Lorenz J. Falling* Woosun Jang Sourav Laha Thomas Götsch Maxwell W. Terban Sebastian Bette Rik Mom Juan-Jesús Velasco-Vélez Frank Girgsdies Detre Teschner Andrey Tarasov Cheng-Hao Chuang Thomas Lunkenbein Axel Knop-Gericke Daniel Weber Robert Dinnebier Bettina V. Lotsch Robert Schlögl Travis E. Jones* J. Am. Chem. Soc. 2024

Full Article:https://pubs.acs.org/doi/10.1021/jacs.4c10312

The Oxygen Evolution Reaction (OER) is crucial for many energy conversion processes, providing a proton source for applications like green hydrogen production from water or methanol synthesis from carbon dioxide. Iridium oxohydroxides (IOHs) stand out as exceptional OER catalysts due to their unique balance of activity and stability in acidic electrolytes.

Earlier research indicated that the equilibrium state of IOHs varied with their atomic structure. While amorphous IOHs offered superior performance, they exhibited poor stability in acidic electrolytes. Conversely, crystalline IOHs maintained better catalytic stability but showed reduced activity. Rule-of-thumb approaches have been used to minimize the amount of precious IOHs catalyst while retaining catalytic performance, but the atomic-level correlation of IOHs with their activity and stability remains not fully understood, hindering future rational design.

In this study, we designed nanocrystalline IrOOH as the primary material and discovered its superior catalyst utilization and predictable structure. We found that the chemical stability of crystalline IOHs allowed its activity to surpass that of amorphous IOHs. The triangular oxygen-dense bonding in IrOOH provides structural integrity, while the electronic gap states enable reversible reduction behavior, mitigating the damaging effects of reduction potential. Its reactivity stems from coordinatively unsaturated edge sites with radical characteristics, specifically oxyl radicals (μ
1
​
-O oxyls).

By comparing our findings with existing literature, we’ve established a simple set of rules that can predict the stability and reactivity of IOHs based on their atomic models. We hope these rules will inspire future atomic design strategies for OER catalysts.