Space-Confined Strategy to Fe₇C₃ Nanoparticles Wrapped in Porous Fe-/N-Doped Carbon Nanosheets for Efficient Oxygen Electrocatalysis

Abstract

The development of economical, high-efficiency, and robust bifunctional oxygen electrocatalysts toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable but challenging. Herein, we develop a space-confined strategy with a sacrificial template for preparing Fe7C3 nanoparticles embedded in an interconnected porous graphene-like Fe-/N-doped carbon matrix (Fe7C3@FeNC). This approach relies on pyrolysis of precursor hybrids of an iron–ellagic acid (Fe–EA) complex and polydopamine (PDA) from the pyrocondensation polymerization of dopamine (DA) that are confined in the interlayer gaps of the sacrifice template g-C3N4. Such a functionalized configuration can avoid the uncontrollable growth of polydopamine (PDA) during the usual solution polymerization and postsynthetic removal of the template. The as-prepared Fe7C3@FeNC catalyst shows an impressive half-wave potential of 0.83 V for ORR and a low overpotential of 358 mV for reaching the current density of 10 mA cm–2 for OER in alkaline solution. Moreover, when used as an air cathode for the Zn-air battery, the Fe7C3@FeNC-based device also exhibits remarkable performance with a narrow charge–discharge voltage gap and high cycling stability. The space-confined strategy is unique, and the bifunctionality of Fe7C3@FeNC with hierarchical structures is appealing and may be of value for practical applications in energy conversion and storage systems.