Oxygen reduction reaction at Pt single crystals: a critical overview

Abstract

Oxygen reduction reaction (ORR) dynamics at platinum single crystal surfaces is reviewed, and experimental results in acid and alkaline solutions are discussed in the framework of theoretical studies. Special emphasis is devoted to point out the role of the surface charge, water structure and adsorbed oxygen containing species. Additionally, discussion about the possible relevance of hydrogen peroxide as an intermediate species is also included. It is shown that the ORR is a complex process affected by many different factors and so neither surface charge nor oxygen-containing species coverage alone are a determining factor of the electrode activity. Instead, adlayer structures and the relation between adsorbed water, H₂O_ads, water dissociation products, OH_ads or O_ads, and PtO oxide species coverage affect the whole energetics of the adsorption processes and may determine the surface reactivity. Finally, if H₂O₂ is an intermediate product in the ORR mechanism, it would be crucial to find a suitable catalyst able to effectively reduce H₂O₂ at high potentials and inhibit its oxidation.