bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulating an Applied Voltage in Molecular Dynamics Using Charge Optimized Many Body (COMB3) Potentials
Authors: Antony Andrew Charles , Akhade Sneha A. , Liang Tao , Janik Michael J. , Maranas Janna K , Sinnott Susan B. 
Published: February 2020

Technological development of energy sources such as fuel cells and batteries has been enhanced by the progress of computational models and simulations used to study these electrochemical systems, more specifically, the electrode/electrolyte interface. Here, we present a methodology for applying a voltage during a dynamic charge molecular dynamics (MD) simulation. Our method is developed within the third generation charge optimized many body (COMB3) potential [1] framework and implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software package [2]. The COMB3 potential incorporates the electronegativity-equalization (EE) principle in its dynamic charge equilibration scheme. The EE principle requires the electronegativity at all atomic sites be equal, assuming fixed atomic positions. The partial charge on each atom is dynamically equilibrated by solving Euler-Lagrange equations of motion, a method developed by Rick et al. [3]. Only changes in the charge equations of motion are shown for brevity, but a complete description of the charge equilibration steps in COMB3 can be found in ref. 1. Electrode COMB3 (ECOMB3) development includes a simplistic view of varying the atomic charge equations of motion during the charge equilibration steps to simulate an applied voltage for various electrochemical systems. In ECOMB3, the mean electronegativities at the cathode and anode differ by an applied voltage, V. This electronegativity imbalance generates a new set of charge equations of motion for the anode and cathode while the electrolyte (non-electrode) equation of motion remains unchanged. Using the ECOMB3 method, we simulate an applied voltage for a system of liquid water between two Cu electrodes. The aim of these simulations is to study the differing dynamical and structural properties of water molecules at the Cu/H2O interface as opposed to molecules in the bulk. More specifically, we analyze the charge density distribution across the interface to demonstrate the practicality of using a charge transfer scheme in such a simulation. We also report density distribution profiles for atomic oxygen and hydrogen in water, indicating the ordering of molecules near the interface.

References

[1] T. Liang et al., Materials Science & Engineering R-Reports 74(2013).
[2] S. Plimpton, Journal of Computational Physics 117(1995).
[3] S. W. Rick, S. J. Stuart, and B. J. Berne, Journal of Chemical Physics 101 (1994).
Computational Analysis of Solvent Effects on Electron Transfer in Organic Radical Battery Cathode Materials
Authors: Kemper Travis , Larsen Ross E. , Gennett Thomas 
Published: February 2020

Organic polymers and molecules containing stable radical groups are currently of interest in a variety of electronic and energy storage applications. However, in many of these systems very little is understood about the fundamental mechanisms by which charge is transported. This includes electron transport, ionic migration as well as molecular rearrangements and solvent reorganization. This work focuses on utilizing modeling, specifically large scale molecular dynamics simulations and electronic structure calculations to understand charge transport at a molecular level for the prototypical nitroxide radical containing polymer poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA). Transport in PTMA films occurs homogeneously between the radical-containing groups, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). Considering the Marcus formalism, that the rate of transfer depends on several properties of the molecular system: the energy of an electron at each TEMPO site; the electronic coupling between pairs of TEMPO sites; and the molecular reorganization energy associated with the homogeneous electron transfer reaction. Furthermore we performed simulations to evaluate the electron transfer process in a pure PTMA film and a PTMA film swelled by acetonitrile, similar to what would happen in solution. This was accomplished by quantum mechanical calculations to find the site energy of each TEMPO group in the film and then compute the electronic density of states and the related distribution of charge-transfer reaction enthalpies. In addition, pairs of TEMPO groups were extracted and the inter- and intra-chain electronic coupling was also calculated. Utilizing this data, we found that based on the inter-TEMPO coupling values and the distances between sites the electronic-coupling-weighted radial distribution function to predict the effective electron transfer lengths as a function of solvent concentration. Finally, the implications of these results for how transport occurs within other organic radical polymer materials will be discussed in greater detail.
(Invited) Thermodynamics of Deposition Flux Dependent Intrinsic Film Stress
Authors: Rost Marcel J. 
Published: February 2020

The growth of polycrystalline films at temperatures above ~0.2 of the melting temperature is accompanied by compressive stress development after film closure.
Mysteriously, a significant part of this stress has a reversible nature: it disappears when the deposition is stopped and re-emerges upon resumption. Chason [1] even showed the corresponding inverse behavior during electrochemical etching
All these observations clearly point towards a steady-state, flux (etching rate) dependent equilibrium phenomenon, which should, therefore, be treated properly by thermodynamics.
It has been suggested that the variation of the surface chemical potential upon starting/stopping of the deposition may cause adatoms to diffuse in/out of the grain boundaries leading to the development/relaxation of the intrinsic compressive film stress.
However, film growth involves a myriad of atomic processes such that the mystery is not yet solved and new mechanisms and ideas are still published frequently.
Here we present an analytical derivation, in which we address, for the first time, the reason
why
additional atoms want to get incorporated in the grain boundaries. This background delivers the required driving force independently of the precise way the atoms get incorporated. In this sense we are not proposing a new model, but delivering the basis for all different models proposed.
To derive the driving force, we calculate the variation of the chemical potential of the surface, the grain boundaries, and the film. Surprisingly, using pure thermodynamic arguments, our results fully agree with the magnitude of the reversible compressive stress:

the tremendous stress levels observed in the experiments can indeed be explained by the flux induced density variations in the extremely dilute adatom gas on the surface!

[1] Shin and Chason, Phys. Rev. Lett. 103, 056102 (2009)
E-mail:rost@physics.leidenuniv.nl
Web: www.physics.leidenuniv.nl/rost
(Invited) Electrodeposition of Fe-Pt Magnetic Films and Multilayers with Largemagnetic Anisotropy for Magnetic Recording and Microsystems
Authors: Ge Siyuan , Liang Defu , Zangari Giovanni 
Published: February 2020

Alloys of Pt with metals of the Fe group form various phases with large magnetic anisotropy (above 1 MJ/m3), in particular the L10 phases of equiatomic Fe-Pt and Co-Pt. These alloys are promising candidates for permanent magnet components in magnetic MEMS or magnetic storage media.
Electrochemical growth of magnetic films presents unique advantages, such as the close control of the driving force for film growth to finely tune properties via various deposition modalities, and the ability to form micro- or nano-structures of high aspect ratio via purely additive processes. This talk will discuss the electrochemical synthesis, structural characterization and magnetic properties of equiatomic Fe-Pt alloy films, highlighting the unique features afforded by electrochemical processing.
As-deposited equiatomic Fe-Pt alloys are obtained by an underpotential codeposition process; these films exhibit a metastable face-centered cubic structure in the as-deposited condition, but formation of the tetragonal L10 phase and coercivities of up to 14 kOe can be achieved via thermal annealing of the films at only 450C [1, 2]. The composition of Fe-Pt alloys can be easily varied during growth by potential pulsing, enabling the formation of multilayers with a compositional gradient. Thermal annealing of Fe75Pt25/Fe50Pt50 bi- and multi-layers in forming gas results in a significant acceleration of the phase transformation to the L10 phase, enabling the formation of highly coercive films at lower annealing temperature. The quality of the multilayers is inferred by the observation of exchange-coupled behavior at about 5 nm sublayer thickness.
[1] D Liang, JJ Mallett, G Zangari, ACS Appl Mater Interfaces 2 (4) 961-964 (2010);
[2] D. Liang, S. Ge, G. Zangari, IEEE Trans Magn. DOI: 10.1109/TMAG.2015.2394326 (2015)
(Invited) The Electrodeposition of Crystalline Gallium Antimonide Using Electrochemical Liquid-Liquid Solid Deposition (ec-LLS)
Authors: DeMuth Joshua James , Ma Luyao , Maldonado Stephen 
Published: February 2020

Gallium antimonide (GaSb) is a III-V semiconductor that has potential use in a variety of applications including thermophotovoltaics, tandem solar cells and photodetectors.1 Due to its conceivable use in semiconductor devices several thin film growth methods have been established for crystalline GaSb. Electrodeposition of crystalline GaSb films has been previously attempted 2,3 but the deposits contained large amounts of excess antimony and required post-deposition annealing steps. Electrochemical liquid-liquid solid deposition (ec-LLS) is a method in which an electrochemical potential gradient is used to achieve a supersaturation within liquid metal electrode/solvent in order to promote the growth of crystalline semiconductors.4 In this study stoichiometric films of crystalline GaSb were electrodeposited from an Sb­2O3 precursor in aqueous electrolyte via ec-LLS at mild temperatures (40o-90oC) and ambient pressure. In addition, the growth conditions were varied and the observed effects on the resultant materials crystallinity and composition were used to obtain insight on the proposed mechanism of ec-LLS.

References

(1) Kumar, V. et al; J. Appl. Phys., 1997, 81, 5821-5870
(2) McChesney, J et al., Optical Materials, 1996, 6, 63-67
(3) Musiani, M et al., J. Appl. Electrochem., 1989, 20, 868-873
(4) Fahrenkrug, E.; Gu, J.; Maldonado, S. J. Am. Chem. Soc.,2013,
135
, 330-339
Electrodeposition and Characterization of Selective Coatings Based on Black Cobalt for the Conversion of Solar-to-Thermal Energy
Authors: Herrera Zamora Dallely Melissa , Lizama-Tzec Francisco Ivan , Arés Muzio Oscar Eduardo , Oskam Gerko 
Published: February 2020

Solar-thermal energy conversion is achieved by selective coatings on a metallic substrate. The selective coating consist of a thin selectively absorbing film on a highly IR reflective underlying metal. The optical performance of the selective coating depends on the thickness of the respective films, which can be controlled through the electric charge applied during the electrodeposition process. Selective coatings have been deposited on copper substrates by the electrodeposition method. The coating consists of an intermediate reflective layer of electrodeposited bright nickel and an absorbing film of black cobalt. Different times were used for the galvanostatic deposition of black cobalt in order to optimize the optical properties. In order to evaluate the thermal stability, the coatings were exposed to temperature of 300oC. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The visible and IR film reflectance was evaluated before and after the thermal treatment through UV-Vis-NIR spectrophotometer and a Perkin Elmer FTIR spectrophotometer (Frontier MIR/NIR) with an integrating sphere from 2 µm to 15 µm. The spectrophotometry results showed little change in the film reflectance after of the thermal treatment, suggesting a good thermal stability.
Influence of Structural Properties on the Performance of Dye-Sensitized Solar Cells Based on Electrodeposited ZnO
Authors: Canto Aguilar Esdras Josué , Anta Juan Antonio , Oskam Gerko 
Published: February 2020

ZnO is an interesting material for application in the dye-sensitized solar cell (DCS) related to the large variety of low-temperature synthesis methods that allow for easy manipulation of the morphology and texture of the material. In particular, electrodeposition of crystalline ZnO can be achieved at room temperature, making it an excellent method for the preparation of solar cells based on flexible plastic substrates.
We will present results on the performance of dye-sensitized solar cells based on electrodeposited ZnO, describing the electrodeposition method in detail, and compare the results to ZnO-based solar cells prepared using sol-gel synthesis and CVD. The morphology and texture are expected to influence the performance of the dye solar cell via a variety of effects. For instance, the exposed crystal facets may affect the dye bonding, dye coverage, and injection efficiency, the electron transfer kinetics to the solution, and the trap state distribution [1]. Using these materials, we have compared the electron transport and recombination properties using small-signal perturbation techniques [2]. We have also addressed the influence of solution additives on the performance of ZnO-based dye-sensitized solar cells and rationalized the results. The influence of surface facet exposure on dye bonding is highlighted.

References

1. Anta, J. A.; Guillén, E.; Tena-Zaera, R. ZnO-based dye-sensitized solar cells. J. Phys. Chem. C 116, 11413-11425 (2012).
2. Vega-Poot, A.G.; Macías-Montero, M.; Idígoras-León, J. A.; Borrás, A.; Barranco, A.; Gonzalez- Elipe, A. R.; Lizama-Tzec, F. I.; Oskam, G.; Anta, J. A. Mechanisms of electron transport and recombination in ZnO nanostructures for dye-sensitized solar cells. ChemPhysChem. 15, 1088-1097 (2014).
Properties of Cabon Fibers with Electrochemically Formed ZnO Nanorods
Authors: Lee Kyu Hwan , Lim Dongchan , Choi Sung Mook 
Published: February 2020

We presented that aligned arrays of ZnO nanorods grown on surface of carbon fibers can lead to significantly enhanced properyies, such as interfacial strength, wettability of epoxy resin and electric conductivity. ZnO were grown by electrochemical process. We made carbon composit to evaluate interlaminar shear stress. We also observed electrical property and piezo property. Finally we demonstrate continuous formation of ZnO on carbon fiber using semi-pilot scale bath.

Figure 1
(Invited) Toward the Formation of Ordered Nanoparticle Films By Electrophoretic Deposition and the Subsequent Assessment of Order Via Voronoi Tessellation Analysis
Authors: Dickerson James H. 
Published: February 2020

Electrophoretic deposition (EPD) is a liquid phase, materials casting approach whose technological advantages range from ease of application to size scalability, cost effectiveness, and rapid performance. Material coatings, casts, and films assembled by EPD can be fabricated in just a few minutes and can easily be produced in nanometer to centimeter thicknesses across square nanometer to square meter surfaces. EPD and other liquid-phase casting techniques can yield various degrees of order among the fabricated supercrystals. Recently, we observed the evolution of order among nanoparticles (NPs) of cobalt ferrite. We uncovered evidence that the NPs not only arranged into hexagonal close packing arrays when deposited onto silicon substrates by EPD but also appeared to have their crystallographic axes to be oriented collinearly. This discovery could have far reaching ramifications in the rapid assembly of nanomaterials for applications, such as magnetic recording media and catalysis, among others. Further, recently developed statistical measurement tools, specifically Voronoi tessellation analysis, that can be used to quantify the degree of ordering in monolayers of nanoparticles have been applied to the cobalt ferrite and the iron oxide systems. The evolution of order in cobalt ferrite NP monolayers are juxtaposed with that of iron oxide NPs to explore the underlying causes of the differences in ordering based and the physical properties of the NP films.
Construction of Asymmetric Graphene Sandwiches: Decoration Using Semiconductor and Metal Nanostructures
Authors: Toth Peter S , Dryfe Robert AW 
Published: February 2020

The low-dimensional carbon materials, i.e. graphene-based metal and metal oxide nanocomposites fabrication procedure at the polarizable organic/water interface opens an alternative way to prepare catalyst materials.1-2 These graphene-based nanostructures could be useful substrates for catalytic processes, such as the hydrogen evolution or the oxidation of low molecular weight alkanes to liquid alcohol fuels. The polarizable organic/water interface offers the possibility of incorporating, as well as constructing in situ at the interface, highly complex catalytic centers and supports, including photoactive semiconductors, metallic nanostructures.3

Chemical vapor deposition (CVD) on copper foil was employed to grow macroscopic (cm scale) graphene and the high purity CVD GR monolayers assembled at an polarizable organic/water interface.1-2 The semiconductors, titanium oxide (TiO2) and molybdenum disulfide (MoS2) were exfoliated in an organic solvent, and assembled at the interface, then the top of CVD GR was decorated by fishing out either the TiO2 or MoS2 layer. The top-side of CVD GR was also decorated by metal and metal oxide nanoparticles (NPs), i.e. Au, Pd, Pt and PdO, PtO, respectively, using a solution chemistry-based galvanic displacement.1
In situ electrochemical and spontaneous, electroless metal deposition of Pd, Pt, Au and Ag NPs at the interface-assembled previously top-side decorated CVD GR was studied.1-2

We have fabricated a range of different dual-decorated CVD GR-based nanostructures, including semiconductors, metals and metal oxides on top, and metal NPs on bottom-side, respectively. Either the same nanostructures (symmetric decoration), or different ones (asymmetric decoration) were used for the preparation of bi-functionalized graphene sandwiches, which are adsorbed at the organic/water interface. The successful fabrication of such dual-decorated graphene-based metal nanocomposites was confirmed using various microscopic techniques (scanning electron and atomic force microscopies) and several spectroscopic methods (X-ray photoelectron, 3D energy dispersive X-ray tomography, mapping mode Raman spectroscopy and electron energy loss spectroscopy). Taken together it is inferred from these techniques that the location of deposited nanoparticles is on opposite sides of the graphene monolayer.

1. Toth, P. S.; Velický, M.; Ramasse, Q. M.; Kepaptsoglou, D. M.; Dryfe, R. A. W., Advanced Functional Materials, 2015, DOI: 10.1002/adfm.201500277.
2. Toth, P. S.; Ramasse, Q. M.; Velický, M.; Dryfe, R. A. W., Chemical Science, 2015, 6, 1316-1323.
3. Rodgers, A. N. J.; Booth, S. G.; Dryfe, R. A. W., Electrochemistry Communications, 2014, 47, 17-20.
Ion Exchange Membrane Based Ammonia Synthesis
Authors: Xu Hui , McCallum Tom , Kocha Shyam S 
Published: February 2020

In the ammonia industry, Haber-Bosch process leads to produce 500 million tons of nitrogen fertilizer per year, mostly in the form of anhydrous ammonia, ammonium nitrate, and urea. These fertilizers are responsible for up to 50% of worldwide crop yields and sustain one-third of the Earth's population 1. However, the conventional Haber–Bosch process for ammonia synthesis requires high pressure and temperature (up to 300 atm and 500°C) and is extremely energy-intensive. Typically, 8,000-12,000 kWh of energy is required to produce one ton of ammonia (kWh/ton ammonia) 2.
In this work, we have developed an energy-efficient electrochemical approach for ammonia synthesis that utilizes an ion-exchange membrane (IEM) as the electrolyte and selected metal nanomaterials as the catalysts. At the anode the hydrogen oxidation reaction (HOR) takes place releasing protons and electrons. Protons transport through the PEM and reach the cathode where nitrogen is reduced to ammonia with the participation of protons and electrons. At the cathode, highly active and selective nanostructured catalysts are incorporated for enhanced nitrogen reduction reaction (NRR).
Our preliminary experiments demonstrate that more than 10-3 mmol/h-cm² (active membrane area) NH3 production rate was achieved at ambient pressure and 80 °C, which is one order of magnitude higher than typically reported 3. The calculated highest hydrogen conversion is 18%, comparable with typical conversion 14% for the single stage Haber–Bosch process. Since the conversion via the proposed approach is achieved at ambient pressure and 80°C, its overall energy consumption (kWh/ton ammonia) is much lower than that for the Haber–Bosch process. The application of nanostructured high-efficiency NRR catalysts in this work will further enhance the hydrogen conversion and energy efficiency for electrochemical ammonia synthesis.
References:
1. Appl, M., Ammonia, in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH (2006).
2. Smil, V., Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production, The MIT Press, Cambridge, MA, 2001, ISBN 0-262-19449-X.
3.Amar, A, R. Lan, C.T.G. Petit, and S. Tao, “Solid-state electrochemical synthesis of ammonia: a review,” J. Solid State Electrochem., 15, 1845-1860 (2011).

Acknowledgement: The financial support is from the USDA under the Contract Grant No. 2014-33610-21933.