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A Thermodynamic Framework for Predicting Oxygen Vacancy Formation Energies on Electrocatalyst Surfaces
Yuefeng Zhang1, Zhenbin Wang1,2
1Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR 999077, China.
ACS Omega
|June 29, 2026
Summary
Oxygen vacancies are often assumed to boost electrocatalyst performance. However, this study shows they are thermodynamically unstable under operating conditions, challenging current models for oxygen reduction and evolution reactions.
Area of Science:
- Materials Science
- Electrochemistry
- Catalysis
Background:
- Oxygen vacancies (VO) are frequently cited as crucial for transition metal oxide electrocatalyst activity.
- Their stability under realistic electrochemical conditions is not well understood.
Purpose of the Study:
- To develop a thermodynamic framework for calculating VO formation energies.
- To assess the stability of VO in electrocatalysts under operating conditions.
Main Methods:
- Established a thermodynamic framework to calculate VO formation energies.
- Evaluated 19 catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).
- Analyzed VO stability as a function of pH and applied potential.
Main Results:
- VO formation is favorable at standard conditions but energetically costly under operando conditions.
- Formation energies exceed 0.50 eV for ORR and 2.00 eV for OER.
- High thermodynamic barriers suggest VO are unlikely to be stable defects during electrocatalysis.
Conclusions:
- Surface oxygen vacancies are likely unstable under realistic electrocatalytic conditions.
- This challenges the common assumption of vacancy-mediated reaction mechanisms.
- Potential-dependent surface stoichiometry must be considered in modeling catalyst-electrolyte interfaces.
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