Photoelectrochemical Studies of Prussian Blue on n‐Type Semiconductor  ( n ‐ TiO₂ ) 

Electron transfer reactions in the open‐spaced crystal of Prussian blue (PB) by photo‐oxidation at a n‐type semiconductor are discussed. The reduction of PB at electrodes occurs, but the corresponding oxidation is not possible in the dark. The photo‐oxidation of Prussian white (the reduced form of PB) does occur at electrodes in aqueous solutions at potentials about 600 mV less positive than that observed at metallic electrodes. The photo‐oxidation of PB itself also occurs at electrodes at about 1100 mV less positive potentials. The fully oxidized form (Prussian brown) of PB, which can be prepared by photo‐oxidation, is stepwise reduced to PB at −0.16V and to Prussian white at −0.35V vs. SCE. The energy level is represented.