Min-Sang Song

Effect of Multiwalled Carbon Nanotubes on Electrochemical Properties of Lithium/Sulfur Rechargeable Batteries

In order to bestow high electronic conductivity and prevent dissolution of sulfur into the electrolyte, multiwalled carbon nanotubes (MWNTs) were prepared by thermal chemical vapor deposition as an inactive additive material for elemental sulfur positive electrodes for lithium/sulfur rechargeable batteries. The initial discharge capacity of elemental sulfur positive electrode with MWNT is 485 mAh/g sulfur at 2.0 V vs. The cycle life and rate capability of sulfur cathode is increased with addition of MWNT. The MWNT shows a vital role on polysulfide adsorbtion and is a good electric conductor for a sulfur cathode.

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.

Production of hydrogen from sodium borohydride in alkaline solution: development of catalyst with high performance

Abstract The hydrogen production from hydrolysis of sodium borohydride in alkaline solution has been extensively studied. As a result, we have studied that stylene-butadiene-rubber as a binder of catalyst electrode is very effective because their hydrophilic property promotes the infiltration of liquid fuel into the catalyst. The filamentary Ni mixed Co catalyst with superior performance of short initial waiting time and fast hydrolysis of sodium borohydride has been developed and showed a maximum hydrogen production rate of 96.3 ml / min g . Also because hydrogen gas can be generated at room temperature and has a high purity more than 99.99%, it can be directly used as a fuel to PEMFC.

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.

A study of the hydriding kinetics of Mg-(10–20 w/o) LaNi5

Abstract The addition of LaNi 5 allows a considerable increase in the hydrogenation rate of magnesium according to Tanguy et al. [ Mater. Res. Bull. 11 , 1441 (1976)]. The rate-controlling step was determined by comparing their empirical results with the rate equations of each step of the kinetic hydriding model established earlier. The initial rate of the reaction is controlled by the step involving hydrogen adsorption on the metal surface after which the rate-controlling step changes to the diffusion of hydrogen through the hydride phase.

Nature of Insulating-Phase Transition and Degradation of Structure and Electrochemical Reactivity in an Olivine-Structured Material, LiFePO4

Synthesis time using microwave irradiation was varied to elucidate the electrochemical degradation mechanism of LiFePO(4) related to the evolution of Fe(2)P. When the amount of Fe(2)P was above a critical level, LiFePO(4) tended to change into an insulating phase, Li(4)P(2)O(7). The correlation between structural analysis and electrochemical analysis attributed the initial degradation of LiFePO(4) to the low electronic conductivity of Li(4)P(2)O(7), whereas the deficiency of P and O evolved by Li(4)P(2)O(7) resulted in the cyclic degradation of LiFePO(4). This kind of correlation between structure and electrochemical performance in intercalation materials will significantly contribute to an explanation of their degradation mechanism for their application.