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

## TL;DR

This study explains why hollandite IrO2 is more efficient than rutile IrO2 for oxygen evolution reactions, using detailed atomic-level analysis.

## Contribution

The paper reveals the atomistic mechanism behind the enhanced OER activity of hollandite IrO2 surfaces compared to rutile.

## Key findings

- Hollandite IrO2 surfaces exhibit lower overpotentials due to local lattice distortions enhancing π-bonding with *O species.
- The (112) surface of hollandite IrO2 has an O2 desorption energy of 0.45 eV, significantly lower than rutile.
- Lattice distortions in hollandite surfaces weaken σ-bonds and enhance π-bonds, stabilizing *O and improving OER efficiency.

## Abstract

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.

Lattice distortions at tunnel‐structured hollandite IrO2 surfaces reshape Ir‐O bonding: they weaken the σ‐bond contribution in the Ir‐*OH bond while enhancing the π contribution of the Ir‐*O bond. This orbital reorganization in hollandite surfaces stabilizes *O, facilitates the *OH → O step, and lowers the oxygen‐evolution reaction overpotential relative to rutile IrO2