Active, Simple Iridium–Copper Hydrous Oxide Electrocatalysts for Water Oxidation

A series of Ir 1– x Cu x ( x = 0–0.5) hydrous oxide nanoparticles (HO-np) were prepared simply by stirring solutions of IrCl 3 hydrate and CuCl 2 hydrate in aqueous KOH under air. Their water oxidation activities were measured in 0.1 M HClO 4 . The Ir 0.89 Cu 0.11 HO-np was the most active catalyst in the series with mass (Ir) – normalized activity = 142 A g Ir –1 and electrochemically accessible Ir sites normalized activity >180 A mmol Ir –1 (both at 250 mV overpotential). The Ir 0.89 Cu 0.11 HO-nps were stable for 24 h galvanostatic oxidations at 1 mA cm –2 geometric, with only 280 mV overpotential. The average diameter of the Ir 0.89 Cu 0.11 HO-nps was ∼1.30 nm. XPS results suggested that doping with Cu 2+ reduces the overall charge in the lattice, resulting in higher electron density at Ir than in pure Ir HO-np. Preliminary mechanistic investigations showed that the activity enhancement by Cu is not only a surface area effect, and the presence of Cu does not appear to significantly alter the mechanism of the water oxidation reaction.