Achieving Active and Stable Amorphous Ir^VOOH for Water Splitting

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Understanding amorphous iridium (Ir)-based oxides for oxygen evolution reaction (OER) is challenging.
• Previous studies linked higher OER performance in IrOOH to Ir^III species, conflicting with theories favoring high-valence metals.

Purpose of the Study:

• To resolve contradictions regarding the active species in Ir-based OER catalysts.
• To investigate the role of electronic states and structural motifs in amorphous Ir oxyhydroxides.

Main Methods:

• Synthesis of amorphous Lu_1.25IrOOH catalyst.
• Electrochemical evaluation in acidic and alkaline media.
• Ex situ Ir L3-edge and O K-edge X-ray absorption spectroscopy.
• Theoretical calculations.

Main Results:

• Amorphous Lu_1.25IrOOH exhibited ultrahigh OER performance in acidic media.
• The enhanced activity was attributed to Ir^V species with a more d-hole-containing electronic state, induced by cationic vacancies.
• Ir^III species in Lu_1.25IrOOH inhibited OER activity in alkaline media.
• A high proportion of edge-shared [IrO]-[IrO] motifs provided OER stability comparable to IrO₂.

Conclusions:

• Cationic vacancies and the resulting Ir^V state are crucial for high OER activity in acidic media.
• The edge-shared [IrO]-[IrO] motif is a key structural feature for stable OER performance.
• This work provides a rational explanation for the high performance of many Ir-based OER materials.