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 ever worsening energy depletion and global warming issues call for not only urgent development of clean alternative energies and emission control of global warming gases, but also more advanced energy storage and management devices. Supercapacitors, offering transient but extremely high powers, are probably the most important next generation energy storage device. [1] To boost the specific capacitance of supercapacitors, the specific surface area of the electrode materials needs to be as high as possible to promote the electric double-layer capacitances and to accommodate a large amount of superficial electroactive species to participate in faradaic redox reactions. In addition, suitable pore sizes, 2-5 nm, of the porous electrode materials are critical to ease the mass transfer of electrolytes within the pores for fast redox reactions and double-layer charging/discharging. [2][3][4][5] Aerogels are a class of mesoporous materials possessing highly specific surface areas and porosities, [6] from which promising applications in a wide range of areas have been investigated. [7][8][9][10] They are composed of 3D networks of nanoparticles with an average pore size of several nanometers, adjustably falling within the optimal pore sizes of 2-5 nm. Consequently, aerogels are a promising candidate for supercapacitor applications.As to the electrode material, electroactive materials possessing multiple oxidation states/structures that enable rich redox reactions for pseudocapacitance generation are desirable for supercapacitors. Transition metal oxides are such a class of materials that have drawn extensive and intensive research attention in recent years. Among them, RuO 2 is the most prominent one with a specific capacitance as high as 1580 F g À1 , [11] probably the highest ever reported. The commercialization of RuO 2 based supercapacitors, however, is not promising because of the high cost and rareness of Ru. Spinel nickel cobaltite (NiCo 2 O 4 ) is a low-cost, environmentally friendly transition metal oxide, which has been employed in electrocatalytic water splitting (oxygen evolution) [12][13][14] and lithium ion batteries. [15,16] Its application in supercapacitors, however, received much less attention. [16,17] Nickel cobaltite has been reported to possess a much better electronic conductivity, at least two orders of magnitude higher, and higher electrochemical activity than those of nickel oxides and cobalt oxides.[18] It is expected to offer richer redox reactions, including contributions from both nickel and cobalt ions, than the two corresponding single component oxides and is a potential cost-effective alternative for RuO 2 .Based on the above considerations, one would expect nickel cobaltite aerogels, with anticipated good electronic conductivity, low diffusion resistance to protons/cations, easy electrolyte penetration, and high electroactive areas to be a promising candidate for the construction of next-generation, ultrahighperformance supercapacitors. Traditionally, aerogels are prepared with sol-gel...

The utilization of hydrous ruthenium oxide ͑denoted as RuO x •nH 2 O) was promoted by annealing the oxide in air as well as by mixing it with conductive activated carbon ͑AC͒ due to the significant improvement in intra-and interparticle electronic conductivity, respectively. The maximum specific capacitance (C S,RuOx ) of RuO x •nH 2 O, 1340 F/g ͑measured at 25 mV/s͒, very close to the theoretic value, was obtained from a composite consisting of AC and RuO x •nH 2 O coated on graphite ͑denoted as AC-RuO x /G) with 10 wt % of sol-gel-derived RuO x •nH 2 O nanodots annealed in air at 200°C for 2 h. The UV absorption spectral features showed a shift in max to the red as the mean particle size of RuO x •nH 2 O nanodots was increased, attributable to the surface plasmon resonance phenomenon. The average particle size of highly uniform RuO x •nH 2 O nanodots, ranged from 2.05 to 3.01 nm, was estimated from the high-resolution transmission electron microscopy. The dependence of capacitive performance on the size and content of RuO x •nH 2 O nanodots, evidenced by cyclic voltammetry and electrical impedance spectroscopy results, revealed the important influences of interparticle electronic conductivities on the utilization of RuO x •nH 2 O. The RuO x •nH 2 O nanodots with and without annealing in air at 200°C for 2 h showed the amorphous structure from both the X-ray diffraction and electron diffraction analysis.

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