Testing whether the non-faradaic process is due to intercalated protons in the a-TiO2 material was carried out by performing EIS in an aprotic solvent during ferrocenium reduction. To remove all possible intercalating species from the electrolyte, tetrabutylammonium hexafluorophosphate was used as a supporting electrolyte in acetonitrile. Subsequently, a lithium hexafluorophosphate electrolyte was used for comparison purposes. As with the proton, Li + is also able to intercalate into a-TiO2. Therefore, if intercalation is the root cause of the non-faradaic process observed in a-TiO2 protected photocathodes, a clear difference between experiments using these two different supporting electrolytes should be observed.