bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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).
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.