The effect of the double layer on the heat of activation of simple electrode reactions

Chauhan, B. G.; Fawcett, W. Ronald; McCarrick, T. A.

doi:10.1016/s0022-0728(75)80360-3

Cited by 18 publications

(8 citation statements)

References 28 publications

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“…Parsons (12), Frumkin et al (13), Fawcett et aI. (14), and references cited therein]. In the present case, however, the depolarization effect was found to be due to residual impurities in the electrolyte.…”

mentioning

confidence: 46%

Electrodeposition of Gold: Depolarization Effects Induced by Heavy Metal Ions

McIntyre¹,

Peck²

1976

J. Electrochem. Soc.

102

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Addition of trace quantities (ppm) of heavy metal ions such as Pb(II) or Tl(I) to soft gold electroplating baths induces a marked cathode depolarization that extends the current density range in which bright, fine‐grained deposits can be obtained and produces uniform coverage of irregularly shaped substrates. In this study it is shown that the trace foreign metal additives which are most effective as depolarizers are those which tend to deposit uniformly on a gold surface to form an adsorbed monolayer at electrode potentials positive to those where their cathodic deposition as bulk metals begins,i.e., at underpotentials. Of the series of Group B elements (As, Bi, Cd, Cu, Ga, Hg, Pb, Sb, Sn, Tl, and Zn) investigated for depolarization action in alkaline phosphate solutions (pH 8, 70°C), only Pb, Tl, Bi, and Hg were found to induce significant effects. The latter two metals have not previously been reported to act as depolarizers in gold electrodeposition processes. The kinetics of the potential relaxation effects induced by these species under galvanostatic conditions were found to be strongly dependent on mass transport rate, gold deposition rate (i.e., plating current density), and temperature. In addition, it was found that Pb, Bi, Hg, and particularly Tl enhance the anodic dissolution of gold in cyanide‐containing solutions. The ranges of underpotential deposition of the metals Pb, Tl, Bi, and Hg from very dilute (∼5 μM) solutions of their ions in pure phosphate supporting electrolyte at 70°C were determined under steady‐state mass transport conditions at a rotating gold disk electrode. By varying the disk rotational speed and the potential scan rate, it was shown that a significant amount of Pb(II) [the equivalent of ∼20% of a close‐packed monolayer of Pb(0)] is specifically adsorbed in the ionic double layer at the gold surface and is not desorbed even at high anodic potentials. A similar phenomenon was observed for the Bi(III) species. The depolarization induced by the trace heavy metal ions is examined in terms of electrocrystallization and electrocatalytic mechanisms. From the magnitude of the potential relaxation (∼0.2V), its temperature dependence, and the ability of Hg to alloy with Au, it is concluded that screw dislocation generation is not responsible for this effect. Failure of Cs+ ions to enhance the rate of electroreduction of normalAufalse(CN)2− anions and also the ability of Pb(II) to catalyze the electroreduction of O2 indicates that electrostatic repulsion effects are of minor importance. It is concluded that the depolarization phenomenon is caused by an enhancement of nucleation rate produced by the strongly adsorbed foreign metal atoms. In addition, catalytic electrochemical displacement reactions are made possible by the fact that the exchange current densities of the various Mz+/M depolarizer couples are much greater than that of the normalAufalse(CN)2−/normalAu couple and by the specific adsorption of the Mz+species. In the case of Hg, displacement is made thermodynamically possible...

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mentioning

confidence: 46%

Electrodeposition of Gold: Depolarization Effects Induced by Heavy Metal Ions

McIntyre¹,

Peck²

1976

J. Electrochem. Soc.

102

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“…All results obtained are consistent with a model of the inner layer in which its thickness at negative charge densities is determined by the distance of closest approach of a solvated cation, the solvated radius of Na+ being larger than that of K +. A similar explanation can be offered to account for all or part of the cation effect observed for the kinetics of electron transfer reactions occurring at negative charge densities on mercury (24,25).…”

Section: Discussionmentioning

confidence: 97%

The Effects of Counterion Size on the Equilibrium Properties of Charged Interfaces

Fawcett

McCarrick

1976

J. Electrochem. Soc.

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The adsorption of iodide ion at mercury has been studied from two systems at constant ionic strength, namely, xMnormalNaI+false(0.25−xfalse)MnormalNaF and xMKI+false(0.25−xfalse)MKF . The surface excess of adsorbed iodide ions was calculated from differential capacity data using a modified version of the Hurwitz‐Parsons analysis which takes into consideration variation in ionic activity coefficients with solution composition. The iodide surface excess was found to depend on the nature of the cation for a given bulk concentration and electrode charge density; comparison of the present data with those previously published shows a marked dependence of adsorbed surface excess on ionic strength. The effect of counterion nature on ionic adsorption is discussed within the framework of an electrostatic model for adsorption which takes the discrete nature of the charge at the interface into consideration. Counterion effects at charged monolayers, bilayer lipid membranes, and real membranes are compared with those observed at mercury.

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“…This expression was first derived by Frumkin in connection with the analysis of data for the electroreduction of H+ at Hg (22) and can be used to explain the dependence of a, on the nature of the inert cation in this reaction system (23). The effects of the nature of the alkali metal cation on the kinetic parameters for the electroreduction of H+ have been discussed in more detail elsewhere (1,23 For personal use only.…”

Section: Analysis Of Kinetic Data For Simple Electrodementioning

confidence: 99%

“…The effects of the nature of the alkali metal cation on the kinetic parameters for the electroreduction of H+ have been discussed in more detail elsewhere (1,23 For personal use only.…”

Section: Analysis Of Kinetic Data For Simple Electrodementioning

confidence: 99%

The location of the reaction site and discreteness-of-charge effects in electrode kinetics

Fawcett¹

1981

Can. J. Chem.

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This paper is dedicated to Dr. Sam Levine on the occasion of his 70th birthday W. R. FAWCETT. Can. J. Chem. 59, 1844(1981. Discreteness-of-charge effects for simple heterogeneous electron transfer reactions, namely, the self-image effect, the exclusion disc effect, and the effect of local attractive ion-ion interactions, are considered for a variety of reaction sites in the double layer, both in the presence and in the absence of ionic specific adsorption. An expression is derived for the local activity coefficient of the activated complex; this quantity is shown to be a function of both the potential drop across the inner layer and the adsorbed charge density due to specifically adsorbed ions when the standard state is chosen on the basis of the reaction conditions considered in the classical Frumkin theory (reaction site at the outer Helmholtz plane). The consequences of discreteness-of-charge effects for reactions occuring in three different double layer environments of increasing complexity are described. These effects are discussed on the basis of data obtained earlier for the electroreduction of periodate anion in the presence of specifically adsorbed anions.W. R. FAWCETT. Can. J. Chem. 59, 1844 (1981). On a examine les effets du caractere discret des charges lors de reactions simples de transfert heterogtne d'tlectron, en particulier I'effet d'auto-image, I'effet d'exclusion du disque et I'effet des interactions locales ion-ion attractives sur divers sites reactionnels de la couche double en presence ainsi qu'en I'absence d'adsorption ionique specifique. On a deduit une expression pour le coefficient d'activite locale du complexe active; on montre que cette quantitt est une fonction de lachute de potentiel B travers la couche interne et de la densite de charge adsorbee provenant d'ions sptcifiquement adsorbts quand I'Ctat normal est choisi en fonction des conditions de la reaction considerte dans la theorie classique de Frumkin (site rtactionnel au plan exterieur de Helmholtz). On decrit les consequences des effets du caractere discret de la charge de la couche double pour des reactions qui ont lieu dans trois environnements differents de complexite croissante. On discute de ces effets en fonction de donnees relatives a l'electro-reduction de I'anion periodate en presence d'anions sptcifiquement adsorbes que nous avons obtenus anterieurement.[Traduit par le journal]

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The effect of the double layer on the heat of activation of simple electrode reactions

Cited by 18 publications

References 28 publications

Electrodeposition of Gold: Depolarization Effects Induced by Heavy Metal Ions

Electrodeposition of Gold: Depolarization Effects Induced by Heavy Metal Ions

The Effects of Counterion Size on the Equilibrium Properties of Charged Interfaces

The location of the reaction site and discreteness-of-charge effects in electrode kinetics

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