Polyaniline-derived metal-free hollow nitrogen-doped carbon microspheres as an efficient electrocatalyst for supercapacitors and oxygen reduction

To design a highly efficient electrocatalyst for cathodes to suppress the high overpotential for the oxygen reduction reaction (ORR) continually remains a prime goal of fuel cell study. Herein, the production of metal-free hollow nitrogen-doped carbon microspheres (HN-CMs) as an efficient electrode material for the supercapacitors and ORR in an alkaline media is reported. Initially, the PS@PANI core-shell microspheres were produced by coating polyaniline (PANI) layers on polyvinylpyrrolidone (PVP) functionalized polystyrene (PS) microspheres via in-situ chemical polymerization of aniline monomers in presence of ammonium persulphate (APS) as an oxidant. Finally, the core was removed by carbonizing the core-shell microspheres under the N-2 atmosphere at 500 degrees C for 2 h to obtain the HN-CMs as an electrocatalyst. The structure and morphologies of the microspheres were examined by SEM, TEM, XRD, FT-IR, BET, and Raman spectroscopy. The electrochemical analysis was performed by CV, GCD, and EIS. The obtained electrocatalyst exhibited improved electrochemical performances for supercapacitors application and demonstrated better electrocatalytic activity for ORR. For this electrocatalyst, the maximum specific capacitance of 266.7 F g(-1) was obtained in 1 M KOH at scan rate of 5 mV s(-1). Additionally, it has superior catalytic activity and stability via 4-electron process during ORR in the alkaline solution. The contribution of highly intact spherical/hollow structure, good surface area, and large contents of graphitic/pyridinic nitrogen of HN-CMs can improve the mass transportation by facilitating the diffusion pathways which results in the enhancement of its electrochemical and electrocatalytic properties. As a metal-free and cost-effective electrode material, this is supposed to be promising for supercapacitors and fuel cells.