MnO-nitrogen doped graphene as a durable non-precious hybrid catalyst for the oxygen reduction reaction in anion exchange membrane fuel cells

A promising non-precious metal catalyst containing manganese oxide and N-graphene is synthesized and is recognised as an efficient and durable electrocatalyst for the oxygen reduction reaction (ORR) in an alkaline medium. Hydrothermally synthesized Mn3O4 is incorporated into graphene mixed with melamine as a nitrogen source and annealed at a temperature between 700 degrees C and 1000 degrees C. The phase formation, purity and morphological behaviours of pre-formed Mn3O4 and MnO after annealing are systematically studied by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (TEM). The MnO and N-doped graphene (MnO/NG) catalyst enhances ORR activity compared to other combinations of hybrid catalysts, such as Mn3O4/G and MnO/G, as observed from the linear sweep voltammograms. It is found that MnO/NG annealed at 900 degrees C demonstrates excellent ORR catalytic activity in O-2 saturated 0.1 M aqueous KOH electrolyte with a dominant 4e(-) transfer process, as confirmed by both RDE and RRDE measurements. The stability and durability of this optimized catalyst is ascertained by potential cycling between -0.8 and 0.2 V vs. Ag/AgCl up to 10 000 potential cycles; superior durability was found in comparison to the state-of-art Pt/C catalyst. This MnO/NG-900 hybrid catalyst is used as a cathode catalyst, and we fabricate a membrane electrode assembly (MEA) to validate the catalyst in an anion exchange membrane fuel cell (AEMFC). A peak power density of 13 mW cm(-2) at 30 degrees C under ambient pressure is realized; thus, our catalyst appears to be promising as an alternative non-precious metal catalyst for AEMFCs.