Precise Synthesis of ~1-nm Iridium Nanoclusters as a Catalyst for Highly Efficient Oxygen Evolution

Metal nanoclusters (NCs) with a particle size of approximately 1 nm exhibit potential as highly active catalysts owing to their large specific surface areas and unique electronic structures. However, their precise synthesis in air is predominantly limited to coinage metal (Cu, Ag, and Au) NCs. Consequently, the development of a facile synthesis method for NCs composed of diverse metal elements is highly desirable. Accordingly, we focused on iridium (Ir), which is known for its high catalytic activity in numerous reactions. In this study, we established a precise synthesis method for air-stable Ir NCs and investigated their electrocatalytic activity in the oxygen evolution reaction (OER). We demonstrated that stable Ir∼15 NCs can be synthesized employing carbon monoxide and triphenylphosphine as stabilizing ligands. Furthermore, the OER catalysts derived from these Ir∼15 NCs as precursors exhibited a 1.5-fold increase in OER activity compared with commercially available Ir catalysts. These findings are anticipated to provide valuable design guidelines for the synthesis of NCs and the development of highly active electrocatalysts using a broad range of metal species.