MOF衍生的单原子催化剂中γN原子在ORR反应中的远程作用及其调制机制

Abstract

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 γN atom on its neighboring βC atom and the distant metal center was investigated. The results show that the doping of γN with different locations and amounts changes the electronic configuration of the replaced C sites in Fe-N4/C-γNx structures, which in turn affects the charge distribution of the βC 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 βC atoms are thus more likely to adsorb the OH moiety in alkaline electrolyte typically used in experiments. Thus, a γN-modulated βC-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 γN site in analogous SACs.