Metal-Organic Framework Derived N/C Supported Austenite Nanoparticles as Efficient Oxygen Reduction Catalysts

Austenite (-Fe) is thermodynamically unstable at room temperature. Relatively little attention has been directed in the past for the synthesis and properties of -Fe nanoparticles. Herein, we demonstrate a NaOH-assisted and metal-organic framework (MOF)-derived method to prepare a novel catalyst featured by -Fe nanoparticles encapsulated into the porous N-doped carbon matrix. The Fe atoms doped in the MOF structure play an important role in the formation of stable -Fe. The catalysts exhibit superior catalytic activity with the four-electron transfer pathway for oxygen reduction reaction (ORR) in alkaline solution. Besides the Fe-N-x sites, -Fe nanoparticles are believed to play an important role in the superior ORR activity. However, it is suggested that the metal nanoparticles are not ORR active species, whereas they may activate the surrounding N/C layers, thus making the N/C layers more active toward ORR. In addition, the oxidized surface of the metal nanoparticles may also act as active species contributing to the ORR activity.