▎ 摘　　要

We have synthesized a nanostructure with a platinum (Pt) nanocrystal core and a few-layer graphene shell. This graphene-encapsulated Pt nanocrystal (GPN) was fabricated through a simple chemical vapor deposition (CVD) method. After investigating the electrocatalytic activities of GPNs, their ability to act as a relatively good fuel cell catalyst was confirmed. Furthermore, to further improve their catalytic activity, a plasma-assisted nitrogen doping method was developed, and the nitrogen-doped graphene-encapsulated Pt nanocrystal (N-GPN) also demonstrated efficient electroactivities, in fact much higher than those reported for conventional Pt-graphene composite catalysts due to their small particle diameter, uniform size distribution, sufficient graphene-Pt contact, and new generation of activation sites after nitrogen doping. This simple and efficient approach could also be extended to the preparation of other alloy nanocrystals coated with a graphene shell for electrocatalytic or electrochemical sensor applications.