TY - JOUR

T1 - Oxygen Vacancy Formation and Water Adsorption on Reduced AnO2 {111}, {110} and {100} Surfaces (An = U, Pu); A Computational Study

AU - Wellington, Joseph P. W.

AU - Tegner, Bengt

AU - Collard, Jonathan

AU - Kerridge, Andrew

AU - Kaltsoyannis, Nikolas

N1 - This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright ©2018 American Chemical Society after peer review and technical editing by the publisher.To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jpcc.7b11512

PY - 2018/4/5

Y1 - 2018/4/5

N2 - The substoichiometric {111}, {110} and {100} surfaces of UO2 and PuO2 are studied computationally using two distinct yet related approaches based on density functional theory; the periodic electrostatic embedded cluster method (PEECM) and Hubbard-corrected periodic boundary condition DFT. First and second layer oxygen vacancy formation energies and geometries are presented and discussed; the energies are found to be substantially larger for UO2 vs PuO2, a result traced to the substantially more positive An(IV)/An(III) reduction potential for Pu, and hence relative ease of Pu(III) formation. For {110} and {100}, the significantly more stable dissociative water adsorption seen previously for stoichiometric surfaces [J. Nucl. Mater. 2016, 482, 124–134; J. Phys. Chem. C 2017, 121, 1675-1682] is also found for the defect surfaces. By contrast, vacancy creation substantially changes the most stable mode of water adsorption on the {111} surface, such that the almost degenerate molecular and dissociative adsorptions on the pristine surface are replaced by a strong preference for dissociative adsorption on the substoichiometric surface. The implications of this result for the formation of H2 are discussed. The generally very good agreement between the data from the embedded cluster and periodic DFT approaches provides additional confidence in the reliability of the results and conclusions.

AB - The substoichiometric {111}, {110} and {100} surfaces of UO2 and PuO2 are studied computationally using two distinct yet related approaches based on density functional theory; the periodic electrostatic embedded cluster method (PEECM) and Hubbard-corrected periodic boundary condition DFT. First and second layer oxygen vacancy formation energies and geometries are presented and discussed; the energies are found to be substantially larger for UO2 vs PuO2, a result traced to the substantially more positive An(IV)/An(III) reduction potential for Pu, and hence relative ease of Pu(III) formation. For {110} and {100}, the significantly more stable dissociative water adsorption seen previously for stoichiometric surfaces [J. Nucl. Mater. 2016, 482, 124–134; J. Phys. Chem. C 2017, 121, 1675-1682] is also found for the defect surfaces. By contrast, vacancy creation substantially changes the most stable mode of water adsorption on the {111} surface, such that the almost degenerate molecular and dissociative adsorptions on the pristine surface are replaced by a strong preference for dissociative adsorption on the substoichiometric surface. The implications of this result for the formation of H2 are discussed. The generally very good agreement between the data from the embedded cluster and periodic DFT approaches provides additional confidence in the reliability of the results and conclusions.

U2 - 10.1021/acs.jpcc.7b11512

DO - 10.1021/acs.jpcc.7b11512

M3 - Journal article

VL - 122

SP - 7149

EP - 7165

JO - The Journal of Physical Chemistry C

JF - The Journal of Physical Chemistry C

SN - 1932-7447

IS - 13

ER -