Regulation of d-Orbital Electron in Fe-N₄ by High-Entropy Atomic Clusters for Highly Active and Durable Oxygen Reduction Reaction

Simultaneously improving activity and stability is a crucial yet challenge in the development of metallic single-atom-based catalysts. In current work, a novel approach is introduced to address this issue by combining post-adsorption and secondary pyrolysis techniques to create a synergistic catalytic system, in which the single atoms (SAs) Fe sites played in the NC matrix (Fe─NC) are coupled with high-entropy atomic clusters (HEACs). Theoretical calculations reveal that the incorporation of HEACs lead to a rehybridization of the 3d orbital configuration of Fe-N₄, which helps to balance the adsorption/desorption energy of oxygenated intermediates. In situ spectroscopy further reveals that the rate-limiting step of OH^* desorption on HEAC/Fe─NC in oxygen reduction reaction (ORR) is more facile compared to atomic Fe─NC, implying a higher ORR activity. Moreover, the synergistic effect of diffusion activation barriers and configuration entropy contributes to the structural stability of HEAC/Fe─NC, resulting in remarkable durability. Consequently, this unique catalyst exhibits half-wave potentials of 0.927 and 0.828 V in an aqueous solution of KOH (0.1 m) and HClO₄ (0.1 m), respectively, along with excellent durability. The findings propose a novel strategy for modulating the electronic structure of metallic SAs catalysts and enhancing their stability through strong interactions between SAs and HEACs.