Synthesis of Iridium Oxide Nanorods

First, an ethanol solution of IrCl₃ (3 mg mL^–1, 100 mL) and KOH aqueous solution (KOH, 9 M, 300 mL) were stirred continuously at 150 °C in a Teflon mortar to form a uniform dark blue slurry. Then, the slurry was transformed into a homemade mechano-thermal corundum reactor that was fixed in a muffle furnace. The reactor was heated to different temperatures (300–700 °C) by stirring for 2 h. After cooling to room temperature, the samples were washed with double-distilled water and dried by lyophilization. When the heating temperature was 700 °C, the IrO₂NR samples were obtained. The fabrication process is schematically shown in Supplementary Fig. 1.