Surface Platinum Electrooxidation in the Presence of Oxygen

Understanding the influences of Pt surface oxides is crucial for elucidating the oxygen reduction reaction (ORR) in fuel cells, particularly with an eye toward the design of next-generation Pt-based electrocatalysts with improved activity. Although gaseous O-2 is always present during the ORB., the majority of previous Pt surface oxide studies were conducted in the absence of O-2 due to experimental limitations. In this study, multiple in situ techniques were applied to study the ORR on platinum in the presence of O-2. The thin channel flow Pt electrode and the electrochemical quartz microbalance (EQCM) techniques on Pt polycrystalline electrodes suggest that the influence of O-2 in the electrolyte on mass change and charge transfer is negligible. The oxide formation followed a logarithm-growth behavior initiating as early as 0.2 s after potential steps. This suggests that no slow conversion of oxide species (e.g., between OHads and O-ads) takes place. Despite the negligible effect of O-2 on the measured oxide coverage, steady-state X-ray absorption spectroscopy (XAS) measurements conducted on dispersed Pt nanoparticles suggested that, only when under O-2-sparging, place exchange between adsorbed oxide(s) and the Pt surface layer(s) initiated at potentials as low as 0.75 V. This is significantly lower than that observed in an O-2-free electrolyte (>1.1 V). The effects of O-2 on adsorbed oxide species illustrate the complexities of applying model systems to the real world in order to arrive at a comprehensive description of both the oxygen reduction and the Pt dissolution processes.