Composition dependence of the oxygen-evolution reaction rate on Ir_xTi_1-xO₂ mixed-oxide electrodes

Mudcrack-free oxide films of Ir_xTi_1-xO₂ (0 < x ≤ 1) on titanium substrates were obtained, and the effects of the oxide composition on the rate of oxygen-evolution reaction were investigated. At x ≥ 0.6, Ir-rich grains appear on the mudcrack-free surface. In the purely single-phase region (0 < x ≤ 0.5), the pseudo-capacitive charge is proportional to the surface composition, x_s, and the exchange-current density for the oxygen-evolution reaction increases linearly with x_s at 0.2 ≤ x_s ≤ 0.5, with an extrapolated intercept at x_s ∼ 0.15, below which the oxides are inactive.