▎ 摘　　要

Solving the problems of the decrease of exposed active surfaces of Pt nanoparticles due to aggregation and their non-uniform dispersion is key to yielding high catalytic activity. In this work, monodisperse Pt nanocrystals (PtNCs) with a small size (2.8 nm in average diameter) and large exposed active surfaces are obtained by designing, inducing and dispersing the PtNCs on a 3D mesopore-rich nitrogen-doped graphene aerogel (NGA) through a facile one-step coassembly. Such a coassembly of PtNCs with NGA (PtNCs@NGA) has a large specific surface area (1750 m(2) g(-1)), rich mesopores (the ratio of mesopores of 2-5 nm to all mesopores is 78%), and a high N content (3.93 at%). The unique structure of PtNCs@ NGA not only ensures the exposure of the active PtNCs to O-2 and decreases the diffusion time of O-2 inside the pore channels, but also increases the adsorption and diffusion of O-2 in PtNCs@NGA, consequently increasing the oxygen reduction reaction (ORR) speed and yielding better electrocatalytic activity than those of so far reported metal catalysts on carbon materials. The simple and low-cost preparation of the PtNCs@ NGA catalyst renders it the most promising among electrocatalysts for application in fuel cells.