On the electrocatalytic activity of nitrogen-doped reduced graphene Oxide: Does the nature of nitrogen really control the activity towards oxygen reduction?

Synthesis of metal-free electrocatalyst for the cathodic reduction of oxygen is of great interest for fuel cell and metal-air battery applications. The heteroatom-doped graphene/reduced graphene oxide (rGO) is very promising and the nitrogen-doped rGO (N-rGO) is emerging as a new inexpensive electrocatalyst for oxygen reduction reaction (ORR). Herein, we describe the effect of the chemical nature and amount of nitrogen in N-rGO towards ORR in acidic solution. Four different samples of N-rGO with different nitrogen content were synthesized by simple chemical route. The chemical nature and nitrogen content were analyzed with Xray photoelectron spectroscopic measurements. The electrocatalytic performance of the catalyst was examined by cyclic and hydrodynamic voltammetric studies. All the N-rGO samples favor 4-electron pathway for the reduction of oxygen in acidic solution. The onset potential and kinetic current density depends on the nature of the doped nitrogen. It is demonstrated that the chemical nature and the amount of nitrogen actually control the ORR activity. The N-rGO which contains a large amount of pyridinic nitrogen with N/C ratio of 0.074 has high catalytic activity. The carbon bonded to pyridinic nitrogen could be a possible catalytic site in ORR. Our studies suggest that the graphitic nitrogen does not significantly influence the electrocatalytic activity of N-rGO.