Electrochemical nanogravimetric studies of sulfur/sulfide redox processes on gold surface

• Published in: Journal of solid state electrochemistry Vol. 13; no. 12; pp. 1935 - 1944
• Main Authors: Bura-Nakic, Elvira, Róka, András, Ciglenecki, Irena, Inzelt, György
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.12.2009
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Energy Storage; Original Paper; Physical Chemistry; Polysulfide; Na2S; Underpotential Deposition; Electrochemical Quartz Crystal Microbalance; Hydrogen Evolution Reaction
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-008-0742-9

Electrochemical quartz crystal microbalance, combined with cyclic voltammetric, chronoamperometric, and potentiostatic measurements, was used to study electrodeposition/dissolution phenomena at a gold electrode in solutions containing Na 2 S. Spontaneous, open-circuit deposition processes as well as dissolution of the deposits in sulfide-free solutions have also been investigated. The potential range, scan rate, sulfide concentration, and pH have been varied. The results of the piezoelectric nanogravimetric studies are elucidated by a rather complex scheme involving underpotential deposition of sulfur at approximately −0.85 V vs. sodium calomel electrode, reductive dissolution of the deposited sulfur-containing layer at potentials more negative than approximately −0.9 V, and formation of a sulfur-containing multilayer at potentials more positive than −0.2 V. During the reduction of sulfur deposited on Au, a mass increase due to the formation of polysulfide species in the surface layer, accompanied by incorporation of Na + counterions, can be observed that starts at approximately −0.4 V. This is a reversible process, i.e., during the reoxidation, counterions leave the surface layers. Frequency excursions during the electroreduction and reoxidation processes reveal existence of several competitive dissolution–deposition steps. Spontaneous interaction between Au and HS − species results in a surface mass increase at the open-circuit potential, and it also manifests itself in the substantial decrease of the open-circuit potential after addition of Na 2 S to the supporting electrolyte.