Effects of inlet relative humidity (RH) on the performance of a high temperature-proton exchange membrane fuel cell (HT-PEMFC)

Chippar, P.,Kang, K.,Lim, Y.D.,Kim, W.G.,Ju, H. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.6

<P>A high temperature-proton exchange membrane fuel cells (HT-PEMFC) based on phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane is able to operate at elevated temperature ranging from 100 to 200 degrees C. Therefore, it is evident that the relative humidity (RH) of gases within a HT-PEMFC must be minimal owing to its high operating temperature range. However, it has been continuously reported in the literature that a HT-PEMFC performs better under higher inlet RH conditions. In this study, inlet RH dependence on the performance of a HT-PEMFC is precisely studied by numerical HT-PEMFC simulations. Assuming phase equilibrium between membrane and gas phases, we newly develop a membrane water transport model for HT-PEMFCs and incorporate it into a three-dimensional (3-D) HT-PEMFC model developed in our previous study. The water diffusion coefficient in the membrane is considered as an adjustable parameter to fit the experimental water transport data. In addition, the expression of proton conductivity for PA-doped PBI membranes given in the literature is modified to be suitable for commercial PBI membranes with high PA doping levels such as those used in Celtec (R) MEAs. Although the comparison between simulations and experiments shows a lack of agreement quantitatively, the model successfully captures the experimental trends, showing quantitative influence of inlet RH on membrane water flux, ohmic resistance, and cell performance during various HT-PEMFC operations. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.</P>

Numerical modeling and investigation of gas crossover effects in high temperature proton exchange membrane (PEM) fuel cells

Chippar, P.,Ju, H. Elsevier Science B.V., Amsterdam. 2013 International journal of hydrogen energy Vol.38 No.17

Coupled mechanical stress and multi-dimensional CFD analysis for high temperature proton exchange membrane fuel cells (HT-PEMFCs)

Chippar, P.,Oh, K.,Kim, D.,Hong, T.-W.,Kim, W.,Ju, H. Elsevier Science B.V., Amsterdam. 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.17

Numerical analysis of effects of gas crossover through membrane pinholes in high-temperature proton exchange membrane fuel cells

Chippar, P.,Oh, K.,Kim, W.G.,Ju, H. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.6

Durability is a major issue in the widespread commercialization of proton exchange membrane fuel cells (PEMFCs). Various failure modes have been identified over their long runtime. These mainly originate from membrane and catalyst layer failures. One of the most common failure modes in PEMFCs is due to pinhole formation in the membrane and resultant reactant gas crossover through the membrane. Gas crossover induces several critical problems in PEMFCs, including severe reactant depletion in the downstream regions, mixed potential at the electrodes, and formation of local hot spots by hydrogen/oxygen catalytic reaction, which indicates that the cell performance decreases with increasing gas crossover. In this study, we numerically investigate the effects of gas crossover on the performance of a high-temperature PEMFC based on a phosphoric-acid-doped polybenzimidazole (PBI) membrane. In contrast to previous gas-crossover studies [1,2] in which uniform gas crossover throughout the entire membrane has been simply assumed, our focus is on examining the impacts of localized gas crossover due to membrane pinholes. Numerical simulations are carried out via arbitrarily assuming pinholes in the membrane. The simulation results clearly show that the presence of pinholes in the membrane significantly disrupts the species, current density, and temperature distributions. Our findings may improve the fundamental and detailed understanding of localized gas-crossover phenomena through the membrane pinholes and the influence of these phenomena on high-temperature PEMFC operation.

One-dimensional, Transient DMFC Modeling and Simulations

푸루소타마(Purushothama Chippar),고요한(Johan Ko),주현철(Hyunchul Ju) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

A one dimensional two phase, multi-component, transient DMFC model has been developed to investigate transient and thermal behaviors of DMFCs as well as the detailed species transport, methanol crossover, stoichiometric ratio effects on cell performance. The present 1D model considers transport processes through the cell thickness and thereby consists of three DMFC segments namely, anode backing layer, cathode backing layer and membrane with an assumption that catalyst layers are infinitely thin interfaces between backing layers and membrane. Stefan-Maxwell multi-component diffusion equation is employed to formulate methanol and water transport through porous media, while Darcy's law is used to describe liquid flow due to capillary action. The 1D transient DMFC model successfully captures the coupled thermal and transient behaviors of DMFC under various operating conditions and cell designs, which indicates that the present 1D DMFC model is a useful tool in optimizing cell operating conditions and material/design parameters.

Numerical analysis of gas crossover effects in polymer electrolyte fuel cells (PEFCs)

Nam, J.,Chippar, P.,Kim, W.,Ju, H. Applied Science Publishers 2010 APPLIED ENERGY Vol.87 No.12

The gas crossover phenomenon in polymer electrolyte fuel cells (PEFCs) is an indicator of membrane degradation. The objective of this paper is to numerically investigate the effects of hydrogen and oxygen crossover through the membrane in PEFCs. A gas crossover model is newly developed and implemented in a comprehensive multi-dimensional, multi-phase PEFC model developed earlier. A parametric study is carried out to investigate the effects of the crossover diffusion coefficients for hydrogen and oxygen as well as the membrane thickness. The simulation results demonstrate that the hydrogen crossover induces an additional oxygen reduction reaction (ORR) and consequently causes an additional voltage drop, while the influence of oxygen crossover on PEFC performance is relatively insignificant because it leads to the hydrogen/oxygen chemical reaction at the anode side. Finally, using the time-dependent gas crossover data that are available in the literature (measured in days), we conduct gas crossover simulations to examine the effects of increased gas crossover due to membrane degradation on PEFC performance and successfully demonstrate decaying polarization curves with respect to time. This study clearly elucidates the detailed mechanisms of the hydrogen and oxygen crossover phenomena and their effect on PEFC performance and durability.

Numerical study of thermal stresses in high-temperature proton exchange membrane fuel cell (HT-PEMFC)

Oh, K.,Chippar, P.,Ju, H. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.6

The purpose of this work is to numerically examine the thermal stress distributions in a high-temperature proton exchange membrane fuel cell (HT-PEMFC) based on a phosphoric acid doped polybenzimidazole (PBI) membrane. A fluid structure interaction (FSI) method is adopted to simulate the expansion/compression that arises in various components of a membrane electrode assembly (MEA) during the HT-PEMFC assembly processes, as well as during cell operations. First, three-dimensional (3-D) finite element method (FEM) simulations are conducted to predict the cell deformation during cell clamping. Then, a nonisothermal computational fluid dynamic (CFD)-based HT-PEMFC model developed in a previous study [1] is applied to the deformed cell geometry to estimate the key species and temperature distributions inside the cell. Finally, the temperature distributions obtained from these CFD simulations are employed as the input load for 3-D FEM simulations. The present numerical study provides a fundamental understanding of the stress-temperature interaction during HT-PEMFC operations and demonstrates that the coupled FEM/CFD HT-PEMFC model presented in this paper can be used as a useful tool for optimizing HT-PEMFC clamping and operating conditions.

1차원 DMFC 모델을 이용한 메탄올 크로스오버 영향성 연구

고요한(Johan Ko),푸루소타마(Purushothama Chippar),주현철(Hyunchul Ju) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

A 1-dimensional numerical simulation model has been developed for a direct methanol fuel cells (DMFCs). The computational domain for this model includes anode gas diffusion layer(GDL), anode catalyst layer, membrane, cathode catalyst layer and cathode gas diffusion layer. The model determines the channel/GDL boundary conditions by considering the stoichiometry ratio and feeding methanol or air concentrations on anode or cathode channel inlets. Using this 1D model, the effects of methanol crossover on cell performance has been studied under the various operating conditions and cell design parameters such as temperature, feed methanol concentration, current density, stoichiometry ratio, and material properties. According to the 1D simulation results, the amount of methanol crossover highly depends on these parameters and considerably alters DMFC performance in terms of DMFC power density and energy efficiency.