Charge transport in nanostructured metal oxide thin film electrodes

Abstract: Nanostructured metal oxide electrodes are of great interest due to its wide field of potential applications, e.g. solar cells and batteries. The electron transport in nano-structured TiO2 and ZnO thin film electrodes was studied with time-resolved photo-currents and steady-state measurements. The results were discussed using a diffusion model for the electron transport and relations for the photocurrent transients were deduced, The experimental results were fitted to simulations giving diffusion coefficients for the electron transport of 1.5·10-5 cm2/s for TiO2 in 0.7 M LiClO4, 0.6·10-5 cm2/s for dye-sensitized TiO2 in 0.1 M KI and 1·10-4 cm2/s to 1·10-6 cm2/s, depending on potential for ZnO in 0.5 M LiC1O4.The electron transport was found to be dependent on potential, light intensity and electrolyte composition, both in time-resolved and steady-state measurements. The potential dependence was more pronounced for ZnO. Electron scavenging species in the electrolyte such as O2 was found to increase the electron losses and surface treatments with e.g. pyridine was found to decrease electron losses. The electron losses were larger for TiO2 than for ZnO.The intercalation of Li+ ions in TiO2 was studied with chronoamperometry and cyclic voltammerty. The entire area was found to be active in the intercalation process and the chemical diffusion coefficients for the insertion and extraction of Li+ were determined to 1·10-17 cm2/s and 4·10-17 cm2/s, respectively. Kinetic information about the processes was also obtained.