Cathode Overpotential and Electrosorption Effects of Normal Monocarboxylic Acids during Electrodeposition of Copper

Abstract

The cathode overpotential and electrosorption effects of some normal monocarboxylic acids during electrodeposition of copper were studied galvanostatically at current densities up to 20 mA-cm -2. Equations were derived by means of which overpotential increments caused by the blocking action of adsorbed additive can be used to calculate the separate adsorption free-energy contributions of the carboxyl and methylene groups in the additive molecule, and also a coverage-dependent lateral interaction free energy arising primarily from dipole-dipole interaction between adjacent carboxyl groups in the adsorbed phase. The carboxyl group contribution was found to be --1570 cal mole -1 at zero coverage, while the methylene group contribution was --704 cal mole-' and independent of coverage.

The Bockris-Swinkels Isotherm and Low-Coverage Electrosorption of Monocarboxylic Acids on a Copper Cathode

“…A coverage-dependent apparent free energy, assumed to be due to lateral interaction, is also calculable (2), with results similar to those obtained for the adsorption of butanoic and 2-methyl-propanoic acids on mercury (3). Theoretical considerations indicate that the lateral interaction arises primarily from dipoledipole effects in the adsorbed phase (2).…”

“…For normal monocarboxylic acids as additives, the coverage e can then be related to the individual adsorption free energy contributions of the various parts of the adsorbed molecule by writing the Bockris-SWinkels version of the Langmuir isotherm (5) (derived for adsorption involving solvent displacement) in the appropriate form (2) Key words: theory, isotherm, blocking, homologous, additives.…”

“…In Eq. [2], C is the concentration of additive, x is the number of methylene groups in the additive molecule, including the terminal methyl, and n is the solvent displacement number. AG~ and AG~ denote the standard free energy contributions of the polar carboxyl group and each methylene group respectively, 1 while the coverage-dependent parameter g(e) is a Frumkin-like interaction term definable as an apparent standard free energy (8) due to lateral forces between the adsorbed molecules.…”

“…Studies of the effects of normal monocarboxylic acids on the cathode overpotential during electrodeposition of copper from acid sulfate electrolyte have shown (1,2) that specific adsorption free energy contributions due to the individual structural units of such additive molecules can be calculated from overpotential increment and additive concentration data. A coverage-dependent apparent free energy, assumed to be due to lateral interaction, is also calculable (2), with results similar to those obtained for the adsorption of butanoic and 2-methyl-propanoic acids on mercury (3). Theoretical considerations indicate that the lateral interaction arises primarily from dipoledipole effects in the adsorbed phase (2).…”

“…The present paper deals with the electrosorption of monocarboxylic acids in general terms, with restriction to very low or near-zero coverages. The blocking equation (1,2,4) and an appropriate form of the Bockris-Swinkels isotherm (2,5) are assumed applicable, and some pertinent and useful information is derived based on this assumption. Special attention is given to the relationship between the various free energy components and the solvent displacement number n, the number of adsorbed water molecules displaced per molecule of additive in the adsorption "reaction" (5) Asoln.…”