bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Microreactors for Characterization and Benchmarking of Photocatalysts
Authors: Vesborg Peter C. K. , Dionigi Fabio , Bøndergaard Daniel , Pedersen Thomas , Domen Kazunari , Maeda Kazuhiko , Dahl Søren , Hansen Ole , Chorkendorff Ib 
Published: February 2020

In the field of photocatalysis the batch-nature of the typical benchmarking experiment makes it very laborious to obtain good kinetic data as a function of parameters such as illumination wavelength, irradiance, catalyst temperature, reactant composition, etc. Microreactors with on-line mass spectrometry, on the other hand, allow fast and automated acquisition of quantitative kinetic data. [1,2] As an example, we show how microreactor experiments on water splitting using Pt- or Rh-loaded GaN:ZnO photocatalysts quickly rank different catalysts according to their activity for gas-phase water splitting - but also how the activity scales with relative humidity and the crucial role of CrOx "capping" of the Pt- or Rh-co catalyst in order to prevent the loss of H2/O2 product via backward reaction on the precious metal. [3,4] The data suggests that protons transfer via the catalyst surface between the oxygen-evolving sites and the hydrogen evolving co-catalyst sites. Recently, the microreactor experimental platform is being developed to support in-situ UV-VIS-IR spectroscopy [5] and even the introduction of liquid aqueous electrolyte and electrodes - all while retaining high sensitivity time resolved mass spectrometric product detection. [6] [1] Vesborg et al. Chemical Engineering Journal, 160, p. 738-741 (2010) [2] Vesborg et al. J. Phys. Chem. C, 114, p. 11162-11168 (2010) [3] Dionigi et al. Energy & Env. Sci., 4, p. 2937-2942 (2011) [4] Dionigi et al. J. Catal., 292, p. 26-31 (2012) [5] Dionigi et al. Rev. Sci. Instr., 84, p. 103910 (2013) [6] Bøndergaard et al. "Fast and sensitive method for detecting volatile species in liquids", submitted
Impedance Spectroscopy Analysis of Ni/YSZ Interfaces Prepared by Liquid Precursor Deposition
Authors: Buyukaksoy Aligul , Birss Viola 
Published: February 2020

The state-of-the-art material for SOFC anodes is a Ni-yttria-stabilized zirconia (Ni-YSZ) based cermet, due primarily to the excellent electrocatalytic activity of Ni towards H2oxidation. To design and construct Ni-YSZ anodes with maximum performance, it is important to understand the reaction mechanism at the Ni/YSZ interface. Therefore, model anode designs, in which dense Ni films were deposited on dense YSZ electrolytes in the form of regularly spaced strips, have been developed by multiple groups [1, 2] to control the Ni/YSZ interfacial length, with impedance spectroscopy (EIS) used to evaluate performance. However, a consensus has not been reached yet on the exact reaction steps and how they change with temperature. Charge transfer at the Ni/YSZ interface, hydrogen diffusion on Ni surface and hydrogen adsorption/desorption reaction, have all been suggested as the rate-limiting steps in the literature [1, 2]. Thus, a clear identification of the rate limiting step at the Ni/YSZ interface and its correlation with the Ni-YSZ composite anodes is still required.
In this work, solution precursor deposited Ni thin films were deposited on dense Zr oxide discs for comparison with Ni-YSZ composite anodes that were prepared by the infiltration of the Ni solution precursor into porous YSZ scaffolds. EIS analysis was carried out, and a transmission line model, which allows the separation of the porous YSZ scaffold ionic resistance and the Ni/YSZ interfacial impedance, was used to fit the impedance data. The dominant impedance arcs in the thin film Ni anodes and the Ni/YSZ interfacial impedance, extracted from the transmission line modelling of the Ni-YSZ composites, both exhibited an activation energy of ~1.3 eV. The same activation energy obtained for the Ni/YSZ interfacial impedance obtained from both Ni thin film anodes and infiltrated Ni-YSZ anodes validates the transmission line fitting approach while the obtained activation energy value of ~1.3 eV indicates that the charge transfer process occurring at the triple phase boundary is the rate determining reaction step in Ni-YSZ anodes.

Acknowledgements:

The authors gratefully acknowledge the Eyes High PDF Program at the University of Calgary and Alberta Innovates – Technology Futures (AITF) for the support of AB, as well as the Natural Sciences and Engineering Research Council of Canada (NSERC) for the overall financial support of this work.

References:

1. A. Bieberle, L. P. Meier and L. J. Gauckler, J. Electrochem. Soc., 148 (2001) A646.
2. A. Utz, H. Stormer, D. Gerthsen, A. Weber, E and Ivers-Tiffee, Solid State Ionics, 192 (2011) 565.
Stabilization of Ni-YSZ Nanocomposite Anodes by Deposition of a Thin YSZ Overlayer
Authors: Buyukaksoy Aligul , Birss Viola 
Published: February 2020

Micro solid oxide fuel cells (μ-SOFCs) are energy conversion devices that are being considered for portable devices, such as laptop computers and mobile phones. As the low operating temperatures of μ-SOFCs (600 °C) result in high electrode resistances, one solution to this is to increase the triple phase boundary (TPB) length. In order to achieve this goal, ethylene glycol-based polymeric precursors of the Ni and YSZ components, which allow atomic level mixing of ions, were used to form nanocomposite Ni-YSZ thin films in this work. This, in turn, resulted in Ni-YSZ anode layers with an average grain size of ca. 25 nm, producing a very high TPB length (in comparison to conventional Ni-YSZ anodes) and hence a low electrode polarization resistance of 0.64 Ω.cm2 at 550 °C in humidified H2.
It has been reported that Ni-YSZ thin films, prepared by pulsed laser deposition (PLD), exhibit Ni grain growth at operating temperatures (400-600 °C), resulting in a deleterious effect on the long-term stability of the electrode performance [1]. Although the YSZ network within the composite films constrained Ni grain growth to some extent, significant grain growth at the outer surface of the film could not be inhibited [1]. To overcome this problem for the polymeric precursor-deposited Ni-YSZ films developed here, we deposited a thin, porous YSZ layer (ca. 100 nm in thickness) on top of the Ni-YSZ film. This led to a decrease in the polarization resistance degradation rate, from 3.7% per hour at 550 °C in Ni-YSZ thin films to only 0.39 % per hour at the same temperature.The results obtained in this study show that atomic level mixing, resulting from the use of polymeric precursors, yields very good electrode performances that can be stabilized by the application of additional layers. This will allow for significantly lower μ-SOFC cost as a result of the increase in power density and improved robustness.

Acknowledgements:

The authors gratefully acknowledge the Eyes High PDF Program at the University of Calgary and Alberta Innovates – Technology Futures (AITF) for the support of AB, as well as the Natural Sciences and Engineering Research Council of Canada (NSERC) for the overall financial support of this work.

References:

U. P. Muecke, K. Akiba, A. Infortuna, T. Salkus, N. V. Stus and L. J. Gauckler, Solid State Ionics, 178 (2008) 1762.
(Invited) Recent Topics on x-Ray Analysis of Fuel-Cell Catalysts
Authors: Imai Hideto 
Published: February 2020

X-ray analysis utilizing interaction between x-rays and electrons in catalysts provides versatile information on the fuel-cell-catalyst development from basic structural and electronic structural details to reaction and degradation mechanism in in-situ environments.
Quick overview of x-ray analysis methods using various physical phenomena, such as, diffraction, scattering, x-ray absorption, x-ray photo-emission, and latest challenges of their application to the catalyst development for both platinum-based and non-platinum catalysts will be presented.
(Invited) Understanding Fuel Cell Materials Degradation Via Advanced Electron Microscopy Techniques
Authors: More Karren L. 
Published: February 2020

Polymer electrolyte membrane (PEM) fuel cell performance degradation, particularly associated with the cathode catalyst layer, can be directly attributed to the stability and durability of individual material constituents comprising the membrane electrode assemblies (MEAs), including the electrocatalyst, catalyst support, recast ionomer, polymer membrane, and gas diffusion-microporous layers. The structural and chemical changes of these MEA constituents are being quantified via advanced electron microscopy methods to elucidate the specific degradation mechanisms contributing to performance loss, with the ultimate goal being microstructural and compositional improvements that will enhance MEA durability. Research efforts at Oak Ridge National Laboratory have been focused on the high-resolution microstructural and microchemical characterization of as-fabricated fuel cell materials (e.g., the individual materials constituents and the same materials incorporated in fresh MEAs), these materials/MEAs subjected to accelerated stress tests (ASTs) designed to degrade specific MEA components, and field-aged MEAs. These studies are used to establish critical processing-microstructure-performance correlations and to elucidate the individual materials changes contributing to measured MEA degradation, performance loss, and failure. Analytical microscopy methods have been used to mechanistically explain the degradation of various carbon support structures, to quantify Pt loss due to migration, catalyst coalescence, and to understand the structure, distribution, and composition of thin ionomer films within catalyst layers. Understanding and quantifying the structural and compositional changes of the materials comprising the MEA during electrochemical-aging will allow for the implementation of processing changes and critical materials development that are required for optimizing PEM fuel cell durability and performance.
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Research sponsored by (1) the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is an Office of Science User Facility.
Improvement of the Process Model for the Ohmic Loss of the Proton Exchange Membrane Fuel Cell
Authors: Rezaei Niya Seyed Mohammad , Phillips Ryan K. , Hoorfar Mina 
Published: February 2020

The process model is defined as an analytical solution for the governing equations of an electrochemical system which is used to predict the impedance characteristics of the system and identify the relation between different parts of the measured impedances and physicochemical properties and operating conditions [1, 2]. Despite various attempts made towards presenting a process model for proton exchange membrane (PEM) fuel cells, no complete process model is introduced yet [1, 3]. We have focused on developing such a process model by separately modeling the three losses: ohmic, activation, and mass transport. Our first process model of the ohmic loss [3] required an estimation of the water concentration in the catalyst layer which cannot be readily determined experimentally. Moreover, while the water transport in the catalyst layer was considered in the governing equations of the membrane, the water flux from the membrane towards the catalyst layer was not considered in the water flux equation of the catalyst layer. In this study, the ohmic-loss model presented before is improved by calculating the water concentration in the catalyst layer from other inputs as well as considering the water flux from the membrane in the catalyst layer equation. In the new model, the equivalent circuit extracted from the theoretical relation determined for the impedance of the ohmic loss still has the same format as the model presented before [3] (see Figure 1). However, the elements of the equivalent circuit have different theoretical definitions.
In the following equations, subscripts m, cl, and GDL represent the membrane, catalyst layer and cathode gas diffusion layer properties, respectively. l, D, M, F, T and j denote the thickness, diffusion coefficient, molecular mass, Faraday’s constant, temperature and current density, respectively. ρ, σ and λpresent the density, electrical conductivity and water content, respectively. Also,

a = 0.5193 exp(1268(1/303-1/T))

b = 0.326 exp(1268(1/303-1/T))
α = 2.5/(22F)
β = ρmDm/Mm

The model is compared against the measured impedances obtained for a 7.98-cm2cell operated at the 90% relative humidities for the anode and cathode, three different temperatures (65 °C, 70 °C and 75 °C), and two potentials (0.7 V and 0.75 V). The measured impedances are reported in the frequency span of 10-0.01 Hz as the ohmic loss is dominant in this range [3]. The results in Figure 2 show an excellent agreement between the theoretical predictions and the measured impedances.

References

S.M. Rezaei Niya, M. Hoorfar, J. Power Sources, 240, 281 (2013).

P. Agarwal, M. Orazem, J. Electrochem. Soc., 139, 1917 (1992)

S.M. Rezaei Niya, M. Hoorfar, Electrochimica Acta, 120, 193 (2014).

Figure 1
Electrochemical Investigation of Benzil/Aluminum Ion Interactions
Authors: Cheek Graham T. 
Published: February 2020

Introduction
Benzil has been investigated as a model diketone in various electrochemical studies (1-4 ). Previous work in this laboratory has dealt with the effect of metal ion addition on the electrochemical behavior of 9-fluorenone (5). In the present work, the effect of aluminum ion additions to acetonitrile solutions of benzil has been studied. The presence of adjacent carbonyl groups in benzil suggests that benzil reduction products may be effective ligands toward added metal ions. The goal of this study is to determine the effects of these metal/ligand interactions upon the cyclic voltammetric characteristics of the benzil system.
Experimental
Acetonitrile (AN), benzil, and aluminum trifluoromethansulfonate [aluminum triflate, Al(TfO)3] were obtained from Aldrich Chemical Co. Tetraethylammonium tetrafluoroborate [TEA BF4] was purchased from Southwestern Analytical Chemicals (SACHEM). Voltammograms were acquired with a PAR283 potentiostat using PowerSuiteTM software. Potentials are reported with respect to a Ag/AgCl (0.1M EMICl in EMI BF4) reference electrode (Cypress Systems). Vitreous carbon electrodes were obtained from Cypress Systems. All experiments were carried out in a Vacuum Atmospheres drybox.
Results and Discussion
Benzil undergoes two successive electron-transfers in acetonitrile/TEA BF4 (Figure 1a), although the second process is somewhat irreversible due to proton donation from acetonitrile (2-4). The addition of Al(TfO)3 at the 1:1 Al(TfO)3 : benzil level produces a new reduction peak at -0.70V, which is assigned to the reduction of a benzil:Al3+ complex. The second reduction process has become shifted to slightly more positive potentials, suggesting interaction of the benzil radical anion with Al3+. The reduction process at -1.80 in Figure 1a is due to the reduction of Al3+ in the solution. Addition of further Al(TfO)3 to give 2:1 Al(TfO)3 : benzil (Figure 1b) gives the -0.7 V reduction process as the predominant response. This general behavior supports a strong interaction of Al3+ with benzil reduction products, ultimately giving the benzil dianion with each oxygen complexed with one Al3+.

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).

D. Canby, E. Sanders,and G. T. Cheek, J. Electrochem. Soc., 160(7), G3159 (2013).

Figure 1
Pathways to Low Cost Electrochemical Energy Storage: A Comparison of Aqueous and Nonaqueous Flow Batteries
Authors: Darling Robert M. , Gallagher Kevin G. , Brushett Fikile , Ha Seungbum , Kowalski Jeffrey 
Published: February 2020

Energy storage is increasingly viewed as a valuable asset for electricity grids composed of high fractions of intermittent sources, like wind turbines, or unreliable transmission and distribution services. However, the likelihood that batteries will meet the stringent cost and durability requirements of grid applications is largely unquantified. In this work, we investigate conceptual and actual aqueous and nonaqueous flow batteries designed to store energy for hours and analyze the relationships among technological performance characteristics, component cost factors, and system price. The benefit of high voltage associated with the nonaqueous approach must be balanced against the burden of high solubility of active materials. Requirements in harmony with economically effective energy storage are derived for both systems to facilitate comparison.
Colossal Pseudocapacitance in a High Functionality - High Surface Area Carbon Anode Doubles the Energy of an Asymmetric Supercapacitor
Authors: Mitlin David 
Published: February 2020

Here we demonstrate a facile template-free synthesis route to create macroscopically monolithic carbons that are both highly nitrogen rich (4.1-7.6 wt.%) and highly microporous (SA up to 1405 m2 g-1, 88vol% micropores). While such materials, which are derived from common chicken egg whites, are expected to be useful in a variety of applications, they are extremely promising for electrochemical capacitors based on aqueous electrolytes. The Highly Functionalized Activated Carbons (HFACs) demonstrate a specific capacitance > 550 F g-1 at 0.25A g-1 and > 350 F g-1 at 10 A g-1 in their optimized state. These are among the highest values reported in literature for carbon-based electrodes, including for systems such as templated carbons and doped graphene. We show that HFACs serve as ideal negative electrodes in asymmetric supercapacitors, where historically the specific capacitance of the oxide-based positive electrode was mismatched to the much lower specific capacitance of the opposing AC. An asymmetric cell employing HFACs demonstrates a 2X higher specific energy as compared to the one employing a state-of-the-art commercial AC. With 3.5 mg cm-2 of HFAC opposing 5.0 mg cm-2 of NiCo2O4/graphene, specific energies (active mass normalized) of 50 Wh kg-1 at 230 W kg-1 and 28 Wh kg-1 at 1900 W kg-1 are achieved. In terms of volumetric energy density, the improvement is 4X, with the energy density of an asymmetric cell being 76.3 Wh L-1 versus 18.3 Wh L-1 of the symmetric cell. The asymmetric cell performance is among the best in literature for hybrid aqueous systems, and actually rivals cells operating with a much wider voltage window in organic electrolytes.
(Invited) Recent Progress in the Study of Single Molecule Electrochemistry Using Surface-Enhanced and Tip-Enhanced Raman Spectroscopy
Authors: Van Duyne Richard P 
Published: February 2020

During the last few years, there has been an explosion of interest and activity in the field of plasmonics. The goal of plasmonics is to control and manipulate light on the nanometer length scale using the properties of the collective electronic excitations in noble metal films or nanoparticles, known as surface plasmons. An improved understanding of the interactions between adsorbed molecules and plasmonic nanostructures (i.e., molecular plasmonics) is having a significant impact in a number of research areas including electrochemistry, surface science, catalysis for energy conversion and storage, the materials science of nanoparticles, biomedical diagnostics, art conservation science, and nanolithography.
In the first part of this lecture, I will provide some background material on the basic physical concepts underlying molecular plasmonics with an emphasis on surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) spectroscopy, and tip-enhanced Raman spectroscopy (TERS).
In the second part of this lecture, I will focus in on our most recent work in studying single molecule electrochemistry using surface-enhanced and tip-enhanced Raman spectroscopy. I will first describe the development of an instrument that has the capability of combining tip-enhanced Raman spectroscopy at the solid/liquid interface with scanning electrochemical microscopy (SECM). Next the single molecule Raman spectroelectrochemistry of Rhodamine 6G (R6G) at acetonitrile/Ag interface will be discussed. Finally, I will discuss the path forward toward the goal of understanding heterogeneous electron transfer at the single molecule level.
Mixed Ionic / Electronic Conductivity of Electrolyte-Modified Carbon/Zirconia Composites
Authors: Shetzline Jamie A , Creager Stephen 
Published: February 2020

A recently developed method for independently obtaining electronic and ionic contributions to electrical conductivity was used to study conductivity in thin-film samples of carbon/zirconia nanocomposite materials for which molecular and polymer electrolytes were covalently grafted onto the carbon/zirconia particle surfaces. The method relies upon careful control of the nature of the contact between the sample and the current-carrying electrodes. Electronic conductivities are derived from currents obtained when using electronically-conductive glassy carbon electrodes to contact the sample, whereas ionic conductivities are derived from currents obtained when using ionically-conductive Nafion electrodes to contact the sample. Carbon / zirconia samples were prepared from zirconia sol precursors combined with RF carbon aerogels and also with carbon black to produce carbon containing integrated zirconia. Solution-phase treatment with molecular electrolytes containing organo-phosphonate groups resulted in electrolyte attachment via zirconia-phosphonate binding. Thin-film samples of the resulting electrolytes were prepared and their mixed electronic and ionic conductivity studied as functions of temperature and relative humidity
Accumulation of Naturally-Occurring Radionuclide Polonium-210 By Phytoplankton in Urban Sea Bays
Authors: Peydus Daniel , Lazorenko Galyna Evdokymovna , Mychanov Vladimir Sergeevich 
Published: February 2020

Polonium-210 (210Po) is most available naturally occurring isotope of the polonium radionuclide with the half-life time of about 138 days. It forms in the result of 238U-226Ra decay series is 100% alpha-radioactive. These make 210Po convenient for research purposes. Polonium is an extremely toxic element. Because of its self-heating and subsequent transformation into aerosol forms, it is dangerous even at distances far exceeding the range of alpha-particles. Therefore, understanding of 210Po distributions in populated areas is an important environmental topic.
Polonium finds its path into sea basins from the atmosphere and various water systems. In the marine environment it connects with the organic matters and eventually enters into seafood chains. First organisms accumulating polonium relate to phytoplankton.
The present paper reports 210Po distributions have been studied in the Sebastopol bay of the Black sea. The water samples were collected using phytoplankton nets from surface levels of water in the bay. The collection was conducted at three fixed stations and on board of a research vessel at different locations.
The obtained water samples were filtered through the nitro cellular membranes “Sartorius” with the pore diameter 1.2 um. The membranes were dried and the mass of phytoplankton was measured. Polonium was extracted from phytoplankton radiochemical means. Then polonium was deposited on disks made of silver foils. 210Po concentrations were measured using an alpha-spectrometer.