Reduced graphene oxide/α-Ni(OH)(2) composites present high electrochemical properties, with specific capacitance of 1215 F g(-1) at 5 mV s(-1) scan rate, since graphene as conductive matrix provides electronic conduction pathway.

No abstract

Metal oxides and metal hydroxides are interesting, low cost, and low toxicity energy storage materials for electrochemical capacitor applications. Many studies to date have been directed toward replacing RuO 2 1,2 with NiO, 3,4 Co 3 O 4 , 5 MnO 2 , 6 Co(OH) 2 , 7 or Ni(OH) 2 . 8 In recent years Ni(OH) 2 has received much attention due to its superior theoretical electrochemical properties. In particular, β-Ni(OH) 2 has been extensively studied. Despite being a metastable phase, α-Ni(OH) 2 presents itself as a promising material for secondary battery 9 and electrochemical capacitor applications. 10 Two polymorphic forms of layered nickel hydroxide (Ni(OH) 2 ) exist: the αand β-phases. Control over morphology, basal spacing, and types of inorganic materials present is facilitated in the α-Ni(OH) 2 phase; thus manipulation of magnetic, electrical, and ion transport properties can be realized. Both forms have hexagonal crystal structures in which Ni(OH) 2 layers are stacked along the c-axis. A main feature differentiation between these phases is the presence of intercalated species (water and/or anions) within the interlayer galleries of α-Ni(OH) 2 . β-Ni(OH) 2 has a brucite-like structure (a = 3.12 Å, c = 4.6 Å; JCPDS Card No. 14-0117) comprised of perfectly stacked Ni(OH) 2 layers which do not contain water or any charge-balancing anions between its layers. α-Ni(OH) 2 , on the other hand, is a hydrotalcite-like structure (JCPDS Card No. 38-0715) comprised of randomly stacked Ni(OH) 2Àx layers along the c-axis intercalated with water or anions. The basal spacing of α-Ni(OH) 2 can be adjusted from 31.7 to 7.5 Å by adjusting the species intercalated in the interlayer galleries. 11 The size and morphology of α-Ni(OH) 2 particles are affected by several factors: inorganic precursor, solvent, temperature, concentration, and surfactant template. Yang et al. reported the synthesis of α-Ni(OH) 2 with nanoribbon and nanoboard-type structures by a hydrothermal process. 12 Cao et al. reported various α-Ni(OH) 2 morphologies for alkaline rechargeable batteries by reverse micelle/microemulsion and a hydrothermal method. 13 Ida et al. reported the synthesis of layered nickel hydroxide intercalated with dodecyl sulfate, and then successfully eliminated dodecyl sulfate molecules between the Ni(OH) 2 layers, resulting in the formation of hexagonal α-Ni(OH) 2 nanosheets that are potentially useful in ultrathin film devices. 14 In our previous paper we demonstrated a simple, effective coprecipitation synthetic method using alcohol and a dodecyl

Electrochemical characteristics of electrodes for supercapacitors built from RuO 2 /multiwalled carbon nanotube ͑CNT͒ nanocomposites have been investigated. Capacitances have been estimated by cyclic voltammetry at different scan rates from 5-50 mV/s. Electrostatic charge storage as well as pseudofaradaic reactions of RuO 2 nanoparticles have been affected by the surface functionality of CNTs due to the increased hydrophilicity. Such hydrophilicity enables easy access of the solvated ions to the electrode/electrolyte interface, which increases faradaic reaction site number of RuO 2 nanoparticles. The specific capacitance of RuO 2 /pristine CNT nanocomposites based on the combined mass was about 70 F/g (RuO 2 : 13 wt % loading͒, and the specific capacitance based on the mass of RuO 2 was 500 F/g. However, the specific capacitance of RuO 2 /hydrophilic CNT nanocomposites based on the combined mass was about 120 F/g (RuO 2 : 13 wt % loading͒, and the specific capacitance based on the mass of RuO 2 was about 900 F/g. Nanostructured material based on the assembly of carbon nanotubes ͑CNTs͒ have been considered for electrodes of electrochemical energy storage devices, such as Li-ion secondary batteries, 1-3 fuel cell, 4,5 and electrochemical capacitors. 6,7 The CNTs are attractive materials for electrodes of energy storage devices due to their chemical stability, low mass density, good conductivity, and large surface area. 8 Electrochemical capacitors are battery-complementary devices for applications demanding a high power level. 9,10 Two types of electrochemical capacitors are under development: the double layer and redox capacitors. In the former, energy storage arises mainly from the separation of electronic and ionic charges at the interface between high specific-area electrode materials. 11 In the latter, fast faradaic reactions take place at the electrode materials. 12 An electrochemical capacitor of large specific capacitance results when an electrode material that has large specific surface and suitable pore size is combined with a material that can have a fast faradaic reaction. 13 Recently, Niu et al. 6 reported that electrochemical capacitor electrodes prepared from multiwalled CNTs for which the surface is 430 m 2 /g, show the maximum specific capacitance of 113 F/g in solution of 38 wt % H 2 SO 4 used as electrolyte. Ma et al. 14 reported CNT electrodes that showed 15-25 F/g in a solution of 38 wt % H 2 SO 4 . Up to now, the specific capacitances of CNT-based electrodes is between 4 and 146.6 F/g in the solution of H 2 SO 4 . 15 Unfortunately, this value is lower than that of an activated carbon electrode with surface area up to 3000 m 2 /g ͑measured gas adsorption͒. 16 It is a drawback of CNTs to the application of electrochemical capacitors. The modification of the CNT material by a specific additive providing quick pseudocapacitive material such as RuO 2 is another route to enhance capacitance. 17 In this paper, we report on the preparation of RuO 2 nanoparticles as small as 1 nm in diam well dispersed...

No abstract