Stabilization of an Electroless Platinum Plating Bath Using S-Bearing Additives

Moderation of an electroless platinum plating bath by thiol, thioether, disulfide, thiocarbonyl, thiosulfate and sulfide compounds was investigated. The inhibitory effect of stabilizers on catalyzed anodic oxidation of the reducing agent used, sodium borohydride, on platinum surfaces was electrochemically characterized by linear sweep voltammetry. Catalytic oxidation inhibition was found to correlate with chemisorption dynamics to catalytic sites on the platinum surface and the steric structure of the sulfur in the compound. Evaluation of the compounds as moderators in electroless plating revealed that the deposition rate and bath stability correlated with the sodium borohydride oxidation inhibition character. Tiopronin had a moderate inhibitory effect on catalytic sodium borohydride oxidation and functioned as an effective stabilizer in the electroless platinum plating bath. Based on the correlation, an inhibitor concentration optimization method using anodic polarization curves was established. The dynamics of the electroless plating reaction concurred with electrochemical analysis and was comprehensively described by the mixed potential theory. Using cyclic voltammetry, the deposits had similar electrochemical characteristic to that of pure polycrystalline platinum, although less than 0.5 wt% sulfur inclusion was confirmed by elemental analysis. (c) The Author(s) 2015. Published by ECS. All rights reserved.