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Broka, K.; Ekdunge, P.

doi:10.1023/a:1018476612810

Cited by 213 publications

(87 citation statements)

References 17 publications

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“…The fits are shown in agg R Figure 13. As is readily apparent, the PEA model fits the experimental data much better than the others, in agreement with other literature comparisons that used simpler fuel-cell and membrane models [204][205][206]. For the three cases, the PEF model mainly follows the PE model in terms of fitting the curve, with the possible exception of case (c) where the PEF model results in a better fit.…”

Section: Reaction-site Models (Local Length Scale)supporting

confidence: 88%

Macroscopic Modeling of Polymer-Electrolyte Membranes

Weber

Newman

2007

Advances in Fuel Cells

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Section: Reaction-site Models (Local Length Scale)supporting

confidence: 88%

Macroscopic Modeling of Polymer-Electrolyte Membranes

Weber

Newman

2007

Advances in Fuel Cells

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“…For example, one of the pioneering agglomerate modeling studies employed an agglomerate radius ranging from 1-5 μm based on their SEM images. 8 On the other hand, a recent experimental study 40 suggests that the carbon particles form agglomerates of about 100-120 nm. In particular, modeling studies employ a wider range of agglomerate radius of between 0.5-5 μm compared to experimental observations such as.…”

Section: Model Descriptionmentioning

confidence: 99%

An Improved Agglomerate Model for the PEM Catalyst Layer with Accurate Effective Surface Area Calculation Based on the Sphere-Packing Approach

Cetinbas

Advani

Prasad

2014

J. Electrochem. Soc.

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The complex porous structure of the PEM fuel cell catalyst layer (CL) necessitates the use of multiscale modeling strategies such as the agglomerate approach. In this study a 2D steady-state model for the cathode CL is developed using the spherical agglomerate approach. A new, more accurate, method is introduced to determine the effective agglomerate surface area, which plays a key role in estimating diffusion losses in the CL. Specifically, the reduction in the effective surface area due to overlapping particles is modeled geometrically based on a sphere-packing approach. In addition, the equations for the agglomerate model are reformulated to correctly account for the agglomerate surface area reduction due to overlapping particles. The importance of an accurate geometric model for the effective surface area is demonstrated by investigating the effect of CL composition on performance, and the results show that the new method provides more realistic predictions than the existing approach. Results from the new approach for optimal Pt loading, ionomer loading, and Pt|C ratio show good agreement with experimental results. Great strides have been made in proton exchange membrane (PEM) fuel cell research since the introduction of the technology in the early 1960s. Computational models represent a major tool for the design and development of PEM fuel cells because they decrease the dependence on expensive and time-consuming experimental procedures. Accurate computational models can also provide key insights into the fundamental processes that govern fuel cell performance. The overall accuracy of computational models depends strongly on the description of the catalyst layer (CL) as all the critical electrochemical reactions, and heat and mass transport processes occur within the CL. Therefore, developing better modeling strategies for the CL has been an important research objective to obtain a realistic representation of PEM fuel cell behavior.Catalyst layer modeling approaches, which have grown in complexity in the past decades, were described in detail in. 1 Here, we present only a brief review. Among the models reported, the interface model 2-4 is the simplest approach as it represents all of the CL activity as boundary conditions applied at the interface between the membrane and the gas diffusion layer (GDL). The macro-homogenous model [4][5][6][7] is a more advanced approach that utilizes the effective medium theory and approximates the CL as a porous matrix of gas pores, platinum, carbon, and electrolyte. The most comprehensive device-level model to date is the agglomerate approach [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] as it represents CL activity as a multiscale problem. Overall, the CL is assumed to consist of gas pores and aggregates of C|Pt particles that are covered by an electrolyte film. The agglomerate approach attempts to model the C|Pt aggregates (shown schematically in Fig. 1a) that are typically seen in microscopic images of the CL. For simplicity, the aggregate microstructure, de...

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“…and a potential gradient in the ohm's law for ionic current can be replaced by the gradient of local overpotential, (13) where and are the solid-and ionomer-phase potentials, respectively, and U is the theoretical local equilibrium potential of a cathode with respect to the reference O 2 electrode. …”

Section: Kineticsmentioning

confidence: 99%

“…Most CL models using a particle model employ the effectiveness-factor approach for calculating the ORR. 11,13,16,[37][38][39] For a first-order reaction with no other transport limitations, an analytic expression for the effectiveness factor is obtained, 12,14,37 where Φ is the Thiele modulus (11) …”

mentioning

confidence: 99%

Modeling Low-Platinum-Loading Effects in Fuel-Cell Catalyst Layers

Yoon¹,

Weber²

2011

J. Electrochem. Soc.

141

122

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The cathode catalyst layer within a proton-exchange-membrane fuel cell is the most complex and critical, yet least understood, layer within the cell. The exact method and equations for modeling this layer are still being revised and will be discussed in this paper, including a 0.8 reaction order, existence of Pt oxides, possible non-isopotential agglomerates, and the impact of a film resistance towards oxygen transport. While the former assumptions are relatively straightforward to understand and implement, the latter film resistance is shown to be critically important in explaining increased mass-transport limitations with low Pt-loading catalyst layers. Model results demonstrate agreement with experimental data that the increased oxygen flux and/or diffusion pathway through the film can substantially decrease performance. Also, some scale-up concepts from the agglomerate scale to the more macroscopic porous-electrode scale are discussed and the resulting optimization scenarios investigated. IntroductionThe catalyst layer (CL) is a very complex chemical and geometric environment for electrochemical reactions in proton-exchange-membrane fuel cells (PEMFCs). It is composed of supported catalyst particles, ionomer, and gas pores. The reaction occurs at sites where various reacting species such as protons, electrons, and gases meet. Modeling the structure has been approached by various means 1 , and a rigorous mathematical model of the CL is required to capture transport within the different phases, electrochemical reaction, and heat and water generation. Among previous models, one of the most accepted models is an agglomerate particle composed of the ionomer, gas voids, liquid water, and catalyst that is covered by a thin film of ionomer . This idea is supported by various experimental observations such as scanningelectron-and transmission-electron-microscopy studies. In this model, oxygen is dissolved in the ionomer film surrounding the agglomerate, and the dissolved oxygen diffuses to the agglomerate where simultaneous transport and reaction occur. Typically, the agglomerate model is embedded (i.e., distributed uniformly across the CL) into a porous-electrode model to describe the CL fully 1 . _ENREF_29Optimization of the CL for enhancing PEMFC performance is of great interest for researchers and industry. Parametric studies of CLs were accomplished by Yin 14 using an agglomerate model, with the model predicting the general polarization-curve trend as a function of parameters such as gas void fraction 7,16 and ionomer 4,5,10,29 and catalyst loadings 5,10,[30][31][32] within the CL.Similarly, several optimization studies 16,22,30 using an agglomerate model were conducted to obtain optimum design parameters such as catalyst loading, CL thickness, and Pt/C ratio for best performance at a given potential. However, all the studies were based on several assumptions 4 and issues that are not correct validated or possibly correct including a lack of ionomer films and a first-order oxygen dependence for the oxygen redu...

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Untitled

Cited by 213 publications

References 17 publications

Macroscopic Modeling of Polymer-Electrolyte Membranes

Macroscopic Modeling of Polymer-Electrolyte Membranes

An Improved Agglomerate Model for the PEM Catalyst Layer with Accurate Effective Surface Area Calculation Based on the Sphere-Packing Approach

Modeling Low-Platinum-Loading Effects in Fuel-Cell Catalyst Layers

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