Iridium oxide nanoribbons with metastable monoclinic phase for highly efficient electrocatalytic oxygen evolution.

Metastable metal oxides with ribbon morphologies have promising applications for energy conversion catalysis, however they are largely restricted by their limited synthesis methods. In this study, a monoclinic phase iridium oxide nanoribbon with a space group of C2/m is successfully obtained, which is distinct from rutile iridium oxide with a stable tetragonal phase (P42/mnm). A molten-alkali mechanochemical method provides a unique strategy for achieving this layered nanoribbon structure via a conversion from a monoclinic phase K 0.25 IrO 2 (I2/m (12)) precursor. The formation mechanism of IrO 2 nanoribbon is clearly revealed, with its further conversion to IrO 2 nanosheet with a trigonal phase. When applied as an electrocatalyst for the oxygen evolution reaction in acidic condition, the intrinsic catalytic activity of IrO 2 nanoribbon is higher than that of tetragonal phase IrO 2 due to the low d band centre of Ir in this special monoclinic phase structure, as confirmed by density functional theory calculations.