Insights into the critical roles of γN atoms in understanding the oxygen reduction on MOF-derived single-atom catalysts

The development of fuel cells is conducive to achieving carbon peaking and carbon neutrality goals, but the oxygen reduction reaction (ORR) of its cathodes is still kinetically slow due to multi-step proton-coupled electron transfer. Currently, metal-organic frameworks-derived single-atom catalysts (SACs) are emerging as efficient ORR catalysts. However, the outer layer structure of the active site is difficult to be determined, resulting in the uncertainty of the reaction mechanism. Here, the dual effect of the outer γ N atom on its neighboring β C atom and the distant metal center was investigated. The results show that the doping of γ N with different locations and amounts changes the electronic configuration of the replaced C sites in Fe-N 4 /C- γ N x structures, which in turn affects the charge distribution of the β C atom closer to the metal center. And these changes indirectly affect the electron distribution and spin of the metal center through long-range effects, significantly enhancing the ORR performance of the 4-e − paths. More importantly, the electronegativity-enhanced β C atoms are thus more likely to adsorb the OH moiety in alkaline electrolyte typically used in experiments. Thus, a γ N-modulated β C-assisted pathway was predicted and a higher thermodynamic limiting potential of ORR than that of the common 4-e − pathway was achieved. Further wavefunction analysis, based on the potential limiting steps, provided an understanding on the electronic level and revealed the significance of precise design and characteristics of γ N site in analogous SACs.