Size-Controllable Synthesis of Monodisperse Magnetite Nanoclusters as Electrocatalysts for Oxygen Evolution Reaction

Electrochemically splitting water greatly demands low-cost, high-performance oxygen evolution reaction (OER) catalysts. However, synthesizing size-controllable magnetite (Fe 3 O 4 ) nanoclusters as high-performance electrocatalysts poses a great challenge, as the size significantly affects their properties. Here, we present a modified polyol process for tuning the size of Fe 3 O 4 nanoclusters in the presence of an ionic liquid. The average size of the as-prepared nanoclusters, which are composed of nanocrystals with a fixed size ( ∼ 5 . 6 nm), can be effectively adjusted from 236 nm to 63 nm with the increase of the added volume of ionic liquid from 0 μ L to 2 0 μ L. The nanoclusters were successfully used as catalysts for OER, and those with a size of 63 nm showed the highest catalyst activity, possessing 336 mV of overpotential under 20 mA cm − 2 of current density. The result of the double-layer capacitance analysis firmly confirms that the large electrochemical active area of the magnetite nanoclusters provides more catalytic active sites, which leads to higher catalyst activity. Furthermore, the magnetite nanoclusters exhibit stable catalyst performance and can maintain oxygen evolution activity for a long time. This process provides a new strategy for the size-controlled synthesis of other metal oxide nanoclusters that could be an effective substitute for OER noble metal catalysts.