Hemoglobin-derived pyrrolic Fe–N–C in hollow carbon nanospheres for enhanced oxygen reduction electrocatalysts

• Synthesis of pyrrolic Fe–N–C structures derived from hemoglobin. • Synthesis of hollow structures with micropores for rapid mass transport. • Exhibits excellent ORR performance and electrochemical endurance. • The ORR pathway is proposed to elucidate an enhanced ORR activity. Metal-decorated nitrogen-doped carbon (M−N−C) materials have garnered significant attention as potential alternatives to address the high cost of noble metal-based catalysts for the oxygen reduction reaction. However, they still face challenges, such as complex synthesis processes, insufficient durability, heterogeneous active sites, and an incomplete understanding of the underlying mechanisms. In this study, a facile method is presented for introducing pyrrole-type Fe–N–C active sites into N-doped carbon (NC) using hemoglobin (Hb) as a precursor. This approach was combined with an engineered hollow morphology to facilitate electrolyte permeation and increase the active surface area. The resulting Fe-embedded hollow N-doped carbon (Fe/hNC) demonstrated improved ORR activity compared to that of NC, featuring an onset potential of 0.916 V vs. RHE and a half-wave potential of 0.833 V vs. RHE in alkaline media, comparable to that of commercial Pt/C. Moreover, the ORR current density was retained at 80 %–90 % of its initial value after the durability test, representing a substantial improvement over the 50 %–60 % retention observed for Pt/C. This design strategy, which combines hollow morphology and specific Fe precursor modification, offers promising avenues for developing efficient catalysts for energy-conversion systems.