Composition effects of spinel MnxCo3−xO4 nanoparticles on their electrocatalytic properties in oxygen reduction reaction in alkaline media

Abstract

In this work, we synthesized a series of manganese cobalt spinel oxide (MnxCo3−xO4) nanoparticles (NPs) covering the whole composition range (x = 0.0. 0.4, 0.8, 1.4, 1.9, and 3.0) and investigated their electrocatalytic properties in relation with the oxygen reduction reaction (ORR) in alkaline media. The NP samples were synthesized by sonochemical reactions of Mn(OAc)2 and Co(OAc)2 (Ac = acetyl) in a water-dimethylformamide mixed solvent. The four samples in the Co-rich side have the cubic structure whereas the other two samples in the Mn-rich side have the tetragonal structure. The X-ray photoelectron spectroscopy and electrochemical analyses data indicate that the distribution of manganese and cobalt ions between the two metal ion sites of the spinel structure in our NP samples conforms to that of the bulk counterparts in the literature. The electrocatalytic data show that the ORR mechanism is changed when the structure is changed from cubic to tetragonal. The highest ORR activity was observed with the x = 0.4 sample. The electrochemical stability of this sample is higher than that of commercial Pt/C.