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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]

A method of pulse electrodeposition was proposed to synthesize polyaniline (PANI)/MnO2 composite in aniline, H2SO4, and MnSO4 aqueous solution. The PANI/MnO2 composite has rod-like structure and MnO2 particles are distributed on PANI uniformly. To evaluate the performance of the as-prepared materials as supercapacitor electrodes, cyclic voltammetry, galvanostatic charge-discharge measurements, and electrochemical impedance spectroscopy were performed. The PANI/MnO2 composite shows a higher specific capacitance (810 F g−1) than pure PANI (662 F g−1) at a current density of 0.5 A g−1. The cycle life of the composite was also excellent. After 1,000 cycles, it maintained 86.3% of its initial capacitance. POLYM. COMPOS., 36:113-120, 2015. © 2014 Society of Plastics Engineers [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]

Abstract: MnO2 electrode material is successfully synthesized by electrodeposition under supergravity field from manganese acetate solution. The structure of the samples is characterized by X-ray diffraction. The results show that the product is γ-MnO2. Galvanostatic charge/discharge measurements are applied to investigate electrochemical performances of the MnO2 electrodes material prepared under different supergravity fields. MnO2 synthesized under rotational speed 3000rpm exhibits the highest specific surface area and discharge capacitance, the values of which are 68.6% and 19.3% higher than that under normal gravity fields, respectively. It is found that supergravity field can improve the electrochemical performance of MnO2 material. [Copyright &y& Elsevier]

Abstract: A nanoporous titanium carbide derived carbon (TiC-CDC) is successfully synthesized by electrolysis of TiC powder in molten CaCl2. The electrolysis was conducted at 850°C for 48h in argon at an applied constant voltage of 3.1V. The structure of the resulting carbon is characterized by X-ray diffraction, Raman spectroscopy and Transmission electron microscope techniques. Cyclic voltammetry and galvanostatic charge/discharge measurements are applied to investigate electrochemical performances of the TiC-CDC material. The results show that the obtained product is TiC-CDC, which is a mixture of amorphous carbon and ordered graphite phase with a highly degree of graphitization. Cyclic voltammetry measurements on the TiC-CDC do not show any major faradic reactions within the experimental voltage range. A specific capacitance of 160F/g at a current density of 300mA/g was achieved from the sample synthesized at 850°C. [Copyright &y& Elsevier]

Highlights • This paper has a simple synthesis method: one-step hydrothermal method. • Ni-Co layered double hydroxide has a self-assembly sea urchin like structure. • The morphology of Ni-Co layered double hydroxide porous structure determines the large specific surface area. Abstract We report a simple method for the preparation of 3D structure sea urchins Ni-Co layered double hydroxide (NiCo-LDH) with one-step hydrothermal self-assembly. The obtained NiCo-LDH has large specific surface area, porous structure and large interlayer spacing, which causes excellent electrochemical performance. The specific capacitance of the NiCo-LDH electrode, can reach 808.4 C g−1 at the current density of 1 A g−1. Moreover, asymmetric supercapacitors fabricate dusing the negative carbon as positive electrode and NiCo-LDH as activated electrode displays a high energy density of 41.46 Wh/kg at a 212.68 W/kg power density at 1 A g−1. [ABSTRACT FROM AUTHOR]

A highly cross-linked three-dimensional (3D) hierarchical porous NiCo 2 O 4 nanosheet@MnO 2 nanosheet arrays (NNAs) on Ni foam is fabricated by a facile and stepwise hydrothermal approach. The NiCo 2 O 4 @MnO 2 hybrid electrode demonstrates excellent electrochemical properties with high area capacitance of 5.3 F cm -2  at 1 mA cm −2 , tremendous rate performance (68.9% with current density increased to 20 mA cm −2 ), and outstanding cycling stability (90.1% capacitance retention over 5000 cycles at 20 mA cm −2 ). The intriguing performance is related to unique cross-linked porous heterostructure with open geometry that provides large surface areas and superb channels for the electrolyte penetration and ion diffusion. Besides, by analyzing non-faradaic capacitive current upon repeated potential cycling, this honor attributes to not only sufficient Faraday reactions, but also a worthy electrochemical double-layer capacitance (EDLC) contribution with an electrochemical surface area (ESA) value of 616 mF cm −2 (220 F g −1 with a mass loading of 2.8 mg cm −2 ), which approximates to that of porous carbon. [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]

Phosphorus-doped three-dimensional hierarchical porous carbons (P-3DHPCs) have been synthesized by direct pyrolysis of mixture containing glucose, manganese nitrate and sodium hypophosphite without any hard templates. Glucose and sodium hypophosphite are used as carbon and phosphorus source in the facile template-free strategy, respectively. The P-3DHPCs not only possess favorable hierarchical pore structure which is beneficial to ion adsorption and transportation, but also acquire effective heteroatoms doping, further improving the capacitive performance. More importantly, the amount of sodium hypophosphite plays a critical role in textural properties and phosphorus content of P-3DHPCs. The results demonstrate that P-3DHPC-0.2 shows the best electrochemical performance compared to the other samples. High specific capacitance (367 F g −1 at 0.3 A g −1 ) is obtained in 6 M KOH, and the capacitance still maintains 319 F g −1 when tested at 20 A g −1 (ca.88% capacitance retention). Moreover, the P-3DHPC-0.2 also possesses good cycling stability with only a loss of 3.5% after 10000 cycles at 3 A g −1 . The facile preparation method and good electrochemical performance render P-3DHPCs to be a promising candidate for supercapacitor application. [ABSTRACT FROM AUTHOR]

This work report the synthesis of porous carbon with hierarchical pore structure and uniform nitrogen-sulfur-oxygen doping. The favorable pore structure (micro-, meso-, and macro-pores) is beneficial to ion adsorption and transportation, and the doping heteroatoms can introduce electrochemical active sites which contribute to additional pseudocapacitance. Therefore, the carbon material shows good electrochemical performance when employed as supercapacitor electrode. High specific capacitance (367 F g −1 at 0.3 A g −1 ), good rate performance and stable cycling characteristics are obtained in 6 M KOH. In addition, when tested in 1 M H 2 SO 4 , a higher specific capacitance (382 F g −1 at 0.3 A g −1 ) is delivered. Furthermore, the assembled symmetric cell yields a maximum specific energy of 35.3 W h kg −1 in 1 M TEABF 4 /AN, significantly improving the specific energy of carbon-based supercapacitors. [ABSTRACT FROM AUTHOR]

The ultrathin porous carbon shell with the thickness of about 10 nm has been fabricated by a facile method using sodium citrate as carbon precursor without any activation. The electric conductivity of the material is as high as 7.12 S/cm, which contributes to a good rate performance for supercapacitor electrode without any conductive additive. When tested in 6 M KOH by three-electrode system, the C-700 sample exhibits specific capacitance of 251 F g −1 at 1 A g −1 , high rate capability with the specific capacitance of 228 F g −1 at 20 A g −1 , only a loss of 3% after 10000 cycles at a current density of 3 A g −1 . Non aqueous performance was tested in 1 M TEA-BF 4 /acetonitrile, the material can deliver an energy density of 12–17 Wh kg −1 in a two-electrode system. Apparently, the porous carbon with ultrathin structure can provide low-resistant pathways and short ion diffusion channels for energy storage. Therefore, the ultrathin porous carbon shell would be a promising material particularly for applications where high power output performances are required. [ABSTRACT FROM AUTHOR]

Herein, ultrathin MnO 2 nanosheets consisting of crystalline/amorphous phases are prepared by a simple interfacial reaction of surfactant assistance in water-bath with high specific surface area of 317.56 m2 g−1, which can accelerate ionic transport and provide more active sites during electrochemical reaction. The as-synthesized MnO 2 nanosheets electrode exhibits remarkable specific capacitance of 163.3 F g−1 at 1 A g−1 in a three-electrode system using 1 M NaSO 4 as electrolyte, and long-term stability with a capacity retention of 89.3% at 3 A g−1 after 10,000 cycles, which can be ascribed to a structural transition from crystalline to amorphous phase during cycling. Meanwhile, the flexible all-solid-state MnO 2 symmetry micro-supercapacitors (MSCs) using sodium alginate bio-hydrogel as electrolyte, the voltage window of the MSCs can be extended to 1.4 V. The MSCs reveals a high areal capacitance of 129.29 mF cm−2 at a current density of 0.2 mA cm−2. The capacity retention rate up to 94.5% after 4000 cycles, and higher energy density of 35.19 μWh cm−2 at 0.07 mW cm−2, as well as there is no significant capacitance degradation under different bending states, exhibiting a remarkable electrochemical performance and mechanical flexibility. The crystalline/amorphous ultrathin MnO 2 sheets with high specific surface area were prepared through simple preparation process and found the mechanism of the transformation of MnO 2 from crystalline phase to amorphous phase during the cycle providing a new perspective for the design of high-performance MnO 2 electrodes. [Display omitted] • Ultrathin MnO 2 nanosheets are prepared by a simple interfacial reaction of surfactant assistance in water-bath. • The phase structure of ultrathin MnO 2 nanosheets includes crystalline/amorphous states. • The ultrathin MnO 2 nanosheets reveal an ultrahigh specific surface area of 317.56 m2g−1. • The structural transition of ultrathin MnO 2 nanosheets is gradually from crystalline to amorphous phase during cycling. • A flexible micro-supercapacitors based on the ultrathin MnO 2 nanosheets exhibits excellecnt electrochemical performance. [ABSTRACT FROM AUTHOR]

NiO/sulfonated graphene(NiO/SGN) composites were fabricated under the assistance of urea as supercapacitor materials. The composites as prepared possess the leaf vein-like morphology, forming the porous structure that benefits the enhancement of pseudocapacitive performance. Moreover, the introduction of sulfonated graphene contributes to the surface hydroxylation of NiO, which may increase electrochemically active sites on the surface of NiO. The electrochemical measurements demonstrate that specific capacitances of NiO, NiO/thermally reduced graphene(NiO/TRG) and NiO/SGN are 200, 261 and 307 F g −1 at a current density of 5.0 A g −1 respectively, suggesting that the significant improvement of pseudocapacitive performance for NiO/SGN could be expected. The results from electrochemical impedance spectroscopy(EIS) demonstrate that sulfonated graphene can not only provide electron transport channels for its composites similar to thermally reduced graphene, but also benefit the electrolyte penetration in the composites compared with thermally reduced graphene. [ABSTRACT FROM AUTHOR]

The driving force of the phase transition from the layered MnO 2 structure to the stable spinel Mn 3 O 4 phase comes from the oxygen vacancies which can be generated by the long unstable Mn-O bonds in [MnO 6 ] octahedral structure caused by the inserting of potassium ions during discharging. [Display omitted] • A hierarchical MnO x @rGO is prepared as positive electrode for supercapacitors. • The storage mechanism of the reversible phase transition reaction: Mn 3 O 4 ↔ MnO 2. • DFT proves that oxygen vacancies are the driving force for structural transformation. • The MnO x @rGO electrode exhibits high performance for supercapacitors. Herein, in-situ Raman and electrochemical quartz crystal microbalance techniques combined with density functional theory (DFT) calculations are adopted to prove the charge storage mechanism for high-stability MnO x @graphene microspheres electrode in alkaline electrolyte (KOH). The results reveal that the layered MnO 2 phase gradually transformed into the spinel Mn 3 O 4 phase in the process of discharging, accompanied by the insertion of potassium ions. Moreover, the Mn-O bonds length near the potassium ions in [MnO 6 ] octahedral structure becomes longer, while the long unstable Mn-O bonds tend to lose oxygen and create oxygen vacancies, which further transforms the layered structure into stable spinel structure. Furthermore, it is also found that potassium ions can be more easily embedded in the layered MnO 2 with oxygen vacancies due to the lower energy demand compared with the pure MnO 2. Meanwhile, the MnO x @graphene microspheres electrode exhibits a capacity retention as high as 90% after 10,000 cycles at 10 A g−1, indicating a superior cyclic stability. [ABSTRACT FROM AUTHOR]

Abstract: Carbide derived carbons (CDCs) are porous carbons produced by extraction metals from metal carbides. In this paper, nanoporous carbon with large surface area of above 1000 m2/g has been prepared by thermo-chemical etching of titanium carbide (TiC) in chlorine atmosphere. An improved design of accurate control on the reaction time with high yield percentage above 98% is reported. Transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis showed the existence of ordered graphite phase in this mostly amorphous titanium carbide derived carbon (TiC-CDC), and the degree of ordering increased with chlorination temperature. Raman spectra study demonstrated that the TiC-CDC consisted of both D-band and G band of graphitic carbon, and the ratio of the integrated intensities ID/IG decreased with chlorination temperature. T-plot nitrogen sorption measurements proved the co-existence of micropores (<2 nm) and mesopores (2–50 nm), while the highest specific surface area was achieved from sample synthesized at 400 °C. Cyclic voltammetry measurements on the TiC-CDC did not show any major Faradic reactions within the experimental voltage range. A specific capacitance of 138.3 F/g was achieved from sample synthesized at 400 °C. The specific capacitance increased with increasing the amount of microporous area. [Copyright &y& Elsevier]