Non-precious Mn1.5Co1.5O4–FeNx/C nanocomposite as a synergistic catalyst for oxygen reduction in alkaline media

Abstract

In this study we show a method of preparing a high performing catalyst by designing functional nano boundaries in a nanocomposite material. A non-precious nanocomposite material composed of spinel Mn_1.5Co_1.5O₄ nano crystals and FeN_x-functioned graphene nano platelets (FeN_x/C) was synthesized by an ultrasonic process. The crystal structure and elemental composition of the bimetal oxide were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The surface morphology of the Mn_1.5Co_1.5O₄–FeN_x/C nanocomposite was characterized with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The catalytic activity for the oxygen reduction reaction (ORR) was analyzed by an electrochemical method. The enhancement of activity for the ORR at the nanocomposite material is attributed to double synergistic effects from the bimetal particles and the FeN_x/C nano sheets. The nanocomposite material is able to catalyze 4-electron oxygen reduction to generate water in alkaline media with a high kinetic rate constant (7.6 × 10⁻² cm s⁻¹ at 0.7 V vs. reversible hydrogen electrode, RHE). Finally, the activity and stability of the nanocomposite material were compared with that of 40% Pt supported on active carbon (40% Pt/C), which reaches 95% activity and a comparable stability of 40% Pt/C at 0.7 V (vs. RHE).