Ethylenediamine-mediated synthesis of Mn3O4 nano-octahedrons and their performance as electrocatalysts for the oxygen evolution reaction

Mn3O4 octahedrons with well-defined facets exhibit enhanced catalytic activity and sensing characteristics, and have attracted considerable attention in recent years. However, current fabrication methods for Mn3O4 octahedrons generally produce particles of micron and sub-micron sizes, and impurities such as MnO2 and Mn3O4 are often found. We present the synthesis of Mn3O4 nano-octahedrons with a pure Mn3O4 phase and size down to 50 nm based on a hydrothermal method using Mn(NO3)(2) as the manganese source and ethylenediamine (EDA) as the structure-mediating agent. It is found that EDA plays a crucial role in the formation of Mn3O4 nano-octahedrons in regulating both the morphology and the crystal structure of the products. The growth process is proposed to follow a "dissolution-recrystallization" and "cappingmolecule assisted growth" mechanism. As electrocatalysts towards the oxygen evolution reaction, the 50 nm Mn3O4 nano-octahedrons demonstrate a considerably enhanced activity compared to 160 nm Mn3O4 octahedrons.