Photo-induced reforming of alcohols with improved hydrogen apparent quantum yield on TiO2 nanotubes loaded with ultra-small Pt nanoparticles

Photo-induced reforming of methanol, ethanol, glycerol and phenol at room temperature for hydrogen production was investigated with the use of ultra-small Pt nanoparticles (NPs) loaded on TiO₂ nanotubes (NTs). The Pt NPs with diameters between 1.1 and 1.3 nm were deposited on TiO₂ NTs by DC-magnetron sputtering (DC-MS) technique. The photocatalytic hydrogen rate achieved an optimum value for a loading of about 1 wt% of Pt. Apparent quantum yield for hydrogen generation was measured for methanol and ethanol water solutions reaching a maximum of 16% under irradiation with a wavelength of 313 nm in methanol/water solution (1/8 v/v). Pt NPs loaded on TiO₂ NTs represented also a true water splitting catalyst under UV irradiation and pure distilled water. DC-MS method appears to be a technologically simple, ecologically benign and potentially low-cost process for production of an efficient photocatalyst loaded with ultra-small NPs with precise size control.     

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO₂–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO₂–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu_0·45Ni_0·55/TiO₂–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 mol_H2·mol_cat⁻¹ min⁻¹ at 25 °C and low activation energy of 32.8 kJ mol⁻¹. Cu_0.45Ni_0.55/TiO₂–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.     

Highly stable CdS-modified short TiO2 nanotube array electrode for efficient visible-light hydrogen generation

A highly stable photoelectrocatalytic electrode made of CdS-modified short, robust, and highly-ordered TiO₂ nanotube array for efficient visible-light hydrogen generation was prepared via sonoelectrochemical anodization and sonoelectrochemical deposition method. The short nanotube electrode possesses excellent charge separation and transfer properties, while the sonoelectrochemical deposition method improves the combination between CdS and TiO₂ nanotubes, as well as the dispersion of CdS nanoparticles. Different characterization techniques were used to study the nanocomposite electrode. UV-vis absorption and photoelectrochemical measurements proved that the CdS coating extends the visible spectrum absorption and the solar spectrum-induced photocurrent response. Comparing the photoactivity of the CdS/TiO₂ electrode obtained using sonoelectrochemical deposition method with others that synthesized using plain electrochemical deposition, the current density of the former electrode is ∼1.2 times higher that of the latter when biased at 0.5 V. A ∼7-fold enhancement in photocurrent response is obtained using the sonoelectrochemically fabricated CdS/TiO₂ electrode in comparison with the pure TiO₂ nanotube electrode. Under AM1.5 illumination the composite photoelectrode generate hydrogen at a rate of 30.3 μmol h⁻¹ cm⁻², nearly 13 times higher than that of pure titania nanotube electrode. Recycle experiments demonstrated the excellent stability and reliability of CdS/TiO₂ electrode prepared by sonoelectrochemical deposition. This composite electrode, with its strong mechanical stability and excellent combination of CdS and TiO₂ nanotubes, offers promising applications in visible-light-driven renewable energy generation.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

Solvothermal synthesis ZnS–In2S3–Ag2S solid solution coupled with TiO2−xSx nanotubes film for photocatalytic hydrogen production

ZnS–In₂S₃–Ag₂S solid solution coupled with TiO_2-xS_x nanotubes film catalyst has been successfully prepared by a two-step process of anodization and solvothermal methods for the first time. The as-prepared photo-catalysts are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Visible diffuse reflectance spectra (UV–Vis DRS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The results show that the ZnS–In₂S₃–Ag₂S solid solution are deposited on the surface of TiO₂NTs nanotubes under the solvothermal conditions, by which S atoms are incorporated into the lattice of TiO₂ through substituting the sites of oxygen atoms. Such ZnS–In₂S₃–Ag₂S@TiO_2-xS_x nanotubes composite presents the enhanced absorption in visible region and the efficient transfer of photoelectron between the solid solution and TiO_2-xS_x nanotubes, which determines the excellent photocatalytic activity for the photocatalytic hydrogen evolution from aqueous solutions containing the sacrificial reagents of Na₂S and Na₂SO₃ under 500 W Xe lamp irradiation.     

Photoelectrochemical water splitting on highly smooth and ordered TiO2 nanotube arrays for hydrogen generation

To improve the photoelectrochemical (PEC) water splitting efficiency for hydrogen production, we reported the fabrication of lotus-root-shaped, highly smooth and ordered TiO₂ nanotube arrays (TiO₂ NTs) by a simple and effective two-step anodization method. The TiO₂ NTs prepared in the two-step anodization process (2-step TiO₂ NTs) showed better surface smoothness and tube orderliness than those of TiO₂ NTs prepared in one-step anodization process (1-step TiO₂ NTs). Under illumination of 100 mW/cm² (AM 1.5, simulated solar light) in 1 M KOH solution, water was oxidized on the 2-step TiO₂ NTs electrode with higher efficiency (incident-photon-to-current efficiency of 43.4% at 360 nm and photocurrent density of 0.90 mA/cm² at 1.23 V_RHE) than that on the 1-step TiO₂ NTs electrode. The effective photon-to-hydrogen conversion efficiency was found to be 0.18% and 0.49% for 1-step TiO₂ NTs and 2-step TiO₂ NTs, respectively. These results suggested that the structural smoothness and orderliness of TiO₂ NTs played an important role in improving the PEC water splitting application for hydrogen generation.     

Efficient photochemical hydrogen production under visible-light over artificial photosynthetic systems

Photosynthesis of green plants provides an effective blueprint for transform solar energy into useful hydrogen energy. Thereinto, their hierarchical structures are favorable to the light-harvesting. Meanwhile, the functional components (light-harvesting pigments) can absorb visible wavelengths of sunlight, and offer reaction center for the energy transform. Inspired by these, we contrive an artificial photosynthetic system for the high efficiency of H₂-production rate by introducing a similar functional structure (reticular hierarchical structure) and component (CdS/Pt–TiO₂). The CdS/Pt–TiO₂ with hierarchically reticular structure is prepared by transforming wings into TiO₂ via a sol–gel process, and depositing Pt and CdS nanoparticles onto the TiO₂ substrate by photoreduction and chemical bath deposition method, respectively. Contributing to the couple effect of reticular hierarchical structure and ternary hybrid composition, CdS/Pt–TiO₂ nanocomposites exhibit high visible-light photocatalytic H₂-production rate (12.7% apparent quantum efficiency obtained at 420 nm). This concept provides a new horizon to exploit solar energy for sustainable energy by imitating the photosynthesis process from structure and ingredients.     

Effect of anodization voltage on performance of TiO2 nanotube arrays for hydrogen generation in a two-compartment photoelectrochemical cell

Highly ordered TiO₂ nanotube arrays were prepared by anodic oxidation of Ti foil under different anodization voltages in ethylene glycol electrolyte. The morphology and photoelectrochemical performance of the TiO₂ nanotubes (NTs) samples were characterized by FESEM and electrochemical working station. Hydrogen production was measured by splitting water in the two-compartment photoelectrochemical (PEC) cell without any external applied voltage or sacrificial agent. The results indicated that anodization voltage significantly affects morphology structures, photoelectrochemical properties and hydrogen production of TiO₂ NTs. The pore diameter and layer thickness of TiO₂ samples increased linearly with the anodization voltage, which led to the enhancement of active surface area. Accordingly, the photocurrent response, photoconversion efficiency and hydrogen production of TiO₂ nanotubes were also linearly correlated with the anodization voltage.     

A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Syngas production by electrocatalytic reduction of CO2 using Ag-decorated TiO2 nanotubes

Huge efforts have been done in the last years on electrochemical and photoelectrochemical reduction of CO₂ to offer a sustainable route to recycle CO₂. A promising route is to electrochemically reduce CO₂ into CO which, by combination with hydrogen, can be used as a feedstock to different added-value products or fuels. Herein, perpendicular oriented TiO₂ nanotubes (NTs) on the electrode plate were grown by anodic oxidation of titanium substrate and then decorated by a low loading of silver nanoparticles deposited by sputtering (i.e. Ag/TiO₂ NTs). Due to their quasi one-dimensional arrangement, TiO₂ NTs are able to provide higher surface area for Ag adhesion and superior electron transport properties than other Ti substrates (e.g. Ti foil and TiO₂ nanoparticles), as confirmed by electrochemical (CV, EIS, electrochemical active surface area) and chemical/morphological analysis (FESEM, TEM, EDS). These characteristics together with the role of the TiO₂ NTs to enhance the stability of CO₂^·- intermediate formed due to titania redox couple (Ti^IV/Ti^III) lead to an improvement of the CO production in the Ag/TiO₂ NTs electrodes. Particular attention has been devoted to reduce the loading of noble metal in the electrode(14.5 %w/%w) and to increase the catalysts active surface area in order to decrease the required overpotential.     

Improvement of photocatalytic hydrogen generation from CdSe/CdS/TiO2 nanotube-array coaxial heterogeneous structure

The fabrication and characterization of CdSe/CdS/TiO₂ nanotube-array coaxial heterogeneous structure that has potential applications in photocatalytic water splitting and toxic pollutants degradation are investigated. CdSe(top)/CdS(under) double-layer is conformally deposited onto TiO₂ nanotubes by successive ionic layer adsorption and reaction (SILAR) and electrochemical atomic layer deposition (ECALD), respectively, for the CdS under layer and the CdSe top layer. Such double sensitized TiO₂ nanotubular photoelectrode exhibits significant enhancements in photoconversion efficiency, visible light response, and efficient hydrogen generation. The detailed synthesis process and the surface morphology, phase structure, elemental analysis, and photoelectrochemical properties of the resulting films with the CdSe/CdS/TiO₂ nanotube-array coaxial heterogeneous structure are discussed. The photoconversion efficiency of 9.47% and hydrogen generation rate of 10.24 ml h⁻¹ cm⁻² were observed. Both values are a 7-fold enhancement compared with that of the pure TiO₂ nanotube. The as-prepared photoelectrode presents potential application for industrialized photocatalytic hydrogen generation in the future.     

High photoelectrochemical water splitting performance on nitrogen doped double-wall TiO2 nanotube array electrodes

The nitrogen doped double-wall TiO₂ nanotube arrays (N-DW-TiO₂ NTs) have been prepared by a facile two steps electrochemical anodization method, and the nitrogen has been successfully incorporated into the nanotubes in situ anodization process. The unique double walls tubular surface morphology has been achieved by conducting higher anodic voltage in second anodization process than that in the first anodized step. The nitrogen doping and following annealed process in nitrogen atmosphere did not damage the unique, ordered, and vertically aligned structures. Under illumination of simulated solar light (AM 1.5, 100 mW/cm²), the N-DW-TiO₂ NTs presented a high photoelectrochemical water splitting performance, which mainly ascribed to the high surface areas and expended optical absorbance to visible light region. The high surface areas, ordered structure for facilitating electron transfer, and visible light absorbance present the new avenue for improving the solar light application in photoelectrochemical water splitting process for practical hydrogen generation. The N-DW-TiO₂ NTs can be one of promising prototype nanomaterials, and much higher photoconversion efficiency can be expected for the co-doped or sensitized on the N-DW-TiO₂ NTs.     

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO₂ and monoclinic Nb₂O₅. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO₂ counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO₂–Nb₂O₅ composite. Upon their use as photoanodes to split water, the composite TiO₂–Nb₂O₅ NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO₂ NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO₂ with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.     

Functionalization of TiO2 nanotubes with palladium nanoparticles for hydrogen sorption and storage

The use of hydrogen as an energy carrier is an attractive solution toward addressing global energy issues and reducing the effects of climate change. Design of new materials with high hydrogen sorption capacity and high stability is critical for hydrogen purification and storage. In this study, titanium dioxide nanotubes (TiO₂NTs) were modified with palladium nanoparticles (PdNPs) utilizing a facile photo-assisted chemical deposition approach. Electrochemical anodization was employed for the direct growth of TiO₂NTs. The PdNP functionalized TiO₂NTs (TiO₂NT/Pd) were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The hydrogen sorption behaviours and stability of the TiO₂NT/Pd nanocomposites were investigated and compared with nanoporous Pd networks that were deposited on a bulk titanium substrate (Ti/Pd) using cyclic voltammetry (CV) and chronoamperometry (CA). Our studies show that the TiO₂NT/Pd nanocomposites possess a much higher hydrogen storage capacity, faster kinetics for hydrogen sorption and desorption, and higher stability than the nanoporous Pd.     

Photocatalytic hydrogen production enhancement of Z-Scheme CdS quantum dots/Ni2P/Black Ti3+–TiO2 nanotubes with dual-functional Ni2P nanosheets

The Z-Scheme CdS quantum dots/Ni₂P/Black Ti³⁺–TiO₂ nanotubes with dual-functional Ni₂P nanosheets are fabricated by a continuously electrospinning-annealing/reduction-chemical deposition method, there, the TiO₂ nanotubes are fabricated via electrospinning, subsequently, the 2D Ni₂P lamellas grow on the surface of nanotubes and the Ti³⁺/O_v ions are introduced by reduction, then CdS QDs are deposited on the surface of Ni₂P lamellas. Evaluated by the photocatalytic hydrogen production, the photocatalytic performance of Z-Scheme CdS QDs/Ni₂P/B–TiO₂(~3303.85 μmol/g h) exhibits an obvious enhancement of about ~70 folds than unmodified TiO₂. The main reasons for the HER enhancement are ascribed to that the Pt-like behavior 2D Ni₂P and Ti³⁺ ions can accelerate the photo-generated electrons diffusing into water and reduce H₂ activation barrier, the Z-Scheme heterojunction can accelerate the separating and transferring of photo-generated charge carriers, the O_v ions and hollow nanotubes can increase solar utilization, which can be supported by the electrochemical measurements.     

Single crystalline TiO2 nanorods with enhanced visible light activity for solar hydrogen generation

Single crystalline TiO₂ nanorods and polycrystalline nanotubes were fabricated with same length to investigate the effects of their nanostructures on photocatalytic properties for splitting water. In order to enhance the visible light absorbance, TiO₂ nanorods and nanotubes were sensitized with semiconductor nanoparticles such as CdS, CdSe, and CdS/CdSe, and compared in viewpoint of solar hydrogen generation. It was observed that single-crystalline nanorods showed superior photocatalytic properties to polycrystalline nanotubes, and also the potential level of the nanorods with rutile phase was measured as lower than that of the nanotubes with mixture of anatase and rutile. Further improvement of photo-conversion efficiency was obtained by subsequent heat treatments of the sensitized photoelectrodes. It turns out that the improvement is attributed to the improved crystallinity and the increased size of the nanoparticles during the post-annealing treatments. It was demonstrated that TiO₂ nanorods with lower potential level and a single crystalline phase on FTO glass were advantageous for effective charge injection from the sensitized nanoparticles and transport without recombination lost at grain boundaries.     

Enhanced visible-light-photoconversion efficiency of TiO2 nanotubes decorated by pulsed laser deposited CoNi nanoparticles

The pulsed laser deposition (PLD) technique has been used to decorate TiO₂ nanotubes (NTs) with cobalt-nickel (CoNi) nanoparticles (NPs). The TiO₂ NTs were produced beforehand through the controlled anodic oxidation of titanium substrates. The effect of the nature of the PLD background gas (Vacuum, O₂ and He) on the microstructure, composition and chemical bondings of the CoNi-NPs deposited onto the TiO₂-NTs has been investigated. We found that the PLD CoNi-NPs have a core/shell (oxide/metal) structure when deposited under vacuum, while they are fully oxidized when deposited under O₂. On the other hand, by varying the CoNi-NPs loading of the TiO₂-NTs (through the increase of the number of laser ablation pulses (N_LP)), we have systematically studied their photocatalytic effect by means of cyclic-voltammetry (CV) measurements under both AM1.5 simulated solar light and filtered visible light. We show that depositing CoNi-NPs on the substrate under vacuum and He increases the photo-electrochemical conversion effectiveness (PCE) by 600% (at N_LP = 10,000) in the visible light domain, while their overall PCE degrades with N_LP under solar illumination. In contrast, the fully oxidized CoNi-NPs (deposited under O₂) are found to be the most effective catalyst under sunlight with an overall increase of more than 50% of the PCE at the optimum loading around N_LP ~1000. Such catalytic enhancement is believed to result from both an enhanced light absorption by CoO (of which bandgap is of ~2.4 eV) and the formation of a heterojunction between NiO/CoO nanoparticles and TiO₂ nanotubes.     

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.     

In2O3:Sn/TiO2/CdS heterojunction nanowire array photoanode in photoelectrochemical cells

The design of photoanode with highly efficient light harvesting and charge collection properties is important in photoelectrochemical (PEC) cell performance for hydrogen production. Here, we report the hierarchical In₂O₃:Sn/TiO₂/CdS heterojunction nanowire array photoanode (ITO/TiO₂/CdS-nanowire array photoanode) as it provides a short travel distance for charge carrier and long light absorption pathway by scattering effect. In addition, optical properties and device performance of the ITO/TiO₂/CdS-nanowire array photoanode were compared with the TiO₂ nanoparticle/CdS photoanode. The photocatalytic properties for water splitting were measured in the presence of sacrificial agent such as SO₃²⁻ and S²⁻ ions. Under illumination (AM 1.5G, 100 mW/cm²), ITO/TiO₂/CdS-nanowire array photoanode exhibits a photocurrent density of 8.36 mA/cm² at 0 V versus Ag/AgCl, which is four times higher than the TiO₂ nanoparticle/CdS photoanode. The maximum applied bias photon-to-current efficiency for the ITO/TiO₂/CdS-nanowire array and the TiO₂ nanoparticle/CdS photoanode were 3.33% and 2.09%, respectively. The improved light harvesting and the charge collection properties due to the increased light absorption pathway and reduced electron travel distance by ITO nanowire lead to enhancement of PEC performance.     

Efficient solar water splitting using a CdS quantum dot decorated TiO2/Ag2Se photoanode

Metal sulfide photoanodes emerge into an efficient platform for converting light energy into hydrogen by water splitting. Herein, we demonstrate the facile fabrication of a ternary photoanode (TiO₂/Ag₂Se/CdS) by decorating a TiO₂/Ag₂Se electrode with CdS quantum dots. The ternary electrode exhibits low charge transfer resistance, and high-density photocurrent (24.6 mAcm⁻² at 1.23 V). We estimate the photon-to-hydrogen conversion efficiency at 14% (at 0.43 V) due to sulfite oxidation. Also, Ag₂Se improves the electrode stability, highlighting the promising nature of the electrode for practical applications. These excellent photocatalytic properties of TiO₂/Ag₂Se/CdS are achieved by the favorable band-edges positions of CdS and Ag₂Se quantum dots, the broad absorption of solar photons in the UV-to-NIR region, and the separation and transport of charge carriers.