Influence of sintering temperature, pressing, and conformal coatings on electron diffusion in electrophoretically deposited porous TiO2

The electrophoretic deposition of nanoporous $\mathrm{Ti}{\mathrm{O}}_2$ layers allows us to investigate separately the influence of sintering temperature, porosity, and conformal surface coatings on the effective diffusion coefficient $\left(D_{\mathrm{eff}}\right)$ of excess electrons in porous layers. Photocurrent transients were measured to obtain $D_{\mathrm{eff}}$ in nanoporous $\mathrm{Ti}{\mathrm{O}}_2$ layers immersed in aqueous electrolyte. The applied treatments control parameters such as the contact between interconnected nanoparticles, the coordination of nanoparticles in the porous network, and the surface passivation of $\mathrm{Ti}{\mathrm{O}}_2$ nanoparticles. The hierarchy of the different factors for transport optimization in porous $\mathrm{Ti}{\mathrm{O}}_2$ is discussed. Under fixed geometry of the nanoporous network, trapping on surface states can strongly limit electron diffusion in porous $\mathrm{Ti}{\mathrm{O}}_2$ .