In Situ Studies of the Cathodic Stability of Single-Crystalline IrO2(110) Ultrathin Films Supported on RuO2(110)/Ru(0001) in an Acidic Environment

We investigate with in situ surface X-ray diffraction (SXRD) and X-ray reflectivity experiments (XRR) the cathodic stability of an ultrathin single-crystalline IrO2(110) film with a regular array of mesoscopic rooflike structures that is supported on a RuO2(110)/Ru(0001) template. It turns out that the planarity of the single-crystalline IrO2(110) film is largely lost in that IrO2(110) oxide domains delaminate at a cathodic potential of −0.18 V, i.e., the IrO2(110) is morphologically not stable. Obviously, the electrolyte solution is able to reach the RuO2(110) layer presumably through the surface grain boundaries of the IrO2(110) layer. Subsequently, the single-crystalline RuO2(110) structure-directing template is reduced to amorphous hydrous RuO2, with the consequence that the IrO2(110) film loses its adhesion to the template. From in situ XRR experiments during cathodic polarization down to −0.18 V we find that the IrO2(110) film does not swell, while from in situ SXRD experiments, the lattice constants of IrO2(110) are shown to be not affected. The rooflike mesostructure of the IrO2(110) flakes remains intact after cathodic polarization to ‒0.18 V, evidencing that the crystallinity of IrO2(110) is retained.