| 1. |
- Hailu, Girma, 1982-, et al.
(författare)
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Nonlinear optical absorption properties of porphyrins confinedin Nafion membrane
- 2009
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Ingår i: Applied Physics A. - : Springer-Verlag New York. - 0947-8396 .- 1432-0630. ; 96:3, s. 685-689
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear absorption (NLA) properties of five different types of porphyrins were studied using the Z-scan technique. The porphyrins under investigation were confined into Nafion column matrix membrane in order to protect them from possible degradation. The results of the experiments have indicated that all the porphyrins tested exhibited interesting NLA properties. The nonlinear absorption coefficients (β’s) were determined at different porphyrin concentrations by comparing the Z-scan data with the theoretical functions.
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| 2. |
- Lindberg, Simon, 1985, et al.
(författare)
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A VO2 based hybrid super-capacitor utilizing a highly concentrated aqueous electrolyte for increased potential window and capacity
- 2020
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 345
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Tidskriftsartikel (refereegranskat)abstract
- In this work we demonstrate the application of a highly concentrated aqueous electrolyte to a hybrid supercapacitor cell. We combine an 8 m Sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) aqueous electrolyte with a nanostructured VO2-cathode to enhance the voltage widow up to 2.4 V in a full cell. With the enhanced potential window, we are able to exploit the full contribution of the VO2 material, where a part is outside the stability window of standard alkaline aqueous electrolytes. We show that the VO2 material in the highly concentrated electrolyte provides a faradaic contribution even at the highest current density (25 A/g) and in this way increases the energy content also in high power conditions. The full cell shows a good efficiency but also a capacity fade over 500 cycles (39%) which is most likely related to dissolution of VO2.
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| 3. |
- Momodu, Damilola, et al.
(författare)
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Stable ionic-liquid-based symmetric supercapacitors from Capsicum seed-porous carbons
- 2019
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 838, s. 119-128
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a symmetric ionic-liquid based supercapacitor was assembled with porous carbon derived from Capsicum (bell pepper) seeds. The “peppered”-activated carbon (ppAC) was synthesized using varying amounts of KHCO 3 activating agent (AA) at 850 °C carbonization temperature. The best device performance reported was recorded with optimum amounts of AA to raw material. The need for less amount of AA is crucial if the entire activation/carbonization process is to be scaled-up with the cost and final product yield also being important for a viable synthesis. A mechanism of saturation of pores with unreacted AA which leads to lower porosity metrics in the samples with increasing the amount of AA during carbonization/activation was also proposed. Using an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide (EMIM-TFSI), the ppAC-based supercapacitor operated up to a maximum cell voltage of 3.20 V. A specific energy of 37 Wh kg −1 was obtainable with a corresponding practical power density of 0.6 kW kg −1 at 0.5 A g −1 . A specific energy of ∼26 Wh kg −1 was still achievable when the applied current was doubled to 1.0 A g −1 and a high cyclic stability (approx. 99% coulombic efficiency) was proven over 25,000 cycles. Further ageing test performed on the device revealed a remarkable improvement in the electrochemical performance after a 180 h (ca. 1 week) floating time. The obtained results also confirmed a uniquely distributed porous carbon in which the complete utilization of the entire less-corrosive KHCO 3 AA for optimal pore activation at elevated carbonization temperatures. Thus, the efficient design combinations for stable, high-energy and power ionic liquid-based supercapacitors with cheaper biomass-based materials are demonstrated.
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| 4. |
- Oyedotun, Kabir O., et al.
(författare)
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Comparison of ionic liquid electrolyte to aqueous electrolytes on carbon nanofibres supercapacitor electrode derived from oxygen-functionalized graphene
- 2019
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 375
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Tidskriftsartikel (refereegranskat)abstract
- A facial force-driven reflux technique was used to develop fibre-like carbon material from freeze-dried reduced graphene oxide (RGO) firstly prepared by using a modified Hummers method. The carbon nanofibres displayed a high specific surface area of ∼1317.8 m2 g−1, with good pore size distributions which could be beneficial for energy storage applications. Electrochemical measurements of the carbon nanofibre electrodes in a symmetric configuration with aqueous (1 M Na2SO4, 6 M KOH), and protic ionic liquid (1-ethylimidazolium bis(trifluoromethanesulfonly)imide) electrolytes (ILE) displayed excellent electrochemical performance with the dominant electric double layer capacitor (EDLC) behaviour. The fabricated device shows higher electrochemical performance in the ILE due to its larger cell operating potential (3.0 V) as compared with the aqueous electrolytes (0.8 V). The optimized electrochemical properties especially in terms of higher specific energy and superior stability, suggest the material's potential applications as electrode for supercapacitors.
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