Photoimage formation in a TiO2 particle-incorporated prussian blue film

An indium-tin oxide (ITO) electrode coated with prussian blue (PB) film containing TiO2 particles (PB[TiO2]/ITO electrode) was prepared by electrochemical deposition of PB in the presence of suspended TiO2 particles. Irradiation of the prepared film with a high pressure mercury are lamp in a solution containing methanol as an electron donor caused photoinduced reduction of PB to colorless prussian white (PW). Irradiation of a spot on the PB[TiO2] film, however, did not restrict the reduction of PB to the irradiated part, rather the reduction area spread beyond the irradiation zone, the extent being larger with increasing irradiation time. The electron transport from the photoproduced PW to the surrounding PB through the conducting ITO substrate was found to be responsible for the observed spread. Area-selective photoreduction of PB to PW was successfully achieved by inserting a thin ferrocenylmethyltrimethylammonium (FA)-bound Nafion between the PB[TiO2] and ITO to give a PB[TiO2]/Nafion[FA]/ITO electrode. The preparation of this bilayer electrode was accomplished by electrochemically depositing a PB[TiO2] layer onto a Nafion[FA]-coated ITO electrode. FA in the Nafion layer blocked electrochemical reduction of PB to PW, but mediated oxidation of the photoproduced PW. White images were successfully formed in the blue films of the bilayer electrodes by irradiation under open-circuit condition.