Oxygen electroreduction on Ag(1 1 1): The pH effect

• Published in: Electrochimica acta 2007-01, Vol.52 (6), p.2264-2271
• Main Authors: Blizanac, B.B., Ross, P.N., Markovic, N.M.
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions; Oxygen reduction reaction; pH effect; Reversible hydrogen electrode; Rotating ring disk method
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2006.06.047

The rotating ring disk method (RRDE) is applied to investigate the pH effect on oxygen reduction reaction (ORR) on Ag(1 1 1) single crystal surface in 0.1 M KOH and 0.1 M HClO 4. In 0.1 M KOH, the ORR proceeds through 4e − reaction pathway with a very small (0.5–2.5%) peroxide formation in the entire potential range. In 0.1 M HClO 4 the onset potential for the ORR is shifted for ca. 400 mV toward the higher overpotentials compared to the 0.1 M KOH solution. At the low overpotentials, in 0.1 M HClO 4 the ORR proceeds entirely as a 2e − process, i.e, 100% H 2O 2 formation. At higher overpotentials, the initial mixed a 2e − and 4e − reduction is followed by the potential region where the ORR proceeds entirely as a 4e − process, with H 2O formation as a final product. The pH dependent shift in the onset of the ORR as well as the reaction pathway has been explained based on both: a thermodynamic analysis of pH independent rate determining step, and on the pH dependent change in availability of surface active sites and adsorption energies of molecular oxygen and reaction intermediates.