Diffusion limitations to I3-/I- electrolyte transport through nanoporous TiO2 networks

Abstract

Diffusion limitations due to triiodide transport through nanoporous TiO2 networks are investigated with the help of a simple device structure, a nanoporous TiO2 layer directly sintered onto a platinum electrode and immersed in an I3-/I- electrolyte solution. At voltages below 0.3 V, electronic transport in this device is dominated by the catalytic reaction at the Pt/electrolyte interface whereas above approximately 0.4 V current flow is limited by diffusion of triiodide through the nanoporous TiO2 network. Through the analysis of devices with different TiO2 layer thickness and I2 concentrations we calculate a diffusion constant for I3- of 1.24 (±0.02) × 10-5 cm2 s-1 in the bulk of the electrolyte and an effective diffusion constant of 0.44 (±0.02) × 10-5 cm2 s-1 within the pores of the TiO2 network.