In order to understand the behavior of electrons in complex porous structures, we have simulated electron diffusion processes in complex porous structures that have been fabricated using a system for a three-dimensional porous structure simulator, POCO2. For a given porosity, as the overlap ratio representing a necked porous TiO2 structure increased, the coordination number of TiO2 particles increased, resulting in an increase in electron flux and a decrease in trapping time. To gain better insights, we simulated the diffusion of electrons using models with different particle size distributions. This study shows that for a narrower size distribution of TiO2 particles, a better electron diffusion process is realized. This result can be ascribed to the formation of a better TiO 2 coordination network. Consequently, through this study, we have shown that a well-formed neck between TiO2 particles improves the electron diffusion properties of a complex porous material.