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Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe[sub.3]C/Fe[sub.2]O[sub.3] nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe[sub.3]C/Fe[sub.2]O[sub.3] during charge–discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g[sup.−1] at 2 A g[sup.−1], superior to that of NCNF-supported Fe[sub.3]C nanoparticles (NCFC, 261.7 F g[sup.−1]), and NCNFs/Fe[sub.2]O[sub.3] (NCFO, 398.3 F g[sup.−1]). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg[sup.−1] at 800 W kg[sup.−1]. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe[sub.3]C/Fe[sub.2]O[sub.3].

The most prominent and highly visible advantage attributed to supercapacitors of any type and application, beyond their most notable feature of high current capability, is their high stability in terms of lifetime, number of possible charge/discharge cycles or other stability-related properties. Unfortunately, actual devices show more or less pronounced deterioration of performance parameters during time and use. Causes for this in the material and component levels, as well as on the device level, have only been addressed and discussed infrequently in published reports. The present review attempts a complete coverage on these levels; it adds in modelling approaches and provides suggestions for slowing down ag(e)ing and degradation.

The enhanced application performance of hollow-structured materials is attributed to their large surface area with more active sites. In this work, the hollow CoSn(OH)[sub.6] nanocubes with increased surface area and mesopores were derived from dense CoSn(OH)[sub.6] nanocube precursors by alkaline etching. As a result, the hollow CoSn(OH)[sub.6] nanocubes-based cathode electrode exhibited a higher area-specific capacitance of 85.56 µF cm[sup.−2] at 0.5 mA cm[sup.−2] and a mass-specific capacitance of 5.35 mF g[sup.−1] at 0.5 mA cm[sup.−2], which was more extensive than that of the dense precursor. Meanwhile, the current density was increased 4-fold with good rate capability for hollow CoSn(OH)[sub.6] nanocubes.

Nowadays, commercial electric double-layer supercapacitors mainly use porous activated carbons due to their high specific surface area, electrical conductivity, and chemical stability. A feature of carbon materials is the possibility of obtaining them from renewable plant biomass. In this study, fungi (Fomes fomentarius) were used as a bio-template for the preparation of carbon fibers via a combination of thermochemical conversion approaches, including a general hydrothermal pre-carbonization step, as well as subsequent carbonization, physical, or chemical activation. The relationships between the preparation conditions and the structural and electrochemical properties of the obtained carbon materials were determined using SEM, TEM, EDAX, XPS, cyclic voltammetry, galvanostatic measurements, and EIS. It was shown that hydrothermal pretreatment in the presence of phosphoric acid ensured the complete removal of inorganic impurities of raw fungus hyphae, but at the same time, saved some heteroatoms, such as O, N, and P. Chemical activation using H[sub.3]PO[sub.4] increased the amount of phosphorus in the carbon material and saved the natural fungus's structure. The combination of a hierarchical pore structure with O, N, and P heteroatom doping made it possible to achieve good electrochemical properties (specific capacitance values of 220 F/g) and excellent stability after 25,000 charge/discharge cycles in a three-electrode cell. The electrochemical performance in both three- and two-electrode cells exceeded or was comparable to other biomass-derived porous carbons, making it a prospective candidate as an electrode material in symmetrical supercapacitors.

Designing and preparing dual-functional Dawson-type polyoxometalate-based metal–organic framework (POMOF) energy storage materials is challenging. Here, the Dawson-type POMOF nanomaterial with the molecular formula CoK[sub.4][P[sub.2]W[sub.18]O[sub.62]]@Co[sub.3](btc)[sub.2] (abbreviated as P[sub.2]W[sub.18]@Co-BTC, H[sub.3]btc = 1,3,5-benzylcarboxylic acid) was prepared using a solid-phase grinding method. XRD, SEM, TEM et al. analyses prove that this nanomaterial has a core–shell structure of Co-BTC wrapping around the P[sub.2]W[sub.18]. In the three-electrode system, it was found that P[sub.2]W[sub.18]@Co-BTC has the best supercapacitance performance, with a specific capacitance of 490.7 F g[sup.−1] (1 A g[sup.−1]) and good stability, compared to nanomaterials synthesized with different feedstock ratios and two precursors. In the symmetrical double-electrode system, both the power density (800.00 W kg[sup.−1]) and the energy density (11.36 Wh kg[sup.−1]) are greater. In addition, as the electrode material for the H[sub.2]O[sub.2] sensor, P[sub.2]W[sub.18]@Co-BTC also exhibits a better H[sub.2]O[sub.2]-sensing performance, such as a wide linear range (1.9 μM–1.67 mM), low detection limit (0.633 μM), high selectivity, stability (92.4%) and high recovery for the detection of H[sub.2]O[sub.2] in human serum samples. This study provides a new strategy for the development of Dawson-type POMOF nanomaterial compounds.

In the report, we explore a two-step efficient synthetic to purposefully fabricate three-dimensional (3D) NiCo.sub.2S.sub.4 nanosheets for advanced electrochemical supercapacitors. They were characterized for their structural, morphological and electrochemical properties by using XRD, SEM, TEM, cyclic voltammetry and charge discharge methods. The unique designed nanostructure exhibits a high specific capacitance (1257.1 F g.sup.-1 at current density 1 A g.sup.-1), good rate performance (75.7% retention for current increases around 20 times) and excellent cycling stability (80% retention at 5 A g.sup.-1 after 1000 cycles). We are the first step in the synthesis of 3D NiCo.sub.2S.sub.4 flowers, which have a specific capacitance of 700.7 F g.sup.-1 at the current density of 1 A g.sup.-1 and exhibit excellent cycling stability with 95% capacitance retention. The S-NiCo.sub.2S.sub.4//activated carbon asymmetric supercapacitor is can deliver a maximum energy density of 47.3 W h kg.sup.-1 at a power density of 477.3 W kg.sup.-1. Therefore, according to our investigation it can be concluded that the low cost and environmental friendly two-step approach from 3D NiCo.sub.2S.sub.4 nanoflowers to the 3D NiCo.sub.2S.sub.4 nanosheets could be used to deposit efficient 3D NiCo.sub.2S.sub.4 nanosheets for supercapacitor application.

The importance of Super-capacitors (SCs) stems from their distinctive properties including long cycle life, high strength and environment friendly, they are sharing similar fundamental equations as the traditional capacitors; for attaining high capacitances SC using electrodes materials with thinner dielectrics and high specific surface area. In this review paper, all types of SCs were covered, depending on the energy storage mechanism; a brief overview of the materials and technologies used for SCs is presented. The major concentration is on materials like the metal oxides, carbon materials, conducting polymers along with their composites. The composites’ performance was examined via parameters like capacitance, energy, cyclic performance power and the rate capability also presents details regarding the electrolyte materials.

Electrochemical energy storage (EES) devices with high‐power density such as capacitors, supercapacitors, and hybrid ion capacitors arouse intensive research passion. Recently, there are many review articles reporting the materials and structural design of the electrode and electrolyte for supercapacitors and hybrid capacitors (HCs), though these reviews always focus on individual supercapacitors or single HCs. Herein, the conventional capacitor, supercapacitor, and hybrid ion capacitor are incorporated, as the detailed description of conventional capacitors is very fundamental and necessary for the better understanding and development of supercapacitors and hybrid ion capacitors, which are often ignored. Therefore, herein, the fundamentals and recent advances of conventional capacitors, supercapacitors, and emerging hybrid ion capacitors are comprehensively and systematically summarized in terms of history, mechanisms, electrode materials, existing challenges, and perspectives. At the same time, it is believed that a comprehensive and fundamental understanding for capacitor‐related EES devices is provided in the review and has a great guiding role for future development. Herein, the basic principles and recent progress of conventional capacitors, supercapacitor, and emerging hybrid ion capacitor are comprehensively and systematically summarized, from the aspects of history, mechanism, electrode materials, existing challenges, and perspectives. Also, a comprehensive and fundamental understanding is provided for capacitor‐related electrochemical energy storage devices and has a great guiding role for future development.

Micro‐supercapacitors are notorious for their low energy densities compared to micro‐batteries. While MXenes have been identified as promising capacitor‐type electrode materials for alternative zinc‐ion hybrid micro‐supercapacitors (ZHMSCs) with higher energy density, their tightly spaced layered structure renders multivalent zinc‐ions with large radii intercalation inefficient. Herein, through insertion of 1D core‐shell conductive BC@PPy nanofibers between MXene nanosheets, an interlayer structure engineering technique for MXene/BC@PPy capacitor‐type electrodes towards ZHMSCs is presented. Owing to simultaneously achieving two objectives: (i) widening the interlayer space and (ii) providing conductive connections between the loose MXene layers, enabled by the conductive BC@PPy nanospacer, the approach effectively enhances both ion and electron transport within the layered MXene structure, significantly increasing the areal capacitance of the MXene/BC@PPy film electrode to 388 mF cm−2, which is a 10‐fold improvement from the pure MXene film electrode. Pairing with CNTs/MnO2 battery‐type electrodes, the obtained ZHMSCs exhibit an areal energy density up to 145.4 μWh cm−2 with an outstanding 95.8% capacity retention after 25000 cycles, which is the highest among recently reported MXene‐based MSCs and approaches the level of micro‐batteries. The interlayer structure engineering demonstrated in the MXene‐based capacitor‐type electrode provides a rational means to achieve battery‐levelenergy density in the ZHMSCs. The demonstrated interlayer structure engineering synchronously realized the facilitated zinc‐ion and electron transfer kinetics between loose MXene nanosheets, resulting in enhanced charge storage capacity of MXene‐based capacitor‐type electrode toward hybrid micro‐supercapacitor with battery‐level energy density.