Sang Ho Lee

Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor

Different nanostructures (Ns), such as nanobelts, nanobricks and nanosheets, of polypyrrole (PPy) were successfully fabricated on stainless steel substrates by simply varying the scan rate of deposition in the potentiodynamic mode. These PPy Ns were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and surface area measurement. The XRD analysis showed the formation of amorphous PPy thin films, and the FTIR studies confirmed characteristic chemical bonding in the PPy materials. SEM images depicted that a high scan rate of deposition can form multilayer nanosheets with high porosity leading to a system with excellent processability. The PPy nanosheets possess a higher Brunauer-Emmett-Teller (BET) surface area of 37.1 m 2 g -1 than PPy nanobelts and nanobricks. The supercapacitive performances of different PPy Ns were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge techniques in 0.5 M H 2SO 4. A maximum specific capacitance of 586 F g -1 was obtained for multilayer nanosheets at a scan rate of 2 mV s -1. In addition, impedance measurements of the different Ns of PPy electrodes were performed suggesting that the PPy electrodes with multilayer nanosheets are promising materials for the next generation high performance electrochemical supercapacitors.

Standing pillar arrays of C-coated hollow SnO2 mesoscale tubules for a highly stable lithium ion storage electrode

This work reports the direct growth of hollow one-dimensional nanostructure arrays on conducting substrates for use as efficient electrodes in Li-ion batteries. The C-coated hollow SnO2 pillar array structures can be prepared by template-directed synthesis, selective wet etching, and a carbonization route. The well-oriented ZnO nanorod arrays, which are grown on titanium substrates, are used as a sacrificial template for the deposition of SnO2 layers through a simple hydrothermal process. The ZnO portions are selectively removed by wet etching, producing hollow SnO2 arrays that are consecutively covered with carbon layers via the carbonization of glucose. The lithium storage performance of the synthesized C-coated hollow SnO2 pillar array structures is demonstrated by applying them directly to a working electrode without additive materials. The standing pillar array electrode, consisting of C-coated hollow SnO2, exhibits an excellent discharge capacity of ca. 1251.9 mA h g−1 on the first cycle, and it also shows promising cyclability, rate capability, and coulombic efficiency, indicating that C-coated hollow SnO2 arrays fabricated on the current collector can be powerful candidates for a highly stable lithium storage electrode platform.

Honeycomb pattern array of vertically standing core-shell nanorods: Its application to Li energy electrodes

An energy storage electrode system is fabricated via a template method with one-dimensional nanostructures that are hexagonally patterned in a honeycomblike fashion and vertically standing nanorods made of a gold-coated carbon nanotube core and a V2O5 shell layer. The performance of this system for Li insertion and extraction shows an increased capacity along with an enhanced rate performance, which could be attributed to the aligned nanostructures having increased reaction sites, facilitated charge transport, and improved stability in the face of mechanical stress.

Patterned catalyst arrays of Pd/SnO2 core–shell nanowires for electrooxidations of biomass-derived alcohols

Patterned arrays of catalyst nanowires are demonstrated as high-performance electrode platforms in this research. Palladium catalysts synthesized on various patterned arrays of tin dioxide nanowire frameworks exhibit superior performance for electrooxidations of methanol, ethanol, ethylene glycol, and glycerol in alkaline media. This could be attributed to the effective diffusion of the liquid-phase alcohol reactants through the hollow channels formed between the patterned electrode arrays. Comparable electrocatalytic investigations modifying the pattern geometries of these nanowire electrodes enable the design of promising electrode platforms for electrochemical energy conversion applications.

Intracellular Delivery of Bioactive Cargos to Hard-to-Transfect Cells Using Carbon Nanosyringe Arrays under an Applied Centrifugal g-Force.

There is considerable interest in developing a common, universal platform for delivering biomacromolecules such as proteins and RNAs into diverse cells with high efficiency. Here, it is shown that carbon nanosyringe arrays (CNSAs) under an applied centrifugal g-force (cf-CNSAs) can deliver diverse bioactive cargos directly into the cytosol of hard-to-transfect cells with relatively high efficiency and reproducibility. The cf-CNSA platform, an optimized version of a previous CNSA-mediated intracellular delivery platform that adds a g-force feature, exhibits more rapid and superior delivery of cargos to various hard-to-transfect cells than is the case in the absence of g-force. Active species, including small interfering RNAs, plasmids, and proteins are successfully transported across plasma membrane barriers into various cells. By overcoming the limitations of currently available transfection methods, the cf-CNSA platform paves the way to universal delivery of a variety of cargos, facilitating the analysis of cellular responses in diverse cell types.