Bright Platinum Electrodes Research Articles

Iridium and Ruthenium oxide miniature pH sensors: Long-term performance

The characteristics of electrodeposited Iridium oxide films (EIROF), and Ruthenium oxide films (RUOF) under normal and annealed conditions have been investigated. RUOFs were sputter deposited onto a substrate whilst EIROF sensors were made by electrodeposition. The adhesion of the RUOF sensors was investigated on Platinum and Titanium surfaces. The electrical impedance of the two metal oxides was measured in PBS demonstrating that both films have up to a 100 fold higher electrical double layer capacitance than bright Platinum electrodes. The EIROF films show super-Nernstian response, but the formal potential shows a continuous drift with time of approximately 2 mV day−1, measured over 40 days. Both RUOF sensors show approximately Nernstian behaviour. Short term pH precision of the annealed RUOF falls within a confidence interval of ± 0.1 pH, and stability is maintained within a confidence of ± 0.24 pH for up to 147 days. The un-annealed RUOF maintains the same precision but only for 20 days. Compared to EIROF sensors, no drift correction is required for the annealed RUOF making this metal oxide suitable for long term measurements where re-calibration is not possible.

Note: Characterization of electrode materials for dielectric spectroscopy

When measuring the dielectric properties of aqueous samples, the impedance of the electrode/sample interface can limit low frequency measurements. The electrode polarization problem can be reduced by increasing the effective surface area of the electrodes. In this work, impedance spectroscopy was used to characterize and compare three different electrode surfaces that can be used to mitigate this effect: platinum black, iridium oxide, and [polypyrrole/poly(styrenesulphonate)] (PPy/PSS) conducting polymer. All three materials were directly compared with a bright platinum electrode. Equivalent circuit models were used to extract the increase in the effective surface area of the electrodes: platinum black, iridium oxide and PPy/PSS increase the effective capacitance of the electrode by factors of approximately 240, 75, and 790, respectively. The practical aspects of all electrode materials are discussed. These results suggest that iridium oxide and PPy/PSS are good alternatives to the commonly used platinum black, which is prone to mechanical damage (scratches) and is potentially toxic to cells.

Polyfurfural Film Synthesized by Electrochemical Reduction of Furfural on Bright Platinum Electrode

The electroreduction of furfural (2‐furancarboxaldehyde) was confirmed on bright platinum electrode in acetonitrile solutions. The product synthesized was an organic film with good adherence and electrical conductivity. Three electrochemical methods such as CV, chronopotentiometry and chronoamperometry were used in this process. SEM photographs were conclusive to confirm the presence of the film on the electrode surface. The IR and 13C NMR spectra of the resin obtained galvanostatically suggest a complex structure with the presence of the furfural and organic solvent molecules.

Teflon cell for electrical conductivity studies in molten fluorides

A novel conductivity cell for fluoride systems with a low melting point is reported. The instrument concerned is made of Teflon and has bright platinum electrodes. It may be used up to 170 °C. The value of the cell constant is 27.91±0.06 cm−1. The cell may be used with other values of the constant upon changing the capillary diameter of the horizontal cylindrical piece.

Factors Affecting Oxidation‐reduction Processes in an Oxisol with a Seasonal Water Table

AbstractThe weekly fluctuation of the water table was recorded for a period of 2 yr at five sites along a transect of a high plateau area in the Cerrados of Brazil characterized by minimal variation in soil morphology, color, and texture. The soil studied was a Red‐Yellow Latosol, a member of the clayey, oxidic, isohyperthermic family of Typic Acrustoxes. The soil profile to a depth of 200 cm did not show mottling or color chromas of 2 or less at any site. However, the water table was within 0.4 to 2.0 m of the soil surface at some sites for more than 90 d yr−1. Bright platinum electrodes installed at three sites showed only a moderate range of Eh values (700‐500 mV) indicating that no reduction took place in the soil at any depth, in spite of the standing water table. Soil samples taken at the 0‐ to 20‐, 20‐ to 40‐, 40‐ to 60‐ and 60‐ to 80‐cm depth, and subjected to different treatments, were incubated for 90 d at approximately 30 kPa water tension or under waterlogged conditions. Treatments consisted of nutrients, nutrients plus lime, and sucrose at two rates, 0 and 10 g kg−1 of soil. The Fe (II) content measured in moist samples at the end of the incubation period showed that intensive reduction took place under all treatments in soil samples taken from the 0‐ to 20‐ and 20‐ to 40‐cm depths. Samples taken below 40 cm contained a high Fe (II) content only when sucrose was applied. These data suggest that reduction does not occur in the field in the lower part of the soil profile even when a high water table is present due to the lack of a source of energy for microbial activity. It is suggested that the organic matter present in the lower part of the soil profile is too stable and/or too low in available nutrients for the reduction process to take place during the water logging period.

Electroreduction of oxygen in molten NaOH

A study of oxygen electroreduction at a bright platinum electrode has been carried out in molten sodium hydroxide at 350°C. Analysis of potentiostatic and potentiodynamic measurements led to the following results: (1) The electroactive species in oxygen-containing NaOH melts at 350°C is sodium peroxide. (2) A general method of quantitative determination of kinetic and mass transport parameters for certain reactions has been described. (3) The mechanism of oxygen reduction in molten NaOH has been suggested. (4) Kinetic and mass-transport parameters characterizing oxygen reduction in molten NaOH have been calculated. (5) The reaction studied seems to be one of the rare examples of relative invariance of the Tafel slope with temperature.

Kinetic parameters and mechanism of the electrochemical oxidation of L-ascorbic acid on platinum electrodes in acid solutions

The oxidation of l -ascorbic acid has been studied in sulphuric acid solutions at a bright platinum electrode, by employing cyclic voltammetry, controlled-potential electrolysis and potential-step measurements. On the basis of kinetic parameters—Tafel slopes, reaction orders and pH effects—a possible mechanism is proposed for the overall oxidation process. There is evidence of two rapid and thermodynamically reversible charge-transfer steps which are followed by a slow non-activated desorption and rate-determining step. The kinetics are explained with the aid of the Temkin adsorption isotherm.

Kinetic parameters and mechanism of the electrochemical oxidation of L-ascorbic acid on platinum electrodes in acid solutions

The oxidation of l-ascorbic acid has been studied in sulphuric acid solutions at a bright platinum electrode, by employing cyclic voltammetry, controlled-potential electrolysis and potential-step measurements. On the basis of kinetic parameters—Tafel slopes, reaction orders and pH effects—a possible mechanism is proposed for the overall oxidation process. There is evidence of two rapid and thermodynamically reversible charge-transfer steps which are followed by a slow non-activated desorption and rate-determining step. The kinetics are explained with the aid of the Temkin adsorption isotherm.

Electroanalysis of Some of The Organic Substances and the Effect of Halide Ions on Their Determinations in Effluents

AbstractThe electroanalytical technique based on the coverage of bright platinum electrode with methanol, ethanol, butan‐1‐ol, iso‐propanol and phenol as a function of potential and bulk concentration of these compounds in 1M H2SO4 is shown. The interference due to halide ion in the determination of organic substance is reported.

Surface conductivity of glass at the solid/liquid interface

The electrokinetic phenomenon of surface conductivity was studied for capillaries of pure fused silica and of a borosilicate glass, in water, dilute aqueous solutions of HCl and NaCl, in methanol and acetonitrile. Measurements were done in the temperature range between 5 and 30°C by a dc linear voltage sweep technique at a rate of 0.2 V/sec or less, and with applied polarization voltages up to ±40 V. Surface conductivity was calculated from the total specific conductivity measured by two bright platinum electrodes at the mouths of the capillary and from the specific bulk conductivity of the liquid medium measured by a separate pair of Pt electrodes at the same temperature. Absolute values of the surface conductivity were between 10 −9 and 10 −10 ohm −1. Energies of activation were calculated from the slopes, S, of log κ vs 1 T curves, observed within a temperature range from 5 to 30°C. The energies E defined as S = E/ k were: 45–55 kJ/mole for the borosilicate glass, and 25–34 kJ/mole for fused silica in water, in aqueous solutions, and in methanol. In acetonitrile they were 105 kJ/mole for borosilicate glass and 59 kJ/mole for fused silica. The results were interpreted on the basis of the assumption that protonic conductivity is the predominant mode of surface charge transfer, with the rotation of water molecules in the first liquid layer as the rate-determining step.

Electrochemical behaviour and solubility study of hydrogen and acetic acid in molten alkali acetates

The solubility of hydrogen in molten sodium/potassium acetates has been determined in the temperature range 250–300° C. The electrochemical behaviour of hydrogen and acetic acid in the same melt has also been studied at bright platinum electrodes at 250° C.

Use of the coulometrically measured amount of adsorbed hydrogen to determine the active surface area of platinum for the electro-oxidation of iron(II)

The kinetics of the electron transfer reaction between iron(II) and bright platinum electrodes was studied in 2N sulfuric acid and in sulfuric acid containing azide, bromide, chloride, oxalate, thiocyanate and tetrafluoroborate ions. The chloride, bromide, and azide ions were shown to function only as blocking agents for the electron transfer reaction. An increase in the measured current on the addition of oxalate ion was attributed to the formation of an iron(III) complex which increased the rate of desorption of the oxalate from the electrode, thus cleaning the electrode. The results indicated that thiocyanate served as an electron transfer bridge, while tetrafluoroborate increased the rate, probably by ion pairing.

Electric field measurements using inert electrodes

A simple method is described and shown capable of measuring electric field strengths in electrolytes using closely spaced inert electrodes. Measurements were accomplished by monitoring the change in potential between bright platinum electrodes resulting from either a current interruption, or from a current pulse, superimposed on a direct current signal.

Die kathodische Reduktion von Ozon in alkalischen Elektrolyten

The cathodic reduction of ozone according to the overall reaction O3+H2O+2e→O2+2OH− was studied on bright platinum electrodes in KOH electrolytes. The rest potentials deviate from the theoretical values by −300 to −350 mV. They are determined by a mixed potential mechanism involving anodic evolution of O2 and cathodic reduction of O3 as half reactions. Steady-state polarization measurements were carried out. Extrapolation of Tafel-lines to zero over-voltage and the determination of the charge transfer resistance give current densities at the rest potential, which are analogous to exchange current densities. A single electron transfer reaction is found to be the rate controlling step, which is occurring twice for the reduction of one molecule of ozone. A cathodic reaction order of approximately zero is evaluated with respect to OH−-ion concentration. The reaction mechanism is proposed according to $$\begin{gathered} O_3 + e \to O_3 - / \cdot 2 \hfill \\ 2O_3 - + H_2 O \to 2 OH - + O_2 + O_3 \hfill \\ \end{gathered} $$ which is consistent with experimental data.

Solubility and electrochemical behaviour of water in molten alkali metal acetates

The solubility and the electrochemical behaviour of water at bright platinum microelectrodes have been studied in (Na,K) acetates (46.3 mol % CH 3 COONa) eutectic melt in the temperature range 250–290°C. The Henry's law constant has been found to be K =1.21×10 −3 mol kg −1 Torr −1 at 250°C while the enthalpy of the process is −10.2±0.3 kcal mol −1 . The water reduction (H 2 O+ e å1/2H 2 +OH − ) has been found to be a diffusion controlled process proceeding reversibly at bright platinum electrodes. By means of chronopotentiometry the water diffusion coefficient is D H 2 O =1.34×10 −5 cm 2 s −1 at 250°C while the Arrhenius activation energy for diffusion is +9.5±0.5 kcal mol −1 .

Hydrogen evolution at platinum electrodes in molten potassium bisulphate

The hydrogen-evolution reaction at bright platinum electrodes in molten KHSO 4 has been studied over the temperature range from 270 to 430°C by steady-state and transient methods. At low potentials the atom-atom combination step is rate-determining. At high potentials the ion-atom electrochemical desorption step is rate-determining. The two regions are separated by a transition region in which hysteresis is observed. The absorption isotherm for H atoms shows two-dimensional condensation.

A study of the passivation of bright platinum electrodes during chlorine evolution from concentrated sodium chloride solutions

A study of the passivation of bright platinum electrodes during chlorine evolution from concentrated sodium chloride solutions

A study of the passivation of bright platinum electrodes during chlorine evolution from concentrated sodium chloride solutions

A study of the passivation of bright platinum electrodes during chlorine evolution from concentrated sodium chloride solutions

A voltammetric and chronopotentiometric study of molten alkali acetates

The electrochemical behaviour of water, hydrogen ion, and molecular hydrogen has been investigated in (Na,K) acetate melt at 250° with bright platinum electrodes by means of chronopotentiometry and voltammetry.

NITRATE REDUCTION, AND REDOX POTENTIALS MEASURED WITH PERMANENTLY AND TEMPORARILY PLACED PLATINUM ELECTRODES IN SATURATED SOILS

The influence of nitrate-nitrogen on the redox potential measured with permanently and temporarily placed bright platinum electrodes was studied in samples of the Ap, BA and Bt horizons of a Huron silty clay loam in the laboratory. An anaerobic condition was induced by saturating the soils with distilled water. Redox potentials measured with the temporary Pt electrodes decreased with time to about −300 mv, but they were temporarily poised at +200 mv when NO3 was present. Similar results were obtained for untreated soils and for soils treated with 200 ppm NO3-N when measurements were made with the permanent Pt electrodes. With a second addition of 200 ppm NO3-N, the potential measured with the permanent electrodes increased approximately from −300 mv to −200 mv and remained poised at this potential for the duration of the experiment. The Eh values measured with the temporary electrodes increased to +200 mv and remained there temporarily until the NO3 disappeared, and then decreased to −300 mv again. The poising of the permanent electrodes at approximately −200 mv was attributed to the occurrence of chemical reactions at the platinum surface resulting in a reduction of the electrical conductivity or responsiveness of the electrodes.