In Situ Spectroscopic Evidence for Ordered Core–Ultrathin Shell Pt1Co1 Nanoparticles with Enhanced Activity and Stability as Oxygen Reduction Electrocatalysts

To truly understand the origin of the enhanced oxygen reduction reaction (ORR) activity of Pt-based electrocatalysts over pure Pt, it is essential to characterize the electrocatalysts under ORR operating conditions. Herein, we report a dealloyed Pt1Co1 NP catalyst with Pt mass activity ∼4 times higher than that of Pt/C and with superior stability in proton exchange membrane fuel cells (PEMFCs). Advanced microscopy and in situ spectroscopy are combined to show that this electrocatalyst possesses a unique ordered PtCo core–ultrathin with nonporous Pt shell structure, and the structure maintains the desired compositional profiles in the near-surface region even during the ORR in acid. Ab initio FEFF8 calculations based on experimentally derived structures reveal that the catalytic enhancements result from cooperative compressive-strain and ligand effects induced by the Co enrichment in the compact core and near subsurface.