Exfoliated graphite–ruthenium oxide composite electrodes for electrochemical supercapacitors

The performance of exfoliated graphite (EG)–ruthenium oxide (RuOx) composites as binderless electrodes is evaluated for electrochemical capacitors (ECs). A composite of EG–RuOx is prepared by a modified sol–gel process. The material is characterized using X-ray diffraction and microscopy. Electrochemical capacitors with the composite electrodes in the presence of aqueous sulfuric acid (H2SO4) electrolyte are evaluated using voltammetry, impedance and charge–discharge studies. Cyclic voltammetry reveals very stable current–voltage behaviour up to several thousands of cycles, as well as high specific capacitances, e.g., a few hundreds of farads per gram for the composite that contains 16.5 wt.% RuOx.

Glassy carbon ceramic composite electrodes

A new carbon composite electrode material, based on dispersing glassy carbon (GC) microparticles into methyltrimethoxysilane-derived sol, is described in the present paper. The resulting glassy carbon ceramic composite electrodes (GCCEs) combine the electrochemical properties of GC with the advantages of composite electrodes, and thus offer high electrochemical reactivity, low background current and are easy to prepare, modify and renew. The new material has a low double-layer capacitance and a wide potential window. Scanning electron microscopy (SEM) images indicate significant difference in the structure of GCCE and carbon ceramic composite electrode (CCE). The electrochemical properties and advantages of GCCE should find broad utility in electroanalysis.

Cupric hexacyanoferrate nanoparticle modified carbon ceramic composite electrodes

Graphite powder-supported cupric hexacyanoferrate (CuHCF) nanoparticles were dispersed into methyltrimethoxysilane based gels to produce a conducting carbon ceramic Composite, which was used as electrode material to fabricate surface- renewable CuHCF-modified electrodes. Electrochemical behavior of the CuHCF-modifled carbon ceramic composite electrodes was characterized using cyclic and square-wave voltammetry. Cyclic voltammograms at various scan rates indicated that peak currents were surface-confined at low scan rates. In the presence of glutathione, a clear electrocatalytic response was observed at the CuHCF-modified composite electrodes. In addition, the electrodes exhibited a distinct advantage of reproducible surface-renewal by simple mechanical polishing on emery paper, as well as ease of preparation, and good chemical and mechanical stability in a flowing stream.

Sol-gel-derived carbon ceramic composite electrodes bulk-modified with 1 : 12-silicomolybdic acid

1:12-Silicomolybdic acid (SiMo12) doped carbon ceramic composite electrodes were fabricated by incorporating SiMo12 and graphite powder in a methyltrimethoxysilane-based gel and characterized by cyclic and square-wave voltammetry, It was demonstrated that the chemically modified electrodes were suitable for electrocatalytic reduction of bromate, The electrodes had the remarkable advantage of surface renewal owing to bulk modification, as web as simple preparation, good mechanical and chemical stability and reproducibility.

Sol-gel-derived graphite organosilicate composite electrodes bulk-modified with Keggin-type alpha-germanomolybdic acid

A novel inorganic-organic hybrid material incorporating graphite powder and Keggin-type alpha -germanomolybdic acid (GeMo12) in methyltrimethoxysilane-based gels has been produced by the sol-gel technique and used to fabricate a chemically bulk-modified electrode. GeMo12 acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The GeMo12-modified graphite organosilicate composite electrode was characterized by cyclic and square-wave voltammetry. The modified electrode shows a high electrocatalytic activity toward the reduction of bromate, nitrite and hydrogen peroxide in acidic aqueous solution. In addition, the chemically-modified electrode has some distinct advantages over the traditional polyoxometalate-modified electrodes, such as long-term stability and especially repeatability of surface-renewal by simple mechanical polishing.

Analytical Potentialities of Carbon Nanotube/Silicone Rubber Composite Electrodes: Determination of Propranolol

A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone-rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70% (m/m) electrodes with linear dynamic ranges up to 7.0 mu molL(-1) by differential pulse and up to 5.4 mu molL(-1) by square wave voltammetry, with LODs of 0.12 and 0.078 mu molL(-1), respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.

Electrochemical Behavior of Verapamil at Graphite-Polyurethane Composite Electrodes: Determination of Release Profiles in Pharmaceutical Samples

A solid graphite-polyurethane composite electrode has been used to determine release profiles of verapamil, a calcium-channel blocker. The electro-oxidation process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy and showed no adsorption of analyte or oxidation products, unlike at other carbon-based electrodes. Quantification gave linear ranges up to 40molL-1 with cyclic voltammetry and detection limits of 0.7molL-1 by differential pulse and square-wave voltammetry. Commercial product samples were successfully analyzed with results equal to those from spectrophotometry. Because no electrode surface renewal is needed, this electrode material has many advantages.

Preparation of composite electrodes with carbon nanotubes for lithium-ion batteries by low-energy ball milling

Some of the prospective electrode materials for lithium-ion batteries are known to have electronic transport limitations preventing them from being used in the electrodes directly. In many cases, however, these materials may become practical if they are applied in the form of nanocomposites with a carbon component, e.g. via incorporating nanoparticles of the phase of interest into a conducting network of carbon nanotubes. A simple way to prepare oxide-carbon nanotube composites suitable for the electrodes of lithium-ion batteries is presented in this paper. The method is based on low-energy ball milling. An electrochemically active but insulating phase of LiFeTiO4 is used as a test material. It is demonstrated that the LiFeTiO4-carbon nanotube composite is not only capable of having significantly higher capacity (∼105-120 mA h g-1vs. the capacity of ∼65-70 mA h g -1 for the LiFeTiO4 nanoparticles) at a slow current rate but may also operate at reasonably high current rates. © the Partner Organisations 2014.

Performance enhancement of single-walled nanotube-microwave exfoliated graphene oxide composite electrodes using a stacked electrode configuration

We report the development of a stacked electrode supercapacitor cell using stainless steel meshes as the current collectors and optimised single walled nanotubes (SWNT)-microwave exfoliated graphene oxide (mw rGO) composites as the electrode material. The introduction of mw rGO into a SWNT matrix creates an intertwined porous structure that enhances the electroactive surface area and capacitive performance due to the 3-D hierarchical structure that is formed. The composite structure was optimised by varying the weight ratio of the SWNTs and mw rGO. The best performing ratio was the 90% SWNT-10% mw rGO electrode which achieved a specific capacitance of 306 F g-1 (3 electrode measurement calculated at 20 mV s-1). The 90% SWNT-10% mw rGO was then fabricated into a stacked electrode configuration (SEC) which significantly enhanced the electrode performance per volume (1.43 mW h cm-3, & 6.25 W cm-3). Device testing showed excellent switching capability up to 10 A g-1, and very good stability over 10000 cycles at 1.0 A g-1 with 93% capacity retention. © the Partner Organisations 2014.

The reduction of oxygen on iron(II) oxide/poly(3,4-ethylenedioxythiophene) composite thin film electrodes

© 2014 Elsevier Ltd. All rights reserved. Conducting polymers (CPs) are currently being investigated for use in many applications owing to their abilities to catalyze a wide range of electrochemical reactions and act as an effective electrode support for various inorganic and organic electrocatalyst materials. Here, we have found that the deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) through the use of an established base-inhibited chemical vapor-phase polymerization (VPP) procedure using an iron(III) tosylate oxidant results in the co-deposition of electrocatalytic iron(II) oxide species within the film. The presence of these species accounts for the 2-electron reduction of hydrogen peroxide that occurs on these electrodes during the series 4-electron oxygen reduction reaction. Furthermore, this realization leads to the possibility of fabricating thin film inorganic/CP composites of various compositions through careful choice of oxidant in a facile, one-step process. A combination of in situ Raman (487.77 nm laser) and in situ UV-Vis spectroscopy was used to probe the oxidation state of PEDOT in the thin film composite electrodes while reducing oxygen in alkaline conditions. These measurements show that the 2-electron electroreduction of hydrogen peroxide (or HO2 -) occurs only on the iron(II) oxide species in a reaction that is facilitated by an effective electron transfer from the delocalized electron orbitals of the PEDOT matrix. This approach could potentially be used in situ to monitor the electrocatalyst/electrode interface quality of conducting polymer-supported electrocatalysts.

Ascorbate electro-oxidation by modified electrodes: Polypyrrole and polypyrrole/Ni(OH)(2) composite thin films

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Renewable surface electrodes based on dopamine functionalized exfoliated graphite: NADH oxidation and ethanol biosensing

Exfoliated graphite (EG) was modified by covalently attaching dopamine (DA) (3,4-dihydroxyphenethylamine) through amide linkages, using -COOH groups introduced on the EG surface. The modified material was characterized by FT-IR spectroscopy, Xray photoelectron spectroscopy and electrochemical techniques. Composites of DA modified EG dispersed in organically modified silicates were prepared by a sol-get process. Electrodes were fabricated by casting the composites in glass tubes. The sol-gel based electrodes were found to be active for the electrocatalytic oxidation of NADH and biosensing of ethanol in presence of NAD(+) and alcohol dehydrogenase enzyme. The modified composite electrodes were found to be stable for several months. The surface of the electrode could be renewed just by mechanically polishing the electrode using emery sheets. The modified EG was also pressed and restacked in the form of a pellet and the use of this material as a binderless bulk-modified electrode was also demonstrated. The performance of sol-gel derived composite EG electrodes with binderless bulk-modified EG electrodes was compared. (C) 2002 Elsevier Science B.V. All rights reserved.