Activity and stability origin of core-shell catalysts: unignorable atomic diffusion behavior.

The exceptional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances of core-shell catalysts are well documented, yet their activity and durability origins have been interpreted only based on the static structures. Herein we employ a NiFe alloy coated with a nitrogen-doped graphene-based carbon shell (NiFe@NC) as a model system to elucidate the active structure and stability mechanism for the ORR and OER by combining constant potential computations, molecular dynamic simulations, and experiments. The results reveal that the synergistic effects between the alloy core and carbon shell facilitate the formation of Fe-N-C active sites and replenish metal sites when central metal atoms detach. The metal core and catalytic environment function as an "ammunition depot" and "automatic loader," respectively, ensuring long-term stability. Notably, atomic diffusion behaviors are identified as critical for the formation and regeneration of active sites during the ORR/OER. This work provides new insights into the activity and stability of core-shell catalysts and emphasizes the importance of reconstruction and dynamic structural evolution in electrocatalysts.