• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.6-10
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• 2016

Until a recent day, degradation of PEMFC (Proton Exchange Membrane Fuel Cells) has been mainly studied in unit cell. But operation and degradation of real PEMFC going along in stack instead of unit cell. Therefore in this work, ADT (Accelerated Degradation Test) of PEMFC was done in stack and the result from stack's test was compared with that of unit cell. The polymer electrolyte membrane was degraded by repeated electrochemical and mechanical degradation method among several ADT methods. Current densities of MEA at 0.6V decreased in stack and unit cell, 28.4% and 27.8% respectively after ADT for 312 hours. Hydrogen crossover current densities of membrane increased in stack and unit cell, 16.8% and 15.2% respectively after ADT for 312 hours. The result of ADT in stack was similar that of ADT in unit cell, which showed that ADT method of unit cell was available to the stack.

• Journal of Hydrogen and New Energy
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• v.27 no.2
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• pp.144-154
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• 2016

HT-PEMFC (high temperature polymer electrolyte membrane fuel cell) using PA (phosphoric acid) doped PBI (polybenzimidazole) membrane has been researched for extending the lifetime. However, the existing work on durability of HT-PEMFC focuses on identifying degradation causes of lab scale. The short life time of HT-PEMFC is still the problem for its commercialization. In this paper, an operating method to maximize life time of 5kW HT-PEMFC stack are proposed. The proposed method includes major steps such as minimization of OCV (Open Circuit Voltage) exposure, control of the proper stack temperature, and N2 purging for the stack. This long life operating method was based on the fragmentary results of degradation from previous research works. Experimentally, the 5 kW homemade HT-PEMFC stack was operated for a long time based on the proposed method and the stack successfully can operate within the desired degradation rate for the target life time.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.3
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• pp.317-324
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• 2010

It was used as measuring system to diagnose insulating condition, by which was kept a insulating resistance of inner stack and at the same time was cooled electrochemical heat of reaction of FCEV(fuel cell electric vehicle) stack that used a compressed hydrogen gas reacting with oxygen in accordance with variation on thermal degradation of nonconductive heat transfer fluid. Consequently it was developed a cylindrical multi-terminal capacitive-conductive sensor that could be attached to the internal surface of cooling system pipe to evaluate capacitance and conductivity of heat transfer fluid.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.775-780
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• 2011

5-cell DMFC stack was fabricated and operated with the load of 4 A for 4000 hrs. After 4000 hrs operation peak power density of the stack reduced by 27.3%. Two of the five cells did now show performance degradation, the performance of other two was reduced by 40% and the performance of the other decreased by 60%. The amount of performance degradation of each cell by long-term operation did not correlate with the position in the stack. Platinum particle size in the anode catalyst layer of the MEA with the strongest degradation increased and the increase was severer on the position of methanol inlet than on the position of methanol outlet. However, platinum particle size in the cathode catalyst layers did not changed for all the MEA'. Ruthenium crossover from the anode catalyst layer to the cathode catalyst layer through the membrane was observed after 4,000 hrs operation by SEM-EDX and it occurred for all MEA' regardless of the degree of performance degradation. Atomic ratio of ruthenium to platinum in the cathode catalyst layer was the highest in the MEA with the strongest performance degradation.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.289-294
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• 2014

The stability of a solid oxide fuel cell (SOFC) stack is strongly dependent on the magnitude and profile of the internal chemical potential of the solid electrolyte. If the internal partial pressure is too high, the electrolyte can be delaminated from the electrodes. The formation of high internal pressure is attributed to a negative cell voltage, and this phenomenon can occur in a bad cell (with higher resistance) in a stack. This fact implies that the internal chemical potential plays an important role in determining the lifetime of a stack. In the present work, we fabricate planar type anode-supported cells ($25cm^2$) with a bi-layer electrolyte (with locally increased electronic conduction at the anode side) to prevent high internal pressure, and we test the fabricated cells under a negative voltage condition. The results indicate that the addition of electronic conduction in the electrolyte can effectively depress internal pressure and improve the cell stability.

• Membrane Journal
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• v.33 no.3
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• pp.127-136
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• 2023

In this study, the electrochemical performance of a 5-layer fuel cell stack using silica composite membranes as polymer electrolyte membranes was evaluated. It was observed that the flow rate of the fuel gases plays a crucial role in stack performance, particularly being mainly dependent on the flow rate of hydrogen. Increasing the flow rate of oxygen resulted in negligible changes in performance, whereas an increase in the flow rate of hydrogen demonstrated performance improvements. However, this led to an imbalance in the ratio of hydrogen to oxygen flow rates, causing significant degradation in stack performance and durability. A decline in stack performance was also observed over time due to the degradation of stack components. This phenomenon was consistently observed in individual unit cells. Based on these findings, it was emphasized that, in addition to optimizing the performance of each component during stack operation, it is important to optimize design and operating conditions for uniform flow rate control. Lastly, the developed silica composite membrane was assessed to have sufficient performance for application in actual fuel cell systems, exhibiting a performance of over 25 W based on maximum power.

• Journal of Hydrogen and New Energy
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• v.32 no.5
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• pp.315-323
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• 2021

The air-cooled proton exchange membrane fuel cells (PEMFC) stacks, which is widely used in small-sized PEMFC, have a problem in that durability is weaker than that of the water-cooled type. Because the cathode is open to the atmosphere and the structural problem of the air-cooled stack, which is difficult to maintain airtightness, is highly likely to form a hydrogen/air boundary during start-up/shut-down (SU/SD). Through the accelerated durability evaluation of the 20 W air-cooled PEMFC stack, the purpose of this study was to find out the cause of the degradation of the stack and to contribute to the improvement of the durability of the air-cooled PEMFC stack. In this study, it was possible to evaluate durability in a relatively short time by reducing 20-30% of initial performance by repeating SU/SD 1,000 to 1,200 times on an air-cooled PEMFC stack. After disassembling the stack, each cell was divided into two and the performance analysis showed that the electrode degradation was more severe in the anode outlet membrane electrode assembly (MEA), which facilitates air inflow as a whole, than in the inlet MEA. It was shown that the cathode Pt was dissolved/precipitated to deteriorate the polymer ionomer inside the membrane.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.12-19
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• 2022

Cathode open-type PEMFC (Proton Exchange Membrane Fuel Cells) stacks, which are widely used in small transport-type PEMFC, have a problem with poor durability. Through the accelerated durability test of the 13-cell PEMFC stack, we tried to find the cause of the degradation of the stack and to contribute to the improvement of the durability of the cathode open stack. A hydrogen/air boundary is formed during start-up/shut-down (SU/SD) due to the structural problem of the cathode open stack in which the cathode is open to the atmosphere and it is difficult to maintain airtightness, thereby deteriorating the cathode. In this study, it was possible to evaluate the durability in a relatively short time by reducing the 54% of the initial performance by repeating SU/SD 1,800 times on the cathode open stack. After dismantling the stack, each cell was divided into two and the performance was analyzed. Overall, the anode outlet MEA, which facilitates air inflow, showed more severe electrode deterioration than the inlet MEA, confirming that the hydrogen/air boundary formation during SU/SD is the main cause of degradation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.674-690
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• 2021

This study proposes a hybrid marine power system combining dual-fuel generators, a fuel cell, and Vanadium Redox Flow Batteries (VRFB). Rigorous verification and validation of the dynamic modelling and integration of the system are conducted. A case study for the application of the hybrid propulsion system to a passenger ship is conducted to examine its time-variant behaviour. A comprehensive model of the reversible and irreversible capacity degradation of the VRFB stack unit is proposed and validated. The capacity retention of the VRFB stack is simulated by being integrated within the hybrid propulsion system. Reversible degradation of the VRFB stack is precisely predicted and rehabilitated based on the predefined operational schedule, while the irreversible portion is retained until the affected components are replaced. Consequently, the advantages of the VRFB system as an on-board ESS are demonstrated through the application of a hybrid propulsion system for liner shipping with fixed routes.

• International Journal of High-Rise Buildings
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• v.1 no.2
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• pp.99-105
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• 2012

The higher the building height and the larger the temperature difference between the outdoor and indoor space, the more remarkable is the draft driven by the stack effect in high-rise buildings. Moreover, the stack effect can bring about the deterioration of habitability and the degradation of the performance of the indoor control system in high-rise buildings. In this study, as a measure to attenuate the stack effect, the E/V shaft cooling method was proposed and its performance was compared with the conventional stack effect control method for strengthening the air-tightness of the building using a numerical simulation method. The total decreasing ratios on the stack effect in a building were compared, and the probabilities of the secondary problems were analyzed. The results show that the E/V shaft cooling is very effective to decrease the stack effect in a high-rise building in terms of the reduction performance and application. Moreover, this method does not cause secondary problems, such as stack pressure transition to other walls, unlike the conventional stack effect mitigation method.