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- Saeedi Garakani, Sadaf, 1993-
(författare)
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Heteroatom-doped porous carbon materials derived from poly(ionic liquid)s and their composites for battery and catalytic applications
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the past decade, there has been significant interest in heteroatom-doped porous carbons, driven by the distinctive and adjustable physical and chemical properties that they exhibit across scales, from the atomic to the macroscopic level. Particularly, attributes such as conductivity, electron density, high specific surface area, hierarchical pore structure, and oxidation resistance offer a wide range of characteristics for diverse applications. The development of multimodal, hierarchical pore sizes, ranging from micropores to macropores, ensures balanced diffusion resistance and a high surface area for active site accommodation. However, their synthesis usually involves multiple steps or complicated processing to incorporate both hierarchically porous structures and heteroatoms in carbon materials.This PhD thesis explores poly(ionic liquid)s (PILs) for preparation of heteroatom-doped porous carbon materials, driven by the growing demand for functional carbons in industry and academia. The aim of this thesis is to develop straightforward synthetic approaches to introduce various heteroatoms and different pore sizes in the carbonous structure and study their diverse functions. Here, we propose and explore fabrication methods based on two precursors. First, PILs were examined as both the carbon and heteroatom source, serving as a sacrificial template for porous carbons. Second, the delicate structure of wood was employed as a carbon source to generate macropores, while being coated with PILs to introduce heteroatoms or iron-based nanoparticles and create additional micropores. Moreover, the application of these carbonaceous materials was studied in two areas, i.e., batteries and artificial enzymes. This research is likely to contribute to a deeper understanding of synthetic methodologies of heteroatom-doped porous carbon materials and their physiochemical properties for various applications.
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| 2. |
- Schlee, Philipp, et al.
(författare)
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From waste to wealth : From kraft lignin to free-standing supercapacitors
- 2019
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 145, s. 470-480
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Tidskriftsartikel (refereegranskat)abstract
- Pure eucalyptus Kraft lignin derived carbon fiber mats were produced based on a model workflow. It covers the preparation and characterization of the lignin precursor and the carbon materials and its testing in the final application (supercapacitor). Sequential solvent extraction was employed to produce a eucalyptus Kraft lignin precursor which could be electrospun into lignin fibers without any additives. The fiber formation from low molecular weight lignin is assigned to strong intermolecular interactions via hydrogen bonding and π-π-stacking between individual lignin macromolecules which gives rise to association complexes in the electrospinning solution. By stabilization in air, carbonization in N2 and an activation step in CO2, free-standing microporous carbon fiber mats could be produced. These fiber mats possess mainly basic oxygen functional groups which proved to be beneficial when tested as free-standing electrodes in symmetric supercapacitors. Consequently, the CO2-activated fiber mats showed a high specific gravimetric capacitance of 155 F/g at 0.1 A/g, excellent rate capability with 113 F/g at 250 A/g and good capacitance retention of 94% after 6000 cycles when tested in 6 M KOH electrolyte. Therefore, we conclude that lignin itself is a promising precursor to produce microporous, oxygen functionalized carbon fibers serving as free-standing electrodes in aqueous supercapacitors.
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| 3. |
- Schlee, Philipp, et al.
(författare)
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Hardwood : versus softwood Kraft lignin-precursor-product relationships in the manufacture of porous carbon nanofibers for supercapacitors
- 2020
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 8:44, s. 23543-23554
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Tidskriftsartikel (refereegranskat)abstract
- The process of stabilization is essential in the production of carbon fibers from lignins. During stabilization, the initially thermoplastic lignin polymer is converted to a thermoset polymer allowing for high-temperature treatment without a change in shape. In this work, hardwood (HKL) and softwood (SKL) Kraft lignins were stabilized in air at temperatures between 190 and 340 °C before carbonization at 800 °C in a nitrogen atmosphere. Due to the differences in side-chain linkages, functional groups and molar mass, the lignins exhibit different structural changes upon stabilization and hence develop different porosities upon carbonization. Both lignins undergo major crosslinking reactions in the side chains at low temperatures and degradation reactions at high temperatures during stabilization. Crosslinking gives rise to narrow pore size distributions with mainly (sub-) nanometer pores, whereas degradation reactions lead to a more open pore structure with additional mesoporosity (>2 nm). When both types of reactions take place simultaneously, highly accessible (sub-) nanoporosity can be effectively created, which boosts the performance of supercapacitors operating in 6 M KOH(aq). This effect terminates when the crosslinking reactions cease and mainly degradation reactions take place, which occurs in HKL at 340 °C. SKL shows both a lower degree of crosslinking and degradation and hence develops less specific surface area. The optimum performance in an aqueous alkaline supercapacitor is achieved with HKL stabilized at 310 °C. It shows a specific gravimetric capacitance of 164 F g-1 at 0.1 A g-1 and 119 F g-1 at 250 A g-1 with a capacitance retention of more than 90% after 10 000 cycles.
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