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Magnetron sputtered ZnO layers : synthesis, characterization and oxygen reduction investigations

Abstract : Corrosion is a local electrochemical process involving an oxidation reaction that is balanced by a reduction reaction. The oxygen reduction reaction (ORR) is one of the major cathodic reactions in corrosion. The oxygen can be reduced directly into OH- ions or indirectly with hydrogen peroxide as intermediate species. In this Ph.D. thesis, ORR has been investigated on ZnO that is one the most common degraded forms of zinc, a metal of major industrial interest. Model electrodes (textured and non-textured ZnO films) have been deposited on copper substrates using the RF-sputtering technique. The ORR has been investigated in alkaline electrolyte using a rotating ring-disk electrode. During the measurement of the polarization curves, potential-dependent rupturing of the textured ZnO films was observed. Electrochemical impedance spectroscopy was utilized to detect more finely at which potential the rupture of the film was initiated. Non-textured ZnO thin films exhibited a significantly improved mechanical stability and higher ORR activity compared to textured films. A reaction mechanism was proposed for ORR. The prevalence of the direct reduction was quantitatively established but the parallel indirect reduction was active as well. It was possible to show that indirect reduction pathway did not stop at the production of hydrogen peroxide. The latter was further reduced to OH-anions and/or decomposed into oxygen molecules.
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Josiane Soares Costa. Magnetron sputtered ZnO layers : synthesis, characterization and oxygen reduction investigations. Physics [physics]. Université de Bretagne occidentale - Brest, 2019. English. ⟨NNT : 2019BRES0037⟩. ⟨tel-02518586⟩

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