• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.104-104
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• 2015

Due to the demand of the cold neutron flux in the neutron science and beam utilization technology, the cold neutron source (CNS) has been constructed and operating in the nuclear research reactor all over the world. The majority of the heat load removal scheme in the CNS is two-phase thermosiphon using the liquid hydrogen as a moderator. The CNS moderates thermal neutrons through a cryogenic moderator, liquid hydrogen, into cold neutrons with the generation of the nuclear heat load. The liquid hydrogen in a moderator cell is evaporated for the removal of the generated heat load from the neutron moderation and flows upward into a heat exchanger, where the hydrogen gas is liquefied by the cryogenic helium gas supplied from a helium refrigeration system. The liquefied hydrogen flows down to the moderator cell. To keep the required liquid hydrogen stable in the moderator cell, the CNS consists of an in-pool assembly (IPA) connected with the hydrogen system to handle the required hydrogen gas, the vacuum system to create the thermal insulation, and the helium refrigeration system to provide the cooling capacity. If one of systems is running out of order, the operating research reactor shall be tripped because the integrity of the CNS-IPA is not secured under the full power operation of the reactor. To prevent unscheduled reactor shutdown during a long time because the research reactor has been operating with the multi-purposes, the introduction of the standby cooling system (STS) can be a solution. In this presentation, the design considerations are considered how to design the STS satisfied with the following objectives: (a) to keep the moderator cell less than 350 K during the full power operation of the reactor under loss of the vacuum, loss of the cooling power, loss of common electrical power, or loss of instrument air cases; (b) to circulate smoothly helium gas in the STS circulation loop; (c) to re-start-up the reactor within 1 hour after its trip to avoid the Xenon build-up because more than certain concentration of Xenon makes that the reactor cannot start-up again; (d) to minimize the possibility of the hydrogen-oxygen reaction in the hydrogen boundary.

• Applied Chemistry for Engineering
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• v.23 no.5
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• pp.445-449
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• 2012

The activation process of the membrane-electrode assembly (MEA) is important for the mass production of the polymer electrolyte membrane fuel cell. The conventional activation process for the MEA requires excessive time and hydrogen gas and it might become the barrier for the commercialization of the fuel cell. The conventional activation process is based on hydrolysis of ion conducting membrane. In the study, we suggest the cyclic voltammetry (CV) technique as an on-line activation process and the CV activation process consists of two steps : 1) the humidification of the polymer electrolyte membrane and the electrode with 100% RH humidified nitrogen ($N_{2}$) gas, and 2) the removal step of the oxide layer on the surface of the Pt catalyst with CV cycling. The cycling reduces the activation time of the MEA by 2.5 h and use of hydrogen gas by 1/4.

• Journal of Hydrogen and New Energy
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• v.28 no.5
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• pp.471-480
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• 2017

A proton exchange membrane fuel cell (PEMFC) operated at $150^{\circ}C$ was evaluated by a controlling different amount of phosphoric acid (PA) to a membrane-electrode assembly (MEA) without humidification of the cells. The effects on MEA performance of the amount of PA in the cathode are investigated. The PA content in the cathodes was optimized for higher catalyst utilization. The highest value of the active electrochemical area is achieved with the optimum amount of PA in the cathode confirmed by in-situ cyclic voltammetry. The current density-voltage experiments (I-V curve) also shows a transient response of cell voltage affected by the amount of PA in the electrodes. Furthermore, this information was compared with the production variables such as hot pressing and vacuum drying to investigate those effect to the electrochemical performances.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.279-282
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• 2007

When reformer for fuel cell is used, CO in hydrogen gas leads to a seriously decreased membrane electrode assembly (MEA) performance by catalyst poisoning. The effect of CO on performance of modified MEA by sputtering method is studied in this paper. The experimental results show that sputtered Pt and Ru thin film improve a single cell performance of MEA and sputtered metal thin film has a CO tolerance. The air injection process on anode show improved CO tolerance test result. Moreover, Pt, Ru and PtRu thin film by sputtering had influence on the CO tolerance with air injection process.

• Journal of Hydrogen and New Energy
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• v.35 no.3
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• pp.345-351
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• 2024

The unitized regenerative fuel cell (URFC) is a method that can reduce costs and increase system simplification by unitizing a fuel cell system and a water electrolysis system. The spray method is suitable as the membrane electrode assembly (MEA) manufacturing method for URFC because it is easy to control the amount of catalyst, the size of the system is small, and economical manufacturing is possible. In this study, a numerical analysis of the effect of solution concentration on the spray method was performed to use it as basic data for the spray method to be used in MEA manufacturing. As result, as the Nafion solution concentration decreases it was found that the spray speed and the mass flow rate and the discrete phase model concentration increases and the spray range widens.

• Journal of Hydrogen and New Energy
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• v.11 no.1
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• pp.19-27
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• 2000

The polymer electrolyte membrane fuel cell (PEMFC) system was developed. In order to enhance the performance of membrane electrode assembly (MEA), the transfer printing method of the electrocatalyst layer on membrane was developed. The $H_2/O_2$ single cell with an electrode area of $50cm^2$ was fabricated and tested using 20 wt.% Pt/C as an electrocatalyst and the commercial and hand-made MEA such as Nafion 115, Hanwha, Dow, Flemion T and Gore Select. The 100-cell PEMFC stack with an active electrode area of $300cm^2$ was designed and fabricated using 40 wt.% Pt/C and 30 wt.% Pt-Ru/C as a cathode and anode electrocatalysts, respectively. The performance of PEMFC system was obtained to be 7kW (250A at 28V) and 3.5kW (70A at 50V) at $80^{\circ}C$ by flowing $H_2/air$ and methanol reformed fuel gas/air, respectively.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.329-334
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• 2009

This study is to develop a fuel cell system applicable to an in situ NMR (Nuclear magnetic resonance) diagnosis. The in situ NMR can be used in real time monitoring of various reactions occurring in the fuel cell, such as oxidation of fuel, reduction of oxygen, transport phenomena, and component degradation. The fuel cell for this purpose is, however, to be operated in a specifically designed tubular shape toroid cavity detector (TCD), which constrains the fuel cell to have a tubular shape. This may cause difficulties in effective mass transport of reactants/products and uniform distribution of assembly pressure. Therefore, a new flow field designed in a particular way is necessary to enhance the mass transport in the tubular fuel cell. In this study, a tubular-shaped close-type flow field made of non-magnetic material is developed. With this flow field, oxygen is effectively delivered to the cathode surface and the produced water is readily removed from the membrane-electrode assembly to prevent flooding. The resulting DMFC (direct methanol fuel cell) outperforms the open-type flow field and exhibits $36\;mW/cm^2$ even at room temperature.

• Clean Technology
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• v.19 no.1
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• pp.59-64
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• 2013

Pt/carbon Electrode catalysts for PEMFC were synthesized using colloidal method. PSA (platinum sulfite acid) was used as a Pt precursor and CPA (chloroplatinic acid) was also used to replace relatively expensive PSA. Electrode catalysts prepared using PSA showed Pt particle size less than 3.5 nm and Pt yield higher than 90% in 10~40 wt% Pt loading. Electrode catalysts prepared using CPA also showed Pt particle size less than 4.4 nm and Pt yield higher than 80% in 10~40 wt% Pt loading. The MEA (membrane electrode assembly) using 20 wt% Pt/VXC72 showed equivalent I-V curve comparing with commercial electrode catalyst in single cell test.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.93-96
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• 2007

Recently, much attentions have been paid on the commercialization of PEMFC, especially for the applications of residential and portable. In order to achieve the early commercialization of PEMFC, thee are two hurdles to overcome. One is cost down and the other is improvement of durability of the system components. Numerous companies have tried to reduce the production cost and the main research topics have been changed from performance to durability improvement. In this work, acceleration test were performed to find and evaluate the main reason of degradation of the MEA(membrane-electrode assembly) which is one of the core component of the PEMFC system. Based upon the test results, a way to make durable MEA was suggested. Acceleration tests were made by applying high voltage of 1.2V to the several kinds of single cells to increase the growth of catalyst particles. Cell performance, ac-impedance and electrochemically active area measurements were made atfter every 8 hours of acceleration test. Degradations of catalyst and membrane were examined by SEM, TEM and XRD. Obtained results were discussed in terms of structural stability and loss of catalyt and ionomers in the electrode layer. In addition, the way to make highly durable MEA was suggested.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.120.1-120.1
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• 2014

Fast-steering Secondary Mirror prototype (FSMP) of the Giant Magellan Telescope (GMT) has been developed by the consortium consisting of institutes in Korea and the US. In 2014 we are finalizing the FSMP project as combining two sub-systems, the mirror fabricated by Korea Research Institute of Standards and Science (KRISS) and the mirror cell with tip-tilt controlling system developed by Institute for Advanced Engineering (IAE), in the KRISS facility. In the assembly process we will identify potential difficulties or problems for the process, such that this process can be reflected to the further development of the FSM for GMT. In the presentation, we present how the assembly process can be carried out in safety.