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

Abstract

In the present work, nitrogen-doped carbon spheres were synthesized through a simple hydrothermal 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/cm2, which is 0.2 mA/cm2 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.