Metal Loading Effect on the Activity of Co3O4/N-Doped Reduced Graphene Oxide Nanocomposites as Bifunctional Oxygen Reduction/Evolution Catalysts

The development of effective and stable reversible oxygen electrodes is of upmost importance for bringing regenerative energy storage and conversion systems to a commercial reality. However, realization of such electrodes is motivated by low activity and instability of the current electrocatalysts working for both water splitting and oxygen reduction. Herein, we report a series of Co3O4/graphene-based catalysts with different Co mass loadings prepared by using a facile one-step hydrothermal route. N-doped reduced graphene oxide (NRGO) was utilized as a substrate for the deposition of oxide particles. The structural properties and surface composition of the different materials were investigated by powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements. The effect of Co mass loading on the morphostructural properties of oxide nanoparticles and also on their electroactivity towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was addressed. This study revealed the optimum range for metal loading on the graphene substrate. Co3O4/NRGO with a Co mass loading of 30 wt.% exhibits the highest activity towards ORR and OER, with a reversibility criterion of 763 mV. This work is very helpful for the electrocatalysis community, and will allow effective catalysts to be developed for high-power metal/air battery or regenerative fuel cell systems, based on earth-abundant and scalable electro-catalysts.