bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Size and Shape on the Electrochemical Conversion in FeF2 Nanoparticles: A Molecular Dynamics Study
Authors: Ma Ying
Published: February 2020

The increasing demand for high capacity power sources has stimulated much research in lithium ion batteries (LIBs). Recently, an alternative to the intercalation reaction, known as the conversion reaction, has been proposed where multiple valence states of the metal cation can be accessed during the redox cycle, thus leading to a higher energy density. Of special interests are conversion compounds including iron fluorides and iron oxyfluorides. By the use of carbon-iron (oxy)fluoride nano-composites, specific capacities of 540, 620 and 490 mAhg-1 have been demonstrated for FeF2, FeF3 and FeOxF2-x, respectively. Combined experimental and computationally studies have also shed light on the microscopic mechanisms of the electrochemical conversion observed in these materials, however, challenges still remain. In particular, the ionic diffusion pathways during charging and discharging are unclear. It is expected that by altering the size and shape of the nanoparticle, one can effectively modiy the ionic diffusion which may lead to increased electrochemical performance. For this purpose, reactive molecular dynamics simulation are carried out to study the charging and discharging in FeF2 nanoparticles with different sizes and shapes. Their effects on the diffusion process is analyzed, and their role in the macroscopic properties is discussed.
Exploring the Kinetics and Thermodynamics of Voltage Fade
Authors: Vu Anh , Walker Lee K. , Bareno Javier , Chen Zonghai , Lin Chi-Kai , Bass Dean A , Burrell Anthony K. , Bloom Ira
Published: February 2020

Layered-layered, lithium-, manganese-rich, nickel-manganese-cobalt (LMR-NMC) oxides are commonly used as cathode materials for lithium-ion batteries.  They can be thought of as composite materials consisting of (monoclinic) Li2MnO3 and (layered) Li(Ni1-a-bMnaCob)O2 (a>0; b<1) and written as xLi2MnO3▪(1-x) Li(Ni1-a-bMnaCob)O2.  With a desirable combination of low-cost and high energy density, they have attracted much attention for transportation applications. 

During cycling, these materials display voltage fade; i.e., the voltage vs. normalized capacity curve tends to droop.  Voltage fade reduces the energy density of the material during its lifetime and, consequently, a significant research effort is being devoted to prevent it altogether.  In an alternative approach, it may be possible to retard the voltage fade process to the point where it has only a minor impact on battery performance.  However, this approach requires detailed understanding of the kinetics and thermodynamic driving force of voltage fade, of which there is scant information in the literature.  In order to bridge this gap, we explore the effects of cycling temperature and oxygen availability during synthesis on voltage fade.

We cycled half-cells containing 0.5Li2MnO3•0.5LiNi0.375Mn0.375Co0.25O2 (or Li1.50Ni0.1875Co0.125Mn0.6875O2.50) cathodes at 25, 35, 45 and 55°C at a 20 mA/g rate. Analysis of the change in open-circuit voltage values from t=0 for each temperature showed that these data can be fit to a kinetic rate law containing t
1/2 and t terms.  Indeed, the dependence of the coefficients of these terms with temperature suggests two competing chemical processes.

 We explored the response of LMR-NMC oxides using Li1.50Ni0.15Co0.167Mn0.683O2.50 (HL) and Li1.30Ni0.15Co0.167Mn0.683O2.30 (LL) to changes in oxygen partial pressure during synthesis.  The oxygen partial pressures were 1.0, 2.0 × 10-1, 2.0 × 10-2, and 2.0 × 10-3 atm.  There were several partial-pressure-dependent trends in the data.  For example, examining the dependence of the deviation from nominal lithium stoichiometry on pO2 shows that it decreases with increasing pO2 for both the HL and LL material.  These and other trends will be discussed.

This work was performed under the auspices of the DOE Office of Vehicle Technologies, Hybrid and Electric Systems, under Contract No. DE-AC02-06CH11357. 

 The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
Heterogeneities of Ageing in a PEMFC Stack: Links Between Membrane Pinholes, Carbon Corrosion and End-of-Life
Authors: Dubau Laetitia , Castanheira Luis , Chatenet Marian , Maillard Frederic , Dillet Jérôme , Maranzana Gael , Abbou Sofyane , Lottin Olivier , De Moor Gilles , El Kaddouri Assma , Bas Corine , Flandin Lionel , Rossinot Elisabeth , Caqué Nicolas
Published: February 2020

Through a fruitful collaboration between three academic laboratories and a proton-exchange membrane fuel cell (PEMFC) manufacturer, important insights into the origin of cell voltage losses during on-site 110-cell-PEMFC-stack long-term operation (12,860 hours i.e.1.5 years) were provided [1]. The decline of the electrical performance is heterogeneous at the stack and the membrane-electrode assembly (MEA) scales, as shown by the monitoring of individual cell voltages during the aging process and segmented cell characterizations at the end-of-life. The long-term electrical performance losses were bridged to the degradation of the MEA constitutive materials. They mostly originate from the emergence of large size holes in the proton exchange membrane (PEM), which lead to detrimental hydrogen crossover. The hydrogen crossover in turn causes the formation of radical species that actively participate in the irreversible corrosion of the high-surface area carbon support in the cathode region neighboring the hole. The degradation of the carbon support further prevents the efficient access of the reactive gases and the proper removal of the reaction products. Depending on the size of the hole in the membrane, the localized loss of electrical performance may extend to the whole MEA, and depreciate its global performance (Figure 1).

This work was financially supported by Oseo-AII through the H2E project.

 References

[1] L. Dubau, L. Castanheira, M. Chatenet, F. Maillard, J. Dillet, O. Lottin, G. De Moor, C. Bas, L. Flandin, E. Rossinot, N. Caqué, “Carbon corrosion induced by membrane failure: the weak link of PEMFC long term performance”, Int J. Hydrogen Energy, 39 (2014) 21902.

Figure 1
Enhancing Activity and Pt Utilization in Pt-CsH2PO4 Composite Electrodes for Solid Acid Fuel Cells
Authors: Thoi V. Sara , Haile Sossina M
Published: February 2020

The performance and stability of solid acid fuel cells have been improved dramatically in recent years, but the continued reliance of these devices on Pt as a catalyst hinders wide-scale adoption. Electrospray fabrication of CsH2PO4-based electrodes has been shown to produce structures with high surface area, a feature which presumably provides a high number density of triple phase boundaries between the gas, catalyst, and the electrolyte. Here, high activity anodes with only 14 μg cm-1 of Pt were formed by electrospray deposition of a solution of Pt-decorated CNTs and CsH2PO4. The carbon nanotubes serve as interconnects to the current collector as well as a platform for interaction between the Pt and CsH2PO4. Using AC Impedance Spectroscopy and cyclic voltammetry, proton reduction and hydrogen oxidation were observed to occur at the low summed electrode overpotential of 0.1 V (or 0.05 V per electrode) with a current density of 42 mA cm-2. Furthermore, these Pt-CNT-CsH2PO4 composites have the highest Pt utilization to date for solid acid-based electrodes at 61 S mg-1, a 3-fold improvement over the state-of-the-art electrodes with a 50x decrease in Pt loading. We are also using electrospray techniques to form stable Pt-CsH2PO4-polymer composite cathodes. The inclusion of a polymer prevents electrolyte agglomeration and provides long-term stability under normal operating conditions.
Novel Gas Diffusion Layer for PEMFC Based on in-Situ Synthesized Carbon Nanofibers/Carbon Paper Composites
Authors: Gao Yuan , Zheng Jun-Sheng , Ye Li-Cheng , Ma Jian-Xin
Published: February 2020

Gas diffusion layer (GDL) plays an important role in water diffusion process and as a current collection and support of the membrane electrode for proton exchange membrane fuel cell. In this paper, a novel GDL based on in-situ synthesized carbon nanofibers/carbon paper composite was prepared by a chemical vapor deposition process. Scanning electron microscopy (SEM) and high resolution transmission electron microscope (HRTEM) results display that great mass of carbon nanofibers (CNFs) on carbon paper is considerably uniform and has a high length to diameter ratio. The N2 adsorption-desorption results reveal that the specific surface area of GDL based on CNFs/carbon paper composite is obviously larger than that of traditional GDL and the mesopores are the dominant pore structure for GDL based on CNFs/carbon paper composite. Raman spectra exhibit that GDL based on CNFs/carbon paper composite performs a high ratio of edge atoms to basal atoms. Polarization experiments prove that MEA based on GDL based on CNFs/carbon paper composite has a less open-circuit voltage loss, a higher current density and a higher power density compared with MEA based on traditional GDL.
Study of Water Retention Elevation on TiO2 /Nafion Membrane By Using Dynamic AFM
Authors: Kwon Osung , Son ByungRak , Kim Joogon , Park Sam , Lee Dong Ha
Published: February 2020

Among many technical barriers for the commercialization of proton exchange membrane fuel cells (PEMFC), low working temperature and carbon monoxide poisoning to catalyst have to be solved; however, they are not easy problems because they are related intrinsic properties of per-fluorinated Sulfonic Acid (PFSA) electrolytes such as Nafion. Recently, many groups report that TiO2/Nafion composite membrane shows the high proton conductivity under insufficient hydration on the membrane and high temperature operating condition. They conclude that the performance enhancement under low relative humidity and high temperature of the composite membrane is due to water retention increasing on the membrane. [1-2]

DMAFM, which is called tapping mode or non contact mode AFM measures amplitude and phase shift of specimen surface by amplitude modulation. The amplitude and phase shift are induced from the attraction force variation between tip and sample. The phase shift on the membrane is corresponding mechanical properties on the specimen such as viscosity, elasticity, and viscoelasticity.

We are synthesize the TiO2/Nafion composite membrane for high temperature PEMFC and characterize water retention on the membrane at variation conditions by using dynamic at mode atomic force microscopy (DMAFM). Characterization has done by two steps. Firstly, we simultaneously map topography and phase images of TiO2/Nafion composite membrane and pristine Naion under different humidity and temperature. The phase distributions on the composite membrane under different conditions are characterized. Secondly, the histograms from each image are extracted and statistically analyzed.

References

O. Savadogo, Emerging membranes for electrochemical systems Part II. High temperature composite membranes for polymer electrolyte fuel cell (PEFC) applications, Journal of Power Sources 127
(2004) 135–161

E. I. Santiago, R. A. Isidoro, M. A. Dresch, B. R. Matos, M. Linardi, and F.C. Fonseca,  Nafion–TiO2 hybrid electrolytes for stable operation of PEM fuel cells at high temperature, Electrochimica Acta 54, (2009), 4111–4117

Figure 1
Next Generation Anion Exchange Membranes Based on Perfluorinated Polymer Backbones
Authors: Page-Belknap Zachary , Kuo Mei-Chen , Pivovar Bryan S , Herring Andrew M
Published: February 2020

Perflourinated Anion Exchange Membrane (AEM) materials were first presented in 1987 by Toyo Soda Manufacturing Co., Ltd.  Many cation modifications have been reported, but chemistry was limited to a sulfonamide (-SO2-NR-) linkage from the sulfonyl fluoride (-SO2-F) precursor form.  In this project, we started with a sulfonyl fluoride precursor supplied by 3M company.  This is the same precursor used to fabricate the 3M perfluorinated sulfonic acid  (PFSA) proton exchange membrane and can be modified through several chemical approaches.  The 3M ionomer has a shorter side chain than NafionTM without the pendant trifluoromethyl (-CF3) group.  The  3M ionomer provides higher degree of crystallinity, higher modulus, and higher alpha transition temperature (Tα) at a given equivalent weight (EW). The high electron withdrawing character of the perfluorosulfonic acid backbone and side chain is ideal for proton exchange membrane fuel cells, as it makes acids more acidic and can be used to form chemically stable covalent linkages.  However, for perfluoro (PF) anion exchange membrane (AEM), the high electron withdrawing character of the polymer is a challenge as it makes bases less basic and can result in lower stability of chemical bonds. Several Perfluorinated Quaternium ammonium  (PFQA) polymers have been fabricated by us.  We have fabricated several films using this chemistry and measured their ionic conductivity as a function of temperature and relative humidity. Additional insights in to the films behavior was obtained from in-situ SAXS.  An ionomer peak is observed in the SAXS analogous to that observed for PFSA films , but its behavior with increasing swelling is not always the same in a PFQA than for the corresponding PFSA.
(Invited) Dissimilar Interfaces As a Driver to Oxygen Reduction on Perovskite Oxide Surfaces
Authors: Yildiz Bilge
Published: February 2020

Interfaces between dissimilar oxides are attracting significant interest for their potential role in accelerating charge transport and surface reaction kinetics. If well understood and controlled, they can provide a new way to enable high-performance solid-oxide fuel cells, separation membranes as well as fast switching memristors. For example, recent studies have demonstrated that cobaltite hetero-interfaces exhibit orders of magnitude faster oxygen reduction kinetics compared with either single phase. The interfacial strain fields, anisotropy, electronic and chemical interactions between the two phases are the likely mediators behind such an unprecedented enhancement. The underlying mechanisms must be understood quantitatively, so that we can go beyond isolated and empirically found interface structures to rationally designing dissimilar oxide interfaces with superior properties. Towards this goal, we have investigated the local electronic structure at nanometer resolution in model multilayer superlattices and vertical nanostructures that are made of dissimilar cobaltites. To accomplish this, we used a novel combination of in-situ scanning tunneling spectroscopy and focused ion beam milling. We found that the wide band-gap cobaltite is electronically activated at elevated temperatures through an interfacial coupling with a reducible cobaltite. Such electronic activation is expected to facilitate charge transfer to oxygen, and accelerate the reduction kinetics at the surface. Furthermore, based on our computational and experimental work, we have put forth elastic strain to be an important driver of the kinetics of surface reactions and diffusion in functional oxides, and demonstrated these concepts on fluorite, perovskite and Ruddlesden Popper structures. There remains still a large amount of open questions on how dissimilar oxide interfaces impact oxygen diffusion and oxygen exchange on the surfaces. However, these recent results are encouraging for an improved understanding of oxide hetero-interfaces at elevated temperatures and could enable new interfaces with fast oxygen transport and oxygen reduction kinetics.
Surface Composition of Layered Ruddlesden-Popper Lan+1NinO3n+1 (n = 1, 2 and 3) Epitaxial Films
Authors: Wu Kuan-Ting , Téllez Helena , Druce John , Burriel Mónica , Ishihara Tatsumi , Kilner John A. , Skinner Stephen J.
Published: February 2020

Layered Ruddlesden-Popper (RP) type oxides, formulated Lan+1NinO3n+1(n = 1, 2 and 3), have recently been suggested as candidates for intermediate temperature solid oxide fuel cell (IT-SOFC) cathodes. Compared to traditional cathodes (e.g. LSM), these mixed ionic-electronic conductors (MIECs) possess highly promising oxygen surface exchange kinetics, which is not limited to the triple phase boundary (TPB), but the entire surface exposed to the gas phase.

The oxygen surface exchange activity is strongly influenced by the surface composition and atomic surface structure where the adsorption and dissociation of molecular oxygen take place. These effects may influence the rate determining step [1], and consequently the ultimate efficiency of the SOFC device. More importantly, compared to bulk samples, the oxygen transport kinetics for thin-film samples is significantly dominated by the surface process [2]. A series of Lan+1NinO3n+1(n = 1, 2 and 3) epitaxial films have been deposited using pulsed laser deposition (PLD) technique for the fundamentally surface analysis [3]. It is therefore of great importance to understand the surface and near-surface chemical compositions and the structure (or termination) of the obtained films. These investigations will aid in the understanding of the electrochemical properties of lanthanum nickelate cathode materials in surface regions [4].

In this work, the kinetic nature of Lan+1NinO3n+1(n = 1, 2 and 3) epitaxial films deposited by PLD was systematically investigated using high-sensitivity low-energy ion scattering (HS-LEIS). The compositional analysis for the outermost and near-surface of these obtained films was also studied. The results reveal that the phenomena of surface reconstruction may decrease the active surface area during the deposition and post-treatment process of the thin-film materials.

References

[1]        S. B. Adler, Chem. Rev. 2004, 104, 4791.

[2]        G. Kim, S. Wang, A. J. Jacobson, C. L. Chen, Solid State Ionics 2006, 177, 1461.

[3]        K.-T. Wu, Y.-A. Soh, S. J. Skinner, Mater. Res. Bull. 2013, 48, 3783.

[4]        J. Kilner, S. Skinner, H. Brongersma, J. Solid State Electr. 2011, 15, 861.
(Invited) Enhancement of Surface Oxygen Exchange Kinetics for Pr0.1Ce0.9O2-
δ with Deposition of La or Sm Oxide
Authors: Zhao Liang , Perry Nicola H. , Sasaki Kazunari , Bishop Sean R.
Published: February 2020

Fast oxygen exchange kinetics, a key figure of merit in solid oxide fuel cell (SOFC) electrodes, is often dramatically hindered by the presence of even small concentrations of impurities at the surface. Si, for example, is common in ceramics processing. As discussed in this presentation, it was found that rapid degradation of oxygen exchange kinetics occurred on dense thin films of Pr0.1Ce0.9O2-d (PCO), a mixed ionic electronic conducting electrode for SOFCs. A new optical transmission relaxation (OTR) technique was developed to aid in measuring kinetics on the bare film surfaces. A key advantage of this technique is that it does not require current collectors typical of conventional measurements. Si was identified by TEM and XPS as a significant surface impurity, which forms a blocking layer on the electrode surface. Deposition of a La oxide film was found to result in full recovery of oxygen exchange kinetics on the measured sample. La and Si oxides were found to interact with each other as identified by a shift in the O1s XPS peak and a systematic OTR study of films that likely react with Si (e.g. La, Sm oxides) and those that do not (e.g. Nb, Ti, Zn oxides). These results indicate that La may "clean" the surface of the SOFC electrode, thereby dramatically improving oxygen transport kinetics. Preliminary measurements of OTR on a La-PCO solid solution indicates improved long-term electrode kinetics stability, demonstrating the commercial potential of this method to achieve Si impurity tolerance.
Visible Light Responsive B12-TiO2 Hybrid Catalyst Composed of Interfacial Complexation
Authors: Shimakoshi Hisashi , Yonemura Shunsuke , Hisaeda Yoshio
Published: February 2020

The CoI species of the cobalamin derivative (B12) is widely known as a supernucleophile that forms an alkylated complex by reaction with an alkyl halide.  The alkylated complex is a useful reagent for forming radical species as the cobalt-carbon bond is readily cleaved homolytically.1  Our research interest is focused on the application of this catalytic system to various molecular transformations.2  Recently, we have reported the unique catalysis of the cobalamin derivative (B12)-titanium oxide (TiO2) hybrid catalyst in which the B12 complex, cyanoaquacobyrnic acid (CoIII oxidation state), is immobilized on the surface of TiO2 and the B12 complex is reductively activated to form the CoI species by electron transfer from TiO2 under UV-light irradiation.3  The hybrid catalyst mediated the dehalogenation of various organic halides and was applied to the radical-mediated organic reaction via an alkylated complex as a catalytic intermediate.  Though the great advantage of the catalyst is the facile and efficent formation of CoI species by light irradiation, UV light irradiation was required for band gap excitation of TiO2 semiconductor.  To overcome this problem, we synthesized new B12-TiO2 hybrid catalyst (B12-TiO2-Cat) composed of interfacial complexation with catechol as shown in Figure 1a.  As a charge transfer band ascribed to catechol to TiO2 appear in visible region,4 this new hybrid catalyst is expected to work under visible light irradiation.  Futhermore, exploiting the interparticle electron transfer process in the B12-TiO2 and Cat-TiO2 combination system as shown in Figure 1b was investigated.

References:

1. (a) Brown, K. L. Chem. Rev., 2005, 105, 2075; (b) Hisaeda, Y.; Shimakoshi, H., in Handbook of Porphyrin Science, Kadish, K. M.; Smith, K. M.; Guilard, R., Eds. World Scientific: Singapore, 2010; Vol. 10, pp 313-370.

2. (a) Jing, X.; Shimakoshi, H.; Hisaeda, Y. J. Organomet. Chem., 2015, in press; (b) Zhang, W.; Shimakoshi, H.; Houfuku, N.; Song, M.; Hisaeda, Y. Dalton Trans., 2014, 2014, 43, 13972.

3. Shimakoshi, H.; and Hisaeda, Y. et al, (a) ChemPlusChem, 2014, 79, 1250-1253 (Back cover article); (b) Chem. Commun., 2011, 6427-6429; (c) Dalton Trans, 2010, 39, 3302-3307; (d) Chem. Lett., 2009, 38, 468-469; (e) Bull. Chem. Soc. Jpn., 2010, 83, 170-172.

4. (a) Ikeda, S.; Abe, C.; Torimoto, T.; Ohtani, B. J. Photochem. Photobiol. A: Chem. 2003, 160, 61; (b) Tae, E. L.; Lee, S. H.; Lee, J. K.; Yoo. S. S.; Kang, E. J.; Yoon, K. B. J. Phys. Chem. B
2005, 109, 22513; (c) Varaganti, S.; Ramakrishna G. J. Phys. Chem. C
2010, 114, 13917; (d) Kamegawa, T. Seto, H.; Matsuura, S.; Yamashita, H. ACS Appl. Mater. Interfaces, 2012, 4, 6635.

Figure 1
Mechanistic Studies of the Cathodic Cleavage of Diphenylacetaldehyde Derivatives
Authors: Fry Albert Joseph , Tsui Elaine , Baum Evan , Sheludko Boris
Published: February 2020

At the 2014 Electrochemical Society Orlando meeting, we reported the electrochemical oxidation of 1,1-diphenylacetaldehyde (1) in the presence of an equimolar quantity of any of several alcohols (2) in acetonitrile in an undivided cell containing two carbon electrodes (Scheme 1). When the electrolysis was interrupted at its mid-point it was possible to isolate a-alkoxy aldehydes (3) in good yield. When the electrolysis was continued past this point, compounds 3 were further converted to benzhydryl ethers (4)in excellent yields. Since 1 is converted to 3 at the anode via 2, we initially assumed that the ethers 4 are also produced at the anode by subsequent oxidation of 3 to 4.However, two control experiments disproved this hypothesis. First, 3 (independently synthesized by reaction of alpha-bromo-diphenylacetaldehyde2 with cyclohexanol in the presence of silver tetrafluoroborate3) was placed in the anode compartment of a divided cell. It was found to be stable to anodic oxidation. On the other hand, when it was placed in the cathode compartment, it was quickly decarbonylated to 4a

. Likewise, when electrolysis of 1 was carried out in the anode compartment of a divided cell, 3 was produced but was found to be stable to further oxidation. On the other hand, when 3 was placed in the cathode compartment of the divided cell it was readily converted to 4 (Scheme 1). The mechanism of this unusual mild cathodic cleavage reaction is the subject of this report. We hypothesized that the reaction involves initial attack on the carbonyl group by a nucleophilic component of the medium  (X), followed by ejection of a benzhydryl anion (6) from the initial adduct 5. Protonation of 6 by solvent would then afford 4 We believe that X is superoxide ion, generated by reduction of cathodic reduction of traces of oxygen in the medium. Indeed, electrolysis of 3 in the cathode compartment while passing oxygen through the solution quickly converted  3 to 4. Furthermore, this suggests that it should be possible to convert 3 to 4 in a separate non-electrochemical experiment. Indeed, addition of potassium superoxideto a solution of 3 in acetonitrile was found to produce 4 in high yield (Scheme 2). Interestingly, benzophenone (8) is produced when 1 is either (a) electrolyzed in the cathode compartment with oxygen or (b) treated with potassium superoxide. This conversion probably involves initial hydroperoxidation of 3 at the a-position, followed by nucleophilic addition to the carbonyl group and fragmentation. Experiments testing the further scope of these cathodic decarbonylative cleavages will be described.

Figure 1
Nitrogen Containing O- and P-Quinones As Cathode Materials for Lithium Batteries
Authors: Shimizu Akihiro , Tsujii Yutaka , Kuramoto Hiroki , Nokami Toshiki , Inatomi Yuu , Hojo Nobuhiko , Yoshida Jun-ichi
Published: February 2020

Organic cathode materials have received significant research interest as cathode materials of lithium-ion batteries because of sustainability and flexibility. However, they suffer from lower voltages than inorganic materials. To increase the voltage of batteries using organic cathode materials without decreasing the capacity, we replaced the CH moieties b to the carbonyl group of quinones with nitrogen atoms. The coordination of nitrogen atoms to lithium ions in the reduced forms and the greater electronegativity of nitrogen than carbon make reduction energetically more favorable. The lithium batteries using the nitrogen containing o- and p-quinones as cathode materials exhibited voltages higher than 3.0 V (the first stage).
Insights into the Distance Dependence of the Electron Transfer Rate through the Monolayer Protecting Au25 Nanoclusters
Authors: Maran Flavio , Antonello Sabrina , Dainese Tiziano , De Nardi Marco , Venzo Alfonso
Published: February 2020

The monolayer that protects small gold nanoparticles is often represented as the 3D equivalent of 2D self-assembled monolayers (SAMs) on extended gold surfaces. However, despite the growing relevance of monolayer-protected clusters (MPCs) in important applied areas, such as catalysis and nanomedicine, our knowledge of the structure of these 3D SAMs is quite limited. This is particularly true for the MPCs displaying molecule-like properties (core diameters of less than 1.6 nm). We prepared a large series of monodisperse Au25(SCnH2n+1)18 clusters and studied how electrons tunnel through these monolayers. Heterogeneous electron-transfer results, nicely supported by 1H NMR spectroscopy and molecular dynamics results, provide an interesting picture of the effective structure of the 3D monolayers protecting ultrasmall gold clusters. The distance dependence of the electron-transfer rate in solution is also compared with that of electron transport in the solid state.
The Effect of Electron Transfer on a Strongly H-Bonded Ureidopyrimidinone Dimer
Authors: Smith Diane K. , Clare Laurie A.
Published: February 2020

There is much current interest on the role that H-bonding intermediates play in the mechanism of proton-coupled electron transfer. Recently we have been examining this phenomena in detail using an electroactive phenylenediamine based urea, U(H)H (Clare et al., J. Am. Chem. Soc. 2013, 135, 18930-41).  This compound appears to undergo a reversible one electron oxidation to the radical cation in methylene chloride.  We have shown that in fact the oxidation corresponds to two electron oxidation of half the ureas to the quinoidal form, accompanied by proton transfer to the dimethylamino group and subsequent deactivation of the other half of the ureas, 2U(H)H = U(H)+ + H(U)H+ + 2 e-. The reaction gives chemically irreversible voltammetry in acetonitrile as would be expected given that the product quinoidal cation, U(H)+, is harder to reduce than the initially formed radical cation.  However, it gives reversible voltammetry in methylene chloride because the reverse reaction can proceed through the H-bonded complex formed between U(H)+ and H(U)H+, which is easier to reduce than the radical cation alone.  

    We have also studied the voltammetry of U(H)H in the presence of guest molecules that can H-bond to the two urea NH’s.  In these cases, we observed similar overall electrochemistry, with proton transfer accompanying the oxidation of U(H)H.  In contrast, different behavior is observed when the U(H)H redox couple is incorporated into a ureidopyrimidinone framework, 1.  This structure is well-known to form strong H-bonded homo-dimers in less polar solvents such as methylene chloride, and this behavior is maintained with the U(H)H derivative.  As with U(H)H, cyclic voltammetry of 1 in methylene chloride shows a reversible, apparent one electron oxidation. However, there is also an irreversible, apparent half electron oxidation at slightly more positive potentials.  While we were expecting that the reversible one electron oxidation with 1 corresponded to a similar reaction as seen with U(H)H by itself and with the two H-bond guests, UV/Vis spectroelectrochemical evidence along with titration studies with a non-electroactive ureidopyrimidinone strongly suggest that in this case the apparent one electron oxidation is really that, with both ureas in the dimer being oxidized to the radical cation without proton transfer.  Despite the electrostatic repulsion, the dimer holds together at mM concentrations as evidenced by the reversibility of the CV wave.  However, it appears with the removal of one more electron, the dimer breaks apart at these concentrations.  This behavior is notable because the ureidopyrimidinones are currently under intensive investigation as components of supramolecular polymers that possess unique self-healing properties.  Existing systems use heat to break apart the dimers and allow the polymer to self heal.  This work shows that electron transfer may be able to provide a more directed approach to control the fluidity of these materials.

Figure 1
Studies on Aqueous Redox Flow Batteries Based on Water-Soluble Quinone Redox Couples
Authors: Yang Bo , Hoober-Burkhardt Lena , Krishnamoorthy Sankarganesh , Prakash G. K. Surya , Narayan S. R.
Published: February 2020

Abstract

Organic Redox Flow Batteries (ORBAT) based on aqueous electrolyte present a promising solution for grid-scale and distributed electrical energy storage direly needed for integrating the intermittent renewable energy sources because the proposed materials are potentially low cost, eco-friendly, and sustainable [1].  In ORBAT, water-soluble organic redox couples such as benzoquinone and anthraquinone derivatives can be used as both the positive and negative materials.  These materials are exhibit fast kinetics of electron transfer and high charge capacity. The use of water as the solvent lowers the cost and makes the system safe and eco-friendly. In addition, ORBAT does not use any heavy metals.  Researchers at Harvard have also been working on similar systems using bromine as the positive electrode material [2]. Thus, the overall cost can be low enough to achieve the DOE-specified target of $100/kWh for the entire battery system.

In our previous study [1], we have constructed redox flow cells based on quinone compounds, such as 4,5-Dihydroxy-1,3-benzenedisulfonic acid (DSQ) and Anthraquinone-2,6-disulfonic acid (AQDS) and measured the rechargeability and current-voltage characteristics. Since then we have conducted further cycling of these cells. No significant loss of capacity was observed over at least a 100 cycles (Figure 1 a).

However, the charge-discharge efficiency is low initially (Figure 1 b), and this is now understood to arise from the conversion of the oxidation product of DSQ by the Michael Addition reaction to the 2,4,5- trihydroxybenzene-1,3-disulfonic acid [3]. We will describe the polarization characteristics and the mechanism of this reactant transformation as studied by electrochemical methods, NMR, and UV spectroscopy.  These studies offer insights into the requirements for the design of new molecules.

Acknowledgement

The work presented here was funded by ARPA-E (Open FOA DE-AR0000353) and the Loker Hydrocarbon Institute of University of Southern California.

Figure 1. Cycling experiment of 1M DSQ, 1M AQDS, 1M sulfuric acid. Charge and discharge at 80mA/cm2. a) Charge-discharge capacity. b) Charge-discharge efficiency.

References

1. Bo Yang, Lena Hoober-Burkhardt, Fang Wang, G. K. Surya Prakash, and S. R. NarayananJ. Electrochem. Soc. 2014, 161(9).

2. Brian Huskinson, Michael P. Marshak, Changwon Suh, Machael J. Aziz, etc. Nature 505 195-198 January, 2014.

3. Xu, Y.; Wen, Y.;  Cheng, J.; Yanga, Y.;  Xie, Z.; Cao, G. WNWEC, Nanjing, China, Sept 24-26, 2009.Volume:

Figure 1
Tridentate Metal Coordination Complexes As Active Species for Non-Aqueous Redox Flow Batteries
Authors: Laramie Sydney , Brooner Rachel , Sanford Melanie , Thompson Levi T
Published: February 2020

Organometallic complexes with non-innocent ligands are excellent candidates for use in non-aqueous redox flow batteries because of their potential for multiple electron transfer. In this study, the electrochemical properties and solubility of 2,6-bis(1,2,3-triazol-4-yl)pyridine (BTP) and terpyridine (tpy) metal coordination complexes were investigated. A range of BTP ligands were synthesized with various functional groups to understand the impact of the ligand on the properties of Fe, Co, and Ni complexes. The results demonstrate that electron withdrawing groups on the pyridine rings lead to a higher number of redox couples and improved solubility. Additional modifications indicate further functionalization has a strong impact on solubility while only a minimal effect on the electrochemistry. This allows the tuning of these complexes to achieve desirable electrochemical properties and solubility. Based on its attractive combination of reversibility and solubility, 2,6-bis(di(3-(2-methoxyethyl)-1,2,3-triazol-4-yl)-4-butoxycarbonylpyridine)iron(II) tetrafluoroborate(BTP-1) was used to evaluate the cycling stability of the BTP complexes. Bulk electrolysis and charge/discharge experiments in a static H-Cell revealed that this complex had limited stability. Charge/discharge experiments with unsubstituted Fe(tpy)2 show improved stability, but limited solubility. A tpy complex with analogous functionalization to BTP-1 was synthesized and evaluated to exploit both the stability of the terpyridine and the solubility of the BTP metal coordination complexes. This study demonstrates the potential of BTP and tpy metal coordination complexes for use as active species in non-aqueous redox flow batteries.
Towards Long Cycle Life of Soluble Lead-Acid Redox Flow Batteries
Authors: Chen Hsun-Yi , Chang Chih-Wei
Published: February 2020

A redox flow battery (RFB), with the freedom to design its power and energy capacity separately, is one of the most promising candidates for grid power management. The soluble lead acid RFB, which possesses characteristics of simple structure and inexpensive comprising materials, stands out for large-scale stationary storage. However, state-of-the-art lead-acid RFBs have limited cycle life and are not applicable to power grid applications. This study focuses on developing a single-flow, membrane-less, soluble lead acid RFB for grid-scale energy storage.

First, a pilot RFB based on soluble lead-acid chemistry and with a 2 cm2 electrode area is designed and constructed. A parasitic pump with controllable pumping rate is utilized to circulate the electrolyte through the cell. Composite electrodes comprised of carbon and adhesive polymers are fabricated through hot pressing and slurry drying techniques. Different routes have been tried to prepare methanesulfonic acid solution, which serves to dissolve lead, to achieve desired concentrations. Various materials, including 316 stainless steel and graphite, are tested for their long-term stability when they serve as positive and negative current collectors. The performance of lead-acid RFBs with different combination of components is compared. We have achieved voltage efficiency and columbic efficiency both of over 80%, and energy efficiency of over 60% for over 100 cycles of deep charge and discharge.

In addition, activation of electrodes at low current density before cycling is found to be necessary for higher charge efficiency and longer cycle life. Although the mechanism is not completely understood, we find that the activation procedure able to enhance the attachment of lead dioxide on the positive electrode surface, which in turn leads to improved electrode stability. Electrochemical impedance spectroscopy is conducted and the charge transfer resistance after activation is found to be significantly reduced. Other pertinent thermophysical properties are acquired through electrochemical measurements.

Based on our optimization experience of the pilot cell, a scaled-up, soluble lead acid RFB with a 36 cm2 area electrode is built. A magnetic drive pump is used to circulate the electrolyte through the electrolyte storage tank and the battery. The attached figure demonstrates the performance of lead acid redox flow battery with a 36cm2 of electrode area, under an operation current density of 12mA/cm2. New challenges facing scaled up lead-acid RFBs are investigated. For example, after the scaled-up lead-acid RFB is cycled for a long time, we often find certain yellow color byproduct resides at the corner of the electrode, which was rarely seen in the 2 cm2 pilot cell. We believe the byproduct is induced by non-uniform current density distribution in a larger cell. Other factors that could facilitate extension of cycle life and improvement of charge/discharge efficiency will be discussed.

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Low Temperature Preparation and Electrochemical Properties of LiFeSi2O6
Authors: Zhou Shiliang , King Graham , Scanlon David , Sougrati Moulay-Tahar , Melot Brent
Published: February 2020

The growing demand for Li-ion batteries requires the development of inexpensive materials that can be made in a sustainable fashion. Here we report a new low-temperature preparation for and the first electrochemical characterization of LiFeSi2O6, a hugely Earth-abundant, rock-forming mineral. We have found that LiFeSi2O6 undergoes a reversible electrochemical reaction against Li centered around 2 V with capacities near 60% of the theoretical maximum.

However, an extremely slow rate of cycling (C/200) or small particle size of LiFeSi2O6 is required to obtain a reasonable capacity, which indicates that Li+-(de)insertion in LiFeSi2O6 is kinetically hindered. To understand the origin of this kinetic hindering, we conducted Ritveld refinement of the atomic displacement parameters of LiFeSi2O6 against the neutron diffraction data obtained from the HIPD beamline at Los Alamos National Laboratory. The results not only allowed us to clarify the preferred diffusion pathway for Li+ ions in LiFeSi2O6, but also enabled us to link the kinetic hindering in the material to its structural rigidity, which is indicated by the flat-shaped atomic displacement sphere of oxygen atoms along the polyhedra linkages in the LiFeSi2O6 structure.
(Invited) Ultrasensitive Electroanalytical Detection and Study of Single Nanoparticle Catalysts
Authors: Stevenson Keith J
Published: February 2020

The continued interest in nanoparticles (NPs) is due to their numerous properties such as active components in sensors, optics,  energy conversion and energy storage applications.   The development of new analytical tools for characterizing NP properties  in a fast and reproducible manner is sorely needed.  Especially for those to correlate structure-function relationships of NPs and optimize NPs activity for in homogeneous and heterogeneous catalysis. The precise characterization of individual NPs in terms of their size, shape and composition would faciliate better fundamental understanding.  The development of "electrocatalytic amplification" is one such method where single NPs are detected  by measuring electrocatalytic current (or potential) due to the electrochemical processes (oxidation/reduction of the species present in solution) occurring on the surface of the NP whenever a NP collides with an inert UME (gold, platinum, platinum oxide and carbon) which otherwise cannot catalyze the reaction.

           Here we report the application of electrocatalytic amplification method employing inert (non-catalytic) UMEs  (Hg, Bi, Ga) as electrodes for evaluating the catalytic activity of Pt NPs of different shapes (hexagones and cubes) for hydrazine oxidation.  To precisely correlate structure function relationship of Pt NPs, Pt NPs without ligands referred as "naked Pt NPs" were used in this study.  "Naked Pt NPs" were obtained by following the procedure reported previously where polyacrylate capped Pt NPs were synthesized first followed by a strong base treatment (potassium hydroxide) to remove the ligand (polyacrylate) off the NP's surface.  From TEM the average size of polyacrlylate capped hexagonal and cubic Pt NPs was found to be 11.2 ± 2.8 nm and 11.8 ± 1.7 nm respectively.  Hexagonal Pt NPs possess (100) and (111) facets where cubic Pt NPs possess (111) planes as preferential surface facets.  Complete removal of polyacrylate ligand from the Pt NP's surface was confirmed by obtaining CVs, TGA and IR spectra of polyacrylate capped Pt NPs before and after KOH treatment.  Also, Pt NPs retained their size and structure after base treatment.  The integrated charge passed per spike during single NP collision for polyacrylate capped hexagonal and cubic Pt NPs concentrated over a range of (120-210) and (40-100) pC respectively.  Whereas, for naked hexagonal and cubic Pt NPs the integrated charge passed per spike during single NP collision concentrated over a range of (180-400) and (60- 180) respectively.  Naked Pt NPs displayed higher catalytic activity for hydrazine oxidation compared to polyacrylate capped Pt NPs of similar size and size.
Lithium-Ion Battery Cathodes Coated with Ultra-Thin Conductive Films for Long Cycle Life
Authors: Patel Rajankumar L. , Liang Xinhua
Published: February 2020

Atomic layer deposition (ALD), as a thin film deposition technique, has been explored as a viable path to improve the performance of lithium-ion batteries. However, a trade-off between the species transport (capacity) and protection (lifetime), resulting from the insulating properties of ALD films, is the key challenge in ALD technology. Here we report a breakthrough to overcome this trade-off by coating an ultra-thin conformal conductive film by ALD on the surfaces of LiMn2O4 particles. The particles coated with optimized film thickness exhibit a significant improvement in capacity and cycling performance compared to uncoated and insulating ALD film (e.g., Al2O3 and ZrO2) coated samples both at room temperature and 55 °C for long cycling numbers.
Engineered Si Sandwich Electrode: Si Nanoparticles/Graphite Sheet Hybrid on Ni Foam for Next-Generation High-Performance Lithium-Ion Batteries
Authors: Gao Chuihui , Zhao Hailei , Lv Pengpeng
Published: February 2020

Si-based electrodes for lithium ion batteries typically exhibit high specific capacity but poor cycling performance. A possible strategy to improve the cycling performance is to design novel electrode nanostructure. Here we report a design and fabrication of Ni/Si-Nanoparticles/Graphite Clothing hybrid electrodes with sandwich structure. An efficient dip-coating of Si-NPs combined with carbon deposition was adopted to synthesize the unique architecture, where the Si-NPs are sandwiched between the Ni matrix and the graphite clothing. This material architecture offers many critical features that are desirable for high-performance Si-based electrodes, including efficient ion diffusion, high conductivity, and structure durability, thus ensuring the electrode with outstanding electrochemical performance (reversible capacity of 1800 mA h g-1 at 2 A g-1 after 500 cycles). In addition, the hybrid anode does not require any polymeric binder and conductive additives, and holds great potential for application in Li-ion batteries.

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Improving Seebeck Coefficient of Thermogalvanic Cells Using Polyelectrolytes
Authors: Gunawan Andrey , Tarakeshwar Pilarisetty , Buttry Daniel A. , Mujica Vladimiro , Phelan Patrick E
Published: February 2020

Thermogalvanic cells, also known as thermoelectrochemical cells or simply as thermocells, have recently attracted a lot of attention because of their immense potential in converting low-grade thermal energy to electricity. The thermal temperature coefficient of electrode potential (α) in a thermogalvanic cell is directly proportional to the change in entropy (ΔS) of the redox reaction in the cell through the relation (α = ∂E/∂T = ΔS/nF), where E is the cell potential, T the temperature, n the number of electrons involved in the reaction, and F the Faraday’s constant. Although the nature of effects are different, α is often referred to as the Seebeck coefficient. In an ideal thermogalvanic cell, one therefore prefers to employ a redox couple exhibiting the largest α. Therefore, in the current study we discuss an alternate method to enhance ΔS for the electron transfer process. Thus, by coupling a redox process to solution phase complexation, we show that there is marked increase in both the change in entropy and the resulting α. While the change in entropy was calculated using quantum-chemical methods, α was experimentally measured for a Cu/Cu2+ thermogalvanic cell. The results indicate that a complexation of the Cu2+ species with a dissolved polymer, such as poly(acrylic acid) (PAA) or ethylenediaminetetraacetic acid (EDTA), dramatically improve α by up to 75%. We believe, that this novel approach to enhance α, would prove to be useful in the development of thermodynamically more efficient thermogalvanic cells.