The recording of D.C. Polarographic waves and the measurement of the instantaneous current at the end of the life of the mercury drop

Because of the slowness of response of the current detectors used in the infancy of polarography, it has become the custom to measure the average current rather than the instantaneous current at some given time near the end of the life of the mercury drop. McKenzie (1958a) has pointed out that there are a number of theoretical advantages to be gained by measurement of instantaneous diffusion current. The work reported in the present paper shows that this measurement can be made accurately with conventional electronic equipment. Owing to the inherent lag in automatic recording polarographs which measure average current, it is not possible to obtain from the records the half-wave potential and slope with good accuracy. It is shown that the advantages of automatic recording and accuracy in determining the half-wave potential and slope may be realized by recording instantaneous current-voltage curves. Also abnormalities in current-time curves may be readily detected. Apparatus using a conventional recorder and a preamplifier which is a modification of that of Kelley and Miller (1952) is described. A device which can be used to control pen drive is also described.

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Polarography of some coordination compounds of platinum. I. Hexammineplatinum (IV) and Tris(ethylenediamine)platinum(IV) ions

Australian Journal of Chemistry ◽

10.1071/ch9550158 ◽

1955 ◽

Vol 8 (2) ◽

pp. 158 ◽

Cited By ~ 7

Author(s):

JR Hall ◽

RA Plowman

Keyword(s):

Potassium Chloride ◽

Supporting Electrolyte ◽

Platinum Metal ◽

Potassium Nitrate ◽

Diffusion Current ◽

Polarographic Reduction ◽

Wave Potential ◽

Half Wave Potential ◽

Half Wave ◽

Continuous Discharge

The polarographic reduction of tris(ethylenediamine)platinum(IV) and the hexammineplatinum(IV) ions has been studied in potassium chloride, potassium nitrate, and potassium nitrate plus ammonia solutions. Both ions were reduced irreversibly producing similarly shaped waves, showing well-defined diffusion current regions corresponding to two-electron reductions of the complexes. A linear relationship existed between diffusion current and concentration within the range examined. In aqueous potassium chloride and potassium nitrate media, the waves contained slight inflexions at positions corresponding to one-electron additions. The phenomenon suggested the transient presence of platinum(III) ions, and indicated that the half-wave potential of the reduction of the complexes to the trivalent state was very close to the half-wave potential of the reduction from platinum(IV) to platinum(II). The values were so close together as to indicate the improbability of isolating the trivalent complexes. Gelatin enhanced the inflexion in the wave but shifted the wave in a more negative direction. An increased concentration of supporting electrolyte also shifted the wave to a more negative position. In all cases a continuous discharge began at about -1.3 V (v. S.C.E.). This discharge was so far removed from that of the potassium ions of the supporting electrolyte that it was attributed to the discharge of hydrogen. Since the initial reduction of the platinum complexes corresponded to a two-electron change, it can be represented by reduction to a tetrammine ion. It is postulated that at higher applied potentials (namely, -1.3 V v. S.C.E.) the reduction proceeded further, producing platinum metal. This platinum metal would be in an active state, insoluble in mercury, and being on the surface, would lower the overvoltage of hydrogen leading to its discharge at a more positive potential than on a pure mercury surface. This view was supported by the fact that gas bubbles were observed at the dropping electrode when a voltage greater than -1.3 V was applied to the electrode for some time. When ammonia was added to the supporting electrolyte, a wave, without an inflexion, and corresponding to an irreversible two-electron reduction, was obtained at more negative potentials. The bivalent tetrammineplatinum(II) and bis(ethylenediamine)platinum(II) ions also gave polarograms showing the continuous discharge of hydrogen.

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Studies on the influence of some supporting electrolytes on the diffusion current and half-wave potential of the reducible ions in the polarographic studies. I. Reduction of cd++ Ions in CdCl2 and Cd(NO3)2) solution with different concentrations of supporting electrolytes ? KCl, KNO3, K2SO4 and NaCl

Journal für Praktische Chemie ◽

10.1002/prac.19630210116 ◽

1963 ◽

Vol 21 (1-2) ◽

pp. 103-108 ◽

Cited By ~ 1

Author(s):

Amar Nath ◽

Abani K. Bhattacharya

Keyword(s):

Diffusion Current ◽

Wave Potential ◽

Half Wave Potential ◽

Half Wave

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Polarographic current-time curves and the Ilkovic Equation.

Australian Journal of Chemistry ◽

10.1071/ch9580271 ◽

1958 ◽

Vol 11 (3) ◽

pp. 271 ◽

Cited By ~ 5

Author(s):

HA McKenzie

Keyword(s):

Mercury Electrode ◽

Potassium Nitrate ◽

Current Time ◽

Current Voltage ◽

Modified Equations ◽

Dropping Mercury Electrode ◽

Instantaneous Current ◽

Average Current ◽

The One ◽

Oxygen Measurements

The Ilkovic equation for the limiting diffusion current obtained with a dropping mercury electrode predicts that the instantaneous current grows during the life of the mercury drop as the one-sixth power of the time, and that the ratio of the instantaneous current at the end of the drop life (the maximum current) to the average current is 1.17. McKenzie (1948) showed in a preliminary study that these relations are not obeyed. The present paper is concerned with a more detailed study of current-time curves for cadmium(II), lead(II), and thallium(I) ions and oxygen. Measurements are made both in the presence and absence of maximum suppressor (gelatin) in two supporting electrolytes (potassium chloride and potassium nitrate). It is found that the rate of growth of the instantaneous current is not in accordance with the Ilkovic equation. Also, it does not accurately follow the modified equations, such as the Lingane-Loveridge equation, particularly during the early stages of drop life. The ratio of maximum to average current varies for the different electroactive substances, but in all cases examined 1.23<imax./iav.<1.30. An interesting observation is also made on the current-time curves for cadmium(II) in potassium nitrate in the presence of gelatin. At pH values appreciably below the isoelectric point (?pH 5) the current-time curves and the current-voltage curves are distorted. The implications of these results in the measurement of polarographic waves, both in theoretical and analytical applications, are discussed.

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Polarographic studies of α-substituted cystines

Canadian Journal of Chemistry ◽

10.1139/v67-116 ◽

1967 ◽

Vol 45 (7) ◽

pp. 713-717 ◽

Cited By ~ 2

Author(s):

R. J. Thibert ◽

R. J. Walton

Keyword(s):

Hydrochloric Acid ◽

Linear Relationship ◽

Diffusion Current ◽

Polarographic Determination ◽

Wave Potential ◽

Titration Curves ◽

Half Wave Potential ◽

Half Wave ◽

Relationship Of

The polarographic determination of some α-substituted cystines in 0.1 N hydrochloric acid, with thymol as a maximum suppressor, was investigated. A linear relationship of the diffusion current to the concentration of the compound was observed. The influence of substituent, thymol concentration, and pH on the apparent half-wave potential and shape of the polarograms was determined. The systems were not reversible.Potentiometric titration curves were obtained for the α-substituted cystines.

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Half-wave potential-ph diagram for the parabenzoquinone system in n,n-dimethylformamide

Analytical Letters ◽

10.1080/00032716908051282 ◽

1969 ◽

Vol 2 (3) ◽

pp. 123-132 ◽

Cited By ~ 4

Author(s):

J. Badoz-lambling ◽

G. Demange-guerin

Keyword(s):

Wave Potential ◽

Half Wave Potential ◽

Half Wave

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Modified Carbon Nanotubes: Surface Properties and Activity in Oxygen Reduction Reaction

Catalysts ◽

10.3390/catal11111354 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1354

Author(s):

Vera Bogdanovskaya ◽

Inna Vernigor ◽

Marina Radina ◽

Vladimir Sobolev ◽

Vladimir Andreev ◽

...

Keyword(s):

Carbon Nanotubes ◽

Zeta Potential ◽

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

Surface Area ◽

Surface Properties ◽

Reduction Reaction ◽

Wave Potential ◽

Half Wave Potential ◽

Half Wave

In order to develop highly efficient and stable catalysts for oxygen reduction reaction (ORR) that do not contain precious metals, it is necessary to modify carbon nanotubes (CNT) and define the effect of the modification on their activity in the ORR. In this work, the modification of CNTs included functionalization by treatment in NaOH or HNO3 (soft and hard conditions, respectively) and subsequent doping with nitrogen (melamine was used as a precursor). The main parameters that determine the efficiency of modified CNT in ORR are composition and surface area (XPS, BET), hydrophilic–hydrophobic surface properties (method of standard contact porosimetry (MSP)) and zeta potential (dynamic light scattering method). The activity of CNT in ORR was assessed following half-wave potential, current density within kinetic potential range and the electrochemically active surface area (SEAS). The obtained results show that the modification of CNT with oxygen-containing groups leads to an increase in hydrophilicity and, consequently, SEAS, as well as the total (overall) current. Subsequent doping with nitrogen ensures further increase in SEAS, higher zeta potential and specific activity in ORR, reflected in the shift of the half-wave potential by 150 mV for CNTNaOH-N and 110 mV for CNTHNO3-N relative to CNTNaOH and CNTHNO3, respectively. Moreover, the introduction of N into the structure of CNTHNO3 increases their corrosion stability.

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