Aqueous proton transfer across single-layer graphene

Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; Cai, Yu; Raju, Muralikrishna; Zhang, Weiwei; Sacci, Robert L.; Vlassiouk, Ivan; Fulvio, Pasquale F.; Ganesh, Panchapakesan; Wesolowski, David J.; Dai, Sheng; Duin, Adri C. T. van; Neurock, Matthew; Geiger, Franz M.

doi:10.1038/ncomms7539

Cited by 236 publications

(289 citation statements)

References 66 publications

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“…54 Monti et al 53 further extended this parameter set to include amino acids and short peptide structures, allowing ReaxFF to simulate the conformational dynamics of biomolecules in solution (Figure 4g). Aqueous proton transfer across graphene was investigated by Achtyl et al, 51 where ReaxFF helped to establish that proton transfer is enabled by hydroxyl-terminated atomic defects in the graphene sheet (Figure 4h). Hatzell et al 117 used ReaxFF to determine the impact of strong acid functional groups on graphene electrodes in capacitive mixing devices, in which salinity gradients are used for power generation (Figure 4i).…”

Section: Other Applicationsmentioning

confidence: 99%

The ReaxFF reactive force-field: development, applications and future directions

et al. 2016

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The reactive force-field (ReaxFF) interatomic potential is a powerful computational tool for exploring, developing and optimizing material properties. Methods based on the principles of quantum mechanics (QM), while offering valuable theoretical guidance at the electronic level, are often too computationally intense for simulations that consider the full dynamic evolution of a system. Alternatively, empirical interatomic potentials that are based on classical principles require significantly fewer computational resources, which enables simulations to better describe dynamic processes over longer timeframes and on larger scales. Such methods, however, typically require a predefined connectivity between atoms, precluding simulations that involve reactive events. The ReaxFF method was developed to help bridge this gap. Approaching the gap from the classical side, ReaxFF casts the empirical interatomic potential within a bond-order formalism, thus implicitly describing chemical bonding without expensive QM calculations. This article provides an overview of the development, application, and future directions of the ReaxFF method. INTRODUCTIONAtomistic-scale computational techniques provide a powerful means for exploring, developing and optimizing promising properties of novel materials. Simulation methods based on quantum mechanics (QM) have grown in popularity over recent decades due to the development of user-friendly software packages making QM level calculations widely accessible. Such availability has proved particularly relevant to material design, where QM frequently serves as a theoretical guide and screening tool. Unfortunately, the computational cost inherent to QM level calculations severely limits simulation scales. This limitation often excludes QM methods from considering the dynamic evolution of a system, thus hampering our theoretical understanding of key factors affecting the overall behaviour of a material. To alleviate this issue, QM structure and energy data are used to train empirical force fields that require significantly fewer computational resources, thereby enabling simulations to better describe dynamic processes. Such empirical methods, including reactive force-field (ReaxFF), 1 trade accuracy for lower computational expense, making it possible to reach simulation scales that are orders of magnitude beyond what is tractable for QM.Atomistic force-field methods utilise empirically determined interatomic potentials to calculate system energy as a function of atomic positions. Classical approximations are well suited for nonreactive interactions, such as angle-strain represented by harmonic potentials, dispersion represented by van der Waals potentials and Coulombic interactions represented by various polarisation schemes. However, such descriptions are inadequate for modelling changes in atom connectivity (i.e., for modelling chemical reactions as bonds break and form). This motivates the

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Section: Other Applicationsmentioning

confidence: 99%

The ReaxFF reactive force-field: development, applications and future directions

et al. 2016

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“…[28] On the other hand, ab-initio molecular dynamics simulations of water inside nanotube channels [29][30][31] have revealed different mobilities for hydroxide and hydronium ions inside the tubes, depending on the size of the tube and the degree of functionalization of the tube walls. A very recent work [32] reports proton transfer within graphene layers when surrounded by water. Protonated water clusters also provide very valuable information to understand proton and water properties at interfaces.…”

Section: Introductionmentioning

confidence: 99%

Proton transfer in liquid water confined inside graphene slabs

Tahat

Martı́

2015

Phys. Rev. E

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The microscopic structure and dynamics of an excess proton in water constrained in narrow graphene slabs between 0.7 and 3.1 nm wide has been studied by means of a series of molecular dynamics simulations. Interaction of water and carbon with the proton species was modelled using a multistate empirical valence bond Hamiltonian model. The analysis of the effects of confinement on proton solvation structure and on its dynamical properties has been considered for varying densities. The system is organized in one interfacial and a bulk-like region, both of variable size.In the widest interplate separations, the lone proton shows a marked tendency to place itself in the bulk phase of the system, due to the repulsive interaction with the carbon atoms. However, as the system is compressed and the proton is forced to move to the vicinity of graphene walls it moves closer to the interface, producing a neat enhancement of the local structure. We found a marked slowdown of proton transfer when the separation of the two graphene plates is reduced. In the case of lowest distances between graphene plates (0.7 and 0.9 nm), only one-two water layers persist and the two-dimensional character of water structure becomes evident. By means of spectroscopical analysis, we observed the persistence of Zundel and Eigen structures in all cases, although at low interplate separations a signature frequency band around 2500 cm −1 suffers a blue-shift and moves to characteristical values of asymmetric hydronium ion vibrations, indicating some unstability of the typical Zundel-Eigen moieties and their eventual conversion to a single hydronium species solvated by water.

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“…Without atomic level perforations, it is expected that H + would take billions of years to penetrate a graphene sheet [37], yet graphene with holes may act as a molecular colander; such is the modus operandi for a PEM. Further reports indeed support the notion that pristine graphene is impermeable to even protons, which is attributed to the dense electron cloud surrounding graphene; yet there is evidence to suggest that protons can transfer through graphene at rare point defects, as reported by Achtyl et al [38]. Their work uses a novel approach to measuring proton transfer across graphene by observing potential differences of the graphene support material, which is a fused silica that undergoes acid/base reactions with protons that are transferred across graphene.…”

Section: Pristine Graphenementioning

confidence: 73%

“…Intuitively, anionic species present on a surface will trap proton movement through the membrane because of an ion-ion interaction, indicating that graphene-based membranes may benefit from a pH closer to the Point of Zero Charge (PZC) for graphene, which would almost certainly rule out alkaline fuel cells due to the formation of negatively charged surface species. Figure 9.5 depicts computational images for water-mediated proton transfer through atomic defects (proton channels), and shows the extent to which different types of graphene defects will permit protons to transfer through the graphene membrane [38].…”

Section: Pristine Graphenementioning

confidence: 99%

Incorporating Graphene into Fuel Cell Design

Randviir

Banks

2016

NanoScience and Technology

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Since the fabrication and subsequent physical characterisation of graphene in 2004 and 2005, a host of potential uses have been suggested and researched. To date, some have had some success, while others are significantly lacking in critical research due to unforeseen problems with the electrochemical properties of graphene. Of the many applications, fuel cells were predicted to gain benefit from graphene; the focus of this book chapter is to assess whether graphene has a place in fuel cells, and disseminate the current state of research across the globe for this purpose. It is evident that the applicability of graphene as a fuel cell anode, cathode, or proton exchange membrane, is dramatically dependent upon the type of graphene used in the fuel cell design. Pristine graphenes lack the necessary active sites for low energy electrochemical reactions required in fuel cells, and therefore their use as anodes or cathodes is seemingly limited. However pristine graphene may permit protons across atomic scale defects in its lattice and prove to be a good material for a proton exchange membrane when coupled with its tensile strength. Laser-induced graphene is a relatively new technique for the fabrication of graphene but offers a potential route towards manufacture of 3D graphene architectures that could be useful for cathodic reactions such as oxygen reduction. Reduced graphene oxides in their many guises could also be useful, provided that a replicable standard can be formulated for fuel cell anode and cathodes. Graphene oxides also have potential for proton exchange membranes but may suffer from longevity issues as a result of the decreased hydrophobicity allowing swelling of the material when in an aqueous environment. Nitrogen-doped graphenes are also potential candidates for the future of fuel cell research for both anodic and cathodic reactions. The future of graphene as a fuel cell material is predicted to be several years away because the research in this area has not solved issues of longevity, reproducibility, and temperature tolerance, while maintaining a good cell voltage and current density.

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Aqueous proton transfer across single-layer graphene

Cited by 236 publications

References 66 publications

The ReaxFF reactive force-field: development, applications and future directions

The ReaxFF reactive force-field: development, applications and future directions

Proton transfer in liquid water confined inside graphene slabs

Incorporating Graphene into Fuel Cell Design

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