Solid-state thermal exfoliation of graphite nano-fibers to edge-nitrogenized graphene nanosheets for oxygen reduction reaction

Abstract

We demonstrate a simple, single-step and scalable synthesis of edge-nitrogenated graphene nanosheets (E-N-GNS) through thermal exfoliation of graphite platelet nanofibers (GPNF) in the presence of melamine. This material was characterized using different physical characterization techniques which divulges that, the edges are selectively functionalised with pyridinic and pyrrolic type nitrogens leading to the formation of E-N-GNS. Further, the electrocatalytic activity of E-N-GNS towards oxygen reduction reaction (ORR) in alkaline medium was studied using electrochemical techniques to reveal superior electrocatalytic activity of E-N-GNS towards ORR than that of GPNF, perhaps due to the incorporation of N at the edges. The cyclic voltammetry (CV), however, shows a 50 mV and 71 mV positive shift in the onset and peak potentials respectively, which in combination with the rotating ring disk electrode (RRDE) results suggest that ORR follows a direct four electron transfer path on E-N-GNS in comparison with a two electron path on GPNF modified electrodes. This E-N-GNS also shows superior stability for 5000 cycles along with a high methanol-tolerance and durability than that of benchmark ORR electrocatalyst Pt/C (20%) to suggest its potential applications in fuel cells and metal-air batteries.