Phase Transition‐Induced Engineering of Fe‐N‐C Catalysts for Dual Optimization of Active Sites and Mass Transfer in Oxygen Reduction Reaction

ABSTRACT

Fe‐N‐C electrocatalysts are considered promising alternatives to platinum‐based catalysts for advancing the development of metal–air batteries. However, the simultaneous realization of scalable synthesis, hierarchical mass‐transfer pathways, and precise regulation of Fe‐N ₄ sites remains challenging. Different from conventional Fe‐N‐C synthesis, this work develops a phase‐transition strategy in which natural hemin regulates the layered topology of two‐dimensional ZIF‐L. During organic‐solvent‐assisted drying, hemin‐induced lattice perturbation promotes crystal slip‐driven self‐assembly of the ZIF‐L layers, converting the leaf‐like precursor into a regular dodecahedral structure. This phase‐transition process simultaneously reconstructs the pore architecture and local Fe coordination environment, yielding an Fe‐N‐C _T (where “T” stands for phase transition) catalyst with an open hierarchical porous structure and second‐shell N‐regulated Fe‐N ₄ sites. The catalyst exhibits outstanding oxygen reduction reaction performance across electrolytes with different pH values ( E _onset  = 0.853 V [vs. RHE] in 0.5 M H ₂ SO ₄ , 0.945 V [vs. RHE] in 0.1 M KOH, and 0.915 V [vs. RHE] in PBS). Theoretical calculations further reveal that introducing an electron‐withdrawing N atom into the secondary coordination shell reduces the electron density of the connected active site, which indirectly lowers the electron density at the metal center and optimizes its adsorption strength for reaction intermediates. As a result, the exceptional ORR activity enables a zinc–air battery to achieve a peak power density of 189.63 mW cm ⁻² , surpassing that of a Pt/C‐based cell by more than twofold. This work proposes a precise strategy for modulating pore structure and active sites, offering a valuable approach for developing high‐performance carbon‐based ORR electrocatalysts.