INVESTIGATION OF THE POTENTIAL DISTRIBUTION IN POROUS NANOCRYSTALLINETIO2 ELECTRODES BY ELECTROLYTE ELECTROREFLECTION

In order to investigate the potential distribution in porous nanocryst alline TiO2 electrodes, an electrolyte electroreflection (EER) study h as been undertaken. With front-side illumination a weak featureless su b-bandgap EER response is obtained due to surface states present at th e TiO2/electrolyte interface. Back-side illumination (through the indi um tin oxide (ITO) coated glass support) results in EER spectra with a clear feature in the bandgap region, probably due to electric field m odulation in TiO2 particles located at the ITO/TiO2 interface. In indi fferent aqueous electrolyte, steady-state photocurrent generation in p orous nanocrystalline TiO2 electrodes is essentially independent of th e 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 Scien ce S.A.