Oxygen Deficiency and Reactivity of Spinel NiCo₂O₄ (001) Surfaces

Journal Article · Thu Feb 09 00:00:00 EST 2017 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.6b12005· OSTI ID:1480449

Shi, Xiao ^[1]; Bernasek, Steven L. ^[2]; Selloni, Annabella  ^[1]

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1. Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
2. Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States; Science Division, Yale-NUS College, Singapore 138609, Singapore

We carried out density functional theory (DFT) calculations with on-site Hubbard U corrections to investigate the structure, defects, and reactivity of (001) surfaces of spinel NiCo₂O₄ (NCO), a promising catalyst for CO and methane oxidation. By examining surfaces with different Co/Ni compositions, we find that the formation of surface oxygen vacancies (VOs) on NCO(001) is strongly affected by the neighboring cation in the third layer, the computed formation energy being largest (~1.2 eV) for O vacancies coordinated to third layer Co and smallest (~0.5 eV) for VOs coordinated to a Ni neighboring another Ni ion. As a result, VO formation is generally much easier on NCO (001) than on Co₃O₄ (001) surfaces, suggesting that NCO may be a better catalyst than Co₃O₄ for oxidation reactions based on the Mars–Van Krevelen mechanism. Surface oxygen vacancies on reduced NCO surfaces can be healed through dissociative water adsorption at room temperature. In contrast, adsorption of molecular oxygen at VOs is energetically unfavorable under ambient conditions, suggesting that O₂ adsorption may represent the thermodynamic limiting step for oxidation reactions on NCO(001) surfaces.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
• DOE Contract Number: SC0007347; AC02-05CH11231
• OSTI ID: 1480449
• Journal Information: Journal of Physical Chemistry. C, Vol. 121, Issue 7; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English