Achieving Active and Stable Amorphous Ir V O x OH y for Water Splitting.

Evaluating the structural and electronic-state characteristics of long-range disordered amorphous iridium (Ir)-based oxides is still unsatisfying. Compared with the benchmark IrO 2 , the higher oxygen evolution reaction (OER) performance brought by IrO x OH y was normally considered to be associated with the pristine Ir III -containing species. However, such a conclusion conflicts with the opinion that high-valence metals can create excellent OER activity. To resolve such contradictions, we synthesized a pure amorphous Lu 1.25 IrO x OH y (Lu = lutetium) catalyst in this work. In combination with the comprehensive electrochemical evaluation in alkaline and acidic media, ex situ Ir L3-edge and O K-edge X-ray absorption spectroscopy and theoretical calculations revealed that the ultrahigh OER performance of reconstructed IrO x /Lu 1.25 IrO x OH y in acidic media was identified to be driven by the more d-hole-containing electronic state of Ir V created by cationic vacancies. The pristine properties of Ir III -containing Lu 1.25 IrO x OH y conversely inhibit the OER activity in alkaline media. Additionally, the high edge-shared [IrO x ]-[IrO x ] motif proportion structure in amorphous Lu 1.25 IrO x OH y achieves a stable OER process, which exhibits a high S -number stability index similar to IrO 2 . We demonstrate that the key factor of the edge-shared [IrO x ]-[IrO x ] motif with cationic vacancies in Ir V O x OH y could rationally reveal the source for most of the high-performance Ir-based materials.