Ultrafast synthesis of nanocrystalline spinel oxides by Joule-heating method

Spinel oxides, with the formula AB2O4 (A and B represent metal ions) perform superior electrocatalytic characteristic when A and B are transition metals like Co, Fe, Mn, etc. Abundant researches have been attached to the structure designments while methods are often energy-intensive and inefficient. Here, we devised a universal strategy to achieve rapid synthesis of nanocrystalline spinel materials with multiple components (Co3O4, Mn3O4, CoMn2O4 and CoFe2O4 are as examples), where phase formation is within 15 seconds. Under the Joule-heating shock, a crack-break process of microcosmic phase transformation is observed by in situ transmission electron microscopy. The half-wave potential values of Co3O4-JH, Mn3O4-JH, CoMn2O4-JH and CoFe2O4-JH in the electrocatalytic oxygen reduction reaction were 0.77, 0.78, 0.79 and 0.76, respectively. This suggests that the Joule heating is a fast and efficient method for the preparation of spinel oxide electrocatalysts.