Open-Air Synthesis Yields Atom-Precise Iridium Catalyst

Key Takeaways

• Open-air polyol reduction yields stable 15‑atom Ir nanoclusters.
• Ir₁₅/CB catalyst shows 1.5× higher mass activity than commercial Ir.
• Catalyst maintains performance for over 20 hours in acidic OER conditions.
• Atomically precise Ir reduces precious metal usage while boosting efficiency.
• CO and PPh₃ ligands prevent oxidation during open‑air synthesis.

Pulse Analysis

The oxygen‑evolution reaction (OER) is the rate‑limiting step in water electrolysis, demanding a catalyst that can survive harsh acidic environments while delivering high activity. Iridium, the only metal that meets these durability criteria, is scarce and expensive, prompting a race to maximize its surface exposure and minimize the amount needed. Atomically precise nanoclusters, typically under 1 nm, dramatically increase the proportion of active surface atoms, but they have historically oxidized instantly when exposed to air, limiting practical synthesis routes.

The new study circumvents that obstacle by marrying a polyol reduction in ethylene glycol with a dual‑ligand encapsulation strategy. Carbon monoxide and triphenylphosphine bind to the iridium core, forming a protective shell that resists oxidation even when the reaction occurs in ambient conditions. The resulting Ir₁₅ clusters, averaging 0.9 nm on carbon black, exhibit a cationic electronic state that enhances adsorption of OER intermediates and activates the lattice‑oxygen oxidation mechanism. Electrochemical testing shows a 1.5‑fold increase in mass activity over the best commercial iridium catalysts, while maintaining steady performance for more than 20 hours without degradation.

From a market perspective, the ability to produce high‑performance iridium catalysts without inert‑gas facilities could slash capital expenditures for electrolyzer manufacturers. Reducing iridium loading while preserving—or even improving—efficiency directly lowers the levelized cost of green hydrogen, making it more competitive against fossil‑based alternatives. The method’s simplicity also opens pathways for scaling, potentially enabling bulk production of atomically precise catalysts for other critical reactions such as CO₂ reduction. As the hydrogen economy expands, innovations that reconcile cost, durability, and performance will be pivotal, and this open‑air synthesis marks a significant step toward that goal.