3-D mesoporous nitrogen-doped reduced graphene oxide as an efficient metal-free electrocatalyst for oxygen reduction reaction in alkaline fuel cells: Role of π and lone pair electrons

Nitrogen-doped graphenes are promising oxygen reduction reaction (ORR) electrocatalysts for replacement of Pt-based electrocatalysts. In this paper, 3-D mesoporous nitrogen-doped reduced graphene oxides (NRGOs) with different nitrogen contents (1.0-4.7%) were hydrothermally synthesized through manipulation of relative amount of the graphite oxide (GtO) and melamine. Eight characterization techniques including FESEM, TEM, BET, XRD, Raman, FTIR, UV-vis, and XPS were used to evaluate the structural and electronic properties of the prepared nanomaterials. The ORR performance of NRGOs and commercial 20 wt% Pt/C were examined in three electrode cell and direct methanol fuel cell (DMFC) setups. It was revealed that N-content of NRGOs (regardless of their bonding configurations) promotes ORR performance at lower potentials due to activation and strengthen of pi-electrons of graphene framework while pyridinic-N content has significant role in ORR at higher potentials because of activation of their lone pair electrons. Furthermore, the DMFC with NRGO containing 4.1% (4.6 wt%) nitrogen as cathode electrocatalyst, due to its higher selectivity towards ORR, presents superior output power compared to the commercial 20 wt% Pt/C one. (C) 2016 Elsevier Ltd. All rights reserved.