ZnO films on ITO substrates were grown in the nitrate solution at 90 degrees C upon the seed layer prepared by bias-assisted deposition and thermal annealing at 500 degrees C. High concentration of the nitrate solution of 0.5 M compared with 0.1 M results in the formation of three-dimensional skeleton of the seed layer which coarsened into the brush-like ZnO nanostructure. The films, however, exhibit large leakage currents, which is firstly ascribed to the incomplete coverage of the ITO substrate. The formation of dense sublayer formation e.g. by increased electrochemical deposition time and the nanostructured overlayer can result in high performance ZnO photoanode. For the frequency-independent estimation of the flat-band potential of the non-ideal Schottky barrier behavior of the ZnO photoanodes, capacitance spectroscopy is applied for the potential range corresponding to the reverse-bias regime of the Schottky barrier. The shift in the flat-band potential suggests the different ZnO interface characteristics resulted from the preparation conditions. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.