▎ 摘　　要

High performance Pt-free electrocatalyst can be synthesized by adding small amount of exfoliated layered metal oxide (CoO2/Ti-1 xO(2)/RuO2) nanosheets into N-doped reduced graphene oxide (rG-O) matrix. The incorporation of 2D metal oxide nanosheet is highly effective not only in increasing the surface area and pyridinic N content of N-doped rG-O but also in promoting its ion transport. Of prime importance is that, even at low content of metal oxide nanosheet (< 4 wt%), the metal oxide nanosheet-N- doped rG-O nanocomposites exhibit much higher electrocatalyst activity for oxygen reduction reaction with better selectivity and long-term stability than does N-doped rG-O. Such a beneficial effect of metal oxide nanosheet is much more prominent than that of metal oxide nanoparticle, underscoring unique merit of 2D nanosheet morphology. The superior role of metal oxide nanosheet is attributable to the surface expansion, the increase of pyridinic N content, the provision of catalytically active sites, and the enhanced transport of ion and hydrated O-2 upon the addition of metal oxide nanosheet. The present study clearly demonstrates that the incorporation of exfoliated metal oxide 2D nanosheets into the graphene matrix can provide an efficient and scalable method to explore high performance Pt-free electrocatalysts via the optimization of the functionalities of graphene. (C) 2017 Elsevier Ltd. All rights reserved.