Environmental degradation due to the carbon emissions from burning fossil fuels has triggered the need for sustainable and renewable energy. Hydrogen has the potential to meet the global energy requirement due to its high energy density; moreover, it is also clean burning. Photoelectrochemical (PEC) water splitting is a method that generates hydrogen from water by using solar radiation. Despite the advantages of PEC water splitting, its applications are limited by poor efficiency due to the recombination of charge carriers, high overpotential, and sluggish reaction kinetics. The synergistic effect of using different strategies with cocatalyst decoration is promising to enhance efficiency and stability. Transition metal-based cocatalysts are known to improve PEC efficiency by reducing the barrier to charge transfer. Recent developments in novel cocatalyst design have led to significant advances in the fundamental understanding of improved reaction kinetics and the mechanism of hydrogen evolution. To highlight key important advances in the understanding of surface reactions, this review provides a detailed outline of very recent reports on novel PEC system design engineering with cocatalysts. More importantly, the role of cocatalysts in surface passivation and photovoltage, and photocurrent enhancement are highlighted. Finally, some challenges and potential opportunities for designing efficient cocatalysts are discussed.
Semiconducting photoelectrodes emerge as an efficient platform for converting light energy into hydrogen by photoelectrochemical (PEC) water splitting. The present study reports the improvement in PEC performance using metal oxide photoelectrodes sensitized with a narrow-band-gap semiconductor Bi 2 Se 3 , which extends the light response beyond the visible region and generates and transports charge carriers. When Bi 2 Se 3 nanoflowers (NFs) were incorporated into the TiO 2 electrode, the extent of hydrogen production was found to be increased by an order of magnitude. The binary electrode TiO 2 /Bi 2 Se 3 nanocomposite exhibited a decent photocurrent density of 1.76 mA cm −2 at 1.23 V, which is three times superior to that of pure Bi 2 Se 3 NFs. Moreover, the binary TiO 2 /Bi 2 Se 3 electrode delivers the highest solar-to-hydrogen conversion efficiency of 1.01% at 0.6 V and incident photon-to-current conversion efficiency of 10.5%. Furthermore, both Bi 2 Se 3 and TiO 2 /Bi 2 Se 3 electrodes show superior photostabilities for over 6 h. The enhanced PEC activity is attributable to the facile transportation of photoelectrons from Bi 2 Se 3 to TiO 2 electrodes, thereby minimizing the charge recombination.
Visible-light-active
photoelectrodes are more responsive to high-energy
conversion efficiency in photoelectrochemical (PEC) water splitting.
In this work, we fabricated a bismuth sulfide@reduced graphene oxide
(Bi2S3@rGO) nanocomposite photoanode via facile
synthetic methods. Typical results show that the Bi2S3@rGO nanocomposite exhibited a high photocurrent density of
6.06 mA cm–2 and a maximum applied bias photon-to-current
efficiency (ABPE) of 4.2% at 0.32 V. Moreover, Bi2S3 nanorods have more uniform dispersion on the surface of rGO
sheets in the Bi2S3@rGO composite as demonstrated
in the transmission electron microscopy images. In addition, photoluminescence
and impedance studies reveal the enhanced charge-transfer properties
in the Bi2S3@rGO photoelectrode. The enhanced
PEC performance of the composite could be attributed to the effective
visible-light absorption of Bi2S3 and the good
electron-transfer properties of highly conductive rGO nanosheets,
facilitating the charge separation and transportation, leading to
the inhibition of charge recombination.
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