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 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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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.

In this paper, we report highly conductive, highly flexible, light weight and low cost printed graphene for wireless wearable communications applications. As a proof of concept, printed graphene enabled transmission lines and antennas on paper substrates were designed, fabricated and characterized. To explore its potentials in wearable communications applications, mechanically flexible transmission lines and antennas under various bended cases were experimentally studied. The measurement results demonstrate that the printed graphene can be used for RF signal transmitting, radiating and receiving, which represents some of the essential functionalities of RF signal processing in wireless wearable communications systems. Furthermore, the printed graphene can be processed at low temperature so that it is compatible with heat-sensitive flexible materials like papers and textiles. This work brings a step closer to the prospect to implement graphene enabled low cost and environmentally friendly wireless wearable communications systems in the near future.

RuO 2 ‚xH 2 O nanoparticulates in different crystal sizes with various water contents were prepared via a hydrothermal synthesis route, successfully demonstrating the independent control of crystal size and water content of RuO 2 ‚xH 2 O. The crystalline and hydrous nature of hydrothermally derived RuO 2 ‚xH 2 O particulates not only reduces the proton diffusion resistance but also enhances the electronic conductivity for the redox transitions of active species. Novel and unique properties of hydrothermally derived RuO 2 ‚ xH 2 O, i.e., effective inhibition of crystallite coalescence upon annealing, relatively high thermal stability, and maintenance of the original nanostructure, are attributable to the coalescence barrier of RuO 2 ‚xH 2 O crystallites due to the lattice energy. Maintaining/fine-tuning the original nanostructure of annealed RuO 2 ‚ xH 2 O crystallites with high mesoporosity favors the penetration of electrolytes into the whole oxide matrix. This effect of not only reducing the proton diffusion resistance but also improving the electron pathways promotes the utilization of RuO 2 ‚xH 2 O in supercapacitor applications.

Tremendous development in the field of portable electronics and hybrid electric vehicles has led to urgent and increasing demand in the field of high-energy storage devices. In recent years, many research efforts have been made for the development of more efficient energy-storage devices such as supercapacitors, batteries, and fuel cells. In particular, supercapacitors have great potential to meet the demands of both high energy density and power density in many advanced technologies. For the last half decade, graphene has attracted intense research interest for electrical double-layer capacitor (EDLC) applications. The unique electronic, thermal, mechanical, and chemical characteristics of graphene, along with the intrinsic benefits of a carbon material, make it a promising candidate for supercapacitor applications. This Review focuses on recent research developments in graphene-based supercapacitors, including doped graphene, activated graphene, graphene/metal oxide composites, graphene/polymer composites, and graphene-based asymmetric supercapacitors. The challenges and prospects of graphene-based supercapacitors are also discussed.