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 Mn₂O₃ 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 "capping-molecule 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.