Achieving Active and Stable Amorphous Ir^VO_xOH_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 IrO2, the higher oxygen evolution reaction (OER) performance brought by IrOxOHy was normally considered to be associated with the pristine IrIII-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 Lu1.25IrOxOHy (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 IrOx/Lu1.25IrOxOHy in acidic media was identified to be driven by the more d-hole-containing electronic state of IrV created by cationic vacancies. The pristine properties of IrIII-containing Lu1.25IrOxOHy conversely inhibit the OER activity in alkaline media. Additionally, the high edge-shared [IrOx]-[IrOx] motif proportion structure in amorphous Lu1.25IrOxOHy achieves a stable OER process, which exhibits a high S-number stability index similar to IrO2. We demonstrate that the key factor of the edge-shared [IrOx]-[IrOx] motif with cationic vacancies in IrVOxOHy could rationally reveal the source for most of the high-performance Ir-based materials.