Raspodjela napona unutar superkondenzatora za vrijeme redistribucije naboja na poroznim elektrodama

master's thesis

• Title (english): Distribution of potential in supercapacitors during charge redistribution on porous electrodes
• Author: Martin Šumanovac
• Mentor: Zoran Mandić (mentor)
• Committee member: Zoran Mandić (predsjednik povjerenstva)
• Committee member: Marijana Kraljić Roković (član povjerenstva)
• Committee member: Vladimir Dananić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2020-09-24, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering

Abstract

Ovaj rad obuhvaća izradu i testiranje superkondenzatora. Superkondenzatori su izrađeni s elektrodama od aktivnog ugljika kao elektrodnog materijala. Postignuta je željena debljina elektrode od 100 μm uz pomoć uređaja za prevlačenje. Elektrode su stavljene u ćeliju EL CELL „combi“ s platinskom folijom kao pseudo-referentnom elektrodom. Takav tro-elektrodni sustav se koristio za praćenje elektrokemijskog ponašanja i raspodjele potencijala na elektrodama. Ponašanje i raspodjela su se pratila u dva različita elektrolita: tetrabutilamonijum tetrafluoroborat (Bu4NBF4) i tetraetilamonijum tetrafluoroborat (Et4NBF4). Mjerenje se provodilo punjenjem i pražnjenjem kondenzatora kroz 2000 ciklusa, pri konstantnoj struji od 20 mA u rasponu napona od 0,1 – 2,5 V. Tijekom mjerenja istovremeno je praćen potencijal individualnih elektroda, te elektrokemijske karakteristike kondenzatora u cjelini. Metode koje su korištene za praćenje su punjenje i pražnjenje konstantnom strujom te elektrokemijska impedancijska spektroskopija. Dobiveni su grafički prikazi koji pokazuju ponašanje pozitivne i negativne elektrode u elektrolitima Bu4NBF4 i Et4NBF4. Metodom punjenja i pražnjenja konstantnom strujom dobile su se vrijednosti koje pokazuju promjenu kapaciteta pozitivne i negativne elektrode te sveukupnog članka s promjenom veličine iona. Tom metodom su dobivene vrijednosti pada napona nakon punjenja pomoću kojega se je odredio unutarnji otpor. Vrijednost unutarnjeg otpora govori o provodnosti i reflektira utjecaj veličine iona na elektrodu. Kroz više ciklusa punjenja i pražnjenja dolazi do naglog pada kapaciteta koji se kasnije stabilizira zbog postojanja dvije različite vrste naboja. Elektrokemijskom impedancijskom spektroskopijom su određene karakteristike sustava. Impedancijski dijagrami odstupaju od idealnog impedancijskog odziva superkondenzatora zbog položaja pseudo-referente elektrode. Iako postoji odstupanje od idealnog odziva moguće je identificirati karakteristična impedancijska područja. Postojanje visokofrekventnog polukruga ukazuje na kinetičke efekte koji se javljaju na granicama faza elektroda/elektrolit. Mjerenje pri većem broju ciklusa pokazuje razliku u dijagramima dvaju elektrolita.

Abstract (english)

This thesis encompasses the preparation and testing of supercapacitors. Supercapacitors were prepared from the electrodes made of activated carbon as an electrode material. Desired thickness of 100 μm of the electrode was achieved with a coating apparatus. Electrodes are placed in a EL-CELL „combi” cell with a platnium foil as a pseudo-reference electrode. The three-electrode system was used to monitor electrochemical behaviour and charge distribution on the electrodes. Behaviour and charge distribution were monitored in two different electrolytes: tetrabutylammonium tetraflouroborate (Bu4NBF4) and tetraethylammonium tetrafluoroborate (Et4NBF4). Measurements were conducted by constant current charging and discharging of the capacitors trough 2000 cycles. Constant current of 20 mA was applied to cells while the cell potential was limited in the range of 0,1-2,5 V. During measurements the potential of the electrodes was monitored and the characteristics of the supercapacitor were observed. In addition to the galvanostatic charging/discharging with potential limitation a staircase potentiostatic electrochemical impedance spectroscopy was conducted. The obtained results were shown in diagrams comparing the behaviour of the positive and negative electrodes in two different electrolytes. Galvanostatic charging with potential limitation method gave values that show change in the capacitances of positive and negative electrodes as well as the whole cell. From the voltage drop obtained at the start of the discharge the internal resistances could be calculated. Values of internal resistances demonstrate the influence of different conductivities of two electrolytes. During multiple cycles of charging and discharging, capacitance of electrodes rapidly decreases due to the existence of two different types of charge. Characteristics of the electrodes are measured also with staircase potentiostatic electrochemical impedance spectroscopy. The results were shown in Nyquist diagrams which deviate from the ideal impedance response. The reason for the deviation is the position of the pseudo-reference electrode. Nevertheless, it was possible to identify specific regions on impedance diagrams. High-frequency semicircle is an indication of the slow kinetic processes taking place at electrode/electrolyte interfaces. Measurements of impedance at higher number of cycles show a difference between two electrolytes.

• Keywords: superkondenzator; napon; kapacitet; otpor; impedancija; raspodjela; naboj; porozna elektroda
• Keywords (english): supercapacitor; voltage; capacitance; resistance; impedance; distribution; charge; porous electrode
• Language: croatian
• URN:NBN: urn:nbn:hr:149:913154
• Project: Number: IP-2013-11-8825; Title: Elektrokemijski superkondenzator visoke snage i velikog sadržaja energije za primjenu u električnim vozilima; Title: High power-high energy electrochemical supercapacitor for hybrid electric vehicles; Acronym: ESUP-CAP; Leader: Zoran Mandić; Jurisdiction: Croatia; Funder: HRZZ; Funding stream: IP
• Study programme: Title: Environmental Engineering - Graduate study; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka ekoinženjerstva (magistar/magistra inženjer/inženjerka ekoinženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2022-04-20 12:10:25