bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Li-Ion Battery Pack Thermal Managementon Performance and Life
Authors: Shaffer Christian E , Kalupson James F , Sinha Puneet K , Wang Chao-Yang
Published: February 2020

Lithium ion batteries have been widely adopted for hybridized vehicles such as the Chevy Volt and the Nissan Leaf. As the life of Li-ion batteries is strongly coupled to both the load profile and the thermal conditions, the ramifications of thermal management strategy of the battery pack life must be considered. This has been highlighted by several high profile events, for example surrounding reduced range and battery life in high temperature environments.

In this presentation, using commercial AutoLion™ software, we investigate the effects of various thermal management strategies and drive cycles on the life of automotive Li-ion battery packs. Figures 1 and 2 give two examples of capacity and power fade of a 16kWh PHEV battery pack undergoing a standard drive cycle in two different environments: Phoenix, AZ and Portland, ME. Using illustrative examples, we demonstrate how small changes in thermal management can lead to a significant change in the end-of-life performance of Li-ion battery packs.

Acknowledgements

Partial support of this work by the Korean Agency of Defense Development (ADD) is greatly acknowledged.

References

1. T.M. Bandhauer, J Electrochem Soc, 158, R1 (2011).

2. C. Y. Wang and V. Srinivasan, J Power Sources, 110, 364 (2002).

3. V. Srinivasan and C. Y. Wang, J Electrochem Soc, 150, A98 (2003).

4. J.Kalupson, G. Luo, and C.E. Shaffer, “AutoLion™: A Thermally Coupled Simulation Tool for Automotive Li-ion Batteries,” SAE Technical Paper 2013-01-1522, 2013, doi: 10.4271/2013-01-1522. SAE International World Congress and Exhibition, April 16, 2013, Detroit, MI
Cell- and Pack-Level Simulation of Large-Format Li-Ion Battery Safety Events
Authors: Kalupson James F , Wang Qing , Zhao Wei , Sinha Puneet K , Shaffer Christian E , Wang Chao-Yang
Published: February 2020

Owing to their unsurpassed energy density, lithium ion batteries have been adopted for hybridized vehicles, such as the Chevy Volt and the Nissan Leaf, in the aerospace industry, and in stationary energy storage applications. However, as highlighted by several recent high profile safety events, significant challenges remain for the widespread adoption of Li-ion technology in automotive and aerospace applications. These documented safety incidents have been driven by both cell-level and pack level events, and as such, accurate simulation of safety events on both the cell and pack level is needed for fundamental understanding of the underlying physics and safety-conscious design. [1,2,3,4].

In this work, using commercially available AutoLion™ software, we demonstrate cell- and pack-level electrochemical/thermal coupled simulation of various types of safety events, including nail penetration, external short, and internal short. Figures 1 and 2 highlight two types of such safety simulations performed. Figure 1 gives the peak temperature of all four cells in a four-cell pack nail penetration; this simulation highlighting the hotter temperature of the interior cells during multi-cell short. Figure 2 illustrates the voltage and current response of an externally-shorted 25Ah L-ion ion cell. In our presentation, we elucidate on the physics of these shorts on both the cell- and pack-level, and demonstrate how simulation can be used to screen various cell and pack designs for safe implementation of safe Li-ion battery technologies.

Acknowledgements

Partial support of this work by DOE CAEBAT2 program is greatly acknowledged.

References

1. T.M. Bandhauer, J Electrochem Soc, 158, R1 (2011).

2. C. Y. Wang and V. Srinivasan, J Power Sources, 110, 364 (2002).

3. V. Srinivasan and C. Y. Wang, J Electrochem Soc, 150, A98 (2003).

4. J.Kalupson, G. Luo, and C.E. Shaffer, “AutoLion™: A Thermally Coupled Simulation Tool for Automotive Li-ion Batteries,” SAE Technical Paper 2013-01-1522, 2013, doi: 10.4271/2013-01-1522. SAE International World Congress and Exhibition, April 16, 2013, Detroit, MI
Silicon Nanowires Coated with C60 Layer As Anode Materials for Lithium-Ion Secondary Batteries
Authors: Arie Arenst Andreas
Published: February 2020

Silicon nanowires (Si NWs) with C60 coating layer as anode materials for lithium-ion batteries have been successfully synthesized by plasma enhanced chemical vapor deposition and plasma assisted thermal evaporation methods. The morphology, structure and electrochemical performance of C60 coated Si NWs are investigated in further. The results showed that the C60 coated Si NWs electrodes show an initial coulombic efficiency of 77% when cycling between 0 and 1.5 V (versus Li/Li+) at a current density of 100 μAcm-2 . The C60 coated Si NWs electrodes perform a capacity as high as 3377 mAhg−1 at the first cycle. Furthermore, they also demonstrate a good capacity retention compared with the un-coated ones due to the small interfacial resistance at the electrode/electrolyte interface.
Understanding Solution Chemistry and Electrochemistry of Mg-Electrolytes for Rechargeable Mg Batteries
Authors: Liu Tianbiao , Li Guosheng , Shao Yuyan , Cheng Yingwen , Liu Jun
Published: February 2020

Mg batteries with the inherent merits of Mg anode have attracted increasing attention as a promising high energy density battery technology. However, the lack of high performance Mg2+ electrolyte has been a primary technic hurdle to the development of practical Mg2+ batteries.1,2 The current popular methods in preparing Mg2+ electrolytes involve the use of nucleophilic Mg2+ sources, Grignard reagents or analogues (RMgCl, R= alkyl, aryl and amido etc.) and dialkyl (diaryl) magnesium (MgR2). But handling these reactive Mg2+ chemicals is not synthetically feasible, and their presence essentially limits oxidation stability and compatibility of the resulting electrolytes with electrophiles (such as high capacity sulfur cathode). Recently we reported a very simple approach to produce high performance Mg2+ conductive electrolytes, termed as “mono-Cl abstraction”, employing cheap and non-nucleophilic MgCl2 as the Mg2+ source and various Al Lewis acids (AlCl3, AlEtCl2 and AlPh3).3 In this presentation, we will discuss solution chemistry of the “mono-Cl abstraction” approach, which is fundamentally distinct from the reported methods using nucleophilic Mg2+ sources. For example, “mono-Cl abstraction” only involves a single Cl- transmetalation between MgCl2 and Lewis acid but both Cl- and R- transmetalation reactions take place between RMgCl and Lewis acid (see Scheme 1). In addition, electrochemistry of the MgCl2/Al Lewis acid electrolytes will be interpreted based on experimental data and compared to electrolytes reported by others. In meeting with desired electrolytes properties for practical rechargeable Mg-batteries, the presented discussions of electrolyte chemistry in together with new results from our group at PNNL are attempted to provide designing rationales for next generation of Mg2+electrolytes.

(1) Yoo, H. D.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach, D. Energy Environ. Sci.
2013, 6, 2265.

(2) Muldoon, J.; Bucur, C. B.; Oliver, A. G.; Sugimoto, T.; Matsui, M.; Kim, H. S.; Allred, G. D.; Zajicek, J.; Kotani, Y. Energy Environ. Sci.
2012, 5, 5941.

(3) Liu, T.; Li, G.; Shao, Y.; Liu, J. 224th ECS meeting, San Francisco (CA), October, 2013.

Acknowledgment

We thank Pacific Northwest National Laboratory for support of this research through the Lab Directed Research and Development Award. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
Solid State Flexible Supercapacitor Based on Electrospun Nanofibers of Tin Oxide
Authors: Kolathodi Muhamed Shareef , Natarajan T S
Published: February 2020

Here we report the synthesis of nanofibers of Tin oxide (SnO2) by electrospinning method and their application as working electrodes of flexible supercapacitors. The cost effective electrospinning technique is used for the fabrication of Tin oxide nanofibers. As-spun fibers can be collected as aligned and non- aligned fiber mesh based on the geometry of the collector electrode. X-ray Diffraction pattern (XRD), Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) techniques are used for the structural and morphological characterization of as-annealed tin oxide nanofibers. Solid electrolyte cum separator for flexible supercapacitor is prepared from polyvinyl alcohol and phosphoric acid by solution casting method. The electrochemical studies are carried out to measure the performance of the supercapacitors using cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS).
Identification of the Parameters in Equivalent Circuit Model of Lithium-Ion Battery
Authors: Chang Meng-Ting , Lin Yang-Shan , Chen Kuo-Ching
Published: February 2020

Nowadays, rechargeable lithium-ion batteries (LIB) have been commonly used in vehicles and mobile devices. A major environmental issue that concerns the use of lithium-ion battery is how to extend the life cycle of an aged or malfunctioned cell. One possible solution is to examine the response of the individual parts of an LIB and replace only those parts which fail to function well.

Electrochemical Impedance Spectroscopy (EIS) is one of the most popular and convenient methods for battery examination, since it provides us with the general information about cell resistance. A typical impedance spectrum of the lithium-ion cell is composed of two partially overlapped semicircles and a straight line at low frequency end. However, these two semicircles, represented by the two RC circuits which correspond to SEI film and the combined effect of diffusivity, charge transfer, and double layer, are difficult to discriminate.

This study adopted a simple EIS model of LIBs, whose equivalent circuit is shown in Fig. 1 [1]. In this case, each component delineates and models its corresponding physics. We swept the cell over the frequency range from 10 kHz to 0.01 Hz at various states of charge (SOCs). According to the previous works [2, 3] and our proposed fitting procedure, we could precisely fit the experimental spectra by the EIS model, as shown in Fig. 2. The determination of the nine parameters in this model enables us to further simulate the discharge curve, as shown in Fig. 3, which proves to be compatible with that obtained from the experiment [4].

To separate two partially overlapped semicircles, it is necessary to find a method to distinguish Rct
from Rsei
. The charge transfer resistance Rct
can be determined from the expression i

0=RT/nFRct
, where the exchange current density i0
is evaluated by the electrochemical model simulation, and R and T respectively denote the gas constant and the Kelvin temperature. As soon as Rct
is achieved, the curve fitting of the impedance spectrum helps us to obtain the other eight parameters. Further study will be conducted to find the relation between the nine parameters and SOC from the impedance spectrum. This relation is useful for electrochemical model simulation of lithium-ion batteries in the future.
State of Charge and Electrolyte Composition Effects on the Kinetics of Vanadium RFBs
Authors: Hollmann Emma , Aaron Douglas , Sun Che-Nan , Mench Matthew M. , Zawodzinski Thomas A.
Published: February 2020

The all vanadium redox flow battery (VRFB) shows significant potential for grid scale energy storage with load leveling capability.1VRFBs, especially in the low-current, higher-efficiency region of operation, are controlled by the kinetics of the redox reactions in each half-cell. We focus this effort on understanding the effects of state of charge and electrolyte composition on the kinetics of the battery.

The kinetic behavior of each electrode reaction was studied independently in-situ via the inclusion of a dynamic hydrogen electrode in an operating VRFB. The exchange current density was measured at states of charge ranging from 0% SoC to 100% SoC in a VRFB operating at 25°C with a pure sulfuric acid or a mixed sulfuric-hydrochloric acid electrolyte. The kinetics of the positive electrode reaction (Eq. 1) shows a stronger absolute response to state of charge than does the kinetics of the negative electrode reaction (Eq. 2), but the relative variability is actually similar. At each state of charge, the exchange current density of the positive couple was greater than that of the negative couple. When corrected for concentration effects, the exchange current density is remarkably constant as a function of state of charge.

The mixed acid composition has the advantages of significantly increased vanadium solubility and a wider range of battery operating temperatures.2 Preliminary results indicate enhanced exchange current densities for each electrode at 50% SoC as well. The kinetic response of the mixed acid system as a function of state of charge will be determined via in-situstudies using a DHE. Initial investigations of exchange current at higher states of charge for this system were complicated by the generation of chlorine gas during charging steps. Finally, a relatively wide range of operating temperature can be considered with the use of a mixed acid electrolyte. A comparison of the operational advantages of each electrolyte composition and how they impact VRFB kinetics will conclude this talk.

Acknowledgement: We gratefully thank Dr. Imre Gyuk and US DOE Office of Electricity for support of this work.

(1) Ponce de León, C.; Frías-Ferrer, A.; González-García, J.; Szánto, D. A.; Walsh, F. C. J. Power Sources
2006, 160, 716–732.

(2) Li, L.; Kim, S.; Wang, W.; Vijayakumar, M.; Nie, Z.; Chen, B.; Zhang, J.; Xia, G.; Hu, J.; Graff, G.; Liu, J.; Yang, Z. Adv. Energy Mater.
2011, 1, 394–400.
Resolving Anisotropic Interfacial Phenomena Using, In Situ, Grazing Transmission Ultra-Small Angle X-Ray Scattering Together with Electrochemical Impedance Spectroscopy
Authors: Hammons Joshua
Published: February 2020

Inherent to many electrochemical systems is phase formation at or near the electrode surface. Resolving these phases, in-situ, is challenging with the presence of the necessary electrolyte between the working and counter electrodes. The high X-ray flux available at the Advanced Photon Source (APS) allows these phases to be resolved, in-situ, using small angle X-ray scattering (SAXS) in a grazing transmission geometry shown below. Using this geometry, dimensions both parallel and perpendicular to the surface can be resolved, in-situ, concurrently with an electrochemical technique such as electrochemical impedance spectroscopy (EIS).

In this work we show how combined SAXS and EIS is used to resolve unique nanoparticle-solvent interactions that occur in a deep eutectic solvent. Using Ultra-small angle X-ray scattering (USAXS), together with EIS, we were able to resolve ~ 100 nm sized layers that reside above Pd and Ag nanoparticle ensembles on a glassy carbon surface. This study was also performed on the high-energy pinhole SAXS setup, where the distance between the opposing layers was also resolved. While USAXS/SAXS provides information about the size, shape and structure of these phases, the EIS provides their electrochemical response for a comprehensive understanding of interfacial chemistry. These results show how combined USAXS/SAXS and EIS can be used as complementary techniques to resolve otherwise elusive electroactive phases at the interface of electrochemical systems.

This technique is accessible through the general user program at the APS. Some general considerations of the experimental setup are presented, including: signal to noise, geometry and cell capabilities. An overview of beamline capabilities is also presented and consists of USAXS/pinSAXS, USAXS, wide angle X-ray scattering (WAXS), USAXS imaging and the high-energy pinhole SAXS setup. With these capabilities, the 15-ID-D beamline offers the potential for a wide variety of in-situ electrochemical experiments towards an understanding of elusive interfacial phenomena.
The Influence of Geometry on the Stability of Emergent Droplets
Authors: Herescu Alexandru
Published: February 2020

A study of the stability of microdroplets is undertaken numerically to asses the effect of geometry. A droplet emerges from a hole or a pore and it completely detaches when a certain volume of liquid is accumulated. Present study assesses this volume for a polygonal pore, and for a circular hole in a curved surface. Notable differences exist between the stability limits of aforementioned cases and the case of a planar circular hole having the same area.
Ab Initio-Based Multiscale Simulations of Conversion Reactions in Lithium-Ion Batteries
Authors: Franco Alejandro A. , Doublet Marie-Liesse , Nguyen Trong-Khoa , Chehab Jean-Paul , Mammeri Youcef
Published: February 2020

The development of theoretical methods to correlate the chemical and structural properties of electrode materials with their electrochemical behavior in energy storage devices is of crucial importance for consistent interpretation of experimental data and for their optimization toward end-user applications [1-3].

In this work a new multiscale model is presented allowing to describe solid phase formation and separation during discharge-charge in Lithium Ion Battery (LIB) cathodes using conversion materials such as CoO, CuO or CoP [4-5]. The adopted theoretical framework extends a previous approach extensively developed for the multiscale modeling of fuel cells [6-7]. The model is supported on a Cahn-Hilliard-based phase field approach parametrized with ab initio-extracted parameters such as the interphase (solid/solid, solid/liquid) energies and binary (solid/solid phase) diffusion coefficients [8-9]. The electrochemical conversion reaction MO + Li+ + e- ↔ Li2O + M° and associated Li+ and e- transports are locally resolved across the multiphase MO/Li2O/M° system. The integration of this multiscale phase field model into a cell level model accounting for electrolyte/active material interfaces (in house developed simulation package "MS LIBER-T" [10]) allows simultaneously simulating the microstructural evolution of the multiphase active particles (Figure) and the associated potential vs. capacity characteristics during the LIB discharge and charge. Simulation results provide good agreement with experimental findings, in particular for the evolution of the active particles during discharge from microstructured to nanostructured morphologies [4-5,11].

References

[1] A.A. Franco, RSC Advances, 3 (32) (2013) 130.

[2] A.A.Franco, Multiscale Modeling of Electrochemical Conversion and Storage in: The Encyclopedia of Applied Electrochemistry, R. Savinell, K. Ota and G. Kreysa Eds. (Springer) (2013).

[3] A.A. Franco, K.H. Xue, ECS J. Solid State Sc.
Tech., 2 (10) (2013) M3084.

[4] P. Poizot et al., Nature, 407 (2000) 496.

[5] J.M. Tarascon et al., Chem. Mater., 16(2004) 1056.

[6] R. Ferreira de Morais, D. Loffreda, P. Sautet, A. A. Franco, Electrochim. Acta, 56 (28) (2011) 10842.

[7] A. A. Franco, P. Schott, C. Jallut, B. Maschke, Fuel Cells, 7 (2007) 99

[8] A.-L. Dalverny, J.-S. Filhol, M.-L. Doublet, J. Mater. Chem., 21 (2011) 10134.

[9] R. Khatib, A.L. Dalverny, M. Saubanère, M. Gaberscek, M.L. Doublet, J. Phys. Chem. C, 117 (2013) 837.

[10] www.modeling-electrochemistry.com

[11] M. Ebner et al., Science
342 (2013) 716.

Figure. Example of conversion electrode microstructural evolution, during the LIB discharge, calculated by multiscale phase field simulations.
Surface Transport Mechanism and Bi-Pathway ORR Kinetics for Solid Oxide Fuel Cell Cathode
Authors: Zhang Hui , Gong Mingyang , Gerdes Kirk , Liu Xingbo
Published: February 2020

The oxygen reduction reaction (ORR) taking place at the cathode plays a very prominent role in the electrochemical performance and operating efficiency of SOFCs. In this study, the major drive in undertaking modeling simulation of ORR kinetics is to provide useful insight into a fundamental understanding of the detailed surface contribution and parallel ORR kinetics of LSM-type cathodes under different polarization conditions. A continuum method in dense electrode systems combined with a microscopic approach is used to establish the relationship among particle size, polarization properties, and ORR behavior of the SOFC cathode. Here, we employ dense electrodes with a face centered cubic lattice (fcc) structure owing to the complex morphology and structure of porous/composite electrodes. For using bigger particles (e.g.1.0μm), the active reaction zone is extended due to the distribution of absolutely higher concentration of oxygen vacancy. However, mass-transport limitation of adsorbates is responsible for smaller flux value of bulk oxygen vacancy, resulting in slower 2PB kinetics behavior. The results indicate that small fluctuations in the electrode particle size produce a measurable impact in electrode performance, which should be considered in operational performance models.
A Density-Functional Theory Study of the Water−Gas Shift Mechanism on Pt/Ceria(111)
Authors: Kinch Richard T
Published: February 2020

Density-functional theory has been used to model the interactions between ceria(111) and CO adsorbed on platinum in order to provide insights into the mechanism behind the water−gas shift reaction on this material. Morphological studies on ceria show the presence of various defect sites, both cerium and oxygen vacancies, which are believed to be the reason for the catalytic activity of the substrate. Of these defect sites, the reported calculations clearly show the preference for platinum to bind in cerium vacancies, as opposed to a defect-free surface or an oxygen deficiency site. Currently there are two main pathways proposed for this mechanism: a direct redox pathway and a formate-intermediate pathway. In both scenarios the initial step is the same: the oxygen storage capacity of ceria provides the oxygen necessary to oxidize CO into CO2; water then adsorbs and is dissociated in these oxygen vacancies helping reform the ceria surface. The key difference between the two mechanisms is either the desorption of CO2and the formation of H2 when a second water molecule adsorbs at a site where water had been previously dissociated (catalyzed by platinum), or the formation of a formate species from the interaction of the adsorbed CO2 with adjacent water molecules. Energy pathways are mapped for both processes, demonstrating the preference toward the initial direct redox pathway. However, the resulting formation of adsorbed hydroxide species in the oxygen vacancies adjacent to the platinum hinders this pathway. A bifunctional mechanism is then presented as a means to remove these species and thereby form formate. The activation of these adsorbed hydroxides is also studied.
A Combined First-Principles Molecular Dynamics/Density-Functional Theory Study of Ammonia Electrooxidation on Pt(1 0 0) Electrode
Authors: Skachkov Dmitry , Chitturi Venkateswara Rao , Ishikawa Yasuyuki
Published: February 2020

The electrocatalytic oxidation of ammonia on Pt(1 0 0) electrode was studied by first-principles direct molecular dynamics and density functional theory. The mechanism of ammonia electrooxidation on Pt(1 0 0) depends strongly on the surface potentials. The modeling study supports the mechanism posited by Oswin and Salomon for moderate potentials (≥ +0.5 V vs. RHE), and the Gerischer and Maurer's mechanism for lower potentials (< +0.5 V vs. RHE).

At moderate potentials (≥ +0.5 V vs. RHE), the electrooxidation consists of ammonia adsorbing to the surface, and subsequent oxidations of NH3(top), and the intermediates NH2(bridge) and NH(bridge), forming adsorbed bridging nitrogen. Subsequent steps are high submonolayer coverage of N(bridge), followed by spontaneous N(bridge) dimerization. On highly covered Pt(1 0 0) surface, the bridging nitrogen atoms spontaneously dimerize and desorb into solution. The rate-determining step at moderate potentials is NH2(bridge) oxidation. Dimerization of NH2(top)forming hydrazine would be a rare event.

At low potential region (< +0.5 V vs. RHE), oxidation of ammonia becomes a very sluggish process. Two competing pathways for the lower potentials are 1) NH2(top) dimerization forming hydrazine and subsequent oxidation to form molecular nitrogen, and 2) oxidation of NH2(bridge), forming bridging nitrogen N(bridge), followed by N(bridge) dimerization. The rate determing steps at the lower potentials are NH2(top) dimerization and NH2(bridge) oxidation.

Catalytic inactivity of Pt(1 1 1) and Pt(1 1 0) surfaces is attributed to poisoning of the surfaces by strongly adsorbed N(hollow). On both Pt(1 1 1) and Pt(1 1 0) surfaces, nitrogen atoms are strongly bound at hollow sites and dimerization of N(hollow) would not occur because of high activation barrier.

Acknowledgements

The authors gratefully acknowledge financial support from the National Science Foundation.
Electrochemical, Catalytic and O2-Permeation Studies of Iron-Doped Barium Zirconates for Membrane Reactor Applications
Authors: Zhang Haomiao , Suresh Aravind , Carter C. Barry , Wilhite Benjamin A
Published: February 2020

Recently, interest in solid-oxide electrolysis cells (SOECs) with platinum or nickel cermet electrodes capable of reducing combustion effluents to synthesis gas has driven the search for mixed ionic-electronic conductors with suitable catalytic activity for reduction of carbonaceous species. There remains a need for discovering chemically stable electrode materials combining electronic and oxygen-ionic conductivities with suitable catalytic activity for oxidation or reduction. Our research group has focused upon identifying ambivalent transition-metal dopants capable of imparting both electrochemical and catalytic properties to perovskite electrolyte materials. In this study, the authors present a combined electrochemical, catalytic and permeation investigation of iron-doped barium zirconium perovskite in the context of the electrochemical reduction of combustion gas (CO2, H2O) to synthesis gas (CO, H2).

Powders of BaZr0.90Fe0.10O3-δ (BZF10) were synthesized via solid-state reaction and characterized by synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS). The powders were pressed and sintered into 13mm dense button cells, and a porous Pt electrode and a dense Pt blocking electrode were attached to either face of the pellet. The resulting system was used to conduct electrical conductivity relaxation (ECR), electrochemical impedance spectroscopy (EIS), and reaction analysis over a wide range of dry O2, CO2, H2O, and humidified CO, H2 partial pressures at temperatures of 600 – 800oC. Analysis of equilibrium electrical conductivities (σ∞) vs. temperature and partial pressures provides critical insight into the underlying electrochemical mechanisms for surface reaction. Non-linear regression of conductivity vs. time data allows deduction of surface electrochemical reaction rates and solid-state diffusivities of charge carriers, and probing of surface oxygen-acceptor/donor kinetics. BZF10 was verified as an electrochemical stable, mixed ionic-electronic conducting ceramic suitable for SOEC application. The σ∞ vs. O2 partial pressure indicates a high oxygen-ion acceptor activity for Ba0.9Fe0.1ZrO3+δ. Equivalent experiments conducted over a range of CO2 partial pressures (pCO2) indicate a net decrease in σ∞ with respect to pCO2, coinciding with up to a 16% conversion of CO2 to CO and O2 at steady-state. Reduction of the Fe-doped perovskite suggests the formation of a CO3
-2 intermediate during the overall conversion of CO2 to O2 and probing of CO2 reduction activity indicates significant catalytic activity, which is attributed to the oxygen acceptor-donor activity of the Fe-doped perovskite. Experimental results indicate that the material behaves as a mixed oxygen ionic-electronic conductor, with significant catalytic activity for CO2 reduction.
(Invited) Impact of Surface Chemistry on the Electrochemical Performance of Perovskite Cathodes
Authors: Backhaus-Ricoult Monika , Work Kimberley , Adib Kaveh , Gregoratti Luca , Amati Matteo
Published: February 2020

Surface chemistry and reactivity of solid oxide fuel cell (SOFC) and electrolyzer (SOEC) electrodes play a key role for transport and exchange processes, such as the oxygen reduction reaction in SOFC cathodes, and drive electrochemical performance and durability. In order to identify drivers and problems, it is necessary to probe electron and ion transfer and transport processes at electrolyte/electrode interfaces and surfaces and build broad fundamental understanding. This knowledge can then be used to drive the innovation of novel, more powerful electrode materials and cell designs.

We used a combination of spatially resolved scanning photoelectron microscopy and electrochemical measurements to study in situ the surface chemistry of cathode perovskite catalysts and electrolyte in electrochemical model cells during high temperature operation. The electrodes were made of screen-printed (La1-xSrx)MeO3 with Mn, Fe, Co, Ni as transition metal Me and x = 0 – 0.4 and covered a wide range in ionic and electric conductivity from pure ion to mixed conduction. The electrolyte was a thin yttrium-stabilized zirconia sheet. We studied the surface chemistry of oxide catalyst and electrolyte at temperatures between 400 and 700°C, oxygen pressure (10-7bar – 1mbar) and also in humidity and/or hydrocarbon containing environment and demonstrated systematic changes in the perovskite surface termination with oxygen chemical potential. Oxidizing environment was found to promote transition metal termination and presence of various oxygen surface species, while reducing environment drove segregation of strontium to the surface and suppressed the level of surface oxygen.

We also showed that this simple segregation behavior was dramatically changed in presence of impurities. Silica segregated to the surface, forming a glassy, insulating surface layer that slowed down the oxygen incorporation reaction and produced a strong degradation of the cell performance. While the degradation of Ni/NiO electrodes could be reversed by an applied cell voltage, no such remedy was observed for perovskite electrodes.

In our in-situ set up, oxygen in- or excorporation could be driven by an applied electric field across the cell. Oxygen ion flux and electric field caused dynamic changes of catalyst and electrolyte surface chemistry, including redox reaction, changes in surface segregation and long range surface diffusion at the electrode surface. The electrochemical response of the model cells was interpreted in terms of reactions and reaction steps that matched the spectroscopic observations, thus constructing new understanding of the processes in operating electrodes.
Reactions and Transport Pathways in Syngas Fueled Ni/YSZ SOFC Anodes: Experiments and Modeling
Authors: Kromp Alexander , Geisler Helge , Weber André , Ivers-Tiffée Ellen
Published: February 2020

The fuel flexibility of solid oxide fuel cells (SOFC) is highly attractive for numerous technical applications that convert natural gas, kerosene or diesel reformate into electrical energy. For the operation with hydrocarbon fuels, there is a great deal of knowledge about the catalytic reforming chemistry in the SOFC anodes, whereas little is known about the solid/gas electrochemistry. This work reports a comprehensive understanding of the reaction mechanisms and transport pathways that determine the performance of syngas fueled Ni/YSZ anodes.

Based on our initial work, in which the individual loss mechanisms for syngas fueled Ni/YSZ anodes were identified via electrochemical impedance spectroscopy (EIS) [1], a schematic model of the reaction mechanisms and transport pathways is developed (Fig. 1). Since exclusively H2 is electrochemically oxidized at the triple-phase boundary, the CO within the fuel is subsequently oxidized via the water-gas shift reaction [1]. The resulting gas transport properties within the anode substrate feature two transport pathways (H2/H2O and CO/CO2), which are coupled by the water-gas shift reaction.

This schematic model is implemented in a transient finite element method (FEM) simulation [2]. The isothermal model represents the electrochemical fuel oxidation and the heterogeneous reforming chemistry on the catalytically active Ni-sites in terms of global kinetics. The multi component gas transport of the fuel gas species through the porous electrode structure is represented by the Maxwell-Stefan equation. Coherently calculating the complex species transport phenomena and the kinetics of the reforming chemistry, the model is capable to reproduce the multiple semicircles of the measured gas transport impedance. With the help of the FEM model, the characteristics of the measured impedance are explained in detail.

With the validation of the presented reaction diffusion network, an overall understanding of the loss mechanisms for syngas fueled Ni/YSZ anodes has been reported for the first time in literature [3]. With this knowledge, the impact of sulfur-poisoning on (i) the electrochemical fuel oxidation and on (ii) the heterogeneous reforming chemistry within syngas fueled Ni/YSZ anodes can be monitored separately [4].

References

[1] A. Kromp, A. Leonide, A. Weber, E. Ivers-Tiffée, J. Electrochem. Soc., 158 (8), B980-B986 (2011).

[2] A. Kromp, H. Geisler, A. Weber, E. Ivers-Tiffée, Electrochim. Acta 106, 418-424 (2013).

[3] A. Kromp, A. Weber, E. Ivers-Tiffée, ECS. Trans. 57 (1), 3063-3075 (2013).

[4] A. Kromp, S. Dierickx, A. Leonide, A. Weber, E. Ivers-Tiffée, J. Electrochem. Soc., 159 (5), B597-B601 (2012).
Investigation of Electrochemical Carbon Conversion in Hybrid Direct Carbon Fuel Cells
Authors: Lee Jong-Won , Lee Ji-Yong , Lee Seung-Bok , Lim Tak-Hyoung , Park Seok-Joo , Song Rak-Hyun
Published: February 2020

In recent years, direct carbon fuel cells (DCFCs) have received significant attention owing to an increasing need for efficient power generation from coals and other carbon-based solid fuels. In a DCFC with a solid oxide electrolyte (e.g., yttria-stabilized zirconia, YSZ), carbon conversion would take place over three-phase boundaries. There is, however, very little interaction between the solid carbon and the Ni-YSZ anode. A hybrid DCFC design combines the advantages of the solid oxide and molten carbonate fuel cell technologies, where the molten carbonate and solid oxide electrolytes are in direct physical contact. Oxide ions are transported through the solid oxide electrolyte toward the molten carbonate holding the dispersed carbon particles inside the anode compartment. Although promising performances of hybrid DCFCs have been reported in the literature, the mechanistic understanding of the carbon conversion is incomplete. In fact, the reactions at the anode are quite complex and involve multistep transfer of electrons in a sequence of elementary reactions. In this paper, we study the electrochemistry of carbon conversion in a hybrid DCFC using Ni-YSZ anodes with various porous structures. Ni-YSZ anodes are fabricated using PMMA spheres with different diameters as a pore-former to tailor their porous structures (pore volume, size, distribution, and surface area). The polarization behaviors of the DCFC are measured as a function of the porous structure. The results show that among the parameters studied, the surface area plays the most critical role in determining the anodic polarization. The electrochemical carbon conversion reaction is discussed in detail, on the basis of the experimental data obtained from mercury porosimetry, polarization and impedance measurements, and gas chromatography.
Catalytic Enhancement of Solid Carbon Oxidation in HDCFCs
Authors: Deleebeeck Lisa , Ippolito Davide , Hansen Kent Kammer
Published: February 2020

Hybrid direct carbon fuel cells (HDCFCs) consisting of a solid carbon (carbon black)-molten carbonate ((62-38 wt% Li-K)2CO3) mixtures in the anode chamber of an anode-supported solid oxide fuel cell (SOFC)-type full-cell (NiO-yttria-stablized zirconia (YSZ)|YSZ|lanthanum strontium manganite (LSM)-YSZ/LSM) are tested for their electrochemical performance between 700 and 800°C. Performance was investigated using electrochemical impedance spectroscopy (EIS) and current-potential-power density curves. EIS data is interpreted using a model circuit (R-RQ-RQ-RQ), and the dominant processes revealed by the impedance data as a function of temperature, anode and cathode atmospheres, and their flow rates are discussed. In the anode chamber, catalysts are mixed with the carbon-carbonate mixture. These catalysts include various manganese oxides (MnO2, Mn2O3, and Mn3O4, Fig. 1) and doped-ceria (CeO2, Ce1-xGdxO2, Ce1-xRExO2 (RE = Pr, Gd, Sm, etc.)), the effectiveness of these families of catalysts are discussed with respect to electrochemical, chemical and post-mortem analysis.

Fig. 1. Current-potential-power density curves acquired for a blank (SiC) and manganese oxide (MnO2, Mn2O3, Mn3O4) catalysts suspended in the carbon-carbonate mixture in the anode chamber of an HDCFC. 96-4 vol% N2-CO2 (anode), air (cathode), 755°C, 0-600 mA, 50 mA/step. Power density corrected to cathode geometric surface area.
Hydrogen Production Directly Using Petroleum Coke
Authors: Tao Greg Gege
Published: February 2020

Hydrogen is widely used by petroleum refineries in upgrading processes, necessary to facilitate the hydrotreating/catalytic hydrocracking of heavy hydrocarbon molecules, and the reduction of sulfur content. At an industrial scale, three major technologies are presently used to produce hydrogen, depending on the primary energy sources or available feedstock: coal gasification, natural gas steam reforming, and water electrolysis.

Petroleum coke (or petcoke), similar to coal, is a byproduct of refinery processes. The U.S. refineries produce more than 125,000 short tons petcoke per day (st/d), most of which is produced in Calfornia, Texas and Louisiana. With a low heating value (LHV) of 6.024 MMBtu/barrel (equivalent to 8.826 MWhr/st), petcoke produced in the U.S. potentially is worth 17,689 MW electricity assuming 40% efficiency. However, due to larger activation energies, higher sulfur content and less volatile materials than coal, petcoke is not a desirable feedstock for a conventional coal-burnt power plant and more than 62% of petcoke was exported annually.

Instead of purchasing hydrogen over the fence, a refinery potentially can build on-site hydrogen production infrastructure directly utilizing its available resource (petcoke). Materials & Systems Research Inc. currently is developing an advanced hydrogen production process built-upon the solid-oxide electrochemical technology with reduced energy consumption and low costs for CO2 separation & sequestration. In this talk, the hydrogen production process and the development of the electrochemical device will be discussed in detail. Proof-of-concept demonstration of hydrogen production at a 200W stack level will also be presented.
Transition Metal Nitride As Photocatalyst for Visible Light Driven Hydrogen Production
Authors: Chakrapani Vidhya
Published: February 2020

Photoelectrochemical splitting of water is one of the cleanest ways of producing hydrogen. However, the efficiency of this process is less than 1% with the currently used materials. Improvement in the electrode performance is limited by either chemical instability or poor light absorption properties of these materials. Although transition metal oxides are relatively stable during gas evolution, they have wide band gaps and thus absorb only UV part of the solar spectrum. Hence there is an intense search for newer materials with improved chemically stability and optical properties. In this work, we performed post synthesis nitridation of oxide nanowire arrays to form a completely new nitrided phase that has a lower band gap. The photoelectrochemical properties of these nanowire electrodes were characterized by UV-Vis, impedance, and photocurrent spectroscopy. The results are discussed in terms of their water splitting efficiency.

Tungsten oxide nanowire arrays were synthesized by hot filament CVD on both FTO and quartz substrates. Figure 1 shows the SEM image of WO3 array on FTO substrates. Post synthesis nitridation in ammonia resulted in the complete phase transformation to W2N. X-ray diffraction and transmission electron microscopy confirmed their high degree of crystallinity.

Figure 2 shows the Tauc plot obtained from UV-Vis spectroscopy. Oxidized WO3 has a band gap of 3 eV. On the other hand nitridation leads to a reduction in the band gap from 3 eV to 2.5 eV. The photoelectrochemical measurements were done in a three electrode configuration. Figure 3 shows a representative I-V characteristics of WO3 in dark and under simulated AM 1.5 solar light. The electrodes were further characterized by impedance, and photocurrent spectroscopy. The results are discussed in terms of their water splitting efficiency.
Striped Nanorods for Photocatalytic Hydrogen Production
Authors: Teo Gladys Y , Riley Jason D , Ryan Mary P
Published: February 2020

Photovoltaic modules are under active consideration as a major contributor to future energy requirements. Coupled with an electrolyzer, this energy system converts energy harvested from the sun into chemical power. As the demand for a sustainable yet efficient and cost effective approach of producing hydrogen increases, researchers are seeking ways to improve the technology of forming solar fuel. Mimicking the idea of how nature collects and stores solar energy in chemicals bonds through photosynthesis, economically viable water splitting cells capable of splitting water directly at the semiconductor surface are being developed. The catalytic semiconductor is designed to be both a light absorber and an energy converter to store solar energy in the simplest chemical bond, H2, thereby eradicating significant fabrication and system costs involved with the use of separate electrolyzers wired to photovoltaic cells.

In this work, water splitting cells have been designed to consist of multi-component nanorods of titanium dioxide and platinum with well-defined nanostructures to function as photocatalytic cell for hydrogen production. As the TiO2-Pt nanorods are irradiated with light in the presence of a water source, oxygen and hydrogen are evolved at the anode TiO2 and cathode Pt segments of the nanorods respectively. The alternating segments of TiO2 semiconductor and Pt metal enable the control of the direction of charge movement and light absorption pathways in the material, thereby presenting a solution to improving the overall efficiency of photocatalytic hydrogen production.

By employing templated electrodeposition, homogeneous multi-segmented TiO2/Pt nanorods have been successfully fabricated. This simple method of synthesis permits an easier control of the position and composition of TiO2 and Pt along the length of the nanorods, which allows for a customizable and highly reproducible method of obtaining segmented rods with uniformly distributed active sites for efficient catalytic activity. The UV absorption properties of these multi-segmented TiO2/Pt nanorods are then compared to single segmented nanorods consisting of only TiO2.
Low-Voltage Electroreduction of CO2: A Lesson from Geoelectrochemistry in the Seabed
Authors: Nakamura Ryuhei
Published: February 2020

To date, most research on heterogeneous CO2 electroreduction has been aimed at decreasing the large overpotential required for hydrocarbon synthesis. Specifically, most scientists have focused on reducing the external voltage to as low as 1.24 V, as this value represents the thermodynamic limit for producing organic compounds via CO2 reduction coupled with water oxidation [CO2 + H2O to (CH2O) + O2, where (CH2O) represents a carbohydrate].

As an alternative approach, it may be possible to exploit the highly active geoelectrochemical reactions mediated by microorganisms living in deep-sea hydrothermal environments. In such environments, chemolithoautotrophs, as opposed to photoautotrophs, primarily contribute to biomass production through the utilization of geochemical energy sources, such as H2S and H2, emitted from hydrothermal vents. Chemolithoautotrophic bacteria are able to utilize these energy-rich compounds for the production of hydrocarbons at rates that are one order of magnitude higher than that of photosynthesis, and several species can synthesize hydrocarbons using Fe2+ ions as a sole electron source for CO2 reduction. It is worth noting that Fe-oxidizing bacteria utilize the proton-motive force (PMF) generated by the reduction of O2 to H2O to elevate the energy of electrons obtained from Fe2+ oxidation by ~ 1 eV. Thus, although the reversible potential of the Fe3+/Fe2+ redox couple (0.77 V vs SHE) is more positive than that of NAD(P)/NAD(P)H (−0.32 V at pH 7), Fe-oxidizing bacteria are capable of generating NAD(P)H as a source of reductive energy for CO2fixation.

By harnessing the ability of Fe-oxidizing bacteria to elevate intracellular electrons into a higher energetic state, it may be possible to construct an integrated bioelectrochemical process in which the bacteria function not only as effective CO2 reduction catalysts, but also as voltage-multiplier circuits. In this system, CO2 reduction would occur at an external voltage that is one order of magnitude lower than that of conventional heterogeneous electrocatalytic systems. The thermodynamic limit of the external voltage required for the simultaneous reduction and oxidation of CO2 and H2O, respectively, is determined by the difference between the reversible potentials of E(O2/H2O) and E(Fe3+/Fe2+). Thus, the thermodynamic limit of the external voltage is estimated to be 0.035 V at pH 7 if 0.77 V is adopted as the redox potential of the Fe3+/Fe2+ couple. Based on these estimated values, the integrated bioelectrochemical process mediated by Fe-oxidizing bacteria can potentially proceed at an external voltage lower than 1.24 V, and thus provide an approach for utilizing the low-voltage electricity generated from hydro, solar, wind, and geothermal sources for the electrochemical conversion of CO2 to chemical fuels.
Effect of Operation Conditions during Fuel Starvation on Ruthenium Migration from Pt/Ru Anode Catalysts
Authors: Nedellec Yannig , Zaton Marta , Jones Deborah , Geymayer Martin , Hacker Viktor , Aarhaug Thor , Moller-Holst Steffen
Published: February 2020

Membrane electrode assemblies developed for use with reformate and containing Pt/Ru (1:1) anode catalysts, have been submitted to a fuel starvation accelerated stress test (AST) protocol in combination with a range of different operation conditions The fuel-starved MEAs were aged under conditions enabling investigation of the effect of temperature (65, 85 °C), current density (200, 400 mA/cm2), relative humidity (40, 80% RH) and number of starvation/recovery cycles (up to 875 cycles). The MEAs were characterized following the AST using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). This characterization has proven to be particularly useful in understanding the mechanism of degradation leading to performance loss of fuel-starved MEAs, and in correlating the observed extent of MEA modification in terms of migration of catalyst species, to the electrochemical parameters observed in situ.

The results show different trends in the evolution of the Ru/Pt ratio at the anode inlet and outlet regions, which is not unexpected given the greater degree of fuel starvation to the MEA at the anode outlet region, than at the anode inlet. At the anode outlet, the Ru/Pt ratio is <1 in the catalyst layer under all AST conditions, indicating that Ru has been lost due to electrochemical corrosion and leaching. Further, the extent of this depletion appears to be strong, and similar in all cases (0.26-0.39). At the anode inlet, the Ru/Pt ratio in the used MEAs ranged from 1 (i.e. unchanged compared with the pristine MEA) to 0.48, and the exact ratio within this range depended closely on the applied AST conditions. Correlation was also observed between the anode catalyst layer thickness and the extent of Ru loss.

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2010-2013) for the Fuel Cells and Hydrogen Joint Undertaking under grant agreement KEEPEMALIVE no. 245113.