Cold-Start of a PEFC Visualized with High Resolution Dynamic In-Plane Neutron Imaging

Oberholzer, Pierre; Boillat, Pierre; Siegrist, R.; Perego, R.C.; Kastner, Anders; Lehmann, Eberhard; Scherer, Günther G.; Wokaun, Alexander

doi:10.1149/2.085202jes

Cited by 78 publications

(107 citation statements)

References 67 publications

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“…This exposure time is well within the range typically used for neutron imaging on PEFCs (typically between 1 and 25 s [45,[51][52][53][54][55][56][57][58][59]82]). Since the current study investigates steady-state operation, the 12 s temporal resolution is sufficient.…”

mentioning

confidence: 82%

“…This technique is based on attenuation of a neutron by hydrogencontaining compounds such as water, and transparency to neutrons of most fuel cell construction materials (aluminium, stainless steel). Neutron imaging can identify water in the in-plane orientation (with the membrane place parallel to the beam) and through-plane orientation (with the membrane plane perpendicular to the beam), enabling in the first case to differentiate the water content from the cathode and the anode [48][49][50] and in the second case the effect of different designs, components, and operating conditions [45,[51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. Neutron imaging has been combined with other modelling and experimental techniques, such as current mapping [66], CFD models validation [32,51,65], optical imaging [47], neutron scattering [61] and localised EIS [45].…”

Section: Liquid Water Mapping In Fuel Cellsmentioning

confidence: 99%

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The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

Meyer

Ashton

Jervis

et al. 2015

Electrochimica Acta

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In situ diagnostic techniques provide a means of understanding the internal workings of fuel cells so that improved designs and operating regimes can be identified. Here, a novel metrology approach is reported that combines current and temperature mapping with water visualisation using neutron radiography.The approach enables a hydro-electro-thermal performance map to be generated that is applied to an air-cooled, open-cathode polymer electrolyte fuel cell. This type of fuel cell exhibits a particularly interesting coupled relationship between water, current and heat, as the air supply has the due role of cooling the stack as well as providing the cathode reactant feed via a single source. It is found that water predominantly accumulates under the cooling channels (thickness of 70-100 µm under the cooling channels and 5-25 µm in the active channels at 0.5 A cm KeywordsAir-cooled open-cathode polymer electrolyte fuel cell; water mapping; neutron imaging; temperature mapping; current mapping.

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mentioning

confidence: 82%

Section: Liquid Water Mapping In Fuel Cellsmentioning

confidence: 99%

The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

Meyer

Ashton

Jervis

et al. 2015

Electrochimica Acta

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“…This freezing can severely inhibit cell performance and often results in cell failure. [162][163][164][165][166] In recent years, several cold-start targets have been established by the Department of Energy. 167 Two key targets are that the PEFC must be able to start unassisted from -40…”

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confidence: 99%

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

Weber

Borup

Darling³

et al. 2014

J. Electrochem. Soc.

509

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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“…After filling a certain amount of the pore space with ice, the reactant gases are blocked, leading to a breakdown of the electrochemical reaction. Such claims were contradicted by visualization experiments, 3,6 which identified liquid water inside the GDL and flow channels. Furthermore, if all the product water would be systematically frozen, a reproducible operation time proportional to the quantity of water needed to block the electrode would be expected.…”

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confidence: 99%

When Size Matters: Active Area Dependence of PEFC Cold Start Capability

Biesdorf

Stahl

Siegwart

et al. 2015

J. Electrochem. Soc.

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Understanding the freezing mechanism of liquid water within polymer electrolyte fuel cells (PEFC) is crucial for its commercialization for mass market. Although various publications investigated the cold start capability of PEFCs, contradictory behaviors during cold starts at freezing temperatures have been published in literature. Interestingly, differences can be mainly identified between large and small size fuel cells: the latter have a significantly higher cold start capability than large size fuel cells. In order to understand the influence of different active areas, we present measurements of cold starts performed with cells sizes of 1 and 50 cm2 using the same materials, including a large count of experiments (>200) on the 1 cm2 cells to perform statistical analysis. The cold start capability is strongly reduced with an increasing size of the active area, and the operating times changes from stochastic values for small cells to reproducible values for large cells. Both effects can be explained by the higher probability of the aggregate state transition from super-cooled water to ice in large cells. Consequently this paper highlights the implications of downscaling PEFCs to draw conclusions for technical relevant cold-starts.

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Cold-Start of a PEFC Visualized with High Resolution Dynamic In-Plane Neutron Imaging

Cited by 78 publications

References 67 publications

The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

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

When Size Matters: Active Area Dependence of PEFC Cold Start Capability

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