Dealloyed Pt2Os nanoparticles for enhanced oxygen reduction reaction in acidic electrolytes

•Wet chemical formation of Pt2Os nanoparticles.•Selective dissolution of Os atoms from the Pt2Os nanoparticles to form quasi core–shell Pt4Os nanoparticles (dealloying treatment).•Enhanced electrochemical activity and stability for oxygen reduction reaction from the dealloyed sample.•Quantum mechanics computation predicts structural stability for the dealloyed sample.

Carbon-supported Pt2Os (Pt2Os/C) nanoparticles in 3.55 nm 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 (0.29 mA μgPt−1 in mass activity and 1.03 mA cmPt−2 in specific activity) for the oxygen reduction reaction (ORR) in oxygen-saturated 0.1 M 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.

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