Simple synthesis of nitrogen-doped carbon spheres as a highly efficient metal-free electrocatalyst for the oxygen reduction reaction

In the present work, nitrogen-doped carbon spheres were synthesized through a simple hydro thermal treatment using glucose and melamine as inexpensive carbon and nitrogen sources, respectively. The ratio of melamine to glucose and annealing temperature were optimized. The final optimal sample exhibited a catalytic activity for the oxygen reduction reaction (ORR) that was superior than that of commercial 20%Pt/C in 0.1 mol/L KOH. It revealed an onset potential of -22.6 mV and a half-wave potential of -133.6 mV (vs. Ag/AgCl), which are 7.2 and 5.9 mV more positive than those of the 20%Pt/C catalyst, respectively, as well as a limiting current density of 4.6 mA/cm(2), which is 0.2 mA/cm(2) higher than that of the 20%Pt/C catalyst. The catalyst also exhibited higher stability and superior durability against methanol than 20%Pt/C. Moreover, ORRs on this catalyst proceed through a more effective 4e(-) path. The above mentioned superiority of the as-prepared catalyst makes it promising for fuel cells. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.