Atomistic Insights into the Electrochemical Oxygen Evolution Activity of Hollandite IrO₂ Surfaces

Lowering the overpotential for the oxygen-evolution reaction (OER) is central to designing efficient water-splitting catalysts. However, the atomistic origin behind the enhanced OER activity of hollandite IrO₂ compared to rutile has remained unclear. Here, using grand-canonical DFT with an implicit solvation model, the electrochemical stability and reactivity of the most stable hollandite facets, (100) and (112) are elucidated. The thermodynamic analysis identifies that hollandite is more readily oxidized than rutile under the working potential of 1.6 V and predicts potential-driven deintercalation of K⁺ from Hol(112) surface. Fully K-deintercalated hollandite surfaces exhibit lower overpotentials than rutile (110) due to local lattice distortions that enhance π-bonding with *O species. Additionally, the hollandite (112) surface possesses an exceptionally low O₂ desorption energy of 0.45 eV (less than half that of rutile), pointing to a highly efficient O₂-release process. The theoretical predictions clarify the atomistic origin of the experimentally observed OER reactivity of the hollandite phase and provide deeper insight into structure-activity relationships in hollandite IrO₂, providing rational design strategies for next-generation OER catalysts.