Ultrathin Co3O4–Pt core-shell nanoparticles coupled with three-dimensional graphene for oxygen reduction reaction.

Design and synthesis of platinum catalysts within atomic level are of great significance for the practical application of fuel cells. We found that the ultrathin Co(OH) 2 nanoparticles can be converted into Co 3 O 4 –Co core-shell nanostructures through a thermal annealing process in reducing atmosphere, which are uniformly distributed on the surface of 3D graphene (3DG). The Co 3 O 4 –Co core-shell nanoparticles have been successfully transformed into Co 3 O 4 –Pt core-shell nanoparticles via a controlled replacement reaction. The Co 3 O 4 –Pt @3DG contains only a few atomic layers of Pt shell, and presents a high Pt utilization nanostructure. Besides, the 3D graphene serves as a catalysts carrier with open structure, and offers a three-dimensional molecular accessibility and conducive to mass transfer. Significantly, the optimized mass activity and specific activity of 1.018 A/mg Pt and 2.17 mA/cm2 have been achieved on Co 3 O 4 –Pt @3DG at 0.9 V vs RHE, which are 7.6- and 8.1- times higher than those of Pt/C (0.134 A/mg Pt and 0.266 mA/cm2), respectively. The high activity is mainly attributed to the ultrathin core-shell structure with an ultrahigh Pt utilization, and the interaction between the near-surface Co 3 O 4 and the surface Pt shell with a tensile strain to surface Pt shell, and the electrons transfer from Co to Pt. Image 1 • Ultrathin Co(OH) 2 nanoparticles were converted into Co 3 O 4 –Co core-shell, then into Co 3 O 4 –Pt core-shell. • Mass and specific activity of Co 3 O 4 –Pt @3DG showed 7.6- and 8.1- times higher than those of Pt/C. • Ultrahigh Pt utilization and interaction between Co 3 O 4 core and surface Pt shell play important roles for the high activity. • 3D graphene possesses an open and interconnected porous structure, and conducive to the ORR intermediates transfer process. [ABSTRACT FROM AUTHOR]