• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1124-1128
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• 2021

As regulations of emissions from ships become more stringent, electric propulsion systems have been increasingly used to solve this problem in vessels ranging from large merchant ships to small and medium-sized ships. Methods for improving the efficiency of the electric propulsion system include the improvement of power sources; the use of a system linked to environmentally friendly power sources, such as batteries, fuel cells, and solar power; and the development of hardware and control methodology for rectifiers, power conversion devices, and propulsion motors. The method using a phase-shifting transformer with diodes has been widely used for rectification. Power semiconductor devices with grid connection to an environmentally friendly power source using DC distribution, a variable speed power source, and the application of small and medium-sized electric propulsion systems have been developed. Accordingly, the demand for active front-end (AFE) rectifiers is increasing. In this study, a method using a neural network rather than a conventional proportional-integral controller was proposed to control the AFE rectifier. Tested controller data were used to design a neural network controller trained through MATLAB/Simulink. The neural network controller was applied to a rectification system designed using PSIM software. The results indicated the effectiveness of improving the waveform and power factor DC output stage according to the load variation. The proposed system can be applied as a rectification system for small and medium-sized environmentally friendly ships.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.45-51
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• 2023

In order to improve the durability of the PEMFC(Proton Exchange Membrane Fuel Cells) polymer membrane, a radical scavenger and a support are used. In this study, the durability of membranes containing fucoidan extracted from seaweeds and tannic acid serving as a crosslinking agent is evaluated to improve chemical and physical durability. Physical durability is evaluated by measuring tensile strength, and chemical durability is measured by Fenton experiment. Membrane and electrode assembly (MEA) is prepared and mechanical and chemical durability are measured through accelerated durability evaluation in the cell. The tensile strength measurement showed that fucoidan and tannic acid can improve the mechanical durability of the membrane by improving the strain rate and yield strength. It is shown in Fenton experiment that fucoidan acts as a radical scavenger. As a result of the accelerated durability test in the unit cell, fucoidan improved both chemical and mechanical durability, increasing the accelerated durability evaluation time by 38.1% compared to the additive-free membrane. When tannic acid is added, the durability of the polymer membrane is improved by 13.9% by improving the mechanical durability.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.517-522
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• 2023

A chemical/mechanical durability test of polymer membrane evaluation method is used in which air and hydrogen are supplied to the proton exchange membrane fuel cell (PEMFC) and wet/dry is repeated in the open circuit voltage (OCV) state. In this protocol, when wet/dry is repeated, voltage increase/decrease is repeated, resulting in electrode degradation. When the membrane durability is excellent, the number of voltage changes increases and the evaluation is terminated due to electrode degradation, which may cause a problem that the original purpose of membrane durability evaluation cannot be performed. In this study, the same protocol as the department of energy (DOE) was used, but oxygen was used instead of air as the cathode gas, and the wet/dry time and flow rate were also increased to increase the chemical/mechanical degradation rate of the membrane, thereby shortening the durability evaluation time of the membrane to improve these problems. The durability test of the Nafion 211 membrane electrode assembly (MEA) was completed after 2,300 cycles by increasing the acceleration by 2.6 times using oxygen instead of air. This protocol also accelerated degradation of the membrane and accelerated degradation of the electrode catalyst, which also had the advantage of simultaneously evaluating the durability of the membrane and the electrode.

• Korean Chemical Engineering Research
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• v.62 no.1
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• pp.1-6
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• 2024

As the demand for hydrogen electric vehicles for commercial vehicles increases, the durability of PEMFCs must increase more than five times that of passenger cars, so research and development to improve durability is urgent. When the PEMFC membrane electrode assembly (MEA) undergoes chemical degradation, the MEA thickness decreases and pinholes occur. In this study, changes in the performance and durability of the MEA were measured while increasing the clamping pressure of the unit cell after open circuit voltage (OCV) holding, an accelerated chemical degradation experiment. As the clamping pressure increased, the resistance of the polymer membrane and the membrane/electrode contact resistance decreased, improving the I-V performance and reducing the hydrogen permeability. As the hydrogen permeability decreased, the OCV increased. When the pinhole area was removed and the MEA clamping pressure was increased, the hydrogen permeability decreased sharply, confirming that the local degradation has a large effect on the performance and durability of the entire cell. When the pinhole was removed and re-clamping and OCV holding was evaluated, it was confirmed that the durability improved according to the decrease in membrane resistance and hydrogen permeability.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.280-288
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• 2017

Nanocarbon base materials such as, graphene and graphene hybrid with high electrochemical performances have great deal of attention to investigate flexible, stretchable display and wearable electronics in order to develop portable and high efficient energy storage devices. Battery, fuel cell and supercapacitor are able to achieve those properties for flexible, stretchable and wearable electronics, especially the supercapacitor is a promise energy storage device due to their remarkable properties including high power and energy density, environment friendly, fast charge-discharge and high stability. In this study, we have fabricated flexible supercapacitor composed of graphene/conductive polymer composite which could improve its electrochemical performance. As a result, specific capacitance value of the flexible supercapacitor (unbent) was $198.5F\;g^{-1}$ which decreased to $128.3F\;g^{-1}$ (65% retention) after $500^{th}$ bending cycle.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.641-646
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• 2018

Sodium borohydride, $NaBH_4$, shows a number of advantages as hydrogen source for portable proton exchange membrane fuel cells (PEMFCs). Properties of $NaBH_4$ hydrolysis reaction using activated carbon supported Co-B/C, Co-P-B/C catalyst were studied. BET surface area of catalyst, yield of hydrogen, effect of $NaBH_4$ concentration and durability of catalyst were measured. The BET surface area of carbon supported catalyst was over $500m^2/g$ and this value was 2~3 times higher than that of unsupported catalyst. Hydrogen generation of activated carbon supported catalyst was more stable than that of unsupported catalyst. The activation energy of Co-P-B/C catalyst was 59.4 kJ/mol in 20 wt% $NaBH_4$ and 14% lower than that of Co-P-B/FeCrAlloy catalyst. Catalyst loss on activated carbon supported catalyst was reduced to about 1/3~1/2 compared with unsupported catalyst, therefore durability was improved by supporting catalyst on activated carbon.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.758-762
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• 2019

Sodium borohydride,$NaBH_4$, has many advantages as hydrogen source for portable proton exchange membrane fuel cells (PEMFC). When PEMFC is used for marine use, $NaBH_4$ hydrolysis using seawater is economical. Therefore, in this study, hydrogen was generated by using seawater instead of distilled water in the process of hydrolysis of $NaBH_4$. Properties of $NaBH_4$ hydrolysis reaction using activated carbon supported Co-B/C catalyst were studied. The yield of hydrogen decreased as $NaBH_4$ concentration and NaOH concentration were increased during $NaBH_4$ hydrolysis using sea water. At higher concentrations of $NaBH_4$ and NaOH, byproducts adhered to the surface of the catalyst after hydrolysis reaction using sea water, reduced hydrogen yield compared to distilled water. The activation energy of $NaBH_4$ hydrolysis is 59.3, 74.4 kJ/mol for distilled water and sea water, respectively. In order to increase the hydrogen generation rate in seawater as high as distilled water, the reaction temperature has to be increased by $80^{\circ}C$ or more.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.768-773
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• 2019

The Fenton reaction, which evaluates the electrochemical durability of polymer membranes of polymer electrolyte fuel cells (PEMFC), and the degradation of polymer membranes by OCV holding method are compared. The Fenton reaction is a method that can evaluate the chemical durability of the polymer membrane at outside the cell in a shorter time than the OCV Holding method. The Fenton reaction was carried out at 30% hydrogen peroxide, 10 ppm iron, and $80^{\circ}C$ for 24 hours. OCV Holding was driven at $90^{\circ}C$, 30% relative humidity and OCV for 168 hours. The Fenton reaction caused a lot of degradation inside the polymer membrane. On the other hand, in OCV Holding, the membrane thickness was thinned by the entire surface and internal degradation. The fluorine emission rate was more than 10 times higher than that of OCV Holding due to the Fenton reaction. The hydrogen permeation rate increased about 30% at 24 hours of Fenton reaction. At OCV Holding, hydrogen permeability decreased after 24 hours and then increased. As a whole, there was a difference in a membranes deteriorated by Fenton reaction and OCV Holding.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.344-350
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• 2019

Durability is very important for the commercialization of membranes and electrode assemblies (MEA) developed for proton exchange membrane fuel cells (PEMFC). Durability evaluation of stationary PEMFC MEA has a problem that the voltage change rate should be measured for a long time over 1000 hours under constant current conditions. In this study, the electrochemical durability evaluation protocol of membranes (OCV holding method) using to vehicle MEAs was applied to the stationary MEA for the purpose of shortening the durability evaluation time. After operation of the stationary and automobile MEA for 168 hours under conditions of OCV, cathode oxygen, $90^{\circ}C$ and relative humidity of 30%, I-V, LSV, CV, impedance and FER were measured and compared. When the hydrogen permeability, OCV change, ionic conductivity, and fluorine flow rate, which represent the durability of the membrane after degradation, were all examined, it was shown that durability of stationary MEA membrane was better than that of vehicles MEA membrane. In addition, the electrode degradation of stationary MEA was smaller than that of vehicles MEA after degradation operation. It was possible to evaluate in a short time using automotive protocol that the durability of stationary MEA was superior that of vehicle MEA in terms of membrane and the electrode.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.339-344
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• 2021

In order to improve the PEMFC (Proton Exchange Membrane Fuel Cell) durability, it is important to accurately evaluate the durability of the membrane in a short time. Recently, DOE (Department of Energy) reported a protocol that combines the chemical and mechanical durability of membranes to evaluate them effectively. This protocol applies chemical/mechanical deterioration to the membrane by repeating wet/dry while OCV (Open Circuit Voltage) holding. The problem of this protocol is that it is highly affected by electrode degradation due to change cycles in OCV and that the evaluation time is long. By using oxygen instead of air as the cathode gas while leaving the other conditions of the DOE protocol as it is, the durability evaluation time could be reduced from 408 hours to 144 hours. By reducing the number of voltage change cycles to 1/3, the electrode degradation due to the voltage change cycle was reduced to 1/12 when oxygen was used compared to air at the end, thereby enabling more accurate evaluation of polymer membrane durability.