ChemInform Abstract: STUDY OF THE ANODIC DISSOLUTION OF LEAD IN POTASSIUM HYDROXIDE SOLUTIONS

The mechanism of the initial stages of normalPbO formation has been investigated at a Pb anode in 1M normalNaOH solutions, with the use of cyclic voltammetry, transient and steady‐state potential step methods, and modulated surface reflectance spectroscopy (MSRS). It has been found that, following the deposition and dissolution of normalPbfalse(OH)2 at less positive potentials, normalPbO deposition initiates according to an instantaneous three‐dimensional nucleation and growth mechanism under diffusion control. This is supported by the good match of the experimentally obtained i‐t response with the theoretically predicted one, by the observed changes in surface reflectivity with time and the marked effects of electrode rotation on the observed currents. Some dissolution of normalPbO also occurs in these early stages of oxidation, forming the HPbO2− species, consistent with the observed Tafel slope and the excess of the anodic to cathodic charge in cyclic voltammetry. At still higher potentials or longer times, very thick porous normalPbO films can be formed, consistent with film initiation by a nucleation and growth mechanism.

Section: The Materials and Energy Research Centre Tehran Assisted In ...supporting

confidence: 92%

The Lead Anode in Alkaline Solutions: II . The Mechanism of Film Formation

Birss

Shevalier

1987

“…Pb(OH)2 can also undergo a dehydration process (reaction [4]) according to the following reaction scheme Pb(OH)2 ~-PbO + H20 [4] These reactions occur in the range of potential from about 200 to 300 mV vs. RHE, with reaction [3] being the ratedetermining step. The occurrence of reactions [1]- [4] is consistent with the prior suggestions in the literature regarding the early stages of Pb oxidation in alkaline solutions (6)(7)(8)(9)(10)(11).…”

supporting

confidence: 86%

“…Therefore, A(1 -e) is equivalent to the free Pb surface area, i.e., that area of the electrode still accessible to the reactant and not covered by PbO film. When a reaction overpotential, 0, is applied to the electrode, current will flow across the two resistors, Rs and Rp, according to Ohm's law ] = ~/(Rs + Rp) [11] where = st [12] and s is the potential sweep rate. As the film grows laterally at a constant thickness, h, {} increases and Faraday's law can be used to convert the quantity of film formed to the amount of charge passed.…”

Section: Resultsmentioning

confidence: 99%

“…This relationship can readily be derived from Eq. [11] and [15], if the peak parameters [p and Ep are substituted for I and ~l.…”

Section: ] Mmentioning

confidence: 99%

“…Of the published work regarding PbO electrochemistry, most has been based on the results of galvanostatic studies (6)(7)(8)(9)(10)(11). More recently, a photoelectrochemical study of~PbO and PbO2 films, formed by the potentiodynamic sweep method in pH 9 solutions, has been published (12).…”

mentioning

confidence: 99%

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The Lead Anode in Alkaline Solutions: III . Growth of Thick Films

Birss

Shevalier

1990

The mechanism of formation of thick, porous, PbO films at a Pb anode in 1N NaOH solutions was investigated. Film growth initiates by a nucleation process and then proceeds at a rate which is controlled by the increasing resistance of the solution in the narrowing pores of the oxide film. The observed i/E relationships were simulated on the basis of two models of film growth, one involving the spreading of islands of film of constant height, and the other in which nuclei both spread and increase in height until the electrode surface is almost fully covered. The latter model led to a very good fit between the observed and calculated curves.

The Lead Anode in Alkaline Solutions: I . The Initial Oxidation Processes

Birss¹,

Shevalier²

1987

The initial reactions occurring at a Pb anode in alkaline solutions have been investigated using cyclic voltammetry and steady-state and transient potentiostatic methodologies. It has been found that the first step in the reaction is the formation of a PbOH surface intermediate, followed by the deposition of a thin Pb(OH)2 film on the Pb surface. A major portion of this film dissolves to form Pb(OH)3-and the measured Tafel slope of 27 mV/decade of current density is consistent with the dissolution step being the rate-determining step. With the use of the rotating ring disk electrode technique, in which the disk current is separated into that due to the formation of an insoluble surface product and that due to a dissolution reaction, it was found that some of the Pb(OH)2 film dehydrates to form a thin PbO film. At more positive potentials, further PbO film growth occurs, but by a nucleation and growth mechanism.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.218.248.209 Downloaded on 2015-03-29 to IP Vol. 134, No. 4 LEAD ANODE IN ALKALINE PROCESSES 803