Oscillating oxygen evolution at Ta anodes |
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Authors: | Christian Hammer Benjamin Walther Hikmet Karabulut Manuel M Lohrengel |
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Institution: | 1.Institut für Physikalische Chemie,Heinrich-Heine-University of Duesseldorf,Düsseldorf,Germany;2.HC Starck GmbH,Goslar,Germany |
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Abstract: | Anodic Ta oxide films are said to inhibit oxygen evolution. In industry, however, large amounts of gas are evolved during
the anodization of tantalum anodes for electrolytic capacitor fabrication. We quantified the oxygen by fluorescence quenching
in a flow-through cuvette and found that 4% of the anodic charge are consumed for oxygen evolution. In wires or sheets, this
oxygen is removed by diffusion without bubble formation and, thus, not recognized. Due to the large inner area of the sintered
Ta anodes, the oxygen evolution causes strong oscillations of the current density and bubble formation. The amount of oxygen
is proportional to the oxide amount formed in parallel. This is explained by a model where mobile ions during oxide growth
form interband states which allow electron tunneling. Accordingly, stationary no oxygen evolution is observed. |
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