Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

MoS2/CdS rod-like nanocomposites as high-performance visible light photocatalyst for water splitting photocatalytic hydrogen production

This study demonstrates a high-performance visible-light-driven photocatalyst for water splitting H₂ production. CdS nanorods (30 nm in diameters) with shorter radial transfer paths and fewer defects were prepared by a solvothermal method. To mitigate the recombination of electrons and holes, MoS₂ nanosheets with rich active sites were modified on the surface of CdS nanorods by a room-temperature sonication treatment. The photocatalytic water splitting tests show that the MoS₂/CdS nanocomposites exhibit excellent H₂ evolution rates. The highest H₂ evolution rates (63.71 and 71.24 mmol g^?1h^?1 in visible light and simulated solar light irradiation) was found at the 6% MoS₂/CdS nanocomposites, which was 14.61 times and 13.39 times higher than those of the corresponding pristine CdS nanorods in visible light and simulate solar light irradiation, respectively. The apparent quantum efficiency (AQE) of the 6% MoS₂/CdS nanocomposites at 420 nm was calculated to be 33.62%. The electrochemistry tests reveal that the enhanced photocatalytic activity is a result of extra photogenerated charge carries, greatly enhanced charge separation and transfer ability of the MoS₂/CdS composites. This study may give new insights for the rational design and facile synthesis of high-performance and cost-effective bimetallic sulfide photocatalysts for solar-hydrogen energy conversion.     

Highly efficient photocatalytic conversion of gas phase CO2 by TiO2 nanotube array sensitized with CdS/ZnS quantum dots under visible light

With the massive consumption of fossil fuels, energy crisis and effectively reducing CO₂ to curb global warming have become urgent and severe problems in the world. Photocatalytic conversion of CO₂ technology which can convert CO₂ into combustible compounds by using solar energy can solve both of the problems mentioned above. However, the photocatalytic conversion of CO₂ exhibits too low efficiency, especially under visible light. So, in order to improve the photocatalytic efficiency, the composite photocatalysts of TiO₂ nanotube array (TNTA) sensitized by CdS/ZnS quantum dots (QDs) were successfully prepared by anodization method and successive ionic layer adsorption and reaction (SILAR) method in this work. And the composite photocatalysts exhibited a high performance for photocatalytic conversion of gas-phase CO₂ to methanol under visible light. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), and X-ray photoelectric spectroscopy (XPS) were employed to characterize the ingredients and morphologies of the synthesized photocatalysts. And, UV–vis diffuse reflectance spectra (UV–Vis DRS) revealed that CdS/ZnS QDs enhanced the photo-absorption of composite photocatalyst in the visible light region. The main product methanol yield of CdS/ZnS-TNTA under visible light was 2.73 times that of bare TNTA when TNTA was treated by 10 SILAR cycles. Meanwhile, the product yield first increased before decreasing with the increase of the CO₂ flow rate. And the greatest product yield reached up to 255.49 nmol/(cm²-cat·h) with the increase of light intensity. The reaction mechanism was discussed in this paper. This high performance for photocatalytic reduction of CO₂ was primarily attributed to the CdS/ZnS QDs sensitization, which widens the response wavelength range of the catalyst to include visible light and partly inhibits the recombination of electron-hole pairs.     

Additional electron transfer channels of thermostable 0D Cs(Pb: Pt)Br3 perovskite quantum dots /2D accordion-like Ni-MOF nanojunction for photocatalytic H2 evolution

Overcoming the low charge transfer efficiency and poor photothermal stability of halide perovskite quantum dots (QDs) is the booster to achieve photocatalytic applications. In this paper, the Pt²⁺-doped CsPbBr₃ QDs/two-dimensional accordion-like Ni-MOF (CPPB QDs/Ni-MOF) composite was firstly synthesized by fixing the CPPB QDs into the pores of Ni-MOF. Electron separation and transfer efficiency were analyzed by PL spectra and electrochemical data. The photocatalyst exhibited outstanding photocatalytic performance in hydrogen (H₂) evolution. The optimal H₂ evolution efficiency of the composite reached 153.6 μmol h^?1, which was about 9 times than that of pure Ni-MOF and remained 134.8 μmol h^?1 after the cycle test. The splendid efficiency could be benefited from the advantages of 2D layered structure of Ni-MOF and the high charge separation and transmission efficiency of CPPB QDs. Finally, the mechanism of electron migration and additional electron transfer channels between composite interfaces was further demonstrated by density functional theory (DFT) calculations. The present work opens up a novel perspective for photocatalytic applications of doped halide perovskite QDs/Ni-MOF nanocomposites.     

Efficient quantum dot-sensitized solar cell with polystyrene-modified TiO2 photoanode and with guanidine thiocyanate in its polysulfide electrolyte

Monodispersed polystyrene (PS, ca. 300 nm) latex particles are incorporated into a TiO₂ film. A polystyrene-modified TiO₂ film (M-TiO₂) with micro-cluster structure, containing micro/nano-composite pores is thus obtained after sintering. Cadmium sulfide (CdS) quantum dots (CdS-QDs) are accumulated over M-TiO₂ and bare TiO₂ films (B-TiO₂) by successive ionic layer adsorption and reaction (SILAR); we designate these films as M-TiO₂/CdS and B-TiO₂/CdS, respectively. Influence of SILAR cycles used for depositing CdS on B-TiO₂ and M-TiO₂ films on the performance of the pertinent quantum dot-sensitized solar cells (QDSSCs) is studied. The QDSSC with 6 SILAR cycles of M-TiO₂/CdS (M-TiO₂/CdS6) exhibited a solar-to-electricity conversion efficiency (η) of 1.79%, while the cell with B-TiO₂/CdS5 shows an η of 1.35%, under the illumination of one sun. Moreover, guanidine thiocyanate (GuSCN) is found to be a promising additive to the polysulfide electrolyte. The additive renders higher conversion efficiency (2.01%) to its QDSSC. Durability of the CdS-QDSSC is also tested. Scanning electron microscopy (SEM) is used to obtain the images of TiO₂ films and energy-dispersive X-ray spectroscopy (EDX) is employed to study the stoichiometric ratios of M-TiO₂/CdS and B-TiO₂/CdS. Incident photon-to-current conversion efficiencies (IPCE) of the QDSSCs are obtained to confirm the J_SC behaviors of the cells.     

Near-infrared CdSexTe1-x@CdS “giant” quantum dots for efficient photoelectrochemical hydrogen generation

Colloidal quantum dots (QDs) have attracted a lot of attention due to their unique optoelectronic properties. They have been widely used as building block materials for solar technologies such as solar cell, and photoelectrochemical (PEC) water splitting. Hydrogen generation by using QDs as photocatalysts has emerged a promising application in PEC devices. However, it is still very challenging to obtain high-efficiency PEC devices due to the limited absorption wavelength of QDs and the existence of surface traps which prohibit the efficient charge transfer. In this work, we synthesized ternary CdSe_xTe_1-x/CdS (CdSeTe/CdS) “giant” QDs to extend the light absorption to near infrared, matched well with Sun's spectrum. The as-synthesized CdSeTe/CdS “giant” QDs exhibit quasi-type II band alignment as confirmed by its long lifetime and red-shifted emission peak compared with bare CdSeTe QDs. The wide absorption range of “giant” core/shell QDs and their long lifetime can improve the efficient absorption of Sun's spectrum and charge transfer. As a proof-of-concept, a PEC device using QDs sensitized TiO₂ mesoporous thin film as a photoanode was used for hydrogen production. The corresponding photocurrent density was increased to 3.0 mA/cm² with the introduction of CdS shell, which is 1.5 times higher than the PEC device using CdSeTe QDs. This study indicates that ternary or polynary alloyed core/shell QDs can be used as promising optoelectronic materials for applications of PEC devices.     

Development of high quantum efficiency CdS/ZnS core/shell structured photocatalyst for the enhanced solar hydrogen evolution

Development of co-catalyst free, core/shell structured photocatalyst with ultra-thin shell is of great importance towards the stable and continuous hydrogen (H₂) production, where the shell prevents photo-corrosion of the core for longer stability with continuous H₂ generation. Accordingly, herein, we report a one-step, surfactant free hydrothermal process for synthesis of high-efficient CdS/ZnS core/shell structured catalyst for H₂ evolution under natural solar light. The structural and morphological characterizations using XRD and TEM techniques revealed the formation of phase pure CdS/ZnS system, with core and shell thickness of 395 and 15 nm, respectively. XPS studies revealed that the constituted elements in system exist in their native oxidation states, which indicated the stable structural integrity of the individual phase in the core/shell structure. The synergistic optical properties of CdS/ZnS showed the absorption edge around 500 nm and the decreased PL intensity indicated the improved charge recombination resistance in the system. The parametric studies such as synthesis time, core diameters and shell thickness optimization were conducted to study the formation kinetics of the core/shell structure and their photocatalytic efficiencies. Accordingly, the optimized core/shell catalyst showed around 763 and 2.4 folds superior activity when compared to the pristine CdS and ZnS, respectively. Further, the catalyst showed excellent stability for over 100 h with quantum efficiency of 8.78% under the irradiation of 20 W LED light at 420 nm. Based on the obtained results, the observed improved photocatalytic quantum efficiency could be ascribed to their synergistic effects of CdS and ZnS towards increased charge separation and spatial distributions of the carriers due to their core/shell configuration of the materials.     

Efficient photocatalytic hydrogen evolution with high-crystallinity and noble metal-free red phosphorus-CdS nanorods

The photocatalytic production of H₂ by low-cost semiconductors is a promising approach to store solar energy. Photocatalysts with heterojunctions convert visible light into H₂ faster because of more efficient charge separation. The morphology, the structure, and the crystallinity are additional factors to consider when developing a photocatalyst. Here, highly-crystalline CdS nanorod (NR) were synthesized by a facile one-pot process. Under visible light, pure CdS NR produced H₂ 2.1 times faster than conventional CdS nanoparticles (NP). CdS NR were then combined with the semiconductor red phosphorus (RPh). A CdS NR-based heterojunction photocatalyst with RPh_5% had an excellent photocatalytic H₂ evolution rate of 11.72 mmol g⁻¹ h⁻¹, which was 3.6 times higher than pure CdS NR. The apparent quantum efficiency of RPh_5%/CdS NR was 19.57%. Furthermore, RPh_5%/CdS NR exhibited a superior photogenerated charge separation efficiency and was stable with little photocorrosion compared to CdS NP showing the high potential of this heterojunction photocatalyst.     

Vanadium diboride as an efficient cocatalyst coupled with CdS for enhanced visible light photocatalytic H2 evolution

Exploiting active, stable, and cost-efficient cocatalysts is crucial to enhance the photocatalytic performance of semiconductor-based photocatalysts for H₂ evolution from water splitting. Herein, we report on using vanadium diboride (VB₂) as an efficient cocatalyst to enhance the photocatalytic H₂ evolution performance of CdS nanoparticles under visible light irradiation (λ ≥ 420 nm). The CdS/VB₂ composites prepared by a facile solution-mixing method exhibit much improved H₂ evolution activities in 10 vol% lactic acid (LA) solution relative to pristine CdS. The most efficient CdS/VB₂ composite with 20 wt% VB₂ (CB20) exhibits a H₂ evolution rate as high as 12.1 mmol h⁻¹ g⁻¹, which is about 11 times higher than that of CdS alone (1.1 mmol h⁻¹ g⁻¹). Moreover, the highest apparent quantum efficiency (AQE) of 4.4% is recorded on CB20 at 420 nm. The improved photocatalytic activity of CdS/VB₂ composite can be attributed to the excellent cocatalytic effect of VB₂, which can not only enhance the charge separation on CdS but also accelerate the H₂ evolution kinetics. This work demonstrates the great potential of using transition metal brodies (TMBs) as efficient cocatalysts for developing noble-metal-free and stable photocatalysts for solar photocatalytic H₂ evolution.     

Improved H2 evolution under visible light in heterostructured SiC/CdS photocatalyst: Effect of lattice match

This paper reports the results of the photocatalytic activity of hydrogen production from water reduction using a composite catalyst of SiC/CdS with two types of heterointerfaces. Type 1 consists of hexagonal SiC and hexagonal CdS, while type 2 consists of hexagonal SiC and cubic CdS. It was found that type 1 composite exhibited an H₂ evolution rate four times greater than type 2, despite the similar bandgaps and electropotentials of both cubic and hexagonal CdS. Meanwhile, increased BET surface area, good distribution of CdS, strong light absorption and low carrier recombination were observed in type 1 heterointerface. Lattice match is thought to be achieved between two hexagonal compounds with a lattice-constant-relationship of 3a_H-CdS = 4a_H-SiC. Further, the hexagonal SiC surface (006) was shown to have an affinity with the hexagonal CdS (002) facet due to their respective polar properties. The results of this paper demonstrate that lattice match plays an important role in forming efficient heterojunctions, which in turn enhance the photocatalytic performance of composite catalysts and will prove to be helpful in designing new composite photocatalytic systems.     

In-situ growth of CdS quantum dots on g-C3N4 nanosheets for highly efficient photocatalytic hydrogen generation under visible light irradiation

Well dispersed CdS quantum dots were successfully grown in-situ on g-C₃N₄ nanosheets through a solvothermal method involving dimethyl sulfoxide. The resultant CdS–C₃N₄ nanocomposites exhibit remarkably higher efficiency for photocatalytic hydrogen evolution under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 12 wt% CdS showed a hydrogen evolution rate of 4.494 mmol h⁻¹ g⁻¹, which is more than 115 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity induced by the in-situ grown CdS quantum dots is attributed to the interfacial transfer of photogenerated electrons and holes between g-C₃N₄ and CdS, which leads to effective charge separation on both parts.     

Facile preparation of Pt/CdS photocatalyst by a modified photoreduction method with efficient hydrogen production

A series of 0.75 wt% Pt/CdS photocatalysts were successfully synthesized via a modified photoreduction process, with the assistance of a protective agent (polyvinylpyrrolidone, PVP) and/or structural inducer (NaI, NaBr, and NaCl). The physicochemical properties of the obtained 0.75 wt% Pt/CdS photocatalysts were characterized in more detailed. Their photocatalytic efficiencies were evaluated by visible-light photocatalytic hydrogen production. The results show that the photocatalytic activities of 0.75 wt% Pt/CdS photocatalysts for H₂ production mainly depend on the type of structural inducer. Furthermore, a suitable ratio of PVP/NaI is necessary to optimize the photocatalytic performance of Pt/CdS composites. Notably, 0.75 wt% Pt/CdS (PVP/NaI = 4:1) gains the highest hydrogen production activity with a rate of 1155.8 μmol h^?1, which is 1.8 times higher than that of 0.75 wt% Pt/CdS obtained from the traditional photoreduction method (640.9 μmol h^?1) and 17.3 times higher than that of the bare CdS sample (66.9 μmol h^?1). The as-prepared 0.75 wt% Pt/CdS photocatalyst (PVP/NaI = 4:1) also exhibits a good stability. An optimum ratio of PVP/NaI not only causes a decrease in particle size of Pt nanoparticles but also leads to an increase in BET specific surface area of Pt/CdS and an enhanced electron transfer capability of Pt nanoparticles, which should be responsible for the enhanced photocatalytic performance.     

Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS₂/g-C₃N₄ composite photocatalyst through decorating WS₂/g-C₃N₄ 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g⁻¹ h⁻¹ was obtained for such a specially designed CdSe/WS₂/g-C₃N₄ composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C₃N₄ NSs (0.43 mmol g⁻¹ h⁻¹), WS₂/g-C₃N₄ 2D/2D NSs (0.74 mmol g⁻¹ h⁻¹) and CdSe/g-C₃N₄ 0D/2D composites (0.96 mmol g⁻¹ h⁻¹), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS₂/g-C₃N₄ composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C₃N₄ NSs, CdSe QDs and WS₂ NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.     

Prickly Ni3S2 nanowires modified CdS nanoparticles for highly enhanced visible-light photocatalytic H2 production

The photocatalytic water splitting strategy is one of the most promising ways to achieve clean and renewable solar-to-hydrogen energy conversion. In this study, a highly enhanced photocatalytic H₂ production system has been achieved, using CdS nanoparticles (NPs) decorated on prickly Ni₃S₂ nanowires (NWs) as the light-driven photocatalyst. The photocatalyst was prepared by a co-precipitated method in which spiky Ni NWs were employed as starting material for prickly Ni₃S₂ NWs. Characterization analysis (XRD, TEM, XPS, etc.) show the high purity of Ni₃S₂/CdS hybrid structures and the well deposition of CdS NPs on prickly Ni₃S₂ NWs. Besides, the as synthesized Ni₃S₂/CdS photocatalyst exhibit reduced photoluminescence peak intensity, which means the Ni₃S₂ NWs functions as electron collector and transporter to quench the photoluminescence of CdS. This prickly Ni₃S₂/CdS nanocomposite demonstrates a 70 times higher H₂ production rate than that of pure CdS and a quantum efficiency of 12.3% at the wavelength of 400 nm in the absence of noble metals. This enhanced H₂ production activity is better than the one of CdS loaded with 0.5 wt% Pt. Our findings highlight the potential application of Ni₃S₂/CdS hybrid structures for visible light photocatalytic hydrogen yielding in the energy conversion field.     

The CdS/CaTiO3 cubic core-shell composite towards enhanced photocatalytic hydrogen evolution and photodegradation

The CdS/CaTiO₃ cubic core-shell composite is synthesized via a hydrothermal-chemical method. The CdS/CaTiO₃ cubic core-shell composite (CdS/CTO-2) exhibits remarkable photocatalytic HER activity (∼1025.27 μmol·g⁻¹ h⁻¹) and photodegradation enhancement than that of single CaTiO₃ (∼21 folds of HER, ∼19 folds of photodegradation) and single CdS (∼15 folds of HER, ∼15 folds of photodegradation), and a decent stability. There, CdS/CaTiO₃ composite with appropriate potential gradient and CdS with better visible light response can improve carrier efficiency, including increasing carrier transportation, prolonging lifetime and decreasing recombination. Additionally, cubic core-shell microstructure can increase active sites, while maintaining photocatalytic stability.     

Novel CoOx/CdS/TiO2 with multi-shelled porous heterostructure for enhanced charge separation efficiency of photoelectrochemical water splitting

Hydrogen production by solar energy is an efficient and clean approach to fulfill the future energy demand. Herein, a novel multi-shelled porous heterostructure CoO_x/CdS/TiO₂ photoanode was fabricated by the hydrothermal and chemical method. There were more active sites, suitable surface defects and heterojunction structures in the homogeneous-porous-multi-shelled CoO_x/CdS/TiO₂ photoanode. It showed a photocurrent density of 2.89 mA/cm² at 1.23V vs. RHE, which is 2.22 fold of the original TiO₂ photoanode. The heterostructure fabrication of the CdS/TiO₂ could broaden the visible light absorption and enhance the charge separation efficiency. The multi-shelled homogeneous porous structure of the CoO_x/CdS/TiO₂ further enhanced the charge separation efficiency and accelerated the interfacial oxygen evolution kinetics. The mechanism for the enhanced photoelectrochemical water splitting of favorable CoO_x/CdS/TiO₂ photoanode is proposed.     

Enhanced photocatalytic performance of hollow spherical CdS QDs@ZrO2–TiO2 composites with double Z-scheme heterostructures

In this paper, CdS QDs@ZrO₂–TiO₂ hollow spherical composites with double Z-scheme heterostructure modified by CdS QDs were prepared by the sol–gel method and vacuum impregnation method using polystyrene (PS) microspheres synthesized by the self-assembly technique as templates. A series of characterization results show that CdS QDs@ZrO₂–TiO₂ composites treated by PS microspheres have the structure of hollow spheres with uniform size and orderly arrangement. Moreover, the double Z-scheme heterojunction formed between CdS QDs, ZrO₂, and TiO₂ in the composite can optimize the charge transfer path and improve the charge separation efficiency. Results of the photodegradation and the photo-splitting water of CdS QDs@ZrO₂–TiO₂ composites show that, compared with other systems, CdS QDs@ZrO₂–TiO₂ composites have the highest photocatalytic degradation rate of crystal violet, and meanwhile, the photocatalytic hydrogen production rate of the composite under simulated sunlight is more than 100 times that of TiO₂. The good absorption of visible light, the successful construction of double Z-scheme heterojunction, and the unique hollow sphere structure of CdS QDs@ZrO₂–TiO₂ composites are the key factors for enhanced photocatalytic performance.     

Facile in-situ synthesis of α-NiS/CdS p-n junction with enhanced photocatalytic H2 production activity

Constructing active sites on photocatalysts is one of the most effective approaches for promoting photocatalytic H₂ production activity. In this paper, a p-type semiconductor α-NiS is in-situ grown on an n-type semiconductor CdS by a simple solid state method, which results in a strong interfacial contact between α-NiS and CdS. Benefitting from the built-in electric field caused by a p-n junction, the photoinduced electrons of CdS and holes of α-NiS migrate to their interface and recombine rapidly, which results in the formation of a Z system. The more negative CB potential of α-NiS/CdS possesses stronger ability to reduce H⁺ to H₂, thereby exhibiting higher photocatalytic H₂ evolution activity. Furthermore, the strong interface contact is beneficial to the charge migration and promotes the charge separation efficiency. The H₂ evolution rate of 1.0% α-NiS/CdS reaches 9.8 mmol h^?1 g^?1, corresponding to an AQY of 65.7% at λ = 420 nm.     

Fe2P nanoparticles as highly efficient freestanding co-catalyst for photocatalytic hydrogen evolution

Design of non-noble-metal artificial photosynthesis system that can split water with high apparent quantum yield (AQY) and robust stability remains a fundamental challenge. Here we report that a physical mixture of Fe₂P nanopaticles (NPs) and CdS nanosheets (NSs) can gives AQY of photocatalytic hydrogen production as high as 90% at 420 nm monochromatic light with ethanol as electron donor at strong alkaline conditions. The highest rate for hydrogen production reached about 220 mmol g^?1 h^?1. In this hybrid photocatalyst system, free standing Fe₂P NPs act as efficient and robust noble-metal-free co-catalysts and ultrathin CdS NSs are used as the photosensitizer. PL and TRPL results demonstrate that photoexcited electron can transfer from the conduction band of the excited CdS to Fe₂P, which aided charge separation and enhanced the hydrogen evolution activity. Femtosecond transient absorption result reveals that the time-averaged interfacial electron transfer (ET) rate constant (<k_ET>) from CdS NSs to Fe₂P is about 7.4 × 10⁹ s^?1 under the guarantee of the scavenging of photoexcited hole immediately, which is one order faster than the electron relaxation rate in pure CdS NSs.     

Facile fabrication and optimization of bowl-like ZnO/CdS nano-composite thin films with hierarchical nanopores and nano-cracks for high-performance photoelectrochemistry

A special nano-structured composite ZnO/CdS thin film with hierarchical nanopores and nano-cracks has been synthesized by a facile two-step method for the first time, in which both loadings of ZnO and CdS are optimized. We first fabricated the hierarchical nanoporous ZnO thin film through rapid gas/liquid interface assembly and layer-by-layer transfers of bowl-like ZnO nanoparticles for thirteen times. The ZnO nanobowls are prepared by a simple solution chemical reaction without using any templates. After annealing, the assembled ZnO film is sensitized with CdS nanoparticles by successive ionic layer adsorption and reactions for six cycles. Nano-cracks form for the ZnO/CdS nano-composite film by calcination, which is due to the different thermal expansion behavior between the ZnO film and the CdS layer. The facilely optimized ZnO/CdS films can serve as a promising photoanode in a photoelectrochemical cell, and it can generate a saturated photocurrent density as high as 7.8 mA cm^?2 at ?0.9 V (vs. Hg|Hg₂SO₄|saturated K₂SO₄) under visible light illumination of 100 mW cm^?2 in an aqueous solution of 0.5 M Na₂S, corresponding to a solar-to-electricity conversion efficiency of 6.6%.