [ABSTRACT FROM AUTHOR]

Using discarded wastes as carbon precursors to prepare high value-added carbon electrode materials for supercapacitors (SCs) can not only enrich the selection of precursors to reduce the cost but also alleviate the environmental pressure on recovering these wastes. Herein, a porous carbon membrane (DWCM) was fabricated by direct carbonization of decoration waste using KOH as an activator and employed as a binder-free self-supported electrode for aqueous SC. The DWCM electrode features a large specific surface area (917 m2 g−1) and high porosity (0.5 cm3 g−1) and thus exhibits superior electrolyte wettability. Moreover, the DWCM electrode possesses excellent structural integrity and mechanical strength, providing continuous 3D networks for rapid electron transfer. Attributing to the above structural merits, the best DWCM-1-1000 electrode even with a weight of ∼30 mg exhibits the highest specific capacitance (Cs) (areal capacitance, Ca) of 338.2 F g−1 (10.6 F cm−2) at 0.5 A g−1 in a three-electrode system in 6 M KOH. An assembled symmetric SC using two DWCM-1-1000 electrodes can stably operate at a potential window of 0–1.4 V showing a high Cs (Ca) of 138.3 F g−1 (8.9 F cm−2) at 0.2 A g−1. Notably, this SC shows excellent cycling stability (98% capacitance retention and 100% coulombic efficiency after 20 000 cycles) and presents a maximum energy density of 9.7 Wh kg−1 at a power density of 139.6 W kg−1. Also, it is found that reducing the thickness of the electrode will further improve the capacitive performance of the DWCM-based SC device. This work opens a new route of using decoration waste to develop high-performance self-supported porous carbon membranes for practical energy storage. [ABSTRACT FROM AUTHOR]

Doping with d-block metal ions plays a pivotal role in enhancing the specific capacity (Cg) of metal oxides. Here, augmenting the electrochemical performance of ZnCo2O4 is demonstrated by Ni2+ ion doping. An enormous boost in Cg after doping with Ni2+ was noticed due to the high electrical conductivity of Ni. In addition, doping with Ni leads to excellent rate capability and long cycle life. An asymmetric supercapacitor (ASC) fabricated using Ni2+ doped ZnCo2O4 and reduced graphene oxide (rGO) in 3.5 M KOH electrolyte displays an excellent energy density of 40 W h kg−1 and power density of 775 W kg−1 at 1 A g−1. In addition, an all-solid-state flexible asymmetric supercapacitor (ASFAS) device was fabricated to demonstrate its application in flexible electronics. Surprisingly, the as-prepared ASFAS device achieved a high energy density of 26 W h kg−1. Moreover, the device retained 95% of its original capacity over 10 000 cycles. [ABSTRACT FROM AUTHOR]

The rapid development of portable/wearable electronics proposes new demands for energy storage devices, which are flexibility, smart functions and long-time outdoor operation. Supercapacitors (SCs) show great potential in portable/wearable applications, and the recently developed flexible, smart and self-sustainable supercapacitors greatly meet the above demands. In these supercapacitors, conductive polymers (CPs) are widely applied due to their high flexibility, conductivity, pseudo-capacitance, smart characteristics and moderate preparation conditions. Herein, we'd like to introduce the CP-based flexible, smart and self-sustainable supercapacitors for portable/wearable electronics. This review first summarizes the flexible SCs based on CPs and their composites with carbon materials and metal compounds. The smart supercapacitors, i.e., electrochromic, electrochemical actuated, stretchable, self-healing and stimuli-sensitive ones, are then presented. The self-sustainable SCs which integrate SC units with energy-harvesting units in one compact configuration are also introduced. The last section highlights some current challenges and future perspectives of this thriving field. [ABSTRACT FROM AUTHOR]

The development of highly-efficient and low-cost heteroatom-doped porous carbon materials is vitally important for high-performance supercapacitors. Herein, waste phenolic resin-based insulation boards, which naturally contain N and O elements, were deliberately chosen as an absolute "zero"-cost green raw material for the preparation of heteroatom self-doped porous carbon. Through carbonization and activation steps, N/O self-doped porous carbon with a high surface area has been successfully prepared. The constructed symmetrical supercapacitor based on the best sample thermally activated at 600 °C had a specific capacitance of 262.2 F g−1 at 0.5 A g−1. Furthermore, the output energy density was 17.4 W h kg−1 at a power density of 500 W kg−1. Impressively, a significantly stable cycling duration with almost 100% capacitance retention and coulombic efficiency were retained after running 20 000 cycles. Moreover, it took 150 h to self-discharge to half of its maximum voltage. The prominent performance of the constructed symmetrical supercapacitor was attributed to the large specific surface area, hierarchical pore size distribution, and optimal doped heteroatoms in the carbon matrix. This work uncovers a promising strategy of converting waste construction materials into high-value electrode materials for green energy storage applications, such as supercapacitors. [ABSTRACT FROM AUTHOR]

The design and preparation of a reduced graphene oxide (rGO) paper electrode with a reinforced concrete structure is an effective strategy to improve the mechanical properties of flexible electrodes. Therefore, PEDOT:PSS is added as a binder, toughening and conductive agent. CNTs, with good mechanical properties, are added to enhance the strength. Fe2O3 nanoparticles are added to increase the energy storage. According to these assumptions, we successfully prepared a flexible hydrophilic paper electrode with rGO nanosheets, PEDOT:PSS, CNTs and Fe2O3 nanoparticles by a constant temperature vacuum drying method. In addition, the assembled symmetrical supercapacitor exhibits a high capacitance of 1924 mF cm−3 at 1 mA cm−3, an excellent energy density of 35.6 W h kg−1 (at 166 W kg−1) and a remarkable cycle stability of 98.2% retention over 10 000 cycles at 1 mA cm−2. [ABSTRACT FROM AUTHOR]

Here, new carbon-based nanostructures were prepared via a one-step electrochemical method using hexagonal and pentagonal polychlorinated organic rings as the carbon source. The electrochemical growth of carbon nanostructures on substrates was accomplished via electrochemical reduction of organic halides in nonaqueous electrolyte solutions containing hexachlorobenzene (HCB), hexachlorocyclopentadiene (HCCP) and mixtures of HCB and HCCP with molar ratios of 2/2, 2/1.2 and 2/0.6. The effect of HCB/HCCP molar ratio, deposition time and temperature on the morphological and structural properties of the carbon coatings was investigated using spectroscopic and microscopic methods. The performance of the carbon nanostructures as supercapacitors was also studied using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in aqueous Na2SO4 solutions. The structural and chemical properties of the carbon nanostructures was found to depend strongly on the nature and relative molar ratios of the precursors used in the electrochemical reduction process. In the case of a 2/2 molar ratio of HCB to HCCP, mushroom-like carbon nanostructures are obtained, whereas, higher molar ratios of HCB to HCCP (2/1.2 and 2/0.6) result in carbon nanoflowers with graphitic features. Furthermore, the capacitance measurements show that these novel carbon structures are potential candidates for supercapacitor-based energy storage systems because they offer high specific capacitances (332–73 F g−1 at 0.5 A g−1), good cycling stabilities and a maximum energy density of 16 W h kg−1 at a power density of 250 W kg−1. [ABSTRACT FROM AUTHOR]

In our study, a simple method was employed to prepare ultra-micropore-dominated carbon materials with controllable pore size. A mass of heteroatoms was introduced by surface functional group grafting, resulting in enhanced electrochemical performance: the maximum specific capacity of 327.5 F g−1 was obtained at 0.5 A g−1 in 6 M KOH, while that of un-grafted original ultra-microporous carbon was only 188 F g−1, with long-term cycle stability (90.5% of the initial after 10 000 cycles), and excellent rate performance (over 82% at the current density from 0.5 A g−1 to 10 A g−1). The mechanism behind the improved performance was due to the presence of the introduced functional groups that improved the surface wettability of the material and provided additional redox active sites. Their synergistic effects promoted the enhanced electrochemical performance of the ultra-microporous carbon. This study provides a basis for the study of the energy storage mechanism of ultra-microporous carbon and the grafted modification of carbon materials with heteroatom-containing functional groups. [ABSTRACT FROM AUTHOR]

With the ongoing advance of flexible energy storage products for commercial portable electronics application, the fundamental comprehension of the temperature-dependence for supercapacitors is in urgent demand. Although polypyrrole (PPy) has been extensively employed as electrodes for supercapacitor systems, their electrochemical response to extreme thermal environments is rarely discussed. In this work, PPy was rationally constructed on the surface of carbon cloth (CC) as electrodes and a type of high-performance flexible symmetric supercapacitor was assembled with a PVA-H3PO4 gel electrolyte. The electrochemical performance of the supercapacitors was systematically investigated at various surrounding temperatures from 0 °C to 60 °C using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements. The results demonstrated that the areal specific capacitance of the CC/PPy supercapacitor at 0.5 mA cm−2 increased from 52.91 mF cm−2 to 75.08 mF cm−2 and the internal resistance fell by 71.4% when the operating temperature rose from 0 °C to 60 °C. Moreover, cycling stability dropped and the self-discharge behavior accelerated in the supercapacitors with the gradual increase in the external temperature. This study provides a fundamental understanding of the temperature-dependent pseudocapacitive performance of PPy-based flexible supercapacitors, which gives a valuable reference for energy storage system applications. [ABSTRACT FROM AUTHOR]

In this study, mesoporous nickel cobaltate (NiCo2O4) nanomaterials were loaded onto nickel foam through a simple and environment-friendly reagent assisted hydrothermal method. The impacts of reagents on the micro-morphology and electrochemical capacitive properties were studied. The NiCo2O4 nanoneedle arrays prepared with cetyltrimethylammonium bromide (CTAB) as the auxiliary reagent exhibited a relatively higher specific surface area, convenient charge transport channel, excellent specific capacitance (1153.2 F g−1 at a current density of 1 A g−1), remarkable rate performance (10 A g−1, 812 F g−1) and good cycling stability (75% of the initial value is retained at 10 A g−1 after 1000 cycles). The asymmetric supercapacitor assembled by the optimized NiCo2O4 nanomaterial as the positive electrode and activated carbon as the negative electrode provides an energy density of 22.5 W h kg−1 at 800 W kg−1, and displays an excellent cycle performance of 97.1% after 1000 cycles at 1 A g−1. It is suggested that the CTAB-assisted nanoneedle array-structured NiCo2O4 electrode material could be a potential candidate for supercapacitors. [ABSTRACT FROM AUTHOR]

The effective preparation of high porosity carbonaceous electrode materials is a critical and challenging issue for obtaining superior supercapacitors. In this work, a novel KCl-assisted KOH strategy is developed for the preparation of Moringa oleifera branch-based porous carbon materials (PCMs). Benefiting from the liquid environment of in situ formed molten salts, KCl-assisted KOH activation can effectively decrease the usage of KOH, and thus increase the yield of PCMs from 9.8% to 15.6% whilst maintaining their high porosity. Therefore, the obtained PCMs possess a high specific surface area (i.e., 2314–3470 m2 g−1) and pore volume (i.e., 0.94–1.69 cm3 g−1). When used in supercapacitors, a typical PCM electrode exhibits a high capacitance of 421 F g−1 at 0.5 A g−1 and with an excellent cyclic stability of 4% capacity decay after 20 000 charge/discharge cycles in 6 M KOH electrolyte. Additionally, a maximum energy density of 33.0 W h kg−1 can be achieved at 224.0 W kg−1. This attractive electrochemical performance shows PCMs to be a promising material for use in supercapacitors. Furthermore, this research provides a cost-effective and promising route for the preparation of porous carbon with high porosity. [ABSTRACT FROM AUTHOR]

In this study, the binder-free high-performance nanocomposite of Fe3O4/oxygen-functionalized g-C3N4 was fabricated through a one-pot electrophoretic-electrochemical (EP-EC) process. In this process, Fe3O4 nanoparticles were in situ nucleated through a two-step electrochemical-chemical (EC) mechanism on oxygen-functionalized g-C3N4 (O-g-C3N4) sheets electrophoretically embedded on a Ni-foam support. Also, pristine Fe3O4 nanoparticles and O-g-C3N4 sheets were fabricated on Ni foam (i.e. Fe3O4/Ni foam and O-g-C3N4/Ni foam) via the EC and EP processes, respectively. The prepared powders/electrodes were fully characterized through XRD, FT-IR, BET/BJH, Raman spectroscopy, TGA/DSC, FE-SEM and TEM. The morphological observations confirmed the nucleation and growth of Fe3O4 particles on the porous O-g-C3N4 sheets in the structure of the Fe3O4@O-g-C3N4/Ni foam electrode. The formation mechanisms of the pristine Fe3O4 particles, pristine O-g-C3N4 sheets and their nanocomposite on the Ni-foam support were explained based on the electrophoretic-electrochemical deposition processes. Electrochemical evaluation by galvanostatic charge–discharge (GCD) indicated that the fabricated Fe3O4@O-g-C3N4/Ni foam delivered a specific capacitance of 710 F g−1 at 0.5 A g−1 and capacity retention of 94.6% and 80.15% after 8000 GCD cycling at the current load of 0.5 and 3 A g−1, whereas the pristine Fe3O4/NF showed a specific capacitance of 277 F g−1 at 0.5 A g−1 and capacity retentions of 82.4% and 48.9% only, under similar GCD conditions, respectively. These findings prove the superior synergism between the Fe3O4 nanoparticles and oxygen-functionalized g-C3N4 sheets in the composite structure. [ABSTRACT FROM AUTHOR]

Herein, a positive electrode based on three-dimensional (3D) hierarchical CoMn2O4@NiMn-LDH core–shell nanowire arrays was successfully prepared on Ni foam via hydrothermal and calcination methods. The skeleton of the CoMn2O4 nanowire arrays was in situ developed on Ni foam substrates, and hierarchical NiMn-LDH nanosheets were homogeneously overlapped on the surface of CoMn2O4 nanowires. Electrochemical measurements revealed that this electrode represented the faradaic process of battery-type charge storage and exhibited a high specific capacity of 313 mA h g−1 (under 1 A g−1). The corresponding hybrid supercapacitor device, which was assembled by a CoMn2O4@NiMn-LDH cathode and activated carbon anode, possessed a high energy density of 118.8 W h kg−1 with a power density of 799.4 W kg−1. With two devices connected in series, the output voltage could reach 3.2 V and successfully assisted a group of light-emitting diodes turning on. This study provides an efficient strategy to develop next-generation high-performance energy storage devices. [ABSTRACT FROM AUTHOR]