bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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).
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.