TY - JOUR
T1 - Oxygen Deficiency and Reactivity of Spinel NiCo2O4 (001) Surfaces
AU - Shi, Xiao
AU - Bernasek, Steven L.
AU - Selloni, Annabella
N1 - Funding Information:
This work was supported by DoE-BES, Division of Chemical Sciences Geosciences and Biosciences under Award DE-SC0007347. SLB acknowledges support from NSF-DMR1506989. We used resources of the National Energy Research Scientific Computing Center (DoE Contract No. DE-AC02-05CH11231) and the TIGRESS High Performance Computer Center at Princeton University.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/2/23
Y1 - 2017/2/23
N2 - 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.
AB - 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.
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U2 - 10.1021/acs.jpcc.6b12005
DO - 10.1021/acs.jpcc.6b12005
M3 - Article
AN - SCOPUS:85026876340
SN - 1932-7447
VL - 121
SP - 3929
EP - 3937
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 7
ER -