NiCoMnO4 nanoparticles on N-doped graphene: Highly efficient bifunctional electrocatalyst for oxygen reduction/evolution reactions

Low-cost and highly efficient electrocatalysts for oxygen reactions are of high importance for oxygen related energy storage/conversion devices (e.g. Metal-O-2 batteries or fuel cells). In the present study, we synthesized NiCoMnO4 nanoparticles anchored on nitrogen-doped graphene nanosheets as highly efficient bifunctional electrocatalysts for the Oxygen Reduction Reaction (ORR) and for the Oxygen Evolution Reaction (OER). Proper anchoring of NiCoMnO4 nanoparticles on graphene layers was probed with various characterization techniques including X-ray diffraction, energy dispersive X-ray (EDX), Raman, and Fourier transform infrared (FTIR) spectroscopy as well as transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) was also employed to shed light on the oxidation states of metallic atoms and types of doped nitrogen on graphene layers. According to the obtained results, the NiCoMnO4/N-rGO hybrid showed excellent electrocatalytic activity towards ORR (E-onset = 0.92V vs. RHE and high current density of 0.84 mA cm(-2)) and OER (E-onset = 1.5 V vs. RHE and high current density of 14 mA cm(-2)), much better than other evaluated catalysts. It has been shown that the NiCoMnO4/N-rGO catalyzes ORR mostly through 4e process, just as the commercial Pt based catalyst. Moreover, it outperforms the commercial catalyst with very little decay in ORR activity over long continuous operation and shows excellent catalytic selectivity and methanol tolerance. (C) 2016 Elsevier B.V. All rights reserved.