Acid-Base Chemistry of a Model IrO₂ Catalytic Interface

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Iridium oxide (IrO2) is a highly efficient catalyst for the oxygen evolution reaction (OER).
• The atomic-scale structure of the IrO2-water interface is crucial for understanding OER mechanisms but remains largely unknown.
• Investigating this interface is vital for advancing OER catalyst design.

Purpose of the Study:

• To elucidate the hydration structure, proton transfer mechanisms, and acid-base properties of the rutile IrO2(110)-water interface.
• To characterize the proton affinities of different surface sites on IrO2.
• To provide atomic-level insights into the OER process at the IrO2-water interface.

Main Methods:

• Utilizing ab initio based deep neural-network potentials for accurate atomic simulations.
• Employing enhanced sampling simulations to explore reaction pathways and dynamics.
• Calculating acid dissociation constants to determine surface site proton affinities and point of zero charge.

Main Results:

• A significant fraction (approximately 80%) of adsorbed water dissociation was observed at the interface.
• Terminal hydroxy groups exhibited a short lifetime (around 0.5 ns) due to rapid proton exchange.
• Calculated acid dissociation constants yielded a point of zero charge consistent with experimental data.

Conclusions:

• The study reveals rapid proton transfer dynamics at the IrO2(110)-water interface.
• These findings suggest that proton transfer across the double layer into solution may not be the rate-determining step in the OER.
• The atomic-scale understanding of the interface advances the fundamental knowledge of iridium oxide electrocatalysis.