Kyung H. Lee

Synthesis and Electrochemical Properties of Spin-Capable Carbon Nanotube Sheet/MnOx Composites for High-Performance Energy Storage Devices

Inspired by the high specific capacitances found using ultrathin films or nanoparticles of manganese oxides (MnO(x)), we have electrodeposited MnO(x) nanoparticles onto sheets of carbon nanotubes (CNT sheets). The resulting composites have high specific capacitances (C(sp) ≤ 1250 F/g), high charge/discharge rate capabilities, and excellent cyclic stability. Both the C(sp) and rate capabilities are controlled by the average size of the MnO(x) nanoparticles on the CNTs. They are independent of the number of layers of CNT sheets used to form an electrode. The high-performance composites result from a synergistic combination of large surface area and good electron-transport capabilities of the MnO(x) nanoparticles with the good conductivity of the CNT sheets. Such composites can be used as electrodes for lithium batteries and supercapacitors.

Highly Conductive Flexible Multi-Walled Carbon Nanotube Sheet Films for Transparent Touch Screen

Highly conductive and transparent thin films were prepared using highly purified multi-walled carbon nanotube (MWCNT) sheets. The electrical properties of the MWCNT sheet were remarkably improved by an acid treatment, resulting in densely packed MWCNTs. The morphology of the sheets reveals that continuous electrical pathways were formed by the acid treatment, greatly improving the sheet resistance all the while maintaining an excellent optical transmittance. These results encourage the use of these MWCNT sheets with low sheet resistance (450 Ω/sq) and high optical transmittance (90%) as a potential candidate for flexible display applications.

Effect of Carrier Gas on the Growth and Characteristics of Spin-Capable Multiwalled Carbon Nanotubes

Multiwalled carbon nanotube (MWCNT) sheets that can be spun directly from a spin-capable MWCNT forest promise novel applications that utilize the unique and outstanding characteristics of this material. The growth of spin-capable MWCNT forests will be achieved through the understanding of the important factors affecting the forest growth, since the precise conditions necessary for effective spin-capability are extremely sensitive. In this paper, we discuss the effect of carrier gas, the initial catalyst thickness, and the roles of the hydrogen. These factors were investigated in order to assess and understand these critical parameters and thereby develop a repeatable and reliable spin-capable MWCNT growth process.

Effect of acetylene concentration and thermal ramping rate on the growth of spin-capable carbon nanotube forests

Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C2H2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25–6.94% by volume. The MWCNTs grown at C2H2 concentrations between 1.47–3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 °C/min to 70 °C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 °C/min forms suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C2H2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25–6.94% by volume. The MWCNTs grown at C2H2 concentrations between 1.47–3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 °C/min to 70 °C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 °C/min forms suitable sized nanoparticles wit...

A novel microneedle-based non- enzymatic glucose sensor for painless diabetes testing application

In this work, we report the design, fabrication and in-vitro testing of a novel microneedle-based high sensitivity non-enzymatic glucose sensor for diabetes testing application. It consists of 15 by 15 sharp silicon microneedle array (> 300 µm tall) and multi-walled carbon nanotube (MWCNT) forest electrodes coated with platinum nanoparticle. The Pt nanoparticle coated MWCNT electrodes significantly increase the surface area and in turn enhance the sensitivity. Since microneedle is integrated with nanoparticle surface enhanced electrode-based non-enzymatic glucose sensor, this device has a potential to be used for painless diabetes testing for diabetes mellitus patients.

A high sensitive strain sensor using a multi-walled carbon nanotube sheet

A multi-walled carbon nanotube (MWCNT) sheet-based strain sensor is presented in this paper, which possesses a novel fabrication technique that employs a simpler process than that of dispersing CNTs into a liquid or polymer. The sheets were spun from a MWCNT forest grown on a silicon substrate. The electrical resistance of the MWCNT sheets increased linearly with an increased tensile strain. The sheet did not require any chemical grafting or charging in order to work as a sensor, making it an ideal strain sensor. The proposed sensor exhibited excellent piezoresistive behavior under repetitive strain and relaxation, as well as a relatively high sensitivity compared to other methods, highlighting its potential application to high sensitivity pressure and force sensors.

Energy storage devices using spinable CNT sheets

Our focus is on designing and synthesizing nanostructured materials having high specific capacitances. To achieve this, we have electrodeposited ultrathin films and/or nanoparticles of manganese oxides (MnOx) onto sheets of carbon nanotubes (CNTs) using either the linear potential sweep or potentiostatic methods. The morphology and electrochemical properties of the resulting composites depend on the amount of MnOx deposited and deposition conditions. The best composites obtained to date have large specific capacitances (Csp ≤ 1250 F/g), high charge/discharge rate capabilities, and excellent cyclic stability. High performance composites result from both the enhanced surface area and enhanced electron-transport capabilities of MnOx nanoparticles as well as the superior conductivity of the CNT sheets. Related composites are envsioned as electrodes for lithium batteries and super-capacitors.