Mechanistic Principles of Platinum Oxide Formation and Reduction

In polymer electrolyte fuel cells, the platinum catalyst in its active form is found predominantly in an oxidized state. Formation and reduction of surface oxide species determine both the electrocatalytic activity of the oxygen reduction reaction as well as the rate of corrosive Pt dissolution. Understanding of mechanisms and rates of oxide formation and reduction is therefore essential in view of both performance and durability. Pt(111) is the generic model system for fundamental studies in fuel cell electrochemistry and cyclic voltammetry at Pt(111) gives an unabated view of the oxide formation and reduction processes. The unresolved challenge is to develop an electrochemical kinetic model that allows the current response measured in cyclic voltammetry to be de-convoluted and interpreted in relation to independent spectroscopic, imaging and theoretical data. Accordingly, a kinetic model for Pt(111) oxide formation and reduction within the voltage range of 0.65-1.15 V is developed and evaluated against electrochemical, spectroscopic and computational studies. Considering the complexity of surface processes involved and the simplicity of the proposed model, the agreement with the extensive range of data is convincing. The model provides a comprehensive picture of surface electrochemical processes that occur at Pt(111) in the normal operational voltage range of the cathode catalyst for polymer electrolyte fuel cells in automotive applications.