Nitrogen Functionalized Few Layer Graphene Derived from Metal-Organic Compound: A Catalyst for Oxygen Reduction Reaction

Nitrogen functionalized few layer graphene is synthesized by pyrolyzing Co(III) dimer ([Co2(OH)2(OOCCH3)3(bpy)2]NO3.1.5H2O) at 800 °C in a sealed quartz ampule. Above 210 °C, release of 2,2′ bipyridine (Bpy) from the crystals of Co(III) dimer lead to the formation of cobalt based in-situ derived microporous template. At elevated temperature, Bpy decomposes and carbonizes into those micropores resulting few layer graphene. Simultaneously, Bpy condenses into carbon-nitrogen based heterocyclic material such as 2D network of triazine-based moiety (g-C3N4), which present intercalated into the few layer graphene. Presence of g-C3N4 is confirmed using mass spectra, FT-IR and Transmission electron microscope (TEM) analysis. Whereas pyrolysis of cobaltous nitrate and Bpy (1:1 mole ratio) resulted primarily multiwalled carbon nanotubes over graphene. Hence, the formation of nitrogen functionalized graphene is unique to Co(III) dimer. The pyrolyzed Co(III) dimer is able to catalyze electrochemical reduction of oxygen in alkaline medium, which is one of the reactions involved in energy systems such as fuel cells and metal-air batteries. We find that the oxygen reduction reaction activity of the pyrolyzed Co(III) dimer is not sensitive to the presence of EDTA, which could ligate with cobalt ion in the catalyst, but can be suppressed considerably in presence of Bpy due to its π-π interaction with triazine-based moieties. Based on the oxygen reduction reaction conducted in 0.1 N KOH solution consisting 10 mM EDTA or 10 mM Bpy, we surmise that cobalt based template is only promoting the formation of ORR catalytic site and does not take part in the ORR. The onset potential for ORR on pyrolyzed Co(III) dimer (G-TZ-Co) is about 80 mV lower than Pt/C. However, below 0.84 V vs. RHE, the activity of the G-TZ-Co is better than Pt/C. Hence, this catalyst is envisioned as potential replacement for the platinum based catalysts used in the energy systems.