Simultaneous doping of nitrogen and fluorine into reduced graphene oxide: A highly active metal-free electrocatalyst for oxygen reduction

Reduced graphene oxide co-doped with nitrogen and fluorine (N-F/rGO) was successfully prepared by a simple one-step thermal annealing process using a mixture of graphene oxide and ammonium fluoride in an argon atmosphere. X-ray photoelectron spectroscopy demonstrated that the nitrogen and fluorine atoms were successfully doped into the rGO structure at atomic percentages of 2.51 and 0.74, respectively. Nitrogen adsorption-desorption measurement revealed that the as-prepared N-F/rGO has a high surface area (412 m2 g−1) with numerous slit-shaped pores (1.60 cm3 g−1). The electrocatalytic activity of N-F/rGO for oxygen reduction reaction was found to be higher than that of rGO doped only with nitrogen (N/rGO); in fact, it was comparable to the activity of conventional commercial Pt/C in an alkaline electrolyte. In addition, the catalyst exhibited excellent long-term stability/durability, good methanol tolerance, and high selectivity for the four-electron transfer pathway. A possible mechanism is suggested for the improvement conferred by fluorine.