Identifying Key Structural Features of IrO_x Water Splitting Catalysts

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrocatalytic water splitting is vital for sustainable hydrogen production.
• Iridium (hydr)oxides are promising catalysts for water oxidation due to their stability and activity.
• Understanding the structure-activity relationship of amorphous iridium oxide phases is crucial but challenging.

Purpose of the Study:

• To identify key structural motifs in amorphous iridium oxide hydroxide linked to high electrocatalytic water splitting activity.
• To elucidate the structure-activity relationship in X-ray amorphous iridium oxide hydroxide catalysts.
• To guide the rational synthesis of highly active and stable amorphous iridium oxide hydroxide catalysts.

Main Methods:

• Atomic pair distribution function analysis
• Real-space atomic scale imaging
• Local electronic structure measurements

Main Results:

• High electrocatalytic activity correlates with a specific ratio of corner- and edge-sharing IrO6 octahedra.
• The active phase features hollandite-like domains cross-linked by undercoordinated atoms.
• The less active phase contains rutile motifs, leading to faster deactivation.

Conclusions:

• The local arrangement of IrO6 octahedra significantly impacts water splitting performance.
• Amorphous iridium oxide hydroxide with hollandite-like domains exhibits superior activity and stability.
• Rational design of amorphous iridium oxide hydroxide catalysts can be achieved by controlling structural motifs.