In Situ Spectroscopy Study of Oxygen Reduction Reaction Intermediates at the Pt/Acid Interface: Surface-Enhanced Infrared Absorbance Spectroscopy

Increasing demands for the development of efficient electrochemical energy systems such as fuel cells and metal–air batteries have stimulated research interests in investigating the mechanistic pathway of the oxygen reduction reaction (ORR) at the catalyst surface, having direct relevance to these systems. Although past years have witnessed few efforts toward illustrating the mechanistic pathway of the ORR under various pH conditions, the chemical nature of intermediates generated under the acidic conditions still remains a challenge. In the present study, the detection of possible intermediate species formed at the Pt/HClO₄ interface is endeavored using in situ surface-enhanced infrared absorbance spectroscopy (SEIRAS). This is achieved using a simple electrode configuration with polycrystalline Pt deposited on the roughened surface of an Au-coated ZnSe prism to avoid the IR absorbance of the prism. Potential-dependent SEIRAS measurements demonstrate the formation of superoxide anion species at the Pt surface. Spectral analysis under O-isotope (¹⁸O₂) and D₂O conditions corroborate the detection of superoxide species. A systematic study of the ORR intermediates and their surface coverage paves a way for efficient catalyst design.