bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Picture of the Electrochemical Double Layer Based on Modern Continuum Thermodynamics
Authors: Landstorfer Manuel , Dreyer Wolfgang , Guhlke Clemens
Published: February 2020

We will revise the widely used concept of inner- and outer Helmholtz planes in electrochemical double layers based on modern continuum thermodynamics. At the metal/electrolyte interface various layers of solvated ions form, namely the inner Helmholtz plane for specifically adsorbed and partially solvated ions, and the outer Helmholtz plane for completely solvated ions closest to the metal surface[1]. It is assumed that all the ionic charge is stored on the respective layer, and that they have a constant width. The potential drop would thus be linear between the inner and the outer Helmholtz layer, which motivates the model concept of a simple plate capacitor.

Based on our new continuum mechanical mixture theory for solvated ions[2] we provide new insights to this model conception. It turns out that neither the inner, nor the outer Helmholtz plane can be modeled as rigid planes which are supposed to behave like simple plate capacitors. The picture of the inner Helmholtz plane (IHP) we draw is based on a surface mixture theory, which incorporates partial solvation, and shows that there is actually no potential drop across the metal/IHP layer. The outer Helmholtz plane results from the saturation of solvated ions closest to the metal surface and grows with an increasing applied potential. Hence, in both cases the model concept of simple plate capacitors is doubtable.

Evidence of this picture comes from a remarkable agreement to single crystal experimental data regarding the computed differential capacity C(U)[3-4].

In consequence, the different types of layers in the space charge region are naturally incorporated in our new mixture theories and an explicit modeling or descriptionof the space charge layer is not necessary.

[1] D. M. Kolb, Angewandte Chemie, 2001, 113, 1198–1220.

[2] W. Dreyer, C. Guhlke, M. Landstorfer, Electrochemistry Communications, 2014, DOI: 10.1016/j.elecom.2014.03.015

[3] G. Valette, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1981, 122, 285 – 297.

[4] G. Valette, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1982, 138, 37 – 54.
Separation of Heavy Bivalent Metals Extracted by Electrodeposition Using a STEEL Substrate from Wastewater
Authors: Addi Yassine
Published: February 2020

ABSTRACT

Heavy metals contaminated waste water sludge is classified as hazardous solid waste(1). For this reason it needs to be properly treated to prevent releasing heavy metals to the environment.

The sludge was treated in a batch reactor (2) by sulfuric acid to extract the contained heavy metals ( Cu; Cd; Ni and Zn).

The effects of sulfuric acid concentration and solid to liquid ratio on the heavy metal removal efficiencies were investigated. The experimental results showed that the total and individual heavy metal removal efficiencies increased with increasing sulfuric acid concentration, but decreased with increasing solid to liquid ratio.

For 5g/L solid to liquid ratio, more than 99,9% of heavy metals can be removed from the sludge by treating with 0,5 M sulfuric acid in 2h.

The separation, of metals extracted by sulfuric acid from the sludge, is carried out by plating on steel substrate (3).

The electrode position is performed in two different media: acid and basic media. A comparative study of the two plating media was studied.

References;

(1) B.Johnke, B.Wiebusch, Fuel Energy Abstract.38(1997)350

(2) M.A.Styllanou,D.Kollia,K.J.Haralambous,V.J.Inglezakis,K.G.Moustakas,M.D.Loizidou, Desalination215(2007)73-81

(3) Mortaga M.Abou-Krisha, Applied surface science 252(2005)1035-1048
Enhancement of Activity of Noble Metal Nanoparticles in Oxidative Electrocatalysis through Modification with Mixed-Metal Oxo-Species
Authors: Rutkowska Iwona Agnieszka , Wadas Anna , Ozimek Weronika , Zagubien Ewelina , Sek Jakub P. , Kulesza Pawel J.
Published: February 2020

Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts.

We pursue a concept of utilization of hybrid mixed metal (tungsten(VI)/zirconium(IV), tungsten(VI)/titanium(IV), tungsten(VI)/cerium(IV)) oxides as matrices for supporting and activating noble metal nanoparticles (e.g. Pt, Pt-Ru, Pd, Ru or Rh) during electrooxidation of methanol, ethanol, dimethyl ether and formic acid. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites.

The concept of utilization of mixed metal oxide supports to active noble metal catalytic sites will be extended to oxidation of such inert reactants as arsenate(III) and nitrate(III) that of importance to analytical chemistry, namely to electroanalytical determinations of toxic oxoanions. Mechanistic considerations will be provided, and comparison will be made to the behavior of small organic molecules mentioned above.
Self-Assembling of Thiol Monolayers on Copper, Copper-Nickel Alloy and Nickel Using Ionic Liquid as Reducing Medium
Authors: Mekhalif Zineb , Rajalingam Sundar , Devillers Sébastien , Delhalle Joseph
Published: February 2020

Self-assembling of molecules on metal surfaces is one way to chemically modify surfaces for various applications. Thiol self-assemblies on metal surfaces like gold, silver and copper are formed easily while thiol monolayers on economically important metal surfaces like copper, copper-nickel and nickel surfaces are yet to be explored due to the less affinity for sulphur and rapid oxidation of metal under ambient atmosphere. Seminal works from our laboratory have shown the use of electrochemical reduction using acids as a feasible way to remove metal oxides layers and form SAMs on metal.

Ionic liquids are promising as efficient solvents for surface modifications. They have several advantages such as non volatile, recyclable and in particular large electrochemical window.

In the present study, we are exploring the use of 2- hydroxyethanolamine formate (HEAF) ionic liquid ionic as a solvent to electrochemically reduce the oxide layers and and the impact on the self-assembly process of thiol monolayers on copper, copper-nickel alloy and nickel substrates. It is shown that HEAF is suitable medium to reduce the metal passive oxide layers and good quality thiol monolayers can be formed on copper, copper-nickel alloy and nickel substrates by immersion in 0.05 M ethanolic solution for 18 h. The monolayers formed were characterized using different electrochemical (CV, LSV) and spectroscopic techniques (XPS, PM-IRRAS).
Electrochemical Investigations of Benzil in Nonaqueous Media
Authors: Cheek Graham T.
Published: February 2020

Introduction

The electrochemical behavior of the aromatic diketone benzil has been studied in a number of solvents (1-4). The benzil system is particularly interesting because of its ability to undergo various reactions accompanying the reduction process. Most of the solvent systems studied to date have involved proton-donating properties to some degree, so the use of the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ( BMPY TfO ) provides a useful contrast to the other solvents.

Experimental

All electrochemical experiments were carried out in a Vacuum Atmospheres glovebox. Cyclic voltammograms were obtained on a PAR 283 potentiostat using PowerSuite software. Potentials are reported with respect to an Ag/AgCl reference electrode. 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate (BMPY TfO) was prepared by a literature method (5). Benzil was obtained from Aldrich Chemical Company.

Results and Discussion

As can be observed from Figure 1(a), benzil undergoes electrochemical reduction in BMPY TfO in two successive, reversible electron-transfer steps. Figure 1(b) shows the voltammetric behavior for only the first process. In contrast, reduction in other nonaqueous solvents such as acetonitrile and dimethylformamide (2,3) involves considerable irreversibility for the second process. The low proton-donating ability of BMPY TfO seems largely to account for this effect. The ionic liquid BMPY TfO, then, serves as a suitable solvent for observing relatively uncomplicated voltammetric behavior of benzil, presenting the possibility of studying the effect of added proton donors in this solvent.

References

H. E. Stapelfeldt and S. P. Perone, Analytical Chemistry,
41(4), 623 (1969).

M. D. Ryan and D. H. Evans, J. Electroanal. Chem., 67, 333 (1976).

M. Chandrasekaran, M. Noel and V. Krishnan,J. Chem. Soc., Perkin Trans.2, 979 (1992).

G. T. Cheek, ECS Transactions, 6(6), 47 (2007).

L. Crowhurst, N. L. Lancaster, J. M. P. Arlandis, and T. Welton, J. Am. Chem. Soc.,
126, 11549 (2004).

Figure 1. Cyclic voltammetry of 40 mM benzil in BMPY TfO at glassy carbon ( 1 mm diameter ).

Scan rate 100 mV/s

(a) Scan to -2.50 V [ black curve ]

(b) Scan reversal at -1.50 V [ red curve ]
Formation Features of Anodic Oxide Films in the KNO3 Melt
Authors: Skatkov Leonid , Gomozov Valeriy
Published: February 2020

The present communication is considered as an extension of earlier investigations of niobium anodized in nitrate melts of salts at oxide recrystallization temperatures. Studied patterns of growth and crystallization of oxide layers are currently subject to be completed with investigations of AOF phase and elemental composition considering the available general data on applicability of the process of metal substrate oxygen saturation and inclusion of electrolyte components to oxide at anodic oxidation [1].

Examination of phase composition applying Auger spectroscopy at layer-by-layer etching with Argon ions has shown that generated films instead of being entire niobium pentoxide layer, as it was seemed to be, has occurred to be a «sandwich» of Nb2O5 , NbO2 and NbO phases (in the direction from oxide surface to niobium). This is similar to what is taking place at thermal oxidation [2]; at the same time within anodic oxidation oxygen is intensively dissolved in niobium substrate, penetrating into it on the depth which substantially exceeds the oxide thickness.

Studying of the possibility of electrolyte components being included into oxide has lead to a result which from the first sight may be considered as contradictory: at growth anodic oxide is saturated not only with anions (which could have been expected similar to anodic oxidation in hydrous electrolytes), but also with cations.

Considering the fact that the issue of cations presence in AOF is of great interest, potassium quantitative content in oxide has additionally been inspected by the method of fluorescent X-ray test as to intensity of K-fluorescent X-rays excluding background. As for potassium model KCl crystal has been applied. Assuming 50% potassium content in the model and linear dependence of radiation intensivity from concentration of the element it has been calculated potassium concentration value constituting the rate close to 9%, which together with the abovementioned data of X-ray diffractometry survey allows to point on formation of potassium solid compounds in niobium oxide at AOF crystallization.
An Electrochemical Study of Uranium (III) and (IV) Species in Fused Alkali Chlorides
Authors: Maltsev Dmitry S. , Volkovich Vladimir A. , Vladykin Evgeny N. , Vasin Boris D.
Published: February 2020

Pyroelectrochemical methods are considered as prospective technique for reprocessing spent nuclear fuels (SNF). These methods have a number of obvious advantages in comparison with the existing aqueous extraction processes. The advantages include significantly lower volumes of liquid radioactive wastes, high radiation stability of alkali chlorides used as working media, absence of neutron moderators. The eutectic mixture of lithium, potassium and sodium chlorides is one of possible low melting solvents (Tf= 529 K) that can be employed for practical realization of the process. However, there is no information concerning uranium behavior and properties in this melt. In the present work we studied the behavior and determined main electrochemical and thermodynamic properties of uranium in LiCl-KCl-CsCl eutectic melt. The measurements were performed between 573–1073 K employing potentiometry, chronopotentiometry and cyclic voltammetry.

Uranium formal standard electrode potentials in LiCl-KCl-CsCl eutectic were determined using electromotive force method. E*U(III)/U(0)linearly increases with temperature and between 576-1067 K can be described by the following equation:

E*U(III)/U(0) = -2.901 + 6•10-4• T (± 0.029) V [1]

From the results of the electrochemical measurements the Gibbs free energy change of the formation of uranium trichloride in LiCl-KCl-CsCl melt at 576-1067 K was calculated:

ΔG*UCl3 = -839.8 + 161.7•10-3• T (± 2.6) (kJ/mol) [2]

The results (Е*U(III)/U(0), ΔG*UCl3) obtained in the present work for LiCl-KCl-CsCl melt are in a good agreement with the available literature data for the melts of other cationic composition, Fig. 1.

Uranium (IV)/(III) electrochemical reduction was studied using cyclic voltammetry and chronopotentiometry. Examples of the experimental results are shown in Figs 2 and 3. Analysis of the cyclic voltammograms showed that U(IV) → U(III) reduction is a reversible one-electron diffusion controlled process, and this conclusion was confirmed by chronopotentiometric data. The diffusion coefficients of U(III) and U(IV) ions were obtained using both techniques, Fig.4-5, and they are satisfactorily described by the equations [3-6]:

cyclic voltammetry:

lgDU(III) = -3268.47/T – 0.82 (±0.15) cm2/s [3]

lgDU(IV) = -2033.43/T – 2.26 (±0.13) cm2/s [4]

chronopotentiometry:

lgDU(III) = -2470.14/T – 0.79 (±0.17) cm2/s [5]

lgDU(IV) = -4331.02/T + 1.25 (±0.11) cm2/s [6]
Thermodynamic Analysis of Solutions of Oxides in the Alkali Melts
Authors: Skryptun Igor N
Published: February 2020

The thermodynamic analysis of solutions of metal oxides in molten alkalis was carried out. The analysis is performed using the model subregular ionic solutions.
Electrorefining Process for the Treatment of Zr-Alloy Cladding Hull Wastes from Used Nuclear Fuels
Authors: Lee Chang Hwa , Lee Yoo Lee , Jeon Min Ku , Choi Yong Taek , Kang Kweon Ho , Park Guen-Il , Park Kyung-Tae
Published: February 2020

The pyroelectrochemical process has been widely used for the treatment of used nuclear fuel owing to its high proliferation resistance as well as a substantial reduction capability of high level nuclear wastes by recovering valuable materials such as uranium (U) and transuranic (TRU) elements. The pyroprocess developing at KAERI consists of a head-end process that produces feed materials through a disassembly/chopping/decladding of used fuel assemblies and a back-end process that recovers U and TRU from the feed materials by a series of molten salt processes such as electroreduction, electrorefining, and electrowining. At the head-end process, metal wastes including cladding hulls and hardware are generated in amounts of about 2.5 tons and 1.0 tons per 10 tons of U, respectively. In particular, the cladding hull wastes are expected to be categorized as an intermediate- or a GTCC level waste owing to the radioactivated elements produced during the reactor operation and residue of used nuclear fuel adhered to the surface. Although the commercialized methods used for the treatment of cladding hull wastes such as a simple compaction and melting process are able to reduce the volume of wastes, the activity level of all waste cannot be changed. Therefore, alternative approaches that can recover a major element of hull waste, zirconium (Zr), have been studied to lower the activity as well as reduce the volume/weight of the waste. This study demonstrates a Zr electrorefining process for the treatment of cladding hull wastes in molten salt systems. The electrolytes for the experiments include chloride-, fluoride-based, and mixed salts with initiators. The operating conditions are varied to enhance the morphology of recovered Zr, thereby reducing the incorporated salt into the deposit. By electrorefining Zr from fresh cladding hull tubes such as Zirlo and Zircaloy-4, the characteristics of Zr deposits will be examined using SEM, XRD, and ICP-AES.
Solid Oxide Membrane for Reduction of Ce0.8Gd0.2O2 and TiO2 in LiCl-Li2O
Authors: Olson Luke Christopher , Garcia-Diaz Brenda L. , Brinkman Kyle
Published: February 2020

A solid oxide membrane was used in a three electrode electrochemical cell to separately reduce, both Ce0.8Gd0.2O2 and TiO2 in molten solution of LiCl-Li2O. The Ce0.8Gd0.2O2 was used as a surrogate for UO2, with the goal of using a similar technique during potential nuclear fuel reprocessing scenarios. The solid oxide membrane was a closed-end yttria stabilized zirconia tube inserted in an electrochemical cell with an argon cover gas. A tungsten electrode was used as a quasi reference, and a graphite basket was used to separately hold both Ce0.8Gd0.2O2 and TiO2 powders. One end of the YSZ tube was held at room temperature, while the closed end was submerged in the molten salt at 650 °C. A platinum bearing paint coated the inside of the SOM and facilitated electrical contact from the nonconductive cold region to the conductive hot region. Argon gas was swept through the solid oxide membrane and an oxygen detector, where the oxygen pumped through the membrane during reduction was monitored. Initial oxygen evolution was measured using the oxygen meter and readings were observed to correlate to reduction of the Ce0.8Gd0.2O2 and TiO2 as determined from electrochemical data. The reduced Ce and Ti oxides were examined post experiment via SEM, EDS, and XRD. EDS and XRD were used to prove partial reduction in both the Ce0.8Gd0.2O2 and TiO2, but complete reduction to the metallic state was not observed for either oxide to date. EDS analysis found reduction of the TiO2 to as low as Ti0.8O0.2 (with trace Cl, Li could not be detected). EDS analysis of the Ce0.8Gd0.2O2 found evidence of reduction to Ce0.8Gd0.2O (with trace Cl, Li not detected). XRD found evidence of LiTiO2, LiTi2O4, and (Li0.54Ti2.86)O6 from the TiO2 basket/electrode. Analysis of reduced products may have been impacted from air exposure during analysis. Fragility of the electrode basket used for the TiO2 experiment was believed to be the limiting factor in achieving reduction, and further experiments are ongoing using a more robust metallic basket/electrode design.
(Max Bredig Award in Molten Salt & Ionic Liquid Chemistry) Molten Salts and Ionic Liquids: Where Have We Been and Where Are We Going? An Electrochemist’s Perspective
Authors: Hussey Charles L.
Published: February 2020

From the very beginnings of molten or fused salt chemistry in the early 19th century with the preparation of alkali metals from their molten hydroxides by Sir Humphrey Davy, the formulation of the laws of electrolysis by Michael Faraday from experiments with molten lead halides, and the eventual development of the civilization-changing Hall-Héroult process for the large scale production of aluminum in 1886, there has always existed a common theme of electrochemical applications. Molten salt electrolytes can be prepared from almost any stable salt, but the most commonly employed systems are based on alkali carbonates, halides, hydroxides, and nitrates and their mixtures. These melts have found applications in batteries and fuel cells; the electrowinning, surface treatment, and heat treatment of metals; and even in the electrochemical processing of spent nuclear fuel. Many are commonly employed at temperatures well over 1000 oC!

Latecomers to the field of molten salt chemistry include the class of materials known as “ionic liquids,” which are by agreement salts that melt below 100 oC and are usually, but not absolutely, based on organic cations and inorganic anions. Although they can trace their origin to the first report of the room-temperature protic salt, ethylammonium nitrate, by Paul Walden in 1914, their novel properties and electrochemical applications were not really appreciated until the pioneering work of Frank H. Hurley and Thomas P. Wier, who electrodeposited aluminum from room-temperature mixtures of ethylpyridinium bromide and aluminum chloride (U.S. Patents 2,446,331; 2,446,349; and 2,446,350) in 1944. In a sense, it is the work by these early pioneers from which everything else pertaining to ionic liquids has flowed, including the development of the ubiquitous dialkylimidazolium chloride salts and many other quaternary ammonium salts that form the backbones of the fascinating, highly-stable hydrophobic ionic liquids we use as electrochemical solvents today.

In this presentation, the award recipient will provide a brief historical perspective about the electrochemical applications of molten salts and their ionic liquid progeny. He will also describe his work with previous Bredig Award recipients and with many other long-time collaborators and students in the field of molten salts and ionic liquids.
Durability of Active ORR Electrocatalysts
Authors: Balbuena Perla B , Ramos-Sanchez G , Godinez Fernando , Solorza-Feria O. , Gurrola Mayra Polett , Arriaga Luis Gerardo
Published: February 2020

Obtaining extended life of active oxygen reduction reduction (ORR) electrocatalysts is still one of the hardest barriers to overcome for the successful implementation of low-temperature fuel cells. Significant research activity during the last decade has allowed the development of a variety of electrocatalyst materials with excellent activity. Among them, core-shell alloys are the most popular. However, in general their cycle life is very limited.

First-principles calculations based on density functional theory (DFT) have advanced to the point where they are able to provide reasonable predictions not only for activity but also to help elucidating the factors causing catalyst degradation and giving trends for durability of materials in harsh environments.

In this work, we first discuss the requirements of a core-shell alloy for extended durability, on the basis of DFT analysis. We then report results of experiments and DFT simulations about changes induced by the presence of oxides in core-shell structures. Physical and electrochemical characterization confirms the presence of core-shell nanoparticles with a high electrochemical activity towards the ORR. Periodic DFT calculations are used to analyze the shift in the onset of the oxidation potential for Pt, Ni@Pt and NiO@Pt with different number of layers in the shell, and associated changes in electrochemical activity. We conclude with a general discussion of the potential effect of catalyst/substrate interactions to improve the durability of ORR electrocatalysts.
Graphene-Polyaniline Nanofibers Composite as Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media
Authors: Sankararao Mutyala , Mathiyarasu Jayaraman
Published: February 2020

The catalytic oxygen reduction reaction (ORR) has engrossed rising attention due to its importance in energy converting system such as fuel cells. However, the commercialization of fuel cells is still mired by several factors, including the insufficient kinetics of ORR, high cost of noble metal catalysts, and the meager stability of the catalysts especially in alkaline medium. Thus, the important task is to develop a low-cost, stable and more active electrocatalysts for the ORR in alkaline fuel cells. Low-Pt loading or non noble metal cathode catalysts are currently receiving more and more research attention1, 2.

The present work reports the synthesis of a novel Pt free cathode catalyst i.e., graphene-polyaniline nanofiber (GP) composite for ORR. Initially, the polyaniline (PANI) nanofibers and graphene sheets are individually synthesized using simple chemical route. Here, the polymer fibers are acting as interconnecting agents between graphene sheets, which are confirmed by Transmission electron microscopy showed in Fig.1A. Further, the catalytic activity and durability of GP composite were evaluated by linear sweep voltammetry in 0.1 M KOH solution, as showed in Fig.1B. The results confirmed that GP composite exhibited a 100 mV shift in ORR onset potential with enhanced activity compared to graphene alone. The possible ORR mechanism may be given as follows:

.

At graphene

H2O +1/2 O2 → H2O2 (2 electron transfer reaction)

At GP composite

O2 + 2H2O → 4OH- (4 electron transfer reaction)

In addition, the GP composite showed good stability during a potential cycling test. Further structural and composition of graphene and GP composite were characterized using Field emission scanning electron microscopy (FESEM) and Raman spectroscopy (Figures are not shown). Fig. 1A shows the schematic of glassy carbon electrode modified with GP composite. Thus, the present composite developed may be a simple, cost effective one that showed a long durability for ORR. Therefore, it may be an excellent catalyst material of choice for practical fuel cells.

Figure caption

Fig.1 (A) Schematic representation of GP composite preparation, and glassy carbon electrode modification. (B) Liner sweep voltammogram curves for ORR in O2 saturated 0.1 M KOH on (a) Graphene, (b) GP composite and (c) Pt/C 20% . Scan rate 10 mV/s.

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Keynote: In-Situ Visualization of Non-Linear Phenomena during Metastable Pitting Corrosion on Stainless Steel
Authors: Rotermund Harm Hinrich
Published: February 2020

Stainless steels and many other alloys are designed to be corrosion resistant. Nevertheless they can undergo localized pitting corrosion, which may rapidly lead to their failure, with the possibility of catastrophic events as a result. To study the initial steps of metastable pit formation in situ and in real time we adapted the ellipso-microscope for surface imaging (EMSI) [1] and a high resolution, contrast enhanced optical microscope to the electrolyte - stainless steel interface. Utilizing these methods we have been able to explain the sudden corrosion onset by an explosive autocatalytic growth in the number of metastable pits [2].

By applying those different but complementary imaging methods simultaneously the correlation between oxide film weakening and the nucleation of individual pits could be confirmed. The existence of front propagation as a component of the transition to pitting corrosion shows that characteristics of this process are consistent with the behavior of stochastic reaction-diffusion systems [3].

Recently we implemented digital in-line holography as a third imaging tool simultaneously to gather three-dimensional information within the electrolyte, in close proximity to the exposed surface. This enhances the sensitivity for small pitting events and opens new avenues for investigating and understanding the underlying processes. For instance we are now able to follow the trajectories of particles ejected from a pit [4].

Using this arsenal of in situ and real time imaging tools allows us to efficiently study methods to enhance the pitting corrosion resistance of stainless steels; initial results of simple treatments such as emerging the sample just in high purity deionized water at 90 °C for an hour, but nevertheless improving the pitting corrosion resistance in NaCl solutions dramatically, will be discussed [5].

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[4] P.E. Klages et al., Corrosion Science 65, 128–135 (2012)

[5] P.E. Klages et al., Electrochemistry Communications 15, 54–58 (2012)
Multi-Physics Modeling of Electrochemical Conversion of Carbon Dioxide to Formic Acid
Authors: Jain Swati , Georgopoulou Chara , Agarwal Arun , Rode Edward , Sridhar Narasi , Kakalis Nikolaos
Published: February 2020

Electrochemical conversion of CO2, a common greenhouse gas to formic acid, methanol, ethylene, and syngas is being increasingly pursued as a means for CO2 recycle to value added products employing renewable energy and also for energy storage. The authors have been actively involved in advancement of the technology for selective conversion of CO2 to formic acid. Special emphasis of this research is on process modifications for techno-economic feasibility which is imperative for future commercialization. Hence, multi-scale modeling is pursued to aid the experimental design. The reactor design, the catalyst and electrode structure for efficient, scale up of this process requires a comprehensive formulation of the multi-scale and multi-physics process phenomena, including aqueous transportation, membrane transportation, multiphase flow, dispersion, ion migration and surface reactions. This work presents a modeling and numerical simulation approach for understanding the CO2 conversion process to formic acid and model validation. A phenomenological process model of the CO2 conversion process is developed to simulate the process behavior under steady state and transient operating conditions, allowing to study the complex system phenomena and estimate scale-up performance. An approach for calibrating the model input data for such systems from the experimental data is illustrated. This type of calibrating approach could also be applicable to other similar electrochemical systems.
Construction of Arnold Tongue Structures for Coupled Periodic Oscillators
Authors: Montoya Fernando , Rivera Marco Antonio , Escalona Joaquín , Parmananda Punit
Published: February 2020

Arnold tongue structures generated due to the mutual entrainment of two periodic oscillators are studied experimentally and numerically. This mutual entrainment is provoked due to the mutual (bidirectional) coupling between the two oscillators. In experiments, this bidirectional coupling is achieved by immersing a couple of anodes (oscillators) in a common electrolytic solution. A voltage mismatch between these anodes renders the time period of the uncoupled electrochemical oscillators non-identical. Moreover, the coupling strength between the two oscillators is uniquely determined by the distance separating them. Systematically varying the distance between these two anodes as a function of their voltage mismatch, phase locked domains were located. Subsequently, Arnold tongue structures were constructed in the experiments. Numerical simulations, using a model for electrochemical corrosion, corroborate our experimental findings.
Invited: Advantages of Plasma Synthesis of Copper Oxide Nanowires
Authors: Filipič Gregor , Cvelbar Uro
Published: February 2020

Copper oxide is a semiconductor with a narrow band-gap (2.1 or 1.2 eV, depending on the oxidation state of the copper) and was as such a candidate for growing it in nanowire form. The nanowires can be used for electron field emission1, gas and cholesterol detection2,3, solar cells4, and photo-catalysis of water to hydrogen5. Due to extensive research and advancement it is no longer a question of “if we can grow copper oxide nanowires”, nor is it a question of “size or crystallinity”. Up to now the variety of methods have been developed which enable us a control over many attributes of the nanowires: we can grow them long or short, thick or thin, single- or poly-crystalline, we can also chose the oxidation number of copper (copper I or copper II oxide nanowires)6. The research has now progressed into finding how fast we can grow them, what is the most efficient way to grow them, and how precisely can we place them7,8.

Copper oxide nanowires can be grown using different routes: solution based1,9,10, hydrothermal11,12, thermal oxidation13,14 or plasma oxidation15,16. Each has different approach, specifications and results. While other methods are fully described elsewhere, the introduction of the low pressure plasma method for growing copper oxide nanowires on surface of copper will be made. The results of the oxidation will be presented. Furthermore, the advantages and disadvantages of the said process will be exposed especially in comparison to thermal oxidation.

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Cvelbar U., J. Phys. D: Appl. Phys. 44 (2011) 174014;
Invited: Novel Plasma Enhanced Chemical Vapor Deposition Methods Utilizing Radical Reactions
Authors: Sekine Makoto
Published: February 2020

Novel plasma CVD methods with radical enhanced reactions are introduced for microcrystalline Silicon film with high rate, fuctional nano carbon and gallium nitiride film growth at lower temperature.
Invited: Microplasma Spray Deposition of Nanostructured Films for Catalytic, Magnetic, and Photonic Applications
Authors: Koh Travis , Pebley Andrew , Mackie Katie , Gordon Michael
Published: February 2020

We present a hybrid plasma spray deposition technique, based on geometrically-confined, supersonic microplasma jets, which can realize a wide range of metal oxide/sulfide nanoparticles and nanostructured thin film materials (e.g., CuO/CuS, ZnO, SnO2, NiO/NiFe2O4) on virtually any surface. Organometallic precursors are dissociated in a hollow cathode microplasma jet under different reducing/oxidizing atmospheres at high pressure (10-100 torr), creating a directed flux of active metal and oxide species for the subsequent growth of nanostructured films. Interaction of the jet afterglow with the background gas can create additional species (e.g., excited neutrals, radicals, etc.) which participate in film growth. By varying supersonic jet flow characteristics, plasma current, precursor flux, source distance, and deposition time, deposits ranging from isolated nanoparticles to films of fibers, aggregates, nanowires, and dense columns can be realized. The talk will highlight our recent efforts [1-5] in oxide/sulfide nanomaterial synthesis via microplasmas with emphasis on the physics of the jet source, dynamics of the growth process, and applications such as solar cell electrodes, photo(electro)catalysis, and nanogranular films for magnetic exchange bias applications.

[1] T. Koh and M.J Gordon, J. Phys. D: App. Phys.
46, 495204 (2013).

[2] T. Koh, I. Chiles, and M.J Gordon, Appl. Phys. Lett.
103, 163115 (2013).

[3] T. Koh and M.J Gordon, JVST A
31, 061312 (2013).

[4] T. Koh and M.J. Gordon, J. Crystal Growth
363, 69 (2012).

[5] T. Koh, E. O'Hara, and M.J. Gordon, Nanotechnology
23, 425603 (2012).
Invited: Continuum Modeling of Interfacial and Transport Phenomena in Electrochemical Capacitors
Authors: Pilon Laurent , d'Entremont Anna , Girard Henri-Louis
Published: February 2020

Electrochemical capacitors are promising electrical energy storage devices bridging the gap between batteries and conventional dielectric capacitors. They can be divided in two categories: electric double layer capacitors (EDLCs) and pseudocapacitors. EDLCs store electric charge physically in the electric double layer forming at the interfaces between the electrolyte and nanoporous electrodes. During charging or discharging, ions are transported in the electrolyte under the combined influence of diffusion and electrostatic forces as well as steric effects. On the other hand, pseudocapacitors store energy not only via the electric double layer but also via fast surface redox reactions and possibly ion intercalation within the redox-active electrode.

This talk will present physical modeling of interfacial phenomena, transport phenomena, and redox reactions in electrochemical capacitors under charging and discharging conditions. The model accounts for finite ion size, asymmetric electrolytes, and three-dimensional electrode morphology. It also considers faradaic reactions and ion intercalation when simulating pseudocapacitors. Typical cyclic voltammetry measurements will be reproduced numerically for various electrolyte and electrode materials and different scan rates. The results will be used to provide detailed physical interpretation of experimental measurements. Special effort will be made to systematically compare model predictions with experimental data.
MnO2 Inks for the Fabrication of Supercapacitor Electrodes
Authors: Coustan Laura , Ould Amara Salem , Favier Frederic
Published: February 2020

The gap between electronics and users is becoming narrower as the portable electronics comes to wearable. As such, power supply, including storage devices, comes to wearable too. In addition to power and energy, specific characteristics are required for integration: lightweight, thickness, safety, washability, flexibility... and eventually hypoallergenic or biocompatibility. Facing these specifications, integration of storage devices such as Li-ion batteries or supercapacitors in clothes remains an exiting challenge. Supercapacitors based on pseudocapacitive metal oxide -based electrodes operated in neutral aqueous electrolytes could fit most of these requirements. The context of this study is the development of supercapacitor electrodes based on the deposition of MnO2 onto flexible current collectors. Although various approaches have been investigated for the fabrication of high-performance flexible supercapacitors, they have to consider various material/device characteristics including intrinsic flexibility, mechanical integrity of the current collector/electroactive material assemble and retention of the electrochemical performances under stress. The material deposition onto flexible substrates can be carried out by electrodeposition, spin coating, spray or inkjet deposition [1]. Many surfactants have been used such as sodium dodecyl sulfate, Triton X100 or Caffeic acid, for the formulation of the complex MnO2 particle suspensions required for the fabrication of homogeneous and performing electrodes by these latter techniques.

Figure: Cyclic voltammograms of Mn-oxide/free (a), Mn-oxide/SDS (b), Mn-oxide/CA (c), and Mn-oxide/TX100 (d) at a scan rate of 5 mV.s-1 in 1M Na2SO4 aqueous electrolyte.

To enhance the rheological characteristics of the prepared inks, we have considered the use of these surfactants at the preliminary stages of the synthesis of MnO2 particles by wet chemistry. The present study focuses on the impact of three different surfactants used for the synthesis by co-precipitation of MnO2 on the (electro)chemical characteristics of the prepared powders. It also describes various approaches for the fabrication of supercapacitor electrodes based on these MnO2 powders.

[1] J. Keskinen, E. Sivonen, S. Jussila, M. Bergelin, M. Johansson, A. Vaari, M. Smolander, Electrochimica Acta 85 (2012) 302-306
Synthesis of Ni-Co Oxides/Sulfides Nanowire Arrays for Ultrahigh Electrochemical Capacitors
Authors: Xiao Peng , Li Yan Hong , Zhang Yunhuai , Yang Yang
Published: February 2020

Electrochemical capacitors (supercapacitors) have attracted intense attention due to their high power density, fast charge-discharge process, long cycle life and used in many practical applications. Ni-Co composites, also known as ternary metal composites, have excited great interest in recent years because of their high-performance in supercapacitors. Owing to the coupling of two metal species, these materials could render the composites with rich redox reactions and improved electronic conductivity, which are beneficial to electrochemical applications. In particular, the tunable compositions in the Ni-Co oxides provide vast opportunities to manipulate the crystal structure and its physical/chemical properties. During the past years, different shapes and structures of Ni-Co oxides/sulfides were investigated and most of the researches were focused on NiCo2X4 (X=O, S). Very few works investigated Ni-Co composites with different Ni-Co molar ratio and its fabrication of free standing electrode structure.

Here we report the interesting formation of Ni-Co oxides and Ni-Co sulfide nanowire arrys (NWAs) with Ni/Co molar ratio at 1: 1 and their derived free standing structure on different substrates for ECs. Ni-Co oxides NWAs were synthesized on ordered TiO2 nanotubes and Ni foam respectively by a facile hydrothermal method. Ni-Co sulfides NWAs were fabricated through S2- ion exchange using synthesized Ni-Co oxides nanowires as precursor. The electrochemistry testes showed that this self-supported electrode is able to deliver ultrahigh specific capacitance. To raise the cell voltage and thereby boost the energy density more effectively, we use the Ni-Co sulfides NWAs for the battery-like Faradic electrode and activated carbon for the capacitive electrode to compose an asymmetric cell, and this has extended the cell voltage to 1.8V in an aqueous electrolyte, resulting in high energy density, high power density and good cycling stability all together. To the best of our knowledge, such a prototype device has not been fabricated and explored before.
One-Step Synthesis of Carbon Supported Nb2O5 Particles for Electrochemical Capacitor Applications by Oxidation of Layered Nb2C
Authors: Beidaghi Majid , Zhang Chuanfang , Lukatskaya Maria , Maloney Ryan , Dunn Bruce , Gogotsi Yury
Published: February 2020

The crystalline network of orthorhombic niobium oxide (T-Nb2O5) offers two-dimensional transport pathways for fast intercalation of lithium ions, leading to its high and rate independent intercalation pseudocapacitance. Unlike many other lithium intercalation metal oxides, T-Nb2O5 can be charged in short periods of time, making it suitable as a supercapacitor electrode material. This is due to the fast solid-state diffusion and no structural change of T-Nb2O5 upon intercalation of Li ions. For practical applications of Nb2O5 and other metal oxides in supercapacitors, thick electrodes with large mass loadings are necessary. This, however, will result in ohmic losses and ion transport limitations due the relatively low electrical conductivity of the oxide and limited ion diffusion through the electrode thickness. To address these limitations, we have successfully prepared the layered Nb2O5/carbon hybrid materials through controlled oxidation of layered Nb2C (also called Nb2C-MXene). As-prepared Nb2O5/C well inherited the two dimensional structure of the precursor with Nb2O5 nanocrystals formed between the MXene layers. A detailed study of oxidation temperatures and durations was conducted to achieve nanostructured of T- Nb2O5 and XRD, SEM and TEM studies show the uniform formation T-phase of Nb2O5 on carbon sheets after oxidation at 850℃. The electrochemical characterization of thick electrodes of synthesized material show very promising performance, with specific capacitance of about 350 F/g in 1M LiClO4 /EC/DMC (1:1 in volume ratio) electrolyte. The performance of developed electrodes is believed to be highly dependent of layered two-dimensional structure of Nb2O5/carbon hybrid materials.

Acknowledgements: Authors acknowledge Dr. Mengqiang Zhao for his help with TEM studies. Support from DOE via Sandia National Laboratory is appreciated.
Graphitic Layer Coated Porous Carbon for Energy Storage Applications
Authors: Yoon Hana , Yeon Sun-Hwa , Yoo Jung-Joon , Wook Ahn
Published: February 2020

Electrochemical capacitors (ECs) provide higher power densities than most batteries and higher energy densities than conventional dielectric capacitors. Activated carbons are the most widely used electrode material for ECs because of their high surface area and relatively good electrical conductivity. Graphitic layer coated porous carbon with a three-dimensional hierarchical structure can facilitate ion and electron transport by providing a smaller resistance and shorter diffusion pathways, is highly recommended as a promising electrode material for the advanced ECs. Herein, we report the synthesis of graphitic layer coated porous carbon and their electrochemical performance for energy storage device applications.