Conditions Of Voltammetry Research Articles

Characterization of the Tunisian petroleum refineries caustic effluent

A heterogeneous spent soda effluent generated from Tunisian petroleum refineries has been filtrated and separated in four solid fractions with a particle diameter of 160 to 100, 100 to 40, 40 to 16 and 16 to 10 µm and the fifth one with diameters < 10 µm obtained after total evaporation of the remained filtrate. Spectroscopic characterizations of the condensed phases by means of X-ray induced photoelectron and IR absorption, as well as pH-metry, potentiometry and stationary voltammetry at Ag2S/Ag electrode studies of the filtrate, show that the whole of the separated fractions contain Na2S, NaHS, C2H5SNa, Na2S2O3, Na2SO3 and methyl, ethyl and propyl mercaptans.

ELECTROCATALYSIS OF THE HYDROGEN EVOLUTION REACTION ON CoRe, CoWRe SUPERALLOYS DEPOSITED FROM CITRATE ELECTROLYTE

The reaction of electroreduction of hydrogen ions on binary CoRe and ternary CoWRe alloys electrodeposited from a citrate electrolyte with different amount of potassium perrhenate (0.01 and 0.05 mol·L-1) depending on the deposition current density (5–40 A·cm-2) has been investigated by the method of stationary voltammetry. The kinetic parameters of the reaction have been calculated, and it is shown that the use of ternary alloys allows one to increase the value of exchange current density by almost an order of magnitude and significantly reduce the overvoltage of hydrogen reduction in comparison with cobalt. It is shown that the best electrocatalysts for the reduction of hydrogen in alkaline solution can be ternary CoWRe alloys with a rhenium content of 15–20 at. %.

Revisiting glycerol electrooxidation by applying derivative voltammetry: From well-ordered bulk Pt to bimetallic nanoparticles

Metal nanoparticles are used to catalyze glycerol electrooxidation reaction aiming energy and chemical conversion, yielding carbonyl compounds with high market prices. The energy required to start glycerol electrooxidation is directly measured by the onset potential, determined by stationary voltammetry (dE/dt) in the form of a graph dj/dE (voltammogram). This topic has received much attention in recent years; however, a systematic rationalization of the methods to investigate the new nanomaterials is lacking to date. Here we target the identification of onset potential by revising glycerol electrooxidation on bulk well-ordered surfaces, Pt/C nanoparticles (NPs), and bimetallic NPs by applying derivative voltammetry (d2E/dt2). We revisit data regarding bulk Pt(111), Pt(110), Pt(100), and polycrystalline surface; FTIR in situ of isotopically labeled glycerol on bulk Pt and Pt/C; and concerning Sb-decorated Pt/C NPs. Our analysis shows that the use of conventional voltammetry may hide steps of the reaction and misguide the identification of the onset potential, which is accurately obtained by derivative voltammetry. The distortion induced on the function dj/dE created by an inappropriate current normalization method may disturb the threshold of the function, and the onset potential accordingly. This last point is critical since the catalyst may be mistakenly accepted as an active one.

PECULIARITIES OF ELECTRODEPOSITION OF COBALT—WOLFRAM—RENIUM ALLOY

The methods of stationary voltammetry and chronovoltammetry have been used to study deposition processes of ternary CoWRe alloys at different rhenium content of the electrolyte and deposition current density. It has been found that the limiting currents have a diffusive nature and are proportional to the concentration of perrhenate ions in the electrolyte. The CoWRe alloys should be formed by the discharge of bimetallic citrate complexes of the following composition [(Co)(WO4)(H)(Cit)]2- and rhenium electrodeposition. Rhenium does not form complexes with citrate ions and deposits better in an alloy with iron group metals than in the form of an individual metal from a perrhenate solution. It can be assumed that the discharge of rhenium into the alloy occurs from a surface complex, the nature of which has not yet been established. The alloy current efficiency reaches 93% due to the high overpotential of hydrogen evolution on the alloy surface. According to the results of investigations of the catalytic properties of alloys in the hydrogen reduction reaction, it has been found that with increasing the rhenium content of the electrolyte and alloy, an increase in hydrogen overpotential is observed. Based on the Tafel coefficients found, it was found that in an acidic and neutral medium, the limiting stage of the cathodic and anodic reaction is the transfer of the first electron. In an alkaline medium, the anode process is complicated by the simultaneous transport of two electrons. The found values of corrosion resistance are 1-2 kOm·cm-2 in solutions of 0.01 M H2SO4; 20-110 kOm·cm-2 in 2.5% NaCl; 10-30 kOm·cm-2 in 1.0 M KOH. Based on the dependence of corrosion resistance on the refractory metals content of the alloy and the electrodeposition conditions, the optimum deposition current density of 10 mA·cm-2 has been found.

Electrodeposition of tin(II) from citrate complexes

This paper provides the calculation of the distribution of the concentrations of complex particles of the Sn(II) - citrate - water system in the solution volume, on the surface of the electrode, and in the diffusion layer for the tin citrate electrolyte containing an excess of the ligand. Based on the calculations for the electrodeposition of tin, an electrolyte containing [SnCit]$^{2-}$ complex at pH 8.0 was chosen. The kinetic parameters of the discharge stage, the diffusion coefficient of the electrochemical active ion, and the current efficiency of tin were determined by the methods of stationary voltammetry and chronovoltamperometry. It is shown that the electroreduction of tin is governed by the laws of mixed kinetics and the transfer stage of the second electron is the limiting one. The discharge mechanism and the composition of the electroactive complex, which is [SnCit]$^{2-}$, are proposed. The current density of the deposition of tin coatings with different functional properties is determined as protective coatings and coatings of anodes of Li-ion accumulators.

Improvement of the RDE stationary voltammetry method by consideration the electroactive components migration

Improvement of the RDE stationary voltammetry method by consideration the electroactive components migration

Layer Number Dependence of Li(+) Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution.

A fundamental question facing electrodes made out of few layers of graphene (FLG) is if they display chemical properties that are different to their bulk graphite counterpart. Here, we show evidence that suggests that lithium ion intercalation on FLG, as measured via stationary voltammetry, shows a strong dependence on the number of layers of graphene that compose the electrode. Despite its extreme thinness and turbostratic structure, Li ion intercalation into FLG still proceeds through a staging process, albeit with different signatures than bulk graphite or multilayer graphene. Single-layer graphene does not show any evidence of ion intercalation, while FLG with four graphene layers displays limited staging peaks, which broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate changes in the surface conductivity of FLG during SEI evolution. Observation of ion intercalation on large area FLG was conditioned to the fabrication of "ionic channels" on the electrode. SECM measurements using a recently developed Li-ion sensitive imaging technique evidenced the role of these channels in enabling Li-ion intercalation through localized flux measurements. This work highlights the impact of nanostructure and microstructure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using graphene, an atomically thin interface where surface and bulk reactivity converge.

The kinetics оf cathodic processes at the platinum-borosilicate melt boundary

Stationary voltammetry is used to investigate the cathodic polarization of platinum in sodium borosilicate melt. The influence of the silicon oxide content is estimated for the electrode processes rate. The mechanism of the cathodic processes was specified, taking into account the slowness of adsorbed oxygen ions’ diffusion.

Novel composite Zr/PBI-O-PhT membranes for HT-PEFC applications

Novel composite membranes for high temperature polymer-electrolyte fuel cells (HT-PEFC) based on a poly[oxy-3,3-bis(4′-benzimidazol-2″-ylphenyl)phtalide-5″(6″)-diyl] (PBI-O-PhT) polymer with small amounts of added Zr were prepared. It was shown in a model reaction between zirconium acetylacetonate (Zr(acac)4) and benzimidazole (BI) that Zr-atoms are capable to form chemical bonds with BI. Thus, Zr may be used as a crosslinking agent for PBI membranes. The obtained Zr/PBI-O-PhT composite membranes were examined by means of SAXS, thermomechanical analysis (TMA), and were tested in operating fuel cells by means of stationary voltammetry and impedance spectroscopy. The new membranes showed excellent stability in a 2000-hour fuel cell (FC) durability test. The modification of the PBI-O-PhT films with Zr facilitated an increase of the phosphoric acid (PA) uptake by the membranes, which resulted in an up to 2.5 times increased proton conductivity. The existence of an optimal amount of Zr content in the modified PBI-O-PhT film was shown. Larger amounts of Zr lead to a lower PA doping level and a reduced conductivity due to an excessively high degree of crosslinking.

Electrode processes at the glass carbon/LiCl-CuCl-CuCl2 melt interface

The kinetics of the electrode processes occurring at the glass carbon/LiCl-CuCl-CuCl2\(\left( {N_{CuCl - CuCl_2 } = 0 - 7.5 mol \% } \right)\) melt interface is studied by the coulostatic method, single current pulse chronopotentiometry, and stationary voltammetry at a temperature of 950 K and the atmospheric pressure of chlorine over a melt. The exchange current densities in the molten mixtures are determined by the coulostatic method. These data are used to calculate the transfer coefficient (α = 0.54 ± 0.06) and the rate constant of the electrode reaction Cu2+ + e− ai Cu+ (kS = 0.26 ± 0.02 cm/s). The results of stationary voltammetry in the cathode potential region reveal pronounced limiting currents up to the precipitation of metallic copper on an electrode. The experimental data obtained by chronopotentiometry are used to find the transition times for various current densities over the entire concentration range under study. The dependences plotted in the iτ1/2 = f(i) coordinates suggest the presence of a chemical homogeneous reaction preceding the electrode process. The total value of the rate constants of the forward and back reactions is estimated to be ≈2. The copper mono- and dichloride concentrations are determined in the concentration range under study.

Evidence of the withdrawing effect of a pyridinium N-cation on the electrochemical reduction of gold (III) tetraphenylporphyrin

1-(Au III- meso-tetraphenylporphyrin)-4-pyridinium dication Au IIITPP +-β-Py +, formed by a pyridinium cation bearing a charged gold porphyrin at the N-position, has been synthetised and studied by stationary voltammetry, cyclic voltammetry, UV–Vis spectroelectrochemistry and exhaustive coulometry. The pyridinium cation and the porphyrin ring are both electroactive species on the investigated range of potentials. The obtained results allowed to discriminate the sites of the different charge transfers and to propose a mechanism for the three first electrochemical reduction processes involved. The gold porphyrin reduces before the reduction of the pyridinium cation whose signal is intercalated between two reduction steps of the porphyrin. A transient dimeric gold porphyrin is detected. The withdrawing effect of the pyridinium cation on the reduction potentials of the porphyrin is discussed and quantified.

Oxygen reduction on bornite (Cu5FeS4) in alkaline medium

The electroreduction of molecular oxygen is investigated between −0.1 and −0.5V vs SHE on bornite, Cu5FeS4, at pH9.2 and 14, by means of cyclic voltammetry (CV) and stationary voltammetry (SV), using a double channel electrode flow cell (DCEFC). Using an E/pH diagram established in this work, the CV results suggest that the bornite surface is stable between −0.1 and −0.5V then oxidized to CuS and Fe(OH)3 above −0.1V whereas, below −0.5V the mineral reduces to metal sulphides: Cu2S and FeS. The SV results show that oxygen is reduced to peroxide ions, HO2−. At pH9.2 the generated sulphide ions hinder the oxidation of HO2− on the collector electrode of the DCEFC, due to the formation of a blocking surface layer of elemental sulphur, S, impeding the determination of the kinetic parameters, k1 (direct way) and k 2 (indirect way) of the oxygen electroreduction reaction. In contrast, at pH14, as soluble polysulphides are formed, it was possible to determine these parameters, showing that the bornite is a poor catalyst for oxygen reduction. At pH14, in the presence of potassium ethylxanthate, generally used as a flotation collector, the ethylxanthate ions, C2H5OCSSO−, are oxidized by HO2− to perxanthates, ROCSSO−, while at pH9.2 the oxygen reduction is inhibited due to ethylxanthate chemisoption on the bornite surface.