Surfactant dependent self-organization of Co3O4 nanowires on Ni foam for high performance supercapacitors: from nanowire microspheres to nanowire paddy fields

Novel and flexible asymmetric supercapacitors based on NiCo2O4 nanosheets coated on Al and Cu tapes for wearable devices applications

The binary metal oxides show advantages in energy storage devices. Specifically, nickel cobaltite (NiCo2O4) materials showed promising pseudocapacitive properties, high electrical conductivity and large surface area by virtue of their effective porous structure. NiCo2O4 nanosheets were hydrothermally grown in this work over flexible tapes of Aluminum (Al) and Copper (Cu). A nanosheets structure obtained of NiCo2O4 as confirmed by SEM and AFM images. The measured thickness by 3D profilometer of NiCo2O4 nanosheets based Al framework found to be 4.3 µm compared to 8.4 µm thick of film based-Cu framework. Asymmetric supercapacitor prepared from graphite and NiCo2O4 electrodes separated by filter paper. Acidic aqueous electrolyte of H2SO4 and basic aqueous electrolyte of KOH were employed to verify the cyclic activity and electrochemical reaction of asymmetric prepared supercapacitor devices. The basic KOH electrolyte shows a high stability and better charge transfer/ionic diffusion compared to the acidic H2SO4 electrolyte in particular for NiCo2O4 film-based Cu framework. The energy density and power density values were 0.9 W h kg−1 and 66.45 W kg−1, respectively. The highest specific capacity (in F.g−1) = 10.09 coincides with NiCo2O4/Cu supercapacitor in the basic KOH electrolyte. The charge storage in the supercapacitor system of NiCo2O4 and graphite can be ascribed in the form of Faradic charge transfer and capacitive non-faradic double layer, respectively.

Highly Efficient Electrochemical Sensing of Acetaminophen by Cobalt Oxide-Embedded Nitrogen-Doped Hollow Carbon Spheres

With respect to sensor application investigations, hollow mesoporous carbon sphere-based materials of the spinel type of cobalt oxide (Co₃O₄) and heteroatom-doped materials are gaining popularity. In this contribution, dopamine hydrochloride (DA) and cobalt phthalocyanine (CoPc) precursors were employed to construct a highly homogeneous Co₃O₄-embedded N-doped hollow carbon sphere (Co₃O₄@NHCS) by a straightforward one-step polymerization procedure. The resulting Co₃O₄@NHCS materials may effectively tune the surface area, defect sites, and doping amount of N and Co elements by altering the loading amount of CoPc. The relatively high surface area, greater spherical wall thickness, enriched defect sites, and better extent of N and Co sites are all visible in the best 200 mg loaded Co₃O₄@NHCS-2 material. This leads to significant improvement in pyridine and graphitic N site concentrations, which offers exceptional electrochemical performance. Electrochemical analysis was used to study the electrocatalytic activity of Co₃O₄@NHCSs towards the sensing of pharmacologically active significant compounds (acetaminophen). Excellent sensor properties include the linear range (0.001-0.2 and 1.0-8.0 mM), sensitivity, limit of detection (0.07 and 0.11 μM), and selectivity in the modified Co₃O₄@NHCSs/GCE. The authentic sample (acetaminophen tablet) produces a satisfactory result when used practically.

High performance asymmetric supercapacitors based on Ti3C2T x MXene and electrodeposited spinel NiCo2S4 nanostructures

Spinel metal sulfides have been investigated for a wide range of applications mostly in electrochemical energy storage owing to their better electronic conductivity and high reversible redox activity. Herein, we report a facile fabrication approach for the binder-free supercapacitor electrodes based on spinel NiCo₂S₄ (NCS) on various substrates such as Cu-foil (CF), Ni-foam (NF), and vertical graphene nanosheets grown on carbon tape (VG) via a single step-controlled electrodeposition technique. The obtained electrodeposited NiCo₂S₄ grown on Cu-foil (denoted as CF-NCS) in symmetric assembly shows a high specific capacitance of 167.28 F g^-1 compared to NCS grown on Ni-foam and VG substrates, whereas, symmetric NiCo₂S₄ grown on a VG substrate device exhibits better cycling performance (81% for 3000 cycles) compared to CF-NCS and NF-NCS. Furthermore, an asymmetric supercapacitor was assembled in combination with MXene (Ti₃C₂T _x ) as a negative electrode (denoted as TCX). As a result, the CF-NCS//TCX device exhibits a high areal capacitance of 48.6 mF cm^-2 at 2 mA cm^-2 of current density. We also report good specific capacitance of 54.57 F g^-1 at 2 A g^-1; in addition, the CF-NCS//TCX assembly delivers maximum areal and gravimetric energy density of 14.86 mWh cm^-2 and 14.86 Wh kg^-1 respectively. In contrast, the VG-NCS//TCX device showed improved cycling stability with 85% of capacitance retention over 5000 cycles owing to its highly porous structure and multiple conductive networks in the VG substrate and provides structural stability to NCS with fast ion diffusion. This experiment favors 2D MXene as a capacitive electrode that provides a replacement for carbon-based electrodes in asymmetric assembly with superior electrochemical performance. Hence, the hierarchical NCS structure grown on the various substrates in combination with MXene serve as a promising material for energy storage application.

Impact of mesoporous SiO2 support for Ni/polypyrrole nanocomposite particles on their capacitive performance

The inclusion of mesoporous H2N-SiO2 support in H2N-SiO2/Ni/PPy nanocomposite particles improved their electrochemical performance, suitable for energy storage devices.

Hierarchical Co(OH)F/CoFe-LDH heterojunction enabling high-performance overall water-splitting

Due to the serious energy and environmental issues, hydrogen generation via water splitting has been regarded as a green and promising alternative strategy to the use of fossil fuels.

Carbon Nanotube Fibers Decorated with MnO2 for Wire-Shaped Supercapacitor

Fibers made from CNTs (CNT fibers) have the potential to form high-strength, lightweight materials with superior electrical conductivity. CNT fibers have attracted great attention in relation to various applications, in particular as conductive electrodes in energy applications, such as capacitors, lithium-ion batteries, and solar cells. Among these, wire-shaped supercapacitors demonstrate various advantages for use in lightweight and wearable electronics. However, making electrodes with uniform structures and desirable electrochemical performances still remains a challenge. In this study, dry-spun CNT fibers from CNT carpets were homogeneously loaded with MnO₂ nanoflakes through the treatment of KMnO₄. These functionalized fibers were systematically characterized in terms of their morphology, surface and mechanical properties, and electrochemical performance. The resulting MnO₂-CNT fiber electrode showed high specific capacitance (231.3 F/g) in a Na₂SO₄ electrolyte, 23 times higher than the specific capacitance of the bare CNT fibers. The symmetric wire-shaped supercapacitor composed of CNT-MnO₂ fiber electrodes and a PVA/H₃PO₄ electrolyte possesses an energy density of 86 nWh/cm and good cycling performance. Combined with its light weight and high flexibility, this CNT-based wire-shaped supercapacitor shows promise for applications in flexible and wearable energy storage devices.

Preaddition of Cations to Electrolytes for Aqueous 2.2 V High Voltage Hybrid Supercapacitor with Superlong Cycling Life and Its Energy Storage Mechanism

Electrolyte solutions and electrode active materials, as core components of energy storage devices, have a great impact on the overall performance. Currently, supercapacitors suffer from the drawbacks of low energy density and poor cyclic stability in typical alkaline aqueous electrolytes. Herein, the ultrathin Co₃O₄ anode material is synthesized by a facile electrodeposition, followed by postheat treatment process. It is found that the decomposition of active materials induces reduction of energy density and specific capacitance during electrochemical testing. Therefore, a new strategy of preadding Co²⁺ cations to achieve the dissolution equilibrium of cobalt in active materials is proposed, which can improve the cyclic lifetime of electrode materials and broaden the operation window of electrochemical devices. Co²⁺ and Li⁺ embedded in carbon electrode during charging can enhance H⁺ desorption energy barrier, further hampering the critical step of bulk water electrolysis. More importantly, the highly reversible chemical conversion mechanism between Co₃O₄ and protons is demonstrated to be the fact that a large amount of quantum dots and second-order flaky CoO layers were in situ formed in the electrochemical reaction process, which is first discovered and reported in neutral solutions. The as-assembled device achieves a high operation voltage (2.2 V), excellent cycling stability (capacitance retention of 168% after 10 000 cycles) and ultrahigh energy density (99 W h kg^-1 at a power density of 1100 W kg^-1). The as-prepared electrolytes and highly active electrode materials will open up new opportunities for aqueous supercapacitors with high safety, high voltage, high energy density, and long-lifespan.

Carbon Nanolights in Piezopolymers are Self-Organizing Toward Color Tunable Luminous Hybrids for Kinetic Energy Harvesting

Herein, an all-solid-state sequential self-organization and self-assembly process is reported for the in situ construction of a color tunable luminous inorganic/polymer hybrid with high direct piezoresponse. The primary inorganic self-organization in solid polymer and the subsequent polymer self-assembly are achieved at high pressure with the first utilization of piezo-copolymer (PVDF-TrFE) as the host matrix of guest carbon quantum dots (CQDs). This process induces the spontaneous formation of a highly ordered, microscale, polygonal, and hierarchically structured CQDs/PVDF-TrFE hybrid with multicolor photoluminescence, consisting of very thermodynamic stable polar crystalline nanowire arrays. The electrical polarization-free CQDs/PVDF-TrFE hybrids can efficiently harvest the environmental available kinetic mechanical energy with a new large-scale group-cooperation mechanism. The open-circuit voltage and short-circuit current outputs reach up to 29.6 V cm^-2 and 550 nA cm^-2 , respectively. The CQDs/PVDF-TrFE-based hybrid nanogenerator demonstrates drastically improved durable and reliable features during the real-time demonstration of powering commercial light emitting diodes. No attenuation/fluctuation of the electrical signals is observed for ≈10 000 continuous working cycles. This study may offer a new design concept for progressively but spontaneously constructing novel multiple self-adaptive complex inorganic/polymer hybrids that promise applications in the next generation of self-powered autonomous optoelectronic devices.

Dual Functionalized CuMOF-Based Composite for High-Performance Supercapacitors

Herein, we utilized our previously reported highly porous CuMOF, {[Cu₂(L)(H₂O)₂]·(5DMF)·(4H₂O)}_n, decorated with amine and trifluoromethyl functional groups for energy storage application. This robust framework in CuMOF enhances the chemical and thermal stabilities as well as improves the interfacial binding interactions. The poor conductivity of CuMOF usually restricts its practical utility in energy storage systems, due to which rGO was introduced along with CuMOF to form a CuMOF/rGO composite (1) through a facile ultrasonication technique. The synergistic effects between CuMOF and rGO induce a dramatic enhancement in specific capacitance (462 F g^-1 at 0.8 A g^-1) of 1 with a cycle life of 93.75% up to 1000 cycles. The results highlight 1 as an emerging contestant for next generation supercapacitors.

One-Step In Situ Self-Assembly of Cypress Leaf-Like Cu(OH)2 Nanostructure/Graphene Nanosheets Composite with Excellent Cycling Stability for Supercapacitors

Transition metal hydroxides and graphene composite holds great promise to be the next generation of high performance electrode material for energy storage applications. Here we fabricate the cypress leaf-like Cu(OH)₂ nanostructure/graphene nanosheets composite through one-step in situ synthesis process, employed as a new type of electrode material for high efficiency electrochemical energy storage in supercapacitors. A solution-based two-electrode system is applied to synthesize Cu(OH)₂/graphene hybrid nanostructure, where anodic graphene nanosheets firmly anchor cathodic Cu(OH)₂ nanostructure due to the electrostatic interaction. The in situ self-assembly of Cu(OH)₂/graphene ensures good structural robustness and the cypress leaf-like Cu(OH)₂ nanostructure prompt to form the open and porous morphology. The hybrid structure would facilitate charge transport and effectively mitigate the volume changes during long-term charging/discharging cycles. As a consequence, the Cu(OH)₂/graphene composite exhibits the highest capacitance of 317 mF/cm² at the current density of 1 mA/cm² and superior cyclic stability with no capacitance decay over 20,000 cycles and remarkable rate capability at increased current densities.

3D heterostructured cobalt oxide@layered double hydroxide core–shell networks on nickel foam for high-performance hybrid supercapacitor

3D heterostructured Co₃O₄@LDH networks were grown directly on nickel foam for the positive electrode of a high-performance hybrid supercapacitor.

Fabrication of Cobalt-Nickel-Zinc Ternary Oxide Nanosheet and Applications for Supercapacitor Electrode

Mesoporous cobalt-nickel-zinc ternary oxide (CNZO) nanosheets grown on the nickel foam are prepared by a simple hydrothermal treatment and subsequent calcination process. The physical characterizations show that the as-obtained CNZO nanosheets possess the mesoporous structure and a high specific surface of 75.4 m² g^-1 has been achieved. When directly applied for the binder-free supercapacitor electrode for the first time, the nickel foam supported mesoporous CNZO nanosheet electrode exhibits an ultrahigh specific capacity about 1172.2 C g^-1 at 1 A g^-1. More significantly, an asymmetric supercapacitor based on the as-obtained CNZO positive electrode and an activated carbon negative electrode shows a high energy density of 84.2 Wh kg^-1 at a power density of 374.8 W kg^-1, with excellent cycle stability (keeps 78.8% capacitance retention and 100% coulombic efficiency after 2,500 cycles). The excellent supercapacitive properties suggest that the nickel foam supported CNZO nanosheet electrodes are promising for application as high-performance supercapacitor.

High-performance asymmetric supercapacitors based on monodisperse MnO nanocrystals with high energy densities

Monodisperse spherical MnO nanocrystals (NCs) with a size of 22.5 nm were synthesized by the thermal decomposition of manganese oleate in the presence of oleic acid and 1-octadecene. The as-synthesized MnO NCs show superior electrochemical performances with a specific capacitance of 736.4 F g-1 at a current density of 1 A g-1 and retain 93.3% of initial specific capacitance after 5000 cycles. The MnO NC electrode was successfully assembled in an asymmetric supercapacitor as the cathode with an activated carbon (AC) electrode as the anode. The as-fabricated device can demonstrate remarkable performance with an energy density of 44.2 W h kg-1, a power density of 900 W kg-1, and excellent cycling stability. This work provides a new direction for MnO nanomaterials towards high-performance energy storage devices.

Synthesis of Honeycomb-Like Co₃O₄ Nanosheets with Excellent Supercapacitive Performance by Morphological Controlling Derived from the Alkaline Source Ratio

Honeycomb-like Co₃O₄ nanosheets with high specific surface area were successfully synthesized on porous nickel foam by the facile hydrothermal method followed by an annealing treatment (300 °C), which were used as high-performance supercapacitor electrodes. The effects of the mole ratio of hexamethylenetetramine (HMT) and Co(NO₃)₂ (1:1, 2:1, 3:1, 4:1, 5:1 and 6:1) as the reactants on the morphological evolution and electrochemical performance of the electrodes were investigated in detail. X-ray diffractometry (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were applied to characterize the structure and morphology of the products. The electrochemical performance was measured by cyclic voltammetry (CV) and galvanostatic charge/discharge. The mole ratio of HMT and Co(NO₃)₂ produced a significant effect on the morphological evolution of Co₃O₄. The morphological evolution of Co₃O₄ with the increase in the mole ratio was followed: the nanosheets accompanied with a large number of spherical nanoparticles → the formation of some strip-like particles due to the agglomeration of spherical nanoparticles → the formation of new nanosheets resulting from the growth of strip-like particles → the formation of coarse flower-like particles owing to the connection among the nanosheets → the nanosheets gradually covered with flower-like particles. Accompanied with the change, the specific surface area was increased firstly, and then decreased. A maximum was obtained at a HMT and Co(NO₃)₂ mole ratio of 4:1. The evolution in morphology of Co₃O₄ was responsible for the change in electrochemical performance of the electrode. The specific capacitance value of the electrode prepared at a HMT and Co(NO₃)₂ mole ratio of 4:1 was highest (743.00 F·g⁻¹ at 1 A·g⁻¹ in the galvanostatic charge/discharge test). The similar result was also observed in the CV test with a scanning rate of 5 mV·s⁻¹. Moreover, the electrode also demonstrated an excellent cyclic performance, in which about 97% of the initial specific capacitance remained at 1 A·g⁻¹ for 500 cycles in the galvanostatic charge/discharge test. This excellent electrochemical performance was ascribed to high specific surface area of Co₃O₄ nanosheets that provide added channels and space for the ions transportation.

In situ coating nickel organic complexes on free-standing nickel wire films for volumetric-energy-dense supercapacitors

A self-free-standing core-sheath structured hybrid membrane electrodes based on nickel and nickel based metal-organic complexes (Ni@Ni-OC) was designed and constructed for high volumetric supercapacitors. The self-standing Ni@Ni-OC film electrode had a high volumetric specific capacity of 1225.5 C cm^-3 at 0.3 A cm^-3 and an excellent rate capability. Moreover, when countered with graphene-carbon nanotube (G-CNT) film electrode, the as-assembled Ni@Ni-OC//G-CNT hybrid supercapacitor device delivered an extraordinary volumetric capacitance of 85 F cm^-3 at 0.5 A cm^-3 and an outstanding energy density of 33.8 at 483 mW cm^-3. Furthermore, the hybrid supercapacitor showed no capacitance loss after 10 000 cycles at 2 A cm^-3, indicating its excellent cycle stability. These fascinating performances can be ascribed to its unique core-sheath structure that high capacity nano-porous nickel based metal-organic complexes (Ni-OC) in situ coated on highly conductive Ni wires. The impressive results presented here may pave the way to construct s self-standing membrane electrode for applications in high volumetric-performance energy storage.

Facile fabrication of shape-controlled CoxMnyOβ nanocatalysts for benzene oxidation at low temperatures

We report a new strategy for the design and construction of Co_xMn_yO_β for C₆H₆ oxidation, a representative VOC.

Synthesis of a MnS/NixSy composite with nanoparticles coated on hexagonal sheet structures as an advanced electrode material for asymmetric supercapacitors

A MnS/Ni_xS_y composite with nanoparticles coated on hexagonal sheets was successfully synthesized and exhibited enhanced performance.

Dandelion-like Co3O4 mesoporous nanostructures supported by a Cu foam for efficient oxygen evolution and lithium storage

Novel dandelion-like Co₃O₄ mesoporous nanostructures, supported by a Cu foam, are prepared which hold great promise in the fields of energy storage and conversion.

Flowery nickel–cobalt hydroxide via a solid–liquid sulphur ion grafting route and its application in hybrid supercapacitive storage

In our research, a two-step solid–liquid route was employed to fabricate flowery nickel–cobalt hydroxide with sulphur ion grafting (Ni1Co2–S). The utilization of NaOH/agar and Na₂S/agar could efficiently retard the release rates of OH⁻ or S²⁻ ions at the solid–liquid interface due to strong bonding between agar hydrogel and these anions. Ni1Co2–S generally displays ultrathin flowery micro-frame, ultrathin internal nanosheets and expanded pore size. Besides, the introduction of suitable sulphide species into nickel–cobalt hydroxide could improve its conductivity due to the lower band gap of Ni–Co sulphide. The supercapacitive electrode Ni1Co2–S presented capacitance of 1317.8 F g⁻¹ (at 1 A g⁻¹) and suitable rate performance (77.9% at 10 A g⁻¹ and 59.3% at 20 A g⁻¹). Furthermore, a hybrid supercapacitor (HSC) was developed utilizing positive Ni1Co2–S and negative activated carbon electrodes. As expected, the HSC device exhibited excellent specific capacitance (117.1 F g⁻¹ at 1 A g⁻¹), considerable energy densities (46.7 W h kg⁻¹ at 0.845 kW kg⁻¹ and 27.5 W h kg⁻¹ even at 9 kW kg⁻¹) and suitable cycling performance, which further illuminated the high energy storage capacity of Ni1Co2–S.

The Ni1Co2–S material fabricated via a solid–liquid route achieves high-performance supercapacitive storage.

Electrostatic Self-Assembly of Sandwich-Like CoAl-LDH/Polypyrrole/Graphene Nanocomposites with Enhanced Capacitive Performance

A novel sandwich-like composite with ultrathin CoAl-layered double hydroxide (LDH) nanoplates electrostatically assembled on both sides of two-dimensional polypyrrole/graphene (PG) substrate has been successfully fabricated using facile hydrothermal techniques. The PG not only serves as an excellent conductive and structural scaffold to enhance the transmission of electrons and prevent aggregation of CoAl-LDH nanoplates but also contributes to the enhancement of the specific capacitance. Owing to the homogeneous dispersion of CoAl-LDH nanoplates and its intimate interaction with PG substrate, the resulting CoAl-LDH/PG nanocomposite material exhibits excellent capacitive performance, for example, enhanced gravimetric specific capacitance (864 F g^-1 at 1 A g^-1 ), high rate performance (75% retention at 20 A g^-1), and excellent cycle life (almost no degradation in supercapacitor performance after 5000 cycles) in aqueous KOH solution. Furthermore, the assembled asymmetric capacitor is able to deliver a superhigh energy density of 46.8 Wh kg^-1 at 1.2 kW kg^-1 and maintain 90.1% of its initial capacitance after 10 000 cycles. These results indicate a rational assembly strategy toward a high-performance pseudocapacitive electrode material with excellent rate performance, high specific capacitance, and outstanding cycle stability.

Tailoring the morphology followed by the electrochemical performance of NiMn-LDH nanosheet arrays through controlled Co-doping for high-energy and power asymmetric supercapacitors

Herein, we tailor the surface morphology of nickel-manganese-layered double hydroxide (NiMn-LDH) nanostructures on 3D nickel-foam via a step-wise cobalt (Co)-doping hydrothermal chemical process. At the 10% optimum level of Co-doping, we noticed a thriving tuned morphological pattern of NiMn-LDH nanostructures (NiCoMn-LDH (10%)) in terms of the porosity of the nanosheet (NS) arrays which not only improves the rate capability as well as cycling stability, but also demonstrates nearly two-fold specific capacitance enhancement compared to Co-free and other NiCoMn-LDH electrodes with a half-cell configuration in 3 M KOH, suggesting that Co-doping is indispensable for improving the electrochemical performance of NiMn-LDH electrodes. Moreover, when this high performing NiCoMn-LDH (10%) electrode is employed as a cathode material to fabricate an asymmetric supercapacitor (ASC) device with reduced graphene oxide (rGO) as an anode material, excellent energy storage performance (57.4 Wh kg^-1 at 749.9 W kg^-1) and cycling stability (89.4% capacitive retention even after 2500 cycles) are corroborated. Additionally, we present a demonstration of illuminating a light emitting diode for 600 s with the NiCoMn-LDH (10%)//rGO ASC device, evidencing the potential of the NiCoMn-LDH (10%) electrode in fabricating energy storage devices.

Hierarchical Co(OH)F Superstructure Built by Low-Dimensional Substructures for Electrocatalytic Water Oxidation

The development of new materials/structures for efficient electrocatalytic water oxidation, which is a key reaction in realizing artificial photosynthesis, is an ongoing challenge. Herein, a Co(OH)F material as a new electrocatalyst for the oxygen evolution reaction (OER) is reported. The as-prepared 3D Co(OH)F microspheres are built by 2D nanoflake building blocks, which are further woven by 1D nanorod foundations. Weaving and building the substructures (1D nanorods and 2D nanoflakes) provides high structural void porosity with sufficient interior space in the resulting 3D material. The hierarchical structure of this Co(OH)F material combines the merits of all material dimensions in heterogeneous catalysis. The anisotropic low-dimensional (1D and 2D) substructures possess the advantages of a high surface-to-volume ratio and fast charge transport. The interconnectivity of the nanorods is also beneficial for charge transport. The high-dimensional (3D) architecture results in sufficient active sites per the projected electrode surface area and is favorable for efficient mass diffusion during catalysis. A low overpotential of 313 mV is required to drive an OER current density of 10 mA cm^-2 on a simple glassy carbon (GC) working electrode in a 1.0 m KOH aqueous solution.

Galvanic displacement assembly of ultrathin Co3O4 nanosheet arrays on nickel foam for a high-performance supercapacitor

High-performance supercapacitors are very desirable for many portable electronic devices, electric vehicles and high-power electronic devices. Herein, a facile and binder-free synthesis method, galvanic displacement of the precursor followed by heat treatment, is used to fabricate ultrathin Co₃O₄ nanosheet arrays on nickel foam substrate. When used as a supercapacitor electrode the prepared Co₃O₄ on nickel foam exhibits a maximum specific capacitance of 1095 F g^-1 at a current density of 1 A g^-1 and good cycling stability of 71% retention after 2000 cycling tests. This excellent electrochemical performance can be ascribed to the high specific surface area of each Co₃O₄ nanosheet that comprises numerous nanoparticles.

Phosphate Ion Functionalized Co3 O4 Ultrathin Nanosheets with Greatly Improved Surface Reactivity for High Performance Pseudocapacitors

A surface-modified Co₃ O₄ ultrathin nanosheet (denoted as PCO) is reported via controllable phosphate ion functionalization for pseudocapacitors. An energy density of 71.6 W h kg^-1 (at 1500 W kg^-1 ) is achieved by the PCO-based pseudocapacitor. The unique porous nanosheet morphology, high surface reactivity, and fast electrode kinetics of PCO are found to be responsible for the enhanced pseudocapacitive performance.

Pore structure improvement of carbon aerogel and investigation of the supercapacitive behavior of a Co3O4 nanoball/carbon aerogel composite

In the present study, hybrid nanostructures of porous Co₃O₄ nanoball/carbon aerogel were prepared via the in situ growth of Co₃O₄ nanoballs with nanosized uniform structures within the pores of a pre-synthesized atmospheric pressure-dried highly mesoporous carbon aerogel.

A proton-hopping charge storage mechanism of ionic one-dimensional coordination polymers for high-performance supercapacitors

A proton-conducting coordination polymer of Zn²⁺ phosphate and protonated imidazole has been used as a novel supercapacitor material in aqueous electrolytes.

Synthesis of Li2Ni2(MoO4)3 as a high-performance positive electrode for asymmetric supercapacitors

A NASICON-type compound, Li₂Ni₂(MoO₄)₃ was successfully synthesized via a combustion method to be used as positive electrode for asymmetric supercapacitors with good performance.

Interconnected hierarchical NiCo2O4 microspheres as high-performance electrode materials for supercapacitors

Hierarchical NiCo₂O₄ microspheres with large tunnels and abundant mesopores have been prepared, and they exhibit excellent performance in supercapacitor applications.

Three-Dimensional Hierarchical NixCo1-xO/NiyCo2-yP@C Hybrids on Nickel Foam for Excellent Supercapacitors

Active materials and special structures of the electrode have decisive influence on the electrochemical properties of supercapacitors. Herein, three-dimensional (3D) hierarchical Ni_xCo_1-xO/Ni_yCo_2-yP@C (denoted as NiCoOP@C) hybrids have been successfully prepared by a phosphorization treatment of hierarchical Ni_xCo_1-xO@C grown on nickel foam. The resulting NiCoOP@C hybrids exhibit an outstanding specific capacitance and cycle performance because they couple the merits of the superior cycling stability of Ni_xCo_1-xO, the high specific capacitance of Ni_yCo_2-yP, the mechanical stability of carbon layer, and the 3D hierarchical structure. The specific capacitance of 2638 F g^-1 can be obtained at the current density of 1 A g^-1, and even at the current density of 20 A g^-1, the NiCoOP@C electrode still possesses a specific capacitance of 1144 F g^-1. After 3000 cycles at 10 A g^-1, 84% of the initial specific capacitance is still remained. In addition, an asymmetric ultracapacitor (ASC) is assembled through using NiCoOP@C hybrids as anode and activated carbon as cathode. The as-prepared ASC obtains a maximum energy density of 39.4 Wh kg^-1 at a power density of 394 W kg^-1 and still holds 21 Wh kg^-1 at 7500 W kg^-1.

Nanofoaming to Boost the Electrochemical Performance of Ni@Ni(OH)2 Nanowires for Ultrahigh Volumetric Supercapacitors

Three-dimensional free-standing film electrodes have aroused great interest for energy storage devices. However, small volumetric capacity and low operating voltage limit their practical application for large energy storage applications. Herein, a facile and novel nanofoaming process was demonstrated to boost the volumetric electrochemical capacitance of the devices via activation of Ni nanowires to form ultrathin nanosheets and porous nanostructures. The as-designed free-standing Ni@Ni(OH)₂ film electrodes display a significantly enhanced volumetric capacity (462 C/cm³ at 0.5 A/cm³) and excellent cycle stability. Moreover, the as-developed hybrid supercapacitor employed Ni@Ni(OH)₂ film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm³ (at 0.25 A/cm³) and excellent cycle performance (only 14% capacitance reduction for 4500 cycles). Furthermore, the volumetric energy density can reach 33.9 mWh/cm³, which is much higher than that of most thin film lithium batteries (1-10 mWh/cm³). This work gives an insight for designing high-volume three-dimensional electrodes and paves a new way to construct binder-free film electrode for high-performance hybrid supercapacitor applications.