Efficient water oxidation with organometallic iridium complexes as precatalysts

Area of Science:

• Inorganic Chemistry
• Catalysis
• Materials Science

Background:

• Iridium complexes are promising precatalysts for water oxidation.
• Understanding the active species in catalysis is crucial for optimizing efficiency.

Purpose of the Study:

• To investigate the catalytic activity of five iridium complexes in water oxidation.
• To identify the active species responsible for high catalytic performance under varying pH conditions.

Main Methods:

• Spectroscopic analysis (UV-Vis) to characterize transient species.
• Oxygen evolution experiments to measure catalytic activity.
• Dynamic light scattering and transmission electron microscopy to determine particle size.
• Ultrafiltration to differentiate species based on size.

Main Results:

• Catalytic activity of iridium complexes increased with pH.
• A transient species (A) with absorption at 590 nm, attributed to small 0.5–2 nm IrOx clusters, showed high activity.
• A less active species (B), identified as 120 nm nanoparticles, was observed at high oxidant concentrations.

Conclusions:

• The active species in iridium-catalyzed water oxidation are small IrOx clusters (0.5–2 nm).
• Reaction conditions, particularly pH and oxidant concentration, significantly influence the formation of active vs. inactive species.
• Precise control over reaction parameters is essential for maximizing catalytic efficiency.