Crystal-Phase Engineering of Nanowires and Platelets of K _<i>x</i> IrO ₂ for Efficient Water Oxidation

IrO₂ is one of the most widely investigated electrocatalysts for oxygen evolution reaction in an acidic environment. Increasing the mass activity is an effective way of decreasing the loading of Ir, to ultimately reduce costs. Here, we demonstrate the crystal-phase engineering of two different potassium iridate polymorphs obtained by designing a selective solid-state synthesis of either one-dimensional K_0.25IrO₂ nanowires with a hollandite crystal structure or two-dimensional KIrO₂ hexagonal platelets. Both structures present increased specific and mass electrocatalytic activities for the water oxidation reaction in acidic media compared to commercial rutile IrO₂ of up to 40%, with the 1D nanowires outperforming the 2D platelets. XANES, extended X-ray absorption fine structure, and X-ray diffraction investigations prove the structural stability of these two different allotropes of KxIrO₂ compounds upon electrocatalytic testing. These low-dimensional nanostructured 1D and 2D KxIrO₂ compounds with superior mass activity to commercial IrO₂ can pave the way toward the design of new electrocatalyst architectures with reduced Ir loading content for proton exchange membrane water electrolyzer (PEMWE) anodes.