This study demonstrates promising bifunctionality of nitrogen-doped carbon nanostructures (CNX ) for ORR and OER in acidic medium. Although CNX catalysts are not as active as Pt/C in ORR and Ir/C in OER, they exhibit significantly lower combined overpotential for ORR and OER relative to those shown by the two commercial catalysts, which are highly active only for one of the two reactions, but not both. The effect of various nitrogen functionalities on the ORR and OER activity of CNX catalysts was also studied. CNX samples with higher pyridinic-N site density exhibited higher ORR and OER activity. (C) 2017 Elsevier B.V. All rights reserved.