Yong-Mook Kang

Rational Design of 3D Dendritic TiO2 Nanostructures with Favorable Architectures

Controlling the morphology and size of titanium dioxide (TiO(2)) nanostructures is crucial to obtain superior photocatalytic, photovoltaic, and electrochemical properties. However, the synthetic techniques for preparing such structures, especially those with complex configurations, still remain a challenge because of the rapid hydrolysis of Ti-containing polymer precursors in aqueous solution. Herein, we report a completely novel approach-three-dimensional (3D) TiO(2) nanostructures with favorable dendritic architectures-through a simple hydrothermal synthesis. The size of the 3D TiO(2) dendrites and the morphology of the constituent nano-units, in the form of nanorods, nanoribbons, and nanowires, are controlled by adjusting the precursor hydrolysis rate and the surfactant aggregation. These novel configurations of TiO(2) nanostructures possess higher surface area and superior electrochemical properties compared to nanoparticles with smooth surfaces. Our findings provide an effective solution for the synthesis of complex TiO(2) nano-architectures, which can pave the way to further improve the energy storage and energy conversion efficiency of TiO(2)-based devices.

Effects of Nanosized Adsorbing Material on Electrochemical Properties of Sulfur Cathodes for Li/S Secondary Batteries

In order to prevent polysulfide dissolution into liquid electrolytes and to promote the Li/S redox reaction (16Li + S 8 ↔ Li 2 Sn ↔ Li 2 S), nanosized Mg 0.6 Ni 0.4 O, which has the catalytic effect of chemical bond dissociating and is expected to have an adsorbing effect due to the effect of retaining liquid electrolyte of MgO in a Li/iron sulfide secondary battery, 16 was prepared by the sol-gel method as an electrochemically inactive additive for an elemental sulfur cathode for Li/S rechargeable batteries. The Li/S battery using an elemental sulfur cathode with a nanosized Mg 0.6 Ni 0.4 O added showed the improvement of not only the discharge capacity but also cycle durability (maximum discharge capacity: 1185 mAh/g sulfur, C 50 /C 1 = 85%).The rate capability of the sulfur cathode was also increased with the addition of the nanosized Mg 0.6 Ni 0.4 O. From the msults. it is confirmad that the nanosized Mg 0.6 Ni 0.4 O had the polysulfide adsorbing effect and the catalytic elfect of promoting Lt/S redox reaction. Furthermore, it is found that the nanosized Mg 0.6 Ni 0.4 O also increased the porosity of the sulfur cathode.

Cobalt‐Doped FeS2 Nanospheres with Complete Solid Solubility as a High‐Performance Anode Material for Sodium‐Ion Batteries

Considering that the high capacity, long-term cycle life, and high-rate capability of anode materials for sodium-ion batteries (SIBs) is a bottleneck currently, a series of Co-doped FeS2 solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na-storage properties were investigated. The optimized Co0.5 Fe0.5 S2 (Fe0.5) has discharge capacities of 0.220 Ah g(-1) after 5000 cycles at 2 A g(-1) and 0.172 Ah g(-1) even at 20 A g(-1) with compatible ether-based electrolyte in a voltage window of 0.8-2.9 V. The Fe0.5 sample transforms to layered Nax Co0.5 Fe0.5 S2 by initial activation, and the layered structure is maintained during following cycles. The redox reactions of Nax Co0.5 Fe0.5 S2 are dominated by pseudocapacitive behavior, leading to fast Na(+) insertion/extraction and durable cycle life. A Na3 V2 (PO4 )3 /Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g(-1) .

Carbon-Supported and Unsupported Pt Anodes for Direct Borohydride Liquid Fuel Cells

Investigations have been conducted on direct borohydride liquid fuel cells (DBFCs) based on the electio-oxidation of sodium borohydride, NaBH 4 . A comparative study on the use of carbon-supported and unsupported Pt anods catalysts for DBFCs has been made. The effects on anode and fuel cell performance of catalyst loading, binder content, fuel concentration, and pH of supporting solution dissolving NaBH 4 are studied. A maximum power density of 44.2 mW cm -2 to unsupported catalyst of 7 mg cm -2 (under room temperature and air breathing) has been obtained. Cell performance by using the anode with 1.50 mg cm -2 carbon-supported Pt anode catalyst is comparable to that by using the anode with 6 mg cm -2 unsupported Pt anode catalyst. It is found that the carbon-supported catalysts are more cost effective and have higher catalytic activity than the unsupported catalysts. The coulombic efficiencies calculated from the energy density (theoretical capacity 5880 vs. measured capacity) for unsupported and carbon-supported Pt anode catalysts are 62.3 and 68.1%, respectively. The DBFC developed in this work has better performance than the conventional fuel cells using hydrocarbon liquid fuels like methanol.

Tailored Li4Ti5O12 nanofibers with outstanding kinetics for lithium rechargeable batteries

We report on the synthesis of one-dimensional (1D) Li(4)Ti(5)O(12) nanofibers through electrospinning and their outstanding electrochemical performances. Li(4)Ti(5)O(12) with a spinel structure is a promising candidate anode material for lithium rechargeable batteries due to its well-known zero-strain merits. In order to improve the electronic properties of spinel Li(4)Ti(5)O(12), which are intrinsically poor, we processed the material into a nanofiber type of architecture to shorten the Li(+) and electron transport distance using a versatile electrospinning approach. The electrospun Li(4)Ti(5)O(12) nanofiber showed significantly enhanced discharging/charging properties, even at high rates that exceeded 10 C, demonstrating that the nanofiber offers an attractive architecture for enhanced kinetics.

Tailored Oxygen Framework of Li4Ti5O12 Nanorods for High-Power Li Ion Battery

Here we designed the kinetically favored Li4Ti5O12 by modifying its crystal structure to improve intrinsic Li diffusivity for high power density. Our first-principles calculations revealed that the substituted Na expanded the oxygen framework of Li4Ti5O12 and facilitated Li ion diffusion in Li4Ti5O12 through 3-D high-rate diffusion pathway secured by Na ions. Accordingly, we synthesized sodium-substituted Li4Ti5O12 nanorods having not only a morphological merit from 1-D nanostructure engineering but also sodium substitution-induced open framework to attain ultrafast Li diffusion. The new material exhibited an outstanding cycling stability and capacity retention even at 200 times higher current density (20 C) compared with the initial condition (0.1 C).

Na3V2(PO4)3 particles partly embedded in carbon nanofibers with superb kinetics for ultra-high power sodium ion batteries

We here describe the extraordinary performance of NASICON Na3V2(PO4)3-carbon nanofiber (NVP–CNF) composites with ultra-high power and excellent cycling performance. NVP–CNFs are composed of CNFs at the center part and partly embedded NVP nanoparticles in the shell. We first report this unique morphology of NVP–CNFs for the electrode material of secondary batteries as well as for general energy conversion materials. Our NVP–CNFs show not only a high discharge capacity of ∼88.9 mA h g−1 even at a high current density of 50 C but also ∼93% cyclic retention property after 300 cycles at 1 C. The superb kinetics and excellent cycling performance of the NVP–CNFs are attributed to the facile migration of Na ions through the partly exposed regions of NVP nanoparticles that are directly in contact with an electrolyte as well as the fast electron transfer along the conducting CNF pathways.

Phosphidation of Li4Ti5O12 nanoparticles and their electrochemical and biocompatible superiority for lithium rechargeable batteries

Phosphidated-Li(4)Ti(5)O(12) shows high capacity with a significantly enhanced kinetics opening new possibilities for ultra-fast charge/discharge of lithium rechargeable batteries. The in vitro cytotoxicity test proves its fabulous cell viability, indicating that the toxicity problem of nanoparticles can be also solved by phosphidation.

Ordered Mesoporous Cobalt Phosphate with Crystallized Walls toward Highly Active Water Oxidation Electrocatalysts.

A hexagonally ordered mesoporous cobalt phosphate (CoPi) material is prepared by a facile one-pot soft-templating strategy using cetyltrimethylammonium bromide template. Because of its highly accessible surface area and crystalline framework with abundant active sites, the mesoporous CoPi shows a high catalytic activity for the oxygen evolution reaction compared to previously reported noble/transition-metal and nonmetal catalysts.

Tailored materials for high-performance MgB2 wire

High electrical current without dissipation is valuable, not only for power transmission, but also in other fi elds, such as energy storage or high-fi eld magnets for medical applications. The superconductor magnesium diboride (MgB 2 ) has a transition temperature of about 40 K [ 1 ] and thus can be operated without the need for liquid helium, which is expensive. MgB 2 wire made from inexpensive, clean, starting materials will further accelerate the spread of practical superconductor applications. Here we report on an economical way of producing high-performance MgB 2 wire using carbon-encapsulated boron nanopowder and coarse magnesium powder. It was found that carbon encapsulation suppresses surface oxidation, while nanometer-sized boron can be fully reacted with magnesium at low sintering temperature. Ductile magnesium coarse powders are elongated during the cold-working, leading to alignment of voids and enhanced