Nitrogen-doped hollow mesoporous carbon spheres for efficient oxygen reduction.

Extensive investigations have been devoted to nitrogen-doped carbon materials as catalysts for the oxygen reduction reaction (ORR) in various conversion technologies. In this study, we introduce nitrogen-doped carbon materials with hollow spherical structures. These materials demonstrate significant potential in ORR activity within alkaline media, showing a half-wave potential of 0.87 V vs. Reversible Hydrogen Electrode (RHE). Nitrogen-doped hollow carbon spheres (N-CHS) exhibit unique characteristics such as a thin carbon shell layer, hollow structure, large surface area, and distinct pore features. These features collectively create an optimal environment for facilitating the diffusion of reactants, thereby enhancing the exposure of active sites and improving catalytic performance. Building upon the promising qualities of N-CHS as a catalyst support, we employed heme chloride (1 wt%) as the source of iron for Fe doping. Through the carbonization process, Fe-N active sites were effectively formed, displaying a half-wave potential of 0.9 V vs. RHE. Notably, when implemented as a cathode catalyst in zinc-air batteries, this catalyst exhibited an impressive power density of 162.6 mW cm-2.