▎ 摘　　要

We report the electrochemical activity of transition metal ion (Fe, Co and Ni) doped MnOx@N-graphene (MnOx@NG) hybrid catalysts towards oxygen reduction reaction (ORR). The doped catalysts displayed significantly enhanced electrochemical performance than the undoped one. The Fe doped MnOx@NG exhibited highest positive shift in onset potential (0.93 V vs. RHE), highest electron transfer number (n) (3.87) and lowest peroxide yield (6.35 %) in 0.1 M KOH solution. The Co doped catalyst showed highest current density, which is comparable to that of benchmark 20 wt% Pt/C. The XRD analysis showed that the catalyst samples are poorly crystalline and the doping of either Fe or Co or Ni cation induces formation of Mn2O3, whereas the undoped catalyst consists of both Mn2O3 and MnOOH. The STEM (scanning transmission electron microscope) micrographs revealed that in all the samples the MnOx nanostructures are well dispersed on NG and the elemental mapping of the doped catalysts showed uniform distribution of dopants. The X-ray photoelectron spectroscopy (XPS) studies revealed that doping of either cation results an increase in the average Mn valency of the host MnOx. The change in crystal structure and corresponding ORR activity has also been investigated with increase in dopant amount for Fe doped samples.