| Abstract
| - Processes in the dark of electron transport and recombination in several nanoporous titanium dioxide filmshave been studied as a function of the applied potential, using the electrochemical impedance technique.Contact and bulk characteristics have been identified, decoupled, and interpreted, applying a transmissionline model that identifies the following elements: (i) the capacitance of the interface between the exposedsurface of the substrate and the electrolyte, (ii) the electron transport resistance, (iii) the charge-transfer resistancedistributed in the TiO2/electrolyte interface, and (iv) a distributed capacitive element related to charging theporous matrix. The model provides a satisfactory description of the spectra in widely different conditions ofconductivity of the TiO2 phase. The electron conductivity has been determined as a function of applied potentialand coincides for the different samples under study. Classical electrochemical frameworks of transport andinterfacial charge transfer used in porous electrodes do not explain the obtained parameters completely. Amore complete framework is suggested to explain the system on the basis of the following characteristicfeatures: (i) existence of a large density of electron traps, giving rise both to a trap-limited mobility and toan exponentially increasing capacitance, and (ii) band-edge shifts under external polarization potential.
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