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R. Jagenteufel:
"Synthesis and electrochemical chracterization of mesoporous Nb2O5 films";
Betreuer/in(nen): D. Eder; Institut für Materialchemie, 2019.

Fundamental investigations on photochemical and electronic properties of photocatalytically active electrodes require well-defined model systems. We designed ordered mesoporous thin films with uniform pore size distributions and homogeneous pore structures by combining a sol-gel process with evaporation induced self assembly (EISA) and spin coating to synthesize mesoporous niobium pentoxide thin films on substrates for electrochemical characterization. The thin film production was optimized tuning the precursor solution and parameters like spin coating speed, relative humidity level during solvent evaporation and furnace temperature.

The main aim of this work and the reason for using mesoporous films was to eliminate contact resistance with the electrode while allowing a maximum interface with the surrounding gas phase. This concept could be proved by impedance spectra featuring one semicircle solely.

We found that temperatures above 350 °C led to a linear increase of resistance over time. According to our hypothesis this is due to a diffusion process of oxygen vacancies originally located at the surface into the bulk material as well as due to the surface reaction . By consuming electrons as well as oxygen vacancies the amount of free charge carriers is reduced, thus increasing the measured impedance. By altering the measurement conditions we found that UV-irradiation, oxygen partial pressure variation and humidity level strongly influence the effective conductivity. This opens not only the field of photocatalytically active electrodes but also humidity and gas sensing as possible fields of application for the studied material.