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 similar to 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.