• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.7
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• pp.46-52
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• 2006

The effects of surface treatment on the hydrogen storage properties of a $Mg_2Ni$ alloy particle were investigated by the microvoltammetric technique, in which a carbon-filament microelectrode was manipulated to make electrical contact with the particle in a KOH aqueous solution. It was found that the hydrogen storage properties of $Mg_2Ni$ at room temperature were improved by the surface treatment with a nickel plating solution. The sodium salts(sodium phosphate and sodium dihydrogen citrate) contained in the nickel plating solution made the alloy form an amorphous-like state, resulting in an improved hydrogen charge/discharge capacity at room temperature as high as about 150[mAh/g] from the original value of 17[mAh/g]. Potential-step experiment was carried out to determine the apparent chemical diffusion coefficient of hydrogen atom($D_{app}$) in the alloy. Since the alloy particle we used here was a dense, conductive sphere, the spherical diffusion model was employed for data analysis. $D_{app}$ was found to vary the order between $10^{-8}{\sim}10^{-9}[cm^2/s]$ over the course of hydrogenation and dehydrogenation process.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.798-803
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• 2019

The self-discharge behavior of zinc-air batteries is a critical issue induced by corrosion and hydrogen evolution reaction (HER) of zinc anode. The corrosion reaction and HER can be controlled by a gelling agent and concentration of potassium hydroxide (KOH) solution. Various concentrations of KOH solution and polyacrylic acid have been used for gel electrolyte. The electrolyte solution is prepared with different concentrations of KOH (6 M, 7 M, 8 M, 9 M). Among studied materials, the cell assembled with 6 M KOH gel electrolyte exhibits the highest specific discharge capacity and poor capacity retention. Whereas, 9 M KOH gel electrolyte shows high capacity retention. However, a large amount of hydrogen gas is evolved with 9 M KOH solution. In general, the increase in concentration is related to ionic conductivity. At concentrations above 7 M, the viscosity increases and the conductivity decreases. As a result, compared to other studied materials, 7 M KOH gel electrolyte is suitable for Zn-air batteries because of its higher capacity retention (92.00 %) and specific discharge capacity (351.80 mAh/g) after 6 hr storage.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.237-240
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• 2002

Micro catalytic reactors are alternative propulsion device that can be used on a nano satellite. When used with a monopropellant, $H_2O_2$, a micro catalytic reactor needs only one supply system as the monopropellant reacts spontaneously on contact with catalyst and releases heat without external ignition, while separate supply lines for fuel and oxidizer are needed for a bipropellant rocket engine. Additionally, $H_2O_2$ is in liquid phase at room temperature, eliminating the burden of storage for gaseous fuel and carburetion of liquid fuel. In order to design a micro catalytic reactor, an appropriate catalyst material must be selected. Considering the safety concern in handling the monopropellants and reaction performance of catalyst, we selected hydrogen peroxide at volume concentration of 70% and perovskite redox catalyst of lantanium cobaltate doped with strondium. Perovskite catalysts are known to have superior reactivity in reduction-oxidation chemical processes. In particular, lantanium cobaltate has better performance in chemical reactions involving oxygen atom exchange than other perovskite materials. In the present study, a process to prepare perovskite type catalyst, $La_{0.8}Sr_{0.2}CoO_3$, and measurement of its propellant decomposition performance in a test reactor are described.

• Journal of Hydrogen and New Energy
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• v.16 no.4
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• pp.334-342
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• 2005

200-300 nm 직경을 지닌 폴리비닐리덴 플루오라이드 초극세 섬유를 전기방사법으로 제조하였다. 이들을 불응화시킨 후, $800-1800^{\circ}C$ 온도에서 탄화시켜 PVdF 계 탄소나노 섬유를 제조하여 구조 및 기공분석을 하였다. 이들은 20-30 nm 크기의 탄소입자로 이루어져 있으며 탄소나노입자는 1 nm이하의 슬릿형 나노기공을 지니고 있었다. 탄화온도가 증가함에 따라 비표면적은 $1500^{\circ}C$에서 $414\;m^2/g$로 감소하였으나, $1800^{\circ}C$에서는 $1300\;m^2/g$로 급격히 다시 증가하였으며 1 nm 이하의 나노기공만을 지닌 탄소섬유가 얻어졌다. 비표면적 및 기공특성과 수소저장특성을 관계를 조사하기 위하여 Magnetic Syspension Balance(MSB)를 사용한 중량법으로 평가한 이들의 수소저장능은 0.04-0.4wt%이었다.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.709-714
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• 2020

For zinc-air batteries, there are several limitations associated with zinc anodes. The self-discharge behavior of zinc-air batteries is a critical issue that is induced by corrosion reaction and hydrogen evolution reaction (HER) of zinc anodes. Aluminum and indium are effective additives for controlling the hydrogen evolution reaction as well as the corrosion reaction. To enhance the electrochemical performances of zinc-air batteries, mechanically alloyed Zn-Al and Zn-In materials with different compositions are successfully fabricated at 500rpm and 5h milling time. Investigated materials are characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), and energy dispersive spectrometer (EDS). Alloys are investigated for the application as novel anodes in zinc-air batteries. Especially, the material with 3 wt% of indium (ZI3) delivers 445.37 mAh/g and 408.52 mAh/g of specific discharge capacity with 1 h and 6 h storage, respectively. Also, it shows 91.72 % capacity retention and has the lowest value of corrosion current density among attempted materials.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.95-99
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• 2006

Electrochemical properties were studied for a single particle of active material of hydrogen storage alloy $(MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3})$ and nickel hydroxides $(NiOH)_2$ for the secondary Nickel Metal Hydride (Ni-MH) batteries using the microelectrode, which was manipulated to make electrical contact with an active material particle for cyclic voltammograms (CV) and potential-step experiments. As a result of CV test, it was found that three kinds of hydrogen oxidation peaks at -0.9, -0.75 and -0.65 V and hydrogen evolution peak at -0.98 V for hydrogen storage alloy were separately observed and two kinds of peaks of proton oxidation/reduction at 0.45 and 0.32 V and oxygen evolution reaction (OER) at 0.6 V for nickel hydroxides were also more clearly observed. Furthermore hydrogen diffusion coefficient within a single particle was also found to vary the order between $10^{-9}\;and\;10^{-10}cm^2/s$ over the course of hydrogenation and dehydrogenation process for potential-step experiments.

• Korean Journal of Metals and Materials
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• v.50 no.5
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• pp.383-387
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• 2012

The activation of Mg-10 wt%$Fe_2O_3$ was completed after one hydriding-dehydriding cycle. Activated Mg-10 wt%$Fe_2O_3$ absorbed 5.54 wt% H for 60 min at 593 K under 12 bar $H_2$, and desorbed 1.04 wt% H for 60 min at 593 K under 1.0 bar $H_2$. The effect of the reactive grinding on the hydriding and dehydriding rates of Mg was weak. The reactive grinding of Mg with $Fe_2O_3$ is believed to increase the $H_2$-sorption rates by facilitating nucleation (by creating defects on the surface of the Mg particles and by the additive), by making cracks on the surface of Mg particles and reducing the particle size of Mg and thus by shortening the diffusion distances of hydrogen atoms. The added $Fe_2O_3$ and the $Fe_2O_3$ pulverized during mechanical grinding are considered to help the particles of magnesium become finer. Hydriding-dehydriding cycling is also considered to increase the $H_2$-sorption rates of Mg by creating defects and cracks and by reducing the particle size of Mg.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.955-959
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• 2012

To increase the hydrogen storage capacity of Mg-based materials, a sample with a composition of 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ was prepared by planetary ball milling under hydrogen. The absorption and desorption properties of unmilled $MgH_2$, unmilled $LiBH_4$, and 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ were examined. At 648 K the unmilled $MgH_2$ desorbed 5.70 wt% for 60 min. The unmilled $LiBH_4$ desorbed 6.40 wt% H for 780 min at 673 K. The 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ sample desorbed 3.10 wt% H for 50 min, and 3.32 wt% H for 300 min at 623 K at the second cycle.

• Journal of the Korean Institute of Gas
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• v.13 no.1
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• pp.45-51
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• 2009

A safety assessment was performed through the process analysis of hydrogen station. The purpose of this study provides basic information for the standard establishment about hydrogen stations. The processes of hydrogen stations were classified by four steps (process of manufacture, compression, storage, charge). FMEA (Failure Mode and Effect Analysis) method was applied to evaluate safety. Each risk element is following; S (severity), O (occurrence), D (detection). And the priority of order was decided by using RPN (Risk Priority Number) value multiplying three factors. Scenarios were generated based on FMEA results. And consequence analysis was practiced using PHAST program. In the result of C.A, jet fire and explosion were shown as accident types. In case of leakage of feed line in PSA process, concentration of CO gas is considered to prevent CO gas poisoning when the raw material that can product CO gas was used.

• Journal of Hydrogen and New Energy
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• v.22 no.3
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• pp.283-291
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• 2011

Polymer electrolyte membrane fuel cells (PEMFCs) use the bipolar plate of various materials between electrolyte and contact electrode for the stable hydrogen ion exchange activation. The bipolar plate of various materials has representatively graphite and stainless steel. Specially, stainless steels have advantage for low cost and high product rate. In this study, SUS 316 was effectively coated with 600 nm thick F-doped tin oxide (SnOx:F) by electron cyclotron resonance-metal organic chemical vapor deposition and investigated in simulated fuel cell bipolar plates. The results showed that an F-doped tin oxide (SnOx:F) coating enhanced the corrosion resistance of the alloys in fuel cell bipolar plates, though the substrate steel has a significant influence on the behavior of the coating. Coating SUS 316 for fuel cell bipolar plates steel further improved the already excellent corrosion resistance of this material. After coating, the increased ICR values of the coated steels compared to those of the fresh steels. The SnOx:F coating seems to add an additional resistance to the native air-formed film on these stainless steels.