Kye-Hyeok An

Electrochemical Properties of High-Power Supercapacitors Using Single-Walled Carbon Nanotube Electrodes**

We have investigated the key factors determining the performance of supercapacitors constructed using single-walled carbon nanotube (SWNT) electrodes. Several parameters, such as composition of the binder, annealing temperature, type of current collector, charging time, and discharging current density have been optimized for the best performance of the supercapacitor with respect to energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at energy densities in the range from 7 to 6.5 Wh/kg at 0.9 V in a solution of 7.5 N KOH (the currently available supercapacitors have energy densities in the range 6‐7 Wh/kg and power density in the range 0.2‐5 kW/kg at 2.3 V in non-aqueous solvents).

Effect of Gas Exposure on Field Emission Properties of Carbon Nanotube Arrays

Whitesides, Langmuir 2000, 16, 3497. M. Ouyang, C. Yuan, R. J. Muisener, A. Boulares, J. T. Koberstein, Chem. Mater. 2000, 12, 1591. [9] K. Efimenko, W. E. Wallace, J. Genzer, unpublished. [10] M. K. Chaudhury, G. M. Whitesides, Science 1992, 256, 1539. [11] Contact angle experiments were performed using a RamرHart contact angle goniometer, model 100-00. The advancing contact angles were read by injecting 4 lL of deionized water (resistivity >16 MX m); the receding contact angles were determined by removing 3 lL of deionized water from the droplet. Each data point reported in the paper represents an average over three measurements, each on a fresh sample. [12] J. Crank, The Mathematics of Diffusion, Oxford University Press, Oxford 1994. [13] S. R. Wasserman, Y.-T. Tao, G. M. Whitesides, Langmuir 1989, 5, 1074. N. Balachander, C. N. Sukenik, Langmuir 1990, 6, 1621.

Field-emission properties of vertically aligned carbon-nanotube array dependent on gas exposures and growth conditions

We grew vertically aligned carbon nanotubes (CNTs) using microwave plasma-enhanced (MPE) and thermal chemical-vapor deposition (CVD) and characterized their field emission properties. We observe that the flickering and instability in the field emission are due to the metal particles present on the field-emission array (FEA) surface, particularly from the MPECVD-grown samples. The existence of metal particles is an obstacle to obtaining reliable emission properties. The emission properties of the CNT–FEA are studied as a function of gas-exposure time with hydrogen, nitrogen, and oxygen gases. Gas exposures affected turn-on voltage, hysteresis, and the slope of Fowler–Nordheim plots. We observe that the saturation of emission currents is attributed to gas adsorbates present on the surface of the FEA. Oxygen exposures induce more severe degradation on the field-emission properties than nitrogen, whereas emission properties are improved by hydrogen gas exposures that clean the surface of emitters. In addition...

Oxidation-treated of Oxidized Carbons and its Electrochemical Performances for Electric Double Layer Capacitor

The oxidation treatment of several carbon materials with a sodium chlorate and 70 wt.% of nitric acid, combined with heat treatment, were attempted to achieve an electrochemical active material with a larger capacitance. Among pitch, needle coke, calcinated needle coke and natural graphite, the structure of needle coke and calacinated needle coke were changed to the graphite oxide structure with the expansion of the inter-layer. On the other hand, the calcinated needle coke after oxidation and heating at has exhibited largest capacitance per weight and volume of 29.5 F/g and 24.5 F/ml at the two-electrode system in the potential range of 0 to 2.5 V. The electrochemical performance of the calcinated needle coke was discussed with the phenomenon of the electric field activation and the formation of new pores between the expanded inter-layer at first charge.