Acid-Base Chemistry of a Model IrO2 Catalytic Interface

Iridium oxide (IrO2) is one of the most efficient catalytic materials for the oxygen evolution reaction (OER), yet the atomic scale structure of its aqueous interface is largely unknown. Herein, the hydration structure, proton transfer mechanisms, and acid-base properties of the rutile IrO2(110)-water interface are investigated using ab initio based deep neural-network potentials and enhanced sampling simulations. The proton affinities of the different surface sites are characterized by calculating their acid dissociation constants, which yield a point of zero charge in agreement with experiments. A large fraction (& AP;80%) of adsorbed water dissociation is observed, together with a short lifetime (& AP;0.5 ns) of the resulting terminal hydroxy groups, due to rapid proton exchanges between adsorbed H2O and adjacent OH species. This rapid surface proton transfer supports the suggestion that the rate-determining step in the OER may not involve proton transfer across the double layer into solution, as indicated by recent experiments.

Automated summary

This study investigates the hydration structure, proton transfer mechanisms, and acid-base properties of the rutile IrO2(110)-water interface using ab initio based deep neural-network potentials and enhanced sampling simulations. The proton affinities of different surface sites are characterized, and a point of zero charge is obtained. Results show a large fraction of adsorbed water dissociation and a short lifetime of resulting hydroxy groups due to rapid surface proton exchanges, supporting recent experimental findings that the rate-determining step in the oxygen evolution reaction may not involve proton transfer into solution.