Cathode Overpotential and Electrosorption Effects of Straight-Chain Carboxylic Acids during Electrodeposition of Copper

Abstract

The effects of straight-chain carboxylic acids on cathode overpotential during electrodeposition of copper were studied by galvanostatic methods at current densities up to 0.020 A-cm -2. No modification of the chargetransfer mechanism of copper deposition occurred. Overpotential increments caused by lengthening of the carbon chain can be correlated with the reduced concentrations of the carboxylic acids in accordance with Traube's rule. This can be rationalized in terms of the general relation between adsorbability and solubility of the additive. The general behavior is consistent with the blocking theory of additive function according to which overpotential increments are directly dependent on additive adsorbability. The fractional surface coverage calculated from overpotential increments appears to fit a Langmuirtype isotherm from which the free energies of adsorption of the carboxylic acids can be determined. The magnitudes of these free energies are consistent with physical adsorption forces. A relation was derived between the free energy of adsorption and the free energy contributions from the carboxyl group and the carbon chain. This shows that the longer the chain, the higher the adsorbability.Overpotential and adsorbed additives.--The ratedetermining step in electrodeposition varies with the overpotential region (1). The charge-transfer process is believed to be rate-determining at high overpotentials (2) and the accepted mechanism in the case of copper deposition is the two step charge transfer Cu 2+ + e~ Cu + slow Cu + -b e "-> Cu fastThe charge-transfer overpotential ~1 is related to the current density i by the Tafel equation (3) ~1 = a q-blni

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

“…3 are given in the last column in Table II. Overpotentials obtained in this study differ to a degree from those obtained previously with the Hating cell (1). However, just as before (1), and within the accuracy of the measurements, it was found that the An vs. log C relations for all the homologous monocarboxylic acids can be represented by a family of parallel curves equally spaced along the log C axis as shown in Fig.…”

“…This indicates that these compounds do not affect the charge-transfer kinetics of copper deposition, their onIy effect being to increase the true current density in accordance with the simple blocking theory (1,4,5).…”

“…Appropriate adsorption theory can be used to derive quantitative relations between the overpotential increment • and additive concentration C. Calculation of 0 from Eq. [1] for the overpotential increments in Fig. 4, with the Tafel slope taken as the experimental 52 mV, and calculation of the standard free energy of adsorption from the Langmuir-type isotherm (1, 7) [2] where n, the number of water molecules displaced by a molecule of adsorbed additive, is taken as 2 (1,8), results in the family of parallel AG~ VS. 8 curves shown in Fig.…”

Phenolic and non-Phenolic Fractions of the Olive Oil Mill Wastewaters as Corrosion Inhibitor for Steel in HCl medium

“…The values of ∆G ads are all negative indicating that the phenolic fraction is strongly adsorbed on the steel surface [57]. The negative values of ∆G ads indicate that the adsorption is spontaneous [58]. When the absolute value of ∆G ads is higher than 40 kJ /mol, the adsorption could be seen as chemisorption.…”

Inhibition effect of some aromatic amines on copper electrodeposition from acidic baths

“…Regarding the cathodic behavior of copper, it consists basically of two processes: the reduction of Cu(II) to Cu(I) which is the rate determining step and the fast reduction of Cu(I) to metallic Cu. Both processes are extensively reported in the literature [23,24].…”