bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Additively Manufactured Gain Media for Lasers
Authors: Payne Stephen , Cherepy Nerine , Jones Ivy K , Seeley Zachary , Duoss Eric 
Published: February 2020

We are developing an innovative approach for fabricating laser gain media, such as laser rods, based on utilizing the direct ink write (DIW) additive manufacturing methodology, together with ceramics processing. For DIW, the key is to formulate the ink so that has three main properties: (1) experiences shear-thinning so that it can pass through a nozzle of 250-500 mm; (2) encounters considerable “gelation” after exiting the nozzle so that the structure remains relatively firm; and (3) must include ~50% loading of the gain medium by volume, e.g. YAG. In Fig. 1, we see the DIW instrument, an example of a laser rod written with both doped and undoped regions, and the rheology curve for a typical ink. After writing the part, the next steps include heating near 1000C to remove the solvents, cold isostatic pressing to a green body, sintering (usually near 17000C) to about 95% density, and finally heating under pressure (HIP’ing) to generate a clear part. The main advantage of this optical design for a laser rod is that it will strongly induce the TEM00 mode of the laser and thereby increase the beam quality. In this talk we will discuss both the laser physics and the materials issues associated with the new pathways for fabricating laser elements.
This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Figure 1
Systematic First-Principles Calculations of Charge Transfer Transitions of Rare Earth Ions in Oxides Using Simple Cubic Model Cluster
Authors: Takemura Shota , Ogasawara Kazuyoshi 
Published: February 2020

[Introduction] It is important for trap levels to capture carriers for persistent phosphors, and the properties depend on the positions of the trap levels within the band gap [1]. It is necessary to estimate the positions of impurity levels which work as trap levels for material design of the persistent phosphors. As one of the ways, the position of the impurity level within the band gap can be estimated by calculating the charge transfer transition energy from the valence band (Ligand to Metal Charge Transfer: LMCT). However, calculation of the LMCT based on quantum theory is exceedingly difficult in d electron system like transition metal and f electron system like rare earth ion because the calculation requires to consider many-electron effect, symmetry and relativistic effect such as spin-orbit interaction. Recently, we successfully reproduced the LMCT energies and their experimental trend of transition metal ions in α-Al2O3 by performing configuration interaction (CI) calculation using the DVME method [2]. From these results, we expect that the relativistic DVME method can be also applied to rare earth ions. In this study, as a first approach, in order to obtain the LMCT energy for various trivalent RE ions in REO8
13- cubic model cluster, we performed first-principles calculations using the DVME method and constructed the theoretical energy diagram of the rare earth ions, and compared it with the reported LMCT energies in YPO4 [3] and YAG [4].
[Computational Method] We constructed a 9-atom cluster consisting of the central RE ion and the 8 oxygen ions with Oh symmetry (cubic) and 2.4 Å bond length. We considered the ground state configuration 4f
n
2p48 and one-electron excitation configuration 4f
n

+12p47, where n is the number of 4f electrons. In order to improve the computational accuracy, the configuration dependent correction (CDC) was considered. The LMCT energy was calculated as the transition energy from the top of the valence band corresponding to the highest one of the MOs mainly consisting of oxygen 2p orbital to the MO mainly consisting of RE 4f orbital based on the MO calculation using the DV-Xα method and the CI calculation using the DVME method.
[Result] The theoretical LMCT energies calculated with CDC are shown as the diagram in Fig. 1 together with the diagram for the reported values in YPO4 and YAG. The figure shows that the reported trend, especially around Eu to Gd, was successfully reproduced by first-principles calculations. The overestimation for Ho to Tm is probably due to the insufficient consideration of electron correlation.
[1] J. Ueda, et al,. Appl. Phys. Lett. 104, 101904, (2014).
[2] K. Ogasawara, et al., Phys. Rev. B, 64, 115413, (2001).
[3] E. Nakazawa, J. Lumin. 100, 89, (2002).
[4] P. Dorenbos, J. Lumin. 134, 310, (2013).

Figure 1
Analysis of Cerium Oxide Doped Anti-Corrosion Coatings By Scanning Electrochemical Microscopy and Electrochemical Impedance Spectroscopy
Authors: Murphy Jules , Lancaster Fred , Calhoun R. L. 
Published: February 2020

Previously, a protocol was developed to use SECM (scanning electrochemical microscopy) to screen for the effectiveness of new anti-corrosion coatings produced by the Navy.[i]Briefly, increasingly positive potentials at the Al substrate are applied while the tip is in the substrate generation tip collection (SGTC) mode. Poor coatings show significant tip currents while good ones do not.
The current work used this protocol on coatings provided by engineers from Naval Air Systems Command that had been doped with varying amounts of CeO. Initial voltage applications showed coating breakdown with increasing current at ever more positive potentials. However, a maximum was seen and at potentials above 2V, the coatings appear to have improved.
In an effort to elucidate what caused this effect, Electrochemical Impedance Spectroscopy (EIS), laser profiling, and x-ray fluorescence studies were performed to look for changes in the coating. Preliminary EIS results (Figure 1) indicate the resistance due to pores increased after higher potential application hinting the pores may be becoming smaller.[ii]The value of the real component of the complex impedance, where the left side of the semicircle begins, is the sum of the uncompensated resistance and pore resistance. Spectra were taken after the Al substrate was exposed to the indicated DC potential. While not large, it can be seen the resistance increased as the applied potential increased. X-ray results as well as laser profiling (not shown) indicate the coating at and near the surface is changing. The X-ray data show other components of the coating (Ti, Fe, etc) are migrating to/from the surface. The laser generated topographical data also shows morphological changes on the surface all of which may be the cause of the pore size reduction.
All data were taken at the U.S. Naval Academy, an undergraduate only institution, by one student. Projects such as this where the midshipmen conduct two semesters of research under the supervision of a professor, became part of USNA’s chemistry major over a decade ago. While not compulsory, some 70% of the majors elect this option and most result in at least a published conference proceeding. This is even more remarkable in that the students do not have the flexibility to conduct experiments outside the normal school day.

[i] Lee, C., Calhoun, M., Dorriety, W., Hanrahan, R., Lancaster, F., Calhoun, R., ECST, 66 (30) 65-71 (2015).
[ii] Loveday, D., Peterson, P., Rodgers, B., JCT Coatings Tech, Oct, 88-93 (2004).

Figure 1
Elucidating Electro-Hydrodynamics at a Liquid Metal Oxide-Electrolyte Interface Via Electrochemical Impedance Spectroscopy
Authors: Joshipura Ishan D , Dickey Michael D. 
Published: February 2020

This work characterizes the behavior of a eutectic alloy of gallium and indium (75% Ga, 25% In, by weight, ‘EGaIn’) in response to electric fields. The metal is a liquid at room temperature (M.P., 15.5 °C) and exhibits low toxicity. These fluidic metals may be injected into microfluidic systems, fibers, and capillary networks to form soft electronic devices that are soft and compliant. Once injected, the metal remains in its place because of the adhesive nature of its thin native oxide. Preventing the oxide adhesion within microchannels enables reversible actuation of EGaIn. Actuating liquid metals may be useful for soft actuators, reconfigurable optical displays, frequency tunable antennas, and other opto-fluidic technologies.
In this work, we utilize low voltages (<2 V) to reversibly move droplets of EGaIn through microchannels. Pre-wetting the channels with an aqueous solution prior to injecting the metal prevents oxide adhesion; the water forms an interfacial ‘slip-layer’ the metal and channel wall. Thereafter, an applied electric field (~10-20 V/m) actuates the liquid metal by establishing a gradient of surface tension; this effect is known as continuous electrowetting (CEW). Although CEW has been utilized before with mercury, which is toxic, the adhesive nature of the Ga oxide complicates CEW behavior. This work utilizes optical microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) to characterize electro-hydrodynamics of CEW with EGaIn under a variety of conditions. Specifically, we compare electro-hydrodynamic behavior of EGaIn with and without the presence of an oxide ‘skin’. In addition, we elucidate the influence of material properties of the electrolyte on the metal-electrolyte interface. An equivalent circuit model from EIS experiments is proposed to understand the metal-electrolyte interface and to control the movement of the liquid metal within microfluidic systems.
(Invited) Reflections on Rust: Iron Oxide Photoelectrodes for Solar Energy Conversion and Storage
Authors: Rothschild Avner 
Published: February 2020

Solar water splitting is a promising route for sustainable and scalable hydrogen production from renewable sources: water and sunlight. The hydrogen can be used as a clean fuel for refueling fuel cell electric vehicles with zero emissions. Hydrogen can also serve as a feedstock for the production of drop-in liquid fuels by CO2 hydrogenation, and ammonia via the Haber–Bosch process. The greatest challenges towards viable solar water splitting technology lay in the selection and design of photocatalytic materials and devices that harvest sunlight and split water efficiently and produce hydrogen at a competitive cost. To this end photocatalytic materials that are stable in alkaline or acidic aqueous solutions, absorb visible light, promote water oxidation or reduction reactions and comprise of abundant materials must be employed.
Iron oxide (α-Fe2O3, hematite), aka rust, is one of few materials meeting these criteria, but its poor transport properties and fast charge recombination present challenges for efficient charge carrier generation, separation and collection. We explore innovative solutions to these challenges using ultrathin (20-30 nm) films on specular back reflectors. This simple optical cavity design effectively traps the light in otherwise nearly translucent ultrathin films, amplifying the intensity close to the surface wherein photogenerated charge carriers can reach the surface and split water before recombination takes place. This is the enabling key towards the development of high-efficiency iron oxide photoelectrodes whose structure and properties can be tailored by design. However, the design rules for these devices remain elusive because iron oxide behaves differently than conventional semiconductors such as silicon, probably due to the strong correlation between the electrons that give rise to the current and the ions that form the crystalline lattice.
Our first goal is to discover the physico-chemical processes that limit the performance of iron oxide photoelectrode and devise design principles that enable overcoming these limitations through material design at the nanoscale that combines iron oxide together with selective underlayers and overlayers that separate positive and negative charge carriers, thereby reducing recombination losses and increasing efficiency. The second goal is to apply these design principles to construct high-efficiency solar water splitting devices. The third and final goal is to invent new device architectures and operation schemes that enable affordable solar hydrogen production in large-scale applications, closing the gap between basic research on lab-scale devices and a new solar energy technology that provides stable power on demand.

Figure 1
Oxidation−Stable Plasmonic Copper Nanoparticles in Photocatalytic TiO2 Nanoarchitectures
Authors: DeSario Paul A. , Pietron Jeremy , Brintlinger Todd , Parker Joseph F. , Baturina Olga A , Stroud Rhonda , Rolison Debra R. 
Published: February 2020

We describe the incorporation of plasmonic copper (Cu) nanoparticles into titania (TiO2) aerogels and demonstrate surface plasmon resonance (SPR)–driven photoelectrochemical oxidation of methanol under visible light. Copper could provide a more abundant, less expensive alternative to gold and silver as a visible light–active plasmonic metal, however, the propensity of Cu to oxidize at the expense of its plasmonic character greatly limits its potential applications. Most reports of supported, plasmonic Cu nanoparticles describe the necessity of preventing Cu oxidation by maintaining strictly anoxic environments or relying on surface-obscuring chemical stabilizers. We stabilize plasmonic Cu nanoparticles by establishing extensive interfacial contact between Cu nanoparticles and a TiO2 aerogel support. The multiple points of contact between 2–3 nm Cu nanoparticles photodeposited at the networked ~10 nm TiO2 particulates of the aerogel stabilizes Cu against oxidation to an extent that preserves the plasmonic behavior of the nanoparticles, even after long-term exposure to ambient air. The wavelength dependence of photoelectrochemical methanol oxidation at Cu/TiO2 aerogel photoanodes verifies the plasmonic origin of the photoelectrochemistry. Plasmonic behavior is not seen for Cu photodeposited at a commercially available, non-networked TiO2 nanopowder in which the primary particle size is ~10× greater than the size of the supported Cu particle. The divergent behavior of Cu when a 3D Cu||oxide interface is formed on aerogel supports compared to the 1D junction between Cu on commercial TiO2 nanopowder supports highlights the importance of the interfacial design motif on preserving plasmonic Cu.
Self-Formed Catalysts Using Electrochemical (de)Lithiation for Oxygen Evolution Reaction
Authors: Sumaria Vaidish Pravin , Krishnamurthy Dilip , Viswanathan Venkatasubramanian 
Published: February 2020

Oxygen evolution reaction is a key process for enabling solar or electricity-driven water splitting. IrO2 and RuO2 are among the most active catalysts for OER, but material scarcity and high cost limits their usage in large-scale applications.[1] Here, we propose a new strategy for self-forming a range of electrocatalysts through electrochemical lithiation of functional metal oxides by potential control. The lithiated phases provide a strategy to tune the strain and electronic structure and thereby leading to efficient electrocatalysts. The most suitable reaction to demonstrate this strategy is the oxygen evolution reaction, which occurs in highly oxidizing environments.
In this work, we perform a thermodynamic analysis involving density functional theory (DFT) calculations to identify the effect of lithium intercalation into functional metal oxides. The intercalation of lithium ions induces both strain and compositional change. Small strains have been induced through core-shell catalysts and interlayers to significantly enhance the activity of Pt for Oxygen Reduction Reaction (ORR).[2],[3]
We will report on the possibility of using various functional layered metal oxides such as MnO2, CoO2, etc.
It has been shown that extraction of intercalated Li+ ions from LiCoO2 (during charging) causes expansion. When the Li+ ions intercalate, the lattice reversibly returns to its original spacing.[4] Even small change in lattice volume is sufficient to produce enough strain in the lattice to alter its activity for a reaction. We illustrate the concept through the intercalation on CoO2 layer, as shown in the Figure. Upon lithiation, the binding strength of intermediates is affected by the compressive strain induced. We will report on calculations employing the Bayesian Error Estimation function with van der Waals exchange correlation to determine the O*, OOH* and OH* adsorption energies. This is used to determine the theoretical limiting potential, which is determined by UL= max [(ΔGO* - ΔGHO*), 3.2-(ΔGO* - ΔGHO*)]. Promising metal oxide catalysts with corresponding optimal degrees of lithiation will be identified using this framework to maximize activity. We will also use ensemble error estimation capability within BEEF to report on uncertainties associated with these calculations.[5]

References:

1 Lee, Y. et.al. J. Phys. Chem. Lett., 3(3):399–404, 2012.

2 Friebel, D. et. al. J. Am. Chem. Soc., 134 (23), 9664–9671, 2012.

3 Strickler, A.L. ACS Energy Lett., 2 (1), 244-249, 2017

4 Wang, H. et. al. Science, 354(6315):1031–1036, 2016.

5 Wellendorff J. et. al. Phys. Rev. B, 85, 235149, 2012.

Figure 1
Catalyzed Oxidation of Chlorine and Bromine in Room Temperature Chloroaluminate and Bromoaluminate Melts
Authors: Krivan Emese , Foister Shane , Tian Mengkun , Elgammal Ramez Ahmed , Counce Robert , Zawodzinski Thomas A. 
Published: February 2020

The use of haloaluminate room temperature molten salts has potential for interesting battery chemistries. This is particularly true for acidic (excess Lewis acid, e.g. AlCl3, over the organic chloride salts) compositions. In that case, Al is readily plated and stripped, as we discussed some time ago.1

A particularly interesting battery combination arises when the aluminum negative electrode is paired with the evolution of the halogen from the acidic melt. In that case, maximum redox active species concentration is achieved and maximum voltage can be obtained since the entire electrochemical window is utilized. However, several issues with chlorine evolution are known. First, in an acidic melt chlorination of imidazolium cations occurs. This can be partly mitigated by appropriate modification of the cation. A second problem is the somewhat sluggish catalysis of chlorine evolution observed on carbon surfaces.
In this work, we report results of efforts to improve on the latter aspect. Specifically, we describe the catalysis of chlorine evolution by catalytically active surfaces. In particular, we show significant enhancements in onset potential for chlorine evolution using supported Ru catalysts. In Figure 1, we compare the chlorine evolution voltammetry in 1.5:1.0 AlCl3:EMIC on bare glassy carbon to that observed on the same electrode coated with a sample of 60 wt% Ru on multiwalled nanotubes (prepared in-house). The onset of chlorine evolution occurs on the order of 300 mV less positive with the supported Ru catalysts. We have deposited the Ru on various carbon structures to explore the applicability of this catalyst system for batteries and flow batteries. Studies of the same reaction on Pt electrodes show that the supported Ru nanoparticles have similar activity to that of Pt for this reaction.
In addition, similar results were also obtained for bromine evolution. In that case, the lower volatility of the product allowed us to readily observe the bromine oxidation on the reverse scan. This reaction is substantially more reversible on these catalyzed surfaces.
Figure 1: Voltammetry of 60%Ru on MWNT on glassy carbon compared to that of the bare glassy carbon electrode.

Figure 1
Insight into Structure and Transport of the Lithium, Sodium, Magnesium and Zinc Bis(trifluoromethansulfonyl)Imide Salts in Ionic Liquids
Authors: Borodin Oleg , Giffin Guinevere A , Moretti Arianna , Haskins Justin B , Lawson John W , Meda Lamartine , Passerini Stefano 
Published: February 2020

Room temperature ionic liquids (RTILs) have attracted significant attention due to their potential applications for batteries, super-capacitors, actuators, dye sensitized solar cells and thermoelectrochemical cells. RTILs doped with lithium, sodium, magnesium and zinc salts are of primary interest for battery and hybrid capacitor applications. This presentation will focus on insights into structural and transport properties of the alkylpyrrolidinium-based ionic liquids doped with lithium, sodium, magnesium or zinc bis(trifluoromethansulfonyl)imide (TFSI) salts obtained from molecular dynamics (MD) simulations that utilized the many-body polarizable force field (APPLE&P).
After validating the ability of the developed force field to predict ionic conductivity of RTILs doped with Li, Na, Mg and Zn salts, a detailed picture of the metal coordination will be presented. The Li and Na cations were coordinated by 4.7-4.8 oxygen atoms from TFSI anions, while Zn and Mg cations were coordinated by approximately six oxygen atoms from TFSI. In addition to being primarily coordinated by TFSI oxygens, Na cations are also coordinated by fluorine and nitrogen atoms from TFSI to a larger extent than other metal cations. The representative solvates from MD simulations performed at 450 K are shown in Figure 1. The cation-TFSI bidentate vs. monodentate binding motifs and the propensity of salts to form large aggregates were analyzed as a function of temperature. Ionic conductivity, viscosity and self-diffusion coefficients from MD simulations agreed well with experimental data, where available. The cation-TFSI residence times followed the order Na< Li < Mg < Zn. Much longer cation-anion residence times for Zn and Mg compared to those of Na and Li were characteristic of the much slower dissolvation for the doubly charged cations and are expected to result in higher interfacial impedance.
This research was partially supported by NASA Minority University Research and Education Project (MUREP; NASA grant NNX15AP44A and interagency agreement NND16AA29I with ARL for modeling).
Figure 1. Representative metal solvates at 450 K and MD simulation box.

Figure 1
Investigating Barriers to Mg Intercalation in Oxide Spinel Cathodes through First-Principles Calculations
Authors: Chen Tina , Gautam Gopalakrishnan Sai , Huang Wenxuan , Ceder Gerbrand 
Published: February 2020

Multivalent batteries are a promising alternative to Li-ion batteries due to their potential to provide higher energy density. Mg2+ has achieved relative success through Chevrel-structured and thio-spinel cathodes, which can be cycled against a Mg metal anode in a full-cell arrangement. However, the low voltage and capacity of the sulfide cathodes limit the energy density of this system, necessitating the search for more energy-dense Mg cathodes.1 Recent theoretical2 and experimental3 studies indicate that the oxide spinel family presents a set of promising Mg cathodes. One of these, the MgxCr2O4 spinel, has reasonable Mg migration barriers and unprecedented energy density for an intercalation cathode. Using first-principles calculations, we investigate the voltage profile for Mg insertion at room temperature and the activation barriers for Mg diffusion at different Mg concentrations in the Cr2O4 structure. Based on our results, we identify a potential limitation to Mg intercalation in the form of a stable Mg-vacancy ordering in the Cr2O4 lattice, which exhibits high migration barriers for Mg diffusion in addition to a steep voltage change. Hence, for the practical usage of Cr2O4 as a cathode in multivalent batteries, steps must be taken to avoid the formation of the stable ordered phase.

1Canepa et al, Chem. Rev. 2017, 117 (5), pp 4287-4341

2Rong et al, Chem. of Mat. 2015, 27 (17), pp 6016-6021

3 Kim et al, Adv. Mat. 2015, 27 (22), pp 3377-3384