Synergistic effects of SPR and FRET on the photoluminescence of ZnO nanorod heterostructures

Solution-grown ZnO nanorods (NRs) were successfully conjugated with CdSe/ZnS quantum dots (QDs) and Ag nanoparticles (NPs) to suppress intrinsic defect emission and to enhance band-edge emission at the same time. First, high-density and high-crystallinity ZnO NRs of diameter 80–90 nm and length 1.2–1.5 μm were grown on glass substrates using a low-temperature seed-assisted solution method. The as-synthesized ZnO NRs showed sharp photoluminescence (PL) band-edge emission centered at ～377 nm together with broad defect emission in the range of ～450–800 nm. The ZnO NRs were decorated with CdSe/ZnS QDs and Ag NPs, respectively, by sequential drop-coating. The PL of CdSe/ZnS QD||ZnO NR conjugates showed that ZnO band-edge emission decreased by 73.8% due to fluorescence resonance energy transfer (FRET) and charge separation between ZnO and CdSe/ZnS by type II energy band structure formation. On the other hand, Ag NP||CdSe/ZnS QD||ZnO NR conjugates showed increased band-edge emission (by 25.8%) and suppressed defect emission compared to bare ZnO NRs. A possible energy transfer mechanism to explain the improved PL properties of ZnO NRs was proposed based upon the combined effects of FRET and surface plasmon resonance (SPR).     

Periodic FTO IOs/CdS NRs/CdSe Clusters with Superior Light Scattering Ability for Improved Photoelectrochemical Performance

Periodic fluorine‐doped tin oxide inverse opals (FTO IOs) grafted with CdS nanorods (NRs) and CdSe clusters are reported for improved photoelectrochemical (PEC) performance. This hierarchical photoanode is fabricated by a combination of dip‐coating, hydrothermal reaction, and chemical bath deposition. The growth of 1D CdS NRs on the periodic walls of 3D FTO IOs forms a unique 3D/1D hierarchical structure, providing a sizeable specific surface area for the loading of CdSe clusters. Significantly, the periodic FTO IOs enable uniform light scattering while the abundant surrounded CdS NRs induce additional random light scattering, combining to give multiple light scattering within the complete hierarchical structure, significantly improving light‐harvesting of CdS NRs and CdSe clusters. The high electron collection ability of FTO IOs and the CdS/CdSe heterojunction formation also contribute to the enhanced charge transport and separation. Due to the incorporation of these enhancement strategies in one hierarchical structure, FTO IOs/CdS NRs/CdSe clusters present an improved PEC performance. The photocurrent density of FTO IOs/CdS NRs/CdSe clusters at 1.23 V versus reversible hydrogen electrode reaches 9.2 mA cm^?2, which is 1.43 times greater than that of CdS NRs/CdSe clusters and 3.83 times of CdS NRs.     

RGO nanosheets coupled NaNbO3 nanorods based nanocomposite for enhanced photocatalytic and photoelectrochemical water splitting activity

In this present work, reduced graphene oxide (RGO) coupled with hydrothermally grown sodium niobate nanorods (NaNbO₃-NRs) have been successfully synthesized. The photocatalytic performance of RGO/NaNbO₃-NRs photocatalyst demonstrated faster photodegradation of organic methylene blue (MB) dye than bare NaNbO₃-NRs. A ∼6 fold enhancement in the photocatalytic activity of RGO/NaNbO₃-NRs nanocomposite than that of NaNbO₃-NRs has been demonstrated towards the degradation of MB dye under similar light illumination. Furthermore, the potentiality of the fabricated NaNbO₃-NRs and RGO/NaNbO₃-NRs nanocomposite photoanodes have been investigated for photoelectrochemical (PEC) water splitting. The fabricated RGO/NaNbO₃-NRs nanocomposite photoanode showed ∼4 times higher photocurrent density than the NaNbO₃-NRs photoanode. The electrochemical impedance spectroscopy (EIS) and Mott-Schottky (MS) measurements demonstrated that coupling of RGO nanosheets in the RGO/NaNbO₃-NRs nanocomposite reduced the charge transfer resistance (R_ct) at the photoanode/electrolyte interface, increased the donor density (N_d), and reduced flat band potential (V_fb) of the RGO/NaNbO₃-NRs, thus significantly improving the PEC performance of the RGO/NaNbO₃-NRs nanocomposite. The enhancement in the PEC measurements of RGO/NaNbO₃-NRs nanocomposite is attributed to the extended absorption of the visible portion of the solar spectra and increased mobility of the photogenerated charge transport in the RGO nanosheets, which improve the separation efficiency and reduce the recombination process. The possible charge transfer mechanism has been proposed responsible for the enhanced photocatalytic and PEC water splitting performance.     

Enhancing the performance of dye-sensitized solar cells by ZnO nanorods/ZnO nanoparticles composite photoanode

In this paper, ZnO nanorods (NRs) were prepared by a two-step solution phase reaction. A composite photoanode architecture is fabricated by adding 0–0.20 at.% ZnO NRs into ZnO nanoparticles (NPs). The scanning electron microscopy image shows that the average diameter and length of the ZnO NRs are about 50 nm and 2–5 µm, respectively, and the ZnO NRs are uniformly embedded into the ZnO NPs photoanode. The UV–vis spectrum analysis reveals that the amount of dye adsorption of the composite photoanode decreases with increasing ZnO NRs content. Meanwhile, the influence of ZnO NRs contents on the dye-sensitized solar cells (DSSCs) performance is systematically investigated. The photocurrent density–voltage (J–V) characteristics reveal that the device performance of DSSCs can be significantly enhanced by the composite photoanode. Typically, the DSSC with 0.15 at.% ZnO NRs obtains the optimal energy conversion efficiency of 3.8%, which is 28.4% higher than that of the pristine ZnO DSSCs. The electrochemical impedance spectroscopy (EIS) analysis shows that ZnO NRs can provide a direct pathway for accelerating electron transport, extending the electron lifetime, suppressing electron recombination and improving electron collection efficiency. These results indicate that the incorporation of ZnO NRs in the photoanode is an effective way to improve the performance of DSSCs.     

Optimization of CdSe layer on modified ZnO hierarchical spheres by spin-SILAR for efficient CdS/CdSe co-sensitized solar cells

In this study, after CdS quantum dots sensitized ZnO hierarchical spheres (ZnO HS), we used a simple process to deposit CdSe QDs on ZnO by spin-coating-based SILAR, and applied to photoanodes of quantum dots-sensitized solar cells. Before CdS and CdSe QDs deposition, the ZnO HS photoanodes were modified by Zn(CH₃COO)₂·2H₂O methanol solution to further enhance the open-circuit voltage and power conversion efficiency (PCE). The program of modifying photoanodes and the number of CdSe spin-SILAR cycles are evaluated on the optical and electrochemical properties of the cells. As a result, a high energy conversion efficiency of 2.49 % was obtained by using modified ZnO HS/CdS photoanode under AM 1.5 illumination of 100 mW cm^?2. And further decorated by the CdSe QDs, the ZnO HS/CdS/CdSe cell achieved a PCE of 5.36 % due to the modification of ZnO HS nanostructure, the enhanced absorption in the visible region, the lower recombination reaction and higher electron lifetime.     

Elaborately Modified BiVO4 Photoanodes for Solar Water Splitting

Photoelectrochemical (PEC) cells for solar‐energy conversion have received immense interest as a promising technology for renewable hydrogen production. Their similarity to natural photosynthesis, utilizing sunlight and water, has provoked intense research for over half a century. Among many potential photocatalysts, BiVO₄, with a bandgap of 2.4–2.5 eV, has emerged as a highly promising photoanode material with a good chemical stability, environmental inertness, and low cost. Unfortunately, its charge transport properties are modest, at most a hole diffusion length (L_p) of ≈70 nm. However, recent rapid developments in multiple modification strategies have elevated it to a position as the most promising metal oxide photoanode material. This review summarizes developments in BiVO₄ photoanodes in the past 10 years, in which time it has continuously broken its own performance records for PEC water oxidation. Effective modification techniques are discussed, including synthesis of nanostructures/nanopores, external/internal doping, heterojunction fabrication, surface passivation, and cocatalysts. Tandem systems for unassisted solar water splitting and PEC production of value‐added chemicals are also discussed.     

Dye sensitized solar cell of TiO2 nanoparticle/nanorod composites prepared via low-temperature synthesis in oleic acid

Titania (TiO₂) nanorods (NRs) and nanoparticles (NPs) were synthesized using oleic acid as a surfactant and employed as photoanodes for dye sensitized solar cell (DSSC) fabrication. The synthesized NRs and NPs were characterized using transmission electron microscopy and X-ray diffraction. The photovoltaic performances were compared between NRs, NPs, and their composites. The results showed that the power conversion efficiencies (η) of the composites depend on the relative compositions of NRs and NPs in photoanodes, reaching the greatest at 10% NR content. η of the pure NRs DSSC was lower than that of the NPs DSSC. Electrochemical impedance spectroscopy revealed that the highest η at 10% NRs is mainly due to reduced charge transport resistance at the TiO₂/dye/electrolyte interface and electrolyte diffusion resistance, overcoming the reduction of the number of adsorbed dye molecules.     

Growth of ZnO nanorods on TiO2 nanoparticles films and their application to the electrode of dye-sensitized solar cells

A ZnO nanorods (NRs)/TiO₂ nanoparticles (NPs) film has been prepared by electrochemical deposition of ZnO NRs growth on P25 TiO₂ NPs film surfaces. It was found that ZnO NRs/TiO₂ NPs could significantly improve the efficiency of dye-sensitized solar cells owing to its relatively enhanced light-scattering capability and efficient charge transport efficiency. The overall energy-conversion efficiency (η) of 3.48 % was achieved by the formation of ZnO NRs/TiO₂ NPs film, which is 33 % higher than that formed by TiO₂ NPs alone (η = 2.62 %). The charge recombination behavior of cells was investigated by electrochemical impedance spectra, and the results showed that ZnO NRs/TiO₂ NPs film has the longer electron lifetime than TiO₂ NPs alone, which could facilitate the reduction of recombination processes and thus would promote the photocatalysis and solar cell performance.     

Self‐Powered Photoelectrochemical Biosensor Based on CdS/RGO/ZnO Nanowire Array Heterostructure

A CdS/reduced graphene oxide (RGO)/ZnO nanowire array (NWAs) heterostructure is designed, which exhibits enhanced photoelectrochemical (PEC) activity compared to pure ZnO, RGO/ZnO, and CdS/ZnO. The enhancement can be attributed to the synergistic effect of the high electron mobility of ordered 1D ZnO NWAs, extended visible‐light absorption of CdS nanocrystals, and the formed type II band alignment between them. Moreover, the incorporation of RGO further promotes the charge carrier separation and transfer process due to its excellent charge collection and shuttling characteristics. Subsequently, the CdS/RGO/ZnO heterostructure is successfully utilized for the PEC bioanalysis of glutathione at 0 V (vs Ag/AgCl). The self‐powered device demonstrates satisfactory sensing performance with rapid response, a wide detection range from 0.05 mm to 1 mm , an acceptable detection limit of 10 μm , as well as certain selectivity, reproducibility, and stability. Therefore, the CdS/RGO/ZnO heterostructure has opened up a promising channel for the development of PEC biosensors.     

Ternary non-noble metal zinc-nickel-cobalt carbonate hydroxide cocatalysts toward highly efficient photoelectrochemical water splitting

TiO₂ photoanodes have aroused intensive research interest in photoelectrochemical (PEC) water splitting. However, they still suffer from poor electron-hole separation and sluggish oxygen evolution dynamics, leading to the low photoconversion efficiency and limiting commercial application. Here, we designed and fabricated novel ternary non-noble metal carbonate hydroxide (ZNC-CH) nanosheet cocatalysts and integrated them with TiO₂ nanorod arrays as highly efficient photoanodes of PEC cells. Compared with the pristine TiO₂, the photocurrent of photoanode with the optimal amount of ZNC-CH represents 3.2 times enhancement, and the onset potential is shifted toward the negative potential direction of 62 mV. The remarkable enhancement is attributed to the suppressed carrier recombination and enhanced charge transfer efficiency at the interface of TiO₂, ZNC-CH and electrolyte, which is closely related to the zinc elements modulated intrinsic activity of catalysts. Our results demonstrate that the introduction of multimetallic ZNC-CH cocatalysts onto photoanodes is a promising strategy to improve the PEC efficiency.     

Rugged Forest Morphology of Magnetoplasmonic Nanorods that Collect Maximum Light for Photoelectrochemical Water Splitting

A feasible nanoscale framework of heterogeneous plasmonic materials and proper surface engineering can enhance photoelectrochemical (PEC) water-splitting performance owing to increased light absorbance, efficient bulk carrier transport, and interfacial charge transfer. This article introduces a new magnetoplasmonic (MagPlas) Ni-doped Au@Fe_xO_y nanorods (NRs) based material as a novel photoanode for PEC water-splitting. A two stage procedure produces core–shell Ni/Au@Fe_xO_y MagPlas NRs. The first-step is a one-pot solvothermal synthesis of Au@Fe_xO_y. The hollow Fe_xO_y nanotubes (NTs) are a hybrid of Fe₂O₃ and Fe₃O₄, and the second-step is a sequential hydrothermal treatment for Ni doping. Then, a transverse magnetic field-induced assembly is adopted to decorate Ni/Au@Fe_xO_y on FTO glass to be an artificially roughened morphologic surface called a rugged forest, allowing more light absorption and active electrochemical sites. Then, to characterize its optical and surface properties, COMSOL Multiphysics simulations are carried out. The core–shell Ni/Au@Fe_xO_y MagPlas NRs increase photoanode interface charge transfer to 2.73 mAcm⁻² at 1.23 V RHE. This improvement is made possible by the rugged morphology of the NRs, which provide more active sites and oxygen vacancies as the hole transfer medium. The recent finding may provide light on plasmonic photocatalytic hybrids and surface morphology for effective PEC photoanodes.     

Facile preparation and photoelectrochemical properties of CdSe/TiO2 NTAs

In the present work we report the design and synthesis of CdSe/TiO₂ nanotube arrays (NTAs) and their implementation as a photoanode for photoelectrochemical (PEC) application. CdSe nanoparticles with well dispersion were decorated on the inner and outer surfaces of 2.5 μm-long TiO₂ nanotubes via electrodeposition. These CdSe/TiO₂ NTAs exhibit a significant photocurrent responds under visible light illumination (λ ≥ 420 nm). The results presented in this study display a promising method that the photoelectrochemical performance could be improved via composition, size and crystalline control of CdSe/TiO₂ NTAs. And the tubular morphology is also able to facilitate charge transport in nanostructure-based PEC cells. This research demonstrates a new approach, which have great potential applications in fabricating novel heterostructure-photoelectrochemical devices.     

Array of ZnO nanoparticle-sensitized ZnO nanorods for UV photodetection

Vertically aligned ZnO nanorod (NR) arrays have been successfully synthesized on ITO-glass substrate by hydrothermal growth. Chemical bath deposition method was used to deposit ZnO nanoparticles (NPs) onto the ZnO NRs. These structures were applied in fabricating ZnO NPs sensitized ultraviolet (UV) photodetectors (PDs). Incorporation of ZnO NPs onto ZnO NRs results in distinct improvement of optical properties of ZnO NRs, i.e., significant enhancement of emission as well as effective suppression of defects emission in ZnO. Furthermore, there is a noticeable blue-shift in absorption spectra compared with that of ZnO NRs structure. I–V characteristics show that the sensitized structure improved photocurrent almost twice that of unsensitized ZnO NRs. Consequently, these findings may open new opportunities for the integration of different ZnO nanostructures for application in UV region particularly fabrication of UV PDs.     

Photoexcitation of TiO2 photoanode in water splitting

TiO₂ is one of the most promising photoanodes for solar-hydrogen conversion by water splitting. However, the solar-hydrogen efficiency of TiO₂ remains limited because of a low photocurrent generation. A clear understanding of photoexcitations within photoanodes can predict the quantity of photocurrent and consequently determine the solar-hydrogen efficiency. In this work, hydrothermally synthesized rutile TiO₂ nanorods were investigated for their photoelectrochemical (PEC) performance. A photogenerated hole concentration of TiO₂ photoanode was derived as 8.40 × 10¹⁴ cm⁻³ under one sun illumination. In addition, Fermi level pinning associated with high density of surface states was also observed under PEC operation. Base on these results, a series of band diagrams of TiO₂ photoanode were established to describe the photogeneration of holes and current at various bias potential. The main limitation of photocurrent generation is the distribution of surface-trapped states, which determines the hole concentration at the surface and consequently determines the open-circuit potential and the photocurrent density.     

A general synthetic approach for obtaining cationic and anionic inorganic nanoparticles via encapsulation in amphiphilic copolymers

A series of amphiphilic copolymers with variable charge densities on their backbone is synthesized. Positively charged N,N,N-trimethylammonium-2-ethyl methacrylate iodide or negatively charged 2-(methacryloyloxy)ethylphosphonic acid and lauryl methacrylate are used as building blocks. When wrapped around hydrophobically capped inorganic nanoparticles (NPs), the latter are able to disperse in aqueous solutions. Using this method, positively as well as negatively charged colloidal NPs can be synthesized in a reliable way. The method presented herein allows the charge on the NPs to be adjusted to different negative and positive values by using polymers with a variable ratio of charged monomers and lauryl methacrylate. Virtually all kinds of hydrophobic inorganic NPs could be coated with these amphiphilic polymers. The coating procedure is demonstrated for Au particles as well as for CdSe/ZnS quantum dots. To date, wrapping amphiphilic polymers around NPs has led only to anionic NPs. The polymers synthesized in this work allow for positively charged NPs with a high colloidal stability.     

p-n异质结BiVO4/g-C3N4光阳极的制备及其光电化学水解性能

钒酸铋(BVO)可用于光电化学(PEC)水解产氢,但受限于其缓慢的表面水氧化动力学,在电极表面修饰单一的析氧助催化剂达不到理想的性能。本工作在BVO电极表面修饰FeNiO_x助催化剂可以显著降低起始电压,增强光电化学性能。此外,沉积g-C₃N₄后修饰FeNiO_x助催化剂得到的光电极具有更优异的性能。厚度适合的g-C₃N₄纳米片与BVO构成Ⅱ型p-n异质结,有效抑制了光生电子空穴的复合,促进了电极的电荷分离。电化学测试结果表明,沉积了g-C₃N₄后,电极的电荷分离效率达到88.2%,比BVO/FeNiO_x (60.6%)提升了近1.5倍。经过g-C₃N₄和FeNiO_x协同修饰的BVO/g-C₃N₄/Fe Ni O_x电极,表面电荷注入效率达到了90.2%,同时,在1....     

New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar‐Driven Water Splitting

Bismuth vanadate (BiVO₄) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade‐off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO₄ films with well‐controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO₄ film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO₄ dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm^?2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO₄/FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar‐to‐hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.     

TiO2 ALD decorated CuO/BiVO4 p-n heterojunction for improved photoelectrochemical water splitting

Bismuth vanadate (BiVO₄) is a promising photoanode material owing to the narrow bandgap, appropriate band position, and excellent resistance against photocorrosion, however, the performance of photoelectrochemical (PEC) water splitting is largely limited by the poor carrier separation and transport ability. To address these issues, for the first time, we fabricate BiVO₄ film/CuO nanocone p-n junctions as photoanodes by combing a facile spin-coating process and water bath reaction. This structure strengthens the light harvesting and promotes the charge separation and transport ability. The surface defects states are passivated by coating conformally ultrathin TiO₂ onto CuO surface through atomic layer deposition (ALD) technique. Benefiting from the favorable morphology, energy band, and surface treatment, the BiVO₄/CuO/TiO₂ heterojunction generates an improved photocurrent that is much higher than pure BiVO₄. The detailed mechanism investigations indicate that the synergetic optimization of charge separation and injection efficiency in the bulk and surface of photoelectrodes can significantly improve the performance of PEC cells.     

Self-powered photoelectrochemical biosensing platform based on Au NPs@ZnO nanorods array

Photoanodes, which are used in photoelectrochemical (PEC) water splitting, have been shown to be applicable in the construction of a PEC biosensing platform. This was realized by replacing water oxidization with oxidation of an appropriate test molecule. Here, we have demonstrated the feasibility of adopting photoanodes consisting of zinc oxide nanorods arrays decorated with plasmonic gold nanoparticles (Au NPs@ZnO NRs) for the self-powered PEC bioanalysis of glutathione (GSH) in phosphate-buffered saline (PBS) at an applied bias potential of 0 V vs. Ag/AgCl. This heterostructure exhibited enhanced PEC properties because of the introduction of the Au/ZnO interface. Under visible light illumination, hot electrons from surface-plasmon resonance (SPR) at the Au NP surface were injected into the adjacent ZnO and subsequently driven to the photocathode. Under ultraviolet (UV) light illumination, the photogenerated electrons in ZnO tended to transfer to the fluorine-doped tin oxide due to the step-wise energy band structure and the upward energy band bending at the ZnO/ electrolyte interface. These results indicate that plasmonic metal/semiconductor heterostructure photoanodes have great potential for self-powered PEC bioanalysis applications and extended field of other photovoltaic beacons.

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Single-crystalline zinc oxide nanowires as photoanode material for dye-sensitized solar cells

This study reports the use of single-crystalline and well-aligned ZnO nanowires as photoanode material for dye-sensitized solar cells. The ZnO nanowires are grown on fluorine-doped tin oxide coated glass substrates without catalysts by thermal evaporation. In spite of low roughness factors of around 25 for the nanowire photoanodes, the fabricated solar cells yield power conversion efficiencies of around 1.3% under AM 1.5G (100 mW cm-2) illumination. Moreover, fill factors of around 0.5 have been achieved and are relatively high when compared with reported values from ZnO nanowire photoanodes. The results reveal the advantage of using single-crystalline nanowires as photoanode material and provide clues for the advancement of nanowire based dye-sensitized solar cells.