Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7745623 | Solid State Ionics | 2016 | 6 Pages |
Abstract
The oxygen reduction reaction (ORR) at the cathode of the solid oxide fuel cell (SOFC) is investigated by the ab initio MD simulation, focusing on the role of the oxygen vacancy on the oxygen dissociation and reduction reaction. The oxygen molecule easily adsorbs on the nickel atom at the NiO surface as the monodentate superoxide ion (O2â(ad)), which turns quickly to the bidentate peroxide ion (O22Â â(ad)) regardless of the existence of vacancies at surface. The bidentate O22Â â(ad) in the vicinity of the oxygen vacancy dissociates easily, while that on the surface without vacancy is kept undissociated. Nickel atoms next to the oxygen vacancy have more electrons compared with those in the bulk NiO, and therefore, are able to donate more electrons to the adsorbed oxygen molecules, which results in the dissociation of the oxygen molecule. Detailed Mulliken charge analyses in term of bond overlap population on the dissociation process have revealed that dissociation undergoes with two series steps of O22Â â(ad) via Oâ state either in the form of V
-
- O or Oâ(ad) into O2Â â state in the form of VÃO or O2Â â(ad). Moreover, the NEB analyses reveal that the energy decreases monotonically along the reaction path of oxygen dissociation on the NiO surface with vacancies, while there exists the activation energy of about 0.6Â eV in the case without vacancies. Since the dissociation of O22Â â(ad) takes place quickly upon encounter with oxygen vacancy at the surface, it is expected that the probability of meeting O22Â â and V
-
- O per time and area determines the reaction rate of ORR.
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- O or Oâ(ad) into O2Â â state in the form of VÃO or O2Â â(ad). Moreover, the NEB analyses reveal that the energy decreases monotonically along the reaction path of oxygen dissociation on the NiO surface with vacancies, while there exists the activation energy of about 0.6Â eV in the case without vacancies. Since the dissociation of O22Â â(ad) takes place quickly upon encounter with oxygen vacancy at the surface, it is expected that the probability of meeting O22Â â and V
-
- O per time and area determines the reaction rate of ORR.
Related Topics
Physical Sciences and Engineering
Chemistry
Electrochemistry
Authors
Shinya Sugiura, Yasushi Shibuta, Kohei Shimamura, Masaaki Misawa, Fuyuki Shimojo, Shu Yamaguchi,