The significance of the electroless silver plating bath using ethanethiol derivatives as reducing and complex agents lies in it being noncyanide, having near by neutral pH, and providing good storage stability. This is achieved by plating in a composition that is neither immersion for coating electroless nickel substrates nor autocatalytic.
Anodic polarization curves of 2-aminoethanethiol (cysteamine) and N-acetyl-L-cysteine in a basic electrolyte showed that 2-aminoethanethiol acts as a reducing agent and that N-acetyl-L-cysteine is not easily oxidized on silver electrodes. Experiments in polarization confirmed the mixed potential theory including local potentialcurrent relationships for silver deposition. Based on information available on oxidation of the reducing agent, we propose the following partial anodic and cathodic reactions:
Anodic partial reaction
2HSCH₂CH₂NH₂→H₂NCH₂CH₂SSCH₂CH₂NH₂+2H⁺+2e^-
(Cysteamine) (Cystamine)
Cathodic partial reaction
Ag⁺+e^-→Ag