bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid Oxide Membrane for Reduction of Ce0.8Gd0.2O2 and TiO2 in LiCl-Li2o
Authors: Olson Luke Christopher , Garcia-Diaz Brenda Lee , Brinkman Kyle S
Published: February 2020

A solid oxide membrane was used in a three electrode electrochemical cell to separately reduce, both Ce0.8Gd0.2O2 and TiO2 in molten solution of LiCl-Li2O.  The Ce0.8Gd0.2O2 was used as a surrogate for UO2, with the goal of using a similar technique during potential nuclear fuel reprocessing scenarios. The solid oxide membrane was a closed-end yttria stabilized zirconia tube inserted in an electrochemical cell with an argon cover gas.  A tungsten electrode was used as a quasi-reference, and both a graphite basket and Ni basket were used to separately hold Ce0.8Gd0.2O2 and TiO2 powders. One open end of the YSZ tube was held at room temperature, while the other closed end was submerged in the molten salt at 650 °C. A platinum bearing paint coated the inside of the SOM and facilitated electrical contact from the nonconductive cold region to the conductive hot region.  Argon gas was swept through the solid oxide membrane and an oxygen detector, where the oxygen pumped through the membrane during reduction was monitored.  Initial oxygen evolution was measured using the oxygen meter and readings were observed to correlate to reduction of the Ce0.8Gd0.2O2 and TiO2 as determined from electrochemical data.  The reduced Ce and Ti oxides were examined post experiment via SEM, EDS, and XRD.  EDS and XRD were used to prove partial reduction in both the Ce0.8Gd0.2O2 and TiO2, but complete reduction to the metallic state was not observed for either oxide to date.  EDS analysis found reduction of the TiO2 to as low as Ti­0.8O0.2 (with trace Cl).  EDS analysis of the Ce0.8Gd0.2O2 found evidence of reduction to Ce0.8Gd0.2O (with trace Cl).  XRD found evidence of LiTiO2, LiTi2O4, and (Li0.54Ti2.86)O6 from the TiO2 basket/electrode.  Analysis of reduced products may have been impacted from air exposure during analysis.  Operation of the cell for an extended period of time led to degradation of the solid oxide electrode.  The data indicated that the process works as expected, but that further development of solid oxide membranes that are stable for oxide reduction are needed.
Microstructure and Compositional Defects Affects Proton Conductivity and Reactions in Y-doped BaZrO3 Thin Films
Authors: Yang Nan , Di Bartolomeo Elisabetta , Foglietti Vittorio , Cantoni Claudia , Belianinov Alex , Tebano Antonello , Licoccia Silvia , Lee Tien-Lin , Schlueter Christoph , Kalinin Sergei V. , Balestrino Giuseppe , Aruta Carmela
Published: February 2020

Doped perovskite oxides have been widely studied in recent years as proton conducting solid electrolytes for different electrochemical devices, e.g. Solid Oxide Fuel Cells (SOFCs). By using the proton conductor as the electrolyte in a SOFC, the fuel dilution issue can be avoided due to the water formation at the cathode side instead of the anode. Among all the alkaline-earth cerates and zirconates, Y doped BaZrO3  (BZY) has been considered one of the most promising electrolyte for the SOFCs applications for its significant proton conductivity as well as chemical stability.[1] However, most reported fuel cell performance values for this material is much lower than oxide ion conducting ceramics such as YSZ owing to an unavoidable microstructure change, i.e. high grain boundary density and low degree of the crystallinity. 

In order to correlate the microstructure with the conductivity, we prepared BZY thin films by Pulsed Laser Deposition and discussed the effect of the microstructure on the proton conductivity.

In this presentation I will show the conductivity behavior as a function of temperature and thickness by Electrochemical Impedance Spectroscopy (EIS).[2] I will focus on the interface between BZY and substrate NdGaO3 and show the cross-sectional electrochemical activity change with nanoscale resolution by Electrochemical Strain Microscopy (ESM). [3] I will highlight the interplay between the interface defects and the electrochemical performance by comparing the EIS, ESM results with Scanning Transmission Electron microscopy (STEM). I will further show the complementary study by bulk sensitive hard x-ray photoemission spectroscopy measurements which, together with Density Functional Theory calculations, demonstrate that Y and, to some extent, also Zr ions, substitute for Ba near the interface with the substrate. 

[1] A. D’Epifanio, E. Fabbri, E. Di Bartolomeo, S. Licoccia, E. Traversa, Fuel Cells, 1,69-762008 (2008).

[2] V. Foglietti, Nan Yang, A. Tebano, C. Aruta, E. Di Bartolomeo, S. Licoccia, C. Cantoni, G. Balestrino, Applied Physics Letters 104 , 081612 (2014).

[3] Nan Yang, C. Cantoni, V. Foglietti, A. Tebano, A. Belianinov, E. Strelcov, S. Jesse, D. Di Castro, E. Di Bartolomeo, S. Licoccia, S. V. Kalinin, G. Balestrino and C. Aruta, Nano Letters, 10.1021/acs.nanolett.5b00698, (2015).
(Invited) Fundamental Aspects of Electrocatalysis at Work in Water Electrolysis
Authors: Gottesfeld Shimshon
Published: February 2020

Abstract Text:

A general aspect of electrocatalysis described most recently in  [1,2] , is the involvement of the electrode (over)potential in generation of catalytically active sites.  It has been demonstrated that , in a wide variety of ORR  processes taking place in low temperature fuel cells, the electrocatalytic process is "ignited" by a potential-driven change in steady state catalyst surface composition . The common involvement of such potential-driven, surface composition change  in  the mechanism of electrocatalytic processes , has led to the conclusion  that fuel cell electrocatalytic processes , particularly the ORR, are, in general,  "redox mediated" , including so at metal electrocatalysts such as Pt [1,2].

In this paper,  the applicability of the same type mechanism to  electrocatalytic processes in water electrolysis, particularly the OER, is elucidated. Much the same way as in the case of  ORR at a variety of  electrocatalyst surfaces, the OER also exhibits generally a dependence on overpotential of:  'low Tafel slope  of  60 mV/decade ,or lower, at low currents, followed by higher Tafel slope of around 120mV/decade at higher currents '. This general pattern is fully expected  for a mechanism involving  potential activation of surface sites. Inclusion of the change of active site population with potential in the expression for the current potential dependence, results in potential-dependence of the pre-exponential factor, with the consequence of a  low Tafel slope around the standard potential of the redox couple mediator [1,2].

Recently reported polarization curves for the OER ,to be discussed in this talk  (3), exhibit the typical behavior described above. As commonly done, the interpretation was given in the form of change in RDS  with overpotential. The insight proposed here, sugegsts that the RDS may very well remain the same throughout the relevant potential range and the observed change in Tafel slope is fully explained by change with overpoential in steady state, active surface site population.  

Much the same way as in the case of fuel cell electrocatalysis [1,2], the important consequence of such general mechanism is that the effectiveness of the electrocatalyst depends on the magnitude of the overpotential required to activate the surface-redox-mediating system. Proximity of E0,surf.redox to E0,cell process should enable, in principle,  high voltage efficiency of the electrolyzer.

(1) S. Gottesfeld, ECS Trans. 2014 61(31): 1-13

(2) S. Gottesfeld, ECS Trans. 2015 66(29): 13-30

(3) R.I. Doyle and E.G. Lyons. JECS, 160, H42, 2013
Non-Precious Metal Oxygen Evolution Reaction Catalysts for Hydroxide Exchange Membrane Electrolyzers
Authors: Yan Yushan , Zhuang Zhongbin
Published: February 2020

One of the grand challenges facing humanity today is the development of an alternative energy system that is safe, clean, and sustainable and where combustion of fossil fuels no longer dominates. A distributed renewable electrochemical energy and mobility system (DREEMS) could meet this challenge. At the foundation of this new energy system are a number of electrochemical devices including fuel cells, electrolyzers, and flow batteries. For all these devices electrocatalysis plays a critical role in controlling their performance and cost, and thus their commercial viability. In this presentation, we will focus on our recent work on non-precious metal based oxygen evolution catalysts in base.
First Principles Studies of Electrocatalysis: From Methodology Development to Computational Design of Bi-Functional Catalysts with Improved Performance
Authors: Zeng Zhenhua , Greeley Jeff
Published: February 2020

Over the past decade, tremendous advances have made on first principles based modeling of interfacial electrochemistry, which permit not only the mechanistic understanding of the basic thermodynamics and kinetics of complex electrocatalytic reaction networks and but also computational design of new alloy electrocatalysts. [1] Nevertheless, it is still a big challenge for the modeling of electrified interfaces with explicit double layer features (i.e. hydrogen bonds, solvent, electrode potential), which in some instances, yield completely unexpected physical and catalytic properties. For alkaline electrocatalysis at bi-functional three-phase boundaries of ultra-thin 3d transition metal (hydroxy)oxide films, Pt substrates, and the surrounding water,[2,3] it is more challenging, as the interface structures are largely unknown and the large errors in standard DFT calculations on the description of strongly-correlated (hydroxy)oxides. These have significantly impeded the design of new bi-functional catalysts with further improved performance.

In this talk, I will briefly review the methodologies we have recently developed, including a synergistic strategy towards highly accurate prediction of Pourbaix diagram of transition metal (hydroxy)oxides,[4] a simple scheme for fast screening of stable single layer transition metal (hydroxy)oxide film/metal interfaces under electrochemical conditions. Next, using hydrogen evolution reaction as an example, I will demonstrate how these techniques can be applied to understand the steady state, the active phases and the catalytic mechanism of mono- and bi-functional catalysts. Finally, I will show these understandings can be used to design new bi-functional catalysts with improved performances.

If time permit, I will introduce some of our recent developments on explicitly modeling of electrified electrode/electrode interfaces with full double layer features.

[1] J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J. K. Nørskov, Nat. Chem. 2009, 1, 552-556.

[2] Subbaraman, R.; Stamenkovic, V.; Markovic, N. et al, Science 2011, 334, 1256.

[3] Subbaraman, R.; Greeley, J.; Stamenkovic, V.; Markovic, N. et al, Nat Mater 2012, 11, 550

[4] Z. Zeng, M. K. Y. Chan, Z.-J. Zhao, J. Kubal, D. Fan, J. Greeley, J. Phys. Chem. C 2015, 119, 18177
Lateral Size Effect on Oxygen Evolution Reaction Activity of IrO2 Nanosheet
Authors: Takimoto Daisuke , Ayato Yusuke , Mochizuki Dai , Sugimoto Wataru
Published: February 2020

Iridium dioxide (IrO2) is well known as an electrocatalyst with good activity for the oxygen evolution reaction (OER). We demonstrated earlier that IrO2 nanosheets, which are prepared via exfoliation of layered IrO2, exhibited similar performance to IrO2 nanoparticles (2-3 nm in diameter).1) In this study, we show that the OER activity of IrO2 nanosheet can be improved by down-sizing the lateral size of IrO2nanosheets.

IrO2 nanosheet was derived via exfoliation of layered H0.3Ir0.93O2×nH2O through a process reported previously. The lateral size of IrO2 nanosheet was reduced by ultrasonic treatment for 30 min with a homogenizer. The working electrode was prepared by dropping the IrO2 nanosheet on a glassy carbon electrode. A thin layer of Nafion ionomer was cast on the electrode. All electrochemical measurements were conducted in 0.1 M HClO4 (25oC).

The lateral size of as-prepared IrO2 nanosheet decreased from 258 nm to 111 nm by ultrasonic treatment. The electrochemically active surface area for both nanosheets was similar. The OER activity of IrO2 nanosheet with small lateral size was 881 A (g-IrO2)‒1, 1.9 times higher than that of as-prepared IrO2 nanosheet (451 A (g-IrO2)‒1). The edge sites of small lateral nanosheet size were 1.7 times higher than that of as-prepared nanosheets, corresponding well the enhancement in OER activity. The result suggests that the OER activity of IrO2nanosheet was enhanced by down-sizing the lateral size of nanosheet, which increased the amount of edge sites.

1)      W. Shimizu, T. Ishida, S. Miyasaka, Y. Ayato, and W. Sugimoto, 227th ECS meeting, Chicago, IL (2015).
Cobalt Molybdenum Phosphide As a Non-Noble-Metal Catalyst for the Hydrogen Evolution Reaction
Authors: Chen Wei-Fu , Fang Si-Lin , Chen Kuei-Hsien , Chen Li-Chyong
Published: February 2020

To replace Pt electrocatalysts for the HER in acidic electrolytes, several approaches have been exploited on transition metals through modifying the d–states at the Fermi level of the metal center by the alloying nonmetal elements such has sulfur, nitrogen and carbon.1 To further reduce the overpotential and enhance the stability, ternary compounds such as nickel molybdenum nitride2 have been shown enhanced performance in the HER. Very recently, metal phosphides, known as efficient hydrotreating catalysts, have also been demonstrated as HER catalysts, such as MoP,3 CoP,4 and Ni2P.5 Unlike bulk molybdenum dichalcogenides, which show poor activity, hexagonal molybdenum phosphide (MoP) exhibits good HER activity in bulk form, however, its performance is still limited by the intrinsic strong hydrogen binding energy.

In this study, attempts to synergize the electronic properties of cobalt phosphide and molybdenum phosphide by synthesizing ternary cobalt molybdenum diphosphide lead to the formation of an efficient electrocatalyst for the HER. X-ray diffraction data and high-resolution transmission electron microscopy show that this cobalt molybdenum phosphide crystallizes in space group P63/mmc and a formula of CoMoP2 (Figure 1). Incorporation of the sequentially stacked layers of CoP6 and MoP6 prisms on a single CoMoP2 structure brings about a significant enhancement in the HER kinetics and fast charge transfer. Characterization using X-ray absorption, electrochemical impedance analysis and electrochemical activity and Tafel behavior will be discussed.

References

1. W.-F. Chen, J. T. Muckerman and E. Fujita, Chem. Commun.
2013, 49, 8896-8909.

2. W.-F. Chen, K. Sasaki, C. Ma, A. I. Frenkel, N. Marinkovic, J. T. Muckerman, Y. Zhu, R. R. Adzic, Angew. Chem. Int. Ed.
2012, 51, 6131-6135.

3. X. Peng, M. Alam Sk, L. Thia, X. Ge, R. J. Lim, J.-Y. Wang, K. H. Lim and X. Wang, Energy Envirn. Sci.
2014, 7, 2624.

4. Q. Liu, J. Tian, W. Cui, P. Jiang, N. Cheng, A. M. Asiri and X. Sun, Angew. Chem. Int. Ed., 2014, 53, 6710.

5. E. J. Popczun, J. R. McKone, C. G. Read, A. J. Biacchi, A. M. Wiltrout†, N. S. Lewis and R. E. Schaak, J. Am. Chem. Soc., 2013, 135, 9267–9270.

Acknowledgement

This work was carried out at National Taiwan University, and financially supported by Ministry of Science and Technology (Taiwan) and Academia Sinica (Taiwan).

Figure 1
High-Performance Organic Redox Flow Batteries in Aqueous and Nonaqueous Electrolytes
Authors: Wei Xiaoliang , Xu Wu , Duan Wentao , Liu Tianbiao , Huang Jinhua , Vemuri Rama Sesha , Cosimbescu Lelia , Murugesan Vijayakumar , Brushett Fikile R. , Moore Jeffery S. , Liu Jun , Zhang Lu , Wang Wei , Sprenkle Vincent
Published: February 2020

Redox flow battery is a promising large-scale grid energy storage technology. Its advantage of separating energy and power allows independent designs of tank volume and stack size and thus offers tremendous flexibility for different energy/power ratio applications. Traditional inorganic redox materials have suffered limited solubility, low electrochemical reactivity and/or high cost. Instead, organic compounds are being considerably pursued because of their molecular diversity, structural tailorability, environmental benignity, and potential low cost. A number of organic flow battery systems have been investigated.1-3

Here we report several organic redox flow chemistries in aqueous and nonaqueous electrolytes.4,5Promising redox material candidates have been identified with desirable redox potentials, high solubilities, and good electrochemical properties. Flow cells of these systems demonstrated remarkable cell efficiencies and high rate performance. Functional groups present in these molecules play an important role to tune solubility and chemical stability of redox species. Rational molecular engineering will be discussed as a general strategy to improve the battery performance and durability.

References

(1) W. Wang, Q. Luo, B. Li, X. Wei, L. Li, Z. G. Yang, Adv. Funct. Mater.
2013, 23, 970.

(2) K. Gong, Q. Fang, S. Gu, S. Li, Y. Yan, Energ. Environ. Sci.
2015, DOI: 10.1039/C5EE02341F.

(3) G. L. Soloveichik, Chem. Rev.
2015, DOI: 10.1021/cr500720t.

(4) X. Wei, W. Xu, J. Huang, L. Zhang, E. Walter, C. Lawrence, M. Vijayakumar, W. A. Henderson, T. Liu, L. Cosimbescu, B. Li, V. Sprenkle, W. Wang, Angew. Chem. Int. Ed.
2015, 54, 8684.

(5) T. Liu, X. Wei, Z. Nie, V. Sprenkle, W. Wang, Adv. Energy Mater.
2016, 6, DOI: 10.1002/aenm.201501449.

Figure 1. Flow cell cycling performance of: (a) nonaqueous N-methylphthalimide (anolyte)/di-t-butyl-dialkoxybenzene (catholyte) system; and (b) aqueous methyl viologen (anolyte)/HO-TEMPO (catholyte) system.5

Figure 1
Cerium-Hydrogen Redox Flow Cell Optimization
Authors: Tucker Michael C , Weiss Alexandra , Weber Adam Z
Published: February 2020

The Ce/H2 redox flow cell is a promising system for large-scale energy storage due to its high open circuit potential (OCV) relative to other aqueous systems.[1] The system consists of an electrochemical cell which is fed reactants from storage tanks containing gaseous hydrogen (negative side) and an aqueous solution of Ce3+ and Ce4+ (positive side). During discharge, hydrogen is oxidized to protons at the negative electrode. The protons pass through an ion-conducting membrane and react with Cerium(IV) methanesulfonate at the positive electrode to produce Cerium(III) methanesulfonate and methanesulfonic acid (MSA). The electrochemical reactions are shown below with the forward direction corresponding to discharge and the reverse to charge.

Negative: 0.5H2(g) = H+(aq) + e-          E0=0.00V                       (1)

Positive: Ce4+(aq) + e- = Ce3+(aq)         E0=1.5-1.7V                       (2)

Overall: Ce4+(aq) + 0.5H2(g) = Ce3+(aq) + H+(aq)        E0=1.5-1.7V                           (3)

Previous work by Hewa Dewage et. al established proof of concept for this device, demonstrating ~150mW/cm2 peak discharge power using platinized titanium mesh cerium electrode and commercial Pt-on-carbon paper hydrogen electrode.[1] In this work, we further optimize the cell materials, electrolyte composition, and operating protocol. It is found that Pt mesh type and surface area, membrane pretreatment, MSA concentration, and upper cutoff voltage have a large impact on performance. Optimizing these parameters results in power density exceeding 650 mW/cm2, as shown in Figure 1. Cell cycling efficiency is shown as a function of current density in Figure 2. Energy efficiency of 90% is achieved, although at low current density. Inefficiency is dominated by voltaic losses, which are thought to arise from kinetic and mass-transport limitations in the cerium electrode.

This paper will discuss the optimization effort in detail, as well as initial cycling stability results. Based on these results, we conclude that the cerium/hydrogen redox flow cell is indeed a good candidate for large-scale energy storage, due to high cell voltage, promising power density and energy efficiency, and reasonable cerium solubility. Future efforts should focus on developing improved cerium-electrode structures and catalysts, and determining durability of the cell.

References

[1] Hewa Dewage, H., B. Wu, A. Tsoi, V. Yufit. G. Offer, and N. Brandon, J. Mater. Chem. A (2015) 3, 9446-9450.

Figure 1
Anthraquinone Derivatives in Aqueous Flow Batteries
Authors: Gerhardt Michael R. , Tong Liuchuan , Chen Qing , Gordon Roy G. , Aziz Michael J.
Published: February 2020

Aqueous quinone/hydroquinone couples exhibit rapid redox kinetics, require no electrocatalyst, and are potentially very inexpensive, making them attractive candidates for large-scale energy storage devices such as flow batteries [1-3]. We evaluate four anthraquinone derivatives for use as the negolyte in aqueous flow batteries. These anthraquinones are shown to undergo reversible two-electron reduction and oxidation in acidic aqueous solution, with tunable reduction potentials. When paired with a posolyte containing bromine and hydrobromic acid, three of these quinone derivatives exhibit cell voltages above 1 V. These derivatives are evaluated for chemical stability against bromination and stability upon reduction. Two anthraquinone derivatives stable under both conditions are cycled in a flow cell, showing greater than 98% current efficiency at 0.25 A/cm2cycling current. Mechanisms for capacity loss and energy inefficiency are discussed to guide further research.

Figure 1. (a) Cyclic voltammetry of four anthraquinone derivatives, showing two-electron redox events at a range of potentials. (b) Open circuit potential of flow batteries employing quinone/hydroquinone negolytes and bromine/bromide posolyte.  

[1] B. Huskinson, M.P. Marshak, C. Suh, S. Er, M.R. Gerhardt, C.J. Galvin, X. Chen, A. Aspuru-Guzik, R.G. Gordon and M.J. Aziz, “A metal-free organic-inorganic aqueous flow battery”, Nature 505, 195 (2014), http://dx.doi.org/10.1038/nature12909

[2] B. Huskinson, M.P. Marshak, M.R. Gerhardt and M.J. Aziz, “Cycling of a quinone-bromide flow battery for large-scale electrochemical energy storage”, ECS Trans. 61, 27 (2014)

[3] B. Yang, L. Hoober-Burkhardt, F. Wang, G.K. Surya Prakash, and S.R. Narayanan, J. Electrochem. Soc. 161, A1371 (2014)

Figure 1
Effects of Metal Additives on Electrochemical Performance and Behavior of Sodium Metal Chloride Rechargeable Battery
Authors: Choi Joon-Hwan , Ahn Cheol-Woo , Kim Mangi , Choi Jong-Jin , Kim Jong-Woo , Yoon Woon-Ha , Ryu Jungho , Hahn Byung-Dong , Hong Inchul , Kim Woosung , Moon Goyoung , Lee Heesoo
Published: February 2020

Because of the limitation of lithium resources, sodium-based rechargeable batteries started to emerge as potential candidates for medium and large-scale stationary energy storage system (ESS) again. Na-S batteries have been used for large-scale stationary ESS but intrinsically have a risk for explosion. Sodium metal chloride batteries based on Na-NiCl2 chemistry, however, are consisted of safer electrode configuration with nickel, NaCl and NaAlCl4 as cathode ingredients than the Na-S batteries. The Na-NiCl2 batteries offer many attractive properties such as high cell voltage, high theoretical specific energy, and broad range in operating temperature. The nickel chloride electrode plays an important role in the cell performance. It will be discussed why a metal additive must be considered in Na-(Ni,M)Cl2 batteries [M: a metal additive] in this paper. It is because the metal additive protects the chains of the conductive metal from disconnection in the cathode layer of the Na-(Ni,M)Cl2 cells. This concept has been confirmed through investigation of electrochemical behaviors in the Na-(Ni,Fe)Cl2 cells. Especially, Fe shows excellent cycle performance in the Na-(Ni,M)Cl2 cells. Other metal additives can be considered to protect the conductive chains in the Na-(Ni,M)Cl2 cells also.
(Invited) Understanding and Controlling Chemo-Mechanical Coupling in Perovskite Oxides
Authors: Perry Nicola H. , Marrocchelli Dario , Bishop Sean R. , Tuller Harry L.
Published: February 2020

Mixed ionic and electronic conducting perovskites that can readily exchange oxygen with the atmosphere exhibit a chemo-mechanical coupling between their oxygen content and their lattice dimensions. The lattice dilation accompanying oxygen loss, termed “chemical expansion,” beneficially enables new techniques that use measures of strain to determine changes in oxygen content, but deleteriously causes large chemical stresses in devices during operation that can lead to mechanical failure. In this presentation I will describe our work aimed at understanding, across multiple length scales, which factors impact chemical expansion coefficients in perovskites, in order to develop design principles for controlling them. Polycrystalline gallate and titanate perovskites containing multivalent Ni, Fe, and Co have been studied using in situ thermogravimetry, diltometry, and diffraction to probe the chemical expansion process at macroscopic and crystal structure levels. Corresponding simulations using density functional theory, molecular dynamics, and empirical approaches have provided atomistic insight into changes taking place on the anion and cation sublattices during oxygen loss. Factors impacting the magnitude of the chemo-mechanical coupling, including oxygen vacancy radii, charge localization on cations, temperature, crystal symmetry, and defect ordering, have been identified.
(Invited) Ab Initio Studies of Strain Effects on Perovskite Oxygen Vacancy Formation and Migration Energetics
Authors: Morgan Dane , Mayeshiba Tam
Published: February 2020

Oxygen active materials are capable of rapidly transporting oxygen and exchanging it with the environment and have a wide range of applications, including solid oxide fuel cells, gas separation membranes, oxygen sensors, chemical looping devices, and memristors.  Recent work has shown that epitaxial strain can play a significant role in altering the transport of oxygen through oxygen active materials, particularly in fluorite structured compounds.  However, transition metal perovskites are an important class of oxygen active materials that have received only limited attention.  In this work we use ab initio methods to model the coupling of biaxial epitaxial strain with oxygen vacancy formation and migration energetics in a range of transition metal perovskites.  We focus on materials of the form LaBO3, where B = [Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga].  We predict the formation volume and strain response of oxygen vacancy formation energy, demonstrating that non-linear coupling of strain and vacancy formation can yield responses qualitatively different than those expected from simple elasticity arguments.  In particular, as first observed in Ref. [1], we show that in some cases the vacancy can weaken the bonding and lower the elastic constants, which allows the formation of a vacancy to reduce the strain energy.  This effect leads to stabilization of the vacancy under both compressive and tensile strain, even though the vacancy has positive formation volume.

We also predict the migration volume and the strain response of oxygen migration energetics, here finding that values are quite consistent with a simple elastic strain model.[2]  We find that tensile (compressive) biaxial strain reduces (enhances) the oxygen vacancy migration barrier approximately linearly across the systems studied (Figure 1).  The average decrease in migration energy is 66 meV per percent strain for a single selected hop, with a low of 36 and a high of 89 meV decrease in migration barrier per percent strain across all the systems studied.  In general we find that the oxygen transport kinetics can be altered by orders of magnitude in perovskites through strain effects on both vacancy content and migration energetics.  These effects could play a significant role on materials performance at interfaces and in thin-film devices.

[1] W. Donner, C. L. Chen, M. Liu, A. J. Jacobson, Y. L. Lee, M. Gadre, and D. Morgan, Epitaxial Strain-Induced Chemical Ordering in La0.5Sr0.5CoO3-delta Films on SrTiO3, Chemistry of Materials 23, p. 984-988 (2011).

[2] T. Mayeshiba and D. Morgan, Strain Effects on Oxygen Migration in Perovskites, Phys. Chem. Chem. Phys. 17, p. 2715-2721 (2015 ).

Figure 1
Stress/Strain Effect on Non-Stoichiometry of La0.6Sr0.4Co0.2Fe0.8O3-
δ
Authors: Qiu Miaolong , Arai Yoshio , Araki Wakako
Published: February 2020

La0.6Sr0.4Co0.2Fe0.8O3-δ
 (LSCF) is a mixed ionic-electronic conductor and one of the candidates to be used for oxygen separation membrane and cathode material for solid oxide fuel cell. The ionic conductivity of LSCF, which is still by several orders of magnitude lower than its electronic conductivity, needs to be further improved for higher performance of those devices.

LSCF has a cubic perovskite structure. The oxygen vacancies are formed at elevated temperatures above 873 K, while the transition metal ions are reduced for the charge neutrality, accompanied by a sudden volume expansion, i.e., an increase in lattice constant. This implies that the oxygen vacancies could be introduced by applying mechanical strain or stress, as has been discussed in recent reports. In the present study, the oxygen-nonstoichiometry in LSCF was examined under uniaxial compression using coulometric titration technique.

   The test cell consisted of polycrystalline LSCF placed between 8 mol%-yttria stabilized zirconia (YSZ) plates with the platinum paste on the interfaces and on the surfaces, i.e., Pt/YSZ/Pt/LSCF/Pt/YSZ/Pt. The side of LSCF was covered with borosilicate glass. A constant voltage (25 mV to 100 mV) was applied to YSZs using a galvanostat in order to control the oxygen partial pressure in the cell (from 0.0678 to 0.0026). After the measured current reached a constant value (e.g., zero in case there is no leakage), the circuit was opened and the decay current was subsequently measured. The change in the oxygen deficiency was calculated from the integration of the measured decay current. Then, the oxygen non-stoichiometries in LSCF under various oxygen partial pressures were examined. The measurement was conducted under uniaxial compressive stress ranging from 0 to 10 MPa, and all the tests were performed at 1073 K in air. In addition to the above experiment, the relationship between the uniaxial strain and the oxygen non-stoichiometry was estimated based on the mechanical property as well as thermo-chemical-mechanical property at 1073 K based on the literature data, assuming that the oxygen deficiency merely depends on the volume change.

   The oxygen deficiency increased as the oxygen partial pressure was decreased, and there was almost no leakage from the test cell. The obtained results showed a good agreement with the previous reports. There was no significant effect of the applied stress up to 10 MPa on the measured decay current or the oxygen non-stoichiometry, whereas the stress above 20 MPa caused the fracture of the test cell. According to our estimation based on the mechanical and thermo-chemical-mechanical properties, the oxygen deficiency could be decreased by ~0.006 when the uniaxial compressive stress of 100 MPa is applied, which is being examined using a modified experimental setup.
(Invited) Enhancing Cathode ORR Kinetics and Durability through Low-Cost Surface Modification
Authors: Chen Yu , Ding Dong , Wei Tao , Chen Dongchang , Zhang Lei , Rainwater Ben Harris , Liu Meilin
Published: February 2020

One of the key technical challenges facing the commercialization of SOFC technology is to ensure high performance and long-term stability and reliability. Under realistic operating condition, the cathodes are exposed to various contaminants commonly encountered in air (e.g., CO2 and/or H2O) as well as impurities from other cell components (e.g., a Cr-containing interconnect), which may lower the SOFC performance and accelerate cathode degradation. To develop durable, high-performance SOFC cathodes, we have investigated the mechanism of cathode degradation due to contaminant poisoning and developed strategies for mitigating the problem. It is found that surface modification of La0.6Sr0.4Co0.2Fe0.8O3(LSCF) cathodes with robust perovskite catalyst coatings through a solution infiltration method is the most effective and economical approach. Electrochemical impedance spectroscopy, cathode polarization measurement, Raman spectroscopy, and modeling and simulation have been used to quantify the tolerance of catalysts-coated cathodes against various contaminations, including steam, CO2, Cr-containing species, and a combination of them. We have further characterized the kinetics of oxygen reduction reaction (ORR) and long-term stability of homemade cells with blank and catalyst-modified LSCF cathodes exposed to different concentrations of contaminants, demonstrating that surface modification through solution-infiltration is a low-cost approach to enhancing both ORR kinetics and stability of the LSCF cathodes.
Rational Design of Stable Cathode Materials for Solid Oxide Fuel Cells
Authors: Cetin Deniz , Poizeau Sophie , Gopalan Srikanth
Published: February 2020

In this study we consider several heretofore unexplored composite cathode materials systems for solid oxide fuel cells (SOFCs), whose compositions and microstructures have been optimized for high electrocatalytic activity for oxygen reduction reaction and for chemical stability.  The design approach takes into account the need for combining facile oxygen surface reactions with bulk transport.

The new composite cathodes in this study consists of carefully tailored composition of perovskite type MIECs and fluorite type ionic conductors.

In this study, all components of the button cells with composite MIEC cathode functional layer (CFL) were prepared via tape casting. Electrochemical performance of these button cells were analyzed through polarization modelling and impedance spectroscopy at temperatures between 700 and 900°C and at cathode side oxygen partial pressures between 1 and 5x10-2 atm. The effect of cathode microstructure on the cell performance is also discussed.
Understanding Morphology and Ion Transport in Novel Poly (cyclooctene) Based Membranes Under Humidified Conditions
Authors: Sarode Himanshu , Zhang WenXu , Yang Yuan , Coughlin E. Bryan , Herring Andrew M
Published: February 2020

Anion Exchange membranes have been gaining popularity for their applications in fuel cells, CO2electrolysers, redox flow batteries, etc. The main focus has been in the area of synthesizing new polymers for these applications and understanding their morphological and transport properties under humidified conditions of operations. The main aim is toward increasing the ion transport and minimizing degradation over time. Phase separated morphology is one of the pathways to create defined ionic pathways to increase ion conductivity of the AEMs. Here we report morphological study performed on a polycyclooctene based triblock copolymer AEM, for electrochemical applications.

We have performed in situ SAXS under humidified conditions on these AEMs of importance to understand the swelling and morphological behavior. AEMs in this study show lamellar morphology with a d spacing of 39-41nm. We also studied the mechanical properties of these AEMs. Mechanical properties of these membranes are good under dry and low temperature, but above 60°C and hydration the AEMs become soft. Our initial results show that the AEM is stable under alkaline conditions of operation and offers reasonable hydroxide conductivity (70mS/cm @ 60°C) under humidified conditions. Conductivity of these AEMs increases by 4 fold when humidity is increased from 80% to 95%. Overall we report a functional AEM with reasonable properties for electrochemical applications.

Acknowledgements:

We would like to thank the Army Research Office for funding this Multidisciplinary University Research Initiative under contract #W911NF-10-1-0520 and the Colorado School of Mines NMR facility, funded by National Science Foundation under the grant CHE-0923537.
Spectroelectrochemical Insights into the Formation of Robust Interfaces for the Immobilization of Biological and Molecular Electrocatalysts
Authors: Harris Tomos Gwilym Ab Alun , Heidary Nina , Sokolowski Anja , Tzschucke Christoph , Hildebrandt Peter , Zebger Ingo , Fischer Anna
Published: February 2020

The immobilization of enzymatic and molecular catalysts on conductive surfaces is of interest in many different fields of electrocatalysis. The interface between these catalysts and the electrode surfaces plays hereby a critical role for the catalysts efficiency, stability and applicability (e.g. affecting electron transfer).

Surface immobilization strategies hereby involve the functionalization of the electrode surface. In this work the covalent modification of various electrodes for the tailored immobilization of molecular and biological catalysts is presented. Crucial information regarding the surface functionalization process, the interface structure and it’s behavior have been obtained using a combination of electrochemical techniques as well as in-situ Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS). In this way catalyst immobilization, stability and mechanistic aspects could be probed in a large electrochemical window due to the remarkable stability of these covalent interfaces.
Development of Nanostructured Metal Oxides-Platinum Electrodes for Enhanced Electrocatalytic Oxidation of Ethanol
Authors: WANG Youling , Aoul Amel-Tabet , Mohamedi Mohamed
Published: February 2020

Ethanol is an attractive fuel for direct ethanol fuel cells (DEFCs) because it has high theoretical energy density (8.0 kWh/kg) [1], it is nontoxic and can be produced from biomass, which could make DEFCs beneficial low greenhouse gas emission power sources. Platinum is known to be the most active catalyst for the ethanol oxidation reaction (EOR). Nevertheless, at Pt catalyst, the complete oxidation of ethanol to CO2 is not attained, because of CO poisoning and the difficulty in breaking the C-C bond at low temperature, which has a detrimental effect on the fuel cell efficiency [2].

A promising strategy to improve the catalytic activity of DEFC reaction can be obtained by integrating metal oxides with Pt to form platinum-metal oxides-composites. Indeed, due to certain intrinsic properties and functions of their own, several nanostructured metal oxides (MOx) such as CeO2, SnO2, TiO2, MnO2, WOx... are emerging as a distinctive class of electrode materials in energy conversion fields. In such applications, MOx can perform as the electroactive material itself, or as a supporting matrix to enhance catalyst dispersion and its stability against sintering and particles aggregation; or advances certain electrocatalytic reactions when combined with other catalysts. In this presentation, we will discuss our recent advances in the development of nanostructured MOx-Pt catalysts anodes for low temperatures DEFCs. Both nanostructured Pt and Pt-MOx (M: Ce, Sn, Mn, Ti) composites of various surface morphologies (smooth, semi-porous and highly porous) were synthesized at room temperature by adapting and optimising the pulsed laser deposition (PLD) method.

Such composites are systematically characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microRaman spectroscopy, and transmission electron microscopy (TEM) techniques and insights into the physical interaction of MOx with Pt are discussed. Afterwards, we study the electroactivity and durability performances with post-mortem surface morphology of MOx-Pt composites as well as catalytic promoting properties of MOx to Pt towards the EOR.

[1] G. Hoogers,  Fuel cell technology handbook, CRC press, Boca Raton, FL, 2003.

[2] F. Vigier, C. Coutanceau, F. Hahn, E.M. Belgsir, C. Lamy, J. Electroanal. Chem. 563 (2004) 81-89.
(Invited) Plasmonic Metal-Semiconductor Heterojunctions for Photoelectrochemical Energy Conversion
Authors: Wu Nianqiang (Nick) , Cushing Scott Kevin , Li Jiangtian , Chu Deryn
Published: February 2020

This talk will introduce the charge transfer and the energy transfer processes in the plasmonic metal-semiconductor heterojunctions. It will discuss the factors that govern the occurrence and transfer efficiency of both the processes. It will show our effort to improve the photoconversion efficiency of the heterojunctions by utilizing both the charge transfer and the energy transfer processes. The presentation will also deal the theoretical maximum efficiency that can be achieved by the plasmonic metal-semiconductor heterojunctions.
Phenanthroimidazole Mediators - Immobilization on Electrodes and Mechanistic Studies
Authors: Johnson Bruce , Berben Louise , Little R. Daniel , Römelt Michael , Francke Robert
Published: February 2020

The use of redox mediators is a well-established approach in electrosynthesis to lower kinetic barriers, to improve product selectivity and to suppress electrode fouling.[1] Recently we have developed a new series of metal‐free and easy-to-synthesize redox mediators based on the phenanthro[9,10-d]imidazole framework (see figure below, left).[2] Upon anodic oxidation these compounds form stable radical cations which can be used to catalyze the oxidation of benzylic alcohols and ethers. By selection of a suitable substitution pattern the oxidation potential of the mediator can be adapted to the redox potential of a specific redox reaction.

Our efforts are currently focused on the immobilization of alkyne-modified phenanthroimidazoles on carbon electrodes via Cu(I)-catalyzed azide-alkyne cycloaddition (see figure below, right). Our goal is to simplify the product separation after an electrolysis and to improve the long-term stability of the mediator. By attachment to the electrode surface we were able to increase the turnover numbers by several orders of magnitude while maintaining reasonable reaction rates.

Further studies are directed towards a better understanding of the mechanism of the charge transfer between mediator and substrate as well as the chemical follow-up reactions. A combination of spectroelectrochemical experiments and computational studies will be used to discuss possible intermediates and transition states.

References:

[1] R. Francke, R. D. Little, Chem. Soc. Rev.
2014,43
, 2492.

[2] R. Francke, R. D. Little, J. Am. Chem. Soc.
2014, 136, 427.

Figure 1
Electroorganic Construction of Pyrazolidine-3,5-Diones
Authors: Gieshoff Tile , Waldvogel Siegfried R.
Published: February 2020

Pyrazolidin-3,5-diones are an important motif in heterocyclic chemistry, which is highly interesting for pharmaceutical applications. One example is Phenylbutazone, an anti-rheumatic drug in human and veterinary medicine. Additionally, many pyrazolidin-3,5-dione derivatives are regularly tested on their pharmaceutical activity.[1]

In classic heterocycle chemistry, the hydrazinic bond is established by ring closure using the corresponding hydrazine derivatives.[2] Most of them are toxic and require an upstream preparation due to low availability. Therefore, we now present a novel and sustainable synthetic approach to pyrazolidin-3,5-diones using electric current as oxidizing reagent.

This electroorganic approach has some major advantages. Firstly, less or no reagent waste is produced.[3] Secondly, this transformation is an easy and elegant way to build the hydrazine moiety in pyrazolidin-3,5-diones. Thirdly, the required malonic acid diamides can be prepared in high yields from easy available starting materials.[4]

References:

[1] G. Deng, W. Li, J. Shen, H. Jiang, K. Chen, H. Liu, Bioorg. Med. Chem. Lett.
2008, 18, 5497–5502.

[2] U. Funke, H.-F. Grützmacher, Chem. Ber.
1989, 122, 1503–1508.   

[3] H. J. Schäfer, A. J. Bard, M. Stratmann, Organic Electrochemistry, Encyclopedia of Electrochemistry, Wiley-VCH, Weinheim, 2004.

[4] C.-T. Chen, Y.-S. Chan, Y.-R. Tzeng, M.-T. Chen, Dalton Trans.
2004, 17, 2691–2696.

Figure 1
Epoxide Formation Via Radical Cations and Biradicals
Authors: Akaba Ryoichi
Published: February 2020

Epoxide is an important class of compounds, and is frequently formed in alkene oxygenation reactions. Detailed mechanism for the epoxide formation in reactions of alkene oxygenation via electron transfer is not known, however. In order to understand mechanism for the epoxide formation, we have performed a mechanistic study with DFT B3LYP/6-31G(d) level of theory for aliphatic alkenes. We have found that dimerization of peroxy radical cation, which gives the corresponding tetraoxide dication, followed by elimination of molecular oxygen, may be a major pathway for epoxide formation. We have also found that diradical that may be formed from peroxy radical cation via one electron reduction undergoes similar reaction to afford epoxide. Comparison of these results with those of electrochemical oxygenation of an alkene would also be presented.
The Nanomechanics and Nanodynamics of Confined Water
Authors: Khan Shah Haidar , Hoffmann Peter Manfred
Published: February 2020

From oil recovery to molecular biology, nanoconfined water plays important role in many areas of research. However, the mechanics and dynamics of nanoconfined water are not well understood. Over the last ten years, a number of groups have measured the mechanics of confined water using atomic force microscopy (AFM) or surface forces apparatus (SFA) – often with contradictory results. We use a high resolution AFM to measure the mechanics and dynamics of nanoconfined liquids. We have shown that water shows a dynamic “solidification” when confined to a few layers (Phys. Rev. Lett. 2010), a finding that explains the contradictory findings in earlier measurements and points to surprisingly complex behavior in this seemingly simple system. We also discovered an unusual relationship of viscous damping of nanoconfined liquids on the lateral size of the confinement region (App. Phys. Lett. 2014). Here we will review these findings, as well as present new findings such as Young’s modulus of nanoconfined liquids. Also, we will show the profound effect of ion concentration on the dynamics of water at the interface.