Theoretical and experimental studies of imidazolium based ionic liquids for supercapacitors application

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dc.contributor.authorChengula, Plassidius Joachim
dc.date.accessioned2020-10-09T12:39:13Z
dc.date.available2020-10-09T12:39:13Z
dc.date.issued2020-03
dc.descriptionA Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Master’s in Materials Science and Engineering of the Nelson Mandela African Institution of Science and Technologyen_US
dc.description.abstractThe theoretical study of neutral ion pairs of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2]) has been performed. The formation of the neutral ion pairs was considered through interionic reactions involving the [EMIM]+ cation and two anions, [BF4] – and [NTf2] – . Computations were performed by the DFT/6-311++G(d,p) method with B3LYP5 and CAM–B3LYP functionals. The enthalpies of the interionic reactions ΔrH°(0) have been determined theoretically for both ion pairs. In addition, following the available experimental data for [EMIM][NTf2], the enthalpy of the reaction based on experiment was obtained. The recommended values of ΔrH°(0) are as follows: –359 ± 15 kJ mol–1 for [EMIM][BF4] and – 323 ± 9 kJ mol–1 for [EMIM][NTf2]. The thermodynamic stability of the ion pairs was interpreted through analysis of the frontier molecular orbitals as well as simple ionic model. Experimental test on influence of imidazolium-based ionic liquids in electrochemical system was investigated, with the potential window of 2.8 V for both ionic liquids. The specific capacitances were found to be 4.1 F g–1 and 4.3 F g–1 for [EMIM][BF4] and [EMIM][NTf2] respectively, at the lower scan rate of 5 mV s–1 . The maximum current densities reached were 87 mA g–1 and 88 mA g–1 for [EMIM][BF4] and [EMIM][NTf2], respectively. Electrochemical measurements by cyclic voltammetry and electrochemical impedance spectroscopy have been conducted on three electrodes system with the IILs under study. A supercapacitor prototype has been fabricated; conventional charge-discharge tests were done. Keywords: Ionic liquids, density functional theory, thermodynamic functions, supercapacitor, cyclic voltammetry, electrochemical impedance spectroscopyen_US
dc.identifier.urihttps://doi.org/10.58694/20.500.12479/975
dc.language.isoenen_US
dc.rightsAttribution-NonCommercial-NoDerivatives 4.0 International*
dc.rightsAttribution-NonCommercial-ShareAlike 4.0 International*
dc.rights.urihttp://creativecommons.org/licenses/by-nc-sa/4.0/*
dc.subjectResearch Subject Categories::NATURAL SCIENCESen_US
dc.titleTheoretical and experimental studies of imidazolium based ionic liquids for supercapacitors applicationen_US
dc.typeThesisen_US

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