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

• Hollow-structured FeNSC was synthesized using impregnation and pyrolysis method assisted by sacrificial SiO 2 template. • The unique hollow architecture and tri-doping strategy led to outstanding ORR performance. • The FeNSC indicated remarkable half-wave potential (0.877 V vs. RHE) and long-term durability (over 100 h). 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, SiO 2 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. The hollow-structured Fe-, N-, and S-tridoped carbon sphere (FeNSC) as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) was synthesized via facile impregnation and pyrolysis strategy assisted by self-sacrificial SiO 2 template.