Design of best performing hexagonal shaped Ag@CoS/rGO nanocomposite electrode material for electrochemical supercapacitor application

The mixed metal/metal sulphide(Ag@CoS)with reduced graphene oxide(rGO)nanocomposite(Ag@CoS/rGO)was synthesized for the possible electrode in supercapacitors.Ag@CoS was successfully deposited on the rGO nanosheets by hydrothermal method,implying the growth of 2D Ag and CoS-based hexagonal-like structure on the rGO framework.The synthesized nanocomposite was subjected to structural,morphological and electrochemical studies.The XRD results show that the prepared nanocomposite material exhibits a combination of hexagonal and cubic phase due to the presence of CoS and Ag phases together.The band appearing at nearly 470.33 cm^−1 in FTIR spectra can be ascribed to the absorption of S—S bond in the Ag@CoS/rGO nanocomposite.The clear hexagonal structure was analysed by SEM and TEM with the grain sizes ranging from nanometer to micrometer.The electrode material exhibits excellent cyclic stability with a specific capacitance of 1580 F/g at a current density of 0.5 A/g without any loss of capacitive retention even after 1000 cycles.Based on the electrochemical performance,it can be inferred that the prepared novel nanocomposite material is very suitable for using as an electrode for electrochemical supercapacitor applications.

Vertical‑Aligned and Ordered‑Active Architecture of Heterostructured Fibers for High Electrochemical Capacitance

Architecture of fibrous building blocks with ordered structure and high electroactivity that enables quick charge kinetic transport/intercalation is necessary for high-energy-density electrochemical supercapacitors.Herein,we report a heterostruc-tured molybdenum disulfide@vertically aligned graphene fiber(MoS_(2)@VA-GF),wherein well-defined MoS_(2)nanosheets are decorated on vertical graphene fibers by C-O-Mo covalent bonds.Benefiting from uniform microfluidic self-assembly and confined reactions,it is realized that the unique characteristics of a vertical-aligned skeleton,large faradic activity,in situ interfacial connectivity and high-exposed surface/porosity remarkably create efficiently directional ionic pathways,interfa-cial electron mobility and pseudocapacitive accessibility for accelerating charge transport and intercalation/de-intercalation.Resultant MoS_(2)@VA-GF exhibits large gravimetric capacitance(564 F g^(-1))and reversible redox transitions in 1 M H_(2)SO_(4)electrolyte.Furthermore,the MoS_(2)@VA-GF-based solid-state supercapacitors deliver high energy density(45.57 Wh kg-1),good cycling stability(20,000 cycles)and deformable/temperature-tolerant capability.Beyond that,supercapacitors can realize actual applications of powering multicolored optical fiber lamps,wearable watch,electric fans and sunflower toys.

Facile Fabrication of Hierarchical Porous N/O Functionalized Carbon Derived from Blighted Grains Towards Electrochemical Capacitors

The hierarchical porous N/O co-functionalized carbon(HPNOC)was scalably prepared by using the lowcost and renewable blighted grains as the raw material coupled with mild KHCO_3 activation for electrochemical capacitors(ECs).The elemental N was in situ doped in the obtained HPNOC without any N-containing additives.Remarkably,the obtained HPNOC was endowed with a large specific surface area(about 2 624m^2·g^(-1)),high pore volume(about 1.35cm^3·g^(-1)),as well as high-content N/O functionalization(about 1.9%(in atom)N and about 10.2%(in atom)O.Furthermore,the as-resulted HPNOC electrode with a high mass loading of 5mg·cm^(-2 )exhibited competitive gravimetric capacitances of about 373.6F·g^(-1 )at 0.5A·g^(-1),and even about 260.4F·g^(-1 )at a high rate of 10A·g^(-1);superior capacitance retention of about 98.8%at 1A·g^(-1 )over 10 000consecutive cycles;and high specific energy of about 9.6W·h·kg^(-1 )at a power of 500W·kg^(-1),when evaluated as a promising electrode in 6mol KOH for advanced electrochemical supercapacitors.More encouragingly,the green synthetic strategy we developed holds a huge promise in generalizing for other biomass-derived carbon materials for versatile energy-related applications.

MXene-based materials for electrochemical energy storage

Rechargeable batteries and supercapacitors are widely investigated as the most important electrochemical energy storage devices nowadays due to the booming energy demand for electric vehicles and hand-held electronics. The large surface-area-to-volume ratio and internal surface areas endow two-dimensional（2D） materials with high mobility and high energy density; therefore, 2D materials are very promising candidates for Li ion batteries and supercapacitors with comprehensive investigations. In 2011, a new kind of 2D transition metal carbides, nitrides and carbonitrides, MXene, were successfully obtained from MAX phases. Since then about 20 different kinds of MXene have been prepared. Other precursors besides MAX phases and even other methods such as chemical vapor deposition（CVD） were also applied to prepare MXene, opening new doors for the preparation of new MXene. Their 2D nature and good electronic properties ensure the inherent advantages as electrode materials for electrochemical energy storage. In this review, we summarize the recent progress in the development of MXene with emphasis on the applications to electrochemical energy storage. Also, future perspective and challenges of MXene-based materials are briefly discussed regrading electrochemical energy storage.

Ordered Mesoporous Carbon/SnO_2 Composites as the Electrode Material for Supercapacitors

A series of composites as electrode materials for supercapacitors were prepared via incipient wetness impregnation method utilizing ordered mesoporous carbon （OMC） and tin （IV） oxide （SnO2） with different ratio.The structure and electrochemical properties of the OMC/SnO2 composites were characterized by XRD,TEM and cyclic voltammetry （CV）.Pore characteristics were measured by nitrogen adsorption and desorption isotherms.The results show that the structure and electrochemical properties of the composites depend mainly on the loading amount of SnO2 in the ordered mesoporous carbon.The optimum amount of SnCl4 added is found to be 40 % （1.54 g ethanol-based SnCl4·5H2O added to 1 g OMC） of the saturated solution.The specific capacitance of the composite of optimum amount of SnCl4 （200 F g-1） is nearly three times of that of the pristine SnO2 （72 F g-1） at the scan rate of 5 mV s-1,and its specific capacitance is almost equal to that of the ordered mesoporous carbon （126 F g-1） at the scan rate of 200 mV s-1.Meanwhile,it has better specific volumetric energy density than OMC due to its higher density.Besides,in the potential range of 0-0.9 V the composite electrode material exhibits a stable cycle life after 500 cycles.

A facile preparation and electrochemical properties of nickel based compound-graphene sheet composites for supercapacitors

Composites of a nickel based compound incorporated with graphene sheets （NiBC-GS） are prepared by a simple flocculation, using hydrazine hydrate as flocculant and reductant, from a homogeneous intermixture of nickel dichloride and graphene oxide dispersed in N,N-dimethylformamide. Morphology, microstructure and thermal stability of the obtained products were characterized by field-emission scanning electron microscopy, X-ray diffraction and thermal gravimetric analysis. Furthermore, the electrochemical properties of NiBC-GS, as electrode materials for supercapacitors, were studied by cyclic voltammetry and galvanostatic charge]discharge in 2 mol L 1 KOH solution. It was determined that for NiBC-GS annealed at 250 ~C, a high specific capacitance of 2394 F g 1 was achieved at a current density of 1 A g^-1, with 78% of the value （i.e., 1864 F g^-1） retained after 5000 times of repeated galvanostatic charge/discharge cycling. The high specific capacitance and available charge/discharge stability indicate the synthesized NiBC-GS250 composite is a good candidate as a novel electrode material for supercapacitors.

Synthesis, Characterization and Electrochemical Study of Graphene Oxide-Multi Walled Carbon Nanotube-Manganese Oxide-Polyaniline Electrode as Supercapacitor

The synthesis of graphene oxide-multi walled carbon nanotube-manganese oxide-polyaniline namely （GMMP） nanocomposite for application in supercapacitor devices was investigated. Morphology of the nanocomposites was studied by X-ray diffraction （XRD）, Fourier transform infrared （FT-IR） spectrosco- py, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and energy dispersive X-ray micmanalysis （EDX）. The electrochemical properties of nanocomposite based electrodes were in- vestigated by cyclic voltammetry （CV）, galvanostatic charge-discharge and electrochemical impedance spectroscopy （EIS） techniques in 0.5 mol/L Na2SO4. The specific capacitances of 173.00, 127.85, 87.50, 58.65 and 12.00 （mF cm^-2） were obtained for GMMP, GMP （GO-MWCNT-PANI）, GMM （GO-MWCNT-MnO2）, GM （GO-MWCNT） and G （GO） at a scan rate of 10 mV s^-1, respectively. Also, GMMP nanocomposite re- tained 90% initial capacitance after 200 cycle of charge-discharge. The good electrochemical response of this nanocomposite is due to the combination of the electrical double layer capacitance of GO and MWCNT and the gradual introduction of pseudo-capacitance through the redox processes of PANI, -COOH, -OH （in MWCNT-COOH, GO-COOH and GO-OH） and MnO2. This revealed the synergistic effect of PANI, MnO2, -OH -COOH on the carbon based support.

CeO_(2)-clay composites for ultra-long cycle life electrochemical capacitive energy storage application

The lattice expansion caused by the reduction of Ce(Ⅳ)to Ce(Ⅲ)impeded the development of the CeO_(2)as an effective electrode material for electrochemical supercapacitors.Herein,we prepared CeO_(2)-clay composites through a one-step hydrothermal method.The interlayer structures of clays efficiently accommodate volume changes induced by crystal lattice expansion to achieve ultra-long cycle stability.After 60000 charge-discharge cycles,the capacitance retention rate of the assembled asymmetric supercapacitors is as high as~-100%.The key findings of this work reveal the potential application of clays in achieving ultralong cycle stability of the CeO_(2)electrode material,paving the way for further application of the CeO_(2)in electrochemical energy storage.

Template-Free Synthesis of Ordered Mesoporous NiO/Poly (Sodium-4-Styrene Sulfonate) Functionalized Carbon Nanotubes Composite for Electrochemical Capacitors

We report the first example of a practical and efficient template-free strategy for synthesizing ordered mesoporous NiO/poly(sodium-4-styrene sulfonate)(PSS)functionalized carbon nanotubes(FCNTs)composites by calcining a Ni(OH)_(2)/FCNTs precursor prepared by refl uxing an alkaline solution of Ni(NH_(3))x^(2)+and FCNTs at 97 oC for 1 h.The morphology and structure were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.Thermal decomposition of the precursor results in the formation of ordered mesoporous NiO/FCNTs composite(ca.48 wt%NiO)with large specifi c surface area.Due to its enhanced electronic conductivity and hierarchical(meso-and macro-)porosity,composite simultaneously meets the three requirements for energy storage in electrochemical capacitors at high rate,namely,good electron conductivity,highly accessibleelectrochemical surface areas owing to the existence of mesopores,and efficient mass transport from the macropores.Electrochemical data demonstrated that the ordered mesoporous NiO/FCNTs composite is capable of delivering a specifi c capacitance(SC)of 526 F/g at 1 A/g and a SC of 439 F/g even at 6 A/g,and show a degradation of only ca.6%in SC after 2000 continuous charge/discharge cycles.

Precursor synthesis strategy for polycyclic aromatic conjugated polymers on the application of supercapacitors

Polycyclic aromatics (PCAs) possess excellent photoelectric properties, but the construction of such compounds has been a quite challenging subject of study, mainly due to very low solubility. Herein we report a precursor synthesis strategy for polycyclic aromatic conjugated polymers. A soluble precursor polymer, that containing fusible "double U-shaped aromatic"(DUA) and perylenetetracarboxydiimide (PDI) units, was firstly synthesized by Suzuki coupling. The stereo aromatic units in polymer backbone were found to be converted into polycyclic aromatic units, i.e. hexa-peri-hexabenzocoronene (HBC), by chemical or electrochemical oxidation, which resulted in a formation of insoluble polycyclic aromatic conjugated polymers. The electrochemical oxidations that occurred at the interface of electrode and solution exhibited higher cyclization reactivity and leads to the formation of high quality films on the electrode surface. Characterization by Raman and UV-visible (UV-Vis) spectroscopy validated the successful formation of this HBC structure. Some potential applications of such thin films are being explored, and here we focus on the characteristics of supercapacitors based on their excellent electrochemical properties.