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[en] Two gold nanorod-polyaniline (Au-PANI) composites with different contents of Au were prepared by two methods. An ex situ method, in the presence of preformed gold nanorods (AuNRs) and in situ one, when an AuNRs and PANI matrix is produced simultaneously, were used. Both methods were performed in immiscible water/toluene biphasic system as a simple interfacial polymerization process. Optical, structural and morphological characteristics of the formed nanocomposites were identified. It was found that AuNRs are embedded in the conducting emeraldine salt form of PANI. Nanocomposites containing 2.0 and 28.9 wt% of Au were subsequently systematically studied for borohydride oxidation reaction (BOR) for potential application in direct borohydride-peroxide fuel cell (DBPFC). Reaction parameters: number of electrons exchanged, order of reaction and activation energy, were evaluated. Both Au-PANI nanocomposites showed activity for BOR. A laboratory DBPFC was tested reaching specific peak power density of 184 Wg(-1) at 65 degrees C with Au-PANI 1 nanocomposite (containing only 2.0 wt% of Au) as anode.
[en] Cerium oxide (CeO2-δ) ultrafine nanoparticles, with the lower (CeO2-δ -HT) and higher (CeO2-δ -SS) fraction of oxygen vacancies, were used as anchoring sites for the polymerization of aniline in acidic medium. As a result, polyaniline-emeraldine salt (PANI-ES)-based composites (PANI-ES@CeO2-δ -HT and PANI-ES@CeO2-δ -SS) were obtained. The interaction between CeO2-δ and PANI was examined by FTIR and Raman spectroscopy. The PANI polymerization is initiated via electrostatic interaction of anilinium cation and Cl − ions (adsorbed at the protonated hydroxyl groups of CeO2-δ), and proceeds with hydrogen and nitrogen interaction with oxide nanoparticles. Tailoring the oxygen vacancy population of oxide offers the possibility to control the type of PANI-cerium oxide interaction, and consequently structural, electrical, thermal, electronic and charge storage properties of composite. A high capacitance of synthesized materials, reaching ∼294 F g −1 (PANI-ES), ∼299 F g −1 (PANI-ES@CeO2-δ -HT) and ∼314 F g −1 (PANI-ES@CeO2-δ -SS), was measured in 1 M HCl, at a common scan rate of 20 mV s −1 . The high adhesion of PANI with cerium oxide prevents the oxide from its slow dissolution in 1MHCl thus providing the stability of this composite in an acidic solution. The rate of electrochemical oxidation of emeraldine salt into pernigraniline was also found to depend on CeO2-δ characteristics. © 2019 Elsevier Ltd
[en] Hydrogen evolution reaction (HER) was studied in alkaline solution on Pt(poly) electrode modified by spontaneously deposited Ir nanoislands. Comprehensive insight into the characteristics of the bimetallic Ir/Pt(poly) catalysts was obtained by a combination of Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Photoelectron Spectroscopy (XPS) and classical electrochemical techniques. HER investigations have shown that the presence of spontaneously deposited Ir enhances the activity of bare Pt(poly) in alkaline solution. This was attributed to the heterogeneity of the active surface sites and to the electronic interaction between two metals in close contact which together facilitated the adsorption of the H intermediate species. © 2019 Elsevier Ltd
[en] Series of alkylammonium modified smectites with different alkylammoinum/clay ratios was synthesized (H series). The obtained organoclays were used as precursors for carbon-clay composite materials (C series). Both set of materials were characterized by X-ray diffraction (XRD), point of zero charge (pHPZC), N2 adsorption-desorption isotherms, Raman spectroscopy and electron paramagnetic resonance (EPR) analysis. XRD analysis of organomodified clays confirmed incorporation of HDTMA+ into interlamellar space of smectite. Series of carbonized clays showed constant d001 value of 1.4 nm. The pHPZC of two series differed indicating that carbonization changed the profile of pH dependent sites on the clay surface. Textural properties of the H series decreased throughout the series, while in the C series the most developed porous structure was obtained for sample where HDTMA+ loading was equal to cation exchange capacity. Raman spectroscopy showed that amorphous carbon was formed during carbonization process. The obtained materials were used as modifiers of carbon paste electrode and investigated using electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The comparison of electrochemical behavior of H series and C series showed the importance of interlamellar species for charge transfer process. The investigation of influence of composition of carbon paste and form of added carbon showed that performance of carbon-clay based electrodes depended on synergy of different factors. © 2018 Elsevier Ltd
[en] This work shows the potential application of carbon materials prepared by three different ionic liquid-based methods, using 1-butyl-3-methylimidazolium methanesulfonate [bmim][MeSO3], for electrochemical supercapacitors. The effects of [bmim][MeSO3] on morphology, texture and surface chemistry of prepared materials has been explored by SEM/TEM, N2/CO2 adsorption measurements and XPS. The results indicate the possibility of synthesis of carbon materials with tunable physicochemical properties using ionic liquid based methods. The charge storage behavior of all materials was studied in three different pH aqueous electrolytes. The pseudocapacitive and double layer contributions were estimated and discussed from the aspect of the textural changes and the changes of the chemical composition of surface functional groups containing heteroatoms. C[dbnd]O type functional groups, with the contribution of COOH groups, were found to be responsible for a different amount of charge, which could be stored in alkaline and acidic electrolytic solution. The material prepared by direct carbonization of [bmim][MeSO3], showed the best electrochemical performance in alkaline electrolyte with a capacitance of 187 F g−1 at 5 mV s−1 (or 148 F g−1 at 1 A g−1), due to the contribution of both electric-double layer capacitance and pseudocapacitance which arises from oxygen, nitrogen and sulfur functional groups. © 2018 Elsevier Ltd
[en] A facile and fast aqueous phase-based strategy to synthesize silver-polyaniline-polyvinylpyrrolidone (Ag-PANI-PVP) nanocomposites, via chemical oxidative polymerization method is presented. In the presence of polyvinylpyrrolidone (PVP), which has an accelerating effect on the oxidation of aniline with silver nitrate, Ag nanoparticles (AgNPs) were in situ generated in aqueous solution during simultaneous formation of polyaniline (PANI), without any additional reducing agent or complicated treatment. We have demonstrated synthesis of three stabile Ag-PANI-PVP nanocomposites with different content, size, and morphology of Ag nanoparticles by varying the experimental parameters, such as pH and PVP concentration. As a result, this led to different Ag nanostructures (spherical and polyhedral NPs), and, consequently, different morphology of formed nanocomposites (granular and nanosheets). The physicochemical properties of nanocomposites were examined by using different analytical techniques (UV–Vis, TEM, FESEM, FT-IR, XRD, and Raman). It is found that optical properties, electrical conductivity and the content of Ag in the composites vary depending on the synthetic conditions. The electrocatalytic behavior of Ag-PANI-PVP nanocomposites was examined towards the oxygen reduction reaction in acidic and alkaline media. All tested nanocomposites showed high electrocatalytic activity, while the most active catalyst is the one with the highest electrical conductivity (≈0.6 S cm−1) and the lowest Ag content (3.4 wt%), synthesized in the solution without added acid. The simplicity of synthesis and good electrocatalytic efficiency of prepared nanocomposites combined with large-scale availability make them attractive as Pt-free electrocatalysts.
[en] This work present a new approach for the detection of relatively new herbicide pethoxamid (POA), a first electrochemical behavior and determination based on its oxidation on boron-doped diamond electrode in Britton-Robinson buffer solution at pH 4. Square wave voltammetric technique was used for quantification of POA at anodic potential of 1.35 V vs reference Ag/AgCl electrode. The proposed electroanalytical method is operational in the linear working range from 3 to 100 μM of POA with a limit of detection of 1.37 μM. The developed analytical procedure was successfully tested for determination of this herbicide in standard/spiked river water samples and commercial herbicide Successor T SE/spiked river water samples, offering a simple, fast and inexpensive alternative way of pesticide determining to chromatographic methods employed for this purpose.
[en] In this paper, an ion micro dispenser (IMD) was used to initiate a single pit by generating chloride anions above a 316L stainless steel electrode in either H2SO4 or HClO4 electrolyte. The current variations with respect to time provided an unambiguous characterization of the single pit evolution. Different pit shapes were observed depending on both the nature of the electrolyte and potential applied to the electrode. Substituting SO42- for ClO4- gave smaller (in diameter) but deeper pits at the early stage of pitting. However, when using a different setup that allows the sustaining of the pit propagation with a continuous supply of Cl-, the deeper pits were observed in HClO4 rather than H2SO4. The formation of an iron sulphate salt film at the bottom of the pit by precipitation of dissolution products in H2SO4 slowed down the corrosion rate. At high potentials, the repassivation mechanism outweighed the metal dissolution in the ClO4- containing solution. (authors)
[en] The processes of electrochemical deposition of magnesium oxide/hydroxide on glassy carbon (GC) electrode from magnesium nitrate hexahydrate melt have been investigated. A novel procedure predicting a possibility of direct formation of magnesium oxide during electrodeposition from the nitrate melt used is reported. XRD analysis of the obtained deposits showed the formation of magnesium oxide along with magnesium hydroxide. The electrodeposition of magnesium oxide/hydroxide commences in magnesium underpotential (UPD) and continues through the magnesium overpotential (OPD) region. Network of individual or intertwined very thin needles as well as those grouped in flower-like aggregates or honeycomb-like structures were formed in both magnesium UPD and OPD regions. Formation of the long needles was explained through theories of mechanisms of dendrite formation. Hydrogen evolution commences in the magnesium OPD region and increases with the applied overpotential. Holes observed in the deposit originated from the detached hydrogen bubbles. The number, shape and size of the hole strongly depended on both the applied cathodic potential and the hold time of electrodeposition. Magnesium oxides/hydroxides syntheses taking part simultaneously at various applied potentials are a result of reactions between magnesium cations and products of water and nitrate anions reduction processes. Chemical reactions responsible for direct formation of magnesium oxide observed are those of magnesium ions and oxygen ions, formed by nitrate reduction taking part in the close vicinity of the working electrode. (C) 2018 Elsevier Ltd. All rights reserved.
[en] Considerable promotion of RuO2 hosted by perovskite-like structure of rare earth–CoO3 composite and vice versa supercapacitive performances is reported. Spherical, sub-μm-sized, regular spheres of La0.6Sr0.4CoO3 (LSCO), were synthesized by ultrasonic spray pyrolysis. The sphere surface was subsequently hydrothermally doped by RuO2. LSCO and LSCO/RuO2 composites were investigated for their supercapacitive performances in alkaline solution. Microstructure and surface morphology were studied by SEM and XRD. It was found that amorphous Ru species decorate LSCO surface, and possibly incorporate partially into B-site of the LSCO lattice. Electrochemical characterization by cyclic voltammetry (CV), galvanostatic charge-discharge (G-C/DC) and electrochemical impedance spectroscopy (EIS) clearly revealed that capacitive performances of LSCO are considerably improved by addition of 20 mass. % of RuO2. The registered capacitance for LSCO/RuO2 reaches the values of pure RuO2, which reveals the promoting influence of LSCO on RuO2 pseudocapacitance. The EIS analysis showed that RuO2 catalyzes the redox transition of Co species, with simultaneous proportional increase in pseudocapacitive RuO2 abilities while being hosted by LSCO. This intrinsic interactive promotion introduces LSCO/RuO2 composite as unique supercapacitive material. G-C/DC curves showed that LSCO/RuO2 is of modest cyclability with respect to pure LSCO and RuO2, although the capacitance losses with cycling are acceptably low. © 2019 Elsevier Ltd