In situ regulating the accessibility and structure of Fe-based catalytic sites to break trade-off between the activity and stability for oxygen reduction

Abstract

How to synchronously boost the activity and stability of Fe/N-doped carbons (Fe-N-Ce-N-C) for oxygen reduction reaction (ORR) becomes important to promote their commercial applications. Here we synthesize a Fe-N-Ce-N-C catalyst by secondary sintering and removing endogenous CeO₂ nanoparticles to in situ regulate the accessibility and structure of N and O atoms coordinated Fe sites (FeN₂O₂). Theoretical studies indicate that the electron density distribution surrounding the Fe atom in FeN₂O₂ sites exhibits significant differences compared to that in FeN₄, inducing a downward shift of the Fe d-band center. FeN₂O₂ sites present a reduced free energy compared to FeN₄ sites, which contributes to an improved ORR catalytic activity. The Fe-N-Ce-N-C catalyst demonstrates a half-wave potential (E_1/2) of ∼0.906 V (versus RHE) and only 2.2 % reduction of E_1/2 (20 mV) after 30 k cycles of accelerated aging tests, revealing the superior ORR activity and stability in alkaline solution. The home-made zinc–air battery with the target catalyst delivers a high peak power density of 241.1 mW cm⁻² and a low voltage gap of 78.8 mV at 10 mA cm⁻². This work can provide an idea for obtaining available non-precious Fe-based electrocatalysts with a trade-off between activity and stability.