| 1. |
- Blanco, Maria Valeria, et al.
(författare)
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Optimizing carbon coating parameters for obtaining SiO2/C anodes with improved electrochemical performance
- 2021
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Ingår i: Journal of Solid State Electrochemistry. - : Springer Nature. - 1432-8488 .- 1433-0768. ; 25:4, s. 1339-1351
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a comprehensive and systematic study on the use of low-cost and highly abundant carbon precursors to obtain SiO2/C anodes with superior electrochemical performance towards Li-ions. Different SiO2/C composites are prepared by soaking silica nanoparticles in solutions containing 20 wt%, 40 wt%, or 60 wt% of glucose, sucrose, or cornstarch, followed by thermal decomposition of the carbohydrates at 850 degrees C or 1200 degrees C. Structural, microstructural, and textural differences on the composites derived from the different carbon coating treatments are related to the electrochemical performance of the anodes. Composites containing final carbon contents close to 15 wt% show a complete coverage of the SiO2 particles with a nanometric carbon layer and exhibit the best electrochemical results. The increase in the annealing temperature from 850 to 1200 degrees C reduces the porosity of the carbon layer and increases its level of ordering, both having positive effects on the overall electrochemical performance of the electrodes. SiO2/C composites coated with 40 wt% sucrose and heat treated at 1200 degrees C display the best electrochemical performance, delivering a reversible specific capacity of 723 mAhg(-1) at 50 mAg(-1) after 100 cycles, which is considerably higher than the reversible capacity of 233 mAhg(-1) obtained with the uncoated material cycled under the same conditions.
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| 2. |
- Forsberg, Peter, 1983-, et al.
(författare)
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Performance of DLC coatings in heated commercial engine oil
- 2013
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 304:1-2, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- Multilayer Diamond Like Coatings (DLC) are widely used to protect highly loaded components from wear and/or to reduce the friction losses in combustion engines. The uppermost layer of the coating controls the chemical situation in the contact and is therefore a very important part of modern multilayer coatings. To examine the individual performances and assess differences and potentials of modern DLC coatings, four commercially available DLCs designed for automotive components with different doping elements together with an uncoated reference were tested in high performance engine oils heated to 90 °C at two different initial contact pressures. The coefficient of friction generally was higher in the tests with the lower initial contact pressure (approximately 20% for all combinations) and the specific wear rate was also up to 100% higher for some combinations. It was also found that a used motor oil showed up to 30% higher friction than when fresh and at the same time reduced the wear in most cases. The tungsten doped coating showed the highest wear, but also the lowest coefficient of friction. The Si doped coating showed the best wear results, most probably due to the ability to make use of the additives in the oil to form a protecting tribofilm.
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| 3. |
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| 4. |
- Gustavsson, Fredrik, 1977-, et al.
(författare)
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How tribological propertiesof DLC coatings vary in different engine oils at elevated temperature
- 2012
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Ingår i: Nordtrib, Trondheim, Norge.
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Konferensbidrag (refereegranskat)abstract
- Improving fuel economy and tribological properties in automotive applications is a continuous quest, where only a few percent decrease in friction and emissions can make a huge difference. Energy savings and environmental influence are today very important factors when designing new tribological systems for automotive applications.DLC coatings are often seen as a homogenous group of hard amorphous carbon coatings, being chemically inert with great wear resistance in most lubricated environments. However, the hardness can vary within almost an order of magnitude between different DLC variants and combined with large variations in chemical composition, the wear and friction properties may vary significantly, depending on the test conditions.In this study, an experimental coating of amorphous carbon deposited with PA-CVD is compared with three commercially available and optimized DLC coatings, frequently used in automotive applications. The coatings have different hardness, chemical composition and structure.The coatings are tested in a reciprocal sliding test rig, at contact pressures and temperature representative of real engines. The tests are performed at low speeds and are designed to operate in the boundary friction regime, where the need for coatings is the highest. An uncoated reference material is tested with the same parameters to highlight the benefits of the coatings under the different test conditions. Five oils are tested, including four special oils designed with different amounts of additives and one used dully formulated engine oil taken from a real engine.Results show that the DLCs do not behave as a homogenous group, but have different tribological properties depending on the hardness and composition. Interestingly, the ranking of the coatings varies for the different oils. Special attention is put on friction and wear behavior and on how the surfaces have changed during the test. Further, deeper surface analysis of some selected systems is performed using EDS, XPS and TEM.
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| 5. |
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| 6. |
- Görlin, Mikaela, et al.
(författare)
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Aging and Charge Compensation Effects of the Rechargeable Aqueous Zinc/Copper Hexacyanoferrate Battery Elucidated Using In Situ X-ray Techniques
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:50, s. 59962-59974
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Tidskriftsartikel (refereegranskat)abstract
- The zinc/copper hexacyanoferrate (Zn/CuHCF) cell has gained attention as an aqueous rechargeable zinc-ion battery (ZIB) owing to its open framework, excellent rate capability, and high safety. However, both the Zn anode and the CuHCF cathode show unavoidable signs of aging during cycling, though the underlying mechanisms have remained somewhat ambiguous. Here, we present an in-depth study of the CuHCF cathode by employing various X-ray spectroscopic techniques. This allows us to distinguish between structure-related aging effects and charge compensation processes associated with electroactive metal centers upon Zn2+ ion insertion/deinsertion. By combining high-angle annular dark-field-scanning electron transmission microscopy, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy, and elemental analysis, we reconstruct the picture of both the bulk and the surface. First, we identify a set of previously debated X-ray diffraction peaks appearing at early stages of cycling (below 200 cycles) in CuHCF. Our data suggest that these peaks are unrelated to hypothetical ZnxCu1–xHCF phases or to oxidic phases, but are caused by partial intercalation of ZnSO4 into graphitic carbon. We further conclude that Cu is the unstable species during aging, whose dissolution is significant at the surface of the CuHCF particles. This triggers Zn2+ ions to enter newly formed Cu vacancies, in addition to native Fe vacancies already present in the bulk, which causes a reduction of nearby metal sites. This is distinct from the charge compensation process where both the Cu2+/Cu+ and Fe3+/Fe2+ redox couples participate throughout the bulk. By tracking the K-edge fluorescence using operando XAS coupled with cyclic voltammetry, we successfully link the aging effect to the activation of the Fe3+/Fe2+ redox couple as a consequence of Cu dissolution. This explains the progressive increase in the voltage of the charge/discharge plateaus upon repeated cycling. We also find that SO42– anions reversibly insert into CuHCF during charge. Our work clarifies several intriguing structural and redox-mediated aging mechanisms in the CuHCF cathode and pinpoints parameters that correlate with the performance, which will hold importance for the development of future Prussian blue analogue-type cathodes for aqueous rechargeable ZIBs
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| 7. |
- Ojwang, Dickson O., et al.
(författare)
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Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate
- 2016
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:12, s. 5924-5934
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Tidskriftsartikel (refereegranskat)abstract
- Copper hexacyanoferrate, Cu-II[Fe-III(CN)(6)](2/3)center dot nH(2)O, was synthesized, and varied amounts of IC ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as Cu-II[Fe-III(CN)(6)](2/3)-nH(2)O + 2x/3K(+) + 2x/3e(-)K(+) <-> K-2x/3 Cu-II[Fe-x(II).Fe-1-x(II),(CN)(6)](2/3)-nH(2)O. Infrared, Raman, and Mossbauer spectroscopy studies show that Fe-II is continuously reduced to Fell with increasing x, accompanied by a decrease of the a-axis of the cubic Fn (3) over barm unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction similar to 10% of the Fe-III, has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of similar to 26 wt % upon heating to 180 degrees C, above which the structure starts to decompose. The crystal structures of Cu-III[Fe-III(CN)(6)](2/3)center dot nH(2)O and K2/3Cu[Fe(CN)(6)](2/3)center dot nH(2)O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)(6) groups are vacant, and the octahedron around Cull is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the-Cu-N-C-Fe- framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K+ ions.
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| 8. |
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| 9. |
- Renman, Viktor, et al.
(författare)
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Investigation of the Structural and Electrochemical Properties of Mn2Sb3O6CI upon Reaction with Li Ions
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:11, s. 5949-5958
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Tidskriftsartikel (refereegranskat)abstract
- The structural and electrochemical properties of a quaternary layered compound with elemental composition Mn2Sb3O6Cl have been investigated upon reaction with lithium in Li half cells. Operando XRD was used to investigate the potential impact of this particular layered structure on the lithiation process. Although the results suggest that the material is primarily reacted through a conventional conversion mechanism, they also provide some hints that the space between the slabs may act as preferential entry points for lithium ions but not for the larger sodium ions. Cyclic voltammetry, galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed to unravel the details of the reaction mechanism with the lithium ions. It is found that two pairs of reactions are mainly responsible for the reversible electrochemical cycling of this compound, namely, the alloying of Li-Sb and the conversion of MnxOy to metallic Mn with concomitant formation of Li2O upon lithium uptake. A moderate cycling stability is achieved with a gravimetric capacity of 467 mAh g(-1) after 100 cycles between 0.05 and 2.2 V vs Li+/Li despite the large particle sizes of the active material and its nonoptimal inclusion into composite coatings. The electrochemical activity of the title compound was also tested in Na half cells between 0.05 and 2 V vs Ne/Na. It was found that a prolonged period of electrochemical milling is required to fully gain access to the active material, after which the cell delivers a capacity of 350 mAh CI. These factors are demonstrated to clearly limit the ultimate performances for these electrodes.
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| 10. |
- Renman, Viktor, et al.
(författare)
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Manganese Hexacyanomanganate as a Positive Electrode for Nonaqueous Li-, Na-, and K-Ion Batteries
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 123:36, s. 22040-22049
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Tidskriftsartikel (refereegranskat)abstract
- K2Mn[Mn(CN)(6)] is synthesized, characterized, and evaluated as possible positive electrode material in nonaqueous Li-, Na-, and K-ion batteries. This compound belongs to the rich and versatile family of hexacyanometallates displaying distinctive structural properties, which makes it interesting for ion insertion purposes. It can be viewed as a perovskite-like compound in which CN-bridged Mn(CN)(6) octahedra form an open framework structure with sufficiently large diffusion channels able to accommodate a variety of insertion cations. By means of galvanostatic cycling and cyclic voltammetry tests in nonaqueous alkali metal half-cells, it is demonstrated that this material is able to reversibly host Li+, Na+, and K+ ions via electrochemical insertion/deinsertion within a wide voltage range. The general electrochemical features are similar for all of these three ion insertion chemistries. An in operando X-ray diffraction investigation indicates that the original monoclinic structure is transformed into a cubic one during charging (i.e., removal of cations from the host framework) and that such a process is reversible upon subsequent cell discharge and cation reuptake.
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