Page 8 - Read Online

Page 4 of 21 Liu et al. Microstructures 2023;3:2023001 https://dx.doi.org/10.20517/microstructures.2022.23

Figure 2. Schematic diagram of photogenerated hole modulation strategies in photoelectrocatalysis.

cocatalyst loading have been developed. The modification of nanostructure regulates the electrostatic field
on the surface of the catalyst and promotes the migration of holes. The construction of a heterojunction can
realize hole extraction through charge transfer between two semiconductor materials with different energy
level positions. The loading of a cocatalyst can effectively extract the photogenerated holes and carry out
surface reactions by means of energy level matching with the valence band of the semiconductor.

Hole sacrificial agents
In PEC catalysis, the photogenerated holes migrate to the active site and then accumulate, which affects the
subsequent hole migration. The consumption of holes can ensure that the subsequent holes continue to
migrate and improve the PEC efficiency. Commonly used sacrificial agents in PEC systems include Na S-
2
Na SO 3 [20,21] , triethanolamine (TEOA) [22,23] and H O 2 [24-26] and these have been widely used to evaluate
2
2
interfacial charge transfer properties. Thorne et al. measured the photocurrent-voltage curves of a hematite
photoanode and found that the photoanode with H O as hole scavengers has lower onset potential
2
2
values . This means that there will be fewer photogenerated holes accumulated on the surface of the
[24]
photoanode after inducing hole scavengers . Unfortunately, the introduction of excess sacrificial agents
[24]
not only increases the cost but also results in secondary chemical pollution . Alternatively, it is also an
[27]
important research direction to transform sacrificial agents into value-added chemicals through selective
organic synthesis reactions and to cooperate with electrons in the reduction reaction . However, this
[28]
process remains a major challenge. According to the current research background, researchers mainly
prefer to develop efficient PEC catalysts without the use of sacrificial agents.
Nanostructural modification
As mentioned above, researchers are currently working on developing efficient PEC catalysts that do not
use sacrificial agents. PEC performance is sensitive to the electrode surface structure. The valence band