Hideyuki Takagi

High-Power Supercapacitor Electrodes from Single-Walled Carbon Nanohorn/Nanotube Composite

A novel composite is presented as a supercapacitor electrode with a high maximum power rating (990 kW/kg; 396 kW/l) exceeding power performances of other electrodes. The high-power capability of the electrode stemmed from its unique meso-macro pore structure engineered through the utilization of single-walled carbon nanotubes (20 wt %) as scaffolding for single-walled carbon nanohorns (80 wt %). The novel composite electrode also exhibited durable operation (6.5% decline in capacitance over 100 000 cycles) as a result of its monolithic chemical composition and mechanical stability. The novel composite electrode was benchmarked against another high-power electrode made from single-walled carbon nanotubes (Bucky paper electrode). While the composite electrode had a lower surface area compared to the Bucky paper electrode (280 vs 470 m(2)/g from nitrogen adsorption), it had a higher meso-macro pore volume (2.6 vs 1.6 mL/g from mercury porosimetry) which enabled the composite electrode to retain more electrolyte, ensuring facile ion transport, hence achieving a higher maximum power rating (970 vs 400 kW/kg).

Plasma Catalysis for Environmental Treatment and Energy Applications

The current status of plasma-catalysis research and the associated possible applications are outlined. A basic explanation of plasma chemistry is given, which is then used as a foundation to indicate the research vector for the ongoing development of various applications. As an example of an environmental application, volatile organic compound decomposition using plasma-catalysis is discussed in depth, from the fundamental concept to the current industrial application status. As a potential application of plasma-catalysis towards the realization of a future “hydrogen society”, ammonia synthesis is discussed in terms of current social attitudes and regulations, along with historical developments. Additionally, up-to-date information on the fundamentals of the nonthermal plasma interaction with a catalyst is provided.

Effects of Nitric Acid and Heat Treatment on Hydrogen Adsorption of Single-Walled Carbon Nanotubes

The effects of nitric acid treatment and subsequent heat treatment on the hydrogen adsorption properties of single-walled carbon nanotube (SWCNT) samples were investigated. The hydrogen adsorption and desorption isotherms of SWCNTs treated with nitric acid alone and SWCNTs treated with nitric acid and then heated were measured at 77 and 303K over the hydrogen pressure range 0 - 3.5 MPa. Nitric acid treatment increased hydrogen adsorption by opening the nanotubes and changing the bundle structure. Subsequent heat treatment of the acid-treated SWCNT sample further increased hydrogen adsorption by removing functional groups introduced by the acid treatment.

A Mesoporous Carbon-Supported and Cs-promoted Ru Catalyst with Enhanced Activity and Stability for Sustainable Ammonia Synthesis

A mesoporous carbon‐supported Ru catalyst with Cs promotor and an open mesostructure (Cs−Ru/MPC) was prepared by a stepwise wet impregnation method and used for sustainable ammonia synthesis under mild reaction conditions using a wide range of space velocities (SV). The Cs−Ru/MPC catalyst showed higher activity and stability for ammonia synthesis than a reference catalyst with a microporous framework prepared by the same method (an active‐carbon‐supported and Cs‐promoted Ru catalyst (Cs−Ru/AC)). It was found that the mesoporous carbon framework is a suitable medium for the dispersion of the Ru nanoparticles within a narrow size distribution, and it also protected the small Ru nanoparticles against sintering during ammonia synthesis. However, the sintering of Ru nanoparticles on the outer surfaces of the Cs−Ru/AC catalyst was observed, resulting in its deactivation. The results suggest that the Cs−Ru/MPC catalyst is applicable to real operating conditions, where there may be short warm‐up and shut‐down periods for hydrogen production via the electrolysis of water using intermittently available renewable electricity.

Surplus adsorption of bromide ion into π-conjugated carbon nanospaces assisted by proton coadsorption

Nanoporous carbons can preferentially adsorb bromide ions from an aqueous solution of alkali metal bromides, even on π-conjugated surfaces. Our results show a new adsorption mechanism whereby coadsorption of protons enhances the adsorption of the anions onto the carbons.

Adsorption Properties of Surface Modified Carbons with Metal Nanoparticles

The effect of surface modification by nanoparticles of metal compounds was investigated by means of gas and vapor adsorption analysis. The surface of activated carbon fiber cloths was modified by loading of Li2CO3 and MgO nanoparticles. The particles on the carbon surface played as initial adsorption site of water molecules, leading to the promotion of micropore filling without diminishing the micropore volume of the porous carbon supports. The increasing characteristic adsorption energy suggested some interaction between methane molecules and the particles.

Hydrogen adsorption properties of single-walled carbon nanotubes treated with nitric acid

The single-walled carbon nanotube sample (SWCNT) was treated with nitric acid. In addition, the SWCNT sample treated with nitric acid was heat-treated, and the hydrogen adsorption and desorption isotherms of these SWCNT samples were measured at 77 and 303 K over the hydrogen pressure range 0-3.5 MPa. The nitric acid treatment enhanced the amount of hydrogen adsorbed on SWCNT due to opening up the nanotubes and changing the bundle structure. The heat treatment further increased the hydrogen adsorption capacity of acid-treated SWCNT sample owing to the removal of the functional groups introduced by the nitric acid treatment.