Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen Evolution

Nanocrystalline electrocatalysts with chemical composition corresponding to Ir1 -aEuro parts per thousand x M (x) O-2 (M = Co, Ni, and Zn, 0.05 a parts per thousand currency signaEuro parts per thousand x a parts per thousand currency signaEuro parts per thousand 0.2) were prepared by the hydrolysis of H2IrCl6 center dot 4H(2)O solutions combined with nitrates and acetates of Ni, Zn, and Co. X-ray diffraction (XRD) analysis indicates that the dopant Co, Ni, and Zn cations substitute the Ir atoms in the rutile lattice. The prepared materials contain small inclusions of iridium metal on the level comparable with the detection of the XRD technique. The local environment of Co and Zn in the doped IrO2 materials conforms to a rutile model with a homogeneous distribution of the doping elements in the rutile lattice. The incorporated Ni is distributed in the rutile lattice non-homogeneously and tends to form clusters within rutile structure. The incorporation of Ni and Co enhances the activity of the prepared electrocatalysts in oxygen evolution. The modification of the IrO2 via doping process alters also the material's selectivity in the parallel oxygen and chlorine evolution. Incorporation of Co and Zn cations shifts the selectivity of the catalysts toward oxygen evolution in chloride-containing media; the Ni incorporation leads to an enhancement of the selectivity toward chlorine evolution. Chlorine evolution is apparently limited by the number of the active catalytic sites on the electrode surface.