In situ preparation of hollow Mo2C–C hybrid microspheres as bifunctional electrocatalysts for oxygen reduction and evolution reactions

Abstract

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been one of the bottlenecks hindering the commercial application of rechargeable metal–air batteries. It is urgent and necessary to develop non-noble bifunctional catalysts for both the ORR and the OER with high catalytic activity. Herein, an in situ synthetic route to obtain Mo₂C–C hybrid microspheres as bifunctional catalysts has been reported. In this route, the synchronously prepared C microspheres act not only as the template, but also as the reactant. Interestingly, SEM, TEM and XPS results show that core–shell, yolk–shell and pierced structured microspheres could be formed by increasing the content of Mo₂C in the Mo₂C–C hybrids. Additionally, the formation of a non-crystalline amorphous MoO_x (MoO₂ and MoO₃) nano-film appears to improve the conductivity of the as-prepared Mo₂C–C hybrids. Rotating-ring-disk electrode (RRDE) results show that the Mo₂C–C hybrids exhibit enhanced catalytic activity for the ORR and OER compared with that of the C microspheres and Mo₂C. In particular, Mo₂C–C-5 displays excellent bifunctional activity and stability, which is close to the behavior of a commercial Pt/C electrocatalyst for the ORR and a RuO₂ electrocatalyst for the OER.