Ioonsetel vedelikel baseeruvad elektrilise kaksikkihi kondensaatorid

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Elektrilise kaksikkihi kondensaatorid ehk superkondensaatorid on uudsed energiasalvestusseadmed. Võrreldes patareidega on superkondensaatoritel pikem ekspluatatsiooni aeg ning palju kiirem laadimise ja tühjenemise aeg. Seetõttu sobivad superkondensaatorid seadmetesse, kus vajatakse tihedalt korduvaid ja suurt võimsust tagavaid vooluimpulsse. Näiteks kasutatakse superkondensaatoreid tõstukites, bussides, prügiveoautodes, kruvikeerajates, mänguasjades jne. suure hetkevõimsuse saavutamiseks. Antud töös uuritakse toatemperatuuril vedelate soolade ehk ioonsete vedelike kasutamist superkondensaatorite elektrolüüdina. Hinnatakse erinevate ioonsete vedelike keemilise koostise, füüsikaliste omaduste ja temperatuuri mõju superkondensaatori elektrilistele omadustele. Ioonsetel vedelikel baseeruvaid superkondensaatoreid võrreldakse teistel elektrolüütidel baseeruvate superkondensaatoritega. Esitatud andmete põhjal soovitati uuritud ioonsete vedelike hulgast superkondensaatorite elektrolüüdiks kahte ioonset vedelikku (1-etüül-3-metüülimidasoolium tetrafluoroboraati ja 1-etüül-3-metüülimidasoolium tetratsüaanoboraati) kuna need tagasid suurima võimsuse superkondensaatori tühjakslaadimisel.Electrical double-layer capacitors or supercapacitors are novel energy storage devices. Compared to batteries, supercapacitors have longer life-time and much faster charging and discharging times. For these reasons supercapacitors are suitable for applications requiring repetitious current impulses with high power density. For example, supercapacitors are used in loaders, busses, garbage trucks, screwdrivers, toys etc. In this thesis, applicability limits of ionic liquids (salts liquid at room temperature) as electrolytes for electrical double-layer capacitors are studied. The influence of chemical composition, physical properties of ionic liquids and influence of temperature to the electrical behavior of supercapacitors is estimated. Supercapacitors based on ionic liquids are compared to supercapacitors based on other non-aqueous electrolytes. On the basis of data established two ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium tetracyanoborate) from ionic liquids studied are suggested as potential electrolytes for supercapacitors as they provide highest power during the discharge of supercapacitor

The diffusion of H2 adsorbed in three porous carbons investigated with in situ quasi-elastic neutron scattering method

This dataset contains data collected during quasi-elastic neutron scattering experiments on the diffusion of H2 adsorbed in three different carbide-derived carbon materials at temperatures 50-100 K and at three different H2 loading pressures. The data were collected in Helmholtz-Zentrum Berlin in Germany in March 2017 (one sample - C900) and in December 2018 (two samples – C700 and C800)

Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis

Quick characterization methods to determine the structure of carbon materials are sought after for a wide array of technical applications. In this study we present the combined analysis of the structure of carbide-derived carbons (CDCs) with Raman spectroscopy and wide-angle X-ray scattering (WAXS) methods. We present the optimal deconvolution method to be used for the detailed analysis of Raman spectroscopy data of CDCs and comparison to corresponding WAXS results is made. For a broad set of CDCs both WAXS and Raman spectroscopy data showed that the average graphene layer extent increases with synthesis temperature of CDC, while the coherent domain lengths obtained from Raman spectroscopy higher by an average of 4.4 nm. In addition, the presence of correlations between the parameters (D-band width and the parameter A∑D/A∑G) from Raman spectroscopy and the synthesis temperature are established. Based on the WAXS and Raman spectra data analysis the strong influence of the precursor carbide structure on the graphitization pathway is shown

The ortho-para transition, confinement and self-diffusion of H

Microporous carbon materials are promising for hydrogen storage due to their structural variety, high specific surface area, large pore volume and relatively low cost. Carbide-derived carbons are highly valued as model materials because their porous structure is fine-tuned through the choice of the precursor carbide and the synthesis route. This study investigates H2 adsorption in three carbide derived carbons with well-defined pores and pore size distributions with quasi- and inelastic neutron scattering methods. Concerning previous studies, a wider neutron energy transfer window is investigated, and a detailed quantitative evaluation of the graphitic structure is presented. The graphitic structure of the carbon is shown to influence the speed of the ortho-to-para transition of H2. Namely, the ortho-para transition was the slowest in carbon derived from TiC, which also had the smallest average stacking size of graphene layers. The possibility to inhibit the ortho-para transition in cryo-adsorption devices is sought after to mitigate the evaporation of H2 during storage. In addition, the self-diffusion of H2 in different timescales is detected in carbon derived from Mo2C, demonstrating the usefulness of obtaining data in a wide energy window