Surface morphology controls water dissociation on hydrated IrO₂ nanoparticles

Area of Science:

• Materials Science
• Catalysis
• Computational Chemistry

Background:

• Iridium oxide (IrO2) is a crucial electrocatalyst for the oxygen evolution reaction (OER).
• Reducing iridium content in catalysts is essential for large-scale applications, often achieved using nanoparticles.
• Understanding the interface between IrO2 nanoparticles and water is critical for optimizing their electrocatalytic performance.

Purpose of the Study:

• To investigate the factors governing water adsorption and dissociation at the IrO2 nanoparticle-water interface.
• To elucidate the role of nanoparticle size and surface sites in determining catalytic behavior.
• To provide insights for designing more efficient iridium-based electrocatalysts.

Main Methods:

• Density Functional Theory (DFT) calculations with PBE-D2 functional.
• Ab initio molecular dynamics (AIMD) simulations.
• Modeling of IrO2 nanoparticle models of varying sizes, specifically (IrO2)33 and (IrO2)115.

Main Results:

• Water adsorption energy and preferred adsorption structure (molecular vs. dissociated) are determined by metal coordination and hydrogen bonding.
• Adsorption at iridium axial vacant sites favors water dissociation due to stronger Ir-H2O interactions.
• Tip and corner sites on nanoparticles exhibit lower adsorption energies and a preference for molecular water due to limited hydrogen bonding opportunities.

Conclusions:

• Nanoparticle surface structure, particularly the availability of specific coordination sites and hydrogen bonding, significantly impacts water-metal interactions.
• Compared to extended surfaces, IrO2 nanoparticles show lower adsorption energies and reduced water dissociation.
• These findings are vital for advancing the design of highly active and cost-effective iridium oxide electrocatalysts.