The mechanism of formic acid electrooxidation on iron tetrasulfophthalocyanine-modified platinum electrode

The mechanism of formic acid electrooxidation on iron tetrasulfophthalocyanine (FeTSPc) modified Pt electrode was investigated with electrochemical methods. It was found that a “third-body” effect of FeTSPc on Pt electrode predominates during the electrooxidation process based on unusual electrochemical results. The modification leads formic acid electrooxidation to take place through a desired direct pathway, in which the mechanism is proposed to be the gradual dehydrogenation of formic acid and the reaction of formate with hydroxyl species.     

Response mechanism of platinum electrode to uncoupled ions(I)

The transient response mechanism of the platinum electrode to the uncoupled ions may be interpreted with the mixed phase formation (MPF) model of the transient response of precipitate-based ion-selective electrodes to interfering ions for K_xy ≪ 1. It is discovered that the peak height of the transient signal is related to the solubility of M(OH)₂ and hydration heat of M²⁺. The relation between the positive peak height of transient signal of pb²⁺ or cd²⁺ and lga_m obey the Nernst equation, while that of Ca²⁺ or Mg²⁺ does not. The equilibrium potential is not of Nernst response for all ions. Project supported by the National Natural Science Foundation of China.     

Behaviour of the platinum electrode as a pH electrode

The platinum wire electrode behaves as a good pH electrode in the titration of 1.0 and 0.1N sulphuric or hydrochloric acid with the equivalent concentration of sodium hydroxide. The efficiency is greater when sulphuric acid is used. The end-points obtained are very close to those obtained with a glass-calomel system.     

The aluminium indicator electrode in acid-base potentiometric titrations

Aluminium has been employed as an indicator electrode in potentiometric acid-base titrations. The titration curves obtained were approximately 3.6 times broader than those obtained with the antimony electrode.     

The adsorption of carbon monoxide on a platinum electrode

The adsorption of CO from 0.5 M H₂SO₄ solution on platinum has been studied using CO labelled with C-14. The adsorption of CO on Pt occurs in the potential range of hydrogen adsorption as well as in the double layer region. In the whole potential range the rate of adsorption follows first order kinetics. From the surface concentrations and charges for oxidation of adsorbed species it follows that the product of chemisorption consists at least of two kinds of species. One of them is the COOH radical probably formed by the reaction of CO with water.     

Analysis of time-dependent kinetics for the oxidation of methanol on a platinum electrode and reaction mechanism

The reaction kinetics for the oxidation of methanol on a platinum electrode have been examined under precisely controlled conditions. The Tafel relations at constant surface coverages of the strongly adsorbed species show the existence of two potential regions where the predominant reaction path is different. The surface reaction of the strongly adsorbed species with OH(a) is rate determining at E > ca. 0.55 V, while the oxidative adsorption of methanol to form a reactive intermediate becomes the rate-determining step at E < ca. 0.55 V. In the latter potential region, the strongly adsorbed species is not oxidized so that its accumulation on the surface decreases the rate of the oxidative adsorption and thereby the total oxidation rate.     

The use of the molybdenum electrode as indicator for hydrogen ions

The molybdenum clectiode is found to act as a suitable means for the determination of the hydrogen ion concent-ration. Polished electrodes in aerated solutions give potentials which do not vary appreciably with time. The potential measured in solutions of different H⁺-ion activity is a function of pH from 2–11. pKa values determined from neutralization curves of some acids are not much different from those obtained by other authors, using different methods. Polished or aged electrodes in aerated or oxygen-free solutions could be used satisfactorily for determining tlie end-points in neutralization reactions.     

The effect of concentration in electrochemical oxidation of thiocyanate on platinum electrode

Electrochemical oxidation of thiocyanate (SCN⁻) on platinum electrode in the sulfuric acid medium was studied using cyclic voltammetry, in situ UV-visible absorption measurement, rotating ring-disc electrode voltammetry, and electrical impedance spectroscopy. Two oxidation processes are involved in the electrochemical oxidation of SCN⁻ in sulfuric acid medium. The adsorbed SCN⁻ undergoes oxidation at potential values higher than 0.900 V versus saturated calomel electrode (SCE). Trithiocyanate, , is formed as a relatively stable product during the first oxidation process. The potential range of formation increases with increase in concentration of SCN⁻, and it is exclusively produced in the potential range of 0.550 to 1.40 V versus SCE with 1.0 M NH₄SCN solution. The second oxidation process does not produce any stable product, and the products of second oxidation passivate the electrode surface.     

Coulometric argentometry of microgram amounts of sulphide

Summary A method has been developed for the direct determination of microgram amounts of sulphide by constant current coulometric argentometry in the supporting electrolyte 10^–3 M NaCN+0.1 M NaOH. Zero-current potentiometric, biamperometric, and constant current bipotentiometric end-point detection techniques with one or two silver sulphide-silver microelectrodes have been used. The influence of the composition of the supporting electrolyte on the net titration efficiency and the portion of primary electrode reaction at the generator anode in the presence of sulphide have also been investigated. This method permits the determination of 4–85 g of sulphide in a sample volume of 5 ml with an average error of ±1%, also in the presence of about 100 fold weight excess of chloride, bromide, iodide, thiocyanate, and thiosulphate.

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Zusammenfassung Eine Methode zur direkten Bestimmung von Mikrogrammengen Sulfidschwefel wurde ausgearbeitet. Es handelt sich um eine coulometrische Argentometrie, die bei konstantem Strom im Grundelektrolyt 10^–3 M NaCN+0,1 M NaOH verläuft. Zur Indikation werden ein oder zwei Silbersulfid-Silber-Elektroden angewendet. Der Endpunkt wird biamperometrisch (angelegte Spannung 100 mV), bipotentiometrisch (erzwungener Strom 0,5 A) oder potentiometrisch ermittelt. Der Einfluß der Elektrolytenzusammensetzung auf die Titrationsausbeute wurde verfolgt und der Anteil der primären Elektrodenreaktion, die an der Generatorelektrode bei Anwesenheit von Sulfid verläuft, festgestellt und gemessen. In einem Probevolumen von 5 ml können 4–85 g Sulfid mit einem Fehler von ± 1% titriert werden, auch bei einem hundertfachen Überschuß von Chlorid, Bromid, Jodid, Thiosulfat und Thiocyanat.

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Part III: 232, 103 (1967).     

Coulometric argentometry of microgram amounts of sulphide

Summary A coulometric argentometric method has been developed for determining microgram and submicrogram amounts of sulphide, based on the formation of silver sulphide at a silver electrode by constant applied voltage electrolysis. 0.1 N sodium hydroxide has been used as a supporting electrolyte. The electrolytic system consisted of a special cell and of a pair of electrodes (large area saturated calomel electrode and the silver working electrode). The optimum working potential of the silver electrode was found to be –360 mV vs. S.C.E. This method permits determinations of 0.01–20 g of sulphide in sample volumes up to 10 ml, the total volume in the electrolytic cell being 40 ml. In the range of 0.05–20 g of sulphide the accuracy was better than – 5% and the reproducibility was better than 1%; in case of 0.01 g of sulphide the accuracy was found to be about – 10% and the repoducibility amounted to 2.5%.

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Zusammenfassung Eine coulometrisch-argentometrische Methode zur Bestimmung von Mikro- und Submikromengen Sulfid auf Grund der Bildung von Silbersulfid an einer Silberelektrode bei konstanter angelegter Spannung wurde ausgearbeitet. Als Grundelektrolyt wird 0,1 N Natronlauge benutzt. Die Bestimmung wird in einem speziellen Elektrolysiergefäß mit einer groß-flächigen Kalomel- und einer Silberelektrode ausgeführt. Das optimale Potential der Silberelektrode beträgt –360 mV gegen ges. Kalomelelektrode. Die Methode ermöglicht die Bestimmung von 0,01–20 g Sulfid in einer Probe von maximal 10 ml. Zwischen 0,05 und 20 g Sulfid ist der Fehler stets kleiner als – 5%; die Reproduzierbarkeit ist besser als 1%. Bei 0,01 g Sulfid wurde ein Fehler von – 10% und eine Reproduzierbarkeit von 2,5% gefunden.

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Parts I and II: this journal 217, 252, 259 (1966).     

The effect of platinum electrode surfaces on precise primary pH measurements

Journal of Solid State Electrochemistry - For primary pH measurements, a platinum hydrogen electrode and a silver chloride electrode are immersed in the same solution in a cell without transference...     

Kinetics and mechanism of electrochemical reduction of multilayer oxides on a smooth platinum electrode surface in acidic electrolyte

The electrochemical reduction of multilayer oxides which were formed on a smooth Pt electrode surface under severe anodic conditions was investigated using a galvanostatic transient, a linear potential sweep and a potential step technique. Four regions of the surface oxide reduction were distinguished in the galvanostatic E?t curve and four corresponding cathodic current peaks were observed in the potentiodynamic i?E profile. These four regions or peaks are attributed to the reduction of four O-containing layers: an oxygen monolayer adsorbed on the oxide surface, two oxide layers in a first and a second lattice and a multilayer oxide in the deeper lattices having a phase property. The reduction rate of the first lattice oxide layer is determined by a second electron transfer. Under a rapid stripping condition, the reduction of the second oxide layer is considered to be controlled by the place exchange reaction. The extremely large reduction rate of the multilayer oxide compared with the formation rate is explained in terms of the proton-electron model.     

Immobilization of enzyme to platinum electrode and its use as enzyme electrode

A glucose electrode was fabricated by immobilizing glucose oxidase covalently onto a platinized platinum electrode. The sensor showed rapid response with response time of 2—4 s, and also the linear response to the glucose concentration, ranging from 2 x 10^-3 to 5 mM. The sensitivity was found to be correlated with the surface area of a base electrode used.     

Coulometric argentometry of microgram amounts of sulphide

Summary The voltammetric behaviour of the silver sulphide-silver electrode in pure ammoniacal-alkaline electrolytes as well as in the presence of sulphide and the complex cation [Ag(NH₃)₂]⁺ have been investigated. It has been found that the silver sulphide-silver electrode behaves slightly irreversibly in ammoniacal-alkaline solutions of sulphide. On the basis of the results obtained the use of the silver sulphide-silver electrode for constant-current bipotentiometric and biamperometric end-point detection techniques appears to be convenient in the argentometric determination of sulphide.

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Zusammenfassung Das voltammetrische Verhalten der Silbersulfid-Silber-Elektrode wurde in Ammoniak und Natronlauge enthaltenden Lösungen, auch in Anwesenheit von Sulfid und von komplexem Kation [Ag(NH_{3 2}]⁺, untersucht. Es wurde festgestellt, da\ sich die Silbersulfid-Silber-Elektrode in Sulfid enthaltenden Lösungen schwach irreversibel verhÄlt. Die gewonnenen Resultate zeigen die Möglichkeit, die genannte Elektrode zur bipotentiometrischen oder biamperometrischen Endpunktbestimmung bei der argentometrischen Sulfidbestimmung anzuwenden.

     

Electrochemical oxidation of the nickel-EDTA complex on a platinum electrode

The electrochemical formation of a Ni(III)-EDTA (EDTA=ethylenediaminetetra-acetate) precipitate on a Pt electrode is observed. This precipitate can be reduced without dissolution. The electrochemical properties of this precipitate are analysed and compared with those of other tervalent nickel complexes.     

Electrochemical oxidation of some tetrahydropteridine derivatives at the platinum electrode

6 and 7-substituted 2-amino-4-hydroxy-5,6,7,8-tetrahydropteridines are oxidized at a platinum electrode in several waves in the potential range between hydrogen and oxygen evolution potentials. The electrode process in the first (main) anodic wave was investigated in more detail using a stationary and rotating disc platinum electrode. The process in this wave is “semireversible” with an exchange of two electrons. The standard rate constants of this reaction were determined. The oxidation product is deactivated by an irreversible chemical reaction. Some of the products block the surface of the electrode.     

Ionic strength-controlled virtual area of mesoporous platinum electrode

Mesoporous electrodes provide an unusual opportunity to observe the dramatic transition of the electrochemical potential distribution in vicinity to mesoporous surfaces as the ionic strength varies. The experimental results were in accordance with what the classical Gouy-Chapman theory predicts on the basis of the correlation between Debye length (kappa-1) and the diameter of mesopores. Using the phenomenon that the electrochemically effective area of mesoporous electrode depends on the ionic strength, the faradaic current density of dioxygen reduction could be controlled by the electrolyte concentration.