Electron transfer from TiO2 to iodine/iodide electrolytes proceeds via reduction of either I3p>鈥?/sup> or uncomplexed I2 (free iodine), but which route predominates has not previously been determined. By measurement of the electron lifetime while independently varying free iodine or I3p>鈥?/sup> concentrations, we find the lifetime is correlated with free-iodine concentration and independent of I3p>鈥?/sup> concentration. This trend supports the hypothesis that electron recombination to the electrolyte occurs predominantly by iodine reduction rather than reduction of triiodide.