Electrochemistry of Colloidal Palladium An Experimental Study of Sol Formation and Electrocatalysis

The formation of small palladium colloidal particles in aqueous olution by electroless reduction of palladium salts is described. The presence of water-soluble polymers, such aspolyvinylalcohol (PVA) and polyvinylpyrrolidone improves the colloid-chemical stability of the sols. The formation of the colloidal particles can be easily monitored by open-circuit potential measurements. PVA-stabilized Pd sols are highly catalytic for electroless Ni deposition. They readily induce electroless Ni plating on indium tin oxide substrates, where more classical initiation procedures fail. Palladium colloids are of considerable importance for the electroless metallization of dielectric substrates such as plastics and ceramics. The most extensively used system is the so-called SnPd mixed catalyst. ~,2 Pd particles are ob-tained by mixing aqueous PdC]2 and SnC12 solutions, which results in the following redox reaction Sn 2+ +Pd ~'+---> Pd+ Sn 4+ [1] Tin not only acts as the reducing agent for Pd ions, it is also claimed to stabilize the small Pd nuclei (on the order o