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

Abstract 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 π-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.