Amorphous MoSx Research Articles

Embedding amorphous MoSx within hierarchical porous carbon by facile one-pot synthesis for superior sodium ion storage

The design of anode materials with a high specific capacity, high cyclic stability, and superior rate performance is required for the practical applications of sodium-ion batteries (SIBs). In this regard, we introduce in this work a facile, low-cost and scalable method for the synthesis of nanocomposites of amorphous molybdenum sulfide (a-MoSx) and hierarchical porous carbon and have systematically investigated their performance for sodium ion storage. In the synthesis, ammonium molybdate tetrahydrate and thioacetamide are used as molybdenum and sulfur sources, respectively, with abundant corn starch as the carbon source and KOH as an activation agent. A simple pyrolysis of their mixtures leads to the formation of nanocomposites with a-MoSx embedded within a hierarchical porous carbon (MoSx@HPC), which are featured with a high surface area of up to 518.4 m2 g−1 and hierarchical pores ranging from micropores to macropores. It has also been shown that the annealing of MoSx@HPC results in the formation of crystalline MoS2 nanosheets anchored in the hierarchical porous carbon matrix (MoS2@HPC). The as-prepared nanocomposite MoSx@HPC1 at an optimum carbon content of 32 wt% delivers a high specific sodium storage capacity of 599 mAh g−1 at 0.2 A g−1 and a high-rate performance with a retained capacity of 289 mAh g−1 at 5 A g−1. A comparison of the electrochemical performances of MoSx@HPC and MoS2@HPC demonstrates the superior specific capacity, rate performance, and charge transfer kinetics of the former, highlighting the unique advantageous role of amorphous MoSx relative to crystalline MoS2.

Wide-pH-compatible MoSx co-catalyst layer on TiO2 nanowire arrays photoanode for simultaneous acceleration of charge carrier separation and catalytic reactions

The water oxidation reaction is a key reaction for solar water splitting, which requires excellent oxygen evolution co-catalyst to accelerate charges separation efficiency and high catalytic reaction sites for O2 releasing. So far, many earth-abundant co-catalysts can only play roles at a single pH (only in neutral or alkaline electrolyte), but the development of wide-pH compatible co-catalyst with low price are rarely obtained. Herein, amorphous MoSx layer was conformally coated on TiO2 nanowire arrays (NAs) as an active co-catalyst for multi-pH water photo-oxidation. The experimental results showed that the MoSx greatly enhanced the photoelectrochemical (PEC) performance of TiO2 NAs with high photocurrent densities of 1.95, 1.67, and 1.55 mA/cm2 at 1.23 VRHE in acidic, alkaline, and neutral electrolyte, respectively, significantly higher than bare TiO2 and most TiO2/co-catalyst literature values. Density functional theory (DFT) calculations revealed that the MoSx on TiO2 improves electronic interaction at their interface and forms a type-II band structure for more efficient separation of charge carriers. It is also found that high-density active sites provided by MoSx can reduce the Gibbs free energy and overpotential of potential-determining step for OER, which further enhance the adsorption activity of reaction intermediates. Our work contributes to the in-depth understanding of amorphous MoSx as efficient water oxidation co-catalyst for multi-pH PEC water splitting.

Co-doped amorphous MoSx supported on CuO/CM (Cu mesh) with enhanced photocatalytic activity for ammonia synthesis

As one of the world's most significant industrial synthetic chemicals, ammonia has critical applications in many fields. Mo-based catalyst has an excellent effect on photocatalytic nitrogen fixation. Compared with crystalline molybdenum sulfide, low crystalline or amorphous molybdenum sulfide has rich unsaturated defects to improve the photocatalytic activity. Therefore, we used CuO/CM (Cu mesh) as the substrate and a simple electrochemical deposition method to load amorphous MoSx doped with different contents of Co on CuO/CM and successfully synthesized a thin film heterojunction photocatalyst. At the same time, we fabricated a gas-liquid-solid three-phase photocatalytic reactor to evaluate the catalytic activity of the catalyst. Compared with the powder catalyst reported in the literature, because the catalytic reaction of the three-phase gas-liquid-solid three-phase reactor occurs at the gas-liquid interface, the film catalyst can also absorb sufficient N2 in the gas phase while contacting the liquid proton source (water). It can effectively enhance photocatalytic nitrogen fixation efficiency. The constructed film photocatalyst showed good photocatalytic performance and stable structure under the 350 W simulated light source. While exploring the catalyst structure, the photocatalytic effect of the catalyst was evaluated. When the molar ratio of Mo and Co is 1:0.9, the photocatalyst efficiency shows the high photocatalysis at a rate of 1.062 mg·L−1 for 4 h. Compared with pure CuO / CM and MoSx / CuO / CM, the NH3 yield of the catalyst was increased by 7.86 and 7.52 times, respectively. In addition to N2, no other N sources were introduced during the reaction, which ensured the accuracy of the experimental results.

Integrating Amorphous Molybdenum Sulfide Nanosheets with a Co9S8@Ni3S2 Array as an Efficient Electrocatalyst for Overall Water Splitting.

It is highly challenging to design low-cost, efficient electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, a hierarchical heterostructure was constructed on three-dimensional (3D) Ni foam, which contains Ni3S2 nanorods decorated with both Co9S8 and amorphous MoSx nanosheets and Ni3S2 nanowires decorated with amorphous MoSx nanosheets, namely, MoSx@Co9S8@Ni3S2/NF. The synergistic effects from the strong interactions of the heterointerface and unique hierarchical heterostructure endow the MoSx@Co9S8@Ni3S2/NF with abundant active sites and effective mass and electron transport pathways, resulting in excellent activity toward both HER and OER in 1 M KOH. It only gives a low overpotential of 76.5 mV to achieve 10 mA cm-2 for HER and a low overpotential of 310 mV to achieve 100 mA cm-2 for OER. Based on the superior catalytic activity of MoSx@Co9S8@Ni3S2/NF for OER and HER, we demonstrated the activity of overall water splitting using MoSx@Co9S8@Ni3S2/NF as both the anode and cathode. It shows a higher catalytic activity for overall water splitting with a low cell voltage of 1.52 V at 10 mA cm-2 than commercial Pt/C/NF||IrO2/NF (1.61 V) and superior stability. This work provides a platform for the design and preparation of efficient electrocatalysts with various hierarchical heterostructures.

Molybdenum polysulfide electrode with high capacity for all-solid-state sodium battery

All-solid-state sodium secondary batteries have attracted significant attention as an alternative for post‑lithium-ion batteries. However, to obtain all-solid-state sodium secondary batteries with high-energy density, it is necessary to develop a high-capacity positive electrode material. In this study, two types of amorphous (a-)MoSx (x ≃ 6) active electrode materials were prepared using a mechanochemical (MC) process and through the thermal decomposition (TD) of (NH4)2Mo2S12·2H2O. Herein, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) analyses were conducted, and the results revealed significantly different local structures of a-MoSx (MC) and a-MoSx (TD). The all-solid-state sodium cells with a-MoSx (MC) and a-MoSx (TD) possessed high reversible capacities of 510 and 690 mAh g−1, as well as high-capacity retention rates of 80% and 92% for the 2nd to 30th cycles, respectively. XPS analysis of the discharge–charge products further suggested that dissociation and formation of disulfide bonds occurred reversibly during the discharge–charge reaction. This study shows that a-MoSx (MC) and a-MoSx (TD) are promising active electrode materials for all-solid-state sodium batteries.

Amorphous MoSx electro-synthesized in alkaline electrolyte for superior hydrogen evolution

Recently, amorphous MoSx electrocatalysts have attracted lots of attention because their structural flexibility and rich defects can offer enormous sites for hydrogen evolution. In the deposition solution containing various amount of (NH4)2MoS4 and NaOH, amorphous MoSx films have been electrochemically deposited on carbon cloth by using constant potentials method under ambient conditions. The X-ray diffraction patterns show that the resulted samples are amorphous, X-ray photoelectron and Raman spectrum reveal that amorphous MoSx exists defective MoV=O sites coordinated with bridged sulfur. The electrodepositing conditions have been optimized and the optimal MoSx electrode exhibits overpotential of 156 mV in 0.5 mol L−1 H2SO4 and 232 mV in 1.0 mol L−1 KOH without iR correction for hydrogen evolution reaction (HER) at current density of 10 mA cm−2, which surpasses the property of most of the amorphous MoSx-based electrodes. On the basis of MoV=O as the proposed active sites, the possible catalytic pathway is suggested. More importantly, the optimized MoSx electrode shows excellent stability for HER in acidic and alkaline electrolyte. This approach for synthesis of MoSx in alkaline electrolyte may be developed as effective way to prepare high-performance electrocatalytic electrode for HER.

Preparation of MoS2 spheres from Mo plate and elemental sulfur and the effect of sphericalization on electrochemical hydrogen evolution catalysis

The growth of MoS2 catalysts with a controlled morphology has been actively pursued to improve the electrocatalytic activity for hydrogen evolution reaction (HER) by modifying the shape of catalysts. However, it is questionable whether changes in morphological structure affect its intrinsic activity. Here we present a facile hydrothermal synthesis of amorphous MoSx spheres on Mo plates at 180 °C using elemental sulfur. Hydrolysis of elemental sulfur during the hydrothermal synthesis produces H2S and H2SO4 in hot water. Consequently, the surface of the Mo plate is sulfurized by H2S and dissolved by H2SO4 to form amorphous MoSx spheres with diameters in the range of 0.4–0.8 μm on the Mo plate. To investigate the effect of the sphericalization of crystalline MoS2 on its intrinsic activity for the HER, the amorphous MoSx spheres were annealed to form crystalline MoS2 spheres. The Tafel slopes of the amorphous MoSx (∼45 mV/dec) and crystalline MoS2 (∼103 mV/dec) spheres were similar to those of amorphous MoSx and crystalline MoS2 thin films, regardless of whether the shape of the catalyst was sphericalized or not. This reveals that the sphericalization cannot change the intrinsic activity and the HER mechanism on molybdenum sulfide.

Highly enhanced dye adsorption of MoO3 nanoplates fabricated by hydrothermal-calcination approach in presence of chitosan and thiourea

Water pollution by organic dyes poses great challenge to the environment and living organism. Hence effective removal of organic dyes by cost effective methods have received significant attention in recent years. Herein, we report the complete removal of organic dyes (rhodamine B), methylene blue) and eosin yellow) from water via effective adsorption by MoO3 catalyst. Hydrothermally synthesised MoO2 (1) and amorphous MoSx (2) using ammonium molybdate without and with thiourea exhibited low dye adsorption. In contrast, crystalline micro/nanoplates of MoO3 (3 and 4) obtained from calcination of 1 and 2 showed highly enhanced dye adsorption. Particularly 4 showed higher dye adsorption compared to 3. UV–Visible absorption studies confirmed complete removal of organic dyes upon stirring with MoO3 catalyst. Dye removal studies further revealed that cationic dyes are adsorbed faster than anionic dye that could be attributed to the surface charge of MoO3. Interestingly, the adsorbed dyes were not released from MoO3 for more than 50 days. The exhausted MoO3 catalyst can be recovered by annealing at 400 °C. MoO3 catalyst has also been used as packing materials in dropper column and demonstrated effective removal of dyes by passing through dyes separately as well as mixture.

Defect coupled MoSx sites over ZnIn2S4 nanosheets towards efficient H2 evolution

The inefficient separation of photoexcited electrons and holes as well as the lack of sufficient reactive sites are considered as the major factors hindering the catalytic activity of the semiconductors. Herein, we report an environmentally friendly and energy-saving method to realize the co-deposition of amorphous MoSx onto ZnIn2S4 (ZIS) nanosheets, through which effectively enhanced performance of H2 generation from water reduction can be achieved. Furtherly, defect-poor ZIS and defect-rich O-doped ZIS (O-ZIS) were taken as the fabrication matrixes respectively, and larger enhancement resulting from MoSx loading over O-ZIS than that over ZIS was achieved, suggesting the synergistic effect that one plus one is greater than two, primarily due to the remarkably enhanced charge carriers separation and more abundant reaction sites for H2 production resulting from the defect engineering coupled surface active sites constructing. Notably, the optimal MoSx/O-ZIS achieved the H2 evolution rate of 15.32 mmol g−1 h−1, which is 17.8 and 8.5 times as that achieved over blank ZIS and O-ZIS, respectively. This work furnishes a facile paradigm that efficient composite materials can be facilely controlled towards boosted solar energy conversion, which significantly simplifies the activity majorization of the component-designed MoSx/ZIS photocatalysts.

Application of Pulsed Laser Deposition in the Preparation of a Promising MoSx/WSe2/C(В) Photocathode for Photo-Assisted Electrochemical Hydrogen Evolution.

We studied the possibility of using pulsed laser deposition (PLD) for the formation of a MoSx/WSe2 heterostructure on a dielectric substrate. The heterostructure can be employed for effective solar water splitting to produce hydrogen. The sapphire substrate with the conducting C(B) film (rear contact) helped increase the formation temperature of the WSe2 film to obtain the film consisting of 2H-WSe2 near-perfect nanocrystals. The WSe2 film was obtained by off-axis PLD in Ar gas. The laser plume from a WSe2 target was directed along the substrate surface. The preferential scattering of selenium on Ar molecules contributed to the effective saturation of the WSe2 film with chalcogen. Nano-structural WSe2 film were coated by reactive PLD with a nanofilm of catalytically active amorphous MoSx~4. It was established that the mutual arrangement of energy bands in the WSe2 and MoSx~4 films facilitated the separation of electrons and holes at the interface and electrons moved to the catalytically active MoSx~4. The current density during light-assisted hydrogen evolution was above ~3 mA/cm2 (at zero potential), whilst the onset potential reached 400 mV under irradiation with an intensity of 100 mW/cm2 in an acidic solution. Factors that may affect the HER performance of MoSx~4/WSe2/C(В) structure are discussed.

Catalysis of hydrogen evolution reaction by in situ electrodeposited amorphous molybdenum sulfide at soft interfaces

Amorphous molybdenum sulfide (MoSx) is considered a suitable alternative to Pt for catalyzing the hydrogen evolution reaction (HER) in electrochemical water splitting because of its simple and inexpensive preparation process. Herein, the template-free in situ electrodeposition of amorphous MoSx at freestanding soft interfaces is reported for the first time. The biphasic catalysis of the HER by the electrodeposited MoSx at the water-1,2-dichloroethane interface with decamethylferrocene (DMFc) was also investigated. DMFc acts as an organic sacrificial reducing agent for both (NH4)2MoS4 and protons to afford MoSx and H2, respectively. The nucleation of MoSx and the HER was examined using both four-electrode voltammetry and the biphasic reactions at the liquid-liquid interfaces. MoSx particles were collected from the interface and subjected to structural and morphological characterization. The HER kinetics was investigated using the UV-Vis absorption method with varying DMFc+ concentrations. The amount of H2 evolved and the reaction rates obtained over the in situ electrodeposited MoSx catalyst were compared with those obtained over electrodeposited metallic nanoparticles and commercial MoS2 catalysts.

Amorphous MoS nanoparticles grown on cobalt-iron-based needle-like array for high-performance flexible asymmetric supercapacitor

Although flexible supercapacitors have important applications, the development of high-performance flexible supercapacitors still remains a critical challenge owing to the low ion diffusion rate, poor electro-conductivity, and limited active defect sites. Herein, we report the first amorphous MoSx nanoparticles grown on crystalline FeCo-based nanoneedles ([email protected]) via an ethylene glycol-induced strategy. The [email protected] electrode presents an unprecedented specific capacitance of 1956 F g−1 at 1 A g−1 and over 91.1% of capacitance retention even after 6000 cycles because of the unique morphology, the rich defect sites, the high carrier concentration. The [email protected]//AC asymmetric supercapacitor delivers an ultrahigh specific capacitance of 282 F g−1 at 1 A g−1 and an excellent energy density of 88.09 Wh kg−1 along with a power density of 750 W kg−1. And the self-assembled flexible all-solid-state supercapacitor device can be easily bent and twisted with negligible electrochemical properties attenuation.

In Situ Assembly of MoSx Thin‐Film through Self‐Reduction on p‐Si for Drastic Enhancement of Photoelectrochemical Hydrogen Evolution

AbstractStrong coupling between the Si photocathode and a low‐cost cocatalyst is of great significance for enhancing the photoelectrochemical hydrogen evolution. Here, a facile method is proposed to in situ assemble amorphous MoSx (a‐MoSx) thin‐film onto a single crystal p‐Si through a self‐reduction mechanism to achieve strong coupling. In the process of self‐reduction, the (MoS4)2− anion is reduced to form a‐MoSx by the oxidation of H–Si to form SiOx, which is etched further to form H–Si again in the hydrofluoric aqueous solution. The cyclic formation of H–Si and SiOx plays a decisive role in the continuous deposition of a‐MoSx and provides a unique way to synthesize metal sulfides. Such a‐MoSx/p‐Si photocathode exhibits an excellent activity, achieving the optimal onset potential of +0.31 VRHE and the current density of −28.2 mA cm−2 at 0 VRHE with a Faradaic efficiency close to 98%, respectively, outperforming the thermally exfoliated 2H‐MoS2 and 1T‐MoS2 cocatalysts on p‐Si and comparable to the previous studies. The proposed method for uniform deposition at room temperature is simple to carry out and can be used for fabricating other Si‐based photoelectrodes.

Development of highly active hydrogen evolution reaction (HER) catalysts composed of reduced graphene oxide and amorphous molybdenum sulfides derived from (NH4)2MoOmS4-m (m = 0, 1, and 2)

Photochemically synthesized catalysts using (NH4)2MoOmS4-m (m = 0, 1, and 2) as raw materials were studied for the purpose of hydrogen evolution reaction (HER) from H2O. Each starting material is found to generate a composite of MoSx/RGO covered by MoO3 layer, where RGO is reduced graphene oxide. XRD, TEM, XPS, and elemental analysis of the resulting MoSx/RGO reveals that MoSx exists in an amorphous phase and is composed of Mo(IV)Sx (x≈3). The HER activity of each prepared composite is estimated by η10 (the overpotential at 10 mA cm−2 current density), Ts (the Tafel slope) from linear sweep voltammetry (LSV), and turnover frequency (TOF). The composites from m = 0, 1, and 2 show η10: 198, 206, and 297 mV vs. RHE, Ts: 49.1, 46.9, and 89.1 mV dec-1, and TOF: 0.16, 0.20, and 0.10 s−1, respectively. From the viewpoint of Ts and TOF, the composites from m = 0 and 1 display a remarkably efficient activity, but they show the decline of HER performance with the electrochemical reaction time and cycle. The composite from m = 2, however, shows less activity than the others. The origins of the prominent efficiency of the composites from m = 0 and 1 are predicted as follows: (1) Photoirradiation of the starting materials on RGO leads to a selective and confined formation of amorphous Mo(IV)Sx, which is constructed, intriguingly, by abundant reactive bridging S22- ligands. (2) The HER efficiency is related to the presence of the Mo(IV) centers and the bridging S22- ligands. The Ts data suggest that the catalytic HER proceeds by a Volmer–Heyrovsky pathway.

Formation of Effective Electrocatalysts of Hydrogen Evolution MoSx > 2 by Pulsed Laser Ablation Assisted by the Deposition of Mo Nanoparticles

The mechanisms of film formation during pulsed laser ablation of a MoS2 target were studied. The conditions for the deposition of laser erosion plume were determined. This made it possible to obtain coatings with a porous structure consisting of round Mo nanoparticles coated with a thin shell of amorphous molybdenum sulfide MoSx > 2. Due to its hybrid structure, the MoSx > 2/Mo nanomaterial can be effectively used for electro- and photocatalysis of water splitting. The MoSx > 2/Mo films deposited on a glassy carbon substrate are characterized by good current transport and high active surface area. When the film thickness increased due to the increased deposition time, the overvoltage of hydrogen evolution in an acid solution monotonically decreased to 142.5 mV, which was necessary in order to obtain current density of hydrogen evolution of 10 mA/cm2. The catalyst loading was 230 μg/cm2. Further increase in the loading did not significantly reduce the overvoltage. The results indicate that it is promising to use Mo nanoparticles as an ultrafine support for the catalytic nanolayers of amorphous molybdenum sulfide.

Signal-on cathodic photoelectrochemical aptasensing of insulin: Plasmonic Au activated amorphous MoSx photocathode coupled with target-induced sensitization effect

Cathodic photoelectrochemical (PEC) bioassay is more resistant to reductive interferents, and development of high-performance photocathode is imperatively required in precise monitoring target in complex matrices. In this work, a plasmonic Au activated amorphous MoSx photocathode (a-MoSx/Au) was fabricated by sequential electrodeposition. Coupled with a sensitization amplification strategy induced by target-aptamer recognition, an ultrasensitive and high-affinitive signal-on cathodic PEC aptasensor for insulin detection was developed. Under optimum conditions, the sensor exhibits a wide linear range (0.1 pg/mL~100 ng/mL) and an ultralow detection limit (28 fg/mL) even lower than most sensors reported so far. Plasmonic Au activation and target-induced sensitization effect are responsible for high-performance PEC aptasensing of insulin at a-MoSx photocathode.

Performance and Mechanism of Photoelectrocatalytic Activity of MoSx/WO3 Heterostructures Obtained by Reactive Pulsed Laser Deposition for Water Splitting.

This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoSx/WO3 nano-heterostructures obtained by reactive pulsed laser deposition (RPLD) on glass substrates covered with fluorinated tin oxide (FTO). Another focus of the research is the potential of MoSx nanofilms as a precursor for MoOz(S) nanofilms, which enhance the efficiency of the photo-activated oxygen evolution reaction (OER) using the MoOz(S)/WO3/FTO heterostructures. The nanocrystalline WO3 film was created by laser ablation of a W target in dry air at a substrate temperature of 420 °C. Amorphous MoSx nanofilms (2 ≤ x ≤ 12) were obtained by laser ablation of an Mo target in H2S gas of varied pressure at room temperature of the substrate. Studies of the energy band structures showed that for all MoSx/WO3/FTO samples, photo-activated HER in an acid solution proceeded through the Z-scheme. The highest photoelectrochemical HER efficiency (a photocurrent density ~1 mA/cm2 at a potential of ~0 V under Xe lamp illumination (~100 mW/cm2)) was found for porous MoS4.5 films containing the highest concentration of catalytically active sites attributed to S ligands. During the anodic posttreatment of porous MoSx nanofilms, MoOz(S) films with a narrow energy band gap were formed. The highest OER efficiency (a photocurrent density ~5.3 mA/cm2 at 1.6 V) was detected for MoOz(S)/WO3/FTO photoanodes that were prepared by posttreatment of the MoSx~3.2 precursor. The MoOz(S) film contributed to the effective photogeneration of electron–hole pairs that was followed by the transport of photoelectrons from MoOz(S) into the WO3 film and the effective participation of holes possessing strong oxidation ability in the OER on the surface of the MoOz(S) film.

Sandwich‐Structured Fe‐Ni2P/MoSx/NF Bifunctional Electrocatalyst for Overall Water Splitting

AbstractExploring cost‐efficient, high‐active bifunctional electrochemical catalysts with long‐term stability are significant for green economy. Herein, a noble‐metal‐free sandwich‐structured catalyst, prepared with facile hydrothermal method and phosphorization process, in which the amorphous MoSx serves as an intermediate layer between the Fe‐doped Ni2P and Ni foam substrate (Fe‐Ni2P/MoSx/NF) is reported. The obtained free‐standing catalyst performs an enhanced electrochemical activity compared with Fe‐Ni2P/NF and MoSx/NF. The Fe‐Ni2P/MoSx/NF catalyst only requires overpotentials of 246 mV to achieve 10 mA cm−2 and 277 mV to reach 50 mA cm−2 for oxygen evolution reaction process with a low Tafel slope of 59.7 mV dec−1 in alkaline solution. Meanwhile, an overpotential of 112 mV is demanded to reach 10 mA cm−2 for hydrogen evolution reaction. When the Fe‐Ni2P/MoSx/NF is used as two electrodes for overall water splitting, it requires 1.61 V to attain 10 mA cm−2 with prominent durability. This approach provides a versatile strategy to construct excellent bifunctional catalysts for effective water electrolysis.

Reactive Pulsed Laser Deposition of Clustered-Type MoSx (x ~ 2, 3, and 4) Films and Their Solid Lubricant Properties at Low Temperature.

We studied the tribological properties of amorphous molybdenum sulfide (MoSx) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (−100 °C). To obtain films with different sulfur contents (x ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H2S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS3 coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS2 coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS2 coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS4 coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoSx coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoSx films.

Sensitization of vertically grown ZnO 2D thin sheets by MoSx for efficient charge separation process towards photoelectrochemical water splitting reaction

Development of advanced materials for photoelectrochemical (PEC) water splitting has become an essential issue for efficient, green, and economical hydrogen production. In this context, vertically grown thin sheets of ZnO is developed, which can function as an efficient photoanode in PEC water splitting reaction. Further, the PEC activity of ZnO is enriched by decorating a newly developed co-catalyst, which is amorphous MoSx through efficient charge transportation. MoSx nanostructure is decorated on the surface of ZnO nanosheet via electrodeposition technique. MoSx adorned ZnO shows enhanced activity towards photoanodic PEC water splitting compared to bare ZnO. ZnO@MoSx can generate photocurrent density nearly three times higher compared to bare ZnO at an applied potential of ‘0.5998’ V vs. RHE. Sensitization of MoSx on ZnO surface results in an enhancement in carrier density; ZnO@MoSx shows nearly 7.4-times higher carrier density compared to bare ZnO. Maximum photoconversion efficiency, 0.934% is achieved in the case of ZnO@MoSx. The determined band alignment of ZnO and MoSx indicate the formation of type-II heterostructure which allow facile charge carrier separation. Efficient charge separation is also confirmed with the help of PL spectroscopy. It further restricts the electron-hole recombination in ZnO, leading to enhanced PEC activity. ZnO@MoSx thin sheets are very stable even up to 1000 s under chopped illumination condition.