Active Materials for Supercapacitors Application

U posljednjih desetak godina napravljen je značajan iskorak u razvoju aktivnih materijala koji se upotrebljavaju u superkondenzatorima i u dizajniranju samog superkondenzatora. Stoga je u ovom radu dan kratak pregled istraživanja aktivnih materijala za superkondenzatore te je navedena njihova osnovna podjela temeljena na mehanizmima skladištenja naboja. Iz navedenih istraživanja može se zaključiti kako je za uspješan razvoj materijala nužno razumijevanje mehanizma skladištenja naboja i povezivanje strukturnih svojstava materijala s elektrokemijskim svojstvima. Spoznaje o mehanizmu skladištenja omogućuju ciljano dizajniranje materijala te kombiniranje elektroda s različitim mehanizmima, što u konačnici utječe na svojstva ali i na primjenu superkondenzatora. Najznačajniji materijali u ovom području su materijali temeljeni na ugljiku, vodljivi polimeri i metalni oksidi. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.In the last decade, significant breakthrough has been achieved in both the field of active materials and the design of supercapacitors. Herein, we give an overview of the recent advances in this field, and point out the main groups of material that are characterized by the charge-storage mechanism. From the available research literature, it may be concluded that a fundamental understanding of the charge-storage mechanism as well as determining the relationship between the structural properties of materials and electrochemical performances is important for successful development of supercapacitor. The mechanism insight enables targeted material design and the possibility of combining different electrodes that affect the final properties and application of supercapacitor. The most important materials for supercapacitor application are carbon-based materials, conducting polymers, and metal oxides. This work is licensed under a Creative Commons Attribution 4.0 International License

Phenolic compounds removal from mimosa tannin model water and olive mill wastewater by energy-efficient electrocoagulation process

The objective of this work was to study the influence of NaCl concentration, time, and current density on the removal efficiency of phenolic compounds by electrocoagulation process, as well as to compare the specific energy consumption (SEC) of these processes under different experimental conditions. Electrocoagulation was carried out on two different samples of water: model water of mimosa tannin and olive mill wastewater (OMW). Low carbon steel electrodes were used in the experiments. The properties of the treated effluent were determined using UV/Vis spectroscopy and by measuring total organic carbon (TOC). Percentage of removal increased with time, current density, and NaCl concentration. SEC value increased with increased time and current density but it was decreased significantly by NaCl additions (0-29 g L-1). It was found that electro­coagulation treatment of effluents containing phenolic compounds involves complex formation between ferrous/ferric and phenolic compounds

Reduced Graphene Oxide/α-Fe2O3 Fibres as Active Material for Supercapacitor Application

The composite hydrogel, composed of reduced graphene oxide and α-Fe2O3 fibres (rGO/α-Fe2O3), was successfully prepared by the hydrothermal procedure starting from GO and α-Fe2O3 nanofibres. According to the SEM and XRD results, α-Fe2O3 fibres are distributed between rGO sheets increasing the inter-sheet space. The rGO/α-Fe2O3 composite was tested as an active material in supercapacitor by means of cyclic voltammetry, galvanostatic charging/discharging and electrochemical impedance spectroscopy in 0.5 mol dm–3 Na2SO4. The obtained results confirmed a positive effect of the α-Fe2O3 addition on capacitive properties. Improved capacitive properties of the composite make this material suitable for supercapacitor application. This work is licensed under a Creative Commons Attribution 4.0 International License

Electrochemical Characterisation of Sol-Gel Derived SnO2 for Supercapacitor Application

Pseudocapacitive properties of SnO2 and Sb-doped SnO2 were determined in 0.5 mol dm–3 KCl solution. The samples were prepared by sol-gel method and analysed by X-ray powder diffraction (XRPD) and field emission scanning electron microscopy (FE SEM). Rietveld refinement of XRPD data showed the changes in unit cell parameters due to the incorporation of Sb3+ into the host SnO2 lattice, while FE SEM pointed out the differences in morphology caused by doping. Specific capacitance values of 3.67 and 6.89 F g–1 were obtained for SnO2 and Sb-doped SnO2, respectively. Reaction mechanism of SnO2 that corresponds to the obtained mass change was proposed. It was shown that redox reactions of SnO2 and Sb-doped SnO2 are dependent on structural changes since different mass change properties were obtained in comparison to the previous reports carried out for other metal oxides. This work is licensed under a Creative Commons Attribution 4.0 International License

Ugradnja grafenova oksida u sloj vodljivog polimera i naknadna elektrokemijska redukcija

U ovom radu provedena je elektrokemijska sinteza poli(3,4-etilendioksitiofena) (PEDOT) sloja i kompozitnog sloja PEDOT/grafenov oksid (GO). Sinteza je provedena iz elektrolita koji je sadržavao 3,4-etilendiokstiofen (EDOT) u otopini poli(natrij 4-stirensulfonata) (PSS) ili smjesi PSS/GO. Rezultati su pokazali da se dobra pseudokapacitivna svojstva PEDOT slojeva postižu elektrokemijskom sintezom kod 1,00 V te pri trajanju sinteze do 600 s. Za optimalnu koncentraciju PSS određena je vrijednost od 0,01 mol dm–3. Ugradnja GO-a u strukturu vodljivog polimera dokazana je rezultatima UV/Vis spektrofotometrije. Radna elektroda sa slojem PEDOT/GO negativno je polarizirana pri −1,4 V u 0,1 mol dm–3 otopini KCl. Tim postupkom GO je preveden u vodljivi oblik odnosno reducirani grafenov oksid. Poboljšana pseudokapacitivna svojstva ukazala su na uspješno provedenu elektrokemijsku redukciju GO-a u sloju vodljivog polimera. Sintetizirani vodljivi polimeri ispitani su metodom cikličke voltametrije

Characterisation of Pseudocapacitive Properties of Chemically Prepared MnO2 and MnO2/Polypyrrole Composite

U ovom je radu opisana kemijska sinteza uzoraka MnO2 te dva različita kompozita MnO2/polipirol (Kompozit1 i Kompozit2). Kompozit1 priređen je kemijskom reakcijom pirola i KMnO4, dok je Kompozit2 priređen polimerizacijom pirola u prisutnosti prethodno dobivenog MnO2 primjenjujući FeCl3 kao oksidans. S ciljem formiranja elektroda za provođenje elektrokemijskih ispitivanja, uzorci su: 1) tijekom sinteze izravno taloženi na podloge od Pt i ugljikova platna i 2) sintetizirani te naknadno naneseni na podlogu od Pt uz dodatak veziva i aktivnog ugljena, pri čemu su dobivene elektroda MnO2, elektroda Kompozita1 i elektroda Kompozita2. Za sve su elektrode gotovo idealna pseudokapacitivna svojstva dobivena u području potencijala od 0,0 V do 0,6 V prema zasićenoj kalomelnoj elektrodi. Uočeno je, međutim, da polarizacija na potencijalima negativnijim od 0,0 V uzrokuje ireverzibilne promjene u strukturi materijala i gubitak pseudokapacitivnih svojstava kod MnO2 i elektroda Kompozita1, dok elektroda Kompozita2 ostaje stabilna u testiranom području potencijala. Elektroda MnO2 je dodatno ispitana metodom elektrokemijske impedancijske spektroskopije, pri čemu je utvrđeno da polarizacija na potencijalima negativnijim od 0,0 V dovodi do porasta otpora u materijalu elektrode i usporavanja brzine pseudokapacitivne redoks-reakcije Mn4+/Mn3+. Određivanjem morfoloških karakteristika utvrđeno je da se elektroda Kompozita1 sastoji od dviju faza, što ukazuje na odvojen rast MnO2 i polipirola tijekom sinteze. Uzorak Kompozit2 pokazuje znatno homogeniju strukturu površine, gdje su čestice MnO2 prekrivene slojem polipirola. Izgleda da tako istaloženi polipirol osigurava dobru električnu vodljivost uzorka zbog čega su kod elektrode Kompozita2 dobivene najveće vrijednosti specifičnog kapaciteta (23 F g−1 – 31 F g−1). Osim toga, prisutnost polipirola kod elektrode Kompozita2 osigurava stabilnost MnO2 u širokom području potencijala, čime se omogućava konstrukcija elektroda s povećanom gustoćom uskladištene energije.This article describes the synthesis of MnO2 and MnO2/polypyrrole composites. Composite1 was prepared by chemical reaction of pyrrole and potassium permanganate resulting in a product composed of polypyrrole and MnO2. Composite2 was prepared by pyrrole polymerisation in the presence of MnO2, using FeCl3 as oxidant. In order to carry out the electrochemical experiments the samples were: 1) directly precipitated during the synthesis on Pt or carbon cloth supports, and 2) synthesized and subsequently applied on Pt support with the addition of binder and activated carbon, resulting in MnO2 electrode, Composite1 electrode and Composite2 electrode. It has been shown that it is possible to precipitate the sample directly at Pt or carbon cloth support during the chemical synthesis, thus providing a fast and easy procedure of material characterisation. The pseudocapacitive properties of the samples were determined in NaCl solution (concentration 0.5 mol dm−3) using the cyclic voltammetry method. Good pseudocapacitive properties were obtained within the potential window from 0 V to 0.6 V vs. saturated calomel electrode for all tested electrodes. The characteristic of good capacitive response is constant current in a wide potential range. However, during polarisation at potentials more negative than 0.0 V, structural changes and the loss of pseudocapacitive properties occur for MnO2 and Composite1 electrodes in contrast to Composite2, which was stable throughout the potential window. Structural changes and the loss of pseudocapacitive properties are evident from irreversible current peaks in the cyclic voltammogram. The MnO2 sample was additionally tested by means of electrochemical impedance spectroscopy and it was found that for the electrode polarized at potential more negative than 0.0 V the resistance increased and the pseudocapacitive Mn4+/Mn3+ redox reaction rate slowed down. This phenomenon was explained by water intercalation within the material during polarisation at potentials < 0.0 V. In the case of Composite2 electrode, it seems that polypyrrole provided stability of MnO2 within the wide potential window, which resulted in good capacitive response. Furthermore, from the morphological properties of the samples, it was established that Composite1 contained two separate phases, which was ascribed to the independent growth of MnO2 and polypyrrole, while Composite2 was homogeneous and the MnO2 particles were uniformly covered by polypyrrole layer that enabled stability of Composite2 electrode. The MnO2 electrode with the sample subsequently applied on the support showed different behaviour compared to MnO2 electrode with the sample directly precipitated on the support. This was the consequence of higher resistance caused by higher thickness of the sample subsequently applied on the support. Due to the higher resistance, typical reversible capacitive behaviour was not registered. However, better response was obtained for Composite2 electrode with the sample subsequently applied on the support because of the presence of polypyrrole that improved conductivity of the material. For the same reason, the highest value of specific capacitance has been registered for the Composite2 electrode (23 F g−1 − 31 F g−1)

Influence of Multiwalled Carbon Nanotube Modification on Polyurethane Properties: II. Mechanical Properties, Electrical Conductivity and Thermal Stability

U ovom radu istraživan je učinak dodatka višestjenih ugljikovih nanocjevčica (MWCNT) te MWCNT-a modificiranog skupinama COOH (MWCNT-COOH) u rasponu masenih udjela od 0 do 4 % na svojstva poliuretana. Uzorci nanokompozita pripravljani su dispergiranjem nanopunila u otopini poliuretana u acetonu te polaganim isparavanjem otapala pri sobnoj temperaturi. Utjecaj punila na mehanička svojstva kompozita ispitan je testom jednoosnog istezanja, a električna provodnost uzoraka određivana je metodom četiri kontakta. Toplinska postojanost istražena je termogravimetrijskom analizom (TGA). Obje vrste punila MWCNT povećavaju modul, ali snižavaju prekidnu čvrstoću i prekidno istezanje kompozita. Rezultati ispitivanja električne provodnosti pokazali su da se, u odnosu na čisti PU koji ima provodnost reda veličine 10–13 S cm–1, provodnost nanokompozita s masenim udjelom punila MWCNT 0,2 % znatno povećava na vrijednost reda veličine 10–6 S cm–1. Daljnjim povećanjem do masenog udjela obje vrste MWCNT-a 4 %, provodnost se dalje povećava do vrijednosti većih od 10–2 S cm–1. Taj učinak povećanja provodnosti neznatno je jače izražen u sustavima s MWCNT-COOH-om. Rezultati termogravimetrijske analize upućuju na to da se dodatkom obje vrste MWCNT-a znatno poboljšava toplinsku postojanost u istraživanom rasponu udjela nanopunila, pri čemu je ovaj učinak nešto izraženiji za sustave s punilom MWCNT. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.In this paper, the influence of multiwalled carbon nanotubes (MWCNT) and carbon nanotubes modified with COOH groups (MWCNT-COOH) on the mechanical and electrical properties as well as on thermal stability of polyurethane (PU) were investigated. The samples of nanocomposite were prepared by dispersion of the nanofiller in a solution of polyurethane in acetone, followed by slow evaporation of the solvent at room temperature. The effect of the fillers on the mechanical properties of PU nanocomposites was examined by the uniaxial deformation test, and electrical properties of the samples were determined by the four probe method. Thermal stability was investigated by thermogravimetric analysis (TGA). The addition of both types of MWCNTs fillers increases modulus (Fig. 1), due to higher modulus of the nanofillers. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl group in PU matrix, nanocomposites with MWCNT-COOH have higher modulus than nanocomposites with MWCNT filler. Most of the composites have lower strength and elongation at break than PU (Figs. 2 and 3). Smaller MWCNT-COOH aggregates and stronger interactions between this filler and the PU matrix cause less pronounced decreasing of strength at break. Compared to the pure PU, with conductivity of the order of 10–13 S cm–1, the conductivity of the nanocomposite with mass fraction of MWCNT nanofiller 0.2 % substantially increases up to the value of the order 10–6 S cm–1 (Fig. 4). A further increase up to 4 % for both types of MWCNTs, resulted in a further increase in conductivity up to values exceeding 10–2 S cm–1. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl groups in PU matrix, the conductivity increase effect in systems with MWCNTs-COOH is slightly more pronounced. All investigated nanocomposites have potential applications as electric discharge materials and for electrostatic painting. The results of the thermogravimetric analysis indicate that the addition of both types of MWCNTs significantly improves the thermal stability (Figs. 6 and 7). The maximal degradation rate temperature of polyurethane increased by about 45 °C, thereby this effect is slightly more pronounced for systems with MWCNTs (Fig. 7). This work is licensed under a Creative Commons Attribution 4.0 International License