First Example of Protonation of Ruddlesden-Popper Sr2IrO4: A Route to Enhanced Water Oxidation Catalysts

Water electrolysis is considered to be a promising way to store and convert excess renewable energies into hydrogen, which is of high value for many chemical transformation processes such as the Haber-Bosch process. The main challenge to promote the deployment of the polymer electrolyte membrane water electrolysis (PEMVVE) technology lies in the design of robust catalysts for the oxygen evolution reaction (OER) under acidic conditions, since most of the transition metal-based oxides undergo structural degradation under these harsh acidic conditions. To broaden the variety of candidate materials as OER catalysts, a cation-exchange synthetic route was recently explored to reach crystalline pronated iridates with unique structural properties and stability. In this work, a new protonated phase H3.6IrO4 center dot 3.7H(2)O, prepared via Sr2+/H+ cation exchange at room temperature starting from the parent Ruddlesden-Popper Sr2IrO4 phase, is described. This is the first discovery of crystalline protonated iridate forming from a perovskite-like phase, adopting a layered structure with apex-linked IrO6 octahedra. Furthermore, H3.6IrO4 center dot 3.7H(2)O is found to possess not only an enhanced specific catalytic activity, superior to that of other perovskite-based iridates, but also a mass activity comparable to that of nanosized IrOx particles, while showing an improved catalytic stability owing to its ability to reversibly exchange protons in acid.