Electrochemical Preparation of Crystalline Hydrous Iridium Oxide and Its Use in Oxygen Evolution Catalysis.

Even the most stable Ir-based oxides inevitably encounter a severe degradation problem during the oxygen evolution reaction (OER) in acid, resulting in quick formation of amorphous IrO layers on the catalyst surface. Unfortunately, there is still a lack of fundamental understanding of such hydrous IrO layers, including the atomic arrangement, key active structure, compositions, chemical stability, and so on. In this work, we demonstrate an electrochemical strategy to prepare two types of protonated iridium oxides with well-defined crystalline structures: one possesses a 2D layered structure (denoted as α-HIrO) and the other consists of 3D interconnected polymorphs (denoted as β-HIrO). Both protonated iridium oxides demonstrate superior electrochemical stabilities with 6 times suppressed Ir dissolution comparing to the initial LiIrO and rutile IrO. It is hypothesized that the enriched protons and fast diffusions in these two protonated HIrO crystal oxides may promote surface structural stability by suppressing the formation of high-valence Ir species at the solid-liquid interfaces during OER. Overall, the results of this work shed light on the role of proton dynamics toward the OER processes on the catalyst surface in acid media.