Domain structure for an amorphous iridium-oxide water-oxidation catalyst characterized by X-ray pair distribution function analysis

The domain structure of an amorphous, "blue layer" iridium-oxide water-oxidation catalyst film (BL) electrodeposited from the soluble precursor complex, [Cp*Ir(H₂O)₃]SO₄, was characterized by X-ray pair distribution function (PDF) analysis. The results show that the experimental PDF can be fit remarkably well using a single Ir ₅O₂₂ cluster extracted from the rutile lattice. The model includes distortions that indicate the presence of Ir(μ-O)₃Ir or distorted Ir(μ-O)₂Ir substructures, and hence deviations from a rutile structure. The five Ir atom cluster is suggested to represent the population-averaged distribution of metal-oxo clusters in the film. BL is found to be distinguished from other amorphous film water-oxidation catalysts because of the remarkably small domain size and homogeneity. As such, the blue layer catalyst provides a model for investigating ligand-determined metal-oxide cluster assembly and catalyst mechanism. This journal is