Remote Control Electrodeposition: Patterning on Substrates without Direct Electrical Connections

Thesis (Ph.D.)--University of Washington, 2016-06

Avaliação do tratamento eletroquímico (direto e indireto) como alternativa de degradação do corante azul de metileno

Textile industry has been a cause of environmental pollution, mainly due to the generation of large volumes of waste containing high organic loading and intense color. In this context, this study evaluated the electrochemical degradation of synthetic effluents from textile industry containing Methylene Blue (AM) dye, using Ti/IrO2-Ta2O5 and Ti/Pt anodes, by direct and indirect (active chlorine) electrooxidation. We evaluated the influence of applied current density (20, 40 and 60 mA/cm2 ), and the presence of different concentrations of electrolyte (NaCl and Na2SO4), as well as the neutral and alkaline pH media. The electrochemical treatment was conducted in a continuous flow reactor, in which the electrolysis time of the AM 100 ppm was 6 hours. The performance of electrochemical process was evaluated by UV-vis spectrophotometry, chemical oxygen demand (COD) and total organic carbon (TOC). The results showed that with increasing current density, it was possible to obtain 100 % of color removal at Ti/IrO2-Ta2O5 and Ti/Pt electrodes. Regarding the color removal efficiency, increasing the concentration of electrolyte promotes a higher percentage of removal using 0,02 M Na2SO4 and 0,017 M NaCl. Concerning to the aqueous medium, the best color removal results were obtained in alkaline medium using Ti/Pt. In terms of organic matter, 86 % was achieved in neutral pH medium for Ti/Pt; while a 30 % in an alkaline medium. To understand the electrochemical behavior due to the oxygen evolution reaction, polarization curves were registered, determining that the presence of NaCl in the solution favored the production of active chlorine species. The best results in energy consumption and cost were obtained by applying lower current density (20 mA/cm2 ) in 6 hours of electrolysis.

Electrolytes for ceramic oxide fuel cells

The main objective of this dissertation is the development and processing of novel ionic conducting ceramic materials for use as electrolytes in proton or oxide-ion conducting solid oxide fuel cells. The research aims to develop new processing routes and/or materials offering superior electrochemical behavior, based on nanometric ceramic oxide powders prepared by mechanochemical processes. Protonic ceramic fuel cells (PCFCs) require electrolyte materials with high proton conductivity at intermediate temperatures, 500-700ºC, such as reported for perovskite zirconate oxides containing alkaline earth metal cations. In the current work, BaZrO3 containing 15 mol% of Y (BZY) was chosen as the base material for further study. Despite offering high bulk proton conductivity the widespread application of this material is limited by its poor sinterability and grain growth. Thus, minor additions of oxides of zinc, phosphorous and boron were studied as possible sintering additives. The introduction of ZnO can produce substantially enhanced densification, compared to the un-doped material, lowering the sintering temperature from 1600ºC to 1300ºC. Thus, the current work discusses the best solid solution mechanism to accommodate this sintering additive. Maximum proton conductivity was shown to be obtained in materials where the Zn additive is intentionally adopted into the base perovskite composition. P2O5 additions were shown to be less effective as a sintering additive. The presence of P2O5 was shown to impair grain growth, despite improving densification of BZY for intermediate concentrations in the range 4 – 8 mol%. Interreaction of BZY with P was also shown to have a highly detrimental effect on its electrical transport properties, decreasing both bulk and grain boundary conductivities. The densification behavior of H3BO3 added BaZrO3 (BZO) shows boron to be a very effective sintering aid. Nonetheless, in the yttrium containing analogue, BaZr0.85Y0.15O3- (BZY) the densification behavior with boron additives was shown to be less successful, yielding impaired levels of densification compared to the plain BZY. This phenomenon was shown to be related to the undesirable formation of barium borate compositions of high melting temperatures. In the last section of the work, the emerging oxide-ion conducting materials, (Ba,Sr)GeO3 doped with K, were studied. Work assessed if these materials could be formed by mechanochemical process and the role of the ionic radius of the alkaline earth metal cation on the crystallographic structure, compositional homogeneity and ionic transport. An abrupt jump in oxide-ion conductivity was shown on increasing operation temperature in both the Sr and Ba analogues.

Sensor for cysteine based on oxovanadium(IV) complex of Salen modified carbon paste electrode

The electrochemical behavior of a carbon paste electrode modified (CPEM) with N,N′-ethylenebis(salicylideneiminato)oxovanadium(IV) complex ([(VO)-O-IV(Salen)]) was investigated as a new sensor for cysteine. Cyclic voltammetry at the modified electrode in 0.1 mol L-1 KCl Solution (pH 5.0) showed a single-electron reduction/oxidation of the Couple VO3+/VO2+. The CPEM with [VO(Salen)] presented good electrochemical stability in a wide pH range (4.0-10.0) and an ability to electrooxidate cysteine at 0.65 V versus SCE. These results demonstrate the viability of the use of this modified electrode as an amperometric sensor for cysteine determination. © 2004 Elsevier B.V. All rights reserved.

BODIPY-Porphyrazin-Hybride als panchromatische Lichtsammelsysteme für farbstoffsensibilisierte Solarzellen

In farbstoffsensibilisierten Solarzellen (DSSC) spielen Chromophore, die als Lichtsammel- und Energie-/Elektronentransfersysteme fungieren, eine zentrale Rolle. Phthalocyanine mit ihren intensiven Absorptionsbanden um 400 nm und 700 nm besitzen großes Potential für die effektive Sensibilisierung von Solarzellen. Trotz ihrer vielversprechenden physikochemischen Eigenschaften und intensiver Bemühungen erreichen Phthalocyanin-sensibilisierte Solarzellen nicht die Effizienzen, die bisher mit anderen Chromophorklassen erzielt werden konnten. In der vorliegenden Dissertation wurde die Entwicklung effizienter Lichtsammelsysteme für DSSC auf der Basis von Aza-substituierten Phthalocyaninen, sogenannten Pyrazinoporphyrazinen, verfolgt. Ein besonderer Fokus lag dabei auf einer Verbesserung der Absorptionseigenschaften der Chromophore im Bereich ihrer intrinsischen Absorptionslücke zwischen den Maxima um 400 nm und 700 nm. Um diese optische Lücke zu schließen wurden komplementär absorbierende BODIPY-Farbstoffe kovalent an synthetisch maßgeschneiderte Porphyrazine gebunden. Insgesamt wurden sechs neue Porphyrazin-Sensibilisatoren synthetisiert und photophysikalisch sowie elektrochemisch charakterisiert. Alle in dieser Arbeit untersuchten Porphyrazine tragen sterisch anspruchsvolle Tri(p-tolyl)propinyl-Gruppen um Agglomerationen zu vermeiden. Darüber hinaus wurden die Porphyrazine peripher entweder mit Hydroxy- oder Carboxygruppen als Bindungsstellen für oxidische Materialien ausgestattet sowie mit sechs BODIPY-Auxiliarfarbstoffen funktionalisiert, deren Substitutionsmuster variiert wurden. Zur Darstellung der komplexen Porphyrazine wurde eine Syntheseroute erarbeitet, die statistische Cyclisierungen unterschiedlicher Dinitril-Vorstufen beinhaltete und es ermöglichte, funktionelle Gruppen erst am vorgeformten Makrocyclus einzuführen. Die photophysikalische Untersuchung der hochfunktionalisierten Farbstoffe erfolgte über UV/Vis- und Fluoreszenzspektroskopie. Im Fall der BODIPY-Porphyrazin-Hybride schließt die zusätzliche Absorptionsbande der peripheren BODIPY-Einheiten die intrinsische Absorptionslücke der Porphyrazine. Die Hybride zeigen somit eine breite Absorption über den gesamten sichtbaren Spektralbereich mit hohen Extinktionskoeffizienten von ca. 4·10^5 M^−1cm^−1. Mittels Fluoreszenz- und Anregungsspektren wurde ein photoinduzierter Energie-transfer von den BODIPY-Einheiten auf den Porphyrazinkern nachgewiesen. Das elektrochemische Verhalten der BODIPY- und Porphyrazin-Verbindungen wurde mittels Cyclo- und Square-Wave-Voltammetrie untersucht. Die Effizienzen der Lichtenergieumwandlung wurden mit Hilfe von selbst-hergestellten und standardisierten farbstoffsensibilisierten Solarzellen bewertet. Alle Solarzellen zeigten eine messbare Photoaktivität unter Bestrahlung. Die Wirkungsgrade der Zellen lagen jedoch alle unter 1 %. Generell führten die Carboxyl-funktionalisierten Porphyrazine zu besseren Wirkungsgraden als die analogen, mit der tripodalen Ankergruppe ausgestatteten Derivate. Die mit Hilfe von Adsorptionsisothermen ermittelten Bindungskonstanten der Adsorption der Farbstoffe auf der TiO2-Oberfläche zeigten, dass beide Hafteinheiten eine feste Verankerung der Chromophore auf den TiO2-Elektroden ermöglichten. Insgesamt wirkte sich die Präsenz der peripheren BODIPY-Farbstoffe positiv auf die Wirkungsgrade der Solarzellen aus, jedoch nur in geringem Maß. Dieses Ergebnis wurde hauptsächlich auf die geringe Energiedifferenz zwischen der Leitungsbandkante des TiO2 und den LUMO-Energieniveaus der Chromophore zurückgeführt. Zusätzlich scheinen konkurrierende Prozesse wie die direkte Photoelektroneninjektion von den BODIPY-Einheiten in das TiO2 eine wichtige Rolle zu spielen. Neben der Anwendung in DSSC wurde die Wechselwirkung der Porphyrazine mit Graphen untersucht. Hierzu wurden A3B-Porphyrazine mit Pyrenyl-Seitenketten ausgestattet, die eine nicht-kovalente Verankerung des Chromophors auf Graphen ermöglichen. UV/Vis- und Fluoreszenzmessungen gaben u.a. erste Hinweise auf eine elektronische Kommunikation zwischen den beiden Hybridpartnern.

An EQCM Investigation of Electrochemical Precipitation of Mn(OH)(2) and Its Capacitance Behavior

Electrochemical quartz crystal microbalance (EQCM) has been used to study the electrochemical precipitation of Mn(OH)(2) on a Au crystal and its capacitance properties. From the EQCM data, it is inferred that NO3- ions get adsorbed on the Au crystal and then undergo reduction, resulting in an increase in pH near the electrode surface. Precipitation of Mn2+ occurs as Mn(OH)(2), with an increase in mass of the Au crystal. Mn(OH)(2) undergoes oxidation to MnO2, which exhibits electrochemical supercapacitor behavior on subjecting to electrochemical cycling in a Na2SO4 electrolyte. EQCM data indicate mass variations corresponding to surface insertion/extraction of Na+ ions during discharge/charge cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3479665] All rights reserved.

Electrochemical co-deposition of bimetallic Pt-Ru nanoclusters dispersed on poly(3,4-ethylenedioxythiophene) and electrocatalytic behavior for methanol oxidation

Nanoclusters of bimetallic Pt-Ru are electrochemically deposited on conductive polymer, poly(3,4-ethylenedioxythiophene)(PEDOT), which is also electrochemically deposited on a carbon paper substrate. The bimetallic deposition is carried out in an acidic electrolyte consisting of chloroplatinic acid and ruthenium chloride at 0.0 V versus saturated calomel electrode (SCE) on PEDOT coated carbon paper. A thin layer PEDOT on a carbon paper substrate facilitates the formation of uniform, well-dispersed, nano clusters of Pt-Ru of mean diameter of 123 nm, which consist of nanosize particles. In the absence of PEDOT, the size of the clusters is about 251 nm, which are unevenly distributed on carbon paper substrate. Cyclic voltammetry studies suggest that peak currents of methanol oxidation are several times greater on PtRu-PEDOT electrode than on Pt-Ru electrode in the absence of PEDOT. (C) 2011 Elsevier B.V. All rights reserved.

Morphology Controlled Growth of Meso-Porous Co3O4 Nanostructures and Study of Their Electrochemical Capacitive Behavior

The morphology of nanocrystalline Co3O4 synthesized through microwave irradiation of a solution of a cobalt complex is found to depend reproducibly on the conditions of synthesis and, in particular, on the composition of the solvent used. Despite the rapidity of the process, oriented aggregation occurs under certain conditions, depending on solvent composition. Annealing the oriented samples leads to microstructures with significant porosity, rendering the material suitable as electrodes for electrochemical capacitors. Electrochemical analysis of the oxide samples was carried out in 0.1M Na2SO4 electrolyte vs. Ag/AgCl electrode. A stable specific capacitance of 221 F/g was measured for a meso-porous sample displaying oriented aggregation. Stability of these oxide materials were checked for longer charge-discharge cycling. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.002210jes] All rights reserved.

Antioxidant activity and electrochemical elucidation of the enigmatic redox behavior of curcumin and its structurally modified analogues

Here, we report studies on the antioxidant activity and redox behavior of curcumin and its structurally modified synthetic analogues. We have synthesized a number of analogues of curcumin which abrogate its keto-enol tautomerism or substitute the methylene group at the centre of its heptadione moiety implicated in the hydride transfer and studied their redox property. From cyclic voltammetric studies, it is demonstrated that H-atom transfer from CH2 group at the center of the heptadione link also plays an important role in the antioxidant properties of curcumin along with that of its phenolic -OH group. In addition, we also show that the conversion of 1, 3-dicarbonyl moiety of curcumin to an isosteric heterocycle as in pyrazole curcumin, which decreases its rotational freedom, leads to an improvement of its redox properties as well as its antioxidant activity. (C) 2014 Elsevier Ltd. All rights reserved.

Electrochemical fabrication and electronic behavior of polypyrrole nano-fiber array devices

Electrochemically active Polypyrrole (PPy) nano-fiber array device was fabricated via electrochemical deposition method using aluminum anodic oxide (AAO) membrane as template. After alkaline treatment electrochemically active PPy nano-fiber lost electrochemical activity, and became electrochemically inactive PPy. The electronic properties of PPy nano-fiber array devices were measured by means of a simple method. It was found that for an indium-tin oxide/electrochemically inactive PPy nano-fiber device, the conductivity of nano-fiber increased with the increase of voltage applied on the two terminals of nano-fiber. The electrochemical inactive PPy nano-fiber might be used as a nano-fiber switching diode. Both Au/electrochemically active PPy and Au/electrochemically inactive PPy nano-fiber devices demonstrate rectifying behavior, and might have been used for further application as nano-rectifiers. (c) 2005 Elsevier B.V. All tights reserved.

Electrochemical corrosion behavior of cast Mg-Al-RE-Mn Alloys in NaCl solution

The electrochemical corrosion behavior of Mg-6Al-0.4Mn and Mg-6Al-4RE-0.4Mn (RE = Mischmetal) alloys is investigated in 3.5% NaCl solution. The results of corrosion process, polarization behavior, and electrochemical impedance spectroscopy of the alloys reveal that Mg-6Al-4RE-0.4Mn exhibits enhanced corrosion resistance. The addition of RE stabilizes the solid solution and modifies the passive film through a finer microstructure.

Electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd in NaCl solution

The electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd (x = 0, 1, 2 and 4 wt.%) alloys in 3.5% NaCl solution was investigated. The corrosion behavior of the alloys was assessed by open circuit potential measure, potentiodynamic polarization, and electrochemical impedance spectroscopy. The electrochemical results show the intermetallic precipitates with Nd behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. During corrosion, Al2O3 and Nd2O3, in proper ratio, is incorporated into the corrosion film, and enhances the corrosion resistance.

Electrochemical study of ion channel behavior in incorporated poly L-glutamate bilayer lipid membranes

The lipid layer membranes were fabricated on the glassy carbon electrode (GC) and demonstrated to be bilayer lipid membranes by impedance spectroscopy. The formation of incorporated poly L-glutamate bilayer lipid membrane was achieved. The ion channel behavior of the incorporated poly L-glutamate membrane was determined. When the stimulus calcium cations were added into the electrolyte, the ion channel was opened immediately and exhibited distinct channel current. Otherwise, the ion channel was closed. The cyclic voltammogram at the GC electrode coated with incorporated poly L-glutamate DMPC film response to calcium ion is very fast compared with that at the GC electrode coated only with DMPC film. Ion channel current is not dependent on the time but on the concentration of calcium. The mechanism of the ion channel formation was investigated.

Electrochemical and in situ spectroelectrochemical behavior of 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and (Zn(II)OHTTAP)

The characterization of free base porphyrin 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and its zinc(II) complexes [Zn(II)OHTTAP] containing eight thioether groups at the beta -pyrrole positions of the macrocycle was reported. Results obtained by cyclic voltammetry and differential pulse voltammetry indicated a five-electron reduction in five steps for each complex. They were oxidized in two single-electron-transfer steps to yield pi -cation radicals and dications and reduced in three single-electron-transfer steps to yield pi -anion radicals, dianions and trianions, respectively. The redox property of H(2)OHTTAP was unusual as compared to porphyrins (PPs) and phthalocyanines (Pcs). Each process was monitored by in situ thin-layer spectroelectrochemistry, which indicated that only the Ligand was electroactive. The existence of the eight hexylthio groups was responsible for the intrastack interactions and enhanced intracolumnar and intercolumnar electron motions, resulting in improved conductivity. Copyright (C) 2001 John Wiley & Sons, Ltd.