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

Abstract

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, 0.006M KMnO4: 852–933μS/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 140V, which led to the doping of 0.7at. % MnO2 into the high-aspect-ratio nanotubular TiO2 within 10s. 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 140V significantly increased the thickness of the barrier oxide layer, which increased the overpotential in the water oxidation process.