Showing papers by "Jeonghun Kim published in 2015"

Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems

Abstract: Transition metal oxides possessing two kinds of metals (denoted as AxB3-xO4, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe, etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs). The spinel-type transition metal oxides exhibit outstanding electrochemical activity and stability, and thus, they can play a key role in realising cost-effective and environmentally friendly ESSs. Moreover, porous nanoarchitectures can offer a large number of electrochemically active sites and, at the same time, facilitate transport of charge carriers (electrons and ions) during energy storage reactions. In the design of spinel-type transition metal oxides for energy storage applications, therefore, nanostructural engineering is one of the most essential approaches to achieving high electrochemical performance in ESSs. In this perspective, we introduce spinel-type transition metal oxides with various transition metals and present recent research advances in material design of spinel-type transition metal oxides with tunable architectures (shape, porosity, and size) and compositions on the micro- and nano-scale. Furthermore, their technological applications as electrode materials for next-generation ESSs, including metal-air batteries, lithium-ion batteries, and supercapacitors, are discussed.

A one-step roll-to-roll process of stable AgNW/PEDOT:PSS solution using imidazole as a mild base for highly conductive and transparent films: optimizations and mechanisms

Abstract: A recent increase in the demand for transparent electrodes has led to shortage in supply and an increase in the price of indium tin oxide (ITO) films deposited by sputter coating owing to coating speed limitations. Furthermore, flexibility has become one of the essential properties of transparent electrodes, accounting for the rapidly changing trend in electronics. These problems can be overcome by AgNW-based films suitable for flexible and stable conductive electrodes by using wet-coating-processable material and roll-to-roll coating. In this work, we developed an effective method to fabricate a highly conductive, transparent, and stable AgNW/PEDOT:PSS film using roll-to-roll slot-die coating. This coating technique provides higher line speed and greater coating uniformity. Furthermore, the optimized AgNW/PEDOT:PSS solution allows direct one-step coating without any post-treatment, such as high-temperature annealing, mechanical pressure, and solvent washing. We also studied the mechanisms of AgNW corrosion induced by the acidity of PEDOT:PSS and by hydrogen sulfide (H2S) and carbonyl sulfide (OCS) of the atmosphere. Corrosion could be prevented by neutralizing PEDOT:PSS using imidazole, which is a suitable organic compound in terms of both material and processing properties owing to its mild basicity and high melting and boiling points. In addition, the over-coating by a silica-based protecting layer on the AgNW/PEDOT:PSS film resulted in enhanced corrosion protection. The resulting roll film (460 mm in width × 20 m in length) showed suitable electrical (Rs ∼ 75 Ω sq−1) and optical (T > 90% at 550 nm, haziness ∼1.21%, b* ∼ 0.72) properties to replace ITO films in touch screen panels.

A Single-Step Synthesis of Electroactive Mesoporous ProDOT-Silica Structures†

Abstract: The single-step preparation of highly ordered mesoporous silica hybrid nanocomposites with conjugated polymers was explored using a novel cationic 3,4-propylenedioxythiophene (ProDOT) surfactant (PrS). The method does not require high-temperature calcination or a washing procedure. The combination of self-assembly of the silica surfactant and in situ polymerization of the ProDOT tail is responsible for creation of the mesoporosity with ultralarge pores, large pore volume, and electroactivity. As this novel material exhibits excellent textural parameters together with electrical conductivity, we believe that this could find potential applications in various fields. This novel concept of creating mesoporosity without a calcination process is a significant breakthrough in the field of mesoporous materials and the method can be further generalized as a rational preparation of various mesoporous hybrid materials having different structures and pore diameters.

Self‐Doped Conjugated Polymeric Nanoassembly by Simplified Process for Optical Cancer Theragnosis

Abstract: To access smart optical theragnosis for cancer, an easily processable heterocyclic conjugated polymer (poly(sodium3-((3-methyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-3-yl)methoxy)propane-1-sulfonate), PPDS) nanoassembly is fabricated by a surfactant-free one-step process, without the laborious ordinary multicoating process. The conjugated nanoassembly, with a self-doped structure, provides strong absorbance in the near-infrared (NIR) range even in a neutral pH medium and exhibits excellent stability (>six months). In addition, the prepared PPDS nanoassembly shows a high photothermal conversion efficiency of 31.4% in organic photothermal nanoparticles. In particular, the PPDS nanoassembly is stably suspended in the biological medium without any additives. Through a simple immobilization with the anti-CD44 antibody, the prepared biomarker-targetable PPDS nanoassembly demonstrates specific targeting toward CD44 (expressed in stem-like cancer cells), allowing NIR absorbance imaging and the efficient targeted photothermal damaging of CD44-expressing cancer cells, from in vitro 3D mammospheres (similar to the practical structure of tumor in the body) to in vivo xenograft mice tumor models (breast cancer and fibrosarcoma). In this study, the most simplified preparation method is for this organic conjugated polymer-based nanoassembly by a molecular approach is reported, and demonstrated as a highly promising optical nanoagent for optical cancer theragnosis.