Sacrificial template induced Fe-, N-, and S-tridoped hollow carbon sphere as a highly efficient electrocatalyst for oxygen reduction reaction

Abstract

Developing electrocatalysts free from precious metals for oxygen reduction reaction (ORR) is essential for clean energy storage and conversion systems such as metal-air batteries and fuel cells. Herein, hollow-structured Fe-, N-, and S-tridoped carbon (FeNSC) spheres were synthesized by hydrothermal polymerization of polypyrrole, impregnation of iron species, pyrolysis, and a sulfidation processes. During the synthesis procedure, SiO2 nanospheres were used as self-sacrificial templates to achieve a uniform hollow structure. The electronic structure of the highly active Fe–N site was modified by sulfur dopants with relatively low electronegativity, thus efficiently enhancing ORR kinetics. The hollow-structured FeNSC nanospheres exhibited excellent electrocatalytic performance toward the ORR in an alkaline electrolyte, with a remarkable onset potential (0.971 V vs. RHE) and half-wave potential (0.877 V vs. RHE), even outperforming state-of-the-art Pt/C (0.977 and 0.858 V vs. RHE). Furthermore, the FeNSC hollow spheres showed outstanding electrochemical stability over 100 h and methanol tolerance against commercial Pt/C. The findings of this study provide novel insights for designing precious metal-free electrocatalysts with unique hollow structures and heteroatom-doped carbon for energy storage and conversion.