Photoelectrochemical (PEC) water splitting represents a promising route to convert solar energy into clean hydrogen. Constructing tandem cells has emerged as a feasible approach and attracted tremendous attention for self-biased water splitting, especially using low-cost and stable metal oxides. Herein, a state-ofthe-art review of metal oxide-based PEC/photovoltaic (PV) tandem cells and PEC tandem cells is comprehensively presented, with a focus on crucial issues of designing efficient tandem devices from the aspects of the photoanodes, photocathodes, and photovoltaics. Different device configurations and efficiency limitations of tandem cells are introduced, and advances of metal oxide-based PEC/ PV and PEC tandem cells in terms of material design and device optimization are discussed. Metal oxide-based tandem cells have shown solar-to-hydrogen efficiencies of ∼8%, which is approaching practicality. Perspectives on remaining challenges and potential strategies are outlined.
Ag3PO4 has been reported to be an excellent
photocatalyst for O2 evolution from aqueous solution, which
makes it a promising candidate for designing a Z-scheme water-splitting
system. In this work, in order to further improve the photocatalytic
activity, a series of SrTiO3/Ag3PO4 composite photocatalysts was constructed by introducing SrTiO3 (with a less positive valence band minimum) to Ag3PO4 and was synthesized by two consecutive hydrothermal
processes. The obtained photocatalysts were systematically characterized
by XRD, SEM, BET, UV–vis, etc., showing that SrTiO3/Ag3PO4 composites were formed by coating SrTiO3 onto a Ag3PO4 polyhedron. Photocatalytic
O2 evolution results demonstrated that a small amount of
SrTiO3 brought about significant enhancement of photocatalytic
activity of Ag3PO4 and that the apparent quantum
yield at 420 nm reached 16.2% with a molar ratio of SrTiO3 to Ag3PO4 equal to 1/20, which led to the
fact that SrTiO3 could serve as cocatalyst for water oxidation
providing both accelerated electron–hole separation by band
gap alignment and more active sites by enlarged surface area.
Large-scale,
clean, efficient, and sustainable hydrogen production
from water is one of the major goals in solar-to-fuel conversion as
the sun and water represent the two most abundant and geographically
balanced free resources available on earth. Considering that most
of the liquid water available on the earth’s surface is present
in the form of seawater, H2 generation from seawater splitting
is highly desirable for large-scale practical and economical application.
Herein, we report on the first demonstration of direct efficient overall
solar-driven seawater splitting on p-GaN-based nanowire
arrays without any external bias or sacrificial agents from various
types of simulated seawater solutions. A stable solar-to-hydrogen
(STH) conversion efficiency of 1.9% was obtained under concentrated
irradiation, demonstrating its possible utilization for the large-scale,
environmentally friendly, sustainable generation of clean solar fuel.
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