Doping of anodic nanotubular TiO2 electrodes with MnO2 for use as catalysts in water oxidation

• MnO2 is homogenously doped into nanotubular TiO2 by a potential shock method.
• The potential shock voltage was optimized in ethylene glycol.
• The optimal potential shock voltage is 140 V for water oxidation application.
• The doping of 0.7 at.% MnO2 into nanotubular TiO2 is done within 10 s.

MnO2 was homogenously doped into anodic nanotubular TiO2 by a potential shock method, in which a high potential was imposed on the anodic nanotubes immediately after anodization process. We found that the potential shock process is inapplicable in a high-conductivity aqueous electrolyte, e.g. a MnO2 precursor solution (herein, 0.006 M KMnO4: 852–933 μS/m). To avoid exceeding the output compliance of the current source, the potential shock voltage was optimized in ethylene glycol for the application of water oxidation. We found an optimal potential shock voltage of 140 V, which led to the doping of 0.7 at. % MnO2 into the high-aspect-ratio nanotubular TiO2 within 10 s. The TiO2 nanotubes doped with MnO2 were successfully employed as electrodes for the non-noble catalysis of water oxidation. Although the doping concentration of Mn was found to be linearly proportional to the applied potential shock voltages, potential shocks greater than 140 V significantly increased the thickness of the barrier oxide layer, which increased the overpotential in the water oxidation process.

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