Upgrading the properties of reduced graphene oxide and nitrogen-doped reduced graphene oxide produced by thermal reduction toward efficient ORR electrocatalysts

Abstract

N-doped (NrGO) and non-doped (rGO) graphenic materials are prepared by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively, of natural graphites of different particle sizes. An extensive characterization of graphene materials points out that the physical properties of synthesized materials, as well as the nitrogen species introduced, depend on the particle size of the starting graphite, the reduction atmospheres, and the temperature conditions used during the exfoliation treatment. These findings indicate that it is possible to tailor properties of non-doped and N-doped reduced graphene oxide, such as the number of layers, surface area, and nitrogen content, by using a simple strategy based on selecting adequate graphite sizes and convenient experimental conditions during thermal exfoliation. Additionally, the graphenic materials are successfully applied as electrocatalysts for the demanding oxygen reduction reaction (ORR). Nitrogen doping together with the starting graphite of smaller particle size (NrGO325-4) resulted in a more efficient ORR electrocatalyst with more positive onset potentials (Eonset = 0.82 V versus RHE), superior diffusion-limiting current density (jL, 0.26V, 1600rpm = −4.05 mA cm−2), and selectivity to the direct four-electron pathway. Moreover, all NrGOm-4 show high tolerance to methanol poisoning in comparison with the state-of-the-art ORR electrocatalyst Pt/C and good stability.