Structural Organization of Water-Containing Nafion: A Cellular-Automaton-Based Simulation

Mologin, D. A.; Khalatur, Pavel G.; Khokhlov, Alexei R.

doi:10.1002/1521-3919(20020601)11:5<587::aid-mats587>3.0.co;2-p

Cited by 59 publications

(46 citation statements)

References 32 publications

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“…Since this is much higher than the water content required experimentally for conductivity, it was concluded that there may be proton transport through waterdepleted regions either by interfacial diffusion in close promixity to sulfonate groups or through a second ionic phase with smaller channels than those resolvable using mesoscopic simulations. Similarly to the work of Mologin et al 85 described above, these results cast doubt on the utility of the concept of percolation as a direct requirement for the onset of conductivity. The authors conclude that the structures responsible for the low ''percolation'' thresholds for conductivity in PFSA membranes remain elusive, and propose that these be investigated further by multiscale simulations involving both explicit molecular calculations as well as a mesoscale component.…”

Section: Mesoscale Modelsmentioning

confidence: 72%

“…In a later study using coarse-grained methods, Mologin et al 85 described a lattice molecular dynamics (LMD) approach, which they referred to as a ''cellular automaton'' simulation method, based on a coarse-grained model for the polymer chains with variable bond lengths between connected nodes, similar to a bond fluctuation model (BFM), 86 but with deterministic rules for propagation of polymer segments on the lattice as opposed to stochastic evolution in the standard MC approach. According to Khoklov et al, 87,88 the LMD approach is capable of yielding convergence to limiting distribution functions nearly an order of magnitude faster than typical MC lattice-based simulations of polymers.…”

Section: Mesoscale Modelsmentioning

confidence: 99%

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Modelling of morphology and proton transport in PFSA membranes

Elliott

Paddison

2007

Phys. Chem. Chem. Phys.

227

255

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Computational modelling studies of the structure of perfluorosulfonic acid (PFSA) ionomer membranes consistently exhibit a nanoscopic phase-separated morphology in which the ionic side chains and aqueous counterions segregate from the fluorocarbon backbone to form clusters or channels. Although these investigations do not unambiguously predict the size or shape of the clusters, and whether or not the channels percolate the matrix or if the connections between them are more transient, the sequence of co-monomers along the main chain appears strongly to influence the domain size of the ionic regions, with more blocky sequences giving rise to larger domain sizes. The fundamental insight that substantial rearrangement of the sulfonic acid terminated side chains and fluorocarbon backbone takes place during swelling or shrinkage is borne out by both molecular and mesoscale simulations of model PFSA polymers, along with ab initio electronic structure calculations of minimally hydrated oligomeric fragments. Molecularlevel modelling of proton transport in PFSA membranes attests to the complexity of the underlying mechanisms and the need to examine the chemical and physical processes at several distinct time and length scales. These investigations have revealed that the conformation of the fluorocarbon backbone, flexibility of the sidechains, and degree of aggregation and association of the sulfonic acid groups under minimally hydrated conditions collectively control the dissociation of the protons and the formation of Zundel and Eigen cations. The former appear to be the dominant charge carriers when the limiting water content allows only for the formation of a contact ion pair with the tethered sulfonate anion. As the water content increases, solventseparated Eigen ions begin to appear, indicating that the dominant mechanism for diffusion of protons occurs over a region approximately 4 Å away from the sulfonate groups. Finally, both the vehicular and Grotthuss shuttling mechanisms contribute to the mobility of the protons but, surprisingly, they are not always correlated, resulting in a lower overall diffusion coefficient. In summary, as the preceding observations indicate, the state of computational modelling of PFSA membranes has progressed sufficiently over the last decade to enable its use as a powerful predictive tool with which to guide the process of designing novel membrane materials for fuel cell applications.

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Section: Mesoscale Modelsmentioning

confidence: 72%

Section: Mesoscale Modelsmentioning

confidence: 99%

Modelling of morphology and proton transport in PFSA membranes

Elliott

Paddison

2007

Phys. Chem. Chem. Phys.

227

255

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“…It is well known that the proton conductivity of hydrated Nafion membranes starts to increase considerably already at very low water content [3,[12][13][14][29][30][31]. This fact suggests that the ionic conductive channels can exist in the microphase-separated structure of nearly dry membranes [12].…”

Section: Resultsmentioning

confidence: 99%

Atomistic and mesoscale simulation of polymer electrolyte membranes based on sulfonated poly(ether ether ketone)

Комаров

Veselov

Chu

et al. 2010

Chemical Physics Letters

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“…[46][47][48][49] Because of computational limitations, full atomistic models are not able to probe the random morphology of these systems. However, as demonstrated by these simulations and applications to other random composite media, mesoscale models are computationally feasible to capture the morphology.…”

Section: F60mentioning

confidence: 99%

A Multiparadigm Modeling Investigation of Membrane Chemical Degradation in PEM Fuel Cells

Quiroga

Malek

Franco

2015

J. Electrochem. Soc.

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We report a multi-paradigm model of the membrane chemical degradation in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), by combining Coarse-Grained Molecular Dynamics (CGMD) and a multiscale cell performance model. CGMD is used to generate structural databases that relate the amount of detached (degraded) ionomer sidechains with the water content and the resulting PEM meso-microporous structure. The multiscale cell performance model describes the electrochemical reactions and transport mechanisms occuring in the electrodes from an on-the-fly coupling between Kinetic Monte Carlo (KMC) sub-models parametrized with Density Functional Theory (DFT) data and (partial differential equations-based) continuum sub-models. Furthermore, the performance model includes a kinetic PEM degradation sub-model which integrates the CGMD database. The cell model also predicts the instantaneous PEM sidechain content and conductivity evolution at each time step. The coupling of these diverse modeling paradigms allows one to describe the feedback between the instantaneous cell performance and the intrinsic membrane degradation processes. This provides detailed insights on the membrane degradation (sidechain detachment as well as water reorganization within the PEM) during cell operation. This novel modeling approach opens interesting perspectives in engineering practice to predict materials degradation and durability as a function of the initial chemical composition and structural properties in electrochemical energy conversion and storage devices. From the second half of the twentieth century, Polymer Electrolyte Membrane Fuel Cells (PEMFCs) have attracted much attention due to their potential as a clean power source for vehicles traction. Market introduction of FC vehicles is being recognized of highest priority in many developed countries due to their impact on the reduction of energy consumption and greenhouse gas emissions. However, PEMFC technologies have not yet reached all the requirements to be competitive, in particular regarding their high production cost of Membrane Electrode Assemblies and their low durability.Indeed, meso/micro-structural degradation leading to the PEMFC components aging is attributed to several complex physicochemical mechanisms not yet completely understood. The associated components meso/micro-structural changes translate into irreversible longterm cell power degradation.1-3 For instance, dissolution and redistribution of the catalyst reduces the specific catalyst surface area and the electrochemical activity. The corrosion of the catalyst carbon-support and loss or decrease of the hydrophobicity caused by an alteration of the Polytetrafluoroethylene in Catalyst Layers (CLs), Microporous Layers and Gas Diffusion Layers also affect the water management in the cell and thus the electrochemical performance.Regarding the polymer electrolyte in PEMFCs, a large number of materials has been tested, including sulfonated hydrocarbon polymers, phosphoric acid doped polybenzimidazole, polymer-inorganic composit...

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Structural Organization of Water-Containing Nafion: A Cellular-Automaton-Based Simulation

Cited by 59 publications

References 32 publications

Modelling of morphology and proton transport in PFSA membranes

Modelling of morphology and proton transport in PFSA membranes

Atomistic and mesoscale simulation of polymer electrolyte membranes based on sulfonated poly(ether ether ketone)

A Multiparadigm Modeling Investigation of Membrane Chemical Degradation in PEM Fuel Cells

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