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Two-dimensional transition metal dichalcogenides (TMDs) have gained attention as potent catalysts for the hydrogen evolution reaction (HER). The traditional trial-and-error methodology for catalyst development has proven inefficient due to its costly and time-intensive nature. To accelerate the catalyst development process, the Gibbs free energy of hydrogen adsorption (Δ G H ∗ ), computed using the density functional theory (DFT), is widely used as the paramount descriptor for evaluating and predicting HER catalyst performance. However, DFT calculations for Δ G H ∗ are time-consuming and thus pose a challenge for high-throughput screening. Herein, we devise a predictive model for Δ G H ∗ within transition metal-doped TMD systems using a machine learning (ML) framework. We calculate DFT Δ G H ∗ values for 150 TM-doped MX2 (CrS2, MoS2, WS2, MoSe2, and MoTe2) and apply various ML algorithms. We validate the universality of our model by constructing 15 new external test sets. The prediction results show a high correlation coefficient of R 2 = 0.92. Based on feature analysis, the three most important parameters are the number of valence electrons of the doped transition metal, the distance of the valence electrons of the doped transition metal, and the electronegativity of the doped transition metal. Our DFT-based ML model provides a useful guideline for the material development process through Δ G H ∗ prediction and facilitates the efficient design of transition metal dichalcogenide catalysts that exhibit superior HER activity. [ABSTRACT FROM AUTHOR]

Oxygen reduction reactions (ORRs) are unanimously a key factor of system performances in bioelectrochemical systems (BESs), low-temperature fuel cells, and generally in several electrochemical platforms. Platinum (Pt)-based catalyst is the finest electrocatalyst for ORR in BESs; however, it is constrained by its low abundance, high price, and poor catalytic durability in an electrochemical setup for cathodic reaction kinetics. In recent years, significant efforts in trimming the metal-based catalyst up to nanoscale to cater high performance of ORR have been explored. Still, there are many opportunities to improve catalyst performance at cathode through proper selection of an efficient low-cost metal-based ORR catalyst. Molybdenum (Mo) with its multi-dimensional form as 2D and 3D layers and synergistic combination with other non-metals offers prospects of extraordinary performance as low-cost metal-based ORR catalyst over the Pt in delivering enhanced ORR potential. The present review throws light on current requirements of a sturdier catalyst material and thus provides a comprehensive review on the continuing efforts in exploring the possibility of Mo as a low-cost metal-based ORR catalyst. This literature analysis would enlighten the significance of ORR in BESs, followed by the electrochemistry of Mo-based cathodic catalyst, its underlying mechanism and performance limiting factors in the operation of ORR. Moreover, the extensive and systematic acumen in the context of Mo-based catalytic formulations for increased ORR potentials including nano-composite Mo-cathode catalyst; development of Mo-catalyst with varied configurations; carbon-supported Mo-catalyst; morphological changes; surface area modifications; and Mo-coupling with other transition metal and its derivatives were discussed in great detail to provide prospective application of Mo-based catalyst. Lastly, numerous opportunities and projections for future research in fabrication, juxtaposition, and implementation of Mo-based cathodic catalysts and consequent recommendations were discussed as conclusive remarks for bringing out the state-of-the-art review on this subject. [ABSTRACT FROM AUTHOR]

Monolayer transition metal dichalcogenides can normally exist in several structural polymorphs with distinct electrical, optical, and catalytic properties. Effective control of the relative stability and transformation of different phases in these materials is thus of critical importance for applications. Using density functional theory calculations, we investigate the effects of low-work-function metal substrates including Ti, Zr, and Hf on the structural, electronic, and catalytic properties of monolayer MoS2 and WS2. The results indicate that such substrates not only convert the energetically stable structure from the 1H phase to the 1T′/1T phase, but also significantly reduce the kinetic barriers of the phase transformation. Furthermore, our calculations also indicate that the 1T′ phase of MoS2 with Zr or Hf substrate is a potential catalyst for the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

The efficient production of hydrogen through electrocatalytic decomposition of water has broad prospects in modern energy equipment. However, the catalytic efficiency and durability of hydrogen evolution catalyst are still very deficient, which need to be further explored. Here in this work, we prove that introducing a graphene layer (Gr) between the molybdenum disulfide and nickel foam (Ni–F) substrate can greatly improve the catalytic performance of the hybrid. Owing to the excitation of local surface plasmon resonance (LSPR) of gold nanoparticles (NPs), the electrocatalytic hydrogen releasing activity of the MoS2/Gr/Ni–F heterostructure is greatly improved. This results in a significant increase in the current density of AuNPs/MoS2/Gr/Ni–F composite material under light irradiation and in the dark at 0.2 V (versus reversible hydrogen electrode (RHE)), which is much better than in MoS2/Gr/Ni–F composite materials. The enhancement of hydrogen release can be attributed to the injection of hot electrons into MoS2/Gr/Ni–F by AuNPs, which will improve the electron density of MoS2/Gr/Ni–F, promote the reduction of H2O, and further reduce the activation energy of the electrocatalyst hydrogen evolution reaction (HER). We also prove that the introduction of graphene can improve its stability in acidic catalytic environments. This work provides a new way of designing efficient water splitting system. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs) with large specific surface areas and high conductivities are promising catalysts for electrocatalytic hydrogen production. The highly active edges of the 2D metallic TMDCs are the desirable catalytic sites for the hydrogen evolution reaction (HER). Herein, the vanadium diselenide (VSe2) quantum dots with high-density edge sites are prepared by tip sonication of the self-detached VSe2 nanosheets. The spontaneously released VSe2 nanosheets, without chemical-involved transfer, offer a noncontaminated catalyst for HER. Compared to the VSe2 nanosheets, VSe2 quantum dots with a high density of active edges present a significant enhancement of the electrocatalytic performance. The reduced overpotential and transfer resistance indicate the lower Gibbs free energy and faster faradic process of the VSe2 quantum dots for HER. The active edge sites of VSe2 quantum dots show improved catalytic properties in thermodynamic and kinetic aspects. The VSe2 quantum dots loaded on a carbon cloth could be used as a flexible electrode for HER. This work provides an effective way to regulate the defects of the 2D TMDCs for high-performance HER catalysts and also offers a catalyst for flexible HER. [ABSTRACT FROM AUTHOR]

Although it suffers from a heavy dependence on the noble platinum catalyst, the electrochemical hydrogen evolution reaction (HER) is one of the most promising methods for the production of hydrogen. After numerous efforts, it is found that MoS2-based heterostructure may replace platinum as the electrochemical HER catalyst. In this work, the nanocrystalline NiSe2/MoS2 heterostructures were successfully prepared on the carbon fiber paper (CFP) substrate through electrochemical deposition and hydrothermal process. According to a series of electrochemical HER tests and a comparison with other MoS2-based heterostructure catalysts, the CFP/NiSe2/MoS2 catalyst with an overpotential η10 of 143 mV and a Tafel slope of 45 mV dec−1 exhibited an excellent electrochemical HER catalytic performance and durability. In addition, CFP/NiSe2/MoS2 catalyst was treated by plasma to further improve the catalytic performance of the catalyst. [ABSTRACT FROM AUTHOR]

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Hierarchical transition metal dichalcogenide (h-TMDC) nanostructures with abundant active edge sites and good electrical conductivity hold great promise for numerous applications. Here, we report a general method for the chemical synthesis of a series of large-area, free-standing h-TMDC films and their devices by using carbon nanotube (CNT) spiderwebs as both growth promoters and electrical/mechanical reinforcement networks. Our approach allows the seamless integration of h-TMDC nanostructures with abundant active edge sites and CNT networks with good electrical conductivity and mechanical flexibility. As a proof of concept, h-MoSe2/CNT hybrid films with CNT contacts have been chemically synthesized and applied as flexible electrocatalytic devices for hydrogen evolution reaction (HER). Owing to the seamless connection between the CNT contacts and the electroactive h-TMDC/CNT nanostructures, the flexible electrocatalytic devices exhibited excellent mechanical stability and maintained stable electrocatalytic performance under cyclic bendings. Our method can be readily extended to the large-scale production of various h-TMDC/CNT hybrid films and their seamless devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention because of their unique properties and great potential in nano-technology applications. Great efforts have been devoted to fabrication of novel structured TMD monolayers by modifying their pristine structures at the atomic level. Here we propose an intriguing structured 1T-PtTe2 monolayer as hydrogen evolution reaction (HER) catalyst, namely, Pt4Te7, using first-principles calculations. It is found that Pt4Te7 is a stable monolayer material verified by the calculation of formation energy, phonon dispersion, and ab initio molecular dynamics simulations. Remarkably, the novel structured void-containing monolayer exhibits superior catalytic activity toward HER compared with the pristine one, with a Gibbs free energy very close to zero (less than 0.07 eV). These features indicate that Pt4Te7 monolayer is a high-performance HER catalyst with a high platinum utilization. These findings open new perspectives for the functionalization of 2D TMD materials at an atomic level and its application in HER catalysis. [ABSTRACT FROM AUTHOR]

Hydrodesulfurization catalysis ensures upgrading and purification of fossil fuels to comply with increasingly strict regulations on S emissions. The future shift toward more diverse and lower-quality crude oil supplies, high in S content, requires attention to improvements of the complex sulfided CoMo catalyst based on a fundamental understanding of its working principles. In this study, we use scanning tunneling microscopy to directly visualize and quantify how reducing conditions transforms both cluster shapes and edge terminations in MoS2 and promoted CoMoS-type hydrodesulfurization catalysts. The reduced catalyst clusters are shown to be terminated with a fractional coverage of sulfur, representative of the catalyst in its active state. By adsorption of a proton-accepting molecular marker, we can furthermore directly evidence the presence of catalytically relevant S–H groups on the Co-promoted edge. The experimentally observed cluster structure is predicted by theory to be identical to the structure present under catalytic working conditions. [ABSTRACT FROM AUTHOR]

The article discusses the carbon dioxide emissions which are largely driven by fossil fuel combustion and thus there is significant interest in developing alternative carbon-neutral fuels. Also discussed is the molecular hydrogen which is a highly promising fuel that received a great deal of attention since the proposition of a hydrogen economy by John Bockris in 1970.

Recently, transition metal dichalcogenides (TMDs), represented by MoS2, have been proven to be a fascinating new class of electrocatalysts in hydrogen evolution reaction (HER). The rich chemical activities, combined with several strategies to regulate its morphologies and electronic properties, make MoS2 very attractive for understanding the fundamentals of electrocatalysis. In this review, recent developments in using MoS2 as electrocatalysts for the HER with high activity are presented. The effects of edges on HER activities of MoS2 are briefly discussed. Then we demonstrate strategies to further enhance the catalytic performance of MoS2 by improving its conductivity or engineering its structure. Finally, the key challenges to the industrial application of MoS2 in electrocatalytic hydrogen evolution are also pointed out. [ABSTRACT FROM AUTHOR]

Molybdenum based materials are gaining importance as electrocatalysts for hydrogen evolution reaction because of their low cost and good electrocatalytic efficiency. Introducing iron nitride with molybdenum nitride as a composite results in efficient hydrogen evolution activity with current density of $${\sim }120$$ $$\hbox {mA/cm}^{2}$$ at $$-400 \hbox { mV}$$ vs. RHE. The nanocomposites were characterized using powder XRD, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Diffraction, Thermogravimetric Analysis and FTIR Spectroscopy. The electrochemical investigations suggest that the electrocatalytic activity of the composite increases with iron nitride content. The composite exhibits good electrochemical stability upto 42 hours in acidic medium. The hydrogen evolution reaction (HER) follows Volmer-Heyrovsky mechanism where Volmer reaction is the rate determing step. Graphical Abstract: SYNOPSIS Introducing iron nitride in composite with molybdenum nitride leads to higher HER activity in acidic media. The in-situ growth of CNTs in the composites enhances the conductivity and decreases the charge transfer resistance. [ABSTRACT FROM AUTHOR]

Identifying and understanding the active sites responsible for reaction turnover is critical to developing improved catalysts. For the hydrogen-evolution reaction (HER), MoS2 has been identified as an active non-noble-metal-based catalyst. However, only edge sites turnover the reaction because the basal planes are catalytically inert. In an effort to develop a scalable HER catalyst with an increased number of active sites, herein we report a Mo-S catalyst (supported thiomolybdate [Mo3S13]2− nanoclusters) in which most sulfur atoms in the structure exhibit a structural motif similar to that observed at MoS2 edges. Supported sub-monolayers of [Mo3S13]2− nanoclusters exhibited excellent HER activity and stability in acid. Imaging at the atomic scale with scanning tunnelling microscopy allowed for direct characterization of these supported catalysts. The [Mo3S13]2− nanoclusters reported herein demonstrated excellent turnover frequencies, higher than those observed for other non-precious metal catalysts synthesized by a scalable route. [ABSTRACT FROM AUTHOR]

Transition metal chalcogenides have attracted much attention as high-performance electrocatalysts for hydrogen evolution reaction (HER). Here, we synthesized an efficient HER electrocatalyst of amorphous ruthenium sulfide (A-RuS2), exhibiting an overpotential of 141 mV at the current density of 10 mA cm−2 and a Tafel slope of 65.6 mV dec−1. Experiments demonstrate amorphous RuS2 has much better catalytic activity than that of its crystalline counterparts. Our study shows that amorphous RuS2 has increased intrinsic activity and active sites. This work provides a feasible strategy for the development of HER electrocatalysts in amorphous state. [ABSTRACT FROM AUTHOR]

Herein, a simple and facile two-step sonication method was developed for the preparation of nanosheets-like MoS2 wrapped graphene nanohybrids for energy storage and hydrogen evolution reaction (HER) applications. TEM and HR-TEM images revealed that the 120 nm sized lateral diameter of sheet-like MoS2 was completely immobilized on the surfaces of graphene via the probe sonication method. The resultant nanohybrid exhibited bifunctional activities of supercapacitor and HER. With this tailored bifunctional nanoarchitecture, the nanohybrid based electrode showed an improved specific capacitance of 350 F g−1 for a current load of 1 A g−1 with a cyclic efficiency of 85 % in 6 M KOH electrolyte solution. Additionally, the developed MG11 nanohybrid was tested as an electrocatalyst for HER. The latter exhibited a low onset potential of ~125 mV with a Tafel slope of 41 mV/decade. Thus, MG11 nanohybrid presents an excellent prospect for a low-cost electrode for a supercapacitor and an electrocatalyst for hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have unique physicochemical properties. Herein, a low-temperature facile method is demonstrated to synthesize ultrathin tungsten disulfide nanoflakes. They are loosely stacked between layers with highly exposed edges, which provide lots of active sites for electrochemical applications. The by-product of crystalline carbon improves their conductivity, which also enhances their performance in hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]