A Steady-State Impedance Model for a PEMFC Cathode

Guo, Qingzhi; White, Ralph E.

doi:10.1149/1.1648024

Cited by 67 publications

(53 citation statements)

References 12 publications

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“…15,40 Since the solid-phase potential is assumed uniform within the particle and using a reference oxygen electrode, the cathode overpotential can be reduced to…”

Section: Kineticsmentioning

confidence: 99%

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

Yoon¹,

Weber²

2011

J. Electrochem. Soc.

134

121

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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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“…15,40 Since the solid-phase potential is assumed uniform within the particle and using a reference oxygen electrode, the cathode overpotential can be reduced to…”

Section: Kineticsmentioning

confidence: 99%

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

Yoon¹,

Weber²

2011

J. Electrochem. Soc.

134

121

View full text Add to dashboard Cite

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“…catalyst utilization and performance) than on the understanding of kinetic mechanisms [88]. Many studies investigated phenomena occurring in the active layer, and some attention has been paid to the transport limitation inside the gas diffusion layer [89].…”

Section: Ii2 New Preparation Methods Of Efficient Electrode Catalystsmentioning

confidence: 99%

Do not forget the electrochemical characteristics of the membrane electrode assembly when designing a Proton Exchange Membrane Fuel Cell stack

Lamy

Jones

Coutanceau

et al. 2011

Electrochimica Acta

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International audienceThe membrane electrode assembly (MEA) is the key component of a PEMFC stack. Conventional MEAs are composed of catalyzed electrodes loaded with 0.1-0.4 mgPt cm−2 pressed against a Nafion® membrane, leading to cell performance close to 0.8 W cm−2 at 0.6 V. Due to their limited stability at high temperatures, the cost of platinum catalysts and that of proton exchange membranes, the recycling problems and material availability, the MEA components do not match the requirements for large scale development of PEMCFs at a low cost, particularly for automotive applications. Novel approaches to medium and high temperature membranes are described in this work, and a composite polybenzimidazole-poly(vinylphosphonic) acid membrane, stable up to 190 ◦C, led to a power density of 0.5 W cm−2 at 160 ◦C under 3 bar abs with hydrogen and air. Concerning the preparation of efficient electrocatalysts supported on a Vulcan XC72 carbon powder, the Bönnemann colloidal method and above all plasma sputtering allowed preparing bimetallic platinum-based electrocatalysts with a low Pt loading. In the case of plasma deposition of Pt nanoclusters, Pt loadings as low as 10 g cm−2 were achieved, leading to a very high mass power density of ca. 20 kW g−1 Pt . Finally characterization of the MEA electrical properties by Electrochemical Impedance Spectroscopy (EIS) based on a theoretical model of mass and charge transport inside the active and gas diffusion layers, together with the optimization of the operating parameters (cell temperature, humidity, flow rate and pressure) allowed obtaining electrical performance greater than 1.2 W cm−2 using an homemade MEA with a rather low Pt loading

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“…The closest approximation to the structure is one of clumps of carbon grains (agglomerates) coated with and connected by electrolyte, [6,[10][11][12][13][14]. A widely employed approach in modelling the CCL is to assume that the agglomerates are spherical in shape, [6,7,[15][16][17][18][19][20], and to incorporate the agglomerate-level activity into a homogeneous model by assuming that a thin film of electrolyte (or water) introduces a local resistance to the oxygen-motivated by the well-established theory of porous catalysts (see Chapter 3 of [21]). The three main variants are as follows:…”

Section: Introductionmentioning

confidence: 99%

“…• Include internal resistance to the oxygen movement, due to flooding of the agglomerates with electrolyte or liquid water-this yields an effectiveness factor for the oxygen diffusion coefficient, [16,17].…”

Section: Introductionmentioning

confidence: 99%

The effects of water and microstructure on the performance of polymer electrolyte fuel cells

Shah

Kim

Gervais

et al. 2006

Journal of Power Sources

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In this paper, we present a comprehensive non-isothermal, one-dimensional model of the cathode side of a Polymer Electrolyte Fuel Cell. We explicitly include the catalyst layer, gas diffusion layer and the membrane. The catalyst layer and gas diffusion layer are characterized by several measurable microstructural parameters. We model all three phases of water, with a view to capturing the effect that each has on the performance of the cell. A comparison with experiment is presented, demonstrating excellent agreement, particularly with regard to the effects of water activity in the channels and how it impacts flooding and membrane hydration. We present several results pertaining to the effects of water on the current density (or cell voltage), demonstrating the role of micro-structure, liquid water removal from the channel, water activity, membrane and gas diffusion layer thickness and channel temperature. These results provide an indication of the changes that are required to achieve optimal performance through improved water management and MEA-component design. Moreover, with its level of detail, the model we develop forms an excellent basis for a multi-dimensional model of the entire membrane electrode assembly.

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A Steady-State Impedance Model for a PEMFC Cathode

Cited by 67 publications

References 12 publications

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

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

Do not forget the electrochemical characteristics of the membrane electrode assembly when designing a Proton Exchange Membrane Fuel Cell stack

The effects of water and microstructure on the performance of polymer electrolyte fuel cells

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