Organic Electrosynthesis - Fundamentals and Applications of Organic Electrochemistry - page 274

fluoride is formed in the bulk of the graphite,
resulting in suppression of the Faradaic
current. In sharp contrast, only the surface of
the BDD electrode is fluorinated, therefore it
maintains its electroconductivity [116]. Since it
is stable to hydrogen fluoride, this electrode is
expected to be useful for the preparation of
fluorine gas.
6.13 Photoelectrolysis and
Photocatalysis
6.13.1 Photoelectrolysis
When a semiconductor electrode is irradiated,
charge separation occurs to generate electron
(e)-hole (h + ) pairs. The generated electron
works as a reductant, while the hole works as an
oxidant. Honda and Fujishima demonstrated
for the first time the possibility of such
photosensitized electrolysis using the n-type
semiconductor TiO 2 and Pt electrodes, as
shown in Figure 6.34 [117]. When the surface of
the TiO 2 electrode is irradiated with a
wavelength shorter than 410 nm, current flows
to generate oxygen and hydrogen at the
surfaces of the TiO 2 and Pt electrodes,
respectively. TiO 2 is excited under irradiation
to generate electron-hole pairs, and the holes
in the valence band move to the surface,
resulting in oxidation of water, while the
electrons in the conduction band move into the