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Issue 32, 2016
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Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime

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Abstract

In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate [Fraktur R]0O are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the apparent activation energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk (“on top” of the correlation between KO and [Fraktur R]0O for the pure surface exchange regime). The model can thus quantitatively explain the range of apparent activation energies measured in the different regimes: in the surface exchange regime the apparent activation energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher apparent activation energies and simultaneously quantifies the correlation KODO1/2 observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.

Graphical abstract: Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime

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Publication details

The article was received on 31 Mar 2016, accepted on 20 Jul 2016 and first published on 21 Jul 2016


Article type: Communication
DOI: 10.1039/C6CP02131J
Citation: Phys. Chem. Chem. Phys., 2016,18, 22031-22038
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    Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime

    P. Fielitz and G. Borchardt, Phys. Chem. Chem. Phys., 2016, 18, 22031
    DOI: 10.1039/C6CP02131J

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