Efficient and cost-effective production of hydrogen gas from
water using sunlight as the ultimate energy source is one of the
major challenges for researchers in the 21st century. In recent
years, promising results have been reported using semiconductor
materials for the photodriven hydrogen production.
1−10 When a semiconductor material is irradiated by light
with energy higher than its optical band gap (BG), an electron
of the valence band (VB) is promoted to the conduction band
(CB) leaving a hole in the VB. Subsequently, the electrons and
holes migrate to the surface of the semiconductor where they
can be used for the reduction of protons and the corresponding
oxidation process, respectively (black arrows in Figure 1).
However, a major drawback of these systems is that the
semiconductor photocatalytic activity is limited by undesired
radiative and nonradiative recombination processes that occur
in the semiconductor crystal lattice competing directly with the
charge migration and the catalytic process (red arrows in Figure
1).