Successive Ionic Layer Adsorption Reaction Research Articles

Electroactive Prussian Blue Analogues/TiO2 Nanocomposites Obtained through SILAR Assembly in Mesoporous Nanoarchitectures

AbstractThe preparation of nanomaterials for energy applications such as intercalation batteries and materials that can act as substrates for water oxidation is a subject of major interest nowadays. In this work, we report the deposition of Prussian blue (PB) and its cobalt analogue (CoPBA) on mesoporous titania thin films (MTTF) using the successive ionic layer adsorption reaction (SILAR) technique under soft conditions. A bifunctional ligand, 1,10‐phenanthroline‐5,6‐dione (pd), was used to functionalize the titania surface and promote the growth of PB and CoPBA. The resulting PB@MTTF and CoPBA@MTTF nanocomposites were characterized using several techniques and it was determined that PB and CoPBA grow in a controlled and sequential manner, maintaining the mesoporous architecture. Both PB@MTTF and CoPBA@MTTF demonstrated very good electroactive properties, while CoPBA@MTTF exhibited water oxidation capabilities. The flexibility of this PBA@MTTF platform allows the incorporation of any labile transition metal ion or fragment into the structure of the coordination polymer embedded into a mesoporous matrix, opening the door for (photo)electrochemical devices and catalysts.

Hierarchically crystalline copper borate nanosheets as a freestanding electrode for a hybrid supercapacitor

In this study, we have suggested a straightforward approach to fabricating a binder-free electrode of hierarchically crystalline copper borate (Cu-Bi) nanosheets grown on nickel foam using the Successive Ionic Layer Adsorption Reaction (SILAR) method. The best-performing electrode shows a remarkable specific capacitance (Cs) of 2002 Fg−1 at 1 Ag−1 and Cs retention of 85 % for 10,000 GCD cycles. The assembled CB/NF-2//AC device exhibits high cycling stability and achieves a high energy of 52.2 Whkg−1 at a power density of 2622.4 Wkg−1. Remarkably, it reached 152.7 Fg−1 at 2 Ag−1, and the device still has a high capacitance retention of 85 % for 10,000 cycles. This remarkable electrochemical activity could be attributed to: (i) the inherent defects of the prepared electrode via the existence of borates, providing straightforward interaction between the electrolyte and the active species; (ii) designing the hierarchical architecture that could provide a porous nanosheet structure, which generates accessible active sites for quick ion transport, boosting the Cs; (iii) the formation of crystalline Cu-Bi nanosheets, resulting in high stability and superior electrochemical performance compared to the previous amorphous borides; and (iv) the hybridization between the B 2p state and the multiple d-orbitals of transition metals, increasing the electron flow between the atoms. The current work suggests that the growth of hierarchically crystalline Cu-Bi on Ni foam using a low-cost and simple procedure could provide a practical approach to designing hybrid supercapacitors with outstanding electrochemical performance.

Constructing a CdS QDs/silica gel composite with high photosensitivity and prolonged recyclable operability for enhanced visible-light-driven NADH regeneration

Visible-light-driven nicotinamide adenine dinucleotide (NADH) regeneration is one of the most effective measures, and cadmium sulfide (CdS) materials are typically used as low-cost photocatalysts. The CdS photocatalysts, however, still suffer from low regeneration efficiency and poor cycle stability. In this work, the CdS quantum dots (QDs) less than 10 nm embedded onto silica gel (CdS QDs/Silica gel) were constructed for visible-light-driven NADH regeneration by a successive ionic layer adsorption reaction and ball milling method. Results demonstrate that the photosensitivity of the CdS QDs/Silica gel composite was 31 times higher than that of the bulk CdS. Moreover, the conduction band (CB) edge of the CdS QDs/Silica gel composite is −1.34 eV, which is more negative 0.5 eV than that of the bulk CdS. The obtained CdS QDs/Silica gel composites showed the highest NADH regeneration yields of 68.8% under visible-light (LED, 420 nm) illumination and can be reused for over 40 cycles. Finally, the bioactivity of NADH toward enzyme catalysis is further confirmed by the hydrogenation of benzaldehyde to benzyl alcohol catalyzed with an alcohol dehydrogenase as enzyme catalysis.

Investigation of the Optical Properties and Bandgap Energy of CdCuS Using the Successive Ionic Layer Adsorption Reaction (SILAR) Method of Thin Film Deposition

Investigation of the Optical Properties and Bandgap Energy of CdCuS Using the Successive Ionic Layer Adsorption Reaction (SILAR) Method of Thin Film Deposition

Recent Advancements in the Synthetic Mechanism and Surface Engineering of Transition Metal Selenides for Energy Storage and Conversion Applications

Novel catalytic materials are under investigation to find convincing energy alternatives. In this context, transition metal selenides (TMSes) are found to be feasible, ecofriendly, and effective electrocatalysts with futuristic characteristics. A deep and comprehensive investigation on metal selenides for energy conversion and storage application is summarized in this review article. Different methods such as hydrothermal, solvothermal, coprecipitation, hot injection, successive ionic layer adsorption reaction, polyol, and others can be used for the synthesis of metal selenides based electrocatalysts, with different morphologies and compositions. The morphology of metal selenides is strongly controlled by factors such as reaction time, temperature, pH of the reaction medium, and surfactant. The electrochemical applications of metal selenides are governed by morphology, active spots for reaction, surface engineering, and confinement. It is concluded that TMSes deliver high performance with large surface area, which is possible due to their porous or 3D morphology. The TMSes with multimetal or with doping metal/nonmetals perform better compared to single atoms. It is concluded that the reaction mechanism of hydrogen evolution reaction and oxygen evolution reaction is a primary tool to better understand the system to develop more efficient catalysts for practical application.

Performance of CdS/TNTAs Nanocomposite in Removing Ciprofloxacin and Hydrogen Production using Simultaneously Electrocoagulation-Photocatalysis Process

This study used CdS as a pair of TiO2 Nanotube Arrays (TNTAs), considering the position and width of the energy band gap, which is expected to increase photocatalyst performance. The nancomposite was synthesized using the successive ionic layer adsorption reaction (SILAR) method, with Cd(CH3COO)2 and Na2S as precursors. The CdS/TNTAs nanocomposite is expected to reduce the energy band gap to enable the visible and UV spectrum to activate the photocatalyst. Additionally, the formed heterojunction mechanism provides opportunities for the trajectories of electrons and holes to be farther apart and reduce the recombination rate. The degradation ability of CdS/TNTAs nanocomposite in the photocatalytic process was evaluated using samples of ciprofloxacin liquid waste as an antibiotic, which is quite challenging to decompose completely. The ability of the photocatalytic process to produce hydrogen gas was also observed and its performance synergized with the electrocoagulation process. The result showed that the use of CdS as a TNTAs partner in CdS/TNTAs nanocomposites affects increasing photocatalyst performance, both in degrading ciprofloxacin and producing hydrogen gas. Furthermore, the CdS/TNTAs nanocomposite increased the photocatalytic process’s ability to degrade ciprofloxacin and produce hydrogen from 8.5 to 20.5% and 6 to 23.5 mmol/m2 compared to using TNTAs alone. The processing capability is further enhanced when run in synergy with the electrocoagulation process where the removal of ciprofloxacin reaches 86.55% and the hydrogen produced is 2.62×106 mmol/m2. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Construction of BiOCl-TNTs photoelectrochemical sensor for detection of hydrogen peroxide

In this study, BiOCl-TNTs photoelectrochemical sensors were fabricated by a combining technique of successive ionic layer adsorption reaction (SILAR) and anodic oxidation. The characterization techniques and electrochemical tests show that the as-prepared BiOCl-TNTs photoelectrochemical sensor possesses good photoelectric properties. And it has a fast photoelectric response to H2O2. The range of detection of H2O2 is 1 × 10−7 nM to 10 mM, the sensitivity is 14.69 μA mM−1 cm−2 and the lower detection limit is 0.05 nM (S/N = 3), and it exhibits good stability and selectivity. The results indicated that the BiOCl sensitization improved photocurrent response, and enhanced photoelectrocatalytic activity induced by solar energy.

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Development of novel TiN–LiAlSiO4/SnS/AuPd multilayer films for H2 generation by photocatalysis

TiN–LiAlSiO4/SnS/AuPd multilayer films were deposited on glass substrates using screen-printing and SILAR (successive ionic layer adsorption reaction) methods. The films were used as photocatalysts for H2 generation using a solar simulator source. The incorporation of the SnS provokes the presence of particles of different morphology and size, allowing a better light absorption on the surface of the films. In addition, AuPd nanoparticles were deposited on the multilayer films to improve photocatalytic activity. XRD and TEM analysis revealed that whatever the proportion, the main phase is TiN. The SEM images showed that the electrostatic attraction between TiN and SnS is a key factor that influences the morphology of the films. The optical band-gap values for the films were similar (∼3.86 eV). According to profilometry measurements, the thickness of films varies from 218 to 887 nm, and PL results showed that when the thickness decreases the electron-hole pair recombination processes decrease too. The highest H2 generation was reached by T20:L80/SnS/AuPd, around 99 μmol/m2 after 3 h of irradiation, while T80:L20/SnS/AuPd produces only 33 μmol/m2, and coincidentally, showed lower and higher thickness, respectively. Moreover, the presence of AuPd nanoparticles did not provoke any structural and optical modification on the films. However, it caused the existence of active sites for H2 generation and diminish the electron-hole pair recombination, evidenced by PL analysis. Finally, these results corroborate that the film with a low thickness and higher LiAlSiO4 showed better photocatalytic activity because of the inhibition of the electro-hole pair recombination.

Influence of Annealing Temperature on the Properties of SILAR Deposited CdSe/ZnSe Superlattice Thin Films for Optoelectronic Applications

In this work, superlattice thin films of CdSe/ZnSe were fabricated on a non-conductive glass substrate using the successive ionic layer adsorption reaction (SILAR) method to investigate their properties for possible optoelectronic applications. The SILAR process involved a total cycle time of 100 seconds for a complete SILAR cycle with a total of 12 cycles made by depositing alternative layers of CdSe and ZnSe. The deposited thin films were annealed at different temperatures and characterized to determine their optical, elemental, morphological and structural properties using UV-VIS spectroscopy, Scanning electron microscope (SEM)/energy dispersive x-ray spectroscope (EDS) and x-ray diffraction techniques (XRD). The results of the characterizations revealed that optical properties of the films such as absorbance, reflectance, refractive index and extinction coefficient are low but increased as the annealing temperature increases. The bandgap energy was found to decrease from 2.50 eV-1.90 eV for as-deposited film and those annealed between 373 K and 523 K. film thickness was found to range from 130.169 nm to 254.441 nm. The EDS results showed that the target elements such as Cd, Zn, Se and other elements traceable to the nature of substrate used were found to be present in the deposited thin film samples. The results of the XRD showed that the thin films are polycrystalline and the diffraction peaks are influenced by annealing of the sample at a higher temperature such as 523 K. The crystal parameters such as crystallite size, dislocation density and micro-strain of the film at 523 K were found to be 5.546 nm, 3.25 × 1016 l/m2 and 1.13 × 10-2. The SEM results showed that the CdSe/ZnSe superlattice films were composed of tiny nanoparticles of different dimensions and sizes with hollow which increased as the annealing temperature increased from 432 K to 523 K. Possible applications of the deposited superlattice thin films in solar cells and optoelectronic devices were established by virtue of their bandgap energy and other properties.

0D-2D S-scheme CdS/WO3 catalyst for efficiently boosting CO2 photoreduction

Improving the dispersion of active sites and photogenerated carriers’ separation efficiency are of significant for enhancing the CO2 photoreduction. In this research, Zero-dimensional/Two-dimensional (0D-2D) S-scheme CdS/WO3 photocatalysts have been successfully obtained via the simple hydrothermal method and successive ionic layer adsorption reaction. SEM and TEM images provide that CdS Quantum Dots (QDs) are uniformly dispersed on the surface of WO3 nanosheets. WO3 nanosheets can greatly improve the dispersion of the CdS QDs, which can enlarge the adsorption and reaction efficiency of CO2 at the photoreduction sites. CO2 photoreduction tests show that the CdS/WO3 (CW-2) composite expresses excellent CO2 photoreduction ability and great catalytic stability. The yields of CO and CH4 with the CW-2 as catalyst are 64.7 μmol/g·h and 2.3 μmol/g·h, which are about 4.0 and 2.7 times more potent than that of CdS QDs. 13C calibration experiment proves that the C-source of CO and CH4 are obtained by the CO2 photoreduction process. Density functional theory calculation and electron spin resource results confirm the formation of S-scheme heterojunction. A potential synergistic effect of highly dispersed active sites and the S-scheme heterojunction has been provided for enhanced CO2 photoreduction performance.

Enhanced Photoelectrochemical Performance in Engineered Interface 2D Metal Sulfide Heterostructures for Water Splitting

Photoelectrochemical water splitting (PEC) is a viable solution for addressing future environmental and energy concerns. However, due to the high cost of photoelectrodes and the limitations of sluggish kinetics, practical applications are limited. To achieve that goal, effective solutions are still needed to create low-cost photoelectrodes suited for PEC. Transistion metal sulfides (TMS) materials have a high potential for use as photoelectrodes due to their favorable and impressive properties1. The photoactivity of TMS is typically unlimited due to low reflection at the grain boundary. The individual atomic thin sheets with higher surface area compared to bulk materials allow for faster diffusion of photoinduced charge carriers primarily due to the less interface between their grains. Their lower interfacial contact resistance enables enhanced charge dynamics and, as a result, improved electrochemical reaction kinetics. When compared to other TMS, CdS has a direct bandgap and excellent photoactivity. However, its toxicity and photocorrosion make it unsuitable for long-term practical use. WS2 is well-known layered transition metal sulfide that has a 2D molybdenite structure. It is non-toxic in acidic/neutral solutions that are chemically stable. It has been demonstrated to be more stable against oxidation and photo corrosion than CdS, which is extensively employed in photocatalysis2. However, because of the recombination of photoinduced charge carriers, pure WS2 exhibits relatively poor photocatalytic efficiency and stability. As a result, combining WS2 based photoactive nanomaterials with other suitable materials has helped overcome this challenge. Transistion metal sulfides with acceptable band structures for heterostructure construction with WS2 may enable breakthroughs in photocatalytic and photo-electrochemical processes.The primary focus of this work is to construct heterostructures by combining CdS and WS2 and to investigate their role as photoanodes of semiconductor materials in PEC water splitting. In this work, we have synthesised heterostructures using a facile solution-reaction method and Successive Ionic Layer Adsorption Reaction deposition (SILAR) technique which is intrinsically cost effective and scalable3. The heterostructure is characterised by XRD, SEM and TEM. We also studied the performance enhancement of this heterostructure using Linear sweep voltammetry and Electrochemical impedance spectroscopy. Pristine WS2 and CdS showed photocurrent densities of 3 μA cm-2 and 20 μA cm-2. However, heterostructures formation led to much improved photocurrents. Photocurrent densities of 151 μA cm-2 were observed for WS2/CdS heterostructures respectively at 1.23 V vs RHE. The enhanced improvement in photoelectrochemical performance in the case of the heterostructures could be due to the following factors: (a) the intimate interaction of this unique heterostructure improves adhesion and lowers the photoinduced charge transfer barrier; (b) increased light harvesting capability; and (c) improved charge dynamics of photoinduced charge carriers due to proper band alignment. The current study paves the way for further research into the creation of metal sulfide heterostructures that generate analogous photoelectrode materials.Keywords: Photoelectrochemical water splitting, metal sulfides, photoelectrodes.

Mitigation on self-discharge behaviors via morphological control of hierarchical Ni-sulfides/Ni-oxides electrodes for long-life-supercapacitors

To cope up with the sustainable energy storage goals for supercapacitors (SCs), the self-discharge in SC electrodes is a significant hurdle, and thereby, nickel sulfide (NS) with high conductivity is adopted as a test vehicle for understanding the morphological evolution effects for long-life SCs. Herein, honeycomb-like NS is hierarchically formed over hydrothermally grown nickel oxide (NO) via successive ionic layer adsorption reaction (SILAR) method. Their heterostructure shows a fivefold improvement in specific capacitance from 348 F g−1 to 2077 F g−1 at 1 mV s−1 over bare NO. Furthermore, the remarkable upliftment of capacitance retention is achieved from 60.7% to 92.3% even after 3000 cycles via morphological control of NS/NO hetero-structure with the help of highly conductive NS. More importantly, the self-discharge behaviors and synergistic role of leakage current associated with morphological evolution via NS overcoating are studied in detail. In particular, the self-discharge mitigation from 45% (NO) to 35% (NS20/NO) due to the NS/NO heterostructure and the behind mechanism are ascribed to the activated-controlled Faradaic reaction coupled with a charge redistribution. This study emphasizes the potential importance of composite heterostructure by tuning the electrical conductivity and morphological adjustment NO via consecutive overcoating of NS through SILAR as a novel strategy. This enhances charge storage, redox kinetics, and the mitigation of self-discharge properties of the active electrode materials. For practical validation on sustainable energy storage, NS20/NO supercapacitors illuminate the LED for 35% longer than NO after one-time charging, potentially beneficial for the next generation SCs.

Facile preparation of MnO2–TiO2 nanotube arrays composite electrode for electrochemical detection of hydrogen peroxide

The MnO2-TNTA composite electrodes were obtained through depositing MnO2 into TiO2 nanotube arrays (TNTA) by successive ionic layer adsorption reaction (SILAR) and subsequent hydrothermal method. The MnO2-TNTA nanocomposites were used as electrochemical sensors for the detection of hydrogen peroxide (H2O2). The preparation conditions of MnO2-TNTA electrodes and test conditions affect the electrochemical detection performance significantly. The optimal conditions are listed as follows: the number of SILAR cycles, 6 times; KMnO4 solution temperature, 50 °C; supporting electrolyte, 0.5 M NaOH. Under these conditions, the MnO2-TNTA electrode exhibits the best performance for detecting H2O2. The optimized MnO2-TNTA electrode has a minimum detection limit of 0.6 μM (S/N = 3) and a linear range of 5 μM ∼ 13 mM, which is much superior to the previously-reported electrodes. Moreover, the optimized MnO2-TNTA electrode possesses high selectivity, excellent stability and good reproducibility in the detection of H2O2. When used in the determination of H2O2 content in actual samples including disinfectant and milk, it also shows good accuracy, ideal recovery (96.00% ∼ 102.67%) and high precision (RSD < 4.0%).

Preparation and photoelectric properties of holmium-doped bismuth sulfide film

Ho-doped Bi2S3 film (Ho/Bi2S3) was prepared on the FTO substrate by successive ionic layer adsorption reaction (SILAR) and hydrothermal method. The as-prepared films were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), UV–Vis diffuse reflection spectroscopy (DRS), and X-ray Photoelectron Spectroscopy (XPS). EDS and XPS have confirmed the existence of Ho. The Ho3+ ions enter the crystal lattice of Bi2S3 and occupy the Bi3+ sites making some crystals vertical flake-like. The photovoltage of Ho/Bi2S3 increases from 0.203 V to 0.265 V by 30% and the photocurrent density increases from 0.366 mA/cm−2 to 1.09 mA/cm−2 by 1.97 times when the Ho-doping concentration is 0.5 mmol L−1. Moreover, the impurity level introduced by Ho-doping reduces the energy of the electronic transition making Ho/Bi2S3 generate more photo-generated carriers to improve the photoelectric performance.

Mixed phase FeTe: Fe2TeO5 nanopebbles through solution chemistry: Electrochemical supercapacitor application

Mixed phase of iron telluride based thin films consisting of nanopebbles has been grown successfully over conducting stainless steel (SS) substrate through successive ionic layer adsorption reaction (SILAR) process. Crystal structural and elemental states through XPS revealed clear indication of FeTe: Fe 2 TeO 5 mixed phase growth and well supported through FTIR studies. Agglomeration of embedded quantum dots forming nanopebbles like surface architecture resulting in enhanced hydrophilic nature evident through contact angle and higher surface roughness by atomic force micrographs found beneficial as more electroactive surface area for electrolyte ions to interact. This helped to achieve a significant specific capacitance of 591 F/g (166 mF/cm 2 ) @3 mV/s potential scan rate and, 107 F/g (30 mF/cm 2 ) @0.4 mA/cm 2 in NaCl electrolyte. Performed electrochemical impedance spectroscopy (EIS) studies explored clear insight of the solution and charge transfer resistances, and relaxation time constant. Iron telluride based thin film clearly demonstrates very high value of pseudo capacitive contribution than the electric double layer due to the intrinsic pseudocapacitive behavior of mixed phase. • First report on iron telluride based (FeTe: Fe 2 TeO 5 ) thin film synthesis using simple SILAR method and successfully employed as supercapacitor electrode. • Nanopebbles embedded with quantum dots agglomeration responsible for more electrochemical active sites. • Notable specific capacitance of 591 F/g (426 C/g or 166 mF/g) at 3 mV/s by CV and 107 F/g (30 mF/cm 2 ) at 0.4 mA/cm 2 by GCD studies. • Enhanced inner (pseudo q p ) charge storage contributions than outer (EDLC q d l ).

In situ formed CuInS2/SnS2 hybrid on foam-like nickel as bifunctional electrode for water splitting

Developing low-cost, efficient and robust non-noble electrocatalysts for overall water splitting is of primary importance in the future of energy solutions. In this paper, the CuInS2/SnS2 composite nanosheets array on foam-like nickel (CuInS2/SnS2/NF) was synthesized in situ via a facile hydrothermal approach and the successive ionic layer adsorption reaction method (SILAR). The as-obtained heterostructure array exhibits high electrocatalytic activity toward HER with a small overpotential of 78, 191 and 337 mV at 10, 20, and 100 mA/cm2, and remarkably enhanced OER activities with the overpotential of 258, 286 and 382 mV at 10, 20, and 100 mA/cm2 in an alkaline electrolyte. Meanwhile, the CuInS2/SnS2/NF electrode shows a lower tafel slope and outstanding electrochemical stability in both the HER and OER, displaying an excellent application foreground in the field of electrocatalytic water splitting. Moreover, the overall water splitting performance of CuInS2/SnS2/NF electrode was studied, in which the electrode serves as both the anode and cathode, and at a comparatively low voltage of 1.79 V, the current density achieves 100 mA/cm2. This study establishes a primitive strategy for obtaining mixed multimetal sulfides on self-supporting porous metal substrate, which can be used as an efficient bifunctional electrocatalyst, and is of great practical significance in future energy application.

Promoting photoelectrochemical hydrogen production performance by fabrication of Co1-XS decorating BiVO4 photoanode

Photoelectrochemical (PEC) water splitting is an effective way of converting solar energy into hydrogen (H2) energy. However, the carriers’ transmission and the reaction kinetics of the photoelectrode are dilatory, which will influence the conversion efficiency of solar energy to H2. In this work, a novel of BiVO4/Co1-XS photoanode was successfully fabricated through the successive ionic layer adsorption reaction. The photocurrent density of optimal sample BiVO4/Co1-XS (2.9 mA cm−2 at 1.23 VRHE) has reached up to 5 times that of pure BiVO4, and the applied bias photon to current conversion efficiency increased from 0.04% (BiVO4) to 0.4% (BiVO4/Co1-XS). The superior PEC performance of the BiVO4/Co1-XS photoanode is mainly related to the improved conductivities and reaction kinetics. The charge injection efficiency of BiVO4/Co1-XS grew to about 80%, and the charge separation efficiency was up to 34%, revealing that the decoration of Co1-XS could significantly accelerate the transfer speed of photogenerated carriers from the electrode surface to the electrolyte. This work provided an efficient and simple scheme for improving the PEC performance of photoanode, through reasonable design and research.

Tungsten Disulfide Heterostructure for Boosting Charge Carriers and for Enhancing Photoanodic Performance in Water Splitting

Photoelectrochemical water splitting (PEC) is a compelling approach to convert solar energy to chemical energy by liberating hydrogen, making it a possible solution to the worldwide energy crisis by eliminating all carbon dioxide emissions. In practice, no single electrode material can meet all PEC water splitting requirements. The major challenges for PEC are electron-hole pair recombination, stability and reduced absorption of visible light. Transition Metal dichalcogenides (TMD) based heterostructures are being envisioned as novel electrode materials because of their exceptional electrical, chemical, mechanical and thermal stability which include high electron mobility, highly exposed active sites, layer dependent band gap, and higher ionic conductivity etc. TMDs have higher electro conductivity resulting in significant enhancement of the electrochemical performance in PEC. Further, it also exhibits desirable electrochemical behaviour through its oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) as a photoelectrode for water splitting. However, due to poor absorbance and significant reflection at the grain boundaries, the light harvesting ability of bulk or nanosized TMD materials is often limited. The charge carriers produced by light illumination will also reach the surface faster than bulk materials in the semiconductor, because of the lesser transport distance.In the present work, heterostructures consisting of Tungsten disulfide (WS2) and cadmium sulphide (CdS) were synthesized using a hydrothermal method and Successive Ionic Layer Adsorption Reaction (SILAR) deposition method. The presence of these nanostructures was confirmed by XRD, Raman, UV-Visible spectroscopy, SEM, TEM and PL spectroscopy. The morphological study clearly indicates a homogeneous distribution of CdS nanospheres on WS2 nanostructures, indicating close contact between them which helps in efficient charge separation and migration. Further, the continuous nature of the heterostructures of the two materials is not limited to any visible discrete entities. The porosity of the pristine WS2 nanostructures allows CdS nanospheres to deposit inside the pores along the entire thickness of the nanosphere, and hence, the highly homogeneous nature of the heterostructures is obtained as indicated by the physical characterization.Due to this unique structure, the obtained heterostructures showed excellent performance as photoanode. The CdS@WS2 photoanode demonstrated a photocurrent density of 0.15 mA cm−2 at 1.23 V vs. RHE, which is over 20 times higher than that of the pure pristine materials. Further, CdS@WS2 heterostructures, as compared to pure materials, have demonstrated longer emission-decay-life times and dramatically quenched the emission of fluorescence compared to pristine materials. In CdS@WS2 heterostructures, the absorption edge of the WS2 nanostructures also exhibit a considerable increase in light absorption in the total visible spectrum. This results in enhanced charge separation with proper band alignment leading to improvements in electrochemical performance of CdS@WS2 photoelectrodes. Further, the low onset potential further eliminates the need for voltage bias in practical applications.

Fabrication of multilayer 1D TiO2/CdS/ZnS with high photoelectrochemical performance and enhanced stability

Nano TiO2 is a basic photoanode material in the application of new type solar cell for its appropriate bandgap and photoemission. However, traditionally TiO2-based photoanode films are limited in weak photoresponse and effortless recombination. Herein, we increase light absorption range through combined the uniform CdS quantum dots (QDs) by successive ionic layer adsorption reaction (SILAR) method and decrease the recombination of photo-generated electrons/holes through ZnS passivation layer overlaying on TiO2/CdS. Photocurrent response (i-t), photocurrent density-voltage (J-V) curves of TiO2/CdS/ZnS demonstrated the photovoltaic conversion efficiency (η) has been reaching 3.43%, which has 230% and 33% improvement than pure TiO2 and TiO2/CdS.