Ruthenium Oxide‐Doped TiO2 Nanotubes by Single‐Step Anodization for Water‐Oxidation Applications

Single‐step anodization in NH4F‐based ethylene glycol electrolyte containing KRuO4 and H2O led to the production of high‐aspect‐ratio TiO2 nanotubes (NTs) with a doping of ruthenium oxide. These NTs were successfully used as electrodes for water oxidation in KOH. This method offers homogenous incor poration of a small amount of ruthenium oxide (≈0.12 wt %) into 25 μm TiO2 nanotubes without the need for complicated facilities or steps. The addition of H2O into electrolytes is a key step for the stable adhesion of long‐length TiO2 NT films on a substrate. The tips of the TiO2 nanotubes prepared by this novel method are not easily dissolved by electrolyte because the walls of the nanotubes are thickened by a factor of more than two in response to the addition of KRuO4 and H2O. The longest nanotubular TiO2 with a doping of ruthenium oxide and no wall dissolution shows the largest current density in the oxygen‐evolution reaction.