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Hydrotalcite, first found in natural ores, has important applications in supercapacitors. NiCoAl-LDH, as a hydrotalcite-like compound with good crystallinity, is commonly synthesized by a hydrothermal method. Al 3 + plays an important role in the crystallization of hydrotalcite and can provide stable trivalent cations, which is conducive to the formation of hydrotalcite. However, aluminum and its hydroxides are unstable in a strong alkaline electrolyte; therefore, a secondary alkali treatment is proposed in this work to produce cation vacancies. The hydrophilicity of the NiCoAl-OH surface with cation vacancy has been greatly improved, which is conducive to the wetting and infiltration of electrolyte in water-based supercapacitors. At the same time, cation vacancies generate a large number of defects as active sites for energy storage. As a result, the specific capacity of the NiCoAl-OH electrode after 10,000 cycles can be maintained at 94.1%, which is much better than the NiCoAl-LDH material of 74%. [ABSTRACT FROM AUTHOR]

Abstract: A method of pulse electrodeposition under supergravity field was proposed to synthesize MnO2-graphene composites. Supergravity is very efficient for promoting mass transfer and decreasing concentration polarization during the electrodeposition process. The synthesis was conducted on our homemade supergravity equipment. The strength of supergravity field depended on the rotating speed of the ring electrode. 3D flower like MnO2 spheres composed of nanoflakes were acquired when the rotating speed was 3000rpm. Graphene nanosheets play as a role of conductive substrates for MnO2 growing. The composites are evaluated as electrode materials for supercapacitors. Electrochemical results show that the maximum specific capacitance of the MnO2-graphene composite is 595.7Fg−1 at a current density of 0.5Ag−1. In addition, the composite exhibits excellent cycle stability with no capacitance attenuation after 1000 cycles. The approach provides new ideas for developing supercapacitor electrode materials with high performance. [Copyright &y& Elsevier]

Abstract: A method of electrodeposition under supergravity field is proposed to prepare Ni(OH)2/Ni/graphene composites. Particles composed of Ni(OH)2 and Ni are covered by a thin graphene coating. The Ni(OH)2/Ni/graphene composite is evaluated as electrodes for supercapacitors, which shows that the specific capacitance of Ni(OH)2/Ni/graphene is 2609Fg−1 at a current density of 0.5Ag−1 in 6M KOH solution. In addition, it could still reach 1020Fg−1 at a current density of 4Ag−1. On the other hand, electrodeposition under supergravity field could decrease concentration polarization and promote ion diffusion, which is a promising strategy for the fabrication of nanocomposites. [Copyright &y& Elsevier]

Samples of lanthanum-doped nickel hydroxide were prepared by electrodeposition method. The structure and electrochemical properties of the samples were studied by X-ray diffraction and a home-made open three-electrode cell system, respectively. The results show that the deposition process of Ni(OH)2 and La(OH)3 is mainly controlled by electrochemical polarization, which makes it easy to form uniform fine crystals. In addition, La(OH)3 is not a separate phase and lanthanum ions are doped into Ni(OH)2 crystal lattices. When V(0.5 mol/L Ni(NO3)2)/ V(0.25 mol/L La(NO3)3) was 9:1, the lanthanum-doped nickel hydroxide reached the highest discharge capability of 840 F/g with a good cyclic reversibility. The capability still retains 670 F/g when the discharge current reaches 1000 mA/g. [ABSTRACT FROM AUTHOR]

Formation mechanism of hollow Coral-shaped nanostructures. In this work, novel hollow coral-shaped Co 3 O 4 nanostructures are synthesized via a precursor conversion method for the first time, and the detailed process of precursor conversion is revealed. l -ascorbic acid as the structure-directing agent and the origin of oxalate (C 2 O 4 2−) contributes to the formation of the precursors, providing a low-cost and facile method for preparing Co 3 O 4. Hollow coral-shaped Co 3 O 4 nanostructures are obtained by calcining cobalt oxalate precursors in air. The special Co 3 O 4 nanostructures exhibit noticeable pseudocapacitive properties with a capacitance of 626.5 F g-1 at 5 mV s-1 and show superior stability (capacity retention of 99%) and outstanding Coulombic efficiency (˜100%) within 5000 charge–discharge cycles at 10 A g-1. Furthermore, the asymmetric supercapacitor Co 3 O 4 //G fabricated by Co 3 O 4 cathode and graphene hydrogel anode delivers a specific capacitance of 115 F g-1 (47.9 mA h g-1) at 1 A g-1 and attains the maximum energy density of 35.93 Wh kg-1 at the power density of 801.6 W kg-1. The excellent durability of Co 3 O 4 //G is demonstrated by the retention of 85.1% of initial capacitance after 5000 cycles at 5 A g-1. The novel and feasible route proposed in the work is expected to be applied prospectively and widely in preparing Co 3 O 4 pseudo-capacitance material, which owns great application value in supercapacitors, as well as in batteries. [ABSTRACT FROM AUTHOR]

Highlights • The effect of solvent ratio on Co 2 (OH) 3 Cl was studied for the first time. • The highest capacitance of 321.79 F g−1 was got when V water :V glycol = 1:2. • No obvious capacitance decay was observed after 10,000 cycles. Abstract Co 2 (OH) 3 Cl was synthesized by a facile solvothermal method with different solvent ratios of water/glycol (V water :V glycol). The Co 2 (OH) 3 Cl prepared at the ratio of 1:2 showed uniform cubic nanostructure and provided the highest specific capacitance of 321.79 F g−1 at 0.5 A g−1. The capacitance retention and the Coulombic efficiency were both kept at 100% without obvious decay after continuous 10,000 charge-discharge cycles, demonstrating the durability and eximious stability of the Co 2 (OH) 3 Cl when utilized as the supercapacitor electrode material. [ABSTRACT FROM AUTHOR]

Herein we report an in-situ strategy for synthesizing NiO foamed sheet on Ni foam substrate which could achieve great improvement on the areal performance of battery-type supercapacitors. The anchored NiO foamed sheets are synthesized via a precursor growth step by hydrothermal oxidation, and followed by a pore-inducing step through heat treating. The physical characterizations indicate that this film product has a multi-level pore structure with high active surface area. As for electrode material, the anchored sheets could ensure excellent conductivity at the film/substrate interface, and the porous structure could form high free electron/ionic diffusion routes which facilitates the redox reactions for reversible energy storage. The electrochemical measurements show that the areal capacity of as-synthesized electrode could achieve 4.31–3.39 C cm −2 at a wide current range of 10–200 mA cm −2 . The single supercapacitor device exhibits a high areal energy density of 9.84–9.45 W h m −2 at a wide power density of 100–2000 W m −2 . [ABSTRACT FROM AUTHOR]

Cerium-doped nanosheet-based porous δ-MnO 2 microspheres have been successfully prepared via a simple hydrothermal process. Electrochemical measurements showed that appropriate amount of cerium doping can significantly increase the speicific capacitance of δ-MnO 2 . It is found that 1.5% cerium-doped manganese oxides exhibit the best specific capacitance of 382.38 F g −1 at a current density of 1 A g −1 . In terms of ion transport kinetics, cerium doping can shorten the diffusion path length and increase the ion transfer rate by changing the partical size, porosity density and conductivity of manganese oxides materials. [ABSTRACT FROM AUTHOR]