Fe-, N-, and S-tridoped carbon hollow spheres as highly active electrocatalysts for oxygen reduction reaction

초록

Fuel cell using hydrogen generated by renewable energy can be a promising approach to sustainable energy conversion application [1]. However, the performance of fuel cell system is significantly limited by high overpotential of cathode (oxygen reduction reaction, ORR) due to sluggish kinetics of the four-electron involved pathways [2]. Thus, enormous research endeavours have been dedicated to exploring efficient and inexpensive electrocatalysts for enhancing the performances of fuel cell by using various transition metal-based materials [3,4]. In this work, hollow structured Fe-, N-, and S-tridoped carbon (FeNSC) nanosphere was synthesized by impregnation of Fe into polypyrrole-coated SiO2 sphere, followed by chemical etching of SiO2 and carbonization with sulfur powder. The as-prepared FeNSC possess unique hollow structure with average diameter of 500 nm, which can expose abundant active sites (Fe-Nx) and reduce ion-diffusion length, thereby enhancing electrochemical performance toward ORR. Furthermore, simultaneous doping of Fe, N, and S on carbon matrix not only modulate the adsorption-desorption energy of reaction intermediates but also improve intrinsic electrical conductivity. The hollow structured FeNSC nanosphere shows excellent ORR onset-potential (0.971 V vs. RHE) and half-wave potential (0.877 V vs. RHE), which is comparable to state-of-the-art Pt/C electrocatalyst in 0.1 M KOH electrolyte.