Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In situ IR Spectroscopy.

The sluggish kinetics of oxygen reduction to water remains a significant limitation in the viability of proton-exchange-membrane fuel cells, yet details of the four-electron oxygen reduction reaction remain elusive. Herein, we apply in situ infrared spectroscopy to probe the surface chemistry of a commercial carbon-supported Pt nanoparticle catalyst during oxygen reduction. The IR spectra show potential-dependent appearance of adsorbed superoxide and hydroperoxide intermediates on Pt. This strongly supports an associative pathway for oxygen reduction. Analysis of the adsorbates alongside the catalytic current suggests that another pathway must also be in operation, consistent with a parallel dissociative pathway.