Analysis of Proton Transport in Pseudo Catalyst Layers

Iden, Hiroshi; Ohma, Atsushi; Shinohara, Kazuhiko

doi:10.1149/1.3169514

Cited by 75 publications

(93 citation statements)

References 21 publications

(25 reference statements)

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“…Strictly speaking, ineff  is not exactly equal to  , however, they do not seem far from each other because the diffusion layer thickness in the MEA, which corresponds to the ionomer thickness, was thought to be extremely thin (2~3 nm) [30]. Both ineff  and  increased with increasing potential.…”

Section: mentioning

confidence: 97%

Analysis of effective surface area for electrochemical reaction derived from mass transport property

Iden

Kucernak

2014

Journal of Electroanalytical Chemistry

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The effective surface area, eff S , for electrochemical reaction at a Pt electrode was analyzed using mass transport property as a probe. This parameter is different to the socalled electrochemical surface area (ECA), which is usually obtained from the amount of protons which are underpotentially deposited, UPD H , or by CO stripping. The analysis was done using both experimental and numerical methods. In experiments, a rotating disk electrode (RDE) was used under the conditions where the Pt surface can be partially covered by Pt oxides or CO. For numerical analysis, three mass transport models based on diffusion, convection and convective-diffusion were used. As a result, it was found that it is possible to estimate eff S from the change in Koutecky-Levich slope at high rotation speeds. The analysis suggests that eff S does decrease notably from relatively low potential (around 0.4 V), even though it is not obvious in measured currents as the effect is masked by the low rates of mass transport. The analysis also suggests that there is a large difference in eff S with different methods, namely, estimation from the amount of Pt oxides and the analysis derived from mass transport property.Keywords: Effective surface area; RDE; HOR; catalyst Research highlights ▶ Estimation of effective surface area was possible by analyzing mass transport. ▶ Inactive domain size could also be estimated from the analysis. ▶ Effectiveness decreased notably from relatively low potential unlike Pt oxide growth.

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Section: mentioning

confidence: 97%

Analysis of effective surface area for electrochemical reaction derived from mass transport property

Iden

Kucernak

2014

Journal of Electroanalytical Chemistry

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“…38 Studies have shown that this interfacial resistance is a significant component of voltage loss as it scales with reduced platinum loading and that it is much higher than expected based on oxygen permeability through bulk ionomer as discussed in more detail in another section below. [46][47][48][49] Currently in a parametric model, this resistance is accounted for by using an unrealistically thick ionomer or electrolyte layer with bulk ionomer (membrane) transport properties.…”

Section: Journal Of the Electrochemical Society 161 (12) F1254-f1299mentioning

confidence: 99%

“…∇T k [47] whereH i,k is the partial molar enthalpy of species i in phase k, J i,k is the flux density of species i relative to the mass-average velocity of phase k [48] and k…”

Section: Basic Governing Equationsmentioning

confidence: 99%

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Weber

Borup

Darling³

et al. 2014

J. Electrochem. Soc.

485

394

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Polymer-electrolyte fuel cells are a promising energy-conversion technology. Over the last several decades significant progress has been made in increasing their performance and durability, of which continuum-level modeling of the transport processes has played an integral part. In this review, we examine the state-of-the-art modeling approaches, with a goal of elucidating the knowledge gaps and needs going forward in the field. In particular, the focus is on multiphase flow, especially in terms of understanding interactions at interfaces, and catalyst layers with a focus on the impacts of ionomer thin-films and multiscale phenomena. Overall, we highlight where there is consensus in terms of modeling approaches as well as opportunities for further improvement and clarification, including identification of several critical areas for future research. Fuel cells may become the energy-delivery devices of the 21 st century. Although there are many types of fuel cells, polymer-electrolyte fuel cells (PEFCs) are receiving the most attention for automotive and small stationary applications. In a PEFC, fuel and oxygen are combined electrochemically. If hydrogen is used as the fuel, it oxidizes at the anode releasing proton and electrons according toThe generated protons are transported across the membrane and the electrons across the external circuit. At the cathode catalyst layer, protons and electrons recombine with oxygen to generate waterAlthough the above electrode reactions are written in single step, multiple elementary reaction pathways are possible at each electrode. During the operation of a PEFC, many interrelated and complex phenomena occur. These processes include mass and heat transfer, electrochemical reactions, and ionic and electronic transport. * Electrochemical Society Active Member. z E-mail: azweber@lbl.govOver the last several decades significant progress has been made in increasing PEFC performance and durability. Such progress has been enabled by experiments and computation at multiple scales, with the bulk of the focus being on optimizing and discovering new materials for the membrane-electrode-assembly (MEA), composed of the proton-exchange membrane (PEM), catalyst layers, and diffusionmedia (DM) backing layers. In particular, continuum modeling has been invaluable in providing understanding and insight into processes and phenomena that cannot be resolved or uncoupled through experiments. While modeling of the transport and related phenomena has progressed greatly, there are still some critical areas that need attention. These areas include modeling the catalyst layer and multiphase phenomena in the PEFC porous media.While there have been various reviews over the years of PEFC modeling 1-7 and issues, [8][9][10][11][12][13][14] as well as numerous books and book chapters, there is a need to examine critically the field in terms of what has been done and what needs to be done. This review serves that purpose with a focus on transport modeling of PEFCs. This is not meant to be an exhaustive review...

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“…The information of y H+ gained from esterification was further used to estimate the overall conductivity of a catalyst layer using the modified agglomerate model and the correlation between conductivity and ammonium ion content (y NH4+ ). The estimated effective conductivities of a cathode catalyst layer ( Cathode cat ovrall  ) was validated with the available literature data at two extreme conditions (non-poisoned [Iden 2009] and fully ammonium-poisoned [Uribe 2002]) and found to be in good agreement at all humidity ranges. This study showed that the characterization reaction also has the potential to be applied to quantitatively examine the number of proton/acid sites of other proton conducting materials impregnated on other supports (e.g., carbon, Pt/C, alloyed Pt/C) for a PEMFC under a wide range of conditions.…”

Section: 26-4 Conclusionmentioning

confidence: 72%

“…A typical set of model parameters for the effective conductivity calculation at the cathode are given in reference ] and the expression for the overall effective conductivity ( Due to the lack of direct measurements of the conductivity of a poisoned catalyst layer, the accuracy of our predicted effective conductivity was validated using the experimental conductivity of an uncontaminated catalyst layer and the percentage of performance degradation of a fully ammonium-poisoned PEMFC. In Figure 4.2.6-2, the unfilled circles indicate the experimental conductivity at various humidities and 80C of an uncontaminated catalyst layer determined by a hydrogen pump technique employed by reference [Iden 2009] and the dashed line represents a fit of their data. The solid line shows the predicted conductivity of the cathode catalyst layer ( cathode cat overall  ) calculated from Eq.…”

Section: Modified Steady-state Agglomerate Model To Predict the Overamentioning

confidence: 99%

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Goodwin¹,

Colón-Mercado²,

Hongsirikarn³

et al. 2011

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EXECUTIVE SUMMARYThe main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. This project was carried out primarily at Clemson University and the Savannah River National Lab. Fuel cell investigations were done at SRNL while all investigations of the MEA components were carried out at Clemson. Meetings took place weekly at Clemson University and at SRNL with the respective project participants. Joint meetings between researchers at Clemson and SRNL took place quarterly, on average. In addition, frequent communications among project participants took place via e-mail and telephone discussions. On other occasions the researchers met with the technical staff of John Deere for discussions. At least one member of our team routinely participated in the DOE-Sponsored Joint Hydrogen Quality Task Force Meetings (usually conducted monthly).The nature and concentrations of impurities investigated and their impact on fuel cell performance and individual components are given in the table below. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion.Even though already well known as fuel cell poisons, the effects of CO and NH 3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization.New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H 2 -D 2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts.Using a combination of standard catalyst characterization techniques, a structure sensitive catalytic reaction technique (cyclopropane hydrogenolysis), and reaction and transport modeling led to the finding that in the catalyst layer (essentially Nafion/Pt/C) the following best describes the structure. Pt is highly dispersed on the C support, but primarily in the meso-and macropores. The Nafion (ca. 30 wt%) resides primarily on the external surface of the C support where it blocks significant numbers ...

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Analysis of Proton Transport in Pseudo Catalyst Layers

Cited by 75 publications

References 21 publications

Analysis of effective surface area for electrochemical reaction derived from mass transport property

Analysis of effective surface area for electrochemical reaction derived from mass transport property

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

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