3D network-like porous MnCo2O4 by the sucrose-assisted combustion method for high-performance supercapacitors

3D network-like porous MnCo₂O₄ nanostructures have been successfully fabricated through a facile and scalable sucrose-assisted combustion route followed by calcination treatment. Benefiting from its advantages of the unique 3D network-like architectures with large specific surface area (216.15 m² g⁻¹), abundant mesoporosity (2–50 nm) and high electronic conductivity, the as-prepared MnCo₂O₄ electrode displays a high specific capacitance of 647.42 F g⁻¹ at a current density of 1 A g⁻¹, remarkable capacitance retention rate of 70.67% at current density of 10 A g⁻¹ compared with 1 A g⁻¹, and excellent cycle stability (only 6.32% loss after 3000 cycles). The excellent electrochemical performances coupled with facile and cost effective method will render the as-fabricated 3D network-like porous MnCo₂O₄ as a promising electrode material for supercapacitors.     

Highly mesoporous LaNiO3/NiO composite with high specific surface area as a battery-type electrode

This study reports the fabrication and characterization of mesoporous LaNiO₃/NiO composite with a very high specific surface area for a battery-type electrode. The mesoporous LaNiO₃/NiO composite was synthesized via a sol–gel method by using silica gel as a template, the colloidal silica gel was obtained by the hydrolysis and polymerization of tetraethoxysilane in the presence of La and Ni salts. We investigated the structure and the electrochemical properties of mesoporous LaNiO₃/NiO composite in detail. The mesoporous composite sample showed a specific surface area of 372 m² g⁻¹ with 92.7% mesoporous area and displayed remarkable electrochemical performance as a battery-type electrode material for supercapacitor. The specific capacity values were found to be 237.2 mAh g⁻¹ at a current density of 1 A g⁻¹ and 128.6 mAh g⁻¹ at a high current density of 20 A g⁻¹ in 1 M KOH aqueous electrolyte. More importantly, this mesoporous composite also showed an excellent cycling performance with the retention of 92.6% specific capacitance after 60,000 charging and discharging cycles.     

Low-temperature preparation of nitrogen-doped graphene for supercapacitors

A simple method to prepare nitrogen-doped graphene (NG) by a pressure-promoted process at relatively low temperatures is demonstrated. The NG with an atomic N content higher than 10% can be obtained by heating graphene oxide and NH₄HCO₃ in a sealed autoclave at a temperature as low as 150 °C. The product exhibits a specific capacitance of 170 F g⁻¹ at 0.5 A g⁻¹ in 5 M KOH, and a high retention rate of 96.4% of its initial capacitance after 10,000 charge/discharge cycles at a current density of 10 A g⁻¹. Such an easy, cost-effective and low-temperature doping process will be promising for preparing devices based on NG.     

Hydrothermal synthesis of Polypyrrole/MoS2 intercalation composites for supercapacitor electrodes

As a pseudocapacitive electrode materials for supercapacitor, Polypyrrole (PPy) exhibit excellent theoretical specific capacitance. However, it suffers from a poor cycling stability due to structural instability during charge-discharge process. In this work, a novel and facile hydrothermal method has been developed for the intercalation composites of PPy/MoS₂ with multilayer three-dimensional structure. The report result shows that the as-prepared electrode possess a outstanding electrochemical properties with significantly specific capacitance of 895.6 F g⁻¹ at current density of 1 A g⁻¹, higher energy density (3.774 Wh kg⁻¹) at power density of 252.8 kW kg⁻¹, furthermore, it also achieve remarkable cycling stability (~98% capacitance retention after 10,000 cycles) which is attributed to the synergistic effect of PPy and MoS₂. This synthetic strategy integrates performance enables the multilayer PPy/MoS₂ composites to be a promising electrode for energy storage applications.     

Graphitic carbon nitride nanosheet-assisted preparation of N-enriched mesoporous carbon nanofibers with improved capacitive performance

N-enriched mesoporous carbon nanofibers (NMCNFs) were prepared by an electrospinning technique using graphitic carbon nitride (g-C₃N₄) nanosheets both as sacrificial template and N-doping source. The resultant NMCNF film has a high N-doping level of 8.6 wt% and a high specific surface area of 554 m² g⁻¹. When directly used as the electrode material for supercapacitor, the free-standing NMPCNF film shows a significantly improved capacitive performance including a higher specific capacitance (220 F g⁻¹ at 0.2 A g⁻¹) and a better rate capability (∼70% retention at 20 A g⁻¹) than those of microporous carbon nanofiber film prepared using the same process without using g-C₃N₄ nanosheets (145 F g⁻¹ at 0.2 A g⁻¹ and ∼45% retention at 20 A g⁻¹). Moreover, the NMCNFs show superior stability with only a ∼3% decrease of its initial capacitance after 1000 cycles at a high current density of 10 A g⁻¹. More significantly, the energy density of a symmetrical supercapacitor (SC) based on the NMPCNF film can reach 12.5 Wh kg⁻¹ at a power density of 72 W kg⁻¹.     

High performance wire-shaped supercapacitive electrodes based onactivated carbon fibers core/manganese dioxide shell structures

Micro/nano hierarchical structures with uniformly patterned nanostructures shell and activated internal core are promising for boosting electrochemical performance. Here we report the fabrication of wire-shaped supercapacitive electrodes with manganese dioxide (MnO₂) nanostructures shell integrated onto activated carbon fiber (ACF) core. The ACF core is doped with nitrogen heteroatom and shows good conductivity and hydrophilicity, which endow fast ion and electron transport and high accessibility of electrolyte. The MnO₂ nanostructures shell integrated on the ACF core by electrodeposition method together provide significant pseudocapacitive contribution associated with fast faradaic reactions. The electrochemical performance of the fabricated electrodes was evaluated by cyclic voltammetry, galvanostatic charging/discharging and electrochemical impedance spectroscopy techniques. The integrated wire-shaped electrodes, which boost the synergetic effect of MnO₂ nanostructures and ACF, have excellent current collecting capabilities thus resulting high electrochemical performance (with the specific capacitance of 26.64 mF cm⁻¹ at the current density of 0.1 mA cm⁻¹ and 96% capacitance retention after 8000 charging/discharging cycles at the current density of 1 mA cm⁻¹).     

Facile synthesis of NiMn2O4 nanosheet arrays grown on nickel foam as novel electrode materials for high-performance supercapacitors

Nanostructured spinel NiMn₂O₄ arrays have been fabricated by a facile hydrothermal approach and further investigated as binder-free electrode for high-performance supercapacitors. Compared with Mn₃O₄, NiMn₂O₄ exhibited higher specific capacitances (662.5 F g⁻¹ and 370.5 F g⁻¹ in different electrolytes at the current density of 1 A g⁻¹) and excellent cycling stability (~96% capacitance retention after 1000 cycles) in a three-electrode system. Such a novel microstructure grown directly on the conductive substrate provided sufficient active sites for redox reaction resulting in their enhanced electrochemical behaviors. Their improved performances suggested that ultrathin sheet-like NiMn₂O₄ arrays on Ni foam substrate were a promising electrode material for supercapacitors.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

Straightforward synthesis of hierarchical Co3O4@CoWO4/rGO core–shell arrays on Ni as hybrid electrodes for asymmetric supercapacitors

Hierarchical Co₃O₄@CoWO₄/rGO core/shell nanoneedles arrays are successfully grown on 3D nickel foam using a simple, effective method. By virtue of its unique structure, Co₃O₄@CoWO₄/rGO demonstrates an enhanced specific capacitance of 386 F g⁻¹ at 0.5 A g⁻¹ current density. It can be used as an integrated, additive-free electrode for supercapacitors that boasts excellent performance. As illustration, we assemble an asymmetric supercapacitor (ASC) using the as-prepared Co₃O₄@CoWO₄/rGO as the positive electrode and activated carbon as the negative electrode. The optimized ASC displays a maximum energy density of 19.99 Wh kg⁻¹ at a power density of 321 W kg⁻¹. Furthermore, the ASC also presents a remarkably long cycle life along with 88.8% specific capacitance retention after 5000 cycles.     

Mesoporous N-containing carbon nanosheets towards high-performance electrochemical capacitors

We developed a direct carbonization strategy to efficiently fabricate mesoporous N-containing carbon nanosheets (N-CNSs) by using polyaniline nanosheets as a carbon precursor. Physicochemical characterizations revealed that the as-synthesized N-CNSs with 5.9 wt.% N species possessed a well-developed mesoporous architecture with large specific surface area of 352 m² g⁻¹, high mesoporous volume of 0.32 cm³ g⁻¹, and average pore size of ∼5.2 nm. When further utilized as an electrode for electrochemical capacitors, the mesoporous N-CNSs delivered a large specific capacitance of 239 F g⁻¹ at 0.5 A g⁻¹, and even 197 F g⁻¹ at a high current load of 8 A g⁻¹, indicating its good rate behavior. Furthermore, the capacitance degradation of ∼4% over continuous 5000 charge–discharge cycles at 6 A g⁻¹ further verified its good electrochemical stability at high rates for long-term electrochemical capacitors application.     

High performance MnO2 nanoflower supercapacitor electrode by electrochemical recycling of spent batteries

MnO₂ nanoflower is prepared by electrochemical conversion of Mn₃O₄ obtained by heat treatment of spent zinc‒carbon batteries cathode powder. The heat treated and converted powders were characterized by TGA, XRD, FTIR, FESEM and TEM techniques. XRD analyses show formation of Mn₃O₄ and MnO₂ phases for the heat treated and converted powders, respectively. FESEM images indicate the formation of porous nanoflower structure of MnO_2, while, condensed aggregated particles are obtained for Mn₃O₄. The energy band gap of MnO₂ is obtained from UV‒Vis spectra to be 2.4 eV. The electrochemical properties are investigated using cyclic voltammetry, galvanostatic charge‒discharge and electrochemical impedance techniques using three-electrode system. The specific capacitance of MnO₂ nanoflower (309 F g⁻¹ at 0.1 A g⁻¹) is around six times higher than those obtained from the heat treated one (54 F g⁻¹ at 0.1 A g⁻¹). Moreover, it has high capacitance retention up to 93% over 1650 cycles. Impedance spectra of MnO₂ nanoflower show very small resistances and high electrochemical active surface area (340 m² g⁻¹). The present work demonstrates a novel electrochemical approach to recycle spent zinc-carbon batteries into high value supercapacitor electrode.     

The composite material based on Dawson-type polyoxometalate and activated carbon as the supercapacitor electrode

A supercapacitor electrode assembled from activated carbon (AC) and (NH₄)₆[P₂Mo₁₈O₆₂]·14.2H₂O (P₂Mo₁₈) was fabricated for the first time, and showed remarkable electrochemical performance ascribed to the synergy of the double layer capacitance of AC and the pseudocapacitance of P₂Mo₁₈. The investigations indicate that the AC/P₂Mo₁₈ electrode exhibits a specific capacitance of 275 F g^− 1 at a high current density of 6 A g^− 1, which is substantially larger than the 182 F g^− 1 of the AC electrode. In addition, the AC/P₂Mo₁₈ electrode possesses a remarkable rate capability (89%) when the current density is increased from 2 to 6 A g^− 1.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.     

Template synthesis of hollow carbon spheres anchored on carbon nanotubes for high rate performance supercapacitors

A carbon material consisting of hollow carbon spheres anchored on the surface of carbon nanotubes (CNT–HCS) has been synthesized by an easy chemical vapor deposition process using a CNT–MnO₂ hybrid as template. An electrode made of this material exhibits a maximum specific capacitance of 201.5 F g⁻¹ at 0.5 A g⁻¹ and excellent rate performance (69% retention ratio at 20 A g⁻¹). It has impressive cycling stability with 90% initial capacitance retained after 5000 cycles at 5 A g⁻¹ in 6 mol L⁻¹ KOH. Symmetric supercapacitors based on CNT–HCS achieve a maximum energy density of 11.3 W h kg⁻¹ and power density of 11.8 kW kg⁻¹ operated within a wide potential range of 0–1.6 V in 1.0 mol L⁻¹ Na₂SO₄ solution.     

High-performance supercapacitor based on V2O5/carbon nanotubes-super activated carbon ternary composite

A ternary composite of V₂O₅/carbon nanotubes/super activated carbon (V₂O₅/CNTs–SAC) was prepared by a simple hydrothermal method and used as a supercapacitor electrode material. The electrochemical performance of the electrode was analyzed using cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy, which were performed in 2 M NaNO₃ as the electrolyte. The V₂O₅/CNTs–SAC nanocomposite exhibited a specific capacitance as high as 357.5 F g⁻¹ at a current density of 10 A g⁻¹, which is much higher than that of either bare V₂O₅ nanosheets or a V₂O₅/CNTs composite. Furthermore, the capacitance increased to 128.7% of the initial value after 200 cycles, with 99.5% of the maximum value being retained after 1000 cycles. These results demonstrated that the V₂O₅/CNTs–SAC ternary composite is suitable for use as an electrode material for supercapacitors.     

Rational design of nickel cobalt sulfide/oxide core-shell nanocolumn arrays for high-performance flexible all-solid-state asymmetric supercapacitors

The development of wearable electronics has created a surge of interest in designing flexible energy storage device with high energy density and long lifespan. In this work, we have successfully fabricated a flexible asymmetric supercapacitor (ASC) based on the NiCo₂S₄@NiCo₂O₄ nanocolumn arrays (NCAs). The nickel cobalt sulfide/oxide core-shell nanostructures were rationally synthesized through a facile stepwise approach. The NiCo₂S₄@NiCo₂O₄ NCAs based electrode delivered a high specific capacitance of 2258.9 F g⁻¹ at a current density of 0.5 A g⁻¹. The as-assembled flexible ASC device exhibited a high energy density of 44.06 Wh kg⁻¹, a high power density of 6.4 kW kg⁻¹, and excellent cycling stability by retaining 92.5% after 6000 cycles. Excitingly, the electrochemical property of the ASC device could be maintained under severe bending, indicating superior flexibility and mechanical stability. The NiCo₂S₄@NiCo₂O₄ core-shell NCAs possess enormous potential for future wearable electronic applications.     

Preparation and capacitance performance of nitrided lithium titanate nanoarrays

Nitrided lithium titanate (N-Li₄Ti₅O₁₂) nanoarrays with nanowire and nanotube structures were designed as the electrode materials of lithium-ion supercapacitor for electrochemical energy storage. Two types of TiO₂ nanoarrays were used as the precursor which involved TiO₂ nanowire array prepared by hydrothermal process and TiO₂ nanotube array prepared by anodization process. Li₄Ti₅O₁₂ nanoarrays were formed through hydrothermal reaction or sonochemical reaction of TiO₂ nanoarrays with lithium hydroxide and then calcination treatment process. Finally, N-Li₄Ti₅O₁₂ nanoarrays were formed through nitriding treatment of Li₄Ti₅O₁₂ using ammonia as nitrogen source. The electroactive N-Li₄Ti₅O₁₂ nanowire array and nanotube array exhibited the specific capacitance of 607.2 F g⁻¹ and 814.4 F g⁻¹ at a current density of 1 A g⁻¹, respectively. The corresponding capacitance retention was determined to be 92.1% and 94.2% after 1000 cycles at high current density of 5 A g⁻¹. The corresponding capacitance still kept 182.9 and 352.1 F g⁻¹ at much higher current density of 20 A g⁻¹, presenting reasonable rate capability for N-Li₄Ti₅O₁₂ nanoarrays. The improved capacitance performance of N-Li₄Ti₅O₁₂ nanotube array was ascribed to the more amount of TiN and more accessible nanotube surface area, which contributed to the improved conductivity and fast diffusion of electrolyte ions on the surface of electrode. Both N-Li₄Ti₅O₁₂ nanowire array and nanotube array with well-aligned integrative structure exhibited an excellent cycling stability during continuous charge/discharge process. Well-designed N-Li₄Ti₅O₁₂ nanoarrays with high capacitance, good cycling stability and rate capability presented the promising application as feasible electrode materials of lithium-ion supercapacitors for the energy storage.     

Electrospun ZnO–SnO2 composite nanofibers with enhanced electrochemical performance as lithium-ion anodes

ZnO–SnO₂ composite nanofibers with different structures were synthesized by a simple electrospinning approach with subsequent calcination at three different temperatures using polyacrylonitrile as the polymer precursor. The electrochemical performance of the composites for use as anode materials in lithium-ion batteries were investigated. It was found that the ZnO–SnO₂ composite nanofibers calcined at 700 °C showed excellent lithium storage properties in terms of cycling stability and rate capability, compared to those calcined at 800 and 900 °C, respectively. ZnO–SnO₂ composite nanofibers calcined at 700 °C not only delivered high initial discharge and charge capacities of 1450 and 1101 mAh g⁻¹, respectively, with a 75.9% coulombic efficiency, but also maintained a high reversible capacity of 560 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles. Additionally, a high reversible capacity of 591 mAh g⁻¹ was obtained when the current density returned to 0.1 A g⁻¹ after 50 cycling at a high current density of 2 A g⁻¹. The superior electrochemical performance of ZnO–SnO₂ composite nanofibers can be attributed to the unique nanofibrous structure, the smaller particle size and smaller fiber diameter as well as the porous structure and synergistic effect between ZnO and SnO₂.     

Nitrogen-doped porous carbons through KOH activation with superior performance in supercapacitors

A series of nitrogen-doped porous carbons are prepared through KOH activation of a nonporous nitrogen-enriched carbon which is synthesized by pyrolysis of the polymerized ethylenediamine and carbon tetrachloride. The porosity and nitrogen content of the nitrogen-doped porous carbons depend strongly on the weight ratio of KOH/carbon. As the weight ratio of KOH/carbon increases from 0.5 to 2, the specific surface area increases from 521 to 1913 m² g⁻¹, while the nitrogen content decreases from 10.8 to 1.1 wt.%. The nitrogen-doped porous carbon prepared with a moderate KOH/carbon weight ratio of 1, which possesses a balanced specific surface area (1463 m² g⁻¹) and nitrogen content (3.3 wt.%), exhibits the largest specific capacitance of 363 F g⁻¹ at a current density of 0.1 A g⁻¹ in 1 M H₂SO₄ aqueous electrolyte, attributed to the co-contribution of double-layer capacitance and pseudocapacitance. Moreover, it shows excellent rate capability (182 F g⁻¹ remained at 20 A g⁻¹) and good cycling stability (97% capacitance retention over 5000 cycles), making it a promising electrode material for supercapacitors.     

Synthesis of cross-linked graphene aerogel/Fe2O3 nanocomposite with enhanced supercapacitive performance

In this work, cross-linked graphene aerogel (CL-GA) and its composite with Fe₂O₃ nanoparticles (NPs) were synthesized through a one-step hydrothermal procedure by using p-phenylenediamine (PPD). Structural characterizations revealed that in the preparation of the composite PPD acts as a cross-liker and provides high surface area by decreasing restacking of graphene sheets and functions as nitrogen source simultaneously. The electrochemical characteristics of the nanocomposite were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS) and Fast Fourier transform continues cyclic voltammetry (FFTCCV). The results show that cross-linked graphene aerogel/Fe₂O₃ (CL-GA/Fe₂O₃) nanocomposite displays enhanced supercapacitive performance, where it has capacitance of 445 at 1 A g⁻¹, high energy density of 63 W h Kg⁻¹, and 89% capacitance retention after 5000 cycles in 3 M KOH. Presence of PPD considerably improved supercapacitive performance of nanocomposite as a result it could be promising material in synthesis of efficient graphene/metal oxide-based electrode material for high performance supercapacitors.