Low-temperature synthesis of ultrasmall spinel MnxCo3-xO4 nanoparticles for efficient oxygen reduction

Spinel-type manganese-cobalt oxides have been regarded as important class of electrocatalysts for oxygen reduction reaction (ORR). However, they are usually synthesized through oxidation-precipitation under aqueous ammonia and then crystallization at high temperature (150–180 °C), which not only increases the energy consumption but also induces the growth of particles that is unfavorable for ORR. Herein, through a facile precipitation-dehydration method, ultrasmall spinel manganese-cobalt oxide nanoparticles (~5 nm) homogeneously dispersed on conductive carbon black (Mn x Co 3- x O 4 /C) were fabricated at low temperature (60 °C). And the bimetallic composite oxide (Mn 1.5 Co 1.5 O 4 /C) with cubic spinel structure and high Mn content exhibits remarkable enhancement of ORR activity and stability compared with single metal oxide (both Mn 3 O 4 /C and Co 3 O 4 /C). The essential reason for the enhancement of activity can be attributed to the presence of the mixed Mn 3+ and Mn 4+ cations in Mn 1.5 Co 1.5 O 4 /C. Moreover, the ORR activity of Mn 1.5 Co 1.5 O 4 /C is comparable to that of commercial 20 wt% Pt/C, and the relative current density only decreases 1.4% after 12 h test, exceeding that of Pt/C and most reported manganese-cobalt oxide electrocatalysts.