Synthesis and Demonstration of Subnanometric Iridium Oxide as Highly Efficient and Robust Water Oxidation Catalyst

Development of a highly efficient and robust water oxidation catalyst (WOC) with reduced usage of noble metals is extremely crucial for water splitting and CO2 reduction by photocatalysis or electrolysis. Herein, we synthesized subnanometric iridium dioxide clusters supported on multiwalled carbon nanotubes (MWCNTs) by a chemical vapor deposition method (nominated as IrO2/CNT). Benefiting from a mild oxidation process in air at 303 K, the deposited iridium clusters can be controlled to have a narrow size distribution from several atoms to 2 nm, having an average size of ca. 1.1 nm. The subnanometric iridium-containing sample is demonstrated to be highly efficient and robust for water oxidation. The optimal turnover frequency (TOF) of chemical water oxidation on the as-obtained sample can reach 11.2 s–1, and the overpotential of electrochemical water oxidation is 249, and 293 mV at 10 mA cm–2 in 1.0 M KOH (pH: 13.6), and 0.5 M H2SO4 (pH: 0), respectively. On the basis of the structural characterizations and theory simulation, the extraordinary performances of the ultrasmall iridium dioxide are proposed to mainly originate from enhanced number of unsaturated surface Ir atoms and change of local coordination environment. Our work highlights the importance of subnanometric size of iridium dioxide in water oxidation.