Mott-Schottky analysis of flower-like ZnO microstructures with constant phase element behavior

ZnO was prepared using room temperature bipolar electrochemical process in deionized water. Electron microscopy, powder X-ray diffraction, and micro-Raman spectroscopy showed crystallization of the material into the wurtzite hexagonal structure of ZnO, self-organized in micro-sized flower-like shapes that are formed out of individual nanorods preferentially grown along the < 0 0 0 1 > direction. The intrinsic electronic properties were evaluated by potentiodynamic electrochemical impedance spectroscopy using Mott-Schottky analysis of semiconduc-tor/liquid junctions. Because the flat band and carrier density are frequency-dependent, we used an approximation based on fractional order capacitance fitting, and subsequently three different ways to calculate the frequency-independent effective capacitance of the system. The capacitance computed using the four parameters of single-dispersion Randle's model, i.e., pseudocapacitance, dispersion coefficient, and series and parallel resistances, is more recommended for the characterization of the electrochemical system. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim