bluuebunny/crossref_metadata_2025_split 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
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.
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.
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
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