• Transactions of the Korean hydrogen and new energy society
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• v.15 no.2
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• pp.137-143
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• 2004

For hydrogen generation from aqueous alkilne $NaBH_4$ solution, Co-B catalyst was prepared by chemical reduction method using $NaBH_4$ as a reduction chemical. Effects of solution temperature, amount of catalyst loading, $NaBH_4$ concentration, and NaOH (a base-stabilizer) concentration on the hydrogen generation rate were exmanined. Compared to Ru catalyst generally used, the low-cost Co-B catalyst exhibited almost comparable activity to the hydrogen generation reaction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.627-633
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• 2011

Performance of a hydrogen generator for a fuel cell unmanned aircraft was evaluated as the change of temperature environment. Sodium borohydride ($NaBH_4$) was used as a hydrogen source due to its high hydrogen content and good storability. The hydrogen gas was generated by the hydrolysis reaction using a catalytic reactor. Reaction chambers were set up with the range of temperatures from -20 to $60^{\circ}C$. The hydrogen generation rate and temperatures changes of reactor and separator were measured at the $NaBH_4$ concentrations of 20 and 25wt.%. As a result, the hydrogen generation rate was decreased as the repeated reaction cycles. It showed that the hydrogen generation rate was stable at low temperature, while at high temperature the hydrogen generation rate was rapidly decreased. The performance degradation was mainly caused by the catalyst loss and $NaBO_2$ deposition on the catalyst surface.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.196-197
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• 2010

This paper investigates a high performance converter topology for hydrogen gas generation electrolysis system. The proposed converter topology consists of full-bridge inverter, medium frequency transformer, and diode rectifier. Hydrogen gas generation electrolysis process considered in the paper is analyzed and characterized by its equivalent circuit. The electrolysis cell is modeled as effective resistance, capacitance, inductance, and internal emf voltage source. The proposed converter topology provides enhanced efficiency of hydrogen gas generation process under the operating condition of dc output voltage with high frequency ripple on it. The high performance operation of proposed converter is confirmed through the simulation with the electrolysis cell considered in the equivalent circuit model.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.1-7
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• 2022

Interest in hydrogen productions that do not emit carbon dioxide and can produce hydrogen at a low price is increasing. Reforming and electrolysis are widely used, but they have limitations, such as carbon dioxide problems and costs. The methane can be decomposed as hydrogen and solid carbon without carbon dioxide emission at high temperatures. In this research, the methane pyrolysis experiment was conducted at 1,200℃ and 1,400℃ in a ceramic tube. The composition of the produced gas was measured by gas chromatography before carbon blocked the tube. The methane conversion rate and hydrogen selectivity were calculated based on the results. The hydrogen selectivity was derived as 60% and 55% at the highest point at 1,200℃ and 1,400℃, respectively. The produced solid carbon was expected to be carbon black and was analyzed using scanning electron microscope.

• Transactions of the Korean hydrogen and new energy society
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• v.7 no.1
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• pp.3-9
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• 1996

Hydrogen generation by electrical discharge through metal/water system is a viable method for on-demand applications. But its success depends on high energy efficiency defined as the ratio of the amount of consumed metal for a complete reaction with water to the electrical energy input. To improve the energy efficiency the electrical discharge has to sustain the hydrogen generation reaction with a minimal energy dissipation. Some experimental results on the discharge voltage-current profiles are reported and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.115-119
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• 2004

This paper is investigated about the effect of vibration of the water surface for hydrogen gas generation by non-thermal plasma. The vibration of the water surface is more powerful with increasing applied voltage. In this experimental reactor which is made of multi-needle and plate, the maximum acquired hydrogen production rate is about 6.8[ml/sec]. Although the generation of hydrogen gas is increased with elevating time, it is saturated after specific time due to the volume of reactor and the saturation of taylor cone.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.1-11
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• 2013

Additives such as glycerol, methanol, acetone, and ethanol were used to prevent $NaBO_2$ from precipitation, and their effects on hydrogen generation properties of $NaBH_4$ hydrolysis were investigated. When the concentration of additives was 5 wt%, the additives such as methanol, acetone, and ethanol could not prevent $NaBO_2$ precipitation. Although glycerol prevented $NaBO_2$ precipitation, conversion efficiency decreased to 78.0% due to its viscosity. Based on test results, hydrogen generation tests were also performed at various concentration of glycerol and methanol to investigate the concentration effects on hydrogen generation properties. As the concentration of glycerol increased from 1 wt% to 3 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 5 wt%, conversion efficiency decreased due to its viscosity. As the concentration of methanol increased from 5 wt% to 10 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 15 wt%, conversion efficiency decreased due to $NaB(OCH_3)_4$ precipitate. Although conversion efficiency decreased about 1% when 3 wt% glycerol was added, $NaBO_2$ precipitation was prevented. Consequently, addition of 3 wt% glycerol to $NaBH_4$ solution improves stability of hydrogen generation system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.4
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• pp.296-303
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• 2015

The concentration of solute in a $NaBH_4$ solution is limited due to the low solubility of $NaBO_2$. The performance of a hydrogen generation system was evaluated using various concentrations of $NaBH_4$ solution. First, a self-hydrolysis test and a hydrogen generation test for 30 min were performed. The composition of $NaBH_4$ solution was selected to be 1 wt% NaOH + 25 wt% $NaBH_4$+74wt% $H_2O$ by considering the amount of hydrogen loss, stability of hydrogen generation, $NaBO_2$ precipitation, conversion efficiency, and the purpose of its application. A hydrogen generation system for a 200 W fuel cell was evaluated for 3 h. Although hydrogen generation rate decreased with time due to $NaBO_2$ precipitation, hydrogen was produced for 3 h (conversion efficiency: 87.4%). The energy density of the 200 W fuel cell system was 263 Wh/kg. A small unmanned aerial vehicle with this fuel cell system can achieve 1.5 times longer flight time than one flying on batteries.

• Journal of the Korean Applied Science and Technology
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• v.27 no.4
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• pp.415-420
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• 2010

This study is focused on the channel design of bipolar plate in the electrode of hydrogen gas generator. The characteristics of hydrogen gas generation was studied in view of efficiency of hydrogen gas generation rate and a tendency of gas flow through the riv design of electrode. Since the flow rate and flow pattern of generated gas in the two phase flow system are the most crucial in determining the efficiency of hydrogen gas generator, we adopted the commercial analytical program of COMSOL MultiphysicsTM to calculate the theoretical flow rate of hydrogen gas from the outlet of gas generator and flow pattern of two phase fluid in the electrode. In this study, liquid electrolyte flows into the bipolar plate and decomposed into gas phase, two phase flow simulation is applied to measure the efficiency of hydrogen gas generation.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.6
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• pp.606-619
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• 2018

This study focuses on the performance of hydrogen energy based hybrid system in terms of system reliability of electricity generation. With this aim to evaluate the off-grid system of photovoltaic (PV), wind turbine, electrolyzer, fuelcell, $H_2$ tank and storage batteries, 14 different sites in South Korea are simulated using HOMER. Performance analysis includes simulation on the different sites, verification of operational behaviors on regional and seasonal basis, and comparison among a control group. The result shows that the generation performance of hydrogen powered fuelcell is greatly affected by geographical change rather than seasonal effect. In addition, as the latitude of the hybrid systems location decrease, renewable power output and penetration ratio (%) increase under constant electrical load. Therefore, the hydrogen based hybrid system creates the stability of electricity generation, which best suits in the southern part of South Korea.