CATHODE OVERPOTENTIAL AND ELECTROSORPTION EFFECTS OF STRAIGHT-CHAIN CARBOXYLIC ACIDS DURING ELECTRODEPOSITION OF COPPER

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 charge-transfer 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 block ing theory of additive function according to which overpotential increments are directly dependent on additive adsorbability. The fractional surface cov erage calculated from overpotential increments appears to fit a Langmuir-type 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 en ergy 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. © 1969, The Electrochemical Society, Inc. All rights reserved.