Diffusion Limitations to I[sub 3][sup −]/I[sup −] Electrolyte Transport Through Nanoporous TiO[sub 2] Networks

Diffusion limitations due to triiodide transport through nanoporous networks are investigated with the help of a simple device structure, a nanoporous layer directly sintered onto a platinum electrode and immersed in an 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 network. Through the analysis of devices with different layer thicknesses and concentrations we calculate a diffusion constant for of 1.24 in the bulk of the electrolyte and an effective diffusion constant of 0.44 within the pores of the network. © 2003 The Electrochemical Society. All rights reserved.