Oxygen Reduction on Polycrystalline Platinum in Alkaline Solution. III. Platinum Surface Modified by Hydrogen Evolution: Additional Data

 

Carlos Paliteiro,* Elsa Correia

 

Departamento de Química, Universidade de Coimbra, P-3004-535 Coimbra, Portugal

 

Received 11 March 2005; accepted in revised form 6 October 2005

 

 

Abstract

This paper presents and discusses data collected on the electroreduction of O₂ (ORR) in 1 M NaOH on a polycrystalline Pt surface that initially was pretreated by H₂ evolution at -250 mV in deaerated 0.5 M H₂SO₄ and then evolved with time in a spontaneous and rather slow way towards a full Nekrasov (N-Pt) type behavior, both in the cathodic- and in the anodic potential scan. This fact represents a clear demonstration that a polycrystalline metal surface is a dynamic system and allowed us to carry out the thorough study of the mechanism and kinetics of the ORR on a full
N-Pt surface that was not possible in the previous work reported in the Part II of this series. Essentially, we concluded that the change does not alter the ORR mechanism, which is always a series mechanism coupled to disproportionation of the HO₂^- produced; what varies in a given potential range is the value of the rate constants of the different mechanistic steps. It was possible to get absolute values of these constants only for some potential ranges, although the analysis of the data collected provided relative information for the remaining ranges.

Keywords: oxygen reduction, electrocatalytic reduction, physical electrochemistry, metal surface dynamics.

 

 

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* Corresponding author. E-mail address: paliteir@ci.uc.pt