Some aspects of the measurement of hydrogen overpotential

Azzam, A. M.; Bockris, J. O'm.; Conway, B. E.; Rosenberg, Herbert M.

doi:10.1039/tf9504600918

Cited by 70 publications

(52 citation statements)

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“…4), a method that appears to be insensitive to oxygen concentrations lower than 10-"molar (2). In the present work, the action of oxygen has been studied through its effect on the potential (Table I), potential decay curves (Fig.…”

Section: -10mentioning

confidence: 98%

“…The initial potential on a fresh mercury surface became increasingly negative as 0x3 gen was reinoved from the electrolyte (N/5 sulphuric acid) by electro-1: tic reduction a t the mercury cathode (2,8). Such potentials were not stable, l~owever, and changed rapidly to more positive values unless the initial potential was of the order of -0.60 volt.…”

Section: Fig 1 Diagram Of Cellmentioning

confidence: 99%

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The Electrode Behavior of Mercury

Wiebe¹,

Winkler²

1953

Can. J. Chem.

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Mercury electrode potentials in 1V/5 s~~l p h u r i c acid were ~~naffected when the electrolyte was saturated with hydrogen, nitrogen, or helium but were marl;edly affected by trace amounts of oxygen or mercury ions. In the absence of oxygen and mercury ions, a constant potential of -0.61 volt (relative to a saturated calomel electrode) was observed. When current was passed for the first time across a fresh electrode face immersed in oxygen-free electrolyte (i.e. from initial potentials of about -0.61 volt), the potential build-up was nonlinear, but subsequent passage of current gave a linear build-up of potential. U'ith traces of oxygen present, differences in the two types of curves were niasked by reactions that appeared to involve oxygen or oxide on the electrode surface. The initial build-up curve was ascribed to the deposition of a tnonatomic hydrogen film (one atom per metal atom in the surface). The potential build-up curves probably result from a nuniber of simultaneous reactions a t the electrode.From recent studies in this laboratory (15) with copper and silver cathodes immersed in sulphuric acid, it was tentatively concluded that measurement of surface areas by the Bowden-Rideal method (8) depends on the rate of chnrging a condenser at the surface, as distinct from the rate of increase of 111-drogen overvoltage, which appeared to be associated with the deposition of a la)-er of hydrogen on the cathode.Similar experiments with mercury cathodes have yielded the results recorded in the present paper. EXPERIMENTAL AND RESULTSThe cathode ray oscillograpl~ unit and Leeds and Northrup type I< potentiometer arrangement were identical with those described in earlier papers (12, 13).The electrolytic cell, shown in Fig.

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Section: -10mentioning

confidence: 98%

Section: Fig 1 Diagram Of Cellmentioning

confidence: 99%

The Electrode Behavior of Mercury

Wiebe¹,

Winkler²

1953

Can. J. Chem.

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“…1. Overpotential of sample I as a function of the applied current density (A) and the total current density (B).…”

Section: Results a N D Discussionmentioning

confidence: 99%

“…The water was of "conductivity" grade, k = 8X10-7 ohm-' cm.-I, the acid redistilled reagent quality. T h e electrolyte was purged with purified hydrogen and subjected t o lengthy pre-electrolysis, according t o the method recommended by Bocltris and co-workers (1).…”

Section: E X P E R I M E N T a Lmentioning

confidence: 99%

Hydrogen Overpotential on Aluminum

Hansen¹,

Wetmore²

1956

Can. J. Chem.

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The hydrogen overpotential of pure and impure aluminum in 0.1 N HzSOr a t 25" has been studied. The effect of the autocorrosion of the metal has been interpreted and the role of impurities in determining the overpotential and the rest potential has been shown. As well, the build-up and decay of the overpotential has been studied; the behavior is much more complicated than that of noble metals.Studies of hydrogen overpotential on aluminum have been few (2,3,5,6,7,8) and in most cases details of procedure and the degree of purity of the metal are lacking or there is indication that proper experimental precautions (I) have not been taken. In 110 case was the rate of corrosion reported, although it may have been substantial. The investigation reported here was an exploration a t low current densities, for which there are no serious doubts about the homogeneity of current density distribution. E X P E R I M E N T A LT h e electrolyte used for all experiments was 0.1 N H2S01, a concentration selected as a compromise between the desires for high conductivity and low rate of corrosion. The water was of "conductivity" grade, k = 8X10-7 ohm-' cm.-I, the acid redistilled reagent quality. T h e electrolyte was purged with purified hydrogen and subjected t o lengthy pre-electrolysis, according t o the method recommended by Bocltris and co-workers (1).T h e aluminum cathode and platinum anode of the cell were in separate compartments conilected through closed ungreased stopcocks wet with solution. Hydrogel1 was bubbled continuously about both electrodes. An auxiliary cathode of platinum was available for pre-electrolysis. A capillary probe near the cathode surface led t o a reference electrode, 0.1 N H2S04/Hg2S0,, Hg. Four types of cathode material were selected for study: (I) rolled sheet, 99.995% pure, (11) cast polycrystalline, 99.995y0 pure, (111) single crystal, 99.995% pure, and (IV) "commercially pure" ingot, 99.5% pure. T h e cathodes were electropolished in a perchloric acid bath, then mounted in a Teflon box which exposed only one flat face. Unless stated otherwise, current densities mentioned refer to the apparent area of this face.T h e currents used were electronically regulated. T h e potential diit'erence between the probe and cathode was passed to a direct-coupled amplifier of very high impedance (about 1013 ohms) and thence to a torsion string galvanometer (Model TSB-A29, Kipp en Zonen, Delft). The deflection of the galvanometer could be recorded on film in a drum camera. Alternatively, a potentiometer was used for steady state readings. Rates of corrosion were determined by measurement of the weight loss of the sample; a resistance-capacitance bridge 'iManuscript

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“…Traces of H.~S were shown to cause Tafel lines to deviate from linearity toward a limiting overpotential at high current densities. Conditions for pre-electrolysis and criteria of a "pure" solution were evolved (11).…”

Section: Effect Of Trace Impuritiesmentioning

confidence: 99%