Effect of complex formation on the effectiveness of benzhydrazides in the cadmium electrodeposition from perchlorate baths

It is shown that, depending on the nature of a substituent R in the molecule of addition agent, the electroactive species in the electron transfer may be either 2:1 metal-ligand complexes or more stable 1:1 ones. In the former case, the complexes formed in the surface layer blockade the electrode surface, increase Ψ′-potential and thus impede the metal ion discharge; their inhibitive action increases with an increase in the ligand concentration. In the latter case, the complex formation makes the adsorption film be more permeable and thus accelerates the electroreduction reaction. An increase in the addition agent concentration is accompanied with a decrease in its inhibiting effectiveness.