The role of electrochemical impedance spectroscopy (EIS) in the global characterisation of the reduction kinetics of hexacyanoferrate on anodised titanium

To quantify the charge transfer (ct) step during the reduction of hexacyano ferrate, it is studied at a galvanostatically anodised polycrystalline Ti e lectrode, for which a ct controlled current can be observed over a large po tential domain. In particular, the present study aims the characterisation of the electrode semiconducting properties (flat band potential E-fb and do nor density N-D), in contact with the hexacyanoferrate system. Hereto, the use of EIS is essential for the determination of the space charge capacitan ce (C-sc) of the TiO2 layer, as a function of the applied potential E. A me thodology is proposed to determine C-sc in a convenient way. In the high fr equency range of the EIS measurements, only the solid state properties are being probed, and a simple series R-C-sc equivalent circuit becomes suitabl e. The validity of this method is checked through the analysis of different equimolar redox solutions. Finally, the values of E-fb and N-D are determined from the obtained non-li near Mott-Schottky plots (C-sc(-2) vs E). In particular, the donor density N-D is computed numerically from the instantaneous slope, by solving a fini te difference equivalent of the relation for different discrete N-D(E) valu es. (C) 1999 Elsevier Science Ltd. All rights reserved.