bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolutionary Development for Electrokinetic Dewatering of Phosphate Mine Tailings
Authors: Kong Rui , Orazem Mark E. , Huang Yuelong , Yu Dazhi , Lai Han , Moghaddam Saeed , Bloomquist David
Published: February 2020

The processing and storage of phosphatic clay suspensions (or mine tailings) which result as a waste product from phosphate mining industry represent an important economic and environmental problem. A very long time is required to allow gravity-driven settling of clay suspensions with an initial 2-3 wt% solids content, and decades may be required to reach 25-30 wt% solids content. The associated impoundments occupy over 100 square miles of land in Florida alone.

A combination of experimental and modeling approaches were used to explore the use of imposed electric fields to achieve electrokinetic separation. Batch experiments were used to guide the development of a constitutive relationship describing the changes in solids content with time (t) and applied electric field (E)1,2. A linear behavior between final solids content and Et was found in at short times, and the upper limit of separation was controlled by the value of electric field only.

Subsequently, a semi-continuous system was designed for continuous removal of supernatant water. This system allowed measurement of supernatant turbidity, pH, and changes in solids content as functions of applied electric field, flow rate, and settling time. Under pseudo-steady-state operation, low-turbidity water was separated from a clay solids suspension by a combination of electrokinetic dewatering and free settling.

A semi-continuous system, which introduced a rotating belt between electrodes to facilitate removing clay sludge, was designed and tested. The batch experiment set up was used to optimize fabric selection. This equipment was able to continuously producing thickened clay cake with a solids content of up to 33 wt%. Evaluation of parameters including electrode spacing, electric field, and residence time provided an understanding of the path for optimization. A similiar constitutive relationship as in batch experiment was also estanblished which correlates final solids content to electric field and residence time.

All the systems were also evaluated from an econonic perspective. The energy requirement of the semi-continuous operation that facilitated sludge removal had a lower energy requirement value at a given electric field as compared with the result from batch experiments and the previous semi-continuous operation. All systems followed the trend that high electric fields have a high energy requirement.

References

J.P. McKinney, M.E. Orazem, A constitutive relationship for electrokinetic dewatering of phosphatic clay slurries, Miner. Metall. Process. 28 (2011) 49.

J.P. McKinney, M.E. Orazem, Electrokinetic dewatering phosphatic clay settling areas: numerical simulation and economic assessment, Miner. Metall. Process. 28 (2011) 71.
Electropolishing of Kovar Alloy for Vacuum Applications
Authors: Dündar Yasemin , Karakaya Ishak , Demirci Gökhan , Erdogan Metehan , Aras Mustafa Serdal
Published: February 2020

Kovar (53% Fe – 29%Ni - 17% Co) is one of the most commonly used materials in high vacuum applications which quite often require electrical isolation(s). Kovar has thermal expansion coefficient close to that of alumina over the range from brazing to cryogenic temperatures. Therefore, joining problems due to difference in thermal expansion coefficients can be minimized when alumina and Kovar alloy are used together.

For the applications that require long vacuum life, Kovar parts should have smooth surfaces to minimize outgas from the surface due to inadequate cleaning. The surface modifications obtained by electropolishing, i.e., preferentially dissolving macroscopic and microscopic surface roughness without grain attack in the depressions, and surface metal oxide layer dissolution [1,2], are indispensable in high vacuum applications. Electropolishing has also long been proven to be a powerful tool for complex parts that are difficult to polish mechanically. Although it is widely used in the vacuum industry, there is very limited information about the Kovar electropolishing in the literature. There is no systematic study known by the authors that aims to reveal the optimum electropolishing conditions for the Kovar alloy.

A two-electrode linear sweep voltammetry was conducted in a solution of acetic acid, chromic acid and water mixture, where a copper plate was used as the counter and reference electrode. A plot of current density versus applied potential given in Figure 1 was obtained at 9°C. In the light of almost constant current density, namely limiting current plateau region observed in this plot, some experiments were conducted at 30 V for durations of 30, 60, 90 and 120 seconds. Rectangular Kovar samples of 15x15 mm dimensions having about 0.50 μmRa initial surface roughness were electropolished to final surface roughness of about 0.25 μmRa. The surface roughness profiles and their microstructures before and after electropolishing process (EP) are given in Figures 2 and 3, respectively.

Figure Captions:

Figure 1: Current density vs. potential graph in acetic acid, chromic acid and water mixture.

Figure 2: Surface profiles of samples, (a) before and (b) after EP. The horizontal and the vertical scales are embedded to left hand side.

Figure 3: Microstructures of samples, (a) before and (b) after EP.

References

[1] Sova, V. (1986). U. S. Patent No. 4,563,257.

[2] Popov, K. I., Djokic, S. S., & Grgur, B. N. (2002). Fundamental Aspects of Electrometallurgy. New York: Kulluwer Academic Publishers. pp.226-227.
Effect of Co3O4 and CeO2 Infiltration on the Activity of a LSM15/GDC10 Highly Porous Electrochemical Reactor
Authors: Ippolito Davide , Hansen Kent Kammer
Published: February 2020

The reduction of air pollution has become an international concern over the last ten years because of increases in emissions from mobile and stationary sources. Among these sources, volatile organic compounds (VOC) represent a serious environmental problem, together with NOx, SOx and particulate matter, which lead to the formation of ozone in urban and regional areas [1]. The electrocatalytic activity of a porous electrochemical reactor, made of La0.85Sr0.15MnO3±δ (LSM) as electrode and Ce0.9Gd0.1O1.95 (GDC) as electrolyte, was studied for the electrochemical oxidation of propene (C3H6), a major VOC component of Diesel engine exhausts, over a wide range of temperatures. The entire reactor was thought as a highly porous catalytic filter for a possible application in a Diesel exhausts purification system.

The porous reactor was used as a backbone for the infiltration of Co3O4 and Co3O4/CeO2. The effect of the infiltration on the electrochemical properties and catalytic activity of the reactor was investigated by electrochemical impedance spectroscopy (EIS) and gas analysis.

Figure 1 shows the SEM cross-section micrograph of the electrochemical reactor made of 11 alternating layers of electrode (LSM) and electrolyte (GDC).

Figure 2 shows the Nyquist plot of the impedance spectra of Co3O4 infiltrated backbone recorded at OCP with 10% O2 and 10% O2 + 1000 ppm C3H6, 2 L/h, 400 °C.

[1] R. Atkinson, Atmospheric Chemistry of VOCs and NOx, Atmos Environ. 34 (2000) 2063;
Experimental Investigation of Two-Phase Electrolysis and Multiphysics Modelling
Authors: Mandin Philippe , Derhoumi Zine , Roustan Hervé
Published: February 2020

During two-phase electrolysis processes, for example for hydrogen production, there are bubbles which are created at electrodes. This implies a great vertical motion source in the normal earth gravity field and then a quite important natural two-phase convection. All other fields are then affected. Heat, mass and electricity transfers are modified due to both bubbles screening (at surface and in volume) and to bubbles transport promotion.

Many numerical modeling for two-phase processes such as kerosene pulverization in engines or coal combustion sciences have shown the difficulties of these multi-physics processes. Both particles and reactor scales must be considered according with a strong coupling modeling. In these processes the particles injection is “in the flow”. In boiling or electrolysis processes, a new difficulty is added: particles birth or injection is strongly coupled to the local flow properties and leads to a complex boundary condition at surfaces. Electrical and electrochemical properties and processes are disturbed. This disturbance can lead to the modification of the local current density and to anode effects for example.

The both experimental and numerical investigation is here presented. Experiments are performed in laboratory and in zero gravity (CNES grant and parabolic flights opportunities).
Electrochemistry in Molten Oxides: From Electrolyte Design to Oxygen Evolution
Authors: Allanore Antoine
Published: February 2020

The future carbon-free electricity offers substantial promises for electrochemical engineering, in particular its application to materials processing. As a matter of fact, electricity and electrochemical phenomenon have already significantly contributed to modern metal extraction and manufacturing [1]. More developments are however needed to pursue such trends, in particular for the extraction of metals with limited environmental impact. In that respect, molten oxides electrolytes have a particular appeal identified more than a century ago [2], thanks to their remarkable chemical stability at a temperature range that allows the production of liquid metal. This presentation offers first to review the intrinsic performances of molten oxides as electrolytic medium, and their corresponding key physicochemical properties. In a second time, the most recent discoveries related to the oxygen evolution reaction in such electrolyte will be presented, in particular with respect to mass transfer limitations [3] and anode materials design [4].

[1] A. Allanore, Journal of Metals - JOM, vol. 65, issue 2, 131, (2013)

[2] R. H. Aiken, Process of making iron from the ore. US patent 816, 142 (1906)

[3] A. Allanore, Electrochimica Acta, 110, 587-592, (2013)

[4] A. Allanore, L. Yin and D.R. Sadoway, Nature, 497 (7449), 353–356, (2013)
Enhanced Catalytic Activity of Platinum Nanowires on Carbon for the Oxygen Reduction Reaction
Authors: Wainright Robert John , Umasankar Yogeswaran , Ramasamy Ramaraja P
Published: February 2020

Oxygen reduction is one of the most widely studied reactions for electro-catalysis. There has been a lot of work on the development of novel catalyst materials and structures to replace or complement platinum nanoparticles for oxygen reduction electro-catalysis. Modification of catalyst structure, in both shape and size, on the nanometer scale, could be used to minimize both platinum mass and improve platinum utilization. There has been evidence in the literature suggesting that unsupported nanowires1,2, as well as those supported by carbon2,3,4, exhibit higher electrocatalytic activity than nanoparticles of platinum on carbon spheres. Platinum nanowires are unique in the respect that they combine the properties of both bulk and nanostructured platinum. In this work, we synthesized platinum nanowires on carbon black (PtNWs/C) using a procedure adapted and modified from the reported literature5. The synthesized PtNWs/C, as shown in Figure 1, were used to prepare catalyst ink with the addition of 25% Nafion. Rotating disc electrode studies were performed to investigate the electrocatalytic activity of the PtNWs/C for the oxygen reduction reaction. The PtNWs/C showed higher onset potential, smaller Tafel slope, and enhanced electro-kinetic activity compared to the commercially available 20% Pt-C (XC-72) catalyst.Fig. 1: TEM image of platinum nanowires (~4 nm diameter and 50 nm length) on carbon black synthesized by a modified formic acid method.
Distributed PEFC Performance during Cationic Contamination
Authors: Uddin Md. Aman , Wang Xiaofeng , Ozdemir M. Ozan , Qi Jing , Bonville Leonard J. , Pasaogullari Ugur , Molter Trent
Published: February 2020

In our previous studies (1-3), severe performance degradation of PEFCs was observed due to cationic impurities. In this study, we investigate how cations affect the spatial performance distribution in a PEFC using a segmented cell.

The segmented cell hardware consists of an aluminum anode flow field, a segmented aluminum cathode flow field, two aluminum end plates and one cupper current collector. All the aluminum parts were gold plated. Cathode flow field was divided into eight segments. Eight pieces of equal size aluminum current collectors were placed inside a PTFE block and straight flow channels were machined through both the PTFE and the aluminum segments (Figure 1). Total active area of the cell was 5 cm2. 2.85 mM CaSO4solution was introduced in the air stream through a nebulizer (1-3) at a rate of 110 uL/min, corresponding to 21.2 ppm based on dry air flow rate.

Figure 2 shows the voltage and current density distribution profile in each segment. The cell was operated at a constant total current of 1 A. During the baseline test of 24 hours, pure air was injected through cathode. The current in each segment remained constant through this period. Following the baseline test, the contaminant was injected in the air stream. The segments closest to the gas inlet were first affected by the contaminant. The current density in the segments closest to the gas inlet decreased while the segments closest to the outlet increased. Since it was a constant current test, when the current in the segments closest to the gas inlet decrease, other segments picked up that current to maintain total current constant.

During the baseline test, voltage remained constant in all segments. After contaminant injection, the cell voltage started to decrease and after 50 hours, voltages in each segments fluctuated. The voltage fluctuation was found to be mainly due to mass transport loss. The contaminant solution evaporated and deposited on the flow field and the GDL surface (Figure 3), and entered into the GDL which caused the mass transport losses. Moreover, the aluminum flow fields corroded and corrosion byproducts also deposited on the flow field and GDL surface. Throughout the test, there was no significant variation in voltage between segments.

Acknowledgements

The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

References

1. X. Wang, J. Qi, M. O. Ozdemir, M. A. Uddin, L. Bonville, U. Pasaogullari, T. Molter, ECS Trans., 58 (1) 529-536 (2013)

2. J. Qi, X. Wang, M. O. Ozdemir, M. A. Uddin, L. Bonville, U. Pasaogullari, T. Molter, ECS Trans., 58 (1) 537-542 (2013).

3. M. A. Uddin, X. Wang, J. Qi, M. O. Ozdemir, L. Bonville, U. Pasaogullari, T. Molter, ECS Trans., 58 (1) 543-553 (2013).
Impact of MPL Thickness on Water Management of PEMFC By Synchrotron X-ray Radiography
Authors: Lee Jongmin , Yip Ronnie , Antonacci Patrick , Ge Nan , Kotaka Toshikazu , Tabuchi Yuichiro , Bazylak Aimy
Published: February 2020

The polymer electrolyte membrane fuel cell (PEMFC) is an efficient and clean energy conversion device. The performance of PEMFCs at high power operation is governed by product water management. The gas diffusion layer (GDL), a porous carbon fiber sheet, is sandwiched between a catalyst layer and a flow field, providing diffusive pathways for reactant gases and product water. A transient microporous layer (MPL) characterized by sub-micron size pores and hydrophobic contents applied on the GDL or catalyst layer is known to extend limiting current density. Past research [1] has shown that there exists an optimal thickness of MPL. However, the effect of varying MPL thickness has not been studied by visual inspection.

Our research group has successfully investigated liquid water dynamic and distribution in an operating PEMFC using synchrotron radiography [2-3]. For this study, a miniature fuel cell with an active area of 0.48cm2and 0.2mm channel and rib width was designed for improved image quality. MPLs of varying thickness (no MPL, 50μm, 100μm, and 150μm) were coated on TGP-H-60 (Toray Industries Inc.). Each fuel cell was operated according to a pre-determined testing scheme on a Scribner 850e fuel cell testing station (Scribner Inc.). Visualizations were performed at the Biomedical Imaging and Therapy Bending Magnet (05B1-1) beamline at Canadian Light Source Inc. (Saskatoon, Canada). Spatial and temporal resolutions were approximately 10μm and 0.3fps, respectively. Image processing was carried out according to the Beer-Lambert law. The processed image provides information on liquid water profile across components of the fuel cell (Figures 1 and 2). For each types of GDL, liquid water content at the interfaces and within microstructures will be analyzed to isolate effect of MPL thickness on water distribution and performance of the fuel cell.

References:

1. Jin Hyun Nam, Kyi-Jin Lee, Gi-Suk Hwang, Charn-Jung Kim, Massoud Kaviany, Int. J. Heat and Mass Transfer, 52, 2779-2791 (2009).

2. J. Lee, J. Hinebaugh, A. Bazylak, J. Power Source, 227, 123-130 (2013)

3. J. Hinebaugh, J. Lee, A. Bazylak, J. Electrochem. Society, 159 (12) F826-F830 (2012)
Electrodeposition of Cadmium Selenide/Poly-o-Anisidine Composite
Authors: Maranowski Bartosz , Czerwieniec Bartosz , Strawski Marcin , Szklarczyk Marek
Published: February 2020

Cadmium selenide is under interest due to its optical properties: direct bandgap of the width 1.7 eV and higher abrosption coefficient comparatively to indirect semicoductors. These properties make CdSe a promising candidate for wide range of applications: fotovoltaics, hydrogen photogeneration, and electronics. Photocorrosion is the major problem in the application of CdSe in photogalvanic cells as a photoelectrode. To prevent it, we have been electrosynthesized composite CdSe/poly o-anisidine (POMA).

CdSe/POMA composite was obtained via electrodepostion on HOPG surface. The electrodeposition potentials of CdSe and POMA differs, but it will be shown that there are conditions under which it is possible to deposit one compound over another without decomposition of first one especially CdSe which is easy to oxidize in relatively high anodic potentials where o-anisidine starts to polymerize. The deposits were prepared by a cyclic potentiodynamic technique. Cadmium selenide was deposited from a bath containing 5 mM Cd2+ and 1mM SeO2. POMA was deposited from 0.06 M o-anisidine solution.

The Raman and XPS spectroscopies were applied for the chemical composition of synthesized composite films determination. Photoactivity of the samples was monitored by cyclic voltammetry and potentiostatic techniques in 0.1M HClO4. The formation of composite greatly enhances time stability of the CdSe photoelectrode. Additionally, the formation of p/n junction between CdSe and POMA enhance photoresponse of the studied system. The width of band gap for each compound was determined by reflective UV-Vis spectroscopy and STS techniques. Atomic Force Microscopy was used to show morphology of each sample and to determine thickness of each deposited layer by nanoscrathing technique.
Electric Potential Distribution at Interfaces in PEFC by First Principle Simulation
Authors: Zhou Juanjuan , Zhou Xiangyang , Liu Hongtan
Published: February 2020

The electrochemical potential dictates the charge transfer across the interfaces in electrochemical systems including PEFCs. In the present work we use ab initio molecular dynamics (AIMD) methods to evaluate the electric potential distribution across the interfaces and the so called electrochemical potential. In addition, we try to correlate the evolution of the potential distribution with the charge transfer at the interfaces. Four types of interfaces are considered: 1) 2 M H2SO4/Pt, 2) 2M H2SO4+O2/Pt, 3) 2M H2SO4+H2/Pt, and 4) Nafion cluster/Pt. Fig. 1 illustrates the first layer of 2M H2SO4 on top of Pt crystal. No bond formation and breaking was observed in a run of 400 steps. However in the cases for 2M H2SO4+O2/Pt and H2SO4+H2/Pt and, it is observed that either oxygen desorbs from Pt and enters electrolyte in the form of water (Fig. 2) or hydrogen desorbs from Pt and enters electrolyte in the form of proton (Fig. 3). In the case of Nafion on Pt (Fig. 4) no bond formation/breaking between electrolyte species and Pt is observed. Accordingly, as shown in Fig. 5, the variation ranges for the H2SO4+O2/Pt and H2SO4+H2/Pt interfaces are 10 times greater than that for the H2SO4/Pt interface. The variation ranges for the H2SO4+O2/Pt and H2SO4+H2/Pt interfaces are approximately 0.8 e. As shown in Figs. 6, 7, and 8, the interface potential difference for H2SO4+O2/Pt and H2SO4+H2/Pt interfaces is much greater than that of the H2SO4/Pt interface. The first Pt layer locates in high electric field (107 V m-1) zone for the H2SO4+O2/Pt and H2SO4+H2/Pt interfaces while at the first layer Pt for the H2SO4/Pt interface the electric field is close to zero. These findings are believed to be closely related to the slow electron exchange rate rate for the 2 M H2SO4/Pt case and fast electron exchange rate rates for 2M H2SO4+O2/Pt and 2M H2SO4+H2/Pt cases.
ORR on the Different Surfaces with Different Adsorbents: First Principles Molecular Dynamics Simulations
Authors: Ikeshoji Tamio , Otani Minoru , Qian Yumin
Published: February 2020

Oxygen Reduction Reaction (ORR) is the hard task in the fuel cell operations and has been studied extensively not only from practical point of view but also from fundamental one. Although various calculations by both MO and DFT calculations were reported, many of them are under the static conditions (i.e. at 0 K) or they are on simple surfaces. We are currently working for it with more realistic models at a certain temperature under the electric bias. First Principles Molecular Dynamics (FPMD) combined with Effective Screening Medium (ESM) [1,2] to apply the potential on the electrode in the similar manner as the real double layer region. We first used it for the simple electrode reaction of the first step of the hydrogen evolution reaction (Volmer reaction) on Pt(111) [3] and then we are extending it to ORR [4,5,6] on various surfaces with various adsorbents.

Electronic structure calculations in the FPMD are based on DFT with ultrasoft-pseudopotentials and PBE functional for the exchange correlation. Program code "STATE" is used. MD is performed at constant temperature 353 K by a velocity scaling thermostat. Electrode potential is controlled by the charges added by the ESM method shown in the figure.

The last step of ORR (=the first step of oxygen evolution) is

H3O+ + OH(ad) + e– --> 2 H2O

The reversibility of this reaction was confirmed on Pt(111) surface with surface charge density σ = 7 µC/cm2(corresponding to ca. 0.6–0.7 V vs. SHE) [4,5] with a pre-adsorbed OH. With higher or lower σ, reaction was remained in only one side. If we introduce a defect (a pit) on the surface, the reaction did not take place [6].

In order to see an effect of the different surface, we simulated a full ORR from O2adsorption to H2O formation on (111), (110) and (100) surfaces. The main reaction scheme observed in the several time simulations for each surface is (dissociation scheme):

O2 --> 2O(ad)

O(ad) + H3O+ + e– --> OH(ad) + H2O

H3O+ + OH(ad) + e– --> 2 H2O

In some cases, following H2O2 formation takes place as an intermediate species (association scheme).

2O(ad) + e– + H3O+ --> H2O2

We are also testing another kind of coadsorption species as a reaction promoter.

In summary, we could confirm that water liquid layer (not only single or bilayer) on the Pt surface plays an important role to proceed to a complete ORR.

[1] M. Otani and O. Sugino, Phys. Rev. B 73, 115407 (2006). [2] O. Sugino, I. Hamada, M. Otani, Y. Morikawa, T. Ikeshoji Y. Okamoto, Surf. Sci., 601 (2007) 5237. [3] M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, T. Ikeshoji, J. Phys. Soc. Jpn.. 77 (2008) 024802, Phys. Chem. Chem. Phys., 10 (2008) 3609. [4] T. Ikeshoji, M. Otani, I. Hamada and Y. Okamoto, Phys. Chem. Chem. Phys., 13 (2011) 20223. [5] T. Ikeshoji, M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, Y. Qian, and I. Yagi, AIP Advances, 2, 032182 (2012). [6] Y. Qian, I. Hamada, M. Otani, and T. Ikeshoji, Catal. Today, 202, 163-167 (2013).
Dopant Based Stabilization of LiCoO2: Insight from First-Principles Calculations
Authors: Santana Juan A. , Kim Jeongnim , Kent Paul R. , Fernando Reboredo A.
Published: February 2020

LiCoO2 is widely used as cathode material for Li-ion batteries (1). However, the usable specific capacity of LiCoO2 is limited to approximately half of its theoretical capacity. This limitation comes from the mechanical failure of the cathode when more than 50% of Li is deintercalated. The stability of LiCoO2 and its electrochemical performance can be improved by coating its surface with inner metal oxides (2). Such approach has been used for different cathode materials, but the origin of the stabilization effect is poorly understood. The enhanced stability of the cathodes has been rationalized invoking many effects, e.g., i) the inner metal oxides act as a physical barrier to prevent cathode-electrolyte reactions (3), and ii) the layered structure of the cathode material is stabilized by the migration of metal ions from the coating oxides (1). To have a better understanding of the stabilization mechanism, we have performed Density Functional Theory calculations of LiCoO2doped with inner metal ions (Figure 1). Such calculations allow us to study how the migration of metal ions from the coating oxides modify the structure of the cathode materials.

Acknowledgments.Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

Reference:

1. H. Li, Z. Wang, L. Chen, and X. Huang, Adv. Mater., 21, 4593–4607 (2009).

2. Z. Chen, Y. Qin, K. Amine, and Y.-K. Sun, J. Mater. Chem., 20, 7606–7612 (2010).

3. J.-S. Kim et al., J. Electrochem. Soc., 151, A1755–A1761 (2004).

Figure 1. Schematic of some possible sites for metal dopants in LiCoO2: the left and central panels show the dopant on Li and Co sites, respectively, and the right panel shows substitution on both Li and Co sites.
Modeling of Solid Oxide Fuel Cells with Linear and Nonlinear Functionally Graded Electrodes
Authors: Liu Lin
Published: February 2020

Solid Oxide Fuel Cells (SOFCs) have demonstrated high efficiency in full scale trials and are a possible partial solution to maximizing dwindling fossil fuel resources. Functionally graded electrodes have previously been investigated to improve SOFCs performance with optimized microstructure. However, little investigative focus has been put on optimal power output for given electrode microstructures. In this work, a multiscale and multiphysics full cell electrode polarization model of SOFCs has been expanded and developed to incorporate both electrodes microstructure. The macromodel describes the overall cell behavior through activation, Ohmic, and concentration losses based on chemical and concentration potentials. The micromodel outputs effective resistivity of the porous electrode based on microstructural parameters such as pore diameter, particle size, and reaction area. The integration of macro- and micromodels is achieved by passing the micromodel parameters to the macromodel during the solution procedure. The cell-level SOFC model has been utilized to reveal the complex relationship between the transport phenomena, which includes the transports of electron, ion and gas molecules through the electrode and the electrochemical reaction at the triple phase boundaries. The work contributes to our understanding of the cell performance in relation to graded microstructures. The performance of functionally graded electrodes has been analyzed to understand the implications of varying the electrode microstructure. The design guidelines provides in the study can aid selection and development of fabrication process that can further improve SOFC performance.
Computational Thermodynamic Modeling of Mixed Polyanion Glasses for Lithium Ion Battery Cathode Materials
Authors: Shin Dongwon , Kercher Andrew Keith , Kiggans Jim , Dudney Nancy J
Published: February 2020

We have used computational thermodynamic approach to model Lithium-bearing mixed polyanion (LBMP) as an effort to predict electrochemical properties of glass cathode materials. Individual LBMP have been modeled within the framework of the compound energy formalism (CEF) as implemented in the CALPHAD (CALculation of PHAse Diagram) approach [1, 2].

To model the baseline material Li/FePO4 thermodynamic descriptions for the crystalline solid and liquid phases of constituent Fe2O3 and P2O5 have been taken from the Scientific Group Thermodata Europe (SGTE) Substance Database and used as reference states. Thermodynamic model parameters for FePO4 and Fe4(P2O7)3 have been self-consistently evaluated to reproduce Fe2O3-P2O5 pseudo-binary phase diagram reported in the literatures. Afterward thermodynamic model parameters for the FePO4-LiFePO4 pseudo-binary system has been evaluated to represent experimentally determined phase equilibrium data [3, 4]. The model successfully reproduces the miscibility gap at low temperatures by introducing positive interaction between FePO4 and LiFePO4.

FIG. 1. Calculated cell circuit voltage of Li
x
FePO4 of crystalline and glass phases. Different ratios between the liquid and solid phases of LiFePO4 and FePO4(L:S) have been used to model glass phase.

From the developed thermodynamic database the open circuit voltage (OCV) of crystalline and glass Li/FePO4 have been predicted by calculating chemical potential of Li (see FIG. 1). In order to model the Li
x
FePO4 glass phase, different ratios between the liquid and solid phases of LiFePO4 and FePO4(L:S) have been used and ideal mixing between two end-members have been assumed. The glassy form is more sloping, and has a significantly lower potential.

Thermodynamic modeling of Li-Fe2O3-V2O5 has been carried out to incorporate additional polyanion species in the model for the glass cathode materials. From the completed thermodynamic modeling of Li/FeVO4
which combined with the baseline system, the cell voltage of Li/Fe4(0.5P2O7×0.5V2O7)4 has been benchmarked against experimental measurements. The ratio between the solid and liquid thermodynamic descriptions to describe the electrochemical behavior of the LBMP glass materials has been established and will be used for other polyanion species to be added in the baseline system.

Acknowledgement

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy

References

[1] L. Kaufman, H. Bernstein, Computer Calculation of Phase Diagram, New York, Academic Press Inc., 1970.

[2] N. Saunders, A. P. Miodownik, CALPHAD (Calculation of Phase Diagrams): A Comprehensive Guide, Oxford, New York, Pergamon, 1998.

[3] J. L. Dodd, R. Yazami, B. Fultz, Electrochem. Solid State Lett., 9(3): A151-A5, 2006.

[4] C. Delacourt, P. Poizot, J. M. Tarascon, C. Masquelier, Nature Mater., 4(3): 254-60, 2005.
Isomerization of Oxygen-Containing Radical Cations
Authors: Akaba Ryoichi
Published: February 2020

Isomerization is an important reaction mode of organic transformations. Although extensive works have been carried out for isomerization reactions of carbocations and free radicals, few studies have been reported on isomerization reactions of radical cations. In the present work, we would like to report full computational studies of structures and reactivity of peroxy radical cations, which are formed by reactions of molecular oxygen with various aliphatic and aromatic alkenes, and the corresponding carbonyl oxide radical cations that may be formed by a hydrogen, a methyl, or a phenyl migration in the peroxy radical cations.
Synchotron Enabled Ex-Situ and in-Situ Mechanistic Interrogation of Energy Storage Systems
Authors: Takeuchi Esther S , Takeuchi Kenneth J , Marschilok Amy C
Published: February 2020

Introduction

Full understanding of the electrochemical processes taking place in batteries continues to be elusive due to the complex nature of the reactions associated with discharge and charge processes, and the difficulties of analytical interrogation of these reactions. Ex-situ measurements at various states of electrochemical reduction and oxidation can provide mechanistic insight. A direct approach to the interrogation of the reactions taking place inside batteries is to employ in-situ strategies. Unfortunately, in-situ measurements are often hindered by diminution of signal due to the housing of an electrochemical cell or by the need to create special housings that enable the measurement.

Results and Discussion

Strengths and limitations of diffraction and spectroscopy based approaches characterization of energy storage systems will be discussed, with an emphasis on the unique characterization opportunities provided by synchrotron radiation. X-ray absorption spectroscopy (XAS) is sensitive to local structure within a few coordination shells around the absorbing atom, and can therefore characterize local structure even if long-range order is absent.1,2 Energy dispersive x-ray diffraction (EDXRD) approaches allow in-situ measurement of an battery electrode in its native environment.3 Specifically, electrode interrogation as a function of depth by EDXRD will be presented, enabling identification of the chemical reaction front within the battery electrode.

References

1) Patridge, C. J.; Jaye, C.; Tesfaye, A. A.; Ravel, B.; Fischer, D. A.; Marschilok, A. C.; Zhang, P.; Takeuchi, K. J.; Takeuchi, E. S.; Banerjee, S. J. Phys. Chem. C, 2011
,
115
(29),14437–14447.

2) Menard, M. C.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S., Physical Chemistry Chemical Physics. 2013,
15,18539-18548.

3) Takeuchi, E. S.; Marschilok, A. C.; Takeuchi, K. J.; Ignatov, Alexander; Zhong, Zhong; Croft, Mark. Energy and Environmental Science. 2013,
6, 1465-1470.
Nanoimprinted Carbon Structures As High Performance Lithium Ion Battery Anodes
Authors: Wang Peiqi , Li Jiangyu
Published: February 2020

We demonstrated the synthesis of carbon thin film with ordered nanostructure via nanoimprint lithography starting from thermal plastic polymer polyvinylpyrrolidone (PVP). After the pattern is completely transferred onto PVP thin film during the nanoimprinting process, a three-step thermal treatment is performed to convert the polymer into patterned carbon thin film. Feature size of the pattern ranges between 250 nm up to 2 um with various shapes including 1D line, 2D hole and pillar. Characterized with Raman spectroscopy, the carbon thin film shows a high degree of disorder with a small in-plane graphitic crystallite size of about 1.346 nm calculated using the peak intensity of D band and G band of sp2carbon. Those patterned carbon thin film exhibits good electrical conductivity. When used as anode of lithium ion battery, it shows an enhanced cyclic performance compared to those unpatterned carbon thin films and also graphite. Further study with Electrochemical Strain Microscope (ESM) helps to understand the enhanced Li ion storage capacity locally on the nanoscale.

Figure 1. (A) Atomic force microscopy topography scan of imprinted carbon thin film, (B) cyclic charge/discharge performance of imprinted and unpatterned carbon.
Pre-Lithiated Si Micro Wire Array Anodes Vs. Binder Free S8 Cathodes for Next Generation High Energy Storage
Authors: Hagen Markus , González Enrique Quiroga , Dörfler Susanne , Schumm Benjamin , Tübke Jens , Althues Holger , Kaskel Stefan , Föll Helmut
Published: February 2020

Li-S is a popular chemistry to obtain possible future high energy cells. Nevertheless, the unstable ether based electrolyte and safety + reliability concerns due to the Li metal anode are still major hurdles that are difficult to overcome. By replacing the Li anode with Si at least some of these problems can be addressed at the cost of losing some potential energy density.

To compare the Li-S and the LixSiy-S system, optimized and pre-lithiated Si microwire anodes and binder free CNT-S cathodes were used. The capacity retention is greatly dependent on charging conditions and electrolyte additives and will be discussed next to possible degradation effects.

The works is part of the joint project AlkaSuSi – Alkalimetal, sulfur and silicon and was financed by German ministry BMBF.
Aqueous Li-Air Battery Cathode Using Carbon Nanotube Arrays
Authors: Li Yunfeng , Huang Zhongping , Huang Kan , Carnahan David , Xing Yangchuan
Published: February 2020

Li-air batteries (LABs) have attracted great interest due to their high theoretical energy density and several aqueous-organic hybrid electrolyte based Li-air battery (HyLAB) systems have been proposed.1-5The cathode structure for a LAB is critical to its performance, as oxygen from ambient air must be able to diffuse into the cathode. The cathode needs to be highly porous and reactive to achieve large oxygen flux and high power operation.

In this work, we demonstrated a cathode structure with sparsely populated, vertically aligned carbon nanotube arrays (CNTAs). The CNTAs are nitrogen doped with dislocated-graphene stacking grown directly on carbon fiber papers and investigated as hierarchical air cathodes. These metal-free CNTAs were obtained by plasma enhanced chemical vapor deposition (PECVD) on a backing carbon paper, without further electrode processing.

The sparse CNTAs not only provide effective pathways for reacting species, but also show significantly high catalytic activity, which is comparable to a 20% Pt/C electrocatalyst. The high activity of the CNTAs is attributed to the rich graphene edges exposed on the CNT surface and nitrogen doping. Hybrid Li-air batteries with such nanostructured cathode show a consistent discharging capacity of 710 mAh/g and a specific energy of 2057 Wh/kg at 0.5 mA/cm2 in alkaline catholytes. Stable charge-discharge cycling at 0.5 mA/cm2 showed an average potential difference of 1.35 V, indicative of relatively small overpotential and high round trip efficiency. Furthermore, the hybrid Li-air battery based on the hierarchical cathode can reach a power density over 100 W/m2.

References

1. J. Christensen, P. Albertus, R. S. Sanchez-Carrera, T. Lohmann, B. Kozinsky, R. Liedtke, J. Ahmed and A. Kojic, Journal of The Electrochemical Society, 159, R1 (2012).

2. P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature Materials, 11, 19 (2012).

3. L. Li, X. Zhao and A. Manthiram, Electrochemistry Communications, 14, 78 (2012).

4. Y. Li, K. Huang and Y. Xing, Electrochimica Acta, 81, 20 (2012).

5. K. Huang, Y. Li, and Y. Xing, Electrochimica Acta, 103, 44 (2013).
Nanocomposite Ionic Liquid Electrolytes for Li-Ion Batteries
Authors: Kalaga Kaushik , Gullapalli Hemtej , Arava Leela Mohana Reddy , Ajayan Pulickel M
Published: February 2020

Ion-conducting polymer based membranes have been widely studied for several low temperature energy and environmental applications. One major problem with such polymer based membranes is their thermal stability, limiting the operating temperature of the devices. Room Temperature Ionic Liquids (RTILs) constitute an interesting class of compounds that is being investigated for many applications due to their high thermal and electrochemical stability and negligible vapor pressure. These electrolytes can be customized and tailored to achieve desired properties. Due to their intrinsic viscosity, RTILs present intermediate values of ionic conductivity at room temperature and extreme conductivities at higher temperatures. However at high temperatures, RTILs lose mechanical stability due to decrease in viscosity and it becomes an impossible task of forming stable membrane structures. It is thus necessary to provide essential mechanical stability to the RTILs by the use of an ion-permeable separator with comparable thermal and electrochemical stability. Herein, we design and develop RTILs based high temperature stable ion-permeable membrane using boron nanoparticles. Boron nanoparticles serve as fillers to increase the diffusion of RTIL while still being electrically insulating and mechanically robust. The ionic conductivity of thus formed composites has been assessed at temperatures ranging from room temperature to 150°C using Electrochemical Impedance Spectroscopy. Scanning electron micrographs of the composite also show no visible morphological changes indicating high thermal and mechanical stability. Thus, these RTILs based nanocomposite membranes could be an ideal candidate for high temperature application where ionic conductivity is of primary concern.
Simple Solvent-Free Synthesis of Iron-Oxide/Graphene Nanocomposite As Anode Material in Li-Ion Secondary Batteries
Authors: Jang Byungchul , Park Seung-Keun , Piao Yuanzhe
Published: February 2020

Herein, we show a simple solvent-free synthesis of a nanostructured material, composed of uniform sized iron oxide nanoparticles and graphene, for high performance Li-ion secondary battery. The iron-oxide/graphene nanocomposite was directly obtained by heat treatment of a mixture of iron-oleate and graphene. The experimental results showed that uniform sized γ-Fe2O3 nanoparticles were homogeneously embedded in the graphene layers, and they acted as mutual spacers in the nanocomposite to prevent the restacking of the graphene layers and the nanoparticle’s aggregation. As anode material in Li-ion battery, the iron-oxide/graphene nanocomposite exhibits outstanding electrochemical performance due to the synergetic effects of the monodisperse iron oxide nanoparticles and well dispersed graphene. The synthetic procedure is easy to scale up and expected to be extended to prepare other hybrid nanocomposite materials.
Ge/C Composite Electrodeposits As an Anode Material for Lithium Ion Batteries
Authors: Kim Sang-Wan , Ngo Duc Tung , Park Chan-Jin
Published: February 2020

Recently, lithium ion batteries have received considerable attention due to the increased demand for energy storage medium in portable electronic devices. Graphite has been extensively used as a commercial anode material for Li-ion batteries due to its excellent cycling behavior during charge and discharge cycles. However, the theoretical specific capacity of graphite is limited to 339 mAh×g-1. Therefore, it is essential to develop new anode materials with larger capacity as well as good cyclability. In particular, Ge has been reported to a promising anode material due to its large theoretical capacity (1624 mAh×g-1).

However, pure Ge anode suffers from a poor cyclability due to severe mechanical cracking and pulverization caused by significant volume change during the lithiation/delithiation process. To overcome this problem, various attempts have been reported. In particular, electrodeposition is a versatile bottom-up processing method that can be used for the deposition of metals, polymers, and semiconductors in a wide range of microstructures and nanostructures. The method is inexpensive and relatively simple, and especially it can support a good interface strength and electronic conductivity between the coating metals and the substrate.

In this study, the Ge/C composite was prepared by an electrodeposition process on Cu foil in ethylene glycol containing GeCl4 and carbon black. The Ge/C electrode showed better cyclic performance and higher charge capacity than Ge electrode. The improved electrochemical performance of the Ge/C electrode is due to the carbon black. Ge/C is preferable to endure pulverization of active materials by accommodating severe volume expansion during charge-discharge cycling.

The initially deposited Ge grains are relatively uniform with an average size of 20-30 nm. On the other hand, Ge grains with C are regularly deposited, forming clusters. The specific capacities of Ge and Ge/C at 0.1C-rate were about 1100 and 950 mAh×g-1respectively at the first cycle. Furthermore, the Ge/C retains a charge capacity of 860 mAh×g-1 after 40th cycle. The results confirm the Ge/C is more suitable than Ge in the cyclic performance and reversible charge capacity.
Flexible, Large-Area Nanostructured Electrodes for High Performance Supercapacitor
Authors: Yu Zenan , Thomas Jayan
Published: February 2020

Fabrication of highly ordered nanostructures over a large and flexible substrate area has attracted considerable attentions in recent years due to its increasing applicability in potential markets such as energy storage devices, smart paper, displays, etc. Thermal nanoimprint lithography (T-NIL) has become a promising candidate for preparing nanoscale structures since it can print nanostructure in a very short time. However, only thermoplastic materials without a cross-linking reaction during heating process can be printed through T-NIL. Moreover, it is challenging to print a large nanostructured area using T-NIL since it requires a heating and cooling treatment each time a structure needs to be printed. Here, we present a facile method called spin-on nanoprinting (SNAP) to print large area well-ordered nanostructures. We have successfully printed a 1 cm × 1cm footprint with nanostructures within 3 minutes without using any expensive equipment. Moreover, a large nanostructured area can be easily printed by stitching one film next to another. In addition, it is possible to print these structures on a flexible substrate. We have successfully fabricated nanostructured electrode for supercapacitors using SNAP. Our nanostructured electrodes show remarkable charge/discharge ability, high power and energy densities, and good cycle stability. The simplicity of the nanoarchitectured electrodes and their phenomenal performances has shown promising features for future energy storage systems.
Indium Tin Oxide Photonic Crystal with Nanocones for Controllable Light Coupling in Solar Cells
Authors: Chen Biyan , Mathai Cherian J. , Mukherjee Somik , Basuray Sagnik , Gangopadhyay Shubhra
Published: February 2020

We present an indium tin oxide/polymethylsilsesquioxane (ITO/PMSSQ) photonic crystal with grating structure. This topography exhibits multiple coupling resonances in specific regions of the solar spectrum, which can be controlled by tuning the angle and polarization of incident light. The ITO/PMSSQ grating structures are prepared via simple soft lithography procedures using HD-DVDs as templates. The surface topology also includes geometrical singularities such as nanogaps and nanocones, which lead to further enhanced light trapping characteristics as demonstrated by theoretical and experimental results. Together, these singularity-embedded photonic crystal gratings result in extremely concentrated electromagnetic fields at the aforementioned singularities, which could be especially helpful in separating the tightly bonded excitons in organic solar cells and, hence, improve the efficiency significantly.
Surfactants Effects on Electrodeposited Black Chrome-Graphite Encapsulated FeCo Nanoparticles Composite Solar Selective Coatings
Authors: Seshadri Harinipriya , Usmani Belal
Published: February 2020

Abstract

Effects of surfactants such as cetyltrimethylammonium bromide (CTAB) on electrodeposited black chrome-graphite encapsulated FeCo nanoparticles (GE FeCo NPs) composite as solar selective coatings on Ni-coated copper (Cu) substrate were studied. Electrodeposition was done in the presence of different weight proportions of CTAB like 0.2, 0.6, 1, 1.4, and 2 in the electrolyte bath. The surface morphology and thermal analysis of the films were investigated by employing scanning electron microscopy (SEM) and simultaneous thermal analyser, respectively. The chemical compositions of prepared films were determined by energy dispersive system (EDS). The Tafel analysis and Cyclic Voltammetric studies of the coatings were carried out in 3.5% NaCl solution to understand its stability in saline environment. Thermal stability s of the composite coatings increased upto 750ºC in nitrogen atmosphere, after a small weight loss between 400ºC to 500ºC. Corrosion resistance of the composite coatings was also found to be improved in the presence of CTAB.