Electrocatalytic oxidation of benzyl alcohol in alkaline medium on RuO2-coated titanium electrode

The heterogeneous electrocatalytic redox behaviour of RuO₂ electrodes fabricated by thermal decomposition is investigated with and without benzyl alcohol using cyclic voltammetric and potentiodynamic techniques. The cyclic voltammetric results show that benzyl alcohol oxidation is mediated by perruthenate ion electrogenerated at the electrode surface. Evaluation of kinetic parameters in relation to Tafel lines allows the postulation of a plausible reaction scheme in which benzyl alcohol adsorbs on the RuO₂ electrode surface and the rate determining step is chemical reaction between perruthenate and adsorbed species. The reaction orders with respect to benzyl alcohol and OH^– concentrations are 0.85 and 1, respectively. The results in galvanostatic electrolysis show that the major product for benzyl alcohol oxidation in an aqueous solution is benzaldehyde, and the organic yield is affected by such electrolysis conditions as t-butanol concentration, electrolysis current density, KOH concentration and electrolysis temperature.     

Study of IrxRu1−xO2 oxides as anodic electrocatalysts for solid polymer electrolyte water electrolysis

Electrocatalysts of the general formula Ir_xRu_1−xO₂ were prepared using Adams’ fusion method. The crystallite characterization was examined via XRD, and the electrochemical properties were examined via cyclic voltammetry (CV) in, linear sweep voltammetry (LSV) and chronopotentiometry measurements in 0.5 M H₂SO₄. The electrocatalysts were applied to a membrane electrode assembly (MEA) and studied in situ in an electrolysis cell through electrochemical impedance spectroscopy (EIS) and stationary current density–potential relations were investigated. The Ir_xRu_1−xO₂ (x = 0.2, 0.4, 0.6) compounds were found to be more active than pure IrO₂ and more stable than pure RuO₂. The most active electrocatalyst obtained had a composition of Ir_0.2Ru_0.8O₂. With an Ir_0.2Ru_0.8O₂ anode, a 28.4% Pt/C cathode and the total noble metal loading of 1.7 mg cm⁻², the potential of water electrolysis was 1.622 V at 1 A cm⁻² and 80 °C.     

Electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode

The electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode without supporting electrolyte in the liquid organic phase was investigated. A novel Pt-Pb/Nafion® electrode was prepared for the electrolysis of the organic compound in this solid polymer electrolyte (SPEO) system. A reaction mechanism is proposed. No benzyl alcohol was produced using fresh Nafion® as electrode. The selectivity of benzyl alcohol using Pt-Pb/Nafion® as an electrode was almost 100% and only a trace of hydrobenzoin byproduct was found in the catholyte. The optimum faradic yield of benzyl alcohol was 18.70 g F^–1. The primary factors affecting the current efficiency or faradic yield of the cathodic reduction of benzaldehyde to benzyl alcohol were cell voltage, solvent and temperature. The use of a Pt-Pb/Nafion® electrode in a SPE® system for the electrochemical reduction of benzaldehyde was found to be a feasible technique.     

Sulphur content and the hydrogen evolving activity of NiS x deposits using statistical experimental strategies

The effect of such electroplating conditions as current density, thiourea (TU) concentration, temperature and pH on the sulphur content of NiS _x deposited electrodes has been systematically studied using fractional factorial design and response surface methodology. Fractional factorial analysis indicates that the main and interaction effects of TU concentration and current density are the key variables influencing sulphur content in a NiS _x deposit. Empirical models for sulphur content and hydrogen evolution overpotential are fitted and plotted, using central composite experimental design, as contour diagrams in order to facilitate comparison with experimental sulphur content trends and hydrogen evolving activity. The results show that, for deposits containing > 12 wt % sulphur content, hydrogen evolving activity increases with increasing sulphur content, while for those possessing < 12 wt% sulphur content, hydrogen evolution overpotential decreases with increasing electroplating current density.     

Hypochlorite generation on Ru–Pt binary oxide for treatment of dye wastewater

Ruthenium–platinum binary oxides [(Ru + Pt)O _x ] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviour was characterized by cyclic voltammetry (CV) and linear scanning voltammetry (LSV). The effects of electrolyte conditions on the current efficiency (CE) of hypochlorite production on binary (Ru + Pt)O _x electrodes and the treatment of a high salt-containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production occurred on the RP1 (20 mol% Pt in precursor) electrode. The major factors influencing CE for hypochlorite production were the electrolyte flow rate, current density and chloride ion (C1^–) concentration. The RP1 electrode exhibited the best removal of organics and chromophoric groups in the dye wastewater. On this electrode, better removal of organics and chromophoric groups was obtained at 300 mA cm^–2. The colour of black–red dye wastewater became light yellow when a charge of 13.2 A h was passed while the COD of the wastewater decreased from 10 500 to 1250 mg L^–1.     

Evaluation of the phenolic antioxidants of olive (Olea europaea) leaf extract obtained by a green approach: Use of reduced graphene oxide for electrochemical analysis

Abstract

Deep Eutectic Liquids (DELs) have been specially designed, and used for the extraction of bioactive natural products from a bio-waste, since they have attracted much attention from economic and ecological aspects. In this study, an easy, accurate and sensitive detection method has been developed towards a trace amount of oleuropein which is one of the most significant components of the olive leaf extract. TiO_x-modified reduced graphene oxide electrode (TiO_x-RGO@GCE) has been used as the sensing electrode for the quantitative detection of oleuropein. The structural characterization of TiO_x-RGO@GCE has been performed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and atomic force microscopy (AFM) techniques. Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques have been implemented to investigate the electrochemical behavior of oleuropein. The electrochemical experiments revealed that the quasi-reversible reaction is the dominant mechanism on the electrode/electrolyte interface. The linear concentration range of 1–12?µM was obtained with the detection limit of 18.7?nM for oleuropein.     

Nafion/lead oxide–manganese oxide combined catalyst for use as a highly efficient alkaline air electrode in zinc–air battery

In this study, we report the application of an inexpensive and easily prepared lead oxide–manganese oxide catalyst combined with Nafion (designated as Nf/PbMnO_x) as a highly efficient air-cathode for a zinc–air battery. We verify the mechanistic study of the reduction of O₂ for Nf/PbMnO_x in alkaline aqueous solution using rotating ring/disk electrode voltammetry, and also an electrochemical approach using a wall-jet screen-printed ring disk electrode. The presence of Nf/PbMnO_x shows great catalytic activity for the disproportionation reaction of HO₂⁻ to O₂ and OH⁻ with an overall 4e⁻ reduction of O₂ in the first reduction reaction. The 4e⁻ reduction of O₂ was eventually achieved at the Nf/PbMnO_x through evidence from the slope of Koutecky–Levich plots. With these inherent features, we then fabricated the zinc–air battery with the Nf/PbMnO_x catalyst and examine the performance for a practical application with air cathodes.     

Hypochlorite production on Ru-Sn binary oxide electrode and its application in treatment of dye wastewater

Ruthenium-tin binary oxides [(Ru+Sn)O₂] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviours were characterized by cyclic voltammetry and linear-scan voltammetry (LSV) methods. The effects of electrolysis condition for the current efficiency (CE) of hypochlorite production on binary (Ru+Sn)O₂ electrodes and the treatment of a high salt-containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production exists on an RS3 (40 to 80 mol% Sn in coating solution) electrode. The major factors influencing CE for hypochlorite production are the electrolyte flow rate, current density, and chloride (Cl-) concentration. Major factors affecting energy yield are current density, Cl- concentration, and electrode distance. For low current density (300 mA.cm^?2), high Cl- concentration (1 mol.L^?1), and 0.45 cm electrode separation, a high specific energy is obtained. The RS3 electrode exhibits the best removal of organics and chromophor groups in the dye wastewater. On this electrode, better removal of organics and chromophor groups is obtained at 300 mA.cm^?2. The colour of black-red dye wastewater becomes light yellow when a charge of 792 A·min was passed, while the chemical oxygen demand (COD) of this wastewater is decreased from 10500 mg.L^?1 to 1250 mg.L^?1.     

Arsenic detection by nanogold/conducting‐polymer‐modified glassy carbon electrodes

This article discusses the results for the development of a nanogold‐particle/polyaniline‐modified glassy carbon electrode for the detection of arsenic(III) in water. A thin polyaniline film was electropolymerized onto a glassy carbon electrode. The gold nanoparticle was then deposited onto the polyaniline‐coated glassy carbon electrode via potential step electrolysis from 1.1 to 0 V versus Ag/AgCl/NaCl (saturated) for 45 s from a 0.5M H₂SO₄ solution containing 0.1 mM NaAuCl₄ in the absence and presence of a 0.1 mM KI additive. The surface of the modified electrode was examined with scanning electron microscopy. Cyclic and anodic stripping voltammetry of arsenic(III) was performed on the modified electrode. The thus modified nanogold‐particle/polyaniline‐modified glassy carbon electrode prepared in the presence of the I^? (KI) additive showed a high sensitivity in detecting arsenic(III) in water, and with stripping voltammetry, a limit of detection of 0.4 ppb arsenic was obtained, which is much lower than the arsenic guideline limit of the World Health Organization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1306–1311, 2007     

Hydrogen evolution on RuxTi1−xO2 in 0.5 M H2SO4

Hydrogen evolution from 0.5 M H₂SO₄ on Ti electrodes coated with a Ru_xTi_1−xO₂ (x=0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe²⁺ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O₂ coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10⁻⁴ A cm⁻² after activation.     

Production of fluorine with pulsed currents

During the d.c. electrolysis of KF-nHF melts, a passivating film of graphite fluoride (CF_x) is formed on the carbon electrodes, leading to high anodic overvoltage. Pulsed electrolysis enables fluorine production with significant improvements if, during the lowest potential of the pulse, a small reduction current is applied to the carbon electrode, leading to the partial reduction of CF_x. Rectangular or sinusoidal waves have been studied. Very high peak values of the current density (150 A dm^–2,i.e. 10 times more than the values usually reached with d.c) were obtained in some particular cases.     

Electrochemical polymerization of 2-aminothiazole

Electrochemical polymerization of 2-aminothiazole (AT) was studied in acetonitrile with tetrabutylammonium tetrafluoroborate (TBAFB) as the supporting electrolyte via constant potential electrolysis (CPE). The redox behavior of AT was investigated in the same solvent-electrolyte couple by cyclic voltammetry, CV. CPE of AT produced a soluble conducting polymer on the electrode surface. The effects of temperature, monomer concentration and polymerization time on the rate of electrochemical polymerization were also studied. The structural analyses of the polymer were carried out by ¹H-NMR, FTIR and UV–VIS spectroscopies and elemental analysis. Thermal properties were studied by DSC and TGA. Conductivity measurements were carried out by four-probe technique and the number average molecular weight, M _n, of the polymer was determined by cryoscopy.     

Direct electrochemical detection of pyruvic acid by cobalt oxyhydroxide modified indium tin oxide electrodes

An enzyme-free electrode was fabricated by anodic electrodeposition of cobalt oxyhydroxide film on an ITO electrode (CoO_x(OH)_y/ITO) for direct electrochemical detection of pyruvic acid (PA) in solution. Scanning electron microscopy (SEM) and atom force microscopy (AFM) were employed to characterize the morphology of CoO_x(OH)_y film. Cyclic voltammetry (CV) was used to investigate the electrochemical properties of PA on CoO_x(OH)_y/ITO in order to select the optimal potential for the chronoamperometric detection of PA. It was found that the CoO_x(OH)_y/ITO electrode served as an excellent PA sensor with a linear detection range of 1.00 μM to 1.91 mM, a detection limit of 0.55 μM, and a high sensitivity of 417.1 μA mM⁻¹ cm⁻². Moreover, the response time of CoO_x(OH)_y/ITO to PA is less than 10 s, which is the shortest for PA detection reported in literature using electrochemical method. These properties and the high stability of CoO_x(OH)_y/ITO made it a good candidate for developing electrochemical enzyme-free PA sensing device.     

Preparation and electrochemical properties of polyaniline/α‐RuCl3.xH2O composites for supercapacitor

Polyaniline/α‐RuCl₃.xH₂O composites were successfully synthesized by an in‐situ chemical polymerization and employed as new electrode materials in supercapacitors. The synthesized composites were characterized physically by scanning electronic microscope (SEM). The electrochemical capacitance performance of these composites was investigated by cyclic voltammetry, galvanostatic charge–discharge tests and AC impedance spectroscopy with a three‐electrode system in 1 mol l⁻¹ NaNO₃ aqueous solution electrolyte. The polyaniline/α‐RuCl₃.xH₂O composites electrodes showed much higher specific capacitance, better power characteristics and were more promising for application in capacitor than pure polyaniline electrode. The effect and role of α‐RuCl₃.xH₂O in the composite electrode were also discussed in detail. POLYM. COMPOS., 34:2142–2147, 2013. © 2013 Society of Plastics Engineers     

Electrochemistry of pyrylium compounds—II[1]. Structural effects on the voltammetric behavior in acetonitrile

The electrochemical behavior of 25 pyrylium perchlorates and 2 benzopyrylium perchlorates in acetonitrile was investigated using voltammetry and oscillopolarography at a rotating disc electrode, voltammetry at a rotating ring-disc electrode, cyclic voltammetry and coulometry of the potentiostatic reduction. All compounds exhibit two cathodic waves corresponding to the formation of pyranyl radicals P^. and pyranyl anions P^? respectively. The dimerization of P^. leading to bipyranes P₂ decisively influences the voltammetric behavior. This process occurs more rapidly at the carbon atom 4 than at the carbon atom 2 of the pyrylium cation and is reversible in the case of 2,4,6-triaryl-compounds and irreversible in the case of pyrylium cations having H, methyl, benzyl or styryl in position 2 or 4. Some dimerization rate constants were determined and the equilibrium between P^. and the isomers of P₂ is discussed in structural terms.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Effect of microstructure on the electrochemical behavior of Pt/YSZ electrodes

Two types of O₂,Pt/YSZ electrode preparation (Pt/YSZ cermet and sputtered platinum film) have been characterized by SEM and by cyclic voltammetry and chronoamperometry at 450 °C in 20 kPa oxygen. Cyclic voltammetry on the cermet and on the as-sputtered non-porous film electrode evidenced the characteristics of the PtO _x /Pt couple. The corresponding redox reaction occurs at the metal/electrolyte interface and it manifests itself by an anodic wave and one of more cathodic peaks in the voltammogram. Heat treatment of the sputtered electrode at 700 °C in oxygen atmosphere resulted in a porous structure by coalescence of the film. Cyclic voltammetry of the porous film electrode featured the characteristics of the O₂/O²⁻ couple, i.e. the redox reaction of gaseous oxygen occurring at the tpb. Chronoamperometry at anodic potentials showed similar features for both electrode preparations: an initial inhibition, a current peak and a slow activation, the latter being related to the phenomenon of electrochemical promotion of catalysis.     

Electrochemically reductive dechlorination of micro amounts of 2,4,6-trichlorophenol in aqueous medium on molybdenum oxide containing supported palladium

An electrodepositing method is used to prepare a Pd/MoO_x/GC (glass carbon) composite electrode that provides a surface modification with catalytic properties for reductive dechlorination of 2,4,6-trichlorophenol in aqueous medium at ambient temperature. The palladium particles are uniformly dispersed on a MoO_x film that is previously electrodeposited on a GC electrode. XPS (X-ray photoelectron spectroscopy) of this composite electrode presents a broad peak in the Mo (3d) region revealing the existence of Mo⁶⁺ species as well as lower valence states such as Mo⁵⁺, Mo⁴⁺. Compared with the Pd/GC electrode surface, the Pd (3d) region reveals another peak whose binding energy value is higher than in Pd/GC. This peak suggests a strong interaction between the palladium particles and the MoO_x film. This composite electrode shows better performance for electrocatalytic reductive dechlorination of 2,4,6-trichlorophenol than Pd/GC. Totally dechlorinated product (phenol) is observed at the early stage of electrolysis, no intermediate products are observed besides trace amounts of 2,4-dichlorophenol. The formation of trace amounts 2,4-dichlorophenol may occur by direct electronation on the cathode. The influence of current density and substrate concentration are also investigated.     

Study of a gold electrode modified by trans-[Ru(NH3)4(Ist)SO4] to produce an electrochemical sensor for nitric oxide

The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH₃)₄(Ist)SO₄]⁺ to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques. The gold electrode was successfully modified by the trans-[Ru(NH₃)₄(Ist)SO₄]⁺ complex ion using cyclic voltammetry. The experiments show that a monolayer of the film is achieved after ten voltammetric cycles, that NO in solution can coordinate to the metal present in the layer, that dopamine, serotonin and nitrite are interferents for the detection of NO, and that the response for the nitrite is much less significant than the responses for dopamine and serotonin. The proposed modified electrode has the potential to be applied as a sensor for NO.     

Electrochemical behavior of antimony and electrodeposition of Mg–Li–Sb alloys from chloride melts

The electrochemical behavior of Sb(III) ions was investigated in LiCl–KCl molten salt at 673 K. The reaction mechanism and transport parameters of electroactive species were determined by transient electrochemical techniques (such as cyclic voltammetry, square wave voltammetry, chronopotentiometry and chronoamperometry) at a molybdenum electrode. The results showed that electrochemical reduction of Sb(III) in LiCl–KCl melts occurred in a reaction step with an exchange of three electrons. A voltammogram with a different scan rate in LiCl–KCl containing 1.45 × 10⁻⁴ mol cm⁻³ SbCl₃ showed that the deposition/dissolution reaction of Sb(III) ions was not completely reversible. The diffusion coefficient of Sb(III) ions was 1.65(±0.01) × 10⁻⁵ cm⁻² s⁻¹ at 673 K. The electroreduction of Sb(III) ions at an Al electrode was also studied by cyclic voltammetry and open circuit chronopotentiometry in the temperature range of 668–742 K. The redox potential of Sb(III)/Sb at an Al electrode was observed at the more positive potentials values than those at an inert electrode. This potential shift due to the formation of intermetallic compound with Al electrode. AlSb alloys were prepared in LiCl–KCl–SbCl₃ melts at 742 K by potentiostatic electrolysis at an Al electrode. The activity of Sb and the Gibbs energy of AlSb formation were also calculated. Mg–Li–Sb alloys were obtained by galvanostatic electrolysis at 673 K and the electrochemical codeposition of Mg, Li and Sb was investigated on a molybdenum electrode in LiCl–KCl containing MgCl₂ and SbCl₃ melts at 673 K by cyclic voltammetry, chronopotentiometry and chronoamperometry. Cyclic voltammograms, chronopotentiometry and chronoamperometry measurements indicated that the electrochemical codeposition of Mg, Li and Sb metal occurred at current densities lower than −0.466 A cm⁻² or at an applied potential more negative than −2.350 V vs. Ag/AgCl. X-ray diffraction (XRD) suggested that Mg₃Sb₂ and Li₃Sb were formed in Mg–Li–Sb alloys. The distribution of Sb element in Mg–Li–Sb alloys from the analysis of scan electron micrograph (SEM) and energy dispersive spectrometry (EDS) indicated that Sb metal showed a distribution which resembled an interlaced network.