Modulation of d-d orbital hybridization via creating asymmetrical paired iron sites for oxygen reduction reaction

Abstract

Diatomic catalysts bearing unique electronic structures hold promise for accelerating the kinetically sluggish oxygen reduction reaction (ORR). However, a rational design principle for modulating metal sites’ microenvironments to boost activity and stability is challenging. Herein, we present a coordination manipulation strategy to create paired Fe sites directly bonding with the P heteroatom in Fe2P1N5 moieties over a nitrogen-doped carbon matrix (Fe2/NCP). This catalyst delivers high ORR activity with half-wave potentials of 0.94 and 0.82 V in alkaline and acidic conditions, respectively, along with robust structural stability. The strong ORR activity and stability are further validated using zinc-air batteries incorporating the catalyst. Such performance enhancement originates from the electron spin-state modulation and electronic delocalization due to the P doping. This strengthens the d‒d orbital hybridization for spin electron filling in the Fe 3dz2 orbital, which suppresses the electron donation from the absorbate-σ orbital to facilitate *OH desorption. This work underscores the importance of asymmetrical electronic structure manipulation in designing high-performance metal catalysts.