Nanocrystal supracrystal-derived atomically dispersed Mn-Fe catalysts with enhanced oxygen reduction activity

Iron-nitrogen-carbon (Fe-N-C) materials featuring Fe-N₄ moieties are promising candidates to replace commercial Pt/C catalysts for the oxygen reduction reaction (ORR). Here we report a novel Mn-Fe-N/S@mC catalyst comprising atomically dispersed Fe-N₄ sites and a trace amount of Mn-N₂S₂ sites, which are homogeneously anchored on an ordered mesoporous graphitic carbon framework. This dual-metal catalyst is realized based on the chemical conversion of self-assembled Mn_0.43Fe_2.57O₄ nanocrystal supracrystals, with the dual metal sites and the graphitic framework derived from nanocrystal cores and the associated capping ligands, respectively. When evaluated as electrocatalysts for the ORR, Mn-Fe-N/S@mC exhibits excellent catalytic activity in alkaline media, outperforming conventional Pt/C and most non-precious-metal catalysts reported previously. Notably, the synergistic effect of having Fe and Mn together improves the catalytic activity by a factor of ~ 5. To better understand the high efficiency of Mn doping in enhancing the activity of Fe-N₄ sites, density functional theory calculations were carried out, revealing that the synergistic interaction between the dual metal sites reduces the *OH reduction energy barrier during the oxygen reduction pathway.