▎ 摘　　要

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 Co3O4-Co core-shell nanostructures through a thermal annealing process in reducing atmosphere, which are uniformly distributed on the surface of 3D graphene (3DG). The Co3O4-Co core-shell nanoparticles have been successfully transformed into Co3O4-Pt core-shell nanoparticles via a controlled replacement reaction. The Co3O4-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/mgPt and 2.17 mA/cm(2) have been achieved on Co3O4-Pt @3DG at 0.9 V vs RHE, which are 7.6and 8.1 times higher than those of Pt/C (0.134 A/mgPt and 0.266 mA/cm(2)), 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 Co3O4 and the surface Pt shell with a tensile strain to surface Pt shell, and the electrons transfer from Co to Pt. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.