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Dopant driven tuning of hydrogen oxidation mechanism at the pore/nickel/zirconia triple phase boundary

Abstract

The effects of cation dopants in zirconia on the H2 oxidation mechanism at the pore/nickel/zirconia triple phase boundary (TPB) were theoretically examined. Y, Sc, Al, Ce, and Ca were considered as dopants, and on-boundary, O-migration, and H-migration reaction mechanisms were examined. Based on density functional theory calculations, Y as a dopant favored the on-boundary mechanism with water molecule formation within the immediate proximity of the TPB. The corresponding rate-limiting step is H transfer from the nickel surface to the boundary. In contrast, the on-boundary mechanism is not completed with the Al-, Sc-, and Ca-doped systems, due to the dissociation of water molecules at the boundary. In the Al-doped system, the O-migration mechanism is the major reaction pathway due to a low barrier for the rate-limiting step that corresponds to O transfer from zirconia to the nickel surface. H-migration mechanism, which implies water molecule formation on the zirconia surface at a position distant from the boundary, should dominate at the Sc-, Ca, and Ce-doped TPBs, with the lowest activation barrier at the Sc-doped TPB. The reasons for the switching of the reaction mechanisms depending on dopant species are analyzed.

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Publication details

The article was received on 22 Dec 2017, accepted on 19 Mar 2018 and first published on 28 Mar 2018


Article type: Paper
DOI: 10.1039/C7CP08572A
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Dopant driven tuning of hydrogen oxidation mechanism at the pore/nickel/zirconia triple phase boundary

    A. Iskandarov and T. Tada, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C7CP08572A

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