Oxygen evolution during water electrolysis from thin films using bimetallic oxides of Ir-Pt and Ir-Ru

Catalysts are required for both the oxidation of water and the reduction of oxygen. Blended oxides of Ir and Ru are superior for water oxidation whereas mixtures of Pt and Ir perform better when both oxidation of water and reduction of oxygen are required on the same electrode. A strategy for rationing these elements is explored by the formation of a thin film using a dry, flame process. Ir_xPt_1-xO_2-y and Ir_xRu _1-xO_2-y were both deposited from the vapor phase, as thin films, onto substrates of glassy carbon, polypropylene, and quartz. Elemental analysis of the Ir-Pt electrode suggests a stoichiometry of Ir _0.56Pt_0.44O_2-y. Bulk diffraction of the film shows two separate phases consisting of Pt metal and IrO₂. The sample showed signs of spallation after 10 cycles when scanned between 1.2 and 1.7 V. A weak oxygen evolution current of 0.8-0.4 mA/mg was measured at 1.6 V. Elemental analysis of the Ru-Ir film suggests a ratio of Ru_0.41Ir0. 59O_2-y. Phases of a homogeneous solid-solution of IrO₂ and RuO₂ and to a lesser extent Ru metal are shown by bulk X-ray diffraction. An exceptional oxygen evolution current of 25-40 mA/cm² was observed for the Ru_0.41Ir_0.59O_2-y sample corresponding to a normalized mass activity of 400 mA/mg.