Liquid-Water Interactions with Gas-Diffusion-Layer Surfaces

Santamaria, Anthony D.; Das, Prodip K.; MacDonald, James C.; Weber, Adam Z.

doi:10.1149/2.0321412jes

Cited by 114 publications

(113 citation statements)

References 51 publications

(118 reference statements)

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“…The decrease in simulated current density with decreasing temperature is likely due to the two phase model used for the catalyst layer and catalyst layer-GDL interphase. Another potential mechanism for the 2 AEX1 discrepancy at low temperature is the assumption in the simulation that the reactant flow channels remain free of liquid water [34]. The difference in low temperature performance between the 1 and 2 AEX1 simulations is easy to discern when looking at the liquid-water profiles in the anode and cathode GDLs.…”

Section: Model Simulation Results and Discussionmentioning

confidence: 99%

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore‐Network Models

et al. 2016

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Water management remains a critical issue for polymer electrolyte fuel cell performance and durability, especially at lower temperatures and with ultrathin electrodes. To understand and explain experimental observations better, water transport in gas diffusion layers (GDLs) with macroscopically heterogeneous morphologies was simulated using a novel coupling of continuum and pore-network models. X-ray computed tomography was used to extract GDL material parameters for use in the pore-network model. The simulations were conducted to explain experimental observations associated with stacking of anode GDLs, where stacking of the anode GDLs increased the limiting current density. Through imaging, it is shown that the stacked anode GDL exhibited an interfacial region of high porosity. The coupled model shows that this morphology allowed more efficient water movement through the anode and higher temperatures at the cathode compared to the single GDL case. As a result, the cathode exhibited less flooding and hence better low temperature performance with the stacked anode GDL.

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Section: Model Simulation Results and Discussionmentioning

confidence: 99%

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore‐Network Models

et al. 2016

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“…In case of O4, where the lowest TP liquid permeability of the repetition unit domains was identified and the highest pressure drop can be expected, the pressure drop for a liquid water flow rate equivalent to a current density of 3 A/cm 2 is just about 5 Pa. Such low pressure drops are three orders of magnitude away from breakthrough pressures 22,27,44 or pressures that are required for in-plane growth after breakthrough under a rib-structure for Toraytype GDL. 44 Santamaria et al 22 reported similar post-break-through liquid permeabilities of 0.5 × 10 −12 m 2 for Toray TGP-H-030 and TGP-H-060 papers with 5 wt% PTFE that were obtained from liquid water imbibition experiments.…”

Section: Journal Of Thementioning

confidence: 91%

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Eller

Roth

Marone

et al. 2016

J. Electrochem. Soc.

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Polymer electrolyte fuel cells (PEFC) require a sophisticated water management to operate efficiently, especially at high current densities which are needed to reach system cost targets. The description of the complicated two-phase water transport remains a challenge in PEFC models and requires experimental validation on various length scales. In this work, operando X-ray tomographic microscopy (XTM) with scan times of 10 s was used to depict the liquid water at defined conditions at a technically relevant cell temperature of 80 • C. Cells with Toray TGP-H-060 gas diffusion layer (GDL) with microporous layer (MPL) and different rib width were operated with different feed gas humidifications (under-and oversaturated) and current densities between 0.75 to 3.0 A/cm 2 . Based on the quantification of the local and average saturation, the distribution of water cluster size is analyzed. Different categories of the water cluster connectivity are defined and quantified. The analysis is complemented with numerical simulations of the permeability in the liquid phase of the GDL that is correlated to saturation for the different GDL domains. The numerical simulations of the pressure drop of liquid water flow from the catalyst layer toward the gas channels in channel-rib repetition units allows for conclusions on cluster growth mechanisms. In the past two decades, large developments have lead hydrogen fed polymer electrolyte fuel cell (PEFC) technology to the brink of commercialization, e.g. in the stationary sector with more than 100000 deployments in the Enefarm activity 1 as well as in the mobile sector where major car manufacturers have presented first commercial vehicles 2,3 and niche-market commercialization for logistic vehicles. 4While for the automotive market also hydrogen infrastructure is a major barrier for widespread application, in both fields of application, cost of the fuel cell system remains the main hindrance for extensive spread of PEFC technology. Cost is closely tied to materials and manufacturing processes, such as more effective electrocatalyst and more durable membrane materials. These developments are underway and have made significant progress. 5 Cost however is also closely tied to power density of the fuel cell stack. It is obvious that with higher power density less cells or an accordingly smaller cell area with the related reduced material use, is leading to a cost reduction if the high power density materials are of comparable cost.Automotive fuel cells with state of the art materials and cell structures reach today more than 1 W/cm 2 with current densities up to 3 A/cm 2 .5 At such high current densities water management becomes more and more important and has to be properly designed on various scales from the system level to nanoscale structures, including all cell components as flow field plates, gas diffusion layers (GDL), the polymer membrane and the catalyst layer (CL). In order to minimize the ohmic losses, the polymer membrane needs to be well humidified, 6 however at high current den...

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“…If the direction of the flux of water is into the GDL, then a no-flux boundary condition is set. In several simulations reported herein, P L was set higher than P G at the CH|GDL boundary to simulate a GDL with a higher droplet adhesion force, 40 although the same allowance for only fluxes out of the GDL in the liquid phase was maintained. It is well known that droplets along this interface results in higher dynamic liquid pressures before the droplet is removed.…”

Section: −βτmentioning

confidence: 99%

“…This droplet detachment is strongly coupled to the adhesion force of the material on the GDL surface. 40,41,46,78,79 Incorporation of this physics into continuum cell models remains a challenge. 9 However, such effects should essentially impact the water liquid pressure at the boundary, which is the pressure of the droplet at detachment, assuming Darcy's law remains valid.…”

Section: Impact Of Catalyst-layer Thickness-as Shown Inmentioning

confidence: 99%

Understanding Impacts of Catalyst-Layer Thickness on Fuel-Cell Performance via Mathematical Modeling

Zenyuk

Das

Weber

2016

J. Electrochem. Soc.

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145

136

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In this article, a two-dimensional, multiphase, transient model is introduced and used to explore the impact of catalyst-layer thickness on performance. In particular, the tradeoffs between water production and removal through transport or evaporation are highlighted, with a focus on low-temperature performance. For the latter, a case study of an ultra-thin catalyst layer is undergone to explore how various material properties alter the steady-state and startup performance of a cell. The findings provide understanding and guidance to optimize fuel-cell performance with thin electrodes. Polymer-electrolyte fuel cells (PEFCs) have emerged as a promising zero-emission technology for energy conversion due to their thermodynamic efficiency and high energy density.1,2 However, to reduce cost, the amount of precious metal catalyst needs to be lowered. The most common strategy for such catalyst thrifting is to fabricate thinner catalyst layers. The prototypical example of this approach is the nanostructured thin-film (NSTF) electrode, which has several advantages compared to standard carbon-supported Pt electrodes.2 These stateof-the art electrodes have demonstrated improved chemical stability, durability and desired specific power and activity, at the same time having high Pt mass activities. 2,3 Common to these and other lowloaded electrodes are the issues associated with water management in thinner electrodes. Typically, thinner electrodes are susceptible to severe flooding due to their inherently low water capacity and perhaps lack of hydrophobic zones. Such phenomena are particularly pronounced when PEFCs operate at lower temperatures or during startup.Recently, several studies reported water-management mitigation strategies for thinner electrodes including modification of operating conditions and/or component morphologies to ensure successful startup and operation at low temperatures. For example, for NSTF electrodes, Steinbach et al.4,5 reported a novel water-management scheme of increasing the pressure on the cathode to drive water to the anode; coupled with a different anode design, the limiting current density at low temperatures increased by a factor of four. Kongkanand et al. 6,7 demonstrated that water removal and storage capacity of the NSTF electrode can be significantly enhanced by placing an additional Pt/C layer between the electrode and microporous layer. The various empirical findings of NSTF as well as traditional supported thin electrodes 8 can be much better understood by examining the various tradeoffs engendered and complications arising from the use of thin catalyst layers.Currently, the transport mechanisms of water removal behind possible mitigation strategies for thin electrodes are not well understood. In terms of modeling, both pore-scale and continuum models have been generated, although only the latter are germane to understanding cell water and thermal management. 9 Examples of continuum models include bilayer models, such as the one developed by Sinha et al. 10 with a membrane and wat...

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Liquid-Water Interactions with Gas-Diffusion-Layer Surfaces

Cited by 114 publications

References 51 publications

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore‐Network Models

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore‐Network Models

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Understanding Impacts of Catalyst-Layer Thickness on Fuel-Cell Performance via Mathematical Modeling

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