Green synthesis of water splitting electrocatalysts: IrO(2) nanocages via Pearson's chemistry

Highly porous iridium oxide structures are particularly well-suited for the preparation of porous catalyst layers needed in proton exchange membrane water electrolyzers. Herein, we report the formation of iridium oxide nanostructured cages, via a water-based process performed at room temperature, using cheap Cu(2)O cubes as the template. In this synthetic approach, based on Pearson's hard and soft acid–base theory, the replacement of the Cu(2)O core by an iridium shell is permitted by the difference in hardness/softness of cations and anions of the two reactants Cu(2)O and IrCl(3). Calcination followed by acid leaching allow the removal of residual copper oxide cores and leave IrO(2) hierarchical porous structures with outstanding activity toward the oxygen evolution reaction. Fundamental understanding of the reaction steps and identification of the intermediates are permitted by coupling a set of ex situ and in situ techniques including operando time-resolved X-ray absorption spectroscopy during the synthesis.