Iron- and Nitrogen-Functionalized Graphene Nanosheet and Nanoshell Composites as a Highly Active Electrocatalyst for Oxygen Reduction Reaction

In this work, we develop a simple method to thermally synthesize a nonprecious metal-based nitrogen-doped graphene (NG) electrocatalyst using exfoliated graphene (Ex-G) and urea with varying amounts of iron (Fe) precursor. The morphology and structural features of the synthesized electrocatalyst (Fe-NG) were characterized by SEM and TEM, revealing the existence of graphitic nanoshells that potentially contribute to the ORR activity by providing a higher degree of edge plane exposure. The surface elemental composition of the catalyst was analyzed through XPS, which showed a high content of a total N species (similar to 8 at. %), indicative of the effective N-doping, present mostly in the form of pyridinic nitrogen groups. The oxygen reduction reaction (ORR) performance of the catalyst was evaluated by rotating disk electrode voltammetry in alkaline electrolyte and in a zinc-air battery cell. Fe-NG demonstrated high onset and half-wave potentials of -0.023 V, (vs SCE) and -0.110 V (vs SCE), respectively. This excellent ORR activity is translated into practical zinc-air battery performance capabilities approaching that of commercial platinum-based catalyst.