Local-Environment Populations Govern Size-Dependent OER Activity in Supported Subnanometer IrO𝑥 Clusters
5 affiliations
- 1Program in Materials Science and Engineering
- 2University of California San Diego
- 3Aiiso Yufeng Li Family Department of Chemical and Nano Engineering
- 4KAUST Catalysis Center, Physical Sciences and Engineering Division
- 5King Abdullah University of Science and Technology
Abstract
Proton-exchange-membrane water electrolysis is constrained by the high Ir demand of the acidic oxygen evolution reaction (OER), motivating supported subnanometer IrO𝑥 clusters that maximize Ir utilization. At this scale, however, changing cluster size simultaneously alters structure, oxygen coverage, and the distribution of nonequivalent active sites, making it difficult to identify the physical origin of size-dependent activity. Here, we combine systematic structure sampling, density functional theory, implicit solvation, and site-resolved microkinetics to resolve OER thermodynamics across Ir𝑛O𝑥 (𝑛 = 1–30) clusters supported on anatase TiO2(101). The resulting activity landscape is strongly heterogeneous and nonmonotonic with cluster size, with substantial activity variations even among sites on the same cluster. This heterogeneity can be traced to the local oxygen coordination of the active Ir–∗O motif. Increasing oxo-proximal coordination, quantified by CNO,co(Ir∗), raises the ∗OH-to-∗O free-energy cost while lowering that of ∗O-to-∗OOH formation, thereby controlling the energetic balance between the two steps surrounding ∗O. Electronic-structure analysis associates this coordination dependence with charge redistribution at the binding Ir center, changes in Ir–O bonding, and reorganization of the Ir 5d–O 2p electronic structure. Steady-state microkinetics preserves the thermodynamic activity hierarchy, with ensemble rates governed primarily by the most active sites at each cluster size. Single-Ir dissolution thermodynamics further shows that higher local oxygen coordination is associated with greater resistance to Ir loss, extending the significance of local coordination from OER energetics to dissolution stability. These results establish local-environment populations as the structural origin of size-dependent catalytic behavior in subnanometer IrO𝑥 clusters, revealing local coordination rather than cluster size alone as the key structural variable underlying activity and stability.
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BibTeX
@misc{liu2026localenvironment,
title = {{Local-Environment Populations Govern Size-Dependent OER Activity in Supported Subnanometer IrO𝑥 Clusters}},
author = {Guangsheng Liu and Leshen Zhang and Xiao Ma and Abdulrahman Allangawi and Huabin Zhang and Wan-Lu Li},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009834/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009834/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Local-Environment Populations Govern Size-Dependent OER Activity in Supported Subnanometer IrO𝑥 Clusters
AU - Guangsheng Liu
AU - Leshen Zhang
AU - Xiao Ma
AU - Abdulrahman Allangawi
AU - Huabin Zhang
AU - Wan-Lu Li
PY - 2026
DA - 2026/10/04
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009834/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009834/v1
AB - Proton-exchange-membrane water electrolysis is constrained by the high Ir demand of the acidic oxygen evolution reaction (OER), motivating supported subnanometer IrO𝑥 clusters that maximize Ir utilization. At this scale, however, changing cluster size simultaneously alters structure, oxygen coverage, and the distribution of nonequivalent active sites, making it difficult to identify the physical origin of size-dependent activity. Here, we combine systematic structure sampling, density functional theory, implicit solvation, and site-resolved microkinetics to resolve OER thermodynamics across Ir𝑛O𝑥 (𝑛 = 1–30) clusters supported on anatase TiO2(101). The resulting activity landscape is strongly heterogeneous and nonmonotonic with cluster size, with substantial activity variations even among sites on the same cluster. This heterogeneity can be traced to the local oxygen coordination of the active Ir–∗O motif. Increasing oxo-proximal coordination, quantified by CNO,co(Ir∗), raises the ∗OH-to-∗O free-energy cost while lowering that of ∗O-to-∗OOH formation, thereby controlling the energetic balance between the two steps surrounding ∗O. Electronic-structure analysis associates this coordination dependence with charge redistribution at the binding Ir center, changes in Ir–O bonding, and reorganization of the Ir 5d–O 2p electronic structure. Steady-state microkinetics preserves the thermodynamic activity hierarchy, with ensemble rates governed primarily by the most active sites at each cluster size. Single-Ir dissolution thermodynamics further shows that higher local oxygen coordination is associated with greater resistance to Ir loss, extending the significance of local coordination from OER energetics to dissolution stability. These results establish local-environment populations as the structural origin of size-dependent catalytic behavior in subnanometer IrO𝑥 clusters, revealing local coordination rather than cluster size alone as the key structural variable underlying activity and stability.
ER -