bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determining "Apparent" Diffusion of Electrons through a Nafion Membrane Using Hydrodynamic Voltammetry
Authors: Reynolds Marissa Kayle , Paul David W 
Published: February 2020

Nafion is used extensively as a proton exchange membrane in PEM fuel cells. The membrane must be hydrated in order to function properly as an electrolyte and as a physical separation barrier between the anode and the cathode. In this project, potassium ferricyanide is added to the hydrating electrolyte solution and is shown to incorporate into the Nafion membrane. By using hydrodynamic voltammetry, the ferricyanide redox signals can be used as a diagnostic and an investigative tool to study the integrity and swelling properties of the Nafion membrane. When ferricyanide is absent from the hydrating solution, but present in the bulk electrolyte solution during the hydrodynamic voltammetry experiments, the signals produced (or lack thereof) can be used as a diagnostic tool for the physical integrity of the membrane. When ferricyanide is allowed to incorporate into the membrane, the properties of the hydrated membrane can be investigated. An new equation, known as the Tedford equation, was derived to determine the diffusion coefficient of the analyte in the bulk solution and an apparent diffusion of electrons within the membrane itself. The Tedford equation accounts for the dependence on the rotation rate as well as known membrane properties such as thickness and the concentration of the analyte incorporated into the membrane from the bulk solution during hydration.
For a bare rotating disk electrode, the Levich equation can be used to determine the bulk diffusion coefficient (D) by plotting the diffusion limiting current (iL) against the square root of the rotation rate (ω).
iL=0.62nFAD2/3 ν-1/6 C* ω1/2 (1)
The slope is made up of the known variables where n is the number of electrons in the redox reaction, F is Faraday’s constant, A is the electroactive area of the electrode, ν is the kinematic viscosity of the solution, and C* is the concentration of the analyte in the bulk.
The Dahms-Ruff equation can be used to determine the apparent diffusion coefficient of electrons (DE) and the current due to this apparent diffusion (iE).
DE=D+kφ2 Cp* (π/4) (2)
iE=(FADE Cp*)/δm (3)
where k is the rate constant of the redox reaction, φ is the average distance between the redox centers in the membrane, Cp* is the total amount of analyte in the membrane, and δm is the membrane thickness.
Equations 1 and 3 were combined to derive the Tedford equation in relation to the peak current (ip).
ip=0.62nFAD2/3 v-1/6 ω1/2 (C*-Cm )+(nFADE Cm)/δ
m
(4)
This equation can be used to determine the apparent diffusion coefficient of the electrons with the ferricyanide redox centers in the membrane. It can also be used to compare membranes with differing hydration times and possibly to study hydrating properties.
Optical Cooling of CdSe/ZnS Quantum Dots Embedded in PMMA
Authors: Fontenot Ross , Mathur Veerendra , Barkyoumb John 
Published: February 2020

In 1929, the German physicist Peter Pringsheim proposed that anti-Stokes emission can lead to the cooling of bulk matter. Anti-Stokes emission results in photons of shorter wavelength (higher photon energy) than that of the exciting light due to thermal absorption. In solids, the thermal energy is mostly due to the vibrational modes (phonons) of the lattice. Thus, using lasers to cool a solid, one has to irradiate a sample with laser light in the red tail of the absorption spectrum. The material to be cooled would then absorb a photon and absorb extra energy from a phonon to emit a blue-shifted photon of higher energy. By removing these phonons, the material is cooled.
Today, this technique is known as laser cooling of solids or optical refrigeration. It can be used to achieve an all-solid-state cryocooler that is compact, contains no moving parts, has a high reliability, and does not require the use of cryogenic fluids. Laser cooling also allows for the possibility of portable lasers that require no or smaller external cooling systems because the pump wavelength can be adjusted such that spontaneous anti-Stokes luminescence cooling compensates for the stimulated quantum defect heating. A thermally balanced laser such as this would not suffer from thermal defocusing or heat damage; therefore, such solid-state-lasers could achieve higher output powers. Unfortunately, for cooling to occur in solids, the quantum efficiency of the material must be high and nearly all the anti-Stokes luminescence must leave the material without being reabsorbed.
Recently, much research has been performed on rare-earth ions for laser cooling. However, the cooling efficiency of rare-earth ions approaches zero as the temperature decreases. As a result, they have a theoretical cooling limit about 90 K. On the other hand, semiconductors provide more efficient pump light absorption, the potential for lower temperatures of 10 K, and the ability to directly integrate the material into electronic and photonic devices. This coupled with the strong electron-phonon coupling of Group II-VI semiconductors and core-shell quantum dot structure minimizing the reabsorption of the anti-Stokes luminescence, makes direct bandgap semiconductors viable laser cooling candidate materials.
Owing to the possibility for near-unity quantum efficiency of CdSe/ZnS, we have chosen to investigate CdSe/ZnS quantum dots for laser cooling applications. Recently, we have utilized photothermal deflection techniques to show that CdSe/ZnS can be cooled at a microscopic level. Moreover, we developed a new photothermal technique that is capable of discerning heating or cooling inside a material using nothing but the probe deflection thereby eliminating the need for a Stokes and anti-Stokes laser. Using the information gained from the photothermal results, we have begun to cool CdSe/ZnS polymers. This talk will go over the cooling results as well as our new photothermal technique.
Electrodeposition of Carbon from High Temperature Carbonate Melts
Authors: Hughes Matthew , Allen Jessica A , Donne Scott W 
Published: February 2020

The storage and release of electrical energy is vital to the functioning of many necessities of modern life including portable electronic devices, power tools, and automobiles. In the face of our ever-increasing need for better energy storage devices, it is desirable that we continue to investigate superior materials for use in battery and supercapacitor devices. It has long been known that carbons may be produced through the electrolytic reduction of molten carbonates, with the mechanism of this reduction being thought to proceed by way of Eqn 1 [1], i.e.;
CO3
2- + 4e- ---> C+3O2- …(1)
For this research carbons were prepared by varying the electrodeposition parameters around a standard set of conditions (Li2CO3-Na2CO3-K2CO3 electrolyte, 0.25 A/cm2 current density, graphite substrate, 600°C). The research of this group indicates at this point that there exist reproducible patterns in the properties of our carbons based on most of these variables, with the primary result of the research linking decreased current densities, decreased temperatures, and every electrolyte except Li2CO3-Na2CO3, but not substrate to any major degree, to increased capacitive performance.
1. Le Van, K., et al., Electrochemical formation of carbon nano-powders with various porosities in molten alkali carbonates. Electrochimica Acta, 2009. 54(19): p. 4566-4573.
Influence of Calcination Treatments on the Formation of N-Doped Carbon Nanofibers and Their Electrochemical Properties
Authors: Ojeda-López Reyna , Ramos-Sánchez Guadalupe , Esparza-Schulz Juan Marcos , Pérez-Hermosillo Isaac Jhonnatan , Domínguez-Ortiz Armando , González I. 
Published: February 2020

Carbon nanofibers (CNFs) are materials with potential applications as electrode supports for fuel cells, mainly due to their interesting characteristics: i) high surface area, ii) controlled chemical properties, and iii) high electric conductivity. CNFs can be modified by nitrogen doping; this procedure allows the formation of specific sites on the nanofibers surface which, when used as support, lead to controlled size and dispersion of the active material; moreover, the presence of N atoms as dopant causes the modification of the electronic density close to the doping site, specially diminishing the electron density in neighboring C atoms which also catalyze the fuel cell reactions.
In this work we propose a different alternative, the production of the support with the intrinsic formation of dopants in CNFs. N-doped carbon nanofibers were synthetized by electrospinning of polyacrylonitrile (PAN) followed by a two-step calcination process: stabilization and carbonization, the first was carried out under air atmosphere at 553 K while carbonization was conducted in inert atmosphere at five different temperatures, 873, 973, 1073, 1173 and 1273 K. X-ray Photoelectron spectroscopy experiments indicate that depending on the carbonization temperature this process produces different amounts of nitrogen species in the materials. For carbonization temperatures of 873 and 973 K, nitrogen species are mainly found in N-6 form (piridinic) while a small amount of nitrile groups is still present. For the materials with temperature treatment above 1073 K, N-Q (quaternary or graphitic nitrogen) becomes the most abundant nitrogen species, this indicate than the formed N-Q is much more stable than N-6 at higher temperatures.
The stability of the material was evaluated by cyclic voltammetry in acid media in anodic direction. The results indicate that all CNFs present a less positive oxidation onset potential in comparison to carbon Vulcan. This result agrees with thermogravimetric analysis in which N doped CNF decomposition (CO2 formation) is obtained at higher temperatures than commercial supports. Moreover, the CNFs were also evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline conditions. The preliminary results show that as the quantity of N-Q augments, the catalytic activity concomitantly increases as well, i.e. the onset potential for oxygen reduction increases.
Imaging Space Charge Regions in Sm-Doped Ceria Using Strain-Based Scanning Probe Techniques
Authors: Adler Stuart B. , Gerwe Brian S , Esfahani Ehsan N , Wang Peiqi , Chen Qian Nataly , Li Jiangyu 
Published: February 2020

Scanning probe methods have long been employed to conduct local electrochemistry. However, connecting these measurements to macroscopic electrochemical performance of an electrode can be challenging. Workers have recently begun exploring strain-based methods sensitive to local defect concentrations in materials. These include electrochemical strain microscopy (ESM) and more recently scanning thermo-ionic microscopy (STIM). The basis for these techniques will be discussed, with examples involving Li battery materials and the study of grain boundaries in rare-earth doped ceria. Also discussed will be the possible application of these techniques as local witnesses of defect concentrations in complex electrode structures during impedance or other transient measurements.
Measurement and Numerical Simulation of Temperature Distributions of a Micro-Tubular SOEC during H2O/CO2 Co-Electrolysis
Authors: Maeda Atsushi , Watanabe Kentaro , Araki Takuto , Mori Masashi 
Published: February 2020

Power to gas(PtG) has been payed attention as one of the ways to promote introduction of renewable energy. Solid oxide electrolysis cells(SOECs) are one of the electrolysis devices in the PtG. Because of its low electrolysis voltage and high utilization of generated heat, SOECs are expected to be the most attractive electrolysis cell from the viewpoint of energy conversion efficiency. In addition, since SOECs can electrolyze CO2 into CO, which is used as a raw material of alkane, it attracts attention as technique of the recycling of CO2. Thus, in recent years there has been growing interest in developing a co-electrolysis system. Because SOECs are constructed mainly on brittleness ceramics, a detailed understanding of temperature distribution in the cell is important for reducing thermal stress. Although the electrolysis reaction is endothermic, overpotentials and electrical resistivity of cell are factors of heat generation in the cell. Thus, the temperature distribution in SOECs is very complicated.
In this study, the temperature distribution in the micro-tubular cell was measured by thermocouples and a thermal imaging camera. The micro-tubular cell consists of (ZrO2)0.92(Y2O3)0.08 (YSZ)/ YSZ / La0.8Sr0.2MnO3 (LSM). The current collection of air electrode area was performed using Pt paste and wires. During the electrolysis process, the temperature change in the cell was small around gas inlet, and the difference of temperature along a tube length direction to gas outlet increased. Around Pt wire on the surface of the air electrode, the temperature change was maximum. Furthermore, the temperature change around gas outlet increased because of current collector was attached to the edge of fuel electrode at the side of gas outlet. Compared to steam electrolysis, the temperature change during the co-electrolysis process was smaller.
Co-Electrolysis, Quo Vadis?
Authors: Foit Severin Robert , Dittrich Lucy , Vibhu Vaibhav , Vinke Izaak C. , Eichel Rüdiger-Albert , de Haart L.G.J. 
Published: February 2020

Co-electrolysis, the electrochemical conversion of steam and carbon dioxide with the use of renewably generated electricity to produce syngas, can be regarded as the enabling step to the sustainable production of synfuels and high-value chemicals. This advantageous method of beneficial CO2-valorization is predetermined to couple energy-intense sectors such as “traffic and transportation” and “chemical industry”. The needed products for these markets presuppose different syngas compositions through their production routes and according to that determine the applied technology of syngas generation by its achievable H2:CO ratio. The concept of high-temperature co-electrolysis offers both an efficient electrochemical conversion and accessibility to H2:CO distributions from 1:1 to 3:1 by a given set of parameters (temperature, current density, material,…). Though, this is yet to be shown as research has been focused on electrochemical analysis of materials, cells and stacks rather than on product distribution depending on operating parameters and an all-embracing quantitative product analysis[1].
Herein, we examine the possibilities and variety on syngas production with focus on (electrochemical) performance and syngas yield and composition under different conditions, e.g. temperature, current density, substrate composition. The experiments were executed on a cathode supported cell (CeramTec) composed of an LSCF anode, a CGO barrier-layer, an 8YSZ electrolyte and a Ni/8YSZ cathode. The testing took place in the temperature range of 750 to 900 °C with preset cell voltages up to 1.4 V. The ratios of water vapor to carbon dioxide have been set to 3:1, 2:1 and 1:1. Furthermore, the cells have been tested with a 50% water – 50% hydrogen mixture for comparison. I/V-measurements and electrochemical impedance spectroscopy have been conducted under the combinations of mentioned conditions. In addition, a full spectrum analysis of the product gases has been performed, i. e. water was not condensed from the product stream prior to the mass spectrometer. Current densities of up to over 1.7 A·cm-2 with polarization resistances of 24 mΩ·cm-2 have been obtained at 900 °C and a cell voltage of 1.4 V with a 9 nl·h-1 flow of 40% water, 40% CO2 and 20% H2 used. I/V-curves decrease in slope and increase in current density with increasing temperature (figure 1). Further investigation is ongoing and the electrochemical performance and efficiency of syngas production will be presented and discussed in detail.
[1] S. Foit, I. C. Vinke, L. G. J. de Haart, R.-A. Eichel, Angewandte Chemie International Edition
2016, DOI: 10.1002/anie.201607552
Figure 1: I/V characteristics of a Ni/YSZ//YSZ//CGO//LSCF single cell during co-electrolysis of different H2/CO2 mixtures in dependence of temperature

Figure 1
Development of an Advanced Flexible Solid Oxide Fuel Cell Stack Concept
Authors: Minh Nguyen 
Published: February 2020

An advanced flexible solid oxide fuel cell (SOFC) stack concept with the potential for increased reliability, better performance and lower cost is being developed. This stack concept integrates prime-surface interconnects and single cells into a lightweight and compact structure with reliable gas seals for efficient operation at different temperatures depending on selected materials. The concept has several attractive features icluding reduced stack weight and volume, decreased performance losses in stacking, improved sealing, versatility in incorporation of different types of cell construction (for example, conventional sintered cells or thin-film metal supported cells) and flexibility in gas flow configuration. The prime-surface interconnect is a one-piece metal sheet that incorporates both fuel and oxidant flow fields with peaks o one side of the interconnect serving as flow channels (valleys) on the other side; for exampe, the egg-carton shaped prime-surface flow field. The design of the prime-surface interconnect including the key factors impacting on pressure drop, flow uniformity and formability is being evaluated. Hydroforming has been identified as the forming appoach for prime-surface interconnects. Development of metal-supported cells has been initiated. A fabrication process based on sputtering is being developed for producing cells on metal supports for this stack concept.
Cost-Effective PEM Electrolysis: The Quest to Achieve Superior Efficiencies with Reduced Investment
Authors: Friedrich Kaspar Andreas , Lettenmeier Philipp , Stiber Svenja , Ansar Asif Syed , Wang Li , Gago Aldo Saul 
Published: February 2020

Hydrogen is expected to play an important role as a crosslinking technology between power generation on one hand and transport and industry on the other hand. It can directly replace fossil fuels in transport and industry when produced by water electrolysis with renewable energies such as solar or wind. The relevant technologies are either the mature alkaline electrolysis or the newer proton exchange membrane (PEM) water electrolysis. For PEM electrolysis in particular, key components that determine the stack cost are the titanium-based contact elements, such as the bipolar plates (BPP) and the current collectors (CC), and the high iridium loading of electrocatalyst for the OER in state of art membrane electrode assemblies (MEA). However, the cost structure depends on the specific design of the electrolyser.
This presentation will discuss strategies for cost reduction by synthesizing novel electrocatalyst with the aim of lowering the high Ir loading. Our concept can be applied to supported and alloy electrocatalysts. The supports need to be highly stable and exhibit sufficient electronic conductivity. The enhancement of activity achieved with improved electrocatalyst reaches a factor of about 15 with respect to the best commercially available electrocatalyst.
Additionally, the cost reduction achieved by a titanium coating for stainless steel BPPs or CCs for PEM electrolysis will be discussed. We use vacuum plasma spraying (VPS) to coat either dense coatings for corrosion protection of stainless steel components or build up titanium diffusion layers with defined porosity as contact elements for the MEA. The conductivity of the titanium coating can be improved by well-known Pt or Au additions; however, we have also developed promising non-noble conductivity enhancement elements. Furthermore, the VPS coating and production procedure is adaptable to large-scale industrial production.

Acknowledgements

The research leading to these results has received funding from the European Union’s Seventh Framework Program (FP7/ 2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant n° 621237, “ INSIDE- In -situ Diagnostics in Water Electrolyzers“ and from national projects “LastElSys” and “WESpe” by Federal Ministry for Economic Affairs and Energy.

Figure 1
Nickel Vanadium Layered Double Hydroxides Nanostructures for High-Performance Flexible Supercapacitor Applications
Authors: Tyagi Ankit , Gupta Raju Kumar 
Published: February 2020

In recent times, demand for portable electronic devices like mobile phones, cameras and laptops etc. is increasing day by day. Energy storage devices such as batteries and supercapacitors have significant importance because of their high energy density and high power density, respectively.1 Supercapacitor is gaining great amount of attention because it uses less toxic material, offers high power density, excellent electrochemical stability, wide range of operating temperatures and durability. A facile fabrication of low cost, efficient, stable, eco-friendly and earth-abundant electrode materials for supercapacitors is critical.2 Layered double hydroxide (LDH) is new class of material having positively charged hydrotalcite-like layers, weakly bound, intercalating charge compensating anions and water molecules, has showed enormous supercapacitive performance.3 In this work, an ionic lamellar, two-dimensional (2D) nickel-vanadium layered double hydroxide (NiV LDH) nanosheets have been synthesized via facile, cost effective and potentially scalable hydrothermal method. The as-prepared 2D NiV LDH nanosheets coated on Ni foam (NF/NiV LDH) was used as supercapacitor electrode. The electrochemical characterization techniques such as cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to characterize the material for its electrochemical properties, while SEM, TEM, XRD, BET, and XPS etc. techniques have been used for their morphological, structural and physical characterization. High specific capacitance of ~1581 F g-1 at the current density of 1 A g-1 was observed in three-electrode system using KOH as electrolyte, which remained quite high at increased current density of 10 A g-1. This work demonstrates great potential for NiV LDH nanosheets as electrode material for supercapacitor applications.

References

[1] A. Tyagi, K. M. Tripathi, R. K. Gupta, J. Mater. Chem. A 3, (2015) 22507-22541.
[2] A. Tyagi, R. K. Gupta, Nanomaterials: A guide to fabrication and applications, (CRC Press), 261 (2015).
[3] K. Fan, H. Chen, Y. Ji, H. Huang, P. M. Claesson, Q. Daniel, B. Philippe, H. Rensmo, F. Li, Y. Luo, and L. Sun, Nat. commun. 7 (2016) 11981.