Elektrokemijska sinteza nanokompozita grafen/vodljivi polimer i njegova primjena u superkondenzatorima

doctoral thesis

• Title (english): Electrochemical synthesis of graphene/conducting polymer nanocomposite and its application in supercapacitors
• Author: Gabrijela Ljubek
• Mentor: Marijana Kraljić Roković (mentor)
• Mentor: Palma Orlović-Leko (mentor)
• Committee member: Zoran Mandić (predsjednik povjerenstva)
• Committee member: Zlata Hrnjak-Murgić (član povjerenstva)
• Committee member: Željka Petrović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2021-10-29, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Basic Technical Sciences; Materials
• Universal decimal classification (UDC): 54 - Chemistry. Crystallography. Mineralogy ; 620 - Materials testing. Power stations. Economics of energy

Abstract

Cilj ovog rada bio je prirediti otopinu grafenova oksida (GO) pogodnu za sintezu kompozita vodljivi polimer/GO, provesti sintezu vodljivog polimera te primijeniti dobiveni materijal u superkondenzatoru. Proces elektrokemijskog raslojavanja prirodnog grafita proveden je primjenom anodne i katodne polarizacije grafitne elektrode tijekom više ciklusa. Pri tome su kao osnovni elektrolit upotrijebljene površinski aktivne tvari (PAT) natrijev dodecilbenzensulfonat i natrijev dodecilsulfat. Utvrđeno je da je izmjenična anodna i katodna polarizacija učinkovitija od jednokratne polarizacije. Proces je detaljno istražen i optimiziran praćenjem strujnih tranzijenata i promjene boje otopine te primjenom metode cikličke voltametrije (CV). Pokazano je kako elektrokemijsko raslojavanje ovisi o vrsti radne elektrode, PAT i primijenjenom naponu čije vrijednosti su bile manje od onih primijenjenih u dosadašnjim istraživanjima (2,5 V – 3,2 V). Strukturne i morfološke karakteristike tretirane elektrode i produkta dobivenog u otopini PAT određene su primjenom ultraljubičaste i vidljive spektrofotometrije (UV/Vis spektrofotometrije), Ramanove (RAMAN) spektroskopije, infracrvene spektroskopije s Fourierovom transformacijom (FTIR), dinamičkog raspršenja svjetlosti (DLS), pretražnom elektronskom mikroskopijom (SEM) i mikroskopijom atomskih sila (AFM). Na temelju izračunane potrošnje energije (0,038 – 0,084 kWh g^-1) navedeni postupak raslojavanja svrstan je u niskoenergetski proces. Sinteza
poli(3,4-etilendioksitiofena) i polipirola provedena je iz modelnog elektrolita koji je sadržavao komercijalni GO i micelarnu otopinu natrijeva dodecilbenzensulfonata, natrijeva dodecilsulfata ili poli(natrij 4-stirensulfonata). Određeni su optimalni uvjeti sinteze vodljivih polimera i dokazana je ugradnja GO u njihovu strukturu. Radna elektroda sa slojem PEDOT/GO negativno je polarizirana pri -1,4 V u 0,1 mol dm^-3 otopini KCl. Ovim postupkom GO je preveden u vodljivi oblik odnosno reducirani grafenov oksid (rGO). Poboljšana pseudokapacitivna svojstva ukazala su na uspješno provedenu elektrokemijsku redukciju GO u sloju vodljivog polimera. Sintetizirani vodljivi polimeri ispitani su metodama CV, elektrokemijske impedancijske spektroskopije (EIS), UV/Vis spektrofotometrije, te SEM metodom. Odabrani kompozitni slojevi primijenjeni su kao elektrodni materijali u superkondenzatorima. Stabilnost superkondenzatora ispitana je punjenjem/pražnjenjem superkondenzatora pri konstantnoj vrijednosti struje tijekom 1000 ciklusa, na temelju čega su određeni specifični kapacitet, energija i snaga.

Abstract (english)

The aim of this thesis was to prepare graphene oxide (GO)-containing solution which is suitable for the synthesis of a conducting polymer/GO composite, to carry out conducting polymer synthesis and to apply obtained material in supercapacitor. The electrochemical exfoliation of natural graphite was accomplished by anodic and cathodic polarization of natural graphite electrode in sodium dodecylsulfate and sodium dodecylbenzene sulfonate aqueous solution. The multistep change of polarity was more effective compared to single anodic and cathodic polarization. By using cyclic voltammetry (CV) and monitoring the current transients and the colour of the resultant solutions, it was shown that the exfoliation process depends on the type of working electrode, surfactants and applied voltage value. The applied voltages (2.5 V – 3.2 V) were much lower than the values used in previous publications. Structural and morphological characteristics of the obtained materials were determined by ultraviolet-visible (UV/Vis) spectrophotometry, Raman (RAMAN) spectroscopy, Fouirer-transformed infrared spectroscopy (FTIR), dynamic light scattering (DLS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The energy consumption of the process described in this thesis ranges from 0.038 kWh g^-1 to 0.084 kWh g^-1 and therefore this process is considered to be low energy and cost-effective. Different
poly(3,4-ethylenedioxythiophene) and polypyrrole layers were prepared by electrochemical polymerization from an electrolyte which contained commercial GO and sodium dodecylsulfate, sodium dodecylbenzene sulfonate or poly(4-styrene sulfonate) micellar solution. Optimal synthesis conditions were determined and the incorporation of GO in the polymer layer was proven. Obtained layers were characterized by means of CV, electrochemical impedance spectroscopy (EIS), UV/Vis spectroscopy and SEM. PEDOT/GO layer was polarised at the potential of -1.4 V in 0.1 mol dm^-3 KCl solution in order to reduce GO within the polymer layer. The polarization at negative potentials resulted in improved pseudocapacitive properties of the PEDOT layer, which proves the successfull electrochemical reduction of GO. The best nanocomposite materials were used to assemble symmetric supercapacitors. The stability of supercapacitors was determined by their charging/discharging at constant current during 1000 cycles, and the specific capacitance, energy and power were calculated.

• Keywords: elektrokemijsko raslojavanje; grafenov oksid; poli(3 4-etilendioksitiofen); polipirol; prirodni grafit; površinski aktivne tvari; superkondenzator
• Keywords (english): electrochemical exfoliation; graphene oxide; poly(3 4-ethylenedioxythiophene); polypyrrole; natural graphit; surfactants; supercapacitors
• Language: croatian
• URN:NBN: urn:nbn:hr:149:944417
• Promotion: 2021
• 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: Engineering Chemistry - Doctoral Course; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje kemija (doktor/doktorica znanosti, područje prirodnih znanosti, polje kemija)
• Type of resource: Text
• Extent: 198 str. ; 30 cm
• File origin: Born digital
• Access conditions: Open access; Embargo expiration date: 2023-01-01
• Created on: 2023-05-31 12:35:59