Cathode Overpotential and Surface-Active Additives in the Electrodeposition of Copper I. Effects of Some Carboxyl and Amino Compounds

Additives containing carboxyl and amino groups increase the overpoten-tial of a copper cathode during electrolysis in an acid sulfate electrolyte, the amino group being more effective than the carboxyl. At a given additive concentration the overpotential increment apparently depends on the adsorp-tivity and size of the additive molecule. The adsorptivity in turn depends on the number and kind of polar functional groups, the structural relation be-tween electron-donating atoms, and the lattice dimensions of the copper deposit. It is suggested that the behavior of a chemisorbed additive can be understood in terms of two effects, (i) the complete blockage of growth sites by chemisorption bonds and (it) the partial blockage of adjacent sites by the physical bulk of the adsorbed molecule. It is generally believed that the effect of addition agents on cathode overpotential (or polarization) dur-ing electrodeposition of metals arises primari ly be