Pristine WS2 Research Articles

Synthesis of highly efficient novel two-step spatial 2D photocatalyst material WS2/ZnIn2S4 for degradation/reduction of various toxic pollutants

In this article, we report the synthesis, characterization of novel biofriendly 2D/2D heterostructure WS2/ZnIn2S4 material in which 2D WS2 nanosheets are uniformly distributed spatially onto the spherically arranged 2D leaves of ZnIn2S4. We then studied the in-depth photocatalytic degradation activity of this novel nanocomposite and its pristine component materials on cationic dye: malachite green, anionic dye: congo red and reduction of heavy metal: chromium(VI) and the degradation efficiency of composite material was also tested on rhodamine-B, methylene blue, methyl orange dyes and acetaminophen/paracetamol drug. Form factor, structure factor and shape factor analysis has been carried out using X-ray diffractometry (XRD). Bond vibrations, functional groups and phonon vibration mode analysis has been done based on Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Morphological and compositional analysis has been done using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM). Surface area and pore size/distribution was characterized using Brunauer–Emmett–Teller (BET) method and Barrett-Joyner-Halenda Model. Degradation pathways and intermediate products are proposed using the high-performance liquid chromatography (HPLC). Photocatalytic activity of the nanocomposite WS2/ZnIn2S4 is compared with pristine ZnIn2S4 and pristine WS2, which shows more than 50% enhancement in both efficiency and rate of degradation/reduction for all the pollutants. A scavenger study was carried out to get insight of primary and secondary reactive oxygen species (ROS) taking part in degradation. Exciton lifetime, surface charge and stability, and flat band positions were studied based on time-correlated single photon counting (TCSPC) also known as time-resolved photoluminescence (TRPL), zeta potential, and Mott-Schottky respectively. Rate kinetics study was performed to analyze the physical and chemical behaviour of the nanocomposite with pollutants in consideration. Results show ∼100%, ∼90%, and ∼95% degradation efficiency by the heterostructure for malachite green (MG), congo red (CR), and reduction of heavy metal chromium (Cr(VI)) respectively within 5 min, which is a huge improvement as compared to pristine WS2 and pristine ZnIn2S4, both of which show the efficiencies of only ∼25% to∼75% in all the cases.

Moisture-Resistant and Highly Selective NH3 Sensor Based on CdS/WS2 Composite Heterojunction.

This study reports the synthesis of CdS/WS2 composites via a green and ultra-low-cost hydrothermal method. By controlling the relative mass ratio between WS2 and CdS, an n-n type CdS/WS2 heterostructure, with excellent NH3 gas-sensitive properties, was developed and investigated at room temperature. Compared with pristine WS2 and CdS, the CdS/WS2-40%wt composite exhibited excellent selectivity of more than 4 orders of magnitude for sensing NH3, a very short recovery time of 3 s, and ultrahigh selectivity at room temperature. The large specific surface area of the CdS/WS2 composite increased the active sites for the gas-sensitive reaction. Additionally, the 2D morphology of CdS/WS2 and the heterojunction formed between WS2 and CdS contributed to the improved performance. Anti-humidity interference tests showed that the CdS/WS2 sample remained stable under real-time monitoring of NH3 at different ambient humidity values. This study paves the way for designing high-performance gas sensors operating at room temperature.

A facile two-step hydrothermal preparation of 2D/2D heterostructure of Bi2WO6/WS2 for the efficient photodegradation of methylene blue under sunlight

A facile two-step hydrothermal method was successfully used to prepare a photocatalyst Bi2WO6/WS2 heterojunction for methyl blue (MB) photodegradation. Fabricated photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Band gap measurements were carried out by diffuse reflectance spectroscopy (DRS). Results indicated that the prepared heterostructure photocatalyst has increased visible light absorption. Photocatalytic performance was evaluated under sunlight irradiation for methylene blue (MB) degradation as a model dye. Variations in pH (4–10), amount of catalyst (0.025–0.1 g/L), and initial MB concentrations (5–20 ppm) were carried out, whereas all prepared catalysts were used to conduct the tests with a visible spectrophotometer. Degradation activity improved with the pH increase; the optimum pH was approximately 8. Catalyst concentration is directly related to degradation efficiency and reached 93.56% with 0.075 g of the catalyst. Among tested catalysts, 0.01 Bi2WO6/WS2 has exhibited the highest activity and a degradation efficiency of 99.0% in 40 min (min) for MB. MB photodegradation follows pseudo-first-order kinetics, and obtained values of kapp were 0.0482 min−1, 0.0337 min−1, 0.0205 min−1, and 0.0087 min−1 for initial concentrations of 5 ppm, 10 ppm, 15 ppm, and 20 ppm, respectively. The catalyst was reused for six cycles with a negligible decrease in the degradation activity. Heterostructure 0.01 Bi2WO6/WS2 has exhibited a photocurrent density of 16 μA cm−2, significantly higher than 2.0 and 4.5 μA cm−2 for the pristine WS2 and Bi2WO6, respectively. The findings from these investigations may serve as a crucial stepping stone towards the remediation of polluted water facilitated by implementing such highly efficient photocatalysts.

Editors’ Choice—Atomic Layer Etching of Tungsten Disulfide Using Remote Plasma-Induced Oxidation and Wet Etching

WS2 is an emerging semiconductor with potential applications in next-generation device architecture owing to its excellent electrical and physical properties. However, the presence of inevitable surface contaminants and oxide layers limits the performance of WS2-based field-effect transistors (FETs); therefore, novel methods are required to restore the pristine WS2 surface. In this study, the thickness of a WS2 layer was adjusted and its surface was restored to a pristine state by fabricating a recessed-channel structure through a combination of self-limiting remote plasma oxidation and KOH solution etching processes. The reaction between the KOH solution and WOX enabled layer-by-layer thickness control as the topmost oxide layer was selectively removed during the wet-etching process. The thickness of the WS2 layer decreased linearly with the number of recess cycles, and the vertical etch rate was estimated to be approximately 0.65 nm cycle−1. Micro-Raman spectroscopy and high-resolution transmission electron microscopy revealed that the layer-by-layer etching process had a nominal effect on the crystallinity of the underlying WS2 channel. Finally, the pristine state was recovered by removing ambient molecules and oxide layers from the surface of the WS2 channel, which resulted in a high-performance FET with a current on/off ratio greater than 106. This method, which provides a facile approach to restoring the pristine surfaces of transition-metal dichalcogenide (TMDC) semiconductors with precise thickness control, has potential applications in various fields such as TMDC-based (opto)electronic and sensor devices.

Sulfurized Colloidal Quantum Dot/Tungsten Disulfide Multi‐Dimensional Heterojunction for an Efficient Self‐Powered Visible‐to‐SWIR Photodetector

AbstractEmerging semiconducting materials show considerable promise for application in the development of next‐generation optoelectronic devices. In particular, broadband light detection is crucial in various applications, including multispectral imaging and cognition. Therefore, tuning the physical properties of semiconductors and thereby building an efficient heterojunction are important for achieving a high‐performance photodetection device. In this study, a heavy p‐type colloidal quantum dot (CQD) is synthesized through solution‐based sulfurization. The resulting cubic‐shaped CQD exhibits broadband and strong absorption, which enable its broadband absorption. Further, a multidimensional 0D‐2D heterojunction is developed using p‐type CQD and n‐type tungsten disulfide (WS2). This efficient p‐n junction is operated as a fully self‐powered optical sensor and phototransistor under various light illumination conditions. Under the self‐powered condition, the CQD/WS2 heterojunction device exhibits 440‐ and 200‐fold‐higher responsivity and detectivity, respectively, than pristine WS2.

Local hybridized states of adsorbed atomic Sn on WS2 substrate

We study the growth of Sn and the local electronic properties of Sn grown WS2 surfaces by in-situ scanning tunneling microscopy (STM), scanning tunneling spectroscopy, and first principles density functional theory calculations. Our investigations suggest substitutional doping of Sn at the S sites, with Sn atoms occupying a slightly elevated position of 80 pm on the WS2 surface. These results agree well with our STM observations on room temperature growth of atomic Sn, indicating commensurate or nearly commensurate adsorption at the top S sites with a buckling height of 40 ± 10 pm. Pristine WS2 without any S vacancies on the surface exhibits a bandgap of 1.39 eV, while ingap local density of states comprised of W d and S p orbitals are detected when S vacancies are considered. Upon adsorption of Sn atoms, we find the signature of modulated hybridized ingap electronic states of Sn p and W d orbitals with a spin orbit coupling interaction up to 38 meV at the K point of the Brillouin zone. These results throw important light on the future fabrication of Janus like SnWS vertical heterojunctions with atomic level doping accuracy, which will have enormous device applications.

Charge Transfer Modulation in Vanadium-Doped WS2 /Bi2 O2 Se Heterostructures.

The field of photovoltaics is revolutionized in recent years by the development of two-dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS2 is investigated, hereafter labeled V-WS2 , in combination with air-stable Bi2 O2 Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS2 /Bi2 O2 Se, 0.4 at.% V-WS2 /Bi2 O2 Se, and 2at.% V-WS2 /Bi2 O2 Se, respectively, indicating a superior charge transfer in V-WS2 /Bi2 O2 Se compared to pristine WS2 /Bi2 O2 Se. The exciton binding energies for WS2 /Bi2 O2 Se, 0.4at.% V-WS2 /Bi2 O2 Se and 2 at.% V-WS2 /Bi2 O2 Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS2 . These findings confirm that by incorporating V-doped WS2 , charge transfer in WS2 /Bi2 O2 Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi2 O2 Se.

Directing Exfoliation, Slipping, and Corrugation in WS2 through Bubbling with 15 keV He2+ Ion Irradiation

In article number 2200598 by Dambarudhar Mohanta and co-workers, the implantation-led bubbling effects of 15 keV He2+ ions (fluence of ~1015–1016 ions cm−2) in bulk polycrystalline WS2 are reported. The results as regards surface morphology, Raman signature, and the core-level spectra of the pristine and irradiated WS2 are discussed in conjunction with the sheet exfoliation and altered surface constructs.

Synergistic effect of polypyrrole modified WS2 nanosheets on visible light assisted catalysis for the removal of chromium (VI) and humic acid

In this work, a novel nanocomposite was synthesized by the surface modification of tungsten disulphide (WS2) with polypyrrole (PPy) for the photocatalytic removal of heavy metal ions (chromium hexavalent (Cr (VI)) and natural organic contaminant (humic acid (HA)). The morphological analysis of synthesized samples was carried out using Field Emission Scanning Electron Microscopy (FESEM) which shows that PPy nanoparticles (NPs) are randomly distributed on the surface of WS2 nanosheets (NSs). The interlayer spacing of fringe width of WS2 NSs calculated from High Resolution Transmission Electron Microscopy (HRTEM) studies comes out to be 0.65 nm also in coherence with XRD analysis. Elemental analysis of synthesized nanocomposite was confirmed by using X-Ray Photoelectron Spectroscopy (XPS). The synthesized WP nanocomposite shown enhanced efficiencies (ɳCr ∼98.75% and ɳHA ∼77.78%) as compared to negligible efficiency of pristine WS2 (∼15% and 16%) and PPy (∼49% and 40%) for the reduction of Cr (VI) and degradation of HA, respectively. The enhanced removal efficiency of nanocomposite was attributed to decrease in the bandgap (2.03 to 1.80 eV), enhanced carrier concentrations (4.0 × 1030 cm−3 to 3.2 × 1031 cm−3) and low recombination rate (1.85 to 7.40 ns) of WP nanocomposite on the incorporation of PPy in WS2 as evident from UV–Vis, Mott-Schottky technique (MSK) and Time-correlated single-photon counting (TCSPC) decay measurement, respectively. The enhancement in removal efficiency is also attributed to the high surface area (160.36 m2/g) of the nanocomposite as analyzed using Brunauer-Emmett-Teller (BET) technique. The photocatalytic reduction efficiency was also studied as a function of pH (4,7 and 9). The reduction pathways follow second-order rate kinetics with high value of correlation coefficient (R2 ∼ 0.99). The proposed photocatalytic reduction mechanism was supported by a trapping study which shows that the superoxide radicals (⋅O2−) were the primary species taking part in photocatalytic reaction. Reusability test and stability of materials demonstrates promising photocatalytic performance of the synthesized nanocomposite.

Fabrication of layered In2S3/WS2 heterostructure for enhanced and efficient photocatalytic CO2 reduction and various paraben degradation in water

Because of the excessive use of fossil fuels, CO2 emissions into the environment are increasing. An efficient method of converting CO2 to useful carbonaceous products in the presence of light is one way to address the issues associated with energy and environmental remediation. In2S3/WS2 heterostructure has been fabricated using the efficient hydrothermal method. The results of structural, morphological, optical, and photo/electrochemical characterization confirm the formation of a hierarchical, layered heterostructure of type-II. Enhanced photocatalytic activity is observed in InS/WS heterostructure compared to pristine In2S3 and WS2. InS/WS heterostructure exhibit higher photocatalytic activity than pure In2S3 and WS2. For 12 h, photocatalytic CO2 reduction produces 213.4 and 188.6 μmol of CO and CH4, respectively. Furthermore, the photocatalytic ability of the synthesized materials to degrade different parabens (Methyl: MPB, Ethyl: EPB, and Benzyl: BPB) under visible radiation was evaluated. Under optimized conditions, the InS/WS heterostructure degraded 88.6, 90.4, and 95.8% of EPB, BPB, and MPB, respectively, in 90 min. The mechanism of photocatalysis was discussed in detail. MCF-7 cell viability was assessed and found to exhibit low mortality in InS/WS treated MPB aqueous solution. InS/WS heterostructure could improve the fabrication of more sulphide-based layered materials to combat environmental pollution.

Magnetic and Electronic Properties of Edge-Modified Triangular WS2 and MoS2 Quantum Dots

The magnetic and electronic properties of zigzag-triangular WS2 and MoS2 quantum dots are investigated using density functional theory calculations. The pristine WS2 and MoS2 nanodots hold permanent spin on their edges which originates from the unpaired electrons of the transition metals at the edges. The ferromagnetic spin ordering in zigzag-triangular WS2 and MoS2 can be transformed to antiferromagnetic ordering with S = 0 and to nonmagnetic, respectively, by edge passivation with 2H. The calculations of the Curie Temperature indicate that these magnetic states are stable and withstand room temperature. The paramagnetic susceptibility of these structures significantly decreases by edge sulfuration. Moreover, it can be converted to diamagnetic susceptibility by edge passivation with 2H as found in WS2 nanodots. These structures are semiconductors with energy gaps of ~3.3 eV that decrease unexpectedly by edge passivation due to the existence of lone pairs from S atoms that give a high contribution to the low-energy molecular orbitals. With these preferable magnetic properties and controlled electronic ones, WS2 and MoS2 quantum dots are potential candidates for spintronic applications.

A first-principles investigation on the adsorption of octanal and nonanal molecules with decorated monolayer WS2 as promising gas sensing platform

With the broad applications of two-dimensional transition, metal dichalcogenides in gas sensing prompt us to investigate the adsorption and gas sensing properties of the bare and metal-decorated tungsten disulfide (WS2) interaction with nonanal and octanal gas molecules by using first-principles methods. In this regard, first-principles calculations based on density functional theory (DFT) have been employed to study the detection of nonanal and octanal as well-known breast cancer biomarkers. The results showed that the pristine WS2 monolayer is not appropriate to develop gas sensors for the target. Based on the detailed DFT calculations, decoration of the WS2 surface with Ni and Pt could enhance gas detection and sensitivity and tune the energy bandgap. The present results suggested that the adsorption energy of nonanal and octanal has been increased to −2.59 and −2.34 eV after interaction with Ni-decorated WS2. In addition, sensitivity has been enhanced significantly, and the recovery time of 7.76 s for Ni-decorated WS2 was achieved after interaction with octanal gas. As a result, the decorated WS2-based nanosensor might be an auspicious platform for gas detection. Undoubtedly, this work can open up a prospect for the use of excellent Ni-/Pt-decorated WS2 materials to achieve high-efficiency detection of nonanal and octanal gas molecules.

Biomorphic WO3@WS2 heterojunction composites for enhanced NO2 gas-sensing performance at room temperature

The fabrication of heterojunction composites with high activity is an effective way to enhance the room temperature (RT) gas sensing performance. However, it is still challenging for a well-designed heterojunction interface to obtain more excellent sensitivity and response-recovery rate. Herein, the hemp sticks derived from porous carbon were used as bio-templates. WO3@WS2 heterojunction composites with bio-morphology were synthesized via hydrothermal and sulfur vapor transmission methods. 3D hierarchical structure, exposed the S-termination of WS2, and the “SWO” of heterojunction interface WO3@WS2 collectively enhance the WO3@WS2/BC gas sensing performance. The results showed that the WO3@WS2/BC composite sensor exhibited remarkable selectivity to NO2 and reached a response as high as 42.9 toward 100 ppm NO2 at RT, about 3-fold higher than that of pristine WS2 nanosheets, a super-fast response/recovery time (1.6 s/37 s). The WO3@WS2/BC sensor maintained its excellent performance within twelve cycles and three months of storage in air, which has good selectivity for NO2 gas. This study provides a new line of research for developing highly sensitive NO2 detection at RT.

Photoelectric properties of pristine and niobium-doped tungsten disulfide layered crystals

Tungsten disulfide (WS2) is a transition-metal dichalcogenide that is suited to next-generation electronic and optoelectronic devices. Doping is necessary for WS2 applications because it allows the inherent characteristics of WS2 to be tuned to increase its functionality. This study determines the effect of niobium (Nb) doping on the photoelectric properties of WS2 crystals. A chemical vapor transport process is used to grow pristine and Nb-doped WS2 crystals. Scanning electron microscopy images show that the WS2 specimens consist of layered crystals. The photoresponsivity of the samples increases as the incident laser power decreases. Nb-doped WS2 crystals are 92 times more photoresponsive than pristine WS2 crystals at a laser power of 2 × 10−8 W. The ratio of the normalized photocurrent for a Nb-doped sample to that for a pristine sample increases as the frequency of the illumination increases to a maximum value of 11.5 at 104 Hz. Time-dependent photocurrent measurements show that the rise and fall times for Nb-doped WS2 crystals are shorter than those for pristine WS2 crystals by at least an order of magnitude. The results of this study show that Nb doping significantly increases the optical response of WS2 crystals.

Interlayer and Intralayer Excitons in AlN/WS2 Heterostructure

The study of intra and interlayer excitons in 2D semiconducting vdW heterostructures is a very hot topic not only from a fundamental but also an applicative point of view. Due to their strong light-matter interaction, Transition Metal Dichalcogenides (TMD) and group-III nitrides are particularly attractive in the field of opto-electronic applications such as photo-catalytic and photo-voltaic ultra-thin and flexible devices. Using first-principles ground and excited-state simulations, we investigate here the electronic and excitonic properties of a representative nitride/TMD heterobilayer, the AlN/WS2. We demonstrate that the band alignment is of type I, and low energy intralayer excitons are similar to those of a pristine WS2 monolayer. Further, we disentangle the role of strain and AlN dielectric screening on the electronic and optical gaps. These results, although they do not favor the possible use of AlN/WS2 in photo-catalysis, as envisaged in the previous literature, can boost the recently started experimental studies of 2D hexagonal aluminum nitride as a good low screening substrate for TMD-based electronic and opto-electronic devices. Importantly, our work shows how the inclusion of both spin-orbit and many-body interactions is compulsory for the correct prediction of the electronic and optical properties of TMD/nitride heterobilayers.

Filling Selenium into Sulfur Vacancies in Ultrathin Tungsten Sulfide Nanosheets for Superior Potassium Storage.

The development of WS2 as an anode for potassium-ion batteries (PIBs) is severely confined by the low K+ storage capacity and poor intrinsic electrical conductivity. Our previous study demonstrated that the creation of sulfur vacancies (VS) in WS2 can enhance its K+ storage capability. However, it is a big challenge to keep the stability of VS while reserving the excellent activity. Herein, we design Se-filled WS2 nanosheets with VS (VS-WS2-Se NS) for PIBs. The Se heteroatom filling into the VS can not only stabilize and activate them, rendering more active sites to adsorb K+, but also further enhance the electrical conductivity. Consequently, the VS-WS2-Se NS anode presents significantly promoted storage capacity and reaction kinetics, superior to the pristine WS2 and WS2 with only VS. Remarkably, the VS-WS2-Se NS anode exhibits the highest specific capacity of 363.9 mA h g-1 at 0.05 A g-1. Simultaneously, a high reversible capacity of 144.2 mA h g-1 after 100 cycles at 2.0 A g-1 is shown. Ex situ analyses demonstrated that the potassium storage mechanism involves the intercalation and conversion reaction between WS2 and K+. Moreover, DFT calculations revealed that the Se filling into VS can further enhance the electrical conductivity and reduce the K-insertion energy barriers of WS2 and thus account for the outstanding electrochemical performance. This study demonstrates that engineering the vacancies by the heteroatom filling strategy offers a novel and feasible route for designing high-performance electrode materials in various energy-storage systems.

First Principles Study of Photocatalytic Reduction of CO2 to CH4 on WS2-Supported Pt Clusters

CO2 conversion into valuable chemicals and fuels is a sustainable route to the concurrent mitigation of the energy crisis and the greenhouse effect. Herein, first principles calculations were employed to study the photocatalytic CO2 reduction over pristine WS2, S-vacancy WS2, and Pt cluster loaded WS2. Our results indicate that the introducing of S-vacancy and loading of Pt clusters can improve the optical absorption in the visible-light region. Furthermore, S-vacancy can lower the barrier (by about 0.17 eV) for *COOH intermediate formation. For Pt/WS2, the strong metal–support interaction is confirmed by high adsorption energy and charge transfer. Importantly, the electron-rich Pt cluster promotes *CO intermediates to facilitate the formation of *CHO intermediates and to further protonate to CH4. This study provides some useful insights into designing the catalysts for the reduction of CO2 and further widens the applications of WS2-based catalytic materials.

Electronic and optical properties of Nb/V-doped WS2 monolayer: A first-principles study.

The electronic, dielectric, and optical properties of pure and Nb/V-doped WS2 monolayer are being investigated using the first-principles density functional theory (DFT). The electronic band structure calculations reveal that the pure and doped WS2 monolayer is a direct band gap semiconductor. It is seen that the doping not only slightly reduces the band gap but also changes the n-type character of pure WS2 monolayer to the p-type character. Hence, it may be useful for channel material in field effect transistors (FETs). Moreover, the optical studies reveal that the WS2 monolayer shows a significantly good optical response. However, a small ultraviolet shift is observed in the optical response of the doped case compared to the pristine WS2 monolayer. This study suggests that the WS2 monolayer can be a possible optical material for optoelectronic applications, and it can also be a replacement of MoS2 -based future electronics and optoelectronics.

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.

Vacancy engineering in WS2 nanosheets for enhanced potassium‐ion storage

As a promising energy storage technology, potassium-ion batteries (PIBs) have received extensive attention because of the cheap and abundant potassium resources. To date, developing anodes for fast and reversible potassiation/depotassiation is in its infancy. This study reports WS2 nanosheets modified by abundant sulfur vacancies (denoted as Sv-WS2) as anode for PIBs for the first time. Benefiting from the synergistic effects of improved electronic conductivity and more active sites produced by sulfur vacancies, and rich interspace acquired by the connection of adjacent nanosheets, the Sv-WS2 anode displays a high reversible capacity of 303.3 mAh g−1 at 0.05 A g−1 and a high rate performance of 136.6 mAh g−1 at 2.0 A g−1, as compared with that (216.5 and 45.5 mAh g−1) of pristine WS2 (P-WS2). Ex situ characterizations confirm that the Sv-WS2 anode undergoes an intercalation-conversion reaction mechanism. First principles calculations further reveal that the creation of sulfur vacancies can availably lower K-insertion energy barriers and increase the electrical conductivity. This study demonstrates a further direction to effectively enhance the potassium storage capability of transition metal dichalcogenides.