Fabrication of a wearable and foldable photodetector based on a WSe2-MXene 2D-2D heterostructure using a scalable handprint technique.

Several studies on semiconductor material-based single-band, high-performance photosensitive, and chemically stable photodetectors are available; however, the lack of broad spectral response, device flexibility, and biodegradability prevents them from being used in wearable and flexible electronics. Apart from that, the selection of the device fabrication technique is a very crucial factor nowadays in terms of equipment utilization and environmental friendliness. This report presents a study demonstrating a straightforward solvent- and equipment-free handprint technique for the fabrication of WSe2-Ti3C2TX flexible, biodegradable, robust, and broadband (Vis-NIR) photodetectors. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), UV-visible spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirm the formation of a WSe2-Ti3C2TX film. The WSe2-Ti3C2TX van der Waals heterostructure plays a key role in enhancing the optoelectrical properties. The as-prepared photodetector exhibits efficient broadband response with a photoresponsivity and a detectivity of 0.3 mA W-1 and 6.8 × 1010 Jones, respectively, under NIR (780 nm) irradiation (1.0 V bias). Under various pressure and temperature conditions, the device's flexibility and durability were tested. The biodegradable photodetector prepared through the solvent- and equipment-free handprint technique has the potential to attract significant interest in wearable and flexible electronics in the future.

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production.

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Self-Supported Mn-Ni3Se2 Electrocatalysts for Water and Urea Electrolysis for Energy-Saving Hydrogen Production.

Recently, there has been a huge research interest in developing robust, efficient, low-cost, and earth-abundant materials for water and urea electrolysis for hydrogen (H2) generation. Herein, we demonstrate the facile hydrothermal synthesis of self-supported Mn-Ni3Se2 on Ni foam for overall water splitting under wide pH conditions. With the optimized concentration of Mn in Ni3Se2, the overpotential for hydrogen evolution, oxygen evolution, and urea oxidation is significantly reduced by an enhanced electrochemical active surface area. Different electronic states of metal elements also produce a synergistic effect, which accelerates the rate of electrochemical reaction for water and urea electrolysis. Owing to the chemical robustness, Mn-doped Ni3Se2 shows excellent stability for long time duration, which is important for its practical applications. A two-electrode electrolyzer exhibits low cell voltages of 2.02 and 1.77 V for water and urea electrolysis, respectively, to generate a current density of 100 mA/cm2. Finally, the prepared nanostructured Mn-Ni3Se2@NF acts as an electrocatalyst for overall water splitting under wide pH conditions and urea electrolysis for energy-saving hydrogen production and wastewater treatment.

Synergistically Driven CoCr-LDH@VNiS2 as a Bifunctional Electrocatalyst for Overall Water Splitting and Flexible Supercapacitors.

Utilizing alternative energy sources to fossil fuels has remained a significant issue for humanity. In this context, efficient earth-abundant bifunctional catalysts for water splitting and energy storage technologies like hybrid supercapacitors have become essential for achieving a sustainable future. Herein, CoCr-LDH@VNiS2 was synthesized by hydrothermal synthesis. The CoCr-LDH@VNiS2 catalyst entails 1.62 V cell voltage to reach the current density of 10 mA cm-2 for overall water splitting. The CoCr-LDH@VNiS2 electrode illustrates a high electrochemical specific capacitance (Csp) of 1380.9 F g-1 at a current density of 0.2 A g-1 and an outstanding stability with 94.76% retention. Moreover, the flexible asymmetric supercapacitor (ASC) achieved an energy density of 96.03 W h kg-1@0.2 A g-1 at a power density of 539.98 W kg-1 with remarkable cyclic stability. The findings provide a new approach toward the rational design and synthesis of bifunctional catalysts for water splitting and energy storage.

Synergistic 2D MoSe2@WSe2 nanohybrid heterostructure toward superior hydrogen evolution and flexible supercapacitor.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructure is a new age strategy to achieve high electrocatalytic activity and ion storage capacity. The less complex and cost-effective applicability of the large-area TMDC heterostructure (HS) for energy applications require more research. Herein, we report the MoSe2@WSe2 nanohybrid HS electrocatalyst prepared using liquid exfoliated nanocrystals, followed by direct electrophoretic deposition (EPD). The improved catalytic activity is attributed to the exposure of catalytic active sites on the edge of nanocrystals after liquid exfoliation and the synergistic effect arises at HS interfaces between the MoSe2 and WSe2 nanocrystals. As predicted, the HS catalyst achieves a lower overpotential of 158 mV, a smaller Tafel slope of 46 mV dec-1 for a current density of 10 mA cm-2, and is stable for a long time. The flexible symmetric supercapacitor (FSSC) based on the HS catalyst demonstrates the excellent specific capacitance (Csp) of 401 F g-1 at 1 A g-1, 97.20% capacitance retention after 5000 cycles and high flexible stability over 1000 bending cycles. This work presents a less complex and solution-processed efficient catalyst for future electrochemical energy applications.

WSe2crystals on paper: flexible, large area and broadband photodetectors.

The paper-based photodetector has recently captivated a great deal of attention in various opto-electronics applications because of facile, cost effective and green synthesis. Two-dimensional transition metal dichalcogenides materials are promising for photodetection under the broad spectral range. In this work, we have fabricated paper-based device by rubbing the tungsten di-selenide (WSe2) crystals on paper substrate. Low-cost, facile and green synthesis technique was employed to make a high-performance paper-based WSe2photodetector. Paper-based photodetector was fabricated via non-toxic simply rubbing process of WSe2nanosheets on low-cost bio-degradable paper. The photodetector shows good responsivity of 72.5 µA W-1and detectivity at around 2.4 × 107Jones at very low bias (1.0 V) at wavelength of 780 nm, respectively. Due to good photo-absorption strength, photodetector exhibits excellent photo-response over wide wavelength range from visible to near infrared. This device also shows very good flexibility with a stable photo-response. This device shows a general and reliable study for the design of photodetectors that is eco-friendly and cost-effective. Overall studied results of the fabricated device indicate that they have the ability to be used in large-scale preparation of the device.

Photosensitive electrocatalysts based on Ni-WS2nanohybrids for hydrogen evolution reaction.

Efficient hydrogen evolution by electrolysis plays an indispensable role for hydrogen fuel generation in green energy devices. In order to implement high-performance electrocatalytic activity, it is usually necessary to design economically viable, effective and stable electrocatalysts to reduce activation potential barriers. Herein, we report the photosensitive Ni-WS2nanohybrids for enhanced electrocatalytic hydrogen evolution reaction (HER). Optimisation of chemical composition in catalysts has resulted in the rapid water electrolysis which was further promoted by illumination of 532 nm light. Obvious HER has been achieved at over potential of as low as -210 mV versus RHE without and -190 mV versus RHE (at -10 mA cm-2) with illumination. Being a photosensitive electrocatalysts, Ni-WS2Nanohybrids have demonstrated stable time-resolved photoresponse with photocurrent of 12.7 mA cm-2at -250 mV V versus RHE as well as self-powered photodetection with current 0.68 mA cm-2. Finally, HER with improvement under visible light illumination has shown considerable development in clean energy generation by using renewable energy sources.

MoS2/WSe2nanohybrids for flexible paper-based photodetectors.

Flexible photodetectors functionalized by transition metal dichalcogenides have attracted great attention due to their excellent photo-harvesting efficiency. However, the field of optoelectronics still requires advancement in the production of large-area, broad band and flexible photodetectors. Here we report a flexible, stable, broad band and fast photodetector based on a MoS2/WSe2heterostructure on ordinary photocopy paper with pencil-drawn graphite electrodes. Ultrathin MoS2/WSe2nanohybrids have been synthesized by an ultrahigh yield liquid-phase exfoliation technique. The thin sheets of WSe2, and MoS2contain two to four layers with a highly c-oriented crystalline structure. Subsequently, the photodetector was exploited under ultra-broad spectral range from 400 to 780 nm. The photodetector exhibits excellent figure of merit such as on/off ratio of the order of 103, photoresponsivity of 124 mA W-1and external quantum efficiency of 23.1%. Encouragingly, rise/decay time of about 0.1/0.3 s was realized, which is better than in previous reports on paper-based devices.

Highly sensitive and flexible pressure sensor based on two-dimensional MoSe2 nanosheets for online wrist pulse monitoring.

The advancement of portable and flexible electronics that is integrated with multiple sensing functions has increasingly drawn considerable interest. The fabricated sensors would have the ability to sense multiple deformations like pressing, twisting and trivial vibrations such as pulses of wrist vibrations to mimic human skin. Presently, we implemented an easy, cost-effective and optimized fabrication technique for production of pressure sensors based on MoSe2 nanosheets coated on cellulose paper. The present sensor exhibits an incorporation of large pressure sensitivity of 18.42 kPa-1 in pressure range 0.001-0.5 kPa, 7.28 kPa-1 in pressure range 1-35 kPa and 2.63 kPa-1 in pressure range 40-100 kPa, working in broad pressure range (from 0.001 to 100 kPa) and long-term stability up to 200 deformation cycles at 2 kPa. The sensor showed excellent response towards the detection of vibrations of machines including cellular phone, compressor, etc. Besides, the sensor shows excellent environmental stability and exhibits immune piezo-resistive response to temperature variation.

Flexible paper based piezo-resistive sensor functionalised by 2D-WSe2 nanosheets.

High-performance electronics demand extremely sensitive piezo-resistive sensors with important features such as low-fabrication cost, easy implementation, low power consumption and high-pressure sensitivity over broad pressure range. Herein, we report a flexible piezo-resistive paper-based device functionalised by WSe2 nanosheets. An efficient and low-cost fabrication strategy using Whatman filter paper and tissue paper is adopted for versatile sensing applications. The WSe2 nanosheets were synthesized by high-yield and size-controlled liquid phase exfoliation technique. The flexible WSe2 nanosheets-paper sensor shows excellent response in broad pressure range of 1 Pa-100 kPa with exceptionally high sensitivity of 29.24 kPa-1, current responsivity of 70 and response time of 100 ms. The pressure sensor is also employed to recognize the pressure generated due to finger tapping. Encouragingly, the piezo-resistive sensors can also sense extremely small pressure differences of about 1.4 Pa generated by water drops.

Enhanced Antifungal Activity of WS2/ZnO Nanohybrid against Candida albicans.

Candida albicans forms persistent infections through the formation of biofilms that confer resistance to existing antifungal drugs. Biofilm targeting is therefore a promising strategy to combat Candida albicans infections. The WS2/ZnO nanohybrids exhibits considerably improved antibiofilm activity and inhibited the biofilm formation by 91%, which is quite better than that for pristine WS2, which is only 74%. The physical blend prepared by mixing WS2 nanosheets and WS2/ZnO in the ratio of 70:30 showed an antibiofilm activity of 58%, which was intermediate to that observed for pristine materials. The as-synthesized nanohybrid also demonstrates dose-dependent antifungal activity as calculated using the disc diffusion test. WS2/ZnO nanohybrid shows 1.5 times higher activity compared to pristine WS2 nanosheets suggesting that the nanohybrid materials are more effective as novel antifungal materials.

Two-dimensional semiconductor transition metal based chalcogenide based heterostructures for water splitting applications.

Recent research and development is focused in an intensive manner to increase the efficiency of solar energy conversion into electrical energy via photovoltaics and photo-electrochemical reactions. Electrocatalytic and photocatalytic water splitting into hydrogen and oxygen is a promising and emerging technology. Heterogeneous nanostructures based on semiconductor materials have attracted much attention to be used as catalysts, co-catalysts, photocatalysts and photoabsorbers. Development of transition metal dichalcogenide (TMDC) semiconductors with two dimensional (2D) layered structures and peculiar physical and chemical properties are playing a pivotal role in the heterogeneous photocatalytic hydrogen evolution (PHE) reaction. The energy band gap tuning with the thickness of the layers and heterojunction interface formation have given an opportunity to design and develop combinations of both photocatalysts and co-catalysts using semiconductor TMDCs. This contribution summarizes the recent investigations on the 2D semiconductor TMDC (MoS2, WS2, MoSe2 and WSe2) based heterogeneous nanostructures as efficient materials for photocatalytic water splitting applications to produce hydrogen. The literature survey clearly shows that more than 80% of the researchers in this field have worked on MoS2-based heterogeneous nanocomposites, as it is the 2nd most studied material after graphene. It is also evident that among the materials used so far for the PC HER activity, MoS2-based heterogeneous nanocomposites are on top with the highest hydrogen evolution rate and stability. Since the physical and chemical properties of the members are identical, the future research and development would focus on the manipulation of the rest of the TMDC members to achieve the future needs of clean and sustainable energy production.