Self-Assembly of Active IrO₂ Colloid Catalyst on an ITO Electrode for Efficient Electrochemical Water Oxidation

Active catalysts for water oxidation to evolve O₂ are required for the construction of artificial photosynthetic devices that are expected to be promising energy-providing systems in the future. The citrate-stabilized IrO₂ colloid was self-assembled onto an indium tin oxide (ITO) electrode to form a monolayer of the colloidal IrO₂ particles when it was dipped in the colloid solution. The self-assembly could be achieved by a chemical interaction between carboxylate groups on the citrate stabilizer and hydroxyl groups on the ITO surface to form ester bonds. Efficient electrocatalysis for water oxidation was demonstrated using the electrode modified by the self-assembled IrO₂ colloid to yield the highest turnover frequency ((2.3−2.5) × 10⁴ h^-1) of IrO₂ in the hitherto-reported catalysts for electrochemical water oxidation.