By use of the membrane-templated synthesis route, hydrous RuO2 (RuO2.xH2O) nanotubular arrayed electrodes were successfully synthesized by means of the anodic deposition technique. The desired three-dimensional mesoporous architecture of RuO2.xH2O nanotubular arrayed electrodes with annealing in air at 200 degrees C for 2 h simultaneously maintained the facility of electrolyte penetration, the ease of proton exchange/diffusion, and the metallic conductivity of crystalline RuO2, exhibiting unexpectedly ultrahigh power characteristics with its frequency "knee" reaching ca. 4.0-7.8 kHz, 20-40 times better than that of RuO2 single crystalline, arrayed nanorods. The specific power and specific energy of annealed RuO2.xH2O nanotubes measured at 0.8 V and 4 kHz is equal to 4320 kW kg-1 and 7.5 W h kg-1, respectively, demonstrating the characteristics of next generation supercapacitors.

The determinant influences of oxidants on the single-crystalline nature of manganese oxides (i.e., Mn 3 O 4 and MnOOH single crystals) through a low-temperature hydrothermal synthesis route from a simple aqueous solution containing 20 mM Mn(CH 3 COO) 2 • 4H 2 O at 120 °C are demonstrated in this work. The absence of oxygen molecules in the precursor solution limits formation of Mn 3+ , while saturation of oxygen in the precursor solution causes partial oxidation of Mn 2+ , favoring direct synthesis of Mn 3 O 4 single crystals (hausmannite). Addition of K 2 S 2 O 8 causes complete oxidation of Mn 2+ to Mn 3+ , favoring formation of MnOOH single crystals. The shape of as-prepared Mn 3 O 4 examined by HR-TEM is polyhedral, i.e., cubic and rhombohedral, while MnOOH prefers to form nanowires. X-ray diffraction, HRTEM, electron diffraction, and Raman spectroscopic analyses confirm the single-crystalline nature of the as-synthesized Mn 3 O 4 and MnOOH. With potentiodynamic (CV) activation for 200 cycles between 0 and 1.0 V in 1 M Na 2 SO 4 at 25 mV s -1 , the activated Mn 3 O 4 shows relatively high capacitance (∼170 F g -1 obtained at 500 mV s -1 ), high-power nature, and excellent stability for the supercapacitor application. The ideal capacitive responses of activated Mn 3 O 4 are definitely different from those of the potentiodynamically activated MnOOH.

Thick composites composed of crystalline manganese dioxide (MnO 2 ) and multiwall carbon nanotubes ͑MWCNTs͒ were successfully codeposited onto a graphite substrate from an Mn͑AcO͒ 2 •4H 2 O ϩ MWCNTs solution. The rate/nucleation mechanism of MnO 2 deposition was significantly influenced by the introduction of MWCNTs in the plating baths. The specific capacitance of thick MnO 2 -MWCNT composites, measured from cyclic voltammetry ͑CV͒ or chronopotentiometry ͑CP͒ in a potential window of 1.0 V, is monotonously decreased from ca. 160 to 80 F/g with increasing the oxide loading from 1.5 to 4.5 mg/cm 2 . The lower specific capacitance of thick MnO 2 and MnO 2 -MWCNTs deposits is reasonably attributed to the relatively poorer utilization of electroactive species as well as the compact structure in comparison with a thin Mn oxide deposit ͑Ͻ1 m͒. The capacitive performance of these thick MnO 2 deposits in 0.1 M Na 2 SO 4 is significantly improved by the application of electrochemical activation and the introduction of MWCNTs, revealing the promising improvement in the capacity of electrodes.Due to the increase in demands for the power systems with both properties of high-energy and high-power densities, an integration of conventional primary energy storage units ͑e.g., batteries and fuel cells͒ and the electric energy storage devices in the high-power or pulse-power forms ͑e.g., capacitors͒ becomes prime concern in the development of new power systems. On the other hand, the energy density of conventional capacitors are usually too low to be acceptable for several future applications; The development of capacitors with high energy densities ͑i.e., supercapacitors͒ for these applications has become the interesting subject of much research. 1-4 Moreover, it is acceptable and reasonable to separate the high-power and high-energy delivering devices in an integrated power system to enhance their respective performances. Hence, development of supercapacitors becomes an attractive topic in the research for electrochemical energy storage/conversion systems. [1][2][3][4][5][6][7][8] The electrode materials employed in supercapacitors are generally highly porous activated carbon ͑denoted as AC͒ for doublelayer capacitors 6,9 or hydrous transition metal oxides for pseudocapacitors. [1][2][3][4][5]7,8,10 In addition, a relatively high-frequency response is an intrinsic requirement for the supercapacitors in the high-/pulsepower applications, i.e., fast charge/discharge characteristics through a proper utilization of the electroactive materials. 11-13 To meet the above requirements, carbon nanotubes ͑CNTs͒ and composites composed of CNTs and electroactive materials ͑e.g., conducting polymers and hydrous ruthenium oxide͒ were shown to exhibit the promising applicability to supercapacitors. 11,14,15 However, the specific capacitance of CNTs is relatively low because of their relatively low specific surface areas 11,16 and the cost of single-wall CNTs is very high while their capacitive performance is obviously better than that of CNT co...

No abstract