It is crucial to develop electrocatalysts for the oxygen reduction reaction (ORR) for renewable energy applications. Mixed-valence transition-metal oxides with a spinel structure have been explored for this purpose. In this work, we study the influence of the composition of the catalysts (XY2O4, X=Ni, Zn and Y=Co, Mn) on the ORR. The four different types of spinel oxide nanocrystals (NiCo2O4, NiMn2O4, ZnCo2O4, and ZnMn2O4) were synthesized by a simple and scalable method. This allowed for a systematic investigation of the transition-metal influence on the performance of the ORR. Given the general spinel structure of XY2O4, we systematically changed X (Ni, Zn) and Y (Co, Mn). The effects of the presence of different metals in the spinel oxide on the morphology and electrocatalytic properties of the materials toward the ORR were investigated and compared by using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron microscopy, and voltammetry. In general, cobalt-based spinel oxides displayed a significant electrocatalytic activity towards the ORR, with Ni-substituted spinel oxides outperforming their respective Zn-substituted congeners. These findings may have great impact in the research field of renewable energy.
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