Highly active N,S co-doped hierarchical porous carbon nanospheres from green and template-free method for super capacitors and oxygen reduction reaction

Heteroatom doped carbon materials have been emerging as active materials for electrochemical energy generation and storage. The activity of such carbon materials is strongly depended the specific molecular structure of selected precursors and their synthetic strategy. Herein, we report an efficient bifunctional N, S co-doped carbon nanosphere(NS/C) via pyrolysis of poly (2,6-Diaminopyridine) spheres as precursor for the first time, in which 2,6-Diaminopyridine was polymerized in water using ammonium persulfate as both initiator and sulfur source in the absence of templates and surfactants. The resultant NS/C exhibits uniformly spherical structure filled with hierarchical pores, outstanding electronic conductivity and highly effective doping content of N(4.02 at%) and S(0.87 at%) elements. Electrochemical measurements demonstrate that the NS/C not only exhibits outstanding specific capacitance of 800 F/g in 6.0 M KOH and 710 F/g in 1.0 M H2SO4, but also displays excellent catalytic performance for oxygen reduction reaction (ORR) with the onset potential at 1.01 V vs RHE and the half-wave potential at 0.85 V vs RHE in 0.1 M KOH, outperforming the activity of carbon materials previously reported. The superior electrochemical properties of NS/C is directly attributed to the synergetic effect of N,S co-doping and its excellent conductivity, accessibility, high specific surface area as well as hierarchical pore structure.