bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Carbon Anodes for Use in Electrolytic Reduction of Uranium(IV) Oxide
Authors: Motsegood Perry N , Willit James L , Williamson Mark A.
Published: February 2020

Recycling of used nuclear fuel using pyrochemical methods involves a series of molten salt processes performed at elevated temperatures and results in the separation of actinides from fission products. The first step in the pyrochemical treatment of light water reactor (LWR) oxide fuel is electrolytic reduction. This electrochemical operation converts used fuel oxides to metal before electrochemical separations can be performed by electrorefining. Conversion of oxides to metal is commonly performed in molten LiCl-Li2O at 650℃. Electrolytic reduction of UO2, the primary component of used nuclear fuel, has been successfully demonstrated at the kilogram-scale using platinum anodes1-2, but progression toward engineering scale presents different anode material requirements.

Carbon, specifically graphite, is commonly used for ore refining in commercial molten salt processes because it is cost effective, readily available, and easily fabricated to meet scale-up requirements. Use of carbon anodes in LiCl-Li2O results in different salt chemistries, with respect to using platinum or other oxygen evolving electrode materials. In particular, the evolved gaseous byproduct of carbon anodes is CO and CO2, which can react with Li2O to form Li2CO3. If the carbonate concentration is allowed to increase, the desired reaction, namely the transport of oxide from the cathode to the anode via Li2O, is replaced by the undesirable transport of carbon from the anode to the cathode via Li2CO3.

This report will discuss use of carbon as an anode material for the electrolytic reduction of UO2 to uranium metal in molten LiCl-Li2O at 650℃. A discussion of the salt chemistry, minimizing Li2CO3 formation, method developments, cell operation, and reduction efficiency will be presented.

References:

Laszlo Redey and Karthick Gourishankar, “Direct Electrochemical Reduction of Metal-Oxides” US Patent US6540902 B1, Granted April 1, 2003

S. D. Herrmann, S. X. Li, M. F. Simpson and S. Phongikaroon, Separation Science and Technology
2006, 41, 1965-1983.

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The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
(Invited) Designer Ionic Liquids for Improved Magnesium Anode Behavior
Authors: Buttry Daniel A. , Watkins Tylan S , Kumar Ashok
Published: February 2020

Our group has been involved in studies of the complexation and speciation of Mg2+ in ionic liquids as a means to understand the influence of coordination environment on Mg anode electrochemical behavior.1 In this presentation we will focus on the complexation of Mg2+ by bis(trifluoromethylsulfonyl)imide ionic anion (TFSI-), borohydride anion, glyme-based (i.e. PEGylated) solvents and chelating ionic liquids bearing polyethylene glycol-like chelating groups, and on the influence of such complexation on the reversibility of Mg electrodeposition/dissolution.1,2 Complexation is predominantly studied by Raman spectroscopy, which allows facile differentiation of complexed and free species. We show that the lessons learned from such studies of Mg2+ complexation allow the design of new chelating ionic liquids that show markedly improved Mg2+/Mg0 electrochemical behavior compared to the parent TFSI-based ionic liquids. Specifically, we describe reasonable coulombic efficiency (ca. 90%) and current densities (>1 mA/cm2) that are achievable through judicious choice of the complexation environment and other chemical features of the electrolyte system.

We also discuss more generally the factors that act to suppress facile Mg electrodeposition/dissolution. We provide experimental verification of some of the means by which these various factors influence both chemical and electrochemical reversibility of Mg anode behavior.

These results represent the first demonstration of reversible electrochemical deposition/dissolution of Mg in an ionic liquid specifically designed with this task in mind.

Acknowledgment: We acknowledge support from the Army Research Office grant number W911NF-11-1-0432.

References:

“Determination of Mg2+ Speciation in a TFSI--Based Ionic Liquid With and Without Chelating Ethers Using Raman Spectroscopy”, Watkins, T., Buttry, D. A.; J. Phys. Chem. B, 2015, 119(23), 7003-7014. (DOI: 10.1021/acs.jpcb.5b00339)

“Designer Ionic Liquids for Reversible Electrochemical Deposition/Dissolution of Magnesium”, Watkins, T.; Kumar, A.; Buttry, D.A.; J. Am. Chem. Soc.,
2016, 138(2), 641-650 (DOI: 10.1021/jacs.5b11031)
Availability Evaluation of SiC Anode in Chloride Molten Salt Electrolysis
Authors: Takahashi Yoshihiro , Takenaka Toshihide
Published: February 2020

INTRODUCTION

Carbon or graphite is commonly used to anode material in molten salt electrolysis because of their stability and reasonable price. However, they are consumed with CO or CO2generation by electrochemical reaction with oxide ion, and the consumption is undesirable in electrolysis in chloride melt. In this study, the anodic behavior of carbide was investigated to develop the inert anode material.

EXPERIMENTAL

A eutectic mixture of LiCl-KCl (41:59 in mole) with Li2O was used as an electrolytic bath. Anode was a silicon carbide (SiC) rod, and a graphite rod was also used for comparison. Cathode was an Al plate, and reference electrode was a Ag/Ag+ couple, and its potential was calibrated with a Li/Li+couple. The electrodes were inserted into the molten salt at 723 K in an Ar atmosphere. Reactions were studied by cyclic voltammetry and potentiostatic electrolysis. The generated gas by potentiostatic electrolysis was analyzed by gas chromatography. After the electrolysis, the specimen was analyzed by SEM-EDX and XRD.

RESULTS and DISCUSSION

Fig.1 shows typical cyclic voltammograms at the SiC and graphite anode. At the graphite electrode, oxidation current increased around 2.65V (vs. Li/Li+, the same hereinafter) and 3.5V, and arose suddenly above 3.8V. At the SiC electrode, oxidation current was increased around 2.65V, 3.2V, 3.5V and arose suddenly above 4.0V. Bubble formation was seen around 3.5V and above 3.8V (4.0V) at both electrodes. The generated gas at 3.5V was identified as CO2
　by gas chromatograph, and it was considered that the generated gas above 3.8V (4.0V) was Cl2. Gas was not generated around 3.2V at the SiC electrode, and SiO2was detected on by XRD after potentiostatic electrolysis at 3.2V.

The mass of the SiC electrode increased by potentiostatic electrolysis at 3.2V for 4h and 6h, while it decreased by the electrolysis for 8h, as shown in Table 1. The mass didn’t change by potentiostatic electrolysis at 3.5V for 4h, but it decreased by the electrolysis for 6h and 8h. The mass of the SiC electrode tended to decreased with the electrolysis time at both potentials. The mass decreased by the electrolysis at 4.5V even for 4h.

The O content after the potentiostatic electrolysis at higer potential was smaller than that at lower potential as shown in Table 2. The surface of the SiC electrode after the electrolysis was uneven and a dense SiO2layer was not found at the cross-section.

From the result mentioned above, SiO2 formation occurred below 3.2V at SiC, and CO2 was generated around 3.5V. This result indicate that SiO2 formation precedes CO2 generation at SiC, but that the formed SiO2 cannot prevent the consumption of SiC by CO2 generation. The formed SiO2 layer was still uneven and partially peered out during electrolysis. The formation of a dense and coherent SiO2 layer should be necessary to prevent the consumption of SiC by electrolysis in molten chloride.

Figure 1
Currentless Deposition of Niobium-Based Protective Coatings for Application in Molten Salts
Authors: Abramov Aleksandr V. , Polovov Ilya B. , Volkovich Vladimir A. , Rebrin Oleg I.
Published: February 2020

Molten salts, particularly alkali halides, can be used for developing new methods of rare and refractory metals production and pyrochemical reprocessing spent nuclear fuels. Molten salt nuclear reactor now again attracts attention as one of the prospective power generating systems. Wide scale application of fused salts in various areas of technology is hampered by the problem of finding suitable corrosion-resistant materials. Corrosion of metals in molten salts is electrochemical in nature, and therefore the most suitable constructive materials for these media are electropositive refractory metals, for example, niobium. High cost of these materials and the difficulties associated with the mechanical processing and welding limit their application. A way to overcome this problem is forming a protective layer of a refractory metal on the base material. In the present work a novel method of forming niobium-based coatings by currentless deposition in molten salts is proposed.

Nicrofer 6020, Nicrofer 6616, Hasteloy N, and KhN65MVU nickel based alloys and metallic nickel were chosen as the base materials for the present investigation. Corrosion tests were carried out in NaCl–KCl–NbCln (n=3.5 or 5 wt. % niobium) and NaCl–KCl–UCl3 (1 wt. % uranium) melts at 750 oC. Duration of the corrosion tests was 30 h.

Contacting nickel based alloys with NaCl–KCl–NbCln melt leads to increase of the sample mass due to the formation of an alloy between nickel (the base constituent of the studied alloys) and niobium on the sample surface, Figure. Nickel-niobium alloy is formed as a result of disproportionation of niobium (III) ions, 4Nb3+ + 3Nialloy → Ni3Nb + 3Nb4+. Nb(IV) ions produced in the same reaction can be reduced to Nb(III) by niobium metal placed in the melt. Formation of a Ni-Nb alloy layer on the sample surface decreases the rate of the base alloy corrosion.

This Ni-Nb phase forms a continuous layer on the sample’s surface and, therefore, this phase can protect the studied alloy from further corrosion. Such protection would be very useful for construction materials used for niobium electrorefining in molten chlorides; especially since currently the problem of finding suitable materials is one of the limiting factors in producing high-purity niobium.

The samples of Nicrofer 6616 and 6020 alloys with the formed niobium coatings were tested in NaCl–KCl–UCl3 (around 1 wt.% U) melts (30 h exposure at 750 ºС). Here the weight of the samples covered with Ni3Nb phase decreased and the corrosion rates were comparable with those obtained earlier for uncoated samples in uranium-containing melts.

Figure. Microstructure of Hastelloy N (a), KhN65MVU (b), Nicrofer 6616 (с) and Nicrofer 6020 (d) alloy samples after 30 h contact with NaCl–KCl–NbCln melts (n=3.5, 5 wt. % Nb) at 750 ºС.

Figure 1
On the Formation of Clusters of Li8 in Molten Solutions of LiCl-Li
Authors: Merwin Augustus , Phillips William , Chidambaram Dev
Published: February 2020

Numerous base metals can be obtained via electrolytic reduction of their respective oxides in molten LiCl-Li2O electrolytes. In these processes, often times, Li+ is co-reduced to metallic Li. The formation of Li0 is undesirable and leads to a loss of current efficiency and therefore is of significant interest. In spite of its importance, molten mixtures of LiCl and Li are still poorly understood and previous research has demonstrated a variety of phenomena that are seemingly unexplainable. We have custom built a unique setup to conduct in-situ Raman spectroscopy of such molten mixtures. In this work, we show that a Raman active phase forms in the fused salt when Li is electrochemically reduced from Li2O in LiCl. The spectrum was comprised of three fundamental features at 285.5, 302.8, and 318.2 cm-1, with overtones of decreasing intensity at approximately integer multiples of these Raman shifts as Shown in Figure 1. This spectrum was found to be consistent with previously-reported characteristic spectrum of the lithium cluster Li8. The presence of a colloidal suspension of lithium clusters in the molten salt is hypothesized to be the reason behind anomalous physical behavior of LiCl-Li solutions.

Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) through grant DE-NE0008262, and the US Nuclear Regulatory Commission (NRC) under contracts NRCHQ-11-G-38-0039, NRC-38-10-949 and NRC-HQ-13-G-38-0027. Mr. Kenny Osborne serves as the program manager for the DOE awards and Ms. Nancy Hebron-Isreal serves as the grants program officer for the NRC awards.

Figure 1
Ionic Liquid Study: My Personal History
Authors: Watanabe Masayoshi
Published: February 2020

In this talk, I would like to talk about my personal history on ionic liquid research, especially by focusing on why and how I became to be interested in such research. Also, I would like to introduce important researchers who greatly affected my research year by year up to now.
Anodic Dissolution of Tungsten from Super Hard Alloys in Molten Sodium Hydroxide
Authors: Oishi Tetsuo
Published: February 2020

Anodic dissolution of tungsten in a molten sodium hydroxide bath was investigated at 723K in order to simplify a tungsten dissolution step during tungsten recycling process from secondary resources like used super hard alloy tools. Cyclic voltammetry using tungsten, tungsten carbide and cobalt, which is used as binder in super hard alloys, electrodes suggested that tungsten is easily oxidized and dissolves into the melt. Cobalt was also oxidized and formed oxide or hydroxide film. When water vapor was introduced into the system, the obtained cyclic voltammograms changed with the partial pressure of water vapor. Based on the above mentioned results, anodic dissolution was carried out at constant voltage using throw-away tips as actual secondary resources. When the throw-away tip was anodically oxidized, both the tungsten carbide and binder metal of cobalt were dissolved at constant voltage of 1.0 V, and whole the tips were dissolved by a long-term electrolysis of 20 hours. Although the dissolved tungsten remained in the melt, the greater part of dissolved cobalt deposited as metal powder on the cathode. The current efficiencies of tungsten carbide dissolution were calculated to be 96%. When 0.7 atm of water vapor was introduced, the electrolysis was terminated within 5 hours, which indicates the effectiveness of water vapor pressure control in the present process.
Pd Nanoparticle Formation during Constant Potential Electrodepositions in Ionic Liquids
Authors: Shrestha Sujan , Nagib Miyan , Biddinger Elizabeth J
Published: February 2020

Electrodepositions in ionic liquids (ILs) allow for opportunities to improve deposited morphologies, access redox potentials that cannot be achieved in aqueous baths, and utilize less hazardous bath compositions. The driver to utilize ILs for Pd electrodeposition is to minimize hydrogen embrittlement challenges commonly associated with Pd electrodeposition in aqueous electrolytes. Generally, the resulting Pd deposits in ILs are thin films, loosely adhered fine powders or dendritic structures, depending upon the IL selected and the electrochemical parameters used(1, 2). Recently, it has also been shown that electroreduction of Pd in ILs can result in nanoparticles being formed in solution, rather than on an substrate electrode when high overpotentials are used(3).

Previously, we showed Pd nanosphere formation can be controlled through potentiostatic pulse deposition in 1-butyl, 3-methylimidazolium chloride [Bmim][Cl] onto Ni electrode substrates(4). The nanosphere size was found to be a function of cycle time. In contrast, using 1-buty, 1-methylpyrrolidinum dicyanamide [Bmpyrr][DCA] under constant potential conditions, thin film Pd layers on nickel electrode substrates were obtained(5).

We will present how, upon further investigation, these Pd “thin films” formed from constant potential deposition in [Bmpyrr][DCA] are actually agglomerates of nanoparticles that can be scraped off the Ni substrate and dispersed in solution in an unagglomerated state. These nanoparticles have an average size of 6.3 ± 1.6 nm when deposited at -2.3V vs. Fc/Fc+. Further investigation into the conditions for electrodeposition in ILs where it was thought that thin films were formed will also be discussed to better understand if the resulting deposits were truly thin films and not nanoparticle agglomerations.

References

1. M. Jayakumar, K. A. Venkatesan and T. G. Srinivasan, Electrochimica Acta, 52, 7121 (2007).

2. I. W. Sun and C. L. Hussey, J. Electroanal. Chem., 274, 325 (1989).

3. Y. Katayama, Y. Oshino, N. Ichihashi, N. Tachikawa, K. Yoshii and K. Toshima, Electrochimica Acta, 183, 37 (2015).

4. S. Shrestha, M. Nagib and E. J. Biddinger, Journal of The Electrochemical Society, 163, D74 (2016).

5. S. Shrestha and E. J. Biddinger, Electrochimica Acta, 174, 254 (2015).
Electrochemical Deposition of Aluminum and Aluminum-Manganese Alloys in Ionic Liquids
Authors: Ispas Adriana , Vlaic Codruta Aurelia , Camargo Magali Karina , Bund Andreas
Published: February 2020

Aluminum and aluminum-manganese alloys were electrodeposited on low carbon steel substrates from 1-ethyl-3-methyl imidazolium chloride with AlCl3 and MnCl2 salts. We could show that the applied current density influenced drastically the morphology of the deposits. More uniform and smooth deposits were obtained at current densities above 6 mA/cm², while at lower current densities the morphology of the deposits was in the form of plates, which grown parallel to the substrate. The morphology and the composition of the deposited films were characterized by SEM and EDX. X-Ray diffraction (XRD) measurements showed that the Al and some of the AlMn layers have a crystalline structure. The thicknesses of the deposits, and in the case of the AlMn their composition, were estimated from X-Ray Fluorescence measurements.

The corrosion behavior of the layers having different thicknesses (up to 30 µm) was studied by electrochemical impedance spectroscopy and linear polarization in 3.5% NaCl solution. We could show that the AlMn coatings had superior corrosion resistance compared to the pure Al layers.
Combining Mechanical Tension with Natural-Fiber-Welding Treatments of Cellulose Yarns
Authors: Fahey Patrick J , Fox Eric T , Durkin David P. , De Long Hugh C , Trulove Paul C
Published: February 2020

Natural-fiber welding (NFW) is an ionic-liquid based treatment method that partially dissolves a fibrous structure’s polymer chains to allow subsequent polymer-chain entanglement between adjacent fibers. NFW treatments can beneficially alter the tensile properties of treated fibrous structures through this polymer entanglement [1]. Up until now fibrous-structure samples were held in place during NFW treatments by applied force to ensure contact with heated platens or to prevent deformation and warping. This new study, however, purposefully applies force during the NFW treatments to evaluate the effect of applied force upon the resulting material properties of the treated fibrous structure. Understanding what additional effects tension has upon NFW treatments is vital to evaluating not just how to best control warping of experimental samples, but also how to design scaled-up NFW treatment processes that rely upon applied tension for pulling continuous feeds of yarn and cloth through equipment.

To test the effect of mechanical forces during NFW treatment, tension was applied to natural fiber yarns in their axial dimension. The three main variables evaluated were (1) the magnitude of tensile force, (2) the time at which this tensile force began during the course of the NFW treatment, and (3) the NFW treatment parameters previously known to be vital like temperature, time duration, and ratio of 1-ethyl-3-methylimidazolium acetate to yarn. In this presentation we will present results of our investigations of these variables using tensile testing, infrared spectroscopy, con-focal fluorescence microscopy, and scanning electron microscopy.

[1]
L. M. Haverhals, W. M. Reichert, H. C. De Long and P. C. Trulove, "Natural Fiber Welding," Mcromolecular Materials and Engineering, 295, 425-430 (2010).
Potential Dependent IR/Visible Double Resonance Sum Frequency Generation Spectroscopy to Probe Electronic Structure at Electrochemical Interfaces
Authors: Noguchi Hidenori , Yang Shuo , Uosaki Kohei
Published: February 2020

To understand the mechanism and improve the efficiency of processes at solid surfaces both in gas phase such as heterogeneous catalytic reactions, and in liquid phase such as electrochemical reactions, it is essential to have in situ, real time information of geometric structure and electronic structure of the solid/gas or solid/liquid interface, and molecular structures of reactant, product, intermediate, and solvent at the interface. While many techniques to obtain such information are available for solid/gas interfaces, most of them are not applicable to solid/liquid interfaces because of the presence of liquid, mostly water, which interacts strongly with probe such as electron.

 Double resonance sum frequency generation (DR-SFG) spectroscopy, which is a highly surface-sensitive nonlinear optical technique with the tunable frequencies of both incident fundamental lights, i.e., visible and IR, can provide information of surface molecular and electronic structures, which is not obtained by traditional surface vibrational technique. Here, we employed DR-SFG technique to probe potential-dependent electronic structure of CO/Pt interface in acid electrolyte solution. SFG signal due to C-O stretching was observed and was dependent on frequency of visible light as a result of the energetic coupling of electronic transition with the input visible photon and/or output SF photon, i.e., double resonance effect. Furthermore, resonant visible energy linearly depended on electrode potentials. Thus, the electronic resonance could be explained by the transition from Fermi energy, Ef, of Pt to the unoccupied 5anti-bonding state of CO.

 The present work showed that SFG spectroscopy can probe not only the molecular structure but also the electronic structure of electrochemical interface, which is difficult to be determined by other methods.
High-Speed Surface X-Ray Diffraction for Monitoring Structural Changes of Electrode Surfaces: An Application to Methanol Oxidation on Pt(111)
Authors: Shirasawa Tetsuroh , Voelgeli Wolfgang , Arakawa Etsuo , Masuda Takuya , Takahashi Toshio , Uosaki Kohei , Matsushita Tadashi
Published: February 2020

To deeply understand how electrochemical reactions proceed at the electrode/electrolyte interfaces, it is necessary to reveal the interface structures at atomic resolution and in real time. Scanning probe microscopies, synchrotron X-ray scattering and absorption spectroscopy, and surface-sensitive optical methods are often used to observe the interface structures in-situ. Among them, X-ray crystal truncation rod (CTR) scattering, which is one kind of surface X-ray scattering, is a powerful technique to determine the atomic structures across the interface. CTR scattering is widely used to determine static structures, but its application to time-resolved measurements is limited. In the previous time-resolved measurements [e.g. Tamura et al., J. Phys. Chem. B 108, 1992 (2004)], they monitored a specific point in reciprocal space during the electrochemical reaction. Such fixed-single-point measurements can monitor structural changes qualitatively, such as roughening/flattening of the electrode surface and a formation/destruction of a superstructure formed by the lateral periodic array of the adsorbates. However, these measurements can not reveal small positional changes (0.1~0.01 Å) of the interface atoms quantitatively, which often occur with a change of surface adsorbate species or a change of the oxidation state of the adsorbates and/or of the electrode surface. In order to determine the structural change quantitatively, simultaneous measurements of a CTR profile, whose range is wide enough to allow the structural analysis at atomic scale, is needed. In this study, we used an energy-dispersive X-ray CTR scattering technique [T. Matsushita et al., J. Appl. Phys. 110, 102209 (2011)], which enables the simultaneous measurement of a wide range of a CTR profile, to study the electrochemical oxidation of methanol on a Pt(111) electrode. In the methanol oxidation, it is widely accepted that CO molecules are strongly adsorbed on the Pt surface to cause the overpotential. The time-resolved measurement revealed that the height of the topmost atomic layer of Pt was changed by up to about 0.1 Å in the methanol oxidation. The behavior is closely related to the CO adsorption density, referring to the previous infrared spectroscopy measurements [Xia et al., Electrochem. Acta 41, 711 (1996)]. The CO-induced structural change shows a hysteresis with respect to the potential loop (0-1.0V vs. SHE), strongly supporting that the CO-adsorbed surface causes the overpotential. The CTR profile measurements during the potential step chronoamperometry indicates that the formation of a CO-desorbed domain takes several seconds to occur after a positive potential step (0 to 0.8 V), while the CO-rich domain forms within a time resolution of 1 s after a negative potential step (0.95 to 0.6 V).
Structural Behavior of Mixed Metal Oxide Nanoparticles As Electrocatalysts for the Oxygen-Evolution Reaction
Authors: Gliech Manuel , Klingenhof Malte , Bergmann Arno , Strasser Peter
Published: February 2020

The storage of electric energy has become one of the main challenges in infrastructure development. The development of scalable, cost-efficient and robust synthetic routes toward well-defined solid state structures is a major objective in this field.

Electrocatalytic water splitting is a promising way of chemical energy storage wherein the anodic oxygen evolution reaction (OER) is the determining factor. Manganese based oxides have attracted particular attention as non-noble metal catalysts for the OER. Due to their abundance, low price and ecological harmlessness, those materials are promising candidates for a commercial application. Therefore insights into the relations between synthesis conditions, composition, structure and activity as well as stability are of fundamental interest. 1,2

Here, we present the comparison of different synthesis routes for Mixed Oxide Nanoparticles (NPs) of Manganese with Iron and Cobalt. The well characterized (TEM, EDX, XRD) catalysts were tested with respect to the relation of crystal structure to electrocatalytic activity and stability for the OER in alkaline media using Rotating Disk Electrode (RDE) measurements. We report a non-linear relation between composition and activity as well as durability.

Literature:

[1]Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; de Araujo, J. F.; Reier, T.; Dau, H.; Strasser, P. Nat Commun 2015, 6.;

[2]Gliech, M.; Bergmann, A.; Spöri, C.; Strasser, P. Journal of Energy Chemistry 2016.
Nano-Surface Finishing for Electrothermal Instability Evolution Studies
Authors: Yelton W. Graham , Awe T.J. , Pillars Jamin Ryan , Yu E.P. , Peterson K.J. , Rosenthal S.E. , Sinars D.B. , Gomez M.R. , Vesey R.a. , Yates K.C. , Bauer B.S. , Hutchinson T .M. , Fuelling S.
Published: February 2020

Implosion asymmetries generated by the Magneto-Rayleigh-Taylor (MRT) instability commonly limit the performance of the magnetically accelerated targets used to compress high-energy-density plasmas for radiation effects sciences and inertial confinement fusion studies, yet the seed perturbation from which MRT grows is not yet fully understood. Early in the current pulse an electrothermal instability (ETI), which is driven by non-uniform runaway Ohmic heating, may provide a mass perturbation on the target’s surface which exceeds the machining roughness; ETI may then provide the dominant seed from which MRT grows.   

First, surface finishing data and results from experiments on the Sandia National Laboratories Z Machine (20 MA in 100 ns) are presented which measure the implosion stability of magnetically accelerated liners that were diamond machined and DC electropolished. Experiments examined Al 1100 and Al 2099 liners. High surface precipitates of aluminum, iron, and silicon where found in Al 1100 samples whereas Al 2099 samples show surface precipitates rich in copper after DC electropolishing. While the targets used for Z experiments are typically diamond turned to 10-30 nm rms surface roughness, the observed MRT amplitude is unexpectedly large.  Second, surface finishing data and results from experiments on the U. of Nevada, Reno Zebra Facility (1 MA in 100 ns) are presented. These experiments studied the non-uniform heating of high-purity Al 5N, and Al 6061. When intensely Ohmically heated, Al 6061 alloy, which contains distributed non-metallic inclusions, forms 2-3 times as many surface hot spots as 99.999% pure 5N Al rods (with no inclusions).  Various surface finishes were studied, including “as-received” machined, diamond turned, and electropolished post-finished.  All post-finishes required a two-step “onion-skin” approach to remove nano layers of material at a uniform rate across a large scale. This approach involved pulse anodizing the targets to form an oxide favoring high ridges created by the cutting tools. Next, the oxide was selectively removed to the aluminum substrate.  After removing the oxide, the targets were pulse nano-electropolished using chemistries precisely tailored to the alloy. After the nano-electropolishing step, surface profiles were optically characterized using 3D interferometry. The “post-finish” process was repeated until machining defects were minimized.

This work was funded in part by Sandia’s LDRD program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
(Invited) Unassisted Photoelectrochemical Solar Water Splitting with Greater Than 7% Solar-to-Hydrogen Conversion Efficiency
Authors: Park Jong Hyeok
Published: February 2020

The development of new types of energy generation devices is promoted by increasing public awareness that the Earth's oil reserves could run out during this century. As the energy needs of the planet are likely to double within the next 50 years, the stage is set for a major energy shortage, unless renewable energy can cover the substantial deficit left by fossil fuels. Our group has developed new methods to increase light harvesting efficiency to generate electricity and hydrogen production from solar light by applying nano-concepts to materials and/or devices. In this seminar, the unique materials and processes for efficient solar light harvesting for water splitting will be presented.
Synthesis and Characterization of g-C3N4/B12O17Cl2 Composites with Visible-Light Photocatalytic Performance
Authors: Dong Lifeng , Yu Xuegang , Shan Yan
Published: February 2020

With the crisis of energy resources and increased environmental pollution, an environmentally benign process for preparing high-performance visible-light photocatalysts is imperatively demanded. High-performance visible-light photocatalysts are primarily desirable due to their promising applications for renewable energy and a cleaner environment. The search for suitable semiconductors as photocatalysts for the degradation of organic compounds and the splitting of water into hydrogen gas using solar energy is one of the noble missions of material science. Both pure g-C3N4 and B12O17Cl2 have been identified to serve as photocatalysts. In order to further improve photocatalytic parameters, this study explores a novel method for synthesizing g-C3N4/B12O17Cl2 composites. The morphology, compositions, and crystal structures of the composites are characterized by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. Their photocatalytic properties are comparatively studied with pure g-C3N4 and B12O17Cl2, which allows the catalytic mechanisms of the composites to be investigated by studying the relationship of photocatalysis properties and their composition/structures.
Photoelectrochemical Characterization of Tin Sulfide Nanoplatelet Films
Authors: Cheng Wei , Rassoolkhani Alan , Mubeen Syed
Published: February 2020

Advancing solid-state solar-fuel production systems for large-scale deployment requires inexpensive, stable light absorber materials with appropriate band gap for maximizing stored solar energy to chemical potential energy. Here we report crystalline p-type SnS nanoplatelet films synthesized using chemical bath deposition as a potential candidate for solar H2 production. Regenerative photoelectrochemistry using S2-/S2
2- redox couple was used to evaluate the effect of annealing, film thickness, and illumination type (front vs. back) on optoelectronic properties of SnS nanoplatelet films. The photoelectrochemical performance was found to depend critically on the illumination type and annealing conditions with samples annealed at 200°C and illuminated from front-side showing the best performance. After deposition of TiO2 protection layer and Pt catalyst, SnS films exhibited internal quantum efficiency (averaged over the entire solar spectrum at 0 V vs. RHE) of ~13% and were stable for at-least 1 hour in acidic conditions.
Solar Visible Light Storage on WO3-CdS Heterojunction
Authors: Kim Seonghun , Han Dong Suk , Yoon Sun Hee , Abdel-Wahab Ahmed , Park Hyunwoong
Published: February 2020

CdS and WO3 (CdS/WO3) bilayer film electrodes are fabricated to harness solar visible light (l > 420 nm) and store the photogenerated electrons for possible use during the unavailable periods of sunlight. The overall film thickness is approximately 50 - 60 mm while CdS underlayer is slightly thinner compared to WO3 due to a packing effect. The energetics of CdS and WO3 determined by optical and electrochemical analyses indicates cascaded electron transfer from CdS to WO3. The open circuit potential (EOCP) of CdS/WO3 under visible light (ca. -0.35 V vs. SCE) is nearly maintained even upon light-off, with marginal decrease (~0.15 V) in the dark period over 20 h. Neither CdS nor WO3 exhibit such behavior. The electron lifetimes (t) of CdS or WO3 alone are less than 100 sec, whereas coupling of CdS and WO3 increases t to ~2,500 sec at EOCP. In the absence of dissolved O2, t is further increased, suggesting that O2 is the primary electron acceptor. In spite of oxic condition, CdS/WO3 is found to be capable of continuously reducing Cr6+ to Cr3+ and Ag+ to Ag0, respectively, over 6 h after visible light-off. The number of utilized (i.e., stored) electrons in the reductions of Cr6+ and Ag+ are estimated to be ~1.08 ´ 1017 and ~0.87 ´ 1017, respectively. The primary role of CdS is a visible light absorber in the wavelength range of 420 to ca. 565 nm, while transferring the photogenerated electrons to WO3. The electrons stored at WO3 are gradually released to electron acceptors with suitable redox potentials.
Photo-Electrochemical Investigation of Single Crystalline and Polycrystalline TiO2 Nanostructures for Solar Hydrogen Production
Authors: Yang Bee Lyong
Published: February 2020

Solar hydrogen generation by water decomposition in photoelectrochemical cells, one of the promising technologies for environmentally clean energy, has attracted much attention in the past decade. Among photocatalytic materials, titanium dioxide (TiO2) has been considered as one of the promising candidates as a photoanode for water splitting, due to its high chemical stability, proper band edge positions, and inexpensive cost. However, large band gap of TiO2 (3.1eV) results in limited solar-to-hydrogen efficiency. Thus one of the prerequisites of enhancing the solar energy conversion efficiency of the titania is to enhance its visible light activity, which composes a greater portion of the solar spectrum (~45%). Sensitization of the TiO2 with small band gap nanoparticles such a chalcogenide is an effective strategy to improve the visible light response. In this work we performed comparative study of the photocatalytic properties of single-crystalline TiO2 nanorods and polycrystalline nanotubes. Post heat treatment effects of the CdS nanoparticles on both nanorods and nanotubes were confirmed by HRTEM analysis and photoelectrochemical measurements. Improved photocatalytic activity was attributed to the increased particle size, and thus decreasing the band gap. Furthermore, heat treatment led to the improved crystallinity, which was evaluated by UV-Vis and photocurrent measurement.
(Invited) Photocatalytic CO2 reduction with Water By Cu/TiO2: Mechanistic Studies Using in Situ XAS and FTIR
Authors: Liu Lianjun , Miller Jeffrey , Li Ying
Published: February 2020

Cu/TiO2 photocatalysts are extensively studied for CO2 photoreduction with H2O, but the roles of Cu species and the photocatalyst deactivation mechanism are not well understood. In this work, we have employed in situ X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), to explore the surface chemistry of various Cu/TiO2 under CO2 photoreduction environment. We found that H2 reduced Cu/TiO2 exhibited 50% higher activity of CO production than air-calcined Cu/TiO2, resulting from the synergy of OH groups, Cu+ and oxygen vacancies that can provide CO2 adsorption sites, act as hole scavengers, and facilitate the activation of adsorbed CO2. Meanwhile, the consumption of OH groups and Cu+ active sites by holes may result in catalyst deactivation, correlated to the change of oxidation state from Cu+ to Cu2+ and increased coordination number. Strategies to maintain the more active Cu+ species for more stable CO2 photoreduction activity is also discussed.
Photoelectrochemical Hydrogen Production Using a CaFe2O4 Electrode Coated with TiO2 As a Surface Protective Layer
Authors: Ida Shintaro , Futagami Takamitsu , Hagiwara Hidehisa , Sakai Takaaki , Watanabe Motonori , Ishihara Tatsumi
Published: February 2020

CaFe2O4 is a p-type semiconductor with a bandgap of 1.9 eV that can function as a photocathode for photoelectrochemical (PEC) hydrogen production from water. However, there is one issue in that the CaFe2O4 photocathode is likely to decompose during the PEC reaction, which results in a decrease in the photocathodic current. In this study, a TiO2 thin layer was coated on the CaFe2O4 surface by pulsed laser deposition to suppress decomposition.The onset potential was slightly shifted to the negative side by coating of the photocathode with TiO2. Although the photocathodic current was slightly decreased compared with the CaFe2O4 electrode without the TiO2 layer, the decrease in the photocurrent during the PEC hydrogen production reaction was suppressed. In the case of amorphous-like TiO2-coated CaFe2O4, the photocurrent was increased during the PEC hydrogen production reaction. The ratio of the photocurrent after 6 h reaction to the photocurrent at the initial stage of the reaction (5 min) was 120/100. After the PEC reaction, there were no cracks evident on the electrode surface, and the surface morphology was almost the same as the initial morphology. This result indicates that surface degradation of the CaFe2O4 electrode can be suppressed by coating with a thin TiO2 layer.
Non-Precious Metal-Catalyzed Photoelectrodes for Hydrogen Production Via Solar Water Splitting
Authors: Hellstern Thomas R , DeAngelis Alexander D , King Laurie Ann , Chakthranont Pongkarn , Britto Reuben J , Gaillard Nicolas , Jaramillo Thomas F
Published: February 2020

Photoelectrochemical (PEC) water splitting is a promising route for synthesizing hydrogen using solar energy without direct CO2 emissions.[1] Recent performance modelling studies have shown that systems consisting of two semiconducting electrodes can achieve higher efficiencies than single absorber configurations.[2]

Copper gallium diselenide (CGSe) is a promising wide band gap absorber material for application in a tandem PEC device due to its near-ideal band gap, relatively low cost, and good minority carrier transport.[3] Recent studies involving CGSe as a wide band gap photocathode and platinum as a co-catalyst have shown promising activity but limited stability in alkaline electrolyte.[4] However, many opportunities remain to improve the stability and scalability of these electrodes by improving corrosion resistance and incorporating earth abundant catalysts. Recently, excellent electrochemically stable and earth abundant catalysts, molybdenum disulfide and cobalt phosphide, have emerged as viable alternatives to platinum for catalyzing the hydrogen evolution reaction.[5]
[6]

In this work, we discuss our progress in synthesizing transition metal sulfide and phosphide films that provide corrosion resistance and catalyze the hydrogen evolution reaction for a variety of PEC water splitting electrodes including CGSe and silicon. First, we explore the challenges inherent to protecting different classes of semiconductor materials including topological and processing constraints. These challenges are overcome by using atomic layer deposition combined with low temperature sulfidation and phosphidation as an effective route to synthesizing stable, low light absorbing, broadly applicable thin film catalysts for use in PEC water splitting. Next, we discuss techniques for bridging the gap in hydrogen evolution activity between precious and non-precious metal catalysts. Finally, we suggest general strategies for maximizing device performance of non-precious metal catalyzed solar water splitting electrodes.

[1] M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, Q. X. Mi, E. A. Santori, N. S. Lewis, Chem. Rev. 2010, 110, 6446.

[2] L. C. Seitz, Z. Chen, A. J. Forman, B. A. Pinaud, J. D. Benck, T. F. Jaramillo, ChemSusChem 2014, 7, 1372.

[3] B. Marsen, B. Cole, E. L. Miller, Solar Energy Materials and Solar Cells 2008, 92, 1054.

[4] M. Moriya, T. Minegishi, H. Kumagai, M. Katayama, J. Kubota, K. Domen, Journal of the American Chemical Society 2013, 135, 3733.

[5] T. R. Hellstern, J. D. Benck, J. Kibsgaard, C. Hahn, T. F. Jaramillo, Adv. Energy Mater. 2016, 6.

[6] J. D. Benck, S. C. Lee, K. D. Fong, J. Kibsgaard, R. Sinclair, T. F. Jaramillo, Advanced Energy Materials 2014, 4.
Recent Progress in Aqueous Organic Flow Batteries
Authors: Lin Kaixiang , Chen Qing , Beh Eugene S. , Gerhardt Michael R. , Wong Andrew A. , Tong Liuchuan , Bombarelli Rafa Gómez , Marshak Michael P. , Gordon Roy G. , Aspuru-Guzik Alan , Aziz Michael J.
Published: February 2020

Aqueous-soluble redox-active organic molecules such as quinones are potential low-cost alternatives to metal-based redox flow battery (RFB) chemistries, as demonstrated by a high-performance quinone-hydrobromic acid RFB [1-3]. Here we report the performance of new RFBs based on alkaline chemistries that are non-toxic and less corrosive than the acidic chemistry reported earlier. One cell utilizes 2,6-dihydroxy anthraquinone, which is stable and soluble in KOH, as the negolyte, coupled with ferri/ferrocyanide as the posolyte (Fig. 1, top) [4]. Others introduce RFBs to new classes of redox-active organics other than quinones, including one with a simple, single-step low-cost synthesis with good yield, which exhibits extremely high solubility and operates in a cell (Fig. 1, bottom) with >99.98% capacity retention per cycle.

Fig. 1. Top: CV and cell performance for 2,6-DHAQ vs ferri/ferrocyanide alkaline RFB, from [4]. Bottom: CVs and cell performance for very inexpensive non-quinone RFB.

[1] B. Huskinson et al., Nature
505, 195 (2014).

[2] Q. Chen et al.,
J. Electrochem. Soc.
163, A5010 (2016).

[3] Q. Chen et al.,
J. Electrochem. Soc.
163, A5057 (2016).

[4] K. Lin et al.,
Science
349, 1529 (2015).

Figure 1
Design and Optimization of Carbon Foam Electrode for Local Confinement of Bromine in Non-Flowing Single-Chamber Zinc Bromine Batteries
Authors: Biswas Shaurjo , Senju Aoi , Hodson Thomas , Yang Xiaofang , Koel Bruce E. , Steingart Daniel A
Published: February 2020

Zinc Bromine redox flow batteries are well studied, quite inexpensive, and have reasonably high power and energy densities. However, there has been limited commercial implementation of bromine bearing systems in general, and the Zn-Br2 systems in particular, due to the following premises: i) Br2(l), generated at the cathode during charging, can diffuse through the electrolyte and react with Zn deposited at the anode (crossover), leading to self-discharge; ii) Repeated electroplating and dissolution of zinc leads to dendrite formation, which can form a conductive bridge between the electrodes (shorting), and iii) Br2(l) has low miscibility in aqueous solutions (~2.8 vol%) and tends to stratify, resulting in non-uniform concentration distributions. Standard Zn-Br2 flow-cell designs alleviate these limitations with bromine-complexing agents to improve Br2(l) solubility, separation membranes to prevent crossover and shorting, and flowing electrolyte to remove bromine and to minimize dendrite formation.

In the membrane-free, non-flowing single-chamber zinc-bromine (SC-Zn-Br2) battery design zinc dendrites are allowed to form freely and Br2(l) is allowed to stratify; expensive membranes, complexing agents, and pumps are eliminated; and yet overall energy efficiency is improved and cost is lowered. This is achieved by using a highly-porous carbon foam electrode (CFE) for local containment of Br2 generated during cycling, thus preventing crossover. Zinc dendrites are allowed to grow, but react with the highly corrosive Br2(l) on the surface of the CFE and dissolve back into the electrolyte as Zn2+ and Br-ions. This prevents shorting.

Here, we discuss the design, composition, and fabrication of the CFE, and its effects on the performance of SC-Zn-Br2 battery. In particular, we demonstrate the optimization of CFE porosity through processing parameters to maximize the coulombic and energy efficiencies of the cell. We also introduce a color tracking and feedback monitoring scheme to actively control the active species (deep red Br2(l), yellow Br2(aq), and colorless ZnBr2 electrolyte) transport and prevent self-discharge. Finally, we demonstrate the effect of prolonged exposure to Br2(l) after multiple cycles on various CFE compositions using XPS analysis, and the potential degradation mechanisms. We show coulombic and energy efficiencies of 95% and 75%, respectively, for over 1000 cycles for SC-Zn-Br2 cells, with improvements possible with further optimization of the CFE.