▎ 摘　　要

Nanoscale architecturing of platinum group metal-free (PGM-free) electrocatalysts is expected to dramatically improve the overall catalytic performance for oxygen reduction reaction (ORR). Desired structures and morphologies for boosting active site density and enhancing mass and charge transfer are essential for developing next-generation PGM-free electrocatalysts. Herein, we report the design of a M-N-C type catalyst consisting of 3-dimensional graphitic meso-porous carbon spheres wrapped with 2-dimensional graphenized sheets. This heterostructure comprises resultant large electroactive surface area, abundant pore channels, and tuned chemical structures, which provide improved electrocatalytic performance. Meanwhile, these pore structures can be regarded as nano-channel reactors to catalyze ORR with easily accessible active sites, effective mass transfer, and smooth charge transfer. The obtained catalyst delivers a high maximum power density of 0.83 W cm(-2) in a single H-2-O-2 fuel cell measurement, ranking it as one of the most promising PGM-free catalysts in proton exchange membrane fuel cells (PEMFCs). Moreover, reasonable fuel cell stability was also observed through accelerated degradation testing. This work provides a new avenue for PGM-free catalysts design that can be a step towards practical commercial of PEMFCs.