| 1. |
- Ciosek Högström, Katarzyna, 1984-, et al.
(författare)
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Impact of the flame retardant additive triphenyl phosphate (TPP) on the performance of graphite/LiFePO4 cells in high power applications
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 256, s. 430-439
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Tidskriftsartikel (refereegranskat)abstract
- This study presents an extensive characterization of a standard Li-ion battery (LiB) electrolyte containing different concentrations of the flame retardant triphenyl phosphate (TPP) in the context of high power applications. Electrolyte characterization shows only a minor decrease in the electrolyte flammability for low TPP concentrations. The addition of TPP to the electrolyte leads to increased viscosity and decreased conductivity. The solvation of the lithium ion charge carriers seem to be directly affected by the TPP addition as evidenced by Raman spectroscopy and increased mass-transport resistivity. Graphite/LiFePO4 full cell tests show the energy efficiency to decrease with the addition of TPP. Specifically, diffusion resistivity is observed to be the main source of increased losses. Furthermore, TPP influences the interface chemistry on both the positive and the negative electrode. Higher concentrations of TPP lead to thicker interface layers on LiFePO4. Even though TPP is not electrochemically reduced on graphite, it does participate in SEI formation. TPP cannot be considered a suitable flame retardant for high power applications as there is only a minor impact of TPP on the flammability of the electrolyte for low concentrations of TPP, and a significant increase in polarization is observed for higher concentrations of TPP. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
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| 3. |
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| 4. |
- Winter, Johannes, et al.
(författare)
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Charge transfer in alkali-metal-doped polymeric fullerenes
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54, s. 17486-17492
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Tidskriftsartikel (refereegranskat)abstract
- We present room-temperature Raman measurements of pressure-polymerized C60 and compare them with the spectra of RbC60 in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized C60 and the rubidium-doped orthorhombic compound, have the same overall structure and the AC60 compounds can be considered as the doped species of the C60, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency Hg(7) and Hg(8) modes. The low values for the coupling constants compared to the ones in the K3C60 can explain the lack of superconductivity in the AC60 compounds.
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| 5. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Ab initio calculations, Raman and NMR investigation of the plastic crystal di-methyl pyrrolidinium iodide
- 2003
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Ingår i: Electrochimica Acta. - 0013-4686. ; 48:14-16, s. 2283-2289
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Tidskriftsartikel (refereegranskat)abstract
- Above 110 °C the symmetric di-methyl-pyrrolidinium iodide salt forms a plastic crystal phase of interest in the area of new electrolyte materials. In this study ab initio calculations of this material has been conducted in order to assign the vibrational spectra. Raman spectroscopy measurements on the solid salt as well as on the salt dissolved in different solvents has been performed and these have been compared to the theoretical spectra. Furthermore, Raman spectra as a function of temperature have been recorded to investigate possible changes in inter-ionic interaction and/or structure through the phase transition. 1 H NMR linewidth measurements as a function of temperature showed a large decrease in linewidth above 100 °C, attributed here to an increase in mobility in agreement with a previously reported phase transition at ∼ 110 °C. © 2003 Elsevier Science Ltd. All rights reserved.
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| 6. |
- Adebahr, Josefina, et al.
(författare)
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Cation coordination in ion-conducting gels based on PEO-grafted polymers
- 2000
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Ingår i: Solid State Ionics. - 0167-2738. ; 135:1-4, s. 149-154
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Tidskriftsartikel (refereegranskat)abstract
- Ionic conducting polymer gels prepared from PEG-grafted acrylates, ethylene carbonate (EC), dimethyl carbonate (DMC), and LiPF6 are studied by means of infrared and Raman spectroscopy. It is found that the presence of grafted PEO chains substantially changes the coordination of lithium cations from 'cation-solvent' to 'cation-polymer'. Spectroscopic studies show that Li+-PEO coordination is strongly favored in competition with the solvent molecules and dominates completely at ether oxygen to Li-cation ratios (O:Li) of 10:1 and 5:1. At an O:M of 4:1 a solvent-cation interaction arises, in agreement with previously reported MD calculations of a preferred coordination number of 5 in similar systems. The results suggest that the complex interactions which determine long time stability and ionic transport properties can be designed by functionalization of the polymer backbone in PMMA-based gel electrolytes.
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| 7. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Enhancement of ion dynamics in PMMA-based gels with addition of TiO2 nano-particles
- 2003
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Ingår i: Electrochimica Acta. - 0013-4686. ; 48:14-16, s. 2099-2103
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Tidskriftsartikel (refereegranskat)abstract
- Solvent and ion dynamics in PMMA based gels have been investigated as a function of the loading of nanosized TiO 2 particles. The gels have a molar ratio of 46.5:19:4.5:30 of ethylene carbonate (EC), propylene carbonate (PC), lithium perchlorate and PMMA, respectively. A series of samples with 0, 4, 6 and 8 wt.% TiO 2 filler were investigated. The diffusion coefficients for the lithium ions and for the two solvents (EC and PC) were investigated by pfg-NMR. It was shown that the addition of filler to the gel electrolytes enhances the diffusion of the cations, while the diffusion of the solvents remains constant. Raman measurements show no significant changes in ion-ion interactions with the addition of fillers, while the ionic conductivity is seen to decrease. However, the sample with 8 wt.% TiO 2 had a conductivity close to that of the unfilled sample. © 2003 Elsevier Science Ltd. All rights reserved.
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| 8. |
- Adebahr, J, et al.
(författare)
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Ion and solvent dynamics in gel electrolytes based on ethylene oxide grafted acrylate polymers
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106 .- 1089-5647. ; 106:47, s. 12119-12123
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Tidskriftsartikel (refereegranskat)abstract
- Multinuclear pulsed field gradient NMR measurements and theological viscosity measurements were performed on three series of polymer gel electrolytes. The gels were based on a lithium salt electrolyte swollen into a copolymer matrix comprising an acrylate backbone and ethylene oxide side chains. In each series the side chains differed in length and number, but the acrylate-to-ethylene oxide ratio was kept constant. It was found that the self-diffusion coefficient of the cations was much lower than that of the anions, and that it decreased rapidly when the side chains got longer. In contrast, the self-diffusion coefficient of the anions was found to be independent of chain length. In the gel electrolytes, the diffusion coefficients of the solvent molecules are relatively constant despite an increased viscosity with increasing length of the side chains. However, in saltfree gels made for comparison, the diffusion coefficients of the solvent molecules decreased with, increasing length of the side chains, which is consistent with an increased viscosity.
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| 9. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Ion transport in polymer electrolytes containing nanoparticulate TiO2: The influence of polymer morphology
- 2003
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 5:4, s. 720-725
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that composite polymer electrolytes, formed by dispersing nanosized ceramic particles in polyether-based electrolytes, have improved ion transport properties as compared to their unfilled analogues. In the present study polymer electrolytes with different loadings of nano-sized ceramic particles (TiO 2 ) and different polymer chemistry and morphology have been investigated. Of special interest are filler induced effects on polymer, solvent and cationic mobility. Partly crystalline polymer electrolytes based on poly(ethylene oxide) have been compared to fully amorphous polymer electrolytes based on a polyether urethane, as well as gel electrolytes based on PMMA. 7 Li pfg-NMR, linewidth and spin-spin relaxation times as well as 1 H pfg-NMR and spin-spin relaxation times, were measured as a function of temperature and composition. The 1 H spin-spin relaxation measurements reveal increased average polymer mobility with the addition of filler up to a maximum at 4 and 8 wt.% TiO 2 for the fully amorphous and the partly crystalline electrolytes, respectively. The 7 Li linewidth measurements for the fully amorphous system show a broadening of the linewidth with addition of filler. Based on variable temperature measurements this broadening is interpreted as a result of the inhomogeneity introduced by the filler particles. Pulsed field gradient (pfg) diffusion measurements were employed to determine ion and solvent self-diffusion coefficients. In the case of the PMMA-based gel electrolyte and the fully amorphous electrolytes enhanced cation self-diffusion was observed upon addition of TiO 2 .
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| 10. |
- Adebahr, Josefina, et al.
(författare)
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Li-7 NMR measurements of polymer gel electrolytes
- 2002
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Ingår i: Solid State Ionics. - 0167-2738. ; 147:3-4, s. 303-307
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Tidskriftsartikel (refereegranskat)abstract
- Ion conducting polymer gels prepared from (ethylene oxide)(n) grafted methacrylates, ethylene carbonate (EC), gamma butyrolactone (gBL), and lithium hexafluorophosphate are studied by means of nuclear magnetic resonance spectroscopy, This study shows that there are at least two possible lithium sites with different mobility. The lithium-ions with lower mobility dominate at room temperature, but this is changed as the temperature is increased. The NMR results also show that the Li-7 spin-spin relaxation time decreases with increasing length of the grafted ethylene oxide side chains, indicating a stronger interaction between the polymer and the Li-ions, and hence, a lower mobility of the Li-ions. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 11. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Lithium coordination and mobility in gel electrolytes based on an acrylate polymer with ethylene oxide side chains
- 2003
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 13:4, s. 814-817
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Tidskriftsartikel (refereegranskat)abstract
- Multinuclear NMR has been used to investigate the structure and mobility of a series of polymer gel electrolytes. The co-polymers used as matrixes in the gels have acrylate backbones and side chains of ethylene oxide, where the length of the side chains has been varied, while the ratio of acrylate to ethylene oxide has been kept constant. The electrolyte is a mixture of lithium perchlorate and two solvents, ethylene carbonate and gamma butyrolactone. 13 C spectra of the different gel electrolytes shows that both solvents interact with the salt, and that the strength of the interaction increases with decreasing length of the polymer side chains. It also appears that the lithium ions show no selectivity between the two types of solvent. Furthermore, the lithium chemical shift moves progressively upfield with increasing length of the side chains, showing a gradual change in interaction from lithium-solvent to lithium-(ethylene oxide).
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| 12. |
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| 13. |
- Andersson, Ove, et al.
(författare)
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A high-pressure study of PMMA-based gels with and without TiO2 nano-particle filler: a filler induced change in the activation volume
- 2005
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 50:16-17, s. 3217-3223
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Tidskriftsartikel (refereegranskat)abstract
- The ionic conductivity σ of PMMA-based gels with and without nano-particle filler has been investigated at elevated pressure up to 0.9 GPa and in the temperature range 220-330 K to determine the effect of pressure and to obtain the activation volume. Both gels had molar ratios: EC:PC:LiClO 4 :PMMA 53.9:22:5.2:18.9, and one gel contained 8 wt.% TiO 2 nano-particles. At room temperature and atmospheric pressure, the conductivity of the gel with filler is almost the same as that for the gel without filler. At increasing pressure p, σ(p) for both gels exhibits an abrupt change, which is associated with a transition, and consequently there is a pressure induced change in the activation volume for both gels. The activation volume ΔV * in low-pressure state is the same for the gels with and without filler and about 14 cm 3 mol -1 at room temperature, which is typical liquid-like behaviour. In the high-pressure state, ΔV * = 42 and 45.3 cm 3 mol -1 at 294 K for the gels with and without filler, respectively. The results show that the ionic movements are restricted by the rigid environment of the high-pressure state and that the filler affects ΔV * under this condition. In particular, the filler appears to improve the cation transport number as a results of a decreased mobility of large-sized ions in the rigid environment of the high-pressure state. © 2004 Elsevier Ltd. All rights reserved.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Bismarck, A., et al.
(författare)
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Multifunctional epoxy resin for structural supercapacitors
- 2012
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Ingår i: 15th European Conference on Composite Materials: Composites at Venice, ECCM 2012; Venice; Italy; 24 June 2012 through 28 June 2012. - 9788888785332
-
Konferensbidrag (refereegranskat)abstract
- Polymer-based electrolytes based on commercially available epoxy resins were prepared through the addition of a liquid electrolyte, a solution of a lithium salt in an ionic liquid. The polymer monoliths were characterized using impedance spectroscopy, 3-point bending test, scanning electron microscopy (SEM) and nitrogen adsorption (BET). The balance of ionic conductivity and flexural modulus is crucially dependent on the relative proportions of epoxy resin to electrolyte. Also the effect of the liquid electrolyte on curing kinetics and processing was assessed by complex viscosity measurements and differential scanning calorimetry (DSC). Only one out of the three resins investigated exhibited a significant acceleration effect.
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| 18. |
- Brodin, A., et al.
(författare)
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Dipolar interaction and molecular ordering in liquid propylene carbonate: Anomalous dielectric susceptibility and Raman non-coincidence effect
- 2011
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 164:1-2, s. 17-21
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric constant of non-associating fluids normally exhibits a 1/T temperature dependence according to Curie's law. Kirkwood correlation factor in such cases is close to unity and almost independent of the temperature. Recent broadband dielectric studies of a well-known solvent propylene carbonate (PC) revealed anomalous behavior of its loss spectrum, whose amplitude somewhat increases at high temperatures contrary to Curie's law, while it is known from the literature that its Kirkwood factor is close to unity. We analyze the origin of this discrepancy and find, based on recent literature data, that the Kirkwood factor of PC is strongly temperature dependent and significantly differs from unity, which signals the presence of temperature dependent molecular ordering. We find other signatures of this ordering in vibrational spectra of PC, where it leads to splitting of molecular vibrations due to interaction between the transition dipoles of neighboring molecules (the so-called non-coincidence effect). Spectroscopic and dielectric results agree well with each other and reveal the presence of significant temperature-dependent anti-parallel dipolar arrangement. Based on these results, it is likely that other polar liquid:; with large and localized molecular dipoles, albeit traditionally classified as non-associating, in fact do possess significant local molecular order due to dipolar interactions.
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| 19. |
- Brodin, A., et al.
(författare)
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On the structure of archetypal polymer electrolyte PEO:LiCF3SO3
- 2009
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Ingår i: Ukrainian Journal of Physics. - 2071-0194. ; 54:3, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- We report on a systematic micro-Raman and IR spectroscopic investigation of PEO-LiCF3SO3 polymer electrolytes, aimed at revealing the microstructure of ionically conductive amorphous PEO:Li+ complexes. Films (O:Li = 3:1 and 9:1, thickness 2-30 ?m) were cast from acetonitrile solutions and further subjected to different heat treatment procedures within the course of investigations. Polarized optical microscopy was used to reveal the morphology of films. At the stoichiometric composition, the highly crystalline films exhibited a rather uniform (although anisotropic) structure which was examined by polarized micro-Raman spectroscopy to establish the relation between the crystalline structure and its spectroscopic signatures. The systems of nonstoichiometric composition (O:Li=9:1) exhibited a non-uniform, multiphase structure. The structural changes on increasing the temperature, when the relative amount of the disordered phase increases to finally form a uniform melt, have been monitored. We show that anion internal vibrational modes, routinely used to quantify different ionic species in the electrolyte, are substantially influenced by the crystalline field of the complexes, so that conventional analysis of the splitting and the band shift of nondegenerate internal modes in terms of different coordinations is no longer applicable. We show that Raman spectroscopy is a more sensitive probe of the polymer conformational order and the cation coordination than IR spectroscopy. We discuss, based on the obtained experimental evidences, to which extent the crystalline structure of the stoichiometric complex is related to the microstructure of the conductive amorphous phase. Comparative analysis of Raman spectroscopic signatures of the crystalline complex, molten phase, and model low molecular weight (Mw ? 1000 g mol-1) systems allows us to conclude that the structure of amorphous PEO:Li+ complexes is similar (though not identical) to the structure of the crystalline one. The similarity consists in that the polymeric chain "wraps" around a cation in both cases.
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| 20. |
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| 21. |
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| 22. |
- Chakraborty, S., et al.
(författare)
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Mechanistic Insight into the Structure and Dynamics of Entangled and Hydrated lambda-Phage DNA
- 2012
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 116:17, s. 4274-4284
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic dynamics of DNA plays a crucial role in DNA protein interactions and has been emphasized as a possible key component for in vivo chromatin organization. We have prepared an entangled DNA microtube above the overlap concentration by exploiting the complementary cohesive ends of lambda-phage DNA, which is confirmed by atomic force microscopy and agarose gel electrophoresis. Photon correlation spectroscopy further confirmed that the entangled solutions are found to exhibit the classical hydrodynamics of a single chain segment on length scales smaller than the hydrodynamic length scale of single lambda-phage DNA molecule. We also observed that in 41.6% (gm water/gm DNA) hydrated state, lambda-phage DNA exhibits a dynamic transition temperature (T-dt) at 187 K and a crossover temperature (T-c) at 246 K. Computational insight reveals that the observed structure and dynamics of entangled lambda-phage DNA are distinctively different from the behavior of the corresponding unentangled DNA with open cohesive ends, which is reminiscent with our experimental observation.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Ekstrom, Henrik, et al.
(författare)
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Evaluation of a sulfophenylated polysulfone membrane in a fuel cell at 60 to 110 degrees C
- 2007
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 178:13-14, s. 959-966
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Tidskriftsartikel (refereegranskat)abstract
- A novel sulfophenylated polysulfone membrane material has been evaluated in a hydrogen/oxygen fuel cell using Nation-impregnated commercial electrodes. Comparative measurements were performed with Nation membranes to distinguish between different sources of potential losses. The operational temperatures in the experiments ranged from 60 to 110 degrees C, and the effect of different humidifying conditions was investigated. Membranes that were operated over 300 h under fully humidified conditions showed a slight increase in the cell resistance. At lower humidification levels the cell resistance increased significantly. No difference in the membrane composition between active areas and areas not subjected to ionic currents could be detected by ATR-IR or Raman spectroscopy after fuel cell testing. The best fuel cell performance for these membranes was found at 90 degrees C and 100 degrees C. The current density at a cell voltage of 0.5 V ranged between 100 and 200 mA cm(-2) depending on the operating conditions. The relatively low current densities found when using the new membrane material are explained by high ionic contact resistances between the electrodes and the membrane.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Georen, P., et al.
(författare)
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Concentration polarization of a polymer electrolyte
- 2002
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 149:8, s. A1015-A1019
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the salt concentration in a concentrated binary polymer electrolyte was measured in situ by means of confocal Raman spectroscopy during galvanostatic polarization experiments. The electrolyte studied was 0.8 M lithium bis(trifluoromethanesulfone)imide in a copolymer of ethylene- and propylene oxide at 25degreesC. Recent work with a transport model and characterization of the transport properties, for the same electrolyte, was verified with the spectroscopic results of this study. A good agreement between modeled and measured results was found. The spectroscopic method suited well for these studies. The possibilities of using a transport model are briefly demonstrated and discussed.
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| 38. |
- Henriksson, Andreas, 1979, et al.
(författare)
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RIFEL - Ripple and Electromagnetic Fields in Electric Vehicles
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The electrical system in an electrified vehicle consists of high voltage (HV) components interacting in a complex way. The switching interaction in the power electronics results in ripple causing electromagnetic fields, disturbing other electronics and degradation of components. An overview of this can first be obtained when a physical system is built which could lead to unintentional over- or under dimensioning of HV components. This lack of information within the electrical system can lead to late verifications in the project causing substantial cost if changes are needed. This project aims at improving early evaluation of new concepts, create tools and build the necessary competence for a virtual system model that includes the key HV components: battery, electrical motor and power electronics, a simple load along with cable and connectors. This virtual model shall be able to simulate voltage and current ripple generated by the power electronics, initially in a frequency range up to 100 kHz. Results from the simulations shall be presented both in time and frequency domain as well as be expressed in RMS values for easier comparison to measured results. Some of the more important findings are briefly summarised below; For the high voltage battery, the electrical characteristics up to a frequency of roughly 1000 Hz was well determined using an impedance spectroscopy instrument at cell level and then multiplied by the numbers of cells. However for finding the impedance behaviour for frequencies above 1000 Hz, the determination must be done on the battery pack level since bus bars and other component in the complete battery pack will be dominating in this frequency range. From measurements of differential mode impedance in high voltage cables it is found that it is important that the mutual inductance between the centre conductor and shield is included in the model to describe cable impedance below 10 kHz properly. The control of the inverter is very important for the overall behaviour and in this project SVM was used which has been shown to give the lowest current and voltage ripple of the traditional switching schemes. And for the machine model, the temperature variations must be taken into account since the machine parameters has been found to vary with ~20 % over the specified temperature range. The system model is found to agree well with rig measurements well up to 1 MHz with regards to both currents and voltages at the DC and AC sides. Furthermore, measurements in a real car match those in the rig. For time domain simulations, it was decided to use Ansys Simplorer since it can handle the inverter and the electrical machine simulations very well and for frequency domain simulations, it was decided to use LTspice since it is freeware, has support for AC-sweeps, improved switching compared to other SPICE-simulators, and is easy to use. Magnetic field simulations have been calculated and compared to measurements in the driveline rig at Chalmers. It was a good match across the investigated frequency range 10 Hz to 100 kHz. In this project, only internally developed component models were considered. To expand the functionality of the system modelling tool, international interface standards such as the Functional Mockup Interface (FMI) need to be investigated. Consequently, it would be a good idea to include additional automotive OEMs as well as suppliers and software vendors in future research collaborations.
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| 39. |
- Holber, Mikael, 1982, et al.
(författare)
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Raman investigation of degradation and ageing effects in fuel cell membranes
- 2009
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781566777384 ; 25:1 PART 1, s. 807-811
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Tidskriftsartikel (refereegranskat)abstract
- Increased life-time of the proton conducting membrane of polymer electrolyte membrane fuel cells is the key to improve the endurance of fuel cell stacks. Here we present a Raman spectroscopy investigation of a fully fluorinated sulfonated membrane from a 1500h FC steady-state experiment compared with Nafion® membranes aged in hydrogen peroxide and Fenton's solution. The latter approach as an attempt to develop a screening method based on accelerated ageing. In all membranes degradation is evident. The Raman results of the fuel cell tested membrane demonstrate a loss of functional sulfonic acid groups throughout the membrane. The accelerated ageing, on the other hand, results in degradation readily observed: e.g. loss of polymer material, opaque areas, and brittleness. Notably, the relative concentration of functional sulfonic groups stays constant, indicating that the accelerated ageing methods primarily attack the backbone of the membrane. ©The Electrochemical Society.
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| 40. |
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| 41. |
- Holber, Mikael, 1982, et al.
(författare)
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Raman Spectroscopy of an Aged Low Temperature Polymer Electrolyte Fuel Cell Membrane
- 2011
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 11:3, s. 459-464
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Tidskriftsartikel (refereegranskat)abstract
- The cost and durability of the membrane electrode assembly (MEA) are today limiting factors for large-scale commercialisation of the polymer electrolyte membrane fuel cell (PEMFC). The MEA durability in a real working fuel cell (FC) is closely linked to specific operating conditions such as temperature, gas humidity, load dynamics, etc. This often results in both chemical and mechanical degradation of the ion-conducting membrane and subsequent operation failure of the FC. In this study, Raman spectroscopy is used to identify and distinguish between two different degradation processes for a 1,500 h in situ aged FC membrane. The primary process is due to the loss of proton conducting sulphonic acid end groups over the entire membrane. The secondary process is a degradation of the fluorinated backbone concentrated to the cathode interface; making possible the collapse of carbon into the resulting voids of the membrane. Using spatially resolved Raman spectroscopy we can unambiguously observe both the localisation and the state of the carbon inside the membrane; being similar/identical to the microporous layer (MPL).
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| 42. |
- Holomb, Roman, et al.
(författare)
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Ionic liquid structure: the conformational isomerism in 1-butyl-3-methyl-imidazolium tetrafluoroborate ([bmim][BF4])
- 2008
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 39:7, s. 793-805
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Tidskriftsartikel (refereegranskat)abstract
- As a probe of local structure, the vibrational properties of the 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]+ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim] + conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim] + conformers and the [bmim]+- [BF4]- interactions to the vibrational spectra are discussed.
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| 43. |
- Holomb, Roman, et al.
(författare)
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Vibrational spectroscopy and ab initio studies of lithium bis (oxalato) borate (LiBOB) in different solvents
- 2006
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 110:40, s. 11467-11472
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Tidskriftsartikel (refereegranskat)abstract
- The effect of lithium ion coordination with the bis(oxalato)borate (BOB ) [6(0204)2] anion in DMSO, PEG, PPG, and d-PPG has been studied in detail by IR and Raman spectroscopy. Ab initio calculations were performed to allow a consistent analysis of the experimental data. The main features observed in the IR and Raman spectra correspond to the presence of "free", un-coordinated, BOB - anions. Only with use of d-PPG as solvent a small amount of Li + ⋯BOB - ion pairs were detected. The Raman spectra and the calculations together indicate that Li + coordinates bidentately with two end-oxygen atoms of the BOB - anion. The identification of ion pairs can be used to reveal limitations of LiBOB based electrolytes. The results for LiBOB are compared with literature on other Li salts. © 2006 American Chemical Society.
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