Dealloyed Pt₂Os nanoparticles for enhanced oxygen reduction reaction in acidic electrolytes

Carbon-supported Pt₂Os (Pt₂Os/C) nanoparticles in 3.55nm sizes are synthesized from a wet chemical reflux process. Subsequently, the Pt₂Os/C undergoes a dealloying treatment in which multiple cyclic voltammetric scans are imposed to dissolve the Os atoms selectively from the surface of the Pt₂Os nanoparticles. X-ray diffraction signals from the dealloyed sample (DA-Pt₂Os/C) indicate a fcc phase and composition analysis suggests Pt₄Os. Line scans from the scanning transmission electron microscope confirm that the surface of Pt₄Os is depleted with the Os atoms. This agrees with our quantum mechanics (Density Funtional theory) calculations, which predict for the Pt₃Os composition that the surface skin layer is pure Pt. The DA-Pt₂Os/C shows impressive electrocatalytic behaviors (0.29mAμg_Pt^-1 in mass activity and 1.03mAcm_Pt^-2 in specific activity) for the oxygen reduction reaction (ORR) in oxygen-saturated 0.1M aqueous HClO₄ solution, as compared to those of commercially available Pt/C and as-synthesized Pt₂Os/C. In stability test, the DA-Pt₂Os/C demonstrates a better retention of ORR activities and a smaller loss of electrochemical active surface area. We verify experimentally that a four-electron step is responsible for the ORR process occurring on the DA-Pt₂Os/C.