N-doped graphene/carbon composite as non-precious metal electrocatalyst for oxygen reduction reaction

► N-doped graphene/carbon composite electrocatalyst synthesized through a single-step heat-treatment. ► Solid urea is more suitable than gaseous ammonia as nitrogen source for preparing N-doped graphene electrocatalyst. ► Carbon black as spacer and support inhibits the restacking of the graphene sheets. ► The ORR activity of the composite rival that of Pt/C in alkaline and approach that of Pt/C in acid. A non-precious metal electrocatalyst based on nitrogen-doped graphene (NG) was synthesized through a single step heat-treatment of a precursor mixture containing graphene oxide, urea, carbon black (CB) and small amount of iron species. The structure, morphology and composition of the prepared materials were characterized with a variety of techniques. XRD and Raman measurements showed the presence of distorted graphene layers. BET, TEM and cyclic voltammagram results indicated that CB served as spacer to prevent NG sheets from agglomerating, leading to enhanced dispersion of NG sheets. XPS analysis gave a total surface nitrogen concentration of ∼4at.%, with the pyridinic nitrogen being the main component. Rotating electrode measurements revealed that the NG electrocatalyst can efficiently catalyze the oxygen reduction reaction (ORR), with activities equivalent to Pt/C in alkaline medium and approaching to Pt/C in acid medium, and with nearly 4-electron pathway selectivity.