The integrated architecture enables the Ta3N5photoanode to approach the theoretical photocurrent limit for solar water splitting.

BiVO4 and many other semiconductor materials are ideal visible light responsive semiconductors, but are insufficient for overall water splitting. Upon loading water oxidation cocatalyst, for example Co-borate (denoted as CoBi) used here, onto BiVO4 photoanode, it is found that not only the onset potential is negatively shifted but also the photocurrent and the stability are significantly improved. And more importantly, PEC overall water splitting to H2 and O2 is realized using CoBi/BiVO4 as photoanode with a rather low applied bias (less than 0.3 V vs. counter electrode) in a two-electrode scheme, while at least 0.6 V is needed for bare BiVO4. This work demonstrates the practical possibility of achieving overall water splitting using the PEC strategy under a bias as low as the theoretical minimum, which is the difference between the flat band and proton reduction potential for a photoanode thermodynamically insufficient for water reduction. As long as the water oxidation overpotential is overcome with an efficient cocatalyst, the applied bias of the whole system is only used for that thermodynamically required for the proton reduction.

Halide perovskites have attracted increasing scientific interests for photocatalysis because of their remarkable opto‐electronic properties, such as optimal band structures, long charge carrier lifetimes, high photoluminescence quantum yields, and so on. However, pure halide perovskites generally face problems of low stability, lack of active sites, and ineffective extraction of carriers, which limit their applications in photocatalytic reactions. To improve the photocatalytic activity and stability, halide perovskites are composited with other materials. Herein in this mini review, we summarize the recent progresses on the design and development of halide perovskite composites for various photocatalytic reactions including photocatalytic CO2 reduction reaction, photocatalytic hydrogen evolution reaction, photocatalytic pollutant degradation reaction, and so on. Finally, an outlook of halide perovskite for photocatalysis is provided to point up the future challenges and the possible solutions.

Porous chalcogels CoMoS 4 and NiMoS 4 made by a facile solution reaction displayed good electrocatalytic activity in the redox reaction of the I À /I 3 À shuttle. Dye-sensitized solar cells with these ternary compounds as counter electrodes (CEs) showed photovoltaic performance similar to the devices made with noble metal platinum CE (7.46%).Dye-sensitized solar cells (DSSCs) have attracted significant attention as low-cost alternatives to traditional photovoltaic devices. 1,2 In DSSCs, counter electrodes (CEs) with both excellent electrocatalytic activity and high electrical conductivity are indispensable to obtain a low overvoltage and to accelerate the regeneration of I À from I 3 À . Due to the fact that noble metal Pt, the most widely used material for CEs at present, is very expensive, studies have recently been made extensively on low-cost Pt-like alternatives, including carbonbased materials, 3 conducting polymers, 4 and metals in the form of oxides, 5 sulfides, 6-10 selenides, 11 nitrides, 12 and carbides, 13 and great promise has been demonstrated in this field. Extension of the CE materials to ternary compounds may greatly expand this research platform. Catalysts based on molybdenum or tungsten sulfides have been widely used for hydrodesulfurization and hydrogen evolution reaction by electrocatalysis, and introduction of Co or Ni promoters into these matrices results in significant enhancement in the catalytic activities. 14-16 Kanatzidis et al. 17 have most recently reported the synthesis of porous CoMoS 4 and NiMoS 4 via facile solution reactions. In this work, we have applied these ternary materials with and without graphite additives as the counter electrodes in DSSCs. The resulting photovoltaic devices showed power conversion efficiency up to 7.31%, comparable to the DSSCs made with an expensive platinum-based counter electrode (7.46%).Ammonium tetrathiomolybdate (NH 4 ) 2 MoS 4 was obtained by the reaction of (NH 4 ) 6 Mo 7 O 24 Á4H 2 O and (NH 4 ) 2 S aqueous solution at ambient temperature. CoMoS 4 and NiMoS 4 were synthesized as previously described. 17 Briefly, Co(NO 3 ) 2 Á6H 2 O, Ni(NO 3 ) 2 Á6H 2 O and (NH 4 ) 2 MoS 4 were dissolved in formamide separately, and then Co or Ni precursor solution was added into the tetrathiomolybdate solution. In these reactions, cationic species of VIII group metals interacted with thiomolybdate anions, leading to precipitation of solids. As the polymerization proceeded, the viscosity of the solution increased, which eventually solidified to a monolithic black gel. It took 7-14 days for the viscous solution to transform into a rigid gel. The products were then annealed at 300 1C in a nitrogen atmosphere and characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), scanning and high-resolution transmission electron microscopy (HRTEM).Both Ni-and Co-based chalcogels were found to be amorphous, as indicated by the predominant broad features in the XRD patterns (Fig. S1, ESI †). A similar resu...

Barium tantalum oxynitride (BaTaON) with an absorption edge of ca. 660 nm is one of the most promising photocatalysts for solar water splitting, and is usually synthesized by nitriding a mixture of Ba and Ta-containing compounds with a Ba/Ta molar ratio of unity under ammonia flow at high temperature, usually causing a high density of defect sites. Herein, we introduce a novel synthesis method for BaTaON (BTON) by employing Ba-rich LiBaTaO, prepared by a flux method, as a precursor of nitridation. As a comparison, BaTaO was prepared by conventional solid state reaction and used as the precursor. The as-nitrided samples were correspondingly denoted as BTON-Flux and BTON-SSR. It was found that well-crystallized BTON oxynitride can be similarly obtained by both methods, but the BTON-Flux sample exhibits significantly decreased defect density and enhanced surface area relative to the BTON-SSR sample. As a result of their structural differences, the photocatalytic water splitting performance of the BTON-Flux sample, regardless of the H-evolving half reaction in the presence of methanol or Z-scheme overall water splitting, is much better than that of BTON-SSR. This study may open up a novel strategy for preparing oxynitride photocatalyst with decreased defect density for the promotion of solar water splitting.

LaTiO N photocatalysts were prepared by thermal ammonolysis of flux-synthesized La Ti O and La TiO , and were investigated for water oxidation. Though LaTiO N derived from La TiO appears defect-free by UV/Vis/near-IR and electron paramagnetic resonance (EPR) spectroscopy, its performance is much lower than that of conventional La Ti O -derived LaTiO N with defects. It is shown by Mott-Schottky analysis that La TiO -derived LaTiO N has significantly lower donor density; this can result in insufficient built-in electric field for the separation of photogenerated electrons and holes. The lower donor density is also consistent with the smaller difference between the Fermi level and the valence-band maximum, which accounts for a lower oxidative power of the holes. In light of this discovery, the donor density was increased substantially by introducing anion vacancies through annealing in Ar. This resulted in improved performance. The CoO -assisted La TiO -derived LaTiO N annealed at 713 °C has a higher quantum efficiency (25 %) at 450 nm than high-performance conventional CoO /LaTiO N (21 %).

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