Simulation of Proton Transport in Proton Exchange Membranes with Reactive Molecular Dynamics

Arntsen, Christopher; Savage, John R. K.; Tse, Y.-L. S.; Voth, Gregory A.

doi:10.1002/fuce.201600024

Cited by 29 publications

(32 citation statements)

References 76 publications

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“…Proton transport is an important chemical process fundamental to a number of systems within the fields of biology, chemistry, materials science, and engineering. Such systems include the proton transport, coupling, and pumping mechanisms within proteins, 1-4 as well as proton exchange membranes (a common fuel cell material), [5][6][7] the efficient functionalities of which rely on facile and rapid proton transport. Unlike other cations, the transport of a proton in aqueous media relies on two distinct mechanisms: vehicular transport and Grotthuss shuttling, i.e., proton hopping from hydronium ions to neighboring water molecules.…”

Section: Introductionmentioning

confidence: 99%

The hopping mechanism of the hydrated excess proton and its contribution to proton diffusion in water

Arntsen

Chen

Calio

et al. 2021

The Journal of Chemical Physics

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In this work a series of analyses are performed on ab initio molecular dynamics (AIMD) simulations of a hydrated excess proton in water to quantify the relative occurrence of concerted hopping events and "rattling" events, and thus to further elucidate the hopping mechanism of proton transport in water. Contrary to results reported in certain earlier papers, the new analysis finds that concerted hopping events do occur in all simulations, but that the majority of events are the product of proton rattling, where the excess proton will rattle between two or more waters. The results are consistent with the proposed "special-pair dance" model of the hydrated excess proton, wherein the acceptor water molecule for the proton transfer will quickly change (resonate between three equivalent special pairs), until a decisive proton hop occurs. To remove the misleading effect of simple rattling, a filter was applied to the trajectory such that hopping events that were followed by back hops to the original water are not counted. A steep reduction in the number of multiple hopping events is found when the filter is applied, suggesting that many multiple hopping events that occur in the unfiltered trajectory are largely the product of rattling, contrary to prior suggestions. Comparing the continuous correlation function of the filtered and unfiltered trajectories, we find agreement with experimental values for the proton hopping time and Eigen-Zundel interconversion time, respectively.

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Section: Introductionmentioning

confidence: 99%

The hopping mechanism of the hydrated excess proton and its contribution to proton diffusion in water

Arntsen

Chen

Calio

et al. 2021

The Journal of Chemical Physics

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show abstract

“…Computational work has arguably more successfully targeted the transport mechanisms and relation between water and proton transport in PFSA PEMs (reviewed in refs. 25 and 26). An important quality of these theoretical studies is the derived mechanistic insight into the proton transport mechanism for differing hydration and polymer structure.…”

mentioning

confidence: 98%

Correlated interfacial water transport and proton conductivity in perfluorosulfonic acid membranes

Ling

Bonn

Domke

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Water must be effectively transported and is also essential for maximizing proton conductivity within fuel-cell proton-exchange membranes (PEMs). Therefore, identifying relationships between PEM properties, water transport, and proton conductivity is essential for designing optimal PEMs. Here, we use coherent Raman spectroscopy to quantify real-time, in situ diffusivities of water subspecies, bulk-like and nonbulk-like (interfacial) water, in five different perfluorosulfonic acid (PFSA) PEMs. Although the PEMs were chemically diverse, water transport within them followed the same rule: Total water diffusivity could be represented by a linear combination of the bulk-like and interfacial water diffusivities. Moreover, the diffusivity of interfacial water was consistently larger than that of bulk-like water. These measurements of microscopic transport were combined with through-plane proton conductivity measurements to reveal the correlation between interfacial water transport and proton conductivity. Our results demonstrate the importance of maximizing the diffusivity and fractional contribution of interfacial water to maximize the proton conductivity in PFSA PEMs.

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“…Proton transport (PT) plays a pivotal role in, e.g., the functioning of various biomolecules such as proton exchangers, transporters, and pumps (1–3), as well as certain nanomaterials (4, 5). Stable or at least transient “water wires” are believed to be required for proton permeation through confined regions in these systems by exploiting the Grotthuss proton hopping mechanism (6–8).…”

Section: Introductionmentioning

confidence: 99%

A Quantitative Paradigm for Water Assisted Proton Transport Through Proteins and Other Confined Spaces

Voth

2021

Preprint

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Water assisted proton transport through confined spaces influences many phenomena in biomolecular and nanomaterial systems. In such cases, the water molecules that fluctuate in the confined pathways provide the environment and the medium for the hydrated excess proton migration via Grotthuss shuttling. However, a definitive collective variable (CV) that accurately couples the hydration and the connectivity of the proton wire with the proton translocation has remained elusive. To address this important challenge-and thus to define a new quantitative paradigm for facile proton transport in confined spaces-a CV is derived in this work from graph theory, which is verified to accurately describe water wire formation and breakage coupled to the proton translocation in carbon nanotubes and the Cl-/H+ antiporter protein, ClC-ec1. Significant alterations in the conformations and thermodynamics of water wires are uncovered after introducing an excess proton into them. Large barriers in the proton translocation free energy profiles are found when water wires are defined to be disconnected according to the new CV, even though the pertinent confined space is still reasonably well hydrated and-by the simple measure of the mere existence of a water structure-the proton transport would have been predicted to be facile via that oversimplified measure. In this new paradigm, however, the simple presence of water is not sufficient for inferring proton translocation since an excess proton itself is able to drive hydration and, additionally, the water molecules themselves must be adequately connected to facilitate any successful proton transport.

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Simulation of Proton Transport in Proton Exchange Membranes with Reactive Molecular Dynamics

Cited by 29 publications

References 76 publications

The hopping mechanism of the hydrated excess proton and its contribution to proton diffusion in water

The hopping mechanism of the hydrated excess proton and its contribution to proton diffusion in water

Correlated interfacial water transport and proton conductivity in perfluorosulfonic acid membranes

A Quantitative Paradigm for Water Assisted Proton Transport Through Proteins and Other Confined Spaces

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