
600 Fuel Cells
the band structure in which the conduction band (CB) is separated from the
valence band (VB) by a suitable band gap. When light (of which the energy is
larger than the band gap) is irradiated, electrons (e
–
) and holes (h
+
) are gener-
ated in the CBs and VBs, respectively. The photogenerated electrons and holes
cause redox reactions similarly to electrolysis. Water molecules are reduced by
the electrons to form hydrogen and are oxidized by the holes to form oxygen
for overall water splitting. Important points in the semiconductor photocatalyst
materials are the width of the band gap and energy levels of the CBs and VBs.
The bot ...