bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Resonance Methods for Investigation of Electrochemical Phenomena in Direct Alcohol Fuel Cells
Authors: HAN Oc Hee
Published: February 2020

Nuclear magnetic resonance (NMR) spectroscopy has been one of the essential methods to identify chemicals and characterize dynamics and structure of them. Utilizing the advantages of NMR spectroscopy we have investigated electrochemical phenomena occurring in direct alcohol fuel cells (DAFCs) and identified electronic, chemical and structural changes of FC components during each FC assembly and operation process. With the device that we have developed, the functional difference of anode catalysts such as Pt and PtRu could be in situ detected. Liquid state 13C NMR spectroscopy was utilized to analyze the anode exhaust of DAFC and to correlate quantitatively the amount of electrical current generated to the quantities of each chemical product. Magic angle spinning (MAS) NMR spectroscopy and the membrane electrode assembly (MEA) composed of triple-polymer electrolyte membrane layers were employed for the study of methanol crossover and methanol reaction intermediates in a DAFC.

Our work demonstrates that 1) in situ NMR observation of real DAFCs is possible, 2) the in situ and ex situ NMR techniques can be used for the investigation of alcohol oxidation reaction mechanisms, and 3) the electronic, chemical and structural changes of FC components during each FC assembly and operation process can be studied by various NMR methods.
Foam Based Gas Diffusion Electrodes for Reversible Alkaline Electrolysis Cells
Authors: Allebrod Frank , Chatzichristodoulou Christodoulos , Mogensen Mogens Bjerg
Published: February 2020

Alkaline electrolysis cells operated at 250 °C and 40 bar have shown to be able to convert electrical energy into chemical energy in the form of hydrogen at very high efficiencies and power densities. Foam based gas diffusion electrodes and a liquid immobilized electrolyte allow the operation of the newly designed electrolysis cell as a fuel cell, but condensation of steam may lead to blocked pores, thereby inhibiting gas diffusion and decreasing the performance of the cell. In the here presented work we present the application of a hydrophobic, porous, and electro-catalytically active layer to the gas diffusion electrodes. A dispersion with PTFE particles of a particle size of about 1 µm in combination with electro-catalysts, such as silver nanotubes, was used to coat the gas diffusion electrodes. Impedance spectroscopy and cyclic voltammetry measurements were performed to determine the electrochemical characteristics of the cell. The thickness of the electrolyte matrix was reduced to 200 µm, thereby achieving a serial resistance and area specific resistance as low as 60 mΩ cm2 and 150 mΩ cm2, respectively, at a temperature of 200 °C and 20 bar pressure. A new production method was developed to increase the cell size from lab scale (1 cm2) to areas like 25 cm2.
Development of Electrodeposited IrO2 Electrodes and Its Catalytic Activity towards Oxygen Evolution Reaction in Polymer Electrolyte Membrane Based Water Electrolysis
Authors: Lee Byung-Seok , Ahn Snag Hyun , Choi Insoo , Park Hee-Young , Kim Soo-Kil , Lee Kwan-Young , Yoo Sung Jong , Cho EunAe , Kim Hyoung-Juhn , Nam Suk Woo , Jang Jong Hyun
Published: February 2020

Polymer electrolyte membrane based water electrolysis (PEMWE) is an environmental friendly way to produce hydrogen with largely reduced CO2 emission [1]. However, for commercial applications, further cost reduction is highly required. Conventionally, Ir and Ru based electrocatalysts are utilized in anodes (~4 mg/cm2), and Pt based electrocatalysts in cathodes (~1 mg/cm2). In this study, electrodes were fabricated by anodic electrodeposition of IrO2on carbon papers [2], and its catalytic activities towards oxygen evolution electrodes (anodes) were characterized.

By anodic electrodeposition technique, IrO2 was electrodeposited on carbon papers in a three electrode cell (Autolab, PGSTAT302N). A glassy carbon electrode and SCE were utilized as counter and reference electrodes, respectively. The deposition voltage and time were varied to control the loading amount and surface morphology. After electrodepositon, the microstructures and oxidation states of IrO2 deposition were analyzed by field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The amount of deposited IrO2, which was determined by the inductively coupled plasma-mass spectrometry (ICP-MS), was 0.007~0.464 mg/cm2
at various deposition voltages and times.

For single cell tests, cathode electrodes were fabricated by spraying commercial Pt/C (Tanaka, 45.9 wt%) on carbon paper (Pt loading: 0.8 mg/cm2), and commercial Nafion 212 membranes were utilized as polymer electrolytes. Then, the water electrolysis performances were evaluated at 90oC. The highest performance was observed for the electrodes with IrO2 loading of 0.09 mg/cm2. Interestingly, although the anode catalyst loading was largely decreased, the single cell performances in this study were comparable to the previous reports [3-5].

References

[1] F. Mueller-Langer, E. Tzimas, M. Kaltschmitt, S. Peteves, Int
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J
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Hydrogen Energy, 32, 3797, (2007).

[2] K. Yamanaka, Jpn. J. Appl. Phys.
,
28, 632, (1989).

[3] Shidong Song, Huamin Zhang, Xiaoping Ma, Zhigang Shao, Richard T. Baker, Baolian Yi, Int.
J
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Hydrogen Energy, 33, 4955, (2008).

[4] Jinbin Cheng, Huamin Zhang, Guobao Chena, Yining Zhanga,
Electrochim
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Acta, 54, 6250, (2009).

[5] Lirong Ma, Sheng Sui, Yuchun Zhai, Int.
J
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Hydrogen Energy, 34, 678, (2009).
Novel Oxygen Evolution Catalysts for Proton Exchange Membrane Water Electrolysis
Authors: Rasimick Brian , Stocks Allison , Xu Hui
Published: February 2020

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. However, the technology is expensive due to high materials cost for the catalysts, membrane, and bipolar plate. In most commercial processes, iridium (Ir) black is used as an oxygen evolution catalyst at the anode. A high Ir loading (>2mg/cm2) has to be used due to significant anode over-potential loss caused by sluggish kinetics of the oxygen evolution reaction.

The objective of this work is to develop advanced Ir catalysts with enhanced catalytic activity that may lead to decreased Ir loading and/or increased energy efficiency. Two categories of catalysts are being investigated. One is iridium nanotube catalyst, which is synthesized via a porous alumina template.1 The template can be a commercially available anodized alumina membrane with a relatively uniform capillary pore structure. The template was coated with an iridium precursor by subliming iridium precursor at an appropriate temperature. The precursor was then reduced to iridium. The template support was removed by etching with 10% potassium hydroxide. A cross-section of the nanotubes produced by this process is shown in Figure 1. The average length of the Ir nanotubes is 5um and the diameter ranges from 250 – 400 nm with a wall thickness of ≤50 nm. Energy-dispersive X-rayanalysis suggests that the tubes are composed of iridium dioxide. The template pore size and process conditions are being varied to change the dimension of the Ir nanotubes.

In addition to Ir nanotubes, Ir catalysts dispersed on a variety of corrosion-resistant substrates like titanium oxide and indium tin oxide (ITO) are also being developed. The Ir dispersion on these supports may reduce Ir particle size thus potentially enhancing its catalytic activity. Figure 2 shows the TEM image of Ir particles supported on TiO2nanowires with 30 w.t. % Ir loading.

The RDE performance and the electrolyzer performance of these catalysts are being investigated and their comparison with commercial Ir black will be reported.

Acknowledgement:The financial support is from the Department of Energy under the Contract Grant DE- DE-SC0007471. TEM was performed by Drs. Fan Gao and Zhiyong Gu at University of Massachusetts at Lowell.

References

Pivovar AB, et al. J Electrochem Soc, 160, F848-52 (2013).
Theoretical Study of the Morphologic and Structural Characteristics of an Anion Exchange Membrane Used in AEMFC Using DFT
Authors: Castañeda Ramírez Sergio , Ribadeneira Paz Rafael Esteban
Published: February 2020

Anion-exchange membrane fuel cells (AEMFC) have great potential of commercialization at low cost for their use in automotive transportation, portable batteries and power generators with respect to similar technologies as the proton-exchange membrane fuel cells (PEMFC) due to: a) better kinetic characteristics both for the oxygen reduction reaction as for the hydrocarbon oxidation reducing costs of catalysts, b) lower fuel crossover from anode to the rest of the device, c) simpler water management and d) reduced degree of corrosion.

Despite the mentioned advantages, the polymeric materials used as electrolytes show low conductivity and chemical stability values, which limit respectively the efficiency and durability of the fuel cell, and as experimentally these factors have not been optimized yet, it is important to understand the related physicochemical phenomena, being the anion transport primordial. However, the characteristics of the mechanisms associated with that process are not well known particularly the Grotthuss mechanism, which is considered to contribute mostly to the hydroxyl ion mobility.

In order to understand the mentioned mechanism and to improve the description of the ion mobility in AEMFCs is mandatory to carry out a rigorous theoretical study, for which the first step is to describe the appropriate structure of a particular anion exchange membrane. So, the aim of the present research is study the morphological and structural characteristics of the quaternized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene homogeneous membrane synthetized by Qing Hua Zeng and co-workers for different humidification values by means of density functional theory (DFT) techniques, considered the most suitable in terms of prediction and accuracy since there are not almost theoretical studies about structural and morphological characteristics of anion exchange materials used in AEMFC.

With the results obtained, the idea is to evaluate the potentiality of DFT techniques to obtain accurate structures for polymeric membranes and use the one generated for future investigations about the physicochemical characteristics of the Grotthuss mechanism for hydroxyl ions in membranes used in AEMFCs, in order to determine the best morphological and structural characteristics of this type of materials from a theoretical approach.
Contamination and Recovery of PEMFC Cathodes with Organohalides: Chlorobenzene and Bromomethane
Authors: Zhai Yunfeng , Baturina Olga A , Ramaker David E. , St-Pierre Jean , Swider-Lyons Karen
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) are susceptive to airborne contaminants, which can deleteriously adsorb on the platinum electrocatalysts at the cathode and inhibit the oxygen reduction reaction. Numerous inorganic (e.g., Sx, HCl, NaCl) and organic contaminants (alcohols and hydrocarbons) have been studied with the finding that some contaminants adsorb irreversibly, and some can be eliminated by oxidation and/or electrostatic desorption leading to full or partial recovery of the PEMFC performance. This paper describes the impact of the organohalide airborne contaminants, chlorobenzene and bromomethane, on PEMFC performance and recovery.

PEMFCs exposed to 20 ppm chlorobenzene lose significant activity, but the losses can be recovered after exposure to neat air. Under both wet and dry air streams, the cell voltage loss is rapid with a time scale <0.4 h and exceeds 500 mV. The performance recovery is slower than the contamination phase (time scale >3 h) and is incomplete with air (>40 mV loss remains). The effect of contamination with bromomethane is quite different. Bromomethane contamination causes relatively slow degradation (>19 h time scale) and recovery (>11 h time scale) of cell performance, but the losses appear to be largely irreversible (>250 mV).

The electrochemistry of the organohalide contamination processes is studied in combination with cyclic voltammetry, chronoamperometry and impedance spectroscopy. Gas chromatography/mass spectroscopy is used to determine the reaction intermediates and products of the organohalides. X-ray absorption spectroscopy at the Pt L3 edge on catalyst coated membranes that have been exposed to the chlorobenzene and bromomethane have also been carried out over a range of potentials. Analysis of the XAS results suggests that the molecular orientation of the organohalides changes with potential.

ACKNOWLEDGMENTS

This work is supported by the Department of Energy (DE-EE0000467) and the Office of Naval Research. Authors are also grateful to the Hawaiian Electric Company for their ongoing support of the operations of the Hawaii Sustainable Energy Research Facility.
Thin-Film Non-Precious Metal Model Catalysts for Oxygen Reduction Reaction
Authors: Martinez Ulises , Williamson Todd L , Artyushkova Kateryna , Mack Nathan , Purdy Geraldine M , Dumont Joseph H , Kelly D , Gao W , Dattelbaum Andrew M , Mohite Aditya , Gupta Gautam , Zelenay Piotr
Published: February 2020

Non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements, nitrogen and carbon, have been identified as potential alternatives to more scarce Pt-based catalysts currently used in the cathode oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). Nevertheless, understanding the role of each component of state-of-the-art NPMCs remains a significant challenge due to their highly heterogeneous structure. This understanding is necessary for the development of next-generation NPMCs with improved catalytic activity and durability that could ultimately replace Pt-based ORR catalysts. In this work, a bottom-up systematic approach, starting from model graphene-based precursors, has been applied to eliminate the complexity of NPMCs and better understand the role of each component.

Graphene and graphene-oxide (GO) thin-films transferred onto glassy carbon electrodes were used as starting materials. Nitrogen heteroatoms were incorporated into the thin-film substrates either by chemical modification in high-temperature ammonia treatments or by direct chemical activation using a unique high-flux energetic nitrogen atom beam technology, which overcomes thermal activation reaction barriers. Identification and speciation of doped nitrogen heteroatoms was performed via XPS. By varying reaction conditions, different nitrogen contents and species were obtained. Chemical-structure-to-activity relationships were then attempted through detailed physical and electrochemical characterization of the synthesis process to provide detailed information about the importance of each component addition for the formation of active and selective NPMCs.

Acknowledgment

Financial support from the Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program is gratefully acknowledged.
Composition Dependence of Glucose Oxidation at Mediated Glucose Oxidase Bioanodes
Authors: Feliciano Yira , Calabrese Barton Scott
Published: February 2020

In mediated enzyme electrodes, electrons are transferred between the enzyme and electrode surface via a redox species [1]. Previous studies have documented the parameters affecting mediated GOx electrodes and the effect of the composition, mediator structure, pH etc [2]. Our previous work describes the optimization of mediator redox potential for a laccase-catalyzed oxygen reduction electrode [3]. This result leads us to our current research, focused on modelling the composition dependence of the electrode structure, in terms of the balance between loadings of enzyme and mediator.

The electrode under study is a 3 mm diameter glassy carbon rotating disk electrode, modified with a film consisting of glucose oxidase crosslinked with poly(N-VI12[Os(bpy)2Cl]+/2+. The electrochemistry of this electrode, both in terms of mediator redox kinetics and glucose oxidation at pH 7, is studied as a function of GOx, mediator, and crosslinker mass loading. Fig. 1 summarizes cyclic voltammetry (glucose-free) and polarization curves (with glucose) of the modified electrode at a total loading of 0.726 mg cm-2. Glucose-free peak current remains steady at low GOx content, decreasing as mediator content diminishes. An optimum glucose conversion current density is found at 40 wt% GOx, where the catalytic and electron transport properties are balanced.

A mathematical model is used to predict the electrode activity. A key consideration is the film thickness, ℓ, which is assumed to vary according to:

ℓ = km γm + ke γewhere γ
m and γ
e are the mass loadings of mediator and enzyme, respectively, and k
m and k
e represent the effective densities of each component. Electrode thickness is measured independently and correlated to component loading, yielding estimates for the effective densities. This model is correlated to independent measurements of thickness using applied force microscopy (AFM) and profilometry, and the effect of film swelling is considered by experiments with both dry and wet films, applied by both drop deposition and spin coating (Figure 2). ACKNOWLEDGEMENT The authors thank the U.S. Dept. of Education for partial support of this work through a Graduate Assistantship in Areas of National Need (GAANN) fellowship for YF. REFERENCES 1. S. C. Barton, J. Gallaway and P. Atanassov, Chem. Rev., 104, 4867-4886 (2004).

2. N. Mano, F. Mao, and A. Heller, J. Electroanal. Chem., 574, 347–357 (2005).

3. J. W. Gallaway and S. Calabrese Barton, J. Am. Chem. Soc., 130, 8527-8536 (2008).
Electron Transfer Mechanisms in Nanomaterials-Incorporated Metalloprotein-Films on Electrodes
Authors: Krishnan Sadagopan , Kariate Sudhakaraprasad , Walgama Charuksha , Nerimetla Rajasekhara , Matlock Ryan , Premaratne Gayan
Published: February 2020

The contribution of nanomaterials in developing modern ultrasensitive biosensors and biocatalytic systems is immense. Our focus has particularly been on understanding the fundamental electrochemical properties of redox-protein films immobilized on nanostructured electrodes or incorporated with redox-mediating nanomaterials. In the first approach, we designed non-covalently functionalized carbon nanotube modified electrodes with different pyrene derivatives, via the strong π-π stacking, to achieve directed attachment of myoglobin protein or site-specific attachment of small peroxidase-active microperoxidase-11. Direct electron transfer and catalytic properties of covalent versus electrostatic methods of immobilizing protein films and the effect of electrode materials will be discussed.

Our second approach is based on conjugating redox-proteins with magnetic nanomaterials to immobilize on polymer coated electrodes and understand the direct electrochemical properties. Our results provide insights with regard to the direct electron transfer rates, catalytic efficiency, biological long-range electron hopping, and through-bond coupled hopping mechanism on the investigated nanomaterial-redox protein electrodes. We envisage that our findings will aid in designing viable, scalable bioreactors for green synthesis, superior biosensors, and understanding the biological electron transfer processes.

Acknowledgements. Financial support by Oklahoma State University is greatly acknowledged.
Enhancement of the Performance of Dye-Sensitized Solar Cells Containing Nanotubular TiO2 Photoanodes Prepared by Anodizing of Technical Grade Ti Foils and Chemical Modification with Dendrimers
Authors: Díaz-Acosta Cristian Moises , Murcio-Hernández Saachnitee , Sepúlveda Selene , Godínez Luis A. , Manríquez Juan
Published: February 2020

Nanotubular TiO2 photoanodes prepared by anodizing of technical grade Ti foils were sensitized with ruthenium (II) complexes and later chemically coated with dendrimers in order to improve the performance of solar cells containing ruthenium (II) complex-sensitized nanotubular TiO2 electrodes. The experimental results indicate that the presence of dendrimers in these semiconductor oxide films minimizes the loss of photoinjected electrons into the TiO2 nanotubes through the compact TiO2 layer, which partially tops the nanotubular structure at the beginning of the anodizing process. The presence of dendrimers in these photodevices produced a global photovoltaic conversion efficiency of 2.38% that it was significantly higher than that obtained for cells without dendrimers (0.71%).
Role of the Adatoms in the Oxidation of Formic Acid on Platinum Electrodes
Authors: Herrero Enrique
Published: February 2020

Oxidation of formic acid on platinum electrodes is catalyzed by the modification of the surface with different adatoms. Although a correlation between the activity of the modified surface and properties of the adatom can be found, the exact role of the adatom is still subject of debate. In the present communication, a detailed mechanism will be described establishing the roles of the adatom and the platinum surface with the aide of new experimental results and DFT calculations. The electrochemical results show that higher currents and lower onset potentials are recorded for Bi or Pb on Pt(111) electrodes, whereas Se act as a mere third body. Additionally, fast voltammetry experiments indicate that the increase in curretn observed for Bi is not related to the adsorption of formate on the platinum sites. Temperature dependent experiments shows that the increase in currents as the Bi coverage increases is parallel to a diminution of the measured activation energy. To determine the role of the adatom, DFT calculations were carried out. These calculation show that presence of an adatom causes a reorganization of the electronic structure of the surface, where the adatom can have an excess of positive or negative charge. A direct correlation between the excess of positive charge and the catalytic effect is observed. Thus, the adatoms with the highest catalytic effect are those with a largest positive charge. Moreover, these positive charge favors the adsorption of formate on the adatom and the dissociation of formate into CO2 and adsorbed H on Pt. For the most active adatoms, the activation energy of this dissociation process is negligible. These results justify the observed diminution of the experimental activation energy with the coverage.
Control of the Corrosion of Magnesium for Implant Application by Hydrothermally Deposited Biodegradable Calcium Phosphate Coating
Authors: Kaabi Falahieh Asl Sara , Nemeth Sandor , Tan Ming Jen
Published: February 2020

The corrosion protection of hydrothermally deposited calcium phosphate coatings on AZ31 magnesium alloy was studied in simulated body fluid (SBF) solution for their potential use as biodegradable implants. The coating mainly consisted of bioresorbable monetite phases. Potentiodynamic and electrochemical impedance spectroscopy (EIS) confirmed that the coatings provided varying levels of corrosion protection depending on the coating deposition temperature. By increasing the deposition temperature and corresponding growth in coating thickness the corrosion current density of the coated magnesium was 10,000 fold lower compared to the bare metal; indicating significantly enhanced corrosion performance of Mg substrate, reaching the corrosion protection requirement for magnesium implant. The barrier effect of Ca-P layers was further supported by the observed magnitude of anodic and cathodic Tafel slopes. Coated samples displayed much larger slopes than bare Mg substrate.

EIS results showed that the size of capacitance loops and the absolute impedance value (|Z|) increases. By increasing the deposition time the corrosion mechanism was changed as a result of partial delamination of top surface of coating. In agreement with the electrochemical experiments, immersion tests in SBF also indicated large improvement in corrosion protection as the mass loss was reduced almost three times when coating was applied as compared to the bare metal.

The uncoated Mg substrate undergoes severe and non-uniform corrosion after 28 days immersion in SBF solution; while, the coated samples displayed intact coating and no obvious pits were observed on the coating surface.

The described biocompatible and biodegradable coatings significantly improved corrosion resistance of Mg substrate and can be promising candidate for biomedical application.
Ionic Liquids, Superionic Glasses, Quasi-Ionic Liquids, Quasi-Liquid Ionics, All with High Conductivities but Some with Little Fluidity. Where does the Paradigm End?
Authors: Angell C Austen
Published: February 2020

Ionic liquids (ILs) are interesting in electrochemistry mainly because of their ability to carry high ionic currents in two distinct cases: (i) for the aprotic class of ILs it is for current flow within a large window of electrochemical stability and hence the support a range of battery electrochemistries[1], and (ii) for the protic class of ILs (PILs) it is for their tunability within a very wide "acidity window"[2]. For case (i), the stability window can extend to almost 6 volts (liquids), and much more at the oxidative end if the liquid has vitrified[3]. The protic ionic liquids are prepared by proton transfer from a Bronsted acid to a Bronsted base, and have been widely studied. Much less well- studied are the "halide-transfer" ionic liquids in which a halide ion is transferred from a halogenated molecular liquid to a strong Lewis acid[4, 5]. Where the proton transfer can be 100% complete in most cases, it is difficult to obtain 100 % halide transfer. In some cases the conductivity is apparently much more complex in nature involving transient oxygen links to the Lewis acid[6]. This means that members of this class of ionic liquid tend to be of low ionicity relative others examined on a Walden plot, although they can still be highly conducting due to their high fluidities. Finally we will discuss some new cases where the conductivity is liquid-like (10 mScm-1), while the system formally has solidified. These are obtained from ionic liquids that have frozen only in the first stage where the centers of mass have become ordered but the rotational and positional order of alkali cations, remains liquid-like[7].

[1] J.S. Wilkes, Green industrial applications of ionic liquids. (Editors, R. D. Rogers, K. R. Seddon, and S. Volkov.) (2003) 295-320.

[2] C.A. Angell, Y. Ansari, Z.-F. Zhao, Faraday Discussion, 154 (2012) 9-27.

[3] A. Hayashi, S. Hama, F. Mizuno, K. Tadanaga, T. Minami, M. Tatsumisago, Solid State Ionics, 175 (2004) 683-686.

[4] K. Xu, N.D. Day, C.A. Angell, J. Electrochem. Soc. , 143 (1996) L209-L211.

[5] T.G. Tucker, C.A. Angell, (to be published).

[6] K. Xu, S.S. Zhang, C.A. Angell, J. Electrochem. Soc. , 143 (1996) 3548-3554

[7] T.G. Tucker, C.A. Angell, (to be published), (2014).
(3-Aminopropyl)triethoxysilane as a Model Silylamine Reversible Ionic Liquid Used as a Reversible Electrolyte
Authors: Biddinger Elizabeth J. , Jimenez Juan D
Published: February 2020

Ionic liquids can serve as stable electrolytes in solutions and can be particularly useful when using non-aqueous systems where electrolyte solubility can be a concern. Separation of the electrochemical product from the electrolyte, ionic liquid-based or otherwise, can add challenges to the overall process. Use of a switchable electrolyte offers the possibility to reduce or eliminate these separation challenges while maintaining the high conductivity properties required for electrochemical systems. Reversible ionic liquids (RevILs) are a type of switchable solvent that could be used as a switchable electrolyte. Switchable solvents are solvents that can have dramatic step-changes in their properties with the introduction of an external stimulus such as light, heat, or carbon dioxide. RevIL systems can exist in two states: 1) a molecular liquids where it behaves like a traditional solvent with non-ionic and non-viscous properties, and 2) an ionic or reversible ionic liquid state with ionic and viscous properties that is formed in the presence of an external stimulus, commonly CO2. Silylamines are RevIL systems when they are switched in the presence of CO2 and returned to the molecular liquid with heat. The RevIL state is in the form of an ammonium-carbamate ion pair.

Triethoxysilylpropylamine (TEtoxySA) has been investigated as a reversible electrolyte. When in the pure RevIL state, the conductivity is prohibitively low to be used as both the solvent and electrolyte. If the RevIL is diluted in an organic solvent such as methanol, the conductivity of the solution increases by three orders of magnitude and reaches an electrochemically-suitable level. Several reasons likely contribute to the change in conductivity. The pure RevIL is very viscous and the anion and cation are of relatively same size, making mass transfer of the ions difficult. The anion and cation also have strong affinities for each other. In the RevIL-methanol solutions, viscosity drops significantly. Also, the anion and cation become diluted, reducing the interaction with each other. Another possible explanation for the increase in conductivity is that the ammonium cation could transfer its charge to the methanol, resulting in a smaller charge carrier through the system. The properties of TEtoxySA as a reversible surfactant including conductivity and electrochemical window will be presented along with the phenomena associated with increases in conductivity.

Figure 1: Conductivity of TEtoxySA RevIL-methanol mixtures.
Computational Study of Structure, Dynamics and Spectroscopy of Ionic Liquids
Authors: Kim Hyung J , Dhumal Nilesh , Shim Youngseon , Kim Hyunjin
Published: February 2020

In this presentation, we will give highlights of our recent computational study of time-resolved fluorescence, dielectric loss and IR spectroscopy of imidazolium-based ionic liquids and their temperature dependence. Their key spectroscopic features and dielectric behaviors are analyzed and related to ionic liquid structure and dynamics to obtain molecular-level insights. Comparison is made with conventional polar solvents, such as acetonitrile, to illustrate the features that are unique to ionic liquids. Also a brief contact is made with available experimental results.
Direct Electroreduction of Indium and Tin Oxides in Molten Salts
Authors: Qin Bo , Cui Peng , Martinéz Ana Maria , Aune Elizabeth Ragnhild , Haarberg Geir Martin
Published: February 2020

Indium is a rare metal. The largest end use for indium is in thin-film coatings as indium oxide combinined with 10 percent tin oxide (ITO). However, indium has recycling rates less than 1%. Indium and tin are especially well suited for fused salt electrolysis because their low melting points. The electrochemical behaviour of indium and tin oxides was studied by cyclic voltammetry (CV) in molten LiCl-KCl. The direct deoxidation of indium and tin oxides was investigated. A new design of direct eletrolytic reduction was proposed taking into the low melting points of indium and tin.
Electrodeposition of Liquid Metals from Molten Salts
Authors: Haarberg Geir Martin
Published: February 2020

Many important metals are being produced by electrolysis in molten salts (aluminium, sodium, rare earths and other reactive metals). Also industrial electrorefining of aluminium takes place in a molten salt electrolyte. Current efficiency for metal deposition, specific energy consumption and environmental issues are important topics for considering the success of such processes. A wide range of electrolytes including molten salts can be used to electrowin reactive metals. New electrochemical processes are proposed for recycling of metals in molten salts.

Controlled laboratory experiments were carried out to study electrolytic deposition of the liquid metals aluminium, magnesium, lead, indium and tin from molten salt electrolytes. An important feature is the fact that metals are soluble in molten salts. The excess electrons associated with the dissolved metal are in some cases responsible for the presence of electronic conduction in mixtures of molten salts and dissolved metals. In other cases the metal dissolves under the formation of a subvalent species. Diffusion and charge transfer kinetics related to metal deposition processes in molten salts were studied by using electrochemical techniques.
The Behavior of Additives LiF and KF on Current Efficiency in Aluminium Electrolysis
Authors: Cui Peng , Solheim Asbjørn , Haarberg Geir Martin
Published: February 2020

The effect of KF and LiF contents in the melt electrolyte on current efficiency were investigated during aluminum electrolysis using base NaF−AlF3−Al2O3−CaF2 system at 980°C in laboratory scale. The electrolysis was performed with a cryolite ratio of 2.5 and with 4% Al2O3 and 5% CaF2. The duration of each electrolysis experiment was 4h with a graphite anode and a cathodic current density of 0.85Acm-2. The current efficiency was found to vary with the lithium fluoride and potassium fluoride concentration. The effects of KF and LiF on the cathode process were studied using the same system. The alkali metals concentration including K, Na and Li in aluminium were analyzed as a function of the cathodic current density. Results are presented from a study of the influence of electrolyte composition and cathodic current density on current efficiency and cathode process. Also the influence of LiF on current efficiency was studied in an industrial cell.
Electrochemical Synthesis of NiSi2 from a NaCl-NaF-K2SiF6 Melt on a Ni Cathode
Authors: Kochetova Svetlana Anatolevna , Pisanenko Alexandr Dmitrievich , Devyatkin Sergei Vladimirovich
Published: February 2020

Nickel silicides are used as Schottky barrier and as ohmic contacts owing to the combination of properties typical of metal (high electrical conductivity) and nonmetal (low heat conductivity) [1]. Nickel silicides are usually produced by the thermal vacuum spraying of nickel on single-crystalline silicon plates [2]. The objective of this work was to examine the possibility of obtaining nickel silicides by electrolysis of molten salts, containing silicon ions, on a Ni cathode. It can be concluded from thermodynamic calculation that silicon discharge depolarization through NiSi2 formation is 0.110 V at 993K:

I. Ni + 2Si = NiSi2

The electrochemical behaviour of the system NaCl-NaF-K2SiF6 was studied by cyclic voltammetry. A glassy carbon crucible served as a vessel for the melt and as an auxiliary electrode; a Ni wire was used as the working electrode; the measurements were made with respect to glassy carbon reference electrode 7200С in argon atmosphere. Current-potential curves exhibited, at potentials more positive (~100 mV) than silicon discharge potential, a new irreversible electrochemical process followed by a chemical reaction. Up to 25 mm thick dense NiSi2 layers have been obtained by the electrolysis of a NaCl-NaF-K2SiF6 melt on a Ni plate at 7200С in argon atmosphere at current density of 50 mA/cm2 (Fig. 1.), which was confirmed by X-ray phase analysis. The chemical composition map of metallographic section shows the silicon distributions.

On the base of thermodynamic calculation, voltammetric investigation and electrolysis experiments, it has been show that nickel disilicides can by electrochemical synthesized in a NaCl-NaF-K2SiF6
melt at 7200С on a nickel cathode in argon atmosphere.

References

M. Lawrence, A. Dass, David B. Fraser, Chih-shihWei, Appl. Phys. Lett. 58, 1308 (1991).

Y. He, J.Y. Feng, W.Z. Li, Journal of Crystal Growth, 254, 70-74 (2003).

Fig. 1. SEM micrograph: cross-section of a Ni cathode after the electrolysis of a NaCl-NaF-K2SiF6 melts at 7200С in Ar atmosphere.
Electrochemical Synthesis of Composite Materials Based on Nanoscale Powders of Tungsten Carbides with Carbon Nanomaterials in NaCl-KCl Melt
Authors: Novoselova Inessa
Published: February 2020

The peculiarities of the partial and joint electroreduction of tungsten and carbon are studied at Pt and glassy-carbon cathodes in the chloride-oxide melt NaCl-KCl-Na2WO4-NaPO3-CO2 by the method of cyclic voltammetry. The fields of potentials, current densities and correlation of bath components are determined for the high-temperature electrochemical synthesis (HTES) of composite powder mixtures on the basis of tungsten carbides (WC and W2C) with carbon nanomaterials (CNM), monophase powders of WC and W2C. Physical – chemical properties, structural and morphological features of carbide products are studied by the methods of chemical analysis, XRD, SEM, TEM, BET, Raman spectroscopy. Investigations have shown that it is possible to produce by the electrolytic method the composition mixtures of nanosized powders of tungsten carbides (WC and W2C) with CNM of different composition, nanofibers and nanorods of hexagonal α-WC (diameter 25-200 nm, length – about 10 µm) with the specific surface about 40 m2/g, which can be used as electrode material for the different tasks of electrocatalysis.

Figure 1. TEM images and electron diffraction patterns of electrolytic tungsten carbide WC (sample 2.12).
Deposition and Dissolution of Lithium through Lithium Phosphorus Oxynitride Thin Film in Some Ionic Liquids
Authors: Furuya Ryota , Katayama Yasushi , Miura Takashi
Published: February 2020

Aprotic ionic liquids have been studied as alternative electrolytes for rechargeable lithium batteries because of non-volatility, which is expected to improve safety of the batteries. However, most of the organic cations giving room-temperature ionic liquids are instable against metallic lithium. In case of carbonate-based organic electrolytes, a passivation film, so called solid-electrolyte interphase (SEI) film, is known to form as a result of reductive decomposition of organic solvents. The SEI film is considered as a lithium ion conductor, though its nature has not been clarified yet. On the other hand, the reductive decomposition of the organic cations of ionic liquids hardly leads to formation of good SEI film. In the present study, electrochemical deposition and dissolution of lithium were investigated in some aprotic ionic liquids through a typical inorganic lithium ion conductor, lithium phosphorus oxynitraide (LiPON), thin film. Reversible deposition and dissolution of lithium were possible on a nickel electrode covered with LiPON thin film in bis(trifluoromethylsulfonyl)amide (TFSA–) based ionic liquids consisting of 1-butyl-1-methylpyrrolidinium (BMP+) and 1-ethyl-3-methyl imidazolium (EMI+). No cathodic current attributable to reductive decomposition of these cations was observed on the LiPON-coated electrodes, indicating that LiPON thin film acted as an artificial SEI film and that lithium ions were transported between the ionic liquids and LiPON. The deposition of lithium between the nickel electrode and LiPON thin film was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements and X-ray photoelectron spectroscopy.
Comparison of Redox Potentials in Non-Aqueous Solvents: Silver is Not a Noble Metal in the Acidic Ionic Liquid HmimBr
Authors: Pütz Katharina , Himmel Daniel , Radtke Valentin , Krossing Ingo
Published: February 2020

We recently introduced the concept of the Protoelectric Potential Map (PPM) which presents a new combined pH- and redox scale in an absolute sense.[1,2] This concept will also be presented by V. Radtke at this conference. The two scales are thermodynamically well described and are based on the absolute chemical potential of the proton (μ
abs(H+)) and the absolute chemical potential of the electron (μ
abs (e-)) which at standard conditions are the standard Gibbs energy of solvation Δsolv
G°(H+,S) and Δsolv
G°(e–,S), resp.

The PPM allows the quick comparison of redox potentials (reducities) and the pH values of any redox/acid-base system in any media which may lead to completely new insights and applications. Reactions can be predicted: for example, in the PPM the redox system Ag+/Ag in the solvent HmimBr (green line, no 9) lies beneath the Hydrogen line (which denotes the hydrogen evolution reaction HER, red line) signifying that silver in acidic HmimBr is a non-noble metal. These values were calculated with the COSMO-RS model.[3,4]

We here show the experimental determination of the redox potential EAg+/Ag vs SHE in HmimBr confirming the calculated values of Δsolv
G°(H+,HmimBr) and Δsolv
G°(Ag+,HmimBr).

In addition our intension is the establishment of the SHE as anchor in non-aqueous solvents. Together with the energy of transfer of the proton from water to the solvent of interest we are able to introduce absolute redox potentials within the PPM concept.

Here we want to introduce the SHE in HmimBr and show its Nernstian behavior within acidic conditions. The ongoing research in the ionic liquid HmimBr will be discussed.

[1] V. Radtke, D. Himmel, K. Pütz, S. Goll, I. Krossing, Chem. Eur. J.,
2014, DOI: 10.1002/chem.201302473

[2] a) D. Himmel, S.K. Goll, I. Leito, I. Krossing, Angew. Chem., Int. Ed. Engl.
2010, 49, 6885-6888;

b) VIP-Paper: D. Himmel, S.K. Goll, I. Leito, I. Krossing, Chem. Eur. J.
2011, 17, 5808 – 5826.

[3] A. Klamt, J. Phys. Chem. 1995, 99, 2224-2235.

[4] A. Klamt, COSMO-RS: From Quantum Chemistry to Fluid Phase Thermodynamics and Drug Design, Elsevier B.V.,

Amsterdam, 2005, p. 234.
Recovery and Electrowinning of Strategic Critical Materials from Molten Salts
Authors: Martinez Ana Maria
Published: February 2020

Materials scarcity is a complex and global issue. The whole lifecycle of products has to be considered: form mining of materials to recycling of the products at the end of its life time.

Rare earth (RE) elements (lanthanides, yttrium and scandium) are often called "key enablers of green technologies", as they are vital in the development of e.g. hybrid electric vehicles, rechargeable batteries and wind power generators. In addition, RE elements are commonly used in our daily life: flat screens, mobile phones, tablets, economy bulbs, etc. Therefore, the RE metals (REM) have been identified as one of the most critical raw materials, as their forecast scarcity will have a detrimental impact on the economy, society, research and development areas.

Electrolysis from high temperature molten salts (chlorides and fluorides) is the main current industrial route for the production of "light" REM (those with lowest melting point, i.e. Ce, La, Nd, Pr, mischmetal) and their alloys with other transition elements. Today's electrolytic production of REM is mainly carried out in China, using the so-called "Chinese technology", which is rather primitive, little energy effective, and releases environmentally harmful by-products.

Moreover, it is clear that as the demand for raw materials increases, greater efforts will have to be made on recycling, since higher recycling rates will: i) reduce the pressure on demand for primary raw materials; ii) help to reuse valuable materials which would otherwise be wasted, and iii) reduce energy consumption, greenhouse gas emissions and other negative environmental impact from extraction and processing.

In the last years, SINTEF has been involved in investigations related to:

the improvement of the already existing industrial electrolytic processes for the production of REM and alloys, in terms of energy efficiency and reducing environmental impact.

the development of effective methods for the extraction of valuable REM from RE-containing wastes/scrap (secondary sources) based on electrolysis technologies.

An insight of the challenges associated to the forecast of RE shortage will be reported. The issues connected to today's electrolytic production of REM and the necessity of innovative extraction processes from end-of-life or scrap products will also be exposed. At the end, the research activities carried out in this field at SINTEF will be described and experimental results will be presented.
Electrocatalysis of the Oxygen Reduction in Alkaline Media: Comparison of Predominant Reaction Pathways on Various Electrode Materials
Authors: Poux Tiphaine , Savinova Elena R. , Bonnefont Antoine , Truong Phuoc Lai , Ryabova Anna , Kéranguéven Gwénaëlle , Tsirlina Galina , Pham-Huu Cuong
Published: February 2020

The electrochemical oxygen reduction reaction (ORR) in alkaline media has recently attracted much attention due to an increased interest to solid and liquid alkaline fuel cells. In this presentation we will compare three classes of materials: transition metal oxides of the perovskite family, Fe/N/C, and Pt/C in terms of their activity and selectivity in the ORR. By combining the rotating-ring-disc electrode (RRDE) study with microkinetic modeling we will try to understand whether the oxygen reduction on these materials follows a “direct” 4 e- path or the O2 molecule is first reduced to hydrogen peroxide and only then to water, and how the predominant reaction pathways depend on the electrode potential. RRDE measurements in the temperature range from 25 to 75°C will help us to better understand the reaction mechanism. Complementary study of the hydrogen peroxide oxidation/reduction will also be presented. Finally, we will speculate which reaction steps have to be accelerated in order to decrease the overpotential of the ORR.

Acknowledgements

The authors thank E. V. Antipov, S.Ya. Istomin and F.S. Napolskiy of the Moscow State University (Russia) for the synthesis and characterization of perovskite materials and for valuable discussions, P. Simonov of the Boreskov Institute of Catalysis (Novosibirsk, Russia) for supplying Sibunit Carbon, and Tokuyama Company for supplying alkaline ionomer. Financial support from CNRS (France), Russian Foundation for Basic Research, and European Commission within the FP7 FREECATS project is gratefully appreciated.

References

T. Poux, A. Bonnefont, G. Kéranguéven, G. A. Tsirlina, E. R. Savinova, ChemPhysChem, DOI: 10.1002/cphc.201402022.

T. Poux, A. Bonnefont, A. Ryabova, G. Kéranguéven, G. A. Tsirlina, E. R. Savinova, Phys. Chem. Chem. Phys., DOI:10.1039/C4CP00341A.

T. Poux, F. Napolskiy, G. Kéranguéven, S. Istomin, G. Tsirlina, E. Antipov, E. R. Savinova, Catal. Today, 189 (2012) 83–92.

Pavel S. Ruvinskiy, Antoine Bonnefont, Cuong Pham-Huu, and Elena R. Savinova, Langmuir, 2011, 27 (14), pp 9018–9027.