Investigation of the potential distribution in porous nanocrystalline TiO2 electrodes by electrolyte electroreflection

In order to investigate the potential distribution in porous nanocrystalline TiO2 electrodes, an electrolyte electroreflection (EER) study has been undertaken. With front-side illumination a weak featureless sub-bandgap EER response is obtained due to surface states present at the TiO2/electrolyte interface. Back-side illumination (through the indium tin oxide (ITO) coated glass support) results in EER spectra with a clear feature in the bandgap region, probably due to electric field modulation in TiO2 particles located at the ITO/TiO2 interface. In indifferent aqueous electrolyte, steady-state photocurrent generation in porous nanocrystalline TiO2 electrodes is essentially independent of the applied potential. Polarising the nanoporous electrode close to the flat-band potential results in filling of surface states, which causes marked effects on the front- and back-side EER signals as well as on the alternating-photocurrent response. Surface states are located ca. 0.4 eV below the conduction band edge of TiO2. (C) 1997 Elsevier Science S.A.