bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Basal Plane Dislocation Dynamics in PVT-Grown 4H-SiC Crystals during High Temperature Treatment
Authors: Raghothamachar Balaji , Yang Yu , Guo Jianqiu , Dudley Michael 
Published: February 2020

The deformation processes in 4H-SiC crystals are of particular interest because they generate mostly basal plane dislocations (BPDs) which are implicated in the degradation or premature breakdown of SiC power devices [1]. Fundamental understanding of the generation and multiplication of BPDs is critical for design of growth strategies to control the density of BPDs during PVT growth of 4H-SiC crystals. Recently, we reported on the direct observation of thermal gradient induced motion of BPDs through in-situ synchrotron X-ray topography imaging of PVT-grown 4H-SiC wafers subject to high temperature treatment [2]. The multiplication of BPDs by the operation and interactions of multiple Frank-Read sources leading to formation of complex configurations was reported. We have analyzed the series of images recorded during the in-situ experiment in detail to deduce the Burgers vectors and core structures of the moving dislocation segments and measure their individual velocities. Dislocations with Burgers vector along the off-cut 11-20 direction were found to be the only dislocations undergoing deformation during heat treatment. Sample was imaged after heat treatment and the segments of dislocations used for velocity measurements were found to be either pure screw or 60° dislocations comprised of Si cores. Using the kink-diffusion model, the activation energies for dislocation motion have been estimated from the velocity data for each of these dislocation types and found to be 2.21 eV for 60° and 3.28eV for pure screw segments respectively. These values are in good agreement with the macroscopic studies of yielding of semiconductor crystals during high temperature compression and indentation experiments [3,4]. Quantitative expression of the temperature dependent critical resolved shear stress required for dislocation motion has been derived from this analysis.
References:
[1] Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, P. A. Nilsson, J. P. Bergman, and P. Skytt, Mater. Sci. Forum 353-356, 727 (2001)
[2] Yu Yang, Jianqiu Guo, Balaji Raghothamachar, Michael Dudley, Swetlana Weit, Andreas N. Danilewsky, Patrick J. McNally, Brian K. Tanner, Mater. Sci. Forum, 924, 172-175 (2018)
[3] V. Samant, P. Pirouz, Int. J. Refractory Metals and Hard Materials 16.4-6 (1998).
[4] J-L. Demenet, M. H. Hong, P. Pirouz, Scr. Mater., 43, 865-870 (2000).
Radiation Effects in Diamond pHEMTs
Authors: Thapa Aayush , Shahin David , Christou Aris 
Published: February 2020

Field effect transistors (FET) based on diamond have 2-dimensional hole gas (2DHG) as conduction channel. In terms of usability in harsh environment, an important aspect of diamond-based FETs is its promise of radiation hardness. Because of high binding energy of diamond, diamond transistors are predicted to be radiation hard. However, the way radiation affects the 2DHG conduction layer is unknown. This may be a problem as radiation may disrupt the 2D hole concentrations in the 2DHG channel. In this work, radiation effects in diamond with 2DHG layer is explored in two ways: (1) Using Hall effect measurements to monitor changes in transport properties, and (2) measuring current-voltage characteristics for the three-terminal devices to analyze changes in their device properties. Two different types of radiation were used. A cyclotron was used for proton irradiation on diamond substrates, and a high capacity dry cell, panoramic gamma irradiator with 60Co as source material was used for gamma irradiation on diamond-based FETs. Diamond substrates were irradiated with protons at 152 keV and fluence of 1012 particles/cm2. Likewise, diamond-based FETs were irradiated with gammas from a total dose of 100kRad up to 10 MRads and exhibited an annealing effect.
ACKNOWLEDGEMENTS
The authors thank the University of Maryland NanoCenter, the University of Maryland Radiation Facilities and Argonne National Laboratory for equipment and staff support. The effort depicted is sponsored by the Department of Defense, Defense Threat Reduction Agency under Grant No. HDTRA1-17-1-0007. The content of this information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred. The authors acknowledge the assistance in material preparation from Jim Butler of EuclidTech Labs.
Using Multiscale Co-Simulation Modeling Technique to Understand the Transports Interaction inside Gas Channel, GDL, MPL, and CL during PEMFC Operations
Authors: Shimpalee Sirivatch , Satjaritanun Pongsarun , Hirano Shinichi , Zenyuk Iryna V. , Weidner John W. 
Published: February 2020

The objective of this study is to use coupled simulation (co-simulation) approach to model the multidimensional/multiscale/multiphase polymer electrolyte membrane fuel cell (PEMFC) for enhancing the understanding of fuel cell performance and durability implications with structural, material properties and operational conditions. This work also provides the detailed knowledge of transports inside gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL). The local kinetic activity inside nanoscale CL has also been developed and modeled. These knowledge will contribute to enhance the catalyst activity at low current density and mass transport at high current density. This will enrich the development of novel structures that address local oxygen transport resistance in any kind of catalyst layer and this will be well aware of the urgent need for investigating multi-scale phenomena of a physical and electrochemical nature in a fuel cell.
The Lattice Boltzmann Method (LBM) approach is extended to solve the mass transports and kinetic in the CL as shown in Figure 1. In this figure the catalyst layer is included into the model established in the previous work [1-3]. The nanoscale catalyst layer is attached into the microscale gas diffusion layer (GDL) and micro porous layer (MPL) as one computational domain. The macroscale geometry such as flow channel is continued to be computed by conventional CFD [4-5]. Figure 2 shows example of predictions of temperature distribution and oxygen mass fraction inside the cathode macroscale flow-field channel, microscale GDL/MPL, and nanoscale CL from this co-simulation approach.
References:

Satjaritanun et al., J. Electrochem. Soc. 164(11) E3359-E3371, 2017.

Satjaritanun et al., J. Electrochem. Soc. 165(13), F1115-F1126, 2018.

Shimpalee et al., Abstract# I01A-1369, AiMES 2018, Sept. 30 – Oct. 4, 2018, Cancun, Mexico.

Shimpalee et al., J. of Electrochem. Soc. 165 (11), F1019-F1026, 2018.

Shimpalee et al. J. of Electrochem. Soc., 164(11), E3073-E3080, 2017.

Figure 1
Understanding Polymer/Particle Interactions in Fuel-Cell Inks Using Model Systems
Authors: Berlinger Sarah A. , McCloskey Bryan D. , Weber Adam Z. 
Published: February 2020

The formation process of hydrogen fuel-cell catalyst layers (CLs) is poorly understood, and represents a major area of effort with regard to increasing overall cell efficiency and durability. CLs are made from precursor inks that are dispersions of catalyst nanoparticles, ion-conducting polymer, and solvent (typically water and propanol mixtures). The polymer is generally a perfluorinated sulfonic-acid polymer, the prototypical example of which is Nafion. The duality between the strongly acidic sidechains and hydrophobic backbone of the polymer cause it to adopt unique conformations in solution, which are a strong function of the amount of water present in the ink.1 Indeed, tuning the ratio of water to propanol has recently been demonstrated to change the effective pH of these polymer solutions, possibly by changing the amount of exposed sidechains.2

The complex interplay between particle/solvent/polymer interactions govern CL ink and layer properties.3-4 However, much remains unknown about the fundamental forces controlling these interactions. In this study, we explore the polymer/particle interaction, and how it is affected by solvent quality. To do so, we use quartz crystal microbalance with dissipation (QCM-D) with model functionalized substrates that probe specific relevant forces (electrostatic, hydrophobic, etc.) in order to elucidate interactions present on the comparably more-complex carbon-platinum particle surface. Different ionomer dispersions in a variety of solvents are studied to understand ionomer adsorption and desorption behavior. QCM-D data is coupled with calorimetry measurements to extract thermodynamic binding information. Results reveal that hydrophobic interactions are a major driving force for ionomer adsorption.
Acknowledgements
This study was mainly funded under the Fuel Cell Performance and Durability Consortium (FC-PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy under contract number DE-AC02- 05CH11231. S.B. also acknowledges support from the National Science Foundation Graduate Research Fellowship under grant number DGE 1752814.
References

Welch, C.; Labouriau, A.; Hjelm, R.; Orler, B.; Johnston, C.; Kim, Y. S., ACS Macro. Lett.
2012,
1 (12), 1403-1407.

Berlinger, S. A.; McCloskey, B. D.; Weber, A. Z., J. Phys. Chem. B.
2018,
122 (31), 7790-7796.

Dixit, M. B.; Harkey, B. A.; Shen, F.; Hatzell, K. B., J. Electrochem. Soc.
2018,
165 (5), F264-F271.

Hatzell, K. B.; Dixit, M. B.; Berlinger, S. A.; Weber, A. Z., J. Mater. Chem. A
2017,
5 (39), 20527-20533.
Modeling Water Uptake and Pt Utilization in High Surface Area Carbon
Authors: Chowdhury Anamika , Darling Robert M. , Radke Clayton J. , Weber Adam Z. 
Published: February 2020

Reducing the loading of expensive Pt-based catalysts in polymer-electrolyte fuel-cell (PEFC) catalyst layers (CLs) is imperative for wide-scale commercialization. However, a local resistance close to the Pt reaction sites becomes significant at low Pt loadings and hinders adequate performance.1,2 In our previous study, we demonstrated that the local resistance is primarily related to the proton-conducting ionomer thin-film within the CL and consists of: (i) reactant transport resistance due to low permeability of ionomer thin-film (compared to bulk ionomer) and (ii) interfacial resistance due to Pt/sulfonic-moiety interactions.3 Thus, there is need to optimize ionomer design to minimize CL resistance.
In this talk, we investigate the impact of ionomer chemistry, content, and equivalent weight (EW) on CL resistance. Using H2 limiting-current measurements, the total CL resistance is segregated into transport and interfacial components. CL resistance increases monotonically with ionomer content, primarily due to thicker ionomer films. Low EW ionomers demonstrate higher interfacial resistance due to high density of sulfonic groups, whereas higher EW ionomers exhibit higher transport resistance due to low-reactant permeability associated with low-water uptake. These findings are rationalized through comparison of properties and structure/function relationships elucidated by ionomer thin-film studies on planar substrates, thus bringing together model and in-situ studies.
Further, time-permitting, the impact of carbon support (low versus high surface area carbon) on local CL resistance will also be discussed, mainly via modeling water uptake and proton pathways. Overall, the knowledge gained demonstrate pathways towards ameliorating the local resistance and enabling high performing low Pt-loaded PEFCs.

Acknowledgements

We would like to thank Sarah A. Berlinger and Robert Darling for helpful discussions. This work was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.

References:

1. T. A. Greszler, D. Caulk and P. Sinha, J Electrochem Soc, 159, F831 (2012).
2. A. Z. Weber and A. Kusoglu, J Mater Chem A, 2, 17207 (2014).
3. T. Schuler, A. Chowdhury, A. T. S. Freiberg, B. T. Sneed, F. B. Spingler, M. C. Tucker, K. More, C. J. Radke and A. Z. Weber, J Electrochem Soc, 166, F3020 (2019).
Towards Electrochemical Synthesis of Cement — an Electrolyzer-Based Process for Decarbonating CaCO3 while Producing Useful Gas Streams
Authors: Ellis Leah , Badel Andres F , Chiang Miki , Park Richard , Chiang Yet-Ming 
Published: February 2020

Cement production is currently the largest single industrial emitter of CO2, accounting for 8% (2.8 Gtons/year) of global CO2 emissions in 2015. Deep decarbonization of cement manufacturing will require remediation of both the CO2 emissions due to the decomposition of CaCO3 to CaO, and that due to combustion of fossil fuels (primarily coal) in the calcining (~900°C) and sintering (~1,450°C) processes. Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO3 is decarbonated at low pH and Ca(OH)2 is precipitated at neutral to high pH, concurrently producing a high purity O2/CO2 gas mixture (1:2 molar ratio at demonstrated stoichiometric operation) at the anode and H2 at the cathode, as shown in Figure 1. We show that the solid Ca(OH)2 product readily decomposes and reacts with SiO2 to form alite, the majority cementitious phase in Portland cement. Our electrochemical calcination approach produces concentrated gas streams from which the CO2 may be readily separated and sequestered, the H2 and/or O2 may be used to generate electric power via fuel cells or combustors, the O2 may be used as a component of oxyfuel in the cement kiln to further lower CO2 and NOx emissions, or the output gases may be used for other value-added processes including liquid fuel production. Analysis shows that in a scenario where the hydrogen produced by the reactor is combusted to heat the high temperature kiln, the electrochemical cement process can be powered solely by renewable electricity.
Figure 1. Schematic of the electrolyzer-based decarbonation cell. Reactions 1a and 1b are the O2 evolution and H2 evolution half-cell reactions respectively, under near-neutral pH. Reactions 2a and 2b represent the decomposition of CaCO3 and release of CO2. Reaction 3 is the normal formation of water from its component ions. In Reaction 4, the hydroxide ions in Reaction 3 instead go towards the formation of Ca(OH)2, and the protons protonate carbonate ions (Reaction 2b). The overall reaction in which CaCO3 is converted to Ca(OH)2 with the attendant release of H2, O2 and CO2 is shown at the bottom.

Figure 1
Characteristics of Metallic Bipolar Plate for Polymer Electrolyte Membrane Fuel Cells
Authors: Pilinski Nadine , Nagappan Nambi Krishnan , Wagner Peter , Dyck Alexander 
Published: February 2020

The bipolar plate is one of the most significant key components in polymer electrolyte membrane fuel cells (PEMFCs). Bipolar plate (BPP) weight and cost are determining factor for future commercialisation of PEMFC technology. To overcome this major hurdle, metallic bipolar plates are used as a BPP in large number of commercial PEMFCs due to their advantages such as excellent mechanical strength, good electrical and thermal conductivities, low cost, ease of fabrication, gas impermeability, and possibility to make thin plates [1, 2]. However, corrosion remains a major anxiety for metallic bipolar plates use in real PEMFC operating conditions. Further, the formation of passivation layers reduces not only the electrical conductivity but also the overall performance. The aim of this present research is to characterise metallic bipolar plate with respect to corrosion behaviour, surface area and roughness changes and its level of success to meet the DOE requirements for BPPs. Especially, electrochemical stability was investigated in terms of corrosion measurements within a three electrode cell system. Active exposure area of 1 cm2 bipolar plate material was used as working electrode (WE). A platinum wire with an activated carbon felt, and reversible hydrogen electrode employed as a counter electrode (CE), and reference electrode (RE), respectively. Bipolar plates were subjected to chemical storage in 0.5 M H2SO4 at 80 ºC as a function of time. Further, electrochemical stability were evaluated in term of potentiostatic conditions such as open circuit potential (OCV), anodic and cathodic polarisation conditions. Finally, a corrosion analysis is presented using atomic force microscopy (AFM), confocal microscopy and/or µ-computed tomography (µ-CT) as well as inductively coupled plasma with mass spectrometry (ICP-MS) as an attempt to know the surface area changes of corrosion in metallic bipolar plates and their degradation products in acid.
Figure 1: Three-electrode set-up for corrosion measurements (left), AFM picture of metallic BPP (right)

Figure 1
Study on Carbon Corrosion Induced Crack Propagation on Cathode Catalyst Layer in Polymer Electrolyte Membrane Fuel Cell Under Startup-Shutdown Operating Condition
Authors: Li Yunqi , Chen Xiran , Xu Jun 
Published: February 2020

Polymer electrolyte membrane fuel cell (PEMFC) has the advantages of high energy density, high efficiency and theoretically zero emission [1], and is expected to replace the traditional internal combustion engine [2] to solve the problems of severe environmental pollution and resource shortage. However, the wide-spread application of FC generators in vehicles faces two major bottlenecks, i.e. cost and durability. Complex vehicle operating conditions including speed change, startup and shutdown, idling and high power pose great challenges to PEMFC's durability. It is found that under the adverse operating conditions such as startup-shutdown, carbon corrosion induced crack propagation [3] in the cathode catalyst layer is an inevitable attenuation and aging behavior, which ultimately leads to fuel cell performance degradation and failure (Figure 1).
This study intends to use the combination of experimental research, numerical calculation and theoretical analysis. The formation of CO2 is quantified to characterize carbon corrosion rate. The kinetics of carbon corrosion is slow in normal operation. Therefore, the accelerated stress test conditions used in this work were adopted from Ref. [4]. The cell voltage was cycled from a lower potential of 0.6 V for 30 s, to an upper potential of 1.4 V for 60 s, to simulate the high potential during startup-shutdown conditions.
The crack propagation before and after degradation are observed and measured using an optical microscope. The existence and growth of cracks aggravate the carbon corrosion [5], destroy the continuity of catalyst layer, or cause local water flooding [6], which increase the mass transfer resistance and results in a significant performance degradation.
A multiple physical model is set up, that couples carbon corrosion, mechanical properties change and crack growth during the startup-shutdown cycling. The carbon corrosion model and CL agglomerate model are combined to predict performance of CL during startup-shutdown cycles. In addition, the model of stress corrosion crack is established to simulate the crack growth with the carbon corrosion and mechanical properties change. A parametric study was presented to analyze the effect of operation condition (e.g., relative humidity, pressure, maximum and minimum voltage) and structural parameters (e.g., carbon loading, porosity, and ionomer fraction) on the performance degradation and crack growth at various numbers of cycles.
With the wide application of fuel cell, the degradation of catalyst performance is inevitable. This study can fill the gap in the mechanism of crack growth caused by carbon corrosion, as well as provide critical guidance for PEMFC lifetime prediction.

Figure 1
Molecular-Level Engineering of Protected Li Metal Anodes for High Performance Next-Generation Batteries
Authors: Adair Keegan , Zhao Yang , Sun Qian , Li Ruying , Sun Xueliang 
Published: February 2020

Li metal is a promising anode material for next-generation Li-metal battery systems due to its ultra high theoretical capacity (3860 mAh g-1) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, the instability of Li metal towards liquids electrolytes, unstable solid electrolyte interphase (SEI) formation, and dendritic lithium have caused significant safety concerns that have inhibited its commercialization [1]. It is believed that artificial SEI layers formed through various techniques can stabilize the Li metal interface and enable stable electrochemical cycling with higher Coulombic efficiency. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are nanoscale coating techniques that are capable of controlling the interfacial chemistry down to the atomic level [2]. Herein, we demonstrate the effectiveness of these techniques in enabling high performance Li metal anodes for next-generation battery systems. Various polymeric protective coatings are synthesized on Li metal by MLD to enable prolonged lifetime and cycling stability. Metalcones including Alucone and Zircone are explored and shown to greatly enhance the performance of Li-S and Li-O2 systems [3]. Moreover, the ability to fine tune the composition of artificial SEI layers is exemplified by combining ALD/MLD techniques to form hybrid organic/inorganic protection layers to further improve the stability of the Li metal anode. The performance of the protected Li metal anodes are optimized in various electrolyte systems to achieve long life times at relatively high current densities in symmetrical cells and full cells. Furthermore, a better understanding of the role of these organic/inorganic polymeric films are gained through advanced ex-situ and in-situ characterization techniques, providing insight into the mechanism of improved performance. These works display the advantages of ALD/MLD for precise interfacial engineering at the atomic/molecular level towards achieving high performance next-generation batteries.
[1] Cheng, X.B.; Zhang, R.; Zhao, C.Z.; Zhang Q. Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev.,
2017, 117(15), 10403-10473.
[2] Meng, X.; Yang, X.Q.; Sun, X. Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater., 2012, 24(27), 3589-3615.
[3] Zhao, Y.; Goncharova, L.V.; Sun, Q.; Li, X.; Lushington, A.; Wang, B.; Li, R.; Dai, F.; Cai, M.; Sun, X. Robust Metallic Lithium Anode Protection by the Molecular Layer Deposition Technique. Small Methods, 2018, 2(5), 1700417.