The coulometric generation of manganese(II) from a manganese electrode: : The Titration of EDTA

The anodic behavior of a manganese electrode is discussed. Manganese(II) can be generated with greater than 95% current efficiency over a limited current density range in neutral aqueous and methanolic chloride media. The current efficiency for the generation of manganese(II) as a function of current density, supporting electrolyte, solvent, pH, and generation time is given. Electrogenerated manganese(II) is useful in the coulometric titration of 4.460 × 10^-6–2.214 × 10^-5 mol of EDTA in 1.0 M sodium chloride buffered at pH 5.5. The end-point can be detected amperometrically by monitoring the anodic current from the oxidation of manganese(II) at platinum. The titration error is about 1% in replicate determinations. Permanganate can be generated in aqueous sodium hydroxide media but the current efficiencies are less than 20% and irreproducible.     

Effect of absorbed hydrogen on the iron dissolution

The rate of the anodic dissolution of iron in acid sulfate electrolytes is reduced by hydrogen absorbed in the metal. The dependence of the degree of retardation of the anodic process on the concentration of hydrogen atoms in the near-surface layer of the metal is obtained. The difference in the effect the adsorbed and absorbed forms of hydrogen exert on the iron dissolution rate is noted. At a certain content of absorbed hydrogen, the current efficiency for dissolved iron exceeds 100%, and the weight loss of the hydrogen-charged metal is maximum under the conditions of its anodic polarization. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Nickel-Zeolite modified carbon paste electrode as electrochemical sensor for hydrogen peroxide

In the present work, nickel-zeolite modified carbon paste electrode (Ni-ZMCPE) was prepared. The electrochemical behaviour of hydrogen peroxide at the surface of modified electrode was investigated by cyclic voltammetry and chronoamperometry in 0.1 M NaOH supporting electrolyte. The electrochemical characterization of Ni-ZMCPE exhibits redox behavior of Ni(III)/Ni(II) couple in alkaline medium. It has been shown that Ni-ZMCPE improves efficiency of the modified electrode toward hydrogen peroxide electrooxidation (It wasn’t remarkable different on ZMCPE and CPE in the presence and absence of hydrogen peroxide). Moreover, the effects of various parameters such as effect of different percents of Ni-Z to graphite, effect of pH and hydrogen peroxide concentration on the electrooxidation of hydrogen peroxide as well as stability of the Ni-ZMCPE have also been investigated. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of hydrogen peroxide in the range 0.03–0.1 and 0.3–6 mM with amperometric method. The detection limit (S/N = 3) was also estimated to be 1 μM.     

Energy-Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High-Performance Non-Noble-Metal Electrocatalyst

It is highly attractive but challenging to develop earth-abundant electrocatalysts for energy-saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high-performance non-noble-metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy-saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two-electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long-term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Effect of hydrogen sulfide on the iron dissolution rate in a sodium sulfate solution under natural aeration conditions

The influence of hydrogen sulfide (10–100 mg/1) on the Armco iron anodic dissolution in an aerated 0.17 M Na₂SO₄ solution is investigated. During a potentiostatic anodic polarization, the hydrogen sulfide introduction makes the current increase stepwise. The magnitude of the increase depends on the duration of preliminary anodic polarization, electrode potential, and hydrogen sulfide concentration. The anodic metal dissolution activation by hydrogen sulfide is explained by chemical conversion of the oxide-hydroxide passivating film into iron sulfide that is generated at the metal surface in the form of a porous film and does not hinder the electrode dissolution. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Coulometric generation of H+ ions by oxidation of thiols at a platinum anode and by oxidation of mercury in acetic acid—acetic anhydride

The coulometric generation of hydrogen ions by anodic oxidation of propane-1-thiol, butane-1-thiol, 2-mercaptopropionic acid, heptane-1-thiol, 2-mercaptoethanol, methyl and ethyl thioglycollate and p-thiocresol in acetic acid—acetic anhydride (1 + 6 v/v) is described, together with the possibility of coulometric generation of protons by mercury oxidation in the presence of p-thiocresol in the same solvent system.Current-potential curves for the solvent, indicator, titrated bases, mercury and the investigated thiols showed that in acetic acid—acetic anhydride (5 + 95, v/v), mercury and the investigated thiols are oxidized at potentials which are much more negative than those of the titrated bases and other components present in the solution.Titration of potassium hydrogenphthalate and sodium acetate with protons generated by the oxidation of thiols, and of sodium acetate, lithium acetate and pyridine with protons generated by the oxidation of mercury, demonstrated that the oxidation of both thiols and mercury proceeds quantitatively with 100% current efficiency.     

Determination of lead at the ng ml-1 level by reduction to plumbane and measurement by inductively-coupled plasma emission spectrometry

A detection limit of 1 ng ml^-1 for lead is obtained by the reported method. Samples are prepared in 0.5 M hydrochloric acid—0.8 M hydrogen peroxide. Plumbane is produced (with 64% efficiency) by the addition of 5% sodium tetrahydroborate in 0.5% NaOH, and is transported by the argon feed directly to an inductively-coupled argon plasma for emission spectrometry. Decreased hydrogen generation and greater stability of the plasma also contribute to the improved detection limit. The method is shown to be generally applicable to As, Sb, Bi, Sn, Te and Se, with detection limits at the ng ml^-1 level.     

The influence of complexing agents on the effectiveness of electrochemical masking with anionic surfactants in anodic stripping voltammetry

The influence of sodium dodecyl sulphate, sodium dodecyl sulphonate and sodium stearinate on the anodic stripping peaks of Tl(I), Pb(II), Cd(II), Cu(II) and In(III) was investigated. The supporting electrolytes were 0.5M sodium sulphate solution, 0.2M citrate solution (pH 3.7, 4.6 and 7.3), 0.5M tartrate solution (pH 4.4) and 0.1M solution of EDTA (pH 4.4). The composition of complex compounds forming in a solution under experimental conditions was defined. The conditions of ion reduction of metals on hanging mercury electrode during the electrolytical deposition were investigated. The investigation included an analysis of voltammetric curves of the metal ions. The obtained results suggest that "electrochemical masking" is much stronger in electrolytes containing a complexing agent than in the sodium sulphate solution. The influence of the complexing agent may not be explained in terms of the interaction between the form of the complex and the charge of the adsorbed surfactant particles; rather the complexing process is connected with indirect inhibition, i.e., by decreasing the rate of charge transfer reaction.     

Energy‐Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High‐Performance Non‐Noble‐Metal Electrocatalyst

It is highly attractive but challenging to develop earth‐abundant electrocatalysts for energy‐saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high‐performance non‐noble‐metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy‐saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two‐electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long‐term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Anodic generation of cerium (IV) at glassy carbon in acetic acid and coulometric titrations with the generated reagent

Conditions for electrochemical generation of cerium(IV) at glassy carbon in acetic acid in the presence of alkali-metal acetates and sodium perchlorate, respectively, were investigated. A high current efficiency was achieved in anodic oxidation of cerium(III) in acetate supporting electrolytes. Coulometric titration methods for the determination of reducing substances with the generated oxidant were also developed. The end-points were determined by the biamperometric and bipotentiometric methods. The error of the determinations was less than + 2%.     

ESEM observation of the process of hydrogen generation around the micro-droplets forming on AZ91 magnesium alloy

The process of hydrogen generation around micro-droplets on as-cast AZ91 magnesium alloy in an atmosphere of water vapor was in situ observed using an environmental scanning electron microscope (ESEM). The procedure for hydrogen generation was described. It indicated that the cathodic or anodic location gradually changed with the generation of hydrogen bubbles and the formation of corrosion products.     

Reagent injection FIA system for lead determination by hydride generation - quartz-tube atomic absorption spectrometry

A method is proposed for the determination of lead by generation of its hydride and detection by quartz-tube AAS using a reagent injection FIA system based on the injection of sodium tetrahydroborate. Lead hydride generation was carried out using a combination of 0.5 M nitric acid, 10% m/ v hydrogen peroxide and 10% m/ v sodium tetrahydroborate. The characteristic concentration obtained was 3.1 ng mL(-1) and the detection limit was 2.6 ng mL(-1) for an injected volume of 0.125 mL of tetrahydroborate.     

Coulometric generation of H(+) and D(+) ions in aqueous media by anodic oxidation of hydrogen and deuterium dissolved in palladium

Coulometric generation of H(+) and D(+) ions in aqueous media by the oxidation of hydrogen and deuterium dissolved in palladium, is described. Hydrogen and deuterium dissolved in palladium were found to be oxidized at more negative potentials than the oxidation potentials of water and other components present. The H(+) and D(+) ions generated were used for the titration of tris(hydroxymethyl) aminomethane, piperidine, triethylamine and sodium tetraborate, the end-point being determined potentiometrically with a glass electrode and an SCE. In titrations of 0.001-0.1M solutions of the bases, the current efficiency was 100%.     

Solar-powered electrochemical oxidation of organic compounds coupled with the cathodic production of molecular hydrogen

A Bi-doped TiO2 anode, which is prepared from a mixed metal oxide coating deposited on Ti metal, is shown to be efficient for conventional water splitting. In this hybrid photovoltaic-electrochemical system, a photovoltaic (PV) cell is used to convert solar light to electricity, which is then used to oxidize a series of phenolic compounds at the semiconductor anode to carbon dioxide with the simultaneous production of molecular hydrogen from water/proton reduction at the stainless steel cathode. Degradation of phenol in the presence of a background NaCl electrolyte produces chlorinated phenols as reaction intermediates, which are subsequently oxidized completely to carbon dioxide and low-molecular weight carboxylic acids. The anodic current efficiency for the complete oxidation of phenolic compounds ranges from 3% to 17%, while the cathodic current efficiency and the energy efficiency for hydrogen gas generation range from 68% to 95% and 30% to 70%, respectively.     

The effect of platinum(IV) on the coulometric generation of tin(II)

The current efficiency of tin(II) generation has been measured for various electrolytes and electrodes. The best results (>99.9%) were obtained with the paraffin-impregnated graphite electrode in 2M CaCl(2) + 0.2M HCl + 0.2M SnCl(4). In titrations of platinum(IV) with electrogenerated tin(II) in an electrolyte containing chloride or bromide it was found that the presence of platinum(II) or (IV) interferes in the cathodic generation of tin(II). The platinum is reduced to the elemental state at the electrode and causes simultaneous generation of hydrogen which decreases the current efficiency. This effect is more pronounced in chloride media.     

Nanosized rhodium oxide for water oxidation: An organometallic precursor for the preparation of rhodium oxide

Electrochemical production of hydrogen from water splitting is a promising process to allow storage of intermittent energies. However, anodic water oxidation, which is a complicated four‐proton, four‐electron transfer process, affects the efficiency of hydrogen generation due to the need to apply large overpotentials. Herein, we synthesized nanosized rhodium(III) oxide by the thermal decomposition of a known rhodium organometallic precursor and characterized it using scanning and transmission electron microscopies, powder X‐ray diffraction, energy‐dispersive X‐ray, diffuse reflectance infrared and Fourier transform infrared spectroscopies, and electrochemical methods. The results showed that the nanosized rhodium oxide is a promising catalyst for water oxidation.     

Electrochemical reduction of CO2 and degradation of KHP on boron-doped diamond electrodes in a simultaneous and enhanced process

A BDD-BDD system was developed in the simultaneous conversion of CO₂ and wastewater purification in one electrochemical cell.     

Determination of Sb(V) Using Differential Pulse Anodic Stripping Voltammetry at an Unmodified Edge Plane Pyrolytic Graphite Electrode

Antimony(V) determination at an unmodified edge plane pyrolytic graphite (EPPG) electrode using anodic stripping voltammetry (ASV) by depositing beyond the hydrogen wave is shown in this paper. By depositing beyond the hydrogen wave, we report a sensitive method to determine pentavalent antimony at a carbon electrode in 0.25 M HCl. Using differential pulse anodic stripping voltammetry (DPASV), a bare EPPG electrode gave a detection limit of 5.8±0.02 nM without the need for surface modification. This level is greatly within the EU limit for drinking water of 40 nM.     

Magnesium alloys spontaneous dissolution features under external anodic polarization in presence of inhibitors

The effect of benzotriazole (BTA) and sodium ethylenediamine tetraacetate (EDTA) to the magnesium dissolution intensity under external anodic polarization was studied. The inhibiting properties of BTA and EDTA in electrochemical corrosion of magnesium were found in the concentration range from 0.005 to 0.0125 M in sodium sulfate solution and from 0.0025 to 0.03 M in sodium chloride solution. In the presence of inhibitors, magnesium dissolution becomes uniform with decreasing surface hydrogenation and crumbling intensity of small particles into solution.     

Amperometric biosensor for hydrogen peroxide based on the co-electrodeposition of horseradish peroxidase and methylene blue on an ITO electrode modified with an anodic aluminum oxide template

We report on a nano-array sensor for hydrogen peroxide (H₂O₂) that is based on a nanoporous anodic aluminum oxide template. This was used as a matrix for the co-immobilization of horseradish peroxidase (HRP) and methylene blue (MB) on the surface of an indium tin oxide electrode. The immobilized HRP retained its natural activity and MB is capable of efficiently shuttle electrons between HRP and the electrode. The new electrode was characterized by SEM and electrochemical methods. It exhibits fast response, long-term stability, high sensitivity and good selectivity to H₂O₂. Under optimized conditions, it linearly responds to H₂O₂ in the concentration range from 1.0?μM to 26?mM, with a detection limit of 0.21?μM (at S/N?=?3).