Oxygen Reduction on Platinum Surfaces in Acid Media: Experimental Evidence of a CECE/DISP Initial Reaction Path

Author(s)

Gomez-Marin, Ana M. ^{[1, 2]} ; Feliu, Juan M. ^[3] ; Ticianelli, Edson ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Quim Sao Carlos, Fis Quim, Caixa Postal 780, Av Trabalhador Sao Carlense, BR-13560970 Sao Carlos, SP - Brazil

^[2] Technol Inst Aeronaut ITA, Dept Chem, Div Fundamental Sci IEF, BR-12228900 Sao Jose Dos Campos, SP - Brazil

^[3] Univ Alicante, Inst Electroquim, Apt 99, E-03080 Alicante - Spain

• Document type: Journal article
• Source: ACS CATALYSIS; v. 9, n. 3, p. 2238-2251, MAR 2019.
• Web of Science Citations: 2

Abstract

In this work, a detailed kinetic analysis of the oxygen reduction reaction (ORR) on platinum is performed by applying steady and non-steady-state methodologies at stationary and rotating disk electrodes and by comparing experimental results to calculated curves via digital simulations. Results reveal the existence of a complex chemical-electrochemical-chemical-electrochemical initial reaction sequence, a CECE-mechanism, and the possible contribution of a parallel disproportionation process in acid media during the reaction. Under convection-controlled circumstances, the first charge-transfer step would be the rate-determining step (RDS) on bulk electrodes, in agreement with early reports, but at different working conditions other initial steps can become the RDS. Additionally, contrary to the current accepted view, results support the formation of a soluble intermediate in the initial, and fast, chemical reaction, with a short lifetime, compatible with the formation of either the hydroperoxyl radical, HO2{*}, or superoxide anion, O-2(-), followed by a fast protonation. In light of present results, possible mechanisms, including the oxidation of H2O2 that could be produced either by disproportionation or by reduction of HO2{*}, and/or O-2(-), radicals, are discussed. This interrelated reaction scheme would be the principal cause of large ORR overpotentials, but at the same time, it would open the opportunity for designing alternative catalysts beyond fundamental limits imposed by the apparent scaling relations between reaction intermediates, such as OHads, O-ads and HO2ads adsorbates. (AU)

• FAPESP's process: 13/16930-7 - Electrocatalysis V: electrocatalytic processes of chemical and electrical energy interconversion
• Grantee: Edson Antonio Ticianelli
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 14/23486-9 - Development of nanostructured electrocatalysts for electro-oxygen reduction reaction: study of activity and stability
• Grantee: Ana Maria Gómez Marín
• Support Opportunities: Scholarships in Brazil - Post-Doctoral