Browsing by Author "Eskusson, Jaanus"

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    High energy density Zn-ion hybrid capacitor using non-aqueous electrolytes
    (Tartu Ülikool, 2023) Põder, Karl-Sten; Jänes, Alar; Eskusson, Jaanus; Tartu Ülikool. Loodus- ja täppisteaduste valdkond; Tartu Ülikool. Keemia instituut
    Intensive research in the field of supercapacitors has been fuelled by the need for high efficiency energy storage systems. The concept of hybrid capacitor aims to close the gap between batteries and electrical double-layer capacitors in terms of improving the energy density. The purpose of the study was to find out if Zn-ion hybrid capacitors have the necessary characteristics and properties to be alternative future energy storage technology. Different combinations of acetonitrile and propylene carbonate solvents, together with Zn(TFSI)2, Zn(BF4)2 and Zn(OTf)2 salts were tested. Zn and carbon cloth electrode were studied using different physical characterization methods. Electrochemical performance for assembled test cells was measured and compared using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge methods and Ragone plots. Acetonitrile-based systems exhibited promising electrochemical results.
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    Synthesis and characterization of diamond-like carbon thin films prepared by pulsed laser deposition method
    (2009-05-27T10:25:50Z) Eskusson, Jaanus
    arious diamond-like carbon (DLC) films were prepared using four diffe­rent type synthesis setups. Optical micro­scopy data showed that the some film regions grown under excimer laser illu­mination were strongly inter­ference colored and have very wide bandgap (ΔE > 3 eV) at certain energy densities of illumination. Raman scattering data indicated that the additional irradiation of the growing film between the ablation pulses is inevitable to create the individual diamond phase formation into DLC films. The existence of diamond clusters in these films was also confirmed using AFM method. The individual diamond phase forms only in a narrow window of irradiating laser beam energy density. At lower energy densities the irradiation promoted the growth of homogeneous DLC structures with high content of sp3 hybridized carbon. However, at higher laser irradiation intensities the DLC phase decomposition and graphitization takes place. Influence of H2O2 vapor on the film parameters can be described as increasing the number of ordered aromatic carbon rings with decreasing size of the aromatic clusters in DLC films. AFM measurements indicated that the DLC films grown under laser illu­mination conditions were smoother, and especially smooth surfaces were ob­served for the colored films (particles) deposited inside the laser beam irradiated surface regions. At lower deposition temperatures resulted in bigger grain size of the DLC film surface structures. A sudden drop in the root mean square roughness value has been observed in a relatively narrow range of tem­pe­rature from 50 to 100ºC applied. The cyclic voltammetry and impedance data for the DLCE|xM NaF+H2O interface show that this system is nearly ideally polarizable in the potential region –0.4 < E < 1.1 V. The non-linear least squares fitting method of the experimental data shows that an excellent fit of the experimental impedance complex plane plots has been established using a circuit combining the total high frequency series resistance Rel of the electrode system, including the resistance of the bulk diamond film and bulk electrolyte solution, the capacitance C1 and the resistance R3 of the surface film, developed on the surface of the DLCE, the so-called interfacial (i.e. double layer) capacitance C2 (caused by the charging and discharging of the electrical double layer at the internal surface of DLCE), the partial or “true” faradaic reaction resistance of the film R2, the low fre­quency adsorption capacitance C3 and the Warburg-like diffusion impedance ZW. Käesolevas töös sünteesiti erinevaid süsiniku kilesid, kasutades selleks nelja eri­neva aparatuuri konfiguratsiooni. Teatud energia­tihe­dusega eksimeerlaseri kiirguses sünteesitud süsiniku kiled on tugevalt interferents värvilised ja seega ka laia keelutsooni laiusega (ΔE > 3 eV). Raman spektroskoopia uuringu tulemused näitasid, et kasvatusaluse kiirita­mine sadestustsüklite vahel täpselt kontrollitud energiatihedusega laseri kiirega võimaldab tekitada teemandi sarnases süsiniku struktuuris individuaalset tee­mandi faasi. Teemandi faasi tekkimine leiab aset kiiritava laseri kiire väga kitsas energiatiheduse vahemikus, mis samas on energeetiliselt väga lähedal sü­si­niku struktuuri grafitiseerimisele. Leiti, et kõrgematel energiatihedustel leiabki aset samaaegselt teemandi faasi tekkimisega ka olemasoleva teemandi sarnase süsiniku grafitiseerumine. Aatomjõu mikroskoopia mõõtmised näitavad, et madalama kasvatusaluse temperatuuri tulemuseks on suurema teralise pinna tekkimine. Suurimat ruut­keskmise pinnakareduse väärtuse muutust täheldati suhteliselt kitsas tempera­tuuride vahemikus sünteesitud kiledel. Tsüklilise voltamperomeetria ja elektrokeemilise impetantsi andmed näi­tasid, et DLCE|xM NaF+H2O süsteem on peaaegu ideaalselt polariseeritav potentsiaalide vahemikus –0.4 < E < 1.1 V. Eksperimendi andmete mittelineaarne vähimruutude lähendusmeetod näitab, et parim kokkulangevus on saavutatud eksperimentaalsete kompleksimpedantsi sõltuvuste modelleerimisel ekvivalent skeemiga, mis on kombineeritud elektroodi süsteemi kogutakistusest Rel, kile pindkihi mahtuvusest C1 ja pindkihi takistusest R3, kaksikkihi mahtuvusest C2, osalisest või ”tõelisest” faradi reaktsiooni iseloomustavast takistusest R2, adsorptsioonilisest mahtuvusest C3 ja Warburgi difusioonilisest impetantsist Zw.