###### 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 (NrGO\({}_{325}\)-4) resulted in a more efficient ORR electrocatalyst with more positive onset potentials (\(E_{\mathrm{onset}}\) = 0.82 V versus RHE), superior diffusion-limiting current density (\(j_{\mathrm{L,\,0.2 eV,\,1600 rpm}}=-4.05\) mA cm\({}^{-2}\)), and selectivity to the direct four-electron pathway. Moreover, all NrGO\({}_{\mathrm{m}}\)-4 show high tolerance to methanol poisoning in comparison with the state-of-the-art ORR electrocatalyst Pf/C and good stability. graphite; reduced graphene oxide; nitrogen-doped reduced graphene oxide; exfoliation; oxygen reduction reaction; electrocatalysts +
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adatoms [9]. Thus, the presence of nitrogen or boron atoms in the basal planes of graphene layers produce changes to many of their chemical properties. It was proven that the doping of nitrogen into a graphenic nanostructure modifies its chemical and electrical properties, [10]. Thus, the N atoms inserted in the graphene structure increase the electronic density of the graphenic layer, since one more electron is added to the graphenic layer, making it more basic [11; 12]. In addition, the easily tunable surface chemical properties and specific surface area of the graphenic materials make them very versatile materials for application in this field. An extensive number of works have been devoted to the preparation of graphene and N-doped graphene. The synthesis of graphene can be performed using different methods, among them the micromechanical cleavage method [13], chemical vapor deposition (CVD) [14], and epitaxial growth on silicon carbide surfaces [15]. However, they show low productivity and lack of properties' selectivity. One of the common approaches used for a large-scale graphene production is based on the chemical oxidation of graphite (G) flakes to produce graphite oxide (GO) [16; 17] with strong oxidizing agents. GO can be later exfoliated and converted to reduced graphene oxide (rGO) through a reduction procedure. The most used routes for the reduction of GO are chemical [18; 19], electrochemical [20; 21], solvothermal [22; 23], and thermal treatments [24]. The use of thermal reduction is preferred over the rest of the methods due to its simplicity and industrial scalability [25]. The incorporation of nitrogen in graphenic materials to produce N-doped reduced graphene oxide (NrGO) has been described using several methods as well. For example, CVD using NH\({}_{3}\)[26], acetonitrile [27], or pyridine [28] as the N source; the arc discharge of graphite [29] in the presence of pyridine or NH\({}_{3}\); the nitrogen plasma treatment of graphene [30]; and the thermal treatment of GO with melamine [31; 32], urea [33], or NH\({}_{3}\)[9; 34]. The improvement of some of the properties of rGO and NrGO has been undertaken using different synthetic strategies. [PERSON] et al.