Jin-Ho Kim

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.

The Characterization of an Alkaline Fuel Cell That Uses Hydrogen Storage Alloys

The characterization of new type of alkaline fuel cell based on oxidation of chemical hydride has been studied. The chemical hydride can he used as a new fuel source in a fuel cell system. As a result, we have discovered that the electrochemical reaction rate is higher at a normal temperature compared with cells containing other hydrogen fuels where a hydrogen-releasing agent, NaBH 4 , is added to an aqueous alkaline solution of electrolyte as hydrogen fuel. That is, the fuel can be supplied very simply for the cell. If air is supplied to the oxygen cathode made of highly dispersed platinum particles supported in high-surface-area carbon paper, and the hydrogen releasing agent is fed to the alkaline solution of electrolyte at the side of metal hydride anode (ZnCr 0.8 Ni 1.2 alloy), the cell can produce electric current continuously. Also it can be operated at a normal temperature and produce a large amount of energy due to its high energy density of 6,000 Ah/kg or more (for NaBH 4 or KBH 4 ). Therefore, the developed cell has higher electrochemical reaction rate and energy density than the conventional fuel cells using other hydrogen sources.

Nickel sulfide synthesized by ball milling as an attractive cathode material for rechargeable lithium batteries

Abstract Nickel sulfide (NiS) powders were prepared by ball milling and melting as cathode materials for a lithium rechargeable battery which was charged and discharged at room temperature (30xa0°C). The NiS powders prepared by melting were composed of several phases such as Ni 3 S 2 , Ni 7 S 6 , Ni x S 6 , and Ni 3 S 4 , as derived from XRD. In order to synthesize a homogeneous nickel sulfide (NiS) phase, ball milling (BM) was adopted. A homogeneous NiS phase was easily formed after ball milling up to 12 h under an Ar atmosphere. The ball milled NiS particles were relatively large compared to those of the starting materials and they had a nanocrystalline structure. The initial discharge capacity of the NiS positive electrode prepared by ball milling is 580 mAh/g-NiS, at 1.4 V vs. Li/Li + . The NiS powders synthesized by ball milling show a better cycling property than NiS prepared by melting and also had a better rate capability. It exhibited 87% of its theoretical capacity at a current rate of 2C, comparable with that of 1/6C. This may be related with the small sized grains of NiS prepared by ball milling.

Hydrogen storage properties of vanadium-based b.c.c. solid solution metal hydrides

Abstract On the basis of literature reports, several series of vanadium-based solid solutions with a b.c.c. structure were prepared and their hydrogen storage properties were studied in order to develop alloys with high hydrogen capacity and low cost. The V–Ti–Cr alloys were examined by adding other b.c.c. elements (Mn and Fe) and adjusting the corresponding compositions. Increasing the Cr content and the addition of Mn increased the plateau pressure due to lattice contraction, which is beneficial for reducing the first plateau region, although it decreased the maximum hydrogen storage capacity. Furthermore, Mn is an effective element to flatten the plateau pressure. The alloys containing Fe were found to be difficult to activate. A V 0.375 Ti 0.25 Cr 0.30 Mn 0.075 alloy was developed which exhibited an effective hydrogen capacity of 2.2 wt% H after annealing at 1300 °C for 1 h.

A study on the improvement of the cyclic durability by Cr substitution in V–Ti alloy and surface modification by the ball-milling process

Abstract The Ni–MH battery has been developed as a potential power source with a high energy density and excellent performance for mobile electrical appliances and hydride electric vehicles (HEVs). Research and development are, however, still essential for further improvement of the energy density and cycling life. Recently, vanadium-based solid solution hydrogen storage alloys have been considered as promising candidates for negative electrode materials because of their higher reversible hydrogen storage capacities. However, for the practical use of V-based alloy as a negative electrode, it is necessary to improve both the electrocatalytic activity and cyclic durability in alkaline solution. As a novel method for changing the surface properties of an alloy electrode to obtain a higher electro-catalytic activity, we have employed the ball-milling process with Ni powder without deterioration of the alloy bulk properties. In order to overcome the poor cyclic durability of V–Ti alloy, elemental Cr, which forms a protective oxide layer against corrosion in alkaline solution, was partially substituted for V. Through systematic experimentation, a V 0.68 Ti 0.20 Cr 0.12 alloy electrode ball-milled with Ni powder was found to have an advanced discharge capacity of 420 mAh/g and a good cycle life (80% after 200 cycles). For further promotion of the surface catalytic activity, instead of normal Ni powder (spherical Ni powder), filamentary Ni with a larger specific surface was used as a new surface modifier. Under optimum ball-milling conditions (7 wt% filamentary Ni for 25 min), V 0.68 Ti 0.20 Cr 0.12 alloy was effectively coated with Ni particles and showed an increased discharge capacity of 460 mAh/g.

A study on the development of hypo-stoichiometric Zr-based hydrogen storage alloys with ultra-high capacity for anode material of Ni/MH secondary battery

Abstract Some hypo-stoichiometric Zr-based Laves phase alloys were prepared and studied from a viewpoint of discharge capacity for electrochemical application. After careful alloy design of ZrMn 2 -based hydrogen storage alloys through changing their stoichiometry while substituting or adding some alloying elements, the Zr(Mn 0.2 V 0.2 Ni 0.6 ) 1.8 alloy reveals relatively good properties with regard to hydrogen storage capacity, hydrogen equilibrium pressure and electrochemical discharge capacity. In order to improve the discharge capacity and rate-capability, Zr is partially replaced by Ti. The discharge capacity of Zr 1− x Ti x (Mn 0.2 V 0.2 Ni 0.6 ) 1.8 ( x =0.0, 0.2, 0.3, 0.4, 0.6) alloy electrodes at 30°C reaches a maximum value and decreases as the Ti fraction increases. In view of electrochemical and thermodynamic characteristics, the occurrence of a maximal phenomenon of the electrochemical discharge capacity of the alloy is attributed to a competition between decreasing hydrogen storage capacity and increasing rate-capability with Ti fraction. However, as the Ti fraction increases, the discharge capacity decreases drastically with repeated electrochemical cycling. Judging from the analysis of surface composition by Auger electron spectroscopy (AES), the rapid degradation with increasing Ti fraction in Zr-based alloy is ascribed to the fast growth of the oxygen-penetrated layer with cycling. Therefore, it is assured that the stoichiometry and Ti fraction should be optimized to obtain a good cycle life of the electrode maintaining high discharge capacity. On the basis of above results, the hydrogen storage capacity of the alloy with optimized composition (Zr 0.65 Ti 0.35 (Mn 0.3 V 0.14 Cr 0.11 Ni 0.65 ) 1.76 ) is about 1.68 wt% under 10 atm of equilibrium hydrogen pressure and the discharge capacity of the alloy is about 421 mAh/g at a discharge rate of 50 mA/g, which shows the highest level in performance of the Zr-based alloy ever developed.

Ni Nanoparticles-hollow Carbon Spheres Hybrids for Their Enhanced Room Temperature Hydrogen Storage Performance

A glucose hydrothermal method is described for preparing hollow carbon spheres (HCS), which have a regular morphology and a high Brunauer-Emmett-Teller surface area of 28.6 m2/g. Scanning electron microscopy shows that they have thin shells and diameter between 2 and 8 . The HCSs were modified for the enhanced room temperature hydrogen storage by employing Ni nanoparticles on their surface. The Ni-decorated HCSs were characterized by X-ray diffraction, transmission electron microscopy coupled with an energy dispersive spectroscope, and an inductively coupled plasma spectrometer, indicating that fine and well-distributed Ni nanoparticles can be accomplished on the HCSs. The hydrogen uptake capacity in HCSs with and without Ni loading was evaluated using a high-pressure microbalance at room temperature under a hydrogen pressure upto 9 MPa. As much as 1.23wt.% of hydrogen can be stored when uniformly distributed Ni nanoparticles are formed on the HCSs, while the hydrogen uptake capacity of as-received HCSs was 0.41 wt.%. For Ni nanoparticle-loaded HCSs, hydrogen molecules could be easily dissociated into atomic hydrogen and then chemically adsorbed by the sorbents, leading to an enhanced capacity for storing hydrogen.

Preparation and characterization of CoAl 2 O 4 blue ceramic nano pigments by attrition milling

Cobalt aluminate () is a highly stable pigment with excellent resistance to light, weather, etc., which has resulted in widespread use as a ceramic pigment. Due to the unique optical characteristics, is generally used as a coloring agent to decorate porcelain products, glass, paints and plastics. Here, pigments were synthesized by polymerized complex method and solid state reaction. Then pigment were grinded using the attrition milling with 1 mm size zirconia ball for 3 hours. The attrition milling process was performed at the constant speed of 800 rpm and ball to powder weight ratio (BPR) was 100 : 1. The characteristics of synthesized pigment were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and CIE . The XRD patterns of show single phase spinel structure. The particle size of measured by FE-SEM, TEM and PSA analysis was in the range of 100~200 nm. The blue color of obtained pigments could be confirmed through CIE measurement.