Improving the separation efficiency of photogenerated electron-hole pairs and the conductivity of electrons to photoanode substrates are criticalt oa chieve high-performance photoelectrochemical (PEC) water splitting.H ere, aS nS 2 /H-TiO 2 /Ti heterojunction photoanodew as fabricated with SnS 2 nanosheets vertically grown on hydrogen-treated TiO 2 (H-TiO 2 ) nanotube arrays on aT is ubstrate. It showed as ignificantly enhanced photocurrento f4 .0 mA cm À2 at 1.4 V( vs. reversible hydrogen electrode) under AM 1.5 Gi llumination, 70 times higher than that of SnS 2 /TiO 2 /Ti. Kelvin probe force microscopy measurements indicated that photogenerated electrons could be easily transported through the SnS 2 /H-TiO 2 interface but not through the SnS 2 /TiO 2 interface. Through hydrogen treatment, defects were created in H-TiO 2 nanotubes to convert type Ij unctionst ot ypeIIw ith SnS 2 nanosheets.A saresult,a high efficiency of electron-hole separation at the SnS 2 /H-TiO 2 interface and ah igh electron conductivity in H-TiO 2 nanotubes were achieved and improved PEC performance. These findings show an effective route towards high-performance photoelectrodes for water splitting.Photoelectrochemical water splitting is potentially very promising in converting solar energy into clean chemical fuels such as H 2 . [1] Photoanode materials with adequate light absorption, effective charges eparation, and high activity are desirable to construct as olar-to-fuel device with good efficiency.[2] Junctions have been shown to be effective in separating charges through variations in doping( homojunction) or offsets in the conduction and valence band levelsa tt he interface in the heterojunction. [3] Electron-hole pairs are difficult to effectively separatei nt ype Ih eterojunctions, in whicht he valence-and conduction-band edges of one moiety are embedded within those of the other moiety,b ecause both electrons and holes prefert oa ccumulate in the same moiety. [2] Spatial separation of electron-hole pairs can be achieved in type II heterojunctions, in which the valence-and conduction-band edges in one moiety are offset from those in the other moiety,s ot he electrons and holes are separated into two independent moieties across the heterojunction, resulting in longer lifetime and lower recombination rate. [4] Various type II heterostructures such as BiVO 4 /TiO 2 , [5] CdS/TiO 2 , [6] ZnS/ZnO, [7] or Fe 2 O 3 /Fe 2 TiO 5 , [8] have been designed to improve electron-hole separation efficiency.Normally,the type of band alignment between two materials is relatively set owing to their relativelyf ixed valenceand conduction-band positions if those two materials are chosen. Therefore, it would be very attractive if the type of band alignment between two materials could be altered. For example, the transition from type It ot ype II band alignment can greatly improve the performance and therefore broaden the application range of photoelectrochemical( PEC) materials. [9] TiO 2 nanotubes (NTs) have attracted wide interesti nm any photocataly...
Thin SnS2 nanosheets with {001} facets dominating were obtained with the liquid-exfoliation method and exhibit largely improved photocatalytic activity for Cr(vi) reduction.
The chemical bonding of bandgap adjustable organic semiconductors with inorganic semiconducting materials is effective in constructing a high-performance heterogeneous photoanode. In this study, a new asymmetric perylene diimide derivative molecule (N-PDI-P) was synthesized by connecting tert-butoxycarbonyl on an N-site at one end of a PDI molecule through methylene and connecting naphthalene directly onto the other end. This molecule was bonded onto the WO3 film surface, thereby forming the photoanode of organic-inorganic heterojunction. Under light illumination, the photocurrent density of chemically bonded N-PDI-P/WO3 heterojunction was twofold higher than that of physically adhered heterojunction for photoelectrochemical water oxidation at 0.6 V (vs. Ag/AgCl). Energy band structure and charge transfer dynamic analyses revealed that photogenerated electron carriers on the highest occupied molecular orbital (HOMO) of an N-PDI-P molecule can be transferred to the conduction band of WO3. The charge transfer and separation rates were accelerated considerably after the chemical bond formed at the N-PDI-P/WO3 interface. The proposed method provides a new way for the design and construction of organic-inorganic composite heterojunction.
The Cover Feature shows a SnS2 nanosheet/hydrogenated‐TiO2‐Nanotube Array Photoanode for visible light‐driven water splitting. Through hydrogen treatment, defects are created in TiO2 nanotubes, which converts a type I junction to type II in the presence of SnS2. More information can be found in the Communication by Lin, Liu et al. on page 961 in Issue 5, 2019 (DOI: 10.1002/cssc.201802691).
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