Influence of the electrolytes on electron transport in mesoporous TiO2-electrolyte systems

Diffusion coefficients of electrons in mesoporous TiO2-electrolyte systems axe determined by laser pulse induced photocurrent measurements in the presence of a wide range of concentration of Li+, Na+, Mg2+, tetrabutylammonium cation (TBA(+)), or dimethylhexylimidazolium cation (DMHI+) in electrolytes. The total amount of photocharge generated by a laser pulse increases in the order of DMHI+ < TBA(+) < Na+ < Li+. The diffusion coefficients (D-Amb) increase with increasing the cation density. In the case of TBA(+), the increase of the diffusion coefficients is interpreted with ambipolar diffusion mechanism. In the case of Li+, Na+, Mg2+, and DMHI+, each diffusion coefficient increases to some extent with the cation density as in the case of TBA(+), but does not fit well with ambipolar diffusion mechanism with the assumption of constant diffusion coefficient and electrons at the high density of the cations. Electron diffusion in the systems is discussed in terms of the surface cation density arising from the adsorption of cations on the films.