bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inductively Coupled BCl3/Cl2/Ar Plasma Etching of High Al Content AlGaN
Authors: Douglas Erica , Sanchez Carlos , Baca Albert G. , Allerman Andrew , Kaplar Robert J. 
Published: February 2020

III-nitride materials are researched extensively for high power electronics as well as for UV and visible optoelectronics. One of the many attractive qualities of III-nitride materials is their chemical stability. However, this quality can make material processing and device fabrication challenging. Though significant research has been carried out on processing III-nitride materials, comparatively few studies on high aluminum content AlGaN have been reported.
Al and Ga chlorides are volatile, making the gas chemistries of BCl3 and Cl2 attractive for use in dry etching. However, obtaining a smooth surface of AlGaN with a dry etch can be difficult due to two compounding effects: AlClx has a lower volatility than GaClx and the bond energy of Ga-N is lower than that of Al-N. This exploratory work aims to document some of the etch characteristics during inductively coupled plasma reactive ion etching (ICP-RIE) of high aluminum content AlGaN with a BCl3/Cl2/Ar plasma. Etch rate and surface morphology were investigated for Al0.85Ga0.15N. Etch rate lends insight into chemical tendencies of AlGaN alloys, while surface morphology is of interest in structures requiring subsequent processing steps such as gate recessing.
Our results show that lowering rf bias and increasing ICP power leads to smoother surfaces while maintaining an attractive etch rate. Also, the ratio of BCl3 to Cl2 significantly affects the surface roughness. In addition, we show significant improvement of surface roughness, even under sub-optimal etch conditions, by implementing a 1min BCl3/Ar plasma pre-treatment dry etch step prior to introducing Cl2 to the main etch using a BCl3/Cl2/Ar plasma.
This work was supported by the Laboratory Directed Research and Development (LDRD) program at Sandia. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Figure 1
Rotating Disk Electrode System for ORR Measurements at Elevated (>100 C) Temperature and Pressure Conditions
Authors: Fleige Michael J , Wiberg Gustav K H , Arenz Matthias 
Published: February 2020

Rotating disk electrodes (RDE) are widely used for mimicking conditions in polymer electrolyte fuel cells (PEMFCs), for example for ex situ measurements of the catalytic activity of fuel cell catalysts. However, using RDE current densities are much lower compared to fuel cells, as in liquid electrolyte mass transport of dissolved reactant gases is limited by orders of magnitude lower concentrations and diffusion coefficients compared to gas phase. Furthermore, owing greatly reduced gas solubility by increasing vapor pressure of water at elevated temperatures, RDE studies in open systems have been limited to about 60 C.1 Employing RDE at elevated pressure would allow increasing reactant gas solubility and raising the boiling point of water. In addition, conc. phosphoric acid (PA), which is typically not considered in RDE studies due its even lower gas solubility, could be used for RDE measurements at sufficient gas concentration.
This presentation will discuss a developed RDE system that was integrated in an elevated pressure and temperature electrochemical cell setup reported earlier.2
,3 The RDE system is based on a magnet coupled drive, avoiding use of a rotary seal autoclave feed-through as proposed previously.4

We tested the magnet coupled RDE up to 100 bar pressure by studying the ORR on polycrystalline Pt as a test reaction in 0.5 M H2SO4 as well as conc. PA electrolyte. By increasing the pressure of oxygen in the closed cell, the diffusion limited current densities can be increased by almost two orders of magnitude in dilute electrolyte and RDE measurements in conc. PA are enabled. The RDE system also was successfully tested at elevated temperatures up to 140 C. Kinetic measurements of the ORR under elevated pressure conditions are currently in preparation.

1 U. Paulus, T.J. Schmidt, H. Gasteiger, and R.J. Behm, J. Electroanal. Chem. 495, 134 (2001).

2 G.K.H. Wiberg, M.J. Fleige, and M. Arenz, Rev. Sci. Instrum. 85, 085105 (2014).

3 M.J. Fleige, G.K.H. Wiberg, and M. Arenz, under Review.

4 J. McBreen, W.E. O’Grady, and R. Richter, J. Electrochem. Soc. 131, 1215 (1984).
In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells
Authors: Reeping Kyle Wyatt , Walker Robert A 
Published: February 2020

Vibrational Raman spectroscopy coupled with voltammetry and impedance measurements was used to explore the effects of chlorine on solid oxide fuel cell (SOFC) performance and durability. Experiments described in this talk use newly developed vibrational Raman methods to acquire vibrational spectra from SOFC anodes exposed to CH3Cl and CH4.
SOFC anodes were exposed to 110 ppm dry CH3Cl at 650°C for up to four hours while intermittently exposing the cell to methane for ten minute intervals. In these experiments Raman spectroscopy was used to monitor carbon accumulation kinetics and using a new optically accessible apparatus designed to fit on the stage of the Raman microscope. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements performed under CH4 following 1 hour of exposure to CH­3Cl showed marked degradation. This degradation was less apparent when the SOFC was operated with H2 following exposure to CH3Cl. Under methane peak power reduced at a rate of 13.8% per hour in the presence of CH3Cl. EIS with CH4 following exposure to CH3Cl showed a small increase of bulk resistance yet consistent polarization resistance (Rpol) until the end of the final exposure, when Rpol increased dramatically. Observable carbon accumulation during CH3Cl exposure became less pronounced over time and eventually stopped accumulating at all suggesting that the primary effect of the Cl contaminant was deactivation of the Ni catalyst. Interestingly, these effects of Cl on SOFC performance with methane proved largely reversible as performance and carbon accumulation behavior recovered upon removal of the CH3Cl.
Potential of Knudsen Effusion Mass Spectrometry (KEMS) for Thermo Chemical Studies in Materials Science
Authors: Markus Torsten 
Published: February 2020

The determination of valuable thermodynamic data for materials at elevated temperatures is a very important issue in Materials Science. This can be achieved by the elucidation of vaporization processes with high temperature mass spectrometry.
Knudsen Effusion Mass Spectrometry provides the identification of gaseous species present above condensed phases and permits the determination of their partial pressures up to a total pressure of 200 Pa.
The key for establishing model calculations using DG minimization tools like FactSage, Pandat or Thermocalc is the knowledge of the thermodynamic data of molecules and compounds. This includes the partial pressures of gaseous species, the standard enthalpies and entropies of formation of gaseous and condensed phases as well as their enthalpies and entropies of mixing and the knowledge of phases and chemical compounds which are formed upon reactions.
The method will be described and examples and an insight will be given how basic thermodynamic data are derived with the above mentioned method for the incorporation into thermodynamic databases. Examples of investigations carried out in our lab will be given.
Oxidation Behaviors of Ash Free Coals in a Coin Type Direct Carbon Fuel Cell
Authors: Lee Sang-Woo , Kim Tae-Kyun , Kim Yoo-Jeong , Lee Choong-Gon 
Published: February 2020

Ash free coals (AFCs) extracted from bituminous, sub-bituminous, lignite, and anthracite coals were served as fuel in a direct carbon fuel cell (DCFC) and their oxidation behavior were investigated with electrochemical method of steady state polarization. AFCs were produced by a micro-wave method with a polar solvent of NMP. The electrochemical oxidation behaviors of AFCs were investigated in a coin type DCFC. The extraction yields are bituminous > sub-bituminous > lignite > anthracite. However, the open circuit voltages and voltages at a polarization state were similar among the AFCs. Regardless of the raw coal species the AFC has similar oxidation behavior in a direct carbon fuel cell.
Mass Transport in Oxide Thin Films - Visualization and Control
Authors: Kim Jae Jin , Chen Di , Bishop Sean R. , Cook Stuart N. , Tuller Harry L. 
Published: February 2020

Device miniaturization has long stimulated great interest in the development of thin films and means for the characterization of their properties. This trend has more recently been directed towards solid state ionic devices, stimulated by the growing interest in micro-batteries, -fuel cells and –sensors. Mass transport is likewise believed to control the operation of one of the latest memory technologies based on the so-called memristive effect.
Whether in bulk or thin film form, a fundamental understanding of oxygen defect equilibria and transport kinetics is essential for achieving enhanced performance and longevity in many oxide-based device applications. The ability to diagnose a material’s behavior under operating conditions in situ, is therefore of importance. Achieving this in thin films is often more challenging given their low mass and support-film interactions. Here we present experimental results obtained by a novel experimental technique developed in our laboratory capable of simultaneously performing in situ optical absorption and electrochemical impedance spectroscopy (EIS) measurements over a wide range of temperatures and controlled atmospheres. We show, when applied to model materials systems such as PrxCe1-xO2-δ
(PCO), that these techniques are capable of deriving a detailed picture of the defect equilibria and transport properties of such materials and determining whether and to what degree they differ from bulk properties. We also show how monitoring time and spatially dependent changes in optical absorption can be used to study oxygen exchange and diffusion kinetics and discuss the impact of surface chemistry and metal current collector on the reaction kinetics. Finally, we report on recent color front migration studies in PCO films designed to extract oxygen diffusivities.
Vertical-Aligned Nanocomposites Oxide Thin Films with Enhanced Ionic Conductivity
Authors: Su Qing , Zhang Wenrui , Jacob Clement , Yoon Daeil , Manthiram Arumugam , Wang Haiyan 
Published: February 2020

Oxide thin films with high ionic conductivity are crucial for the satisfactory operation of sustainable energy production systems (e.g. fuel cells) that provide efficient and environmental-friendly electricity for human beings. Key materials science efforts associated with developing oxides with high ionic conductivity will be reviewed. Of particular importance for developing thin film oxide materials is high performance and good stability in the operation temperature range. A vertical-aligned nanocomposites (VAN) approach will be reviewed in this talk. It creates vertical interface of two oxide materials and provides a new design paradigm to tune/manipulate functionalities that cannot be obtained in individual constituents.
Within recent extraordinary results in VAN field, two major examples corresponding to ionic conducting oxide thin film will be presented: (1) to design vertical-aligned electrolyte/electrolyte nanocomposites with superior vertical ionic conductivity, and (2) to use vertical-aligned electrode/electrolyte nanocomposites as an interlayer to increase the catalytic reaction probability. Opportunities of tuning/controlling functionality of such VAN systems will be introduced.
Electrochemical Characterization of Columnar Anodic Thin Films Deposited By Pulsed Laser Deposition
Authors: Cavazos Sepulveda Adrian Cesar , Bi Lei , Traversa Enrico 
Published: February 2020

(La0.75Sr0.25)0.95Cr0.5Mn0.5O3-∂ (LSCM) is a promising redox-stable material for solid oxide fuel cell (SOFC) anodes with hydrocarbon fuels. LSCM requires additional catalysts to boost the anodic performance due to a relatively low electrochemical activity for hydrocarbon oxidation. Nickel, which is usually employed as the catalyst, provokes coking and degrades with sulphur. Therefore, an alternative approach to reduce the area specific resistance (ASR) needs to be devised, such as to significantly increase the density of the triple phase boundary (TPB) sites.
A solution can be to create an anode with vertically aligned columns with submicron diameter. To reach this goal, thin films of vertically aligned LSCM columns were deposited by pulsed laser deposition (PLD). Initially, LSCM was deposited on Si wafers to optimize the columnar morphology. Then LSCM anodes were deposited on Sm0.2Ce0.8O2-∂ (SDC) pellets and were subjected to heat treatments under ambient and reducing atmospheres. The morphology of the samples was characterized using scanning electron microscopy (SEM). Electrochemical impedance spectroscopy measurements were performed to investigate the anode performance under H2 and CH4 environments.
Let`s Design the Structural-Defect Twists in Solid State Ionic Films: Strained Architectures for Novel Electronics and Energy Conversion Devices
Authors: Rupp Jennifer L. M. 
Published: February 2020

The next generation of energy conversion and storage devices, information memories and neuromorphic computer logics in electronics rely largely on solving fundamental questions of mass and charge transport of oxygen ionic defects in materials and their structures. Here, understanding the defect kinetics in the solid state material building blocks and their interfaces with respect to lattice and interfacial strains are the prerequisite to design new material properties beyond classic doping. Through this presentation basic theory and model experiments for solid state electro-chemo-mechanics and lattice strain modulations is being discussed as a new route for tuning material and properties in ionic conducting oxide film structures up to new device prototypes. Central are the making and manipulation of the mechanics in solid state ionic conducting heterostructures, in-situ spectroscopic and microscopic techniques coupled with electrochemical micro-measurements to probe near order structural bond strength changes relative to ionic and electronic diffusion kinetics and the materials integration to new optimized device architectures and operation schemes.
We will discuss basic fundamentals of oxygen ionic transport under strain for heterostructures and exemplify their impact on novel classes of electrochemical devices such as for energy harvesting: "Micro-Energy Conversion Membranes under Tuned Strain Fields", and for innovative types of ionically-operated data storage and logics: "Strained Memristor micro-Dots for Information Storage" or "Oxygen-Ionic Controlled Non-Binary Transfer Logics to replace Electronically Operated Transistors".

1) The Effect of Mechanical Twisting on Oxygen Ionic Transport in Solid State Energy Conversion Membranes
Y. Shi, A.H. Bork, S. Schweiger and J.L.M. Rupp
Nature Materials, accepted (2015)

2) A Micro-Dot Multilayer Oxide Device: Let’s Tune the Strain-Ionic Transport Interaction
S. Schweiger, M. Kubicek, F. Messerschmitt, C. Murer and J.L.M. Rupp
ACS Nano, 8, 5, 5032 (2014)

3) Memristor Kinetics and Diffusion Characteristics for Mixed Anionic-Electronic SrTiO3-δ: The Memristor-based Cottrell Analysis Connecting Material to Device Performance
F. Messerschmitt, M. Kubicek, S. Schweiger and J.L.M. Rupp
Advanced Functional Materials, 24, 47, 7448 (2014)
Solvent-Engineering of High-Performance Non-Precious Metal Catalysts
Authors: Martinez Ulises , Dumont Joseph H , Chung Hoon T , Artyushkova Kateryna , Mohite Aditya , Gupta Gautam , Zelenay Piotr 
Published: February 2020

Non-precious metal catalysts (NPMCs) with high volumetric activity and low H2O2 yield are being considered as potential replacement for Pt-based oxygen reduction reaction (ORR) catalysts in the PEFC cathode. State-of-the-art NPMCs are typically synthesized from highly heterogeneous precursors and amorphous carbon materials [1-2], which complicate the understanding and development of new materials with improved activities. Recent efforts have been focused on developing carbon nanostructures with superior structural and functional properties from less complex systems, such as graphene oxide (GO). Catalysts derived from GO are more homogeneous and possess several highly desirable properties, such as good chemical stability and excellent conductivity. More importantly, they can be functionalized in a controlled manner [3]. Our efforts have demonstrated the importance of the effective removal of intercalated water on the structure, and consequently, the ORR activity of GO-based NPMCs [4].
In this study, we report the synthesis of solvent-engineered NPMCs with improved performance based on our findings from the more homogenous GO-based systems (Fig. 1). Despite the widely known presence of residual water in GO and more complex carbon systems, no report exists about the effective removal of water to improve the catalyst activity. In this presentation, we focus on the effect of solvent-engineered pretreatments on the structure and function of the ORR catalysts.

References

Wu, G., More, K. L., Johnston, C. M., Zelenay, P., Science, 332, 443-447 (2011).

Bashyam, R., Zelenay, P., Nature, 443, 63-66 (2006).

Qu, L., Liu, Y., Baek, J.-B., Dai, L., ACS Nano,
4, 1321-1326 (2010).

Gupta, G et al, Highly Tunable and Ordered Graphene-Oxide-Based Materials for Energy Applications, 2014 ECS and SMEQ Joint International Meeting (October, 2014).

Figure 1
Pore Network Modeling of Gas Diffusion Layer As a Support to Better Understand Water Management in Proton Exchange Membrane Fuel Cells
Authors: Pauchet Joel , Prat Marc , Belgacem Najib , Agaesse Tristan , Straubhaar Benjamin 
Published: February 2020

PEMFC (Proton Exchange Membrane Fuel Cells) is considered as a promising solution for producing clean energy. To increase its industrial development for automotive application, performance and durability are still to be improved and cost needs to be reduced.
Water management is one of the most important remaining bottlenecks to increase performance and durability of PEMFC. Nevertheless, despite numerous studies, many questions remain open and for instance it is not possible yet to propose reliable optimization of the porous layers (Gas Diffusion Layer, Active Layer…) to optimize transfers (and especially water management) in the MEA and thus increase performance and durability. One main reason is that water transfers in the MEA, and also the link between structural properties of these layers and performance, are not correctly described and understood. For instance, classical modeling used in PEMFC do not account for these structural properties despite the fact that they have a huge influence on performance.
More descriptive modeling approaches have been proposed in the last years to better understand the link between structural properties of these layers and transfers in the MEA. Amongst those, Pore Network Modeling (PNM) is more and more applied to GDL. This approach, classically used for soil application, allows simulating two-phase flows in porous media taking into account local properties (Pore/Throat Size Distribution, local structure, local wettability…) which is an important progress compared to classical PEMFC modeling based on Darcy approach.
This keynote lecture focuses on PNM and its application to GDL to better understand (gas and liquid) transfers in the MEA and to try and link local structural properties of GDL to the performance of PEMFC. Experimental results are presented all along the discussion either to validate the main hypothesis or to validate the PNM simulations.
After a description of the PNM approach, two-phase transfers inside GDL are discussed: influence of wettability, thickness, local structure…; study of GDL degradation; role of the Micro Porous Layer (MPL); validity of classical Darçy “laws”… The two classical scenarii of water transfers in the GDL (liquid injection and/or condensation) are also discussed. The coupling between PNM and performance model, which is a step towards upscaling of PNM, is introduced by the analysis of performance loss of PEMFC as a function of hydrophobicity loss of GDL. Advanced results comparing two-phase PNM based on real 3D images of GDL and X-Ray tomography of liquid pattern inside the GDL are also presented as a step towards even more representative PNM modeling of MEA components.
Finally it is shown how PNM can be extended to the Active Layers by coupling two-phase transfers to charge transfers by electrochemistry.
Non-PGM Fe-N-C Catalysts for Oxygen Reduction Reaction in Pemfcs: MEA Design and Post-Mortem Analysis
Authors: Stariha Sarah , Serov Alexey , Artyushkova Kateryna , Atanassov Plamen 
Published: February 2020

Clean energy sources are currently in high demand. Fuel cells, such as proton exchange membrane fuel cells (PEMFCs,) are a potential solution. Current technologies use platinum-based catalysts, which are expensive and contribute to over 40% of the total cost of a PEMFC.(1) However, considerable research has been undertaken in the past decade examining non-platinum group metal (non-PGM) catalysts. One rapidly developing class of non-PGM catalysts for oxygen reduction reaction (ORR) are nano-materials based on transition metal-carbon-nitrogen networks (M-N-C).(2) These materials include Fe, Co or Mn salt and N-containing organic precursors (either polymeric or low molecular weight ones).
It is widely recognized that nitrogen moieties of M-N-Cs play a crucial role in the ORR mechanism. It has been suggested that the nitrogen stabilizes the attachment of the transition metals to the underlying carbon support creating the ORR active sites.(2-4) We have examined a number of different organic precursors in our previous research. They include Co-tetramethoxy phenylporphyrin(6), poly(ethyleneimine)(7), 4-aminoantipyrine(1), and carbendazim(8).
The catalysts presented in this work were synthesized using novel organic precursors. These catalysts showed promising results when tested in membrane electrode assembly configurations in both H2/Air and H2/O2. (Fig. 1a and 1b) The two best preforming catalysts (made with imidazole-family of precursors - IFoP Fig. 1c) and the worst performing catalyst (made with phenylenediamine and piperazine organic precursors Fig. 1d) were selected for further chemical post-mortem analysis that will be obtained by high-resolution X-ray Photoelectron Spectroscopy (XPS). XPS allows for the quantification of surface oxides, an increase in surface oxides after testing indicates degradation of the catalyst layer. Focused Ion Beam/Scanning Electron Microscopy (FIB-SEM) will also be used to obtain a visual 2d cross-section and 3d representation of the catalyst layer. Understanding the chemical and morphological changes that occur in catalyst layers during fuel cell operation and its relationship to original properties of the catalysts is of critical importance for designing not only active but also durable M-N-C ORR electrocatalysts.

Acknowledgments: This work is supported by DOE-EERE Fuel Cell Technology Program: “Development of Novel Non Pt Group Metal Electrocatalysts for PEMFC” (S.Mukerjee, PI)

References:

1. M. H. Robson et al. Electrochim. Acta
90, 656-665 (2013).
2. F. Jaouen et al. Energy Environ. Sci.
4, 114-130 (2011).
3. S. Kattel et al. Phys Chem Chem Phys
16, 13800-13806 (2014).
4. U. I. Kramm et al. J. Am. Chem. Soc.
136, 978-985 (2014).
5. U. Tylus et al. J. Phys. Chem. C
118, 8999-9008 (2014).
6. K. Artyushkova et al.. Journal of Power Sources
226, 112-121 (2013).
7. A. Serov et al.. Applied Catalysis B: Environmental
127, 300-306 (2012).
8. A. Serov et al.. Adv. Energy Mater.
4, 7 (2014).

Figure 1