• Journal of Hydrogen and New Energy
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• v.23 no.1
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• pp.8-18
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• 2012

This paper presents a three-dimensional, transient cold-start polymer electrolyte fuel cell (PEFC) model to numerically evaluate the effects of membrane electrode assembly (MEA) design and cell location in a PEFC stack on PEFC cold start behaviors. The cold-start simulations show that the end cell experiences significant heat loss to the sub-freezing ambient and thus finally cold-start failure due to considerable ice filling in the cathode catalyst layer. On the other hand, the middle cells in the stack successfully start from $-30^{\circ}C$ sub-freezing temperature due to rapid cell temperature rise owing to the efficient use of waste heat generated during the cold-start. In addition, the simulation results clearly indicate that the cathode catalyst layer (CL) composition and thickness have an substantial influence on PEFC cold-start behaviors while membrane thickness has limited effect mainly due to inefficient water absorption and transport capability at subzero temperatures.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.338-343
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• 2019

The water transport and water content of the electrolyte membrane greatly affect the performance of the membrane in PEMFC(Proton Exchange Membrane Fuel Cell). In this study, the parameters (electroosmotic coefficient, water diffusion coefficient) of polymer membranes for water transport were measured by a simple method, and water flux and ion conductivity were simulated by using a model equation. One dimensional steady state model equation was constructed by using only the electro-osmosis and diffusion as the driving force of water transport. The governing equations were simulated with MATLAB. The electro-osmotic coefficient of $144{\mu}m$ thick polymer membranes was measured in hydrogen pumping cell, the value was 1.11. The water diffusion coefficient was expressed as a function of relative humidity and the activation energy for water diffusion was $2,889kJ/mol{\cdot}K$. The water flux and ion conductivity results simulated by applying these coefficients showed good agreement with the experimental data.

• Proceedings of the Membrane Society of Korea Conference
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• 2005.05a
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• pp.144-147
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• 2005

• Proceedings of the Membrane Society of Korea Conference
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• 2005.11a
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• pp.212-214
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• 2005

• 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.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.302-306
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• 2017

Humidity affect performance and durability of proton exchange membrane fuel cell (PEMFC). High humidity of gases generally enhance the performance, but high humidity have the danger of flooding. I-V performance, linear sweep voltammetry, cyclo voltammetry, and impedance of micro-channel cell measured with change of relative humidity (RH). Flooding phenomena started at RH 70%. Ion conductivity of membrane reached maximum value at RH 80%. Maximum current density of $1,700mA/cm^2$ (at 0.6 V) was obtained at RH 80%. Therefore the effect of ion conductivity increasement was higher than that of mass transfer decrease by flooding at RH 80%.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.180-184
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• 2005

An experimental study is performed to evaluate the performance and the efficiency by humidifying MEA and by making the double-tied catalyst layers in a fuel cell system which is taken into account the physical and thermal concept. An electrical output produced by PEFC(polymer Electrolyte Fuel Cell) is measured to assess the performance of the stack and the efficiency is also evaluated according to the different situation in which is placed with and without the humidification of MEA (Membrane Electrolyte Assembly). Subsequently, It is found that the measured values of stack voltage and current are influenced by the stack temperature, humidification, and the double-tied catalyst layers which gives more enhanced values to apply for electric units.

• Korean Chemical Engineering Research
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• v.51 no.3
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• pp.370-375
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• 2013

We analyze the effects of CO poisoning and air bleeding on the performance of a PEM (polymer electrolyte membrane) fuel cell stack fabricated using commercial MEA (membrane electrode assembly). Dynamic response data from the experiments on the performance of a stack are identified by obtaining steady-state gains and time-constants of the first-order system model expressed as a first-order differential equation. It is found that the cell voltage of the stack decreases by 1.3-1.6 mV as the CO concentration rises by 1 ppm. The time elapsed to reach a new steady state after a change in the CO concentration is shortened as the magnitude of the change in the CO concentration increases. In general, the steady-state gain becomes bigger and the time-constant gets smaller with increasing the air concentration (air-bleeding level) in the reformate gas to restore the cell voltage. However, it is possible to recover 87%-96% of the original cell voltages, which are measured with free of CO, within 1-30 min by introducing the bleed air as much as 1% of the reformate gas into the stack.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.1-5
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• 2018

In this work, we study the ion conductivity by analyzing the impedance to the high current density range that the PEMFC (Proton Exchange Membrane Fuel Cell) is actually operated. The effect of GDL (Gas Diffusion Layer)presence on impedance was investigated indirectly by measuring hydrogen permeability. When the RH (Relative Humidity)was higher than 60% in the low current range (< $80mA/cm^2$), the moisture content of the polymer membrane was sufficient and the ion conductivity of the membrane was not influenced by the current change. However, when RH was low, ion conductivity increased due to water production as current density increased. The ion conductivity of the membrane obtained by HFR (High Frequency Resistance) in the high current region ($100{\sim}800mA/cm^2$)was compared with the measured value and simulated value. At RH 100%, both experimental and simulated values showed constant ion conductivity without being influenced by current change. At 30~70% of RH, the ionic conductivity increased with increasing current density and tended to be constant.

• Journal of Hydrogen and New Energy
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• v.19 no.2
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• pp.103-110
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• 2008

The most failure mode of PEM fuel cell is gas crossover caused by pinhole formation in MEAs. The degradation phenomena of MEA with pinholes were evaluated in various accelerated operation condition, such as OCV, low humidity and high partial pressure of oxygen. The performances of MEA with pinholes were almost same before and after normal 144 hours operation($70^{\circ}C$, $640mA/cm^2$, 65%RH $H_2/air$). The results of accelerated operation showed that OCV and low humidity condition more deteriorated MEA than gas crossover owing to pinholes. When oxygen was used as cathode gas, the pinholes of MEA were enlarged due to heat of combustion reaction on Pt catalyst of electrodes. This combustion reaction occurred at pinholes near gas inlet and resulted in local MEA failure.