Vertically Oriented Arrays of ReS2 Nanosheets for Electrochemical Energy Storage and Electrocatalysis

Construction of a Three-Phase MnS2/Co4S3/Ni3S2 Heterostructure for Boosting Oxygen Evolution

The rational construction of highly efficient electrocatalysts for the oxygen evolution reaction (OER) plays a critical role in energy conversion systems. Designing heterostructures is a common and effective strategy to improve the performance of electrocatalysts. In this paper, an MnS2/Co4S3/Ni3S2 heterostructure was synthesized on Ni foam using a one-step vulcanization method. It provides a modified electronic structure and plentiful three-phase heterogeneous interfaces that can effectively enrich the active sites and accelerate electron transfer, thereby improving the OER activity. Thanks to the heterostructure, the MnS2/Co4S3/Ni3S2 exhibits a low overpotential of 265 and 304 mV for the OER to reach current densities of 50 and 100 mA/cm2, respectively. Furthermore, the surface reconstruction of MnS2/Co4S3/Ni3S2 has been investigated, which revealed the formation of metal hydr(oxy)oxides evolved during the OER process. This work provides a facile strategy for constructing three-phase heterostructures, shedding light on the development of high-performance, nonprecious metal-based OER electrocatalysts.

Sandwiched ReS2 nanocables with dual carbon coating for efficient K+/Na+ storage performance

In this work, the nanocables of few-layered ReS2 nanosheets sandwiched between carbon nanotubes (CNTs) and nitrogen-doped amorphous carbon (NC) coating (i.e., CNT@ReS2@NC) are synthesized as high-performance anodes of both potassium-ion batteries (PIBs) and sodium-ion batteries (SIBs). The CNT@ReS2@NC nanocables with dual carbon modifications have the several advantages for efficient K+/Na+ storage. The few-layered ReS2 nanosheets with a wide interlayer spacing of 0.64 nm contribute to accelerated reaction kinetics for fast K+/Na+ intercalation/extraction. The carbon nanotube skeleton with a hollow interior can effectively relieve the volume change and serve as a robust conductive network to boost structural stability. The NC layer provides rich defects as active sites and suppresses the shuttle effect of polysulfides produced in discharge/charge processes. Consequently, the CNT@ReS2@NC nanocables possess outstanding electrochemical performance in both PIBs and SIBs owing to the synergistic effect from the different components. A long cycling lifespan of 3500 cycles with a maintained discharge capacity of 125 mAh/g is achieved for CNT@ReS2@NC at 1 A/g in PIBs. In SIBs, it can keep a high capacity of 202 mAh/g over 3000 cycles at 5 A/g. Moreover, the CNT@ReS2@NC||Na3V2(PO4)3 full cell can exhibit remarkable cycling performance, yielding a low capacity decay rate of 0.019 % per cycle over 1000 cycles at 2C.

Chemical vapor deposition growth of graphene and other nanomaterials with 3D architectures towards electrocatalysis and secondary battery-related applications

Recently, two-dimensional (2D) layered materials, such as graphene and transition metal dichalcogenides (TMDCs), have garnered a lot of attention in energy storage/conversion-related fields due to their novel physical and chemical properties. Constructing flat graphene and TMDCs nanosheets into 3D architectures can significantly increase their exposed surface area and prevent the restacking of adjacent 2D layers, thus dramatically promoting their applications in various energy-related fields. Chemical Vapor Deposition (CVD) is a low-cost, facile, and scalable method, which has been widely employed to produce high-quality graphene and TMDCs nanosheets with 3D architectures. During the CVD process, the morphologies and properties of the 3D architectures of such 2D materials can be designed by selecting substrates with different compositions, stacking geometries, and micro-structures. In this review, we focus on the recent advances in the CVD synthesis of graphene, TMDCs, and their hybrids with 3D architectures on different 3D-structured substrates, as well as their applications in the electrocatalytic hydrogen evolution reaction (HER) and various secondary batteries. In addition, the challenges and future prospects for the CVD synthesis and energy-related applications of these unique layered materials will also be discussed.

Evolution of structural and electronic properties standardized description in rhenium disulfide at the bulk-monolayer transition

The structural and electronic properties of ReS2 different forms - three-dimensional bulk and two-dimensional monolayer - were studied within density functional theory and pseudopotentials. A method for standardizing the description of bulk unit cells and "artificial" slab unit cells for DFT research has been proposed. The preference of this method for studying zone dispersion has been shown. The influence of the vacuum layer thickness on specified special high-symmetry points is discussed. Electron band dispersion in both classical 3D Brillouin zones and transition to 2D Brillouin zones in the proposed two-dimensional approach using the Niggli form of the unit cell was compared. The proposed two-dimensional approach is preferable for low-symmetry layered crystals such as ReS2. It was established that the bulk ReS2 is a direct gap semiconductor (band gap of 1.20 eV), with the direct transition lying in the X point of the first Brillouin zone, and it is in good agreement with published experimental data. The reduction in material dimension from bulk to monolayer was conducted with an increasing band gap up to 1.45 eV, with a moving direct transition towards the Brillouin zone center. The monolayer of ReS2 is a direct-gap semiconductor in a wide range of temperatures, excluding only a narrow range at low temperatures, where it comes as a quasi-direct gap semiconductor. The transition, situated directly in the Γ-point, lies 3.3 meV below the first direct transition located near this point. The electronic density of states of ReS2 in the bulk and monolayer cases of ReS2 were analyzed. The molecular orbitals were built for both types of ReS2 structures as well as the electron difference density maps. For all types of ReS2 structures, an analysis of populations according to Mulliken and Voronoi was carried out. All calculated data is discussed in the context of weak quantum confinement in the 2D case.

Electrocatalytic Activation in ReSe2-VSe2 Alloy Nanosheets to Boost Water-Splitting Hydrogen Evolution Reaction

It is challenging to control the electronic structure of 2D transition metal dichalcogenides (TMD) for extended applications in renewable energy devices. Here, ReSe2-VSe2 (Re1- xVxSe2) alloy nanosheets over the whole composition range via a colloidal reaction is synthesized. Increasing x makes the nanosheets more metallic and induces a 1T″-to-1T phase transition at x = 0.5-0.6. Compared to the MoSe2-VSe2 and WSe2-VSe2 alloy nanosheets, ReSe2 and VSe2 are mixed more homogeneously at the atomic scale. The alloy nanosheets at x = 0.1-0.7 exhibit an enhanced electrocatalytic activity toward acidic hydrogen evolution reaction (HER). In situ X-ray absorption fine structure measurements reveal that alloying caused the Re and V atoms to be synergically more active in the HER. Gibbs free energy (ΔGH*) and density of state calculations confirm that alloying and Se vacancies effectively activate the metal sites toward HER. The composition dependence of HER performance is explained by homogenous atomic mixing with the increased Se vacancies. The study provides a strategy for designing new TMD alloy nanosheets with enhanced catalytic activity.

Unleashing the power of boron: enhancing nitrogen reduction reaction through defective ReS2 monolayers

Density functional theory (DFT) calculations were utilized to investigate the electrocatalytic potential of single boron (B) atom doping in defective ReS2 monolayers as an active site. Our investigation revealed that B-doped defective ReS2, containing S and S-Re-S defects, demonstrated remarkable conductivity, and emerged as an exceptionally active catalyst for nitrogen reduction reactions (NRR), exhibiting limiting potentials of 0.63 and 0.53 V, respectively. For both cases, we determined the potential by examining the hydrogenation of adsorbed N2* to N2H*. Although the competing hydrogen evolution reaction (HER) process appeared dominant in the S-Re-S defect case, its impact was minimal. The outstanding NRR performance can be ascribed to the robust chemical interactions between B and N atoms. The adsorption of N2 on B weakens the N-N bond, thereby facilitating the formation of NH3. Moreover, we verified the selectivity and stability of the catalysts for NRR. Our findings indicate that B-doped defective ReS2 monolayers hold considerable promise for electrocatalysis in a variety of applications.

Design principles for 2D transition metal dichalcogenides toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as a promising candidate for next-generation energy storage systems owing to their remarkable energy density, resource availability, and environmental benignity. Nevertheless, severe shuttling effect, sluggish redox kinetics, large volumetric expansion, and uncontrollable dendrite growth hamper the practical applications. To address these intractable issues, two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged expeditiously as an essential material strategy. Herein, this review emphasizes the development and application of 2D TMDs in Li-S batteries. It starts with introducing the fundamentals of Li-S batteries and common synthetic routes of TMDs, followed by summarizing the employment of pristine, hybrid, and defective TMDs in the realm of expediting sulfur chemistry and stabilizing lithium anode. Finally, the development roadmap and possible research directions of TMDs are proposed to offer guidance for the future design of high-performance Li-S batteries.

Rhenium-Based Electrocatalysts for Water Splitting

Due to the contamination and global warming problems, it is necessary to search for alternative environmentally friendly energy sources. In this area, hydrogen is a promising alternative. Hydrogen is even more promising, when it is obtained through water electrolysis operated with renewable energy sources. Among the possible devices to perform electrolysis, proton exchange membrane (PEM) electrolyzers appear as the most promising commercial systems for hydrogen production in the coming years. However, their massification is affected by the noble metals used as electrocatalysts in their electrodes, with high commercial value: Pt at the cathode where the hydrogen evolution reaction occurs (HER) and Ru/Ir at the anode where the oxygen evolution reaction (OER) happens. Therefore, to take full advantage of the PEM technology for green H2 production and build up a mature PEM market, it is imperative to search for more abundant, cheaper, and stable catalysts, reaching the highest possible activities at the lowest overpotential with the longest stability under the harsh acidic conditions of a PEM. In the search for new electrocatalysts and considering the predictions of a Trasatti volcano plot, rhenium appears to be a promising candidate for HER in acidic media. At the same time, recent studies provide evidence of its potential as an OER catalyst. However, some of these reports have focused on chemical and photochemical water splitting and have not always considered acidic media. This review summarizes rhenium-based electrocatalysts for water splitting under acidic conditions: i.e., potential candidates as cathode materials. In the various sections, we review the mechanism concepts of electrocatalysis, evaluation methods, and the different rhenium-based materials applied for the HER in acidic media. As rhenium is less common for the OER, we included a section about its use in chemical and photochemical water oxidation and as an electrocatalyst under basic conditions. Finally, concluding remarks and perspectives are given about rhenium for water splitting.

Selenide-doped bismuth sulfides (Bi2S3-xSex) and their hierarchical heterostructure with ReS2for sodium/potassium-ion batteries

In this work, selenide-doped bismuth sulfides (Bi₂S_3-xSe_x) was successfully prepared through Se doping Bi₂S₃ Se to improve the electronic conductivity and increase the interlayer spacing. Then the anisotropic ReS₂ nanosheet arrays were grown on the surface of Bi₂S_3-xSe_x to form a hierarchical heterostructure (Bi₂S_3-xSe_x@ReS₂). The doping and construction of heterostructure processes can greatly improve the electrochemical conductivity of electrode materials and relieve the volume expansion during the continuous charge/discharge processes. While applied as SIBs anode, the specific capacity of 330 mAh g^-1 was maintained after 450 cycles at the current density of 1.0 A g^-1. It can also keep 200 mAh g^-1 specific capacity after 900 cycles at 1.0 A g^-1 for the anode of PIBs. This heterogeneous engineering and doping dual strategies could provide a good idea for the synthesis of new bimetallic sulfides with outstanding battery performance for SIBs and PIBs.

Photocatalytic Applications of ReS2-Based Heterostructures

ReS2-based heterostructures, which involve the coupling of a narrow band-gap semiconductor ReS2 with other wide band-gap semiconductors, have shown promising performance in energy conversion and environmental pollution protection in recent years. This review focuses on the preparation methods, encompassing hydrothermal, chemical vapor deposition, and exfoliation techniques, as well as achievements in correlated applications of ReS2-based heterostructures, including type-I, type-II heterostructures, and Z-scheme heterostructures for hydrogen evolution, reduction of CO2, and degradation of pollutants. We believe that this review provides an overview of the most recent advances to guide further research and development of ReS2-based heterostructures for photocatalysis.

P-P Orbital Interaction Enables Single-Crystalline Semimetallic β-MoTe2 Nanosheets as Efficient Electrocatalysts for Lithium-Sulfur Batteries

The practical implementation of lithium-sulfur batteries (LSBs) has been impeded by the sluggish redox kinetics of lithium polysulfides (LiPSs) and shuttle effect of soluble LiPSs during charge/discharge. It is desirable to exploit materials combining superior electrical conductivity with excellent catalytic activity for use as electrocatalysts in LSBs. Herein, we report the employment of chemical vapor transport (CVT) method followed by an electrochemical intercalation process to fabricate high-quality single-crystalline semimetallic β-MoTe₂ nanosheets, which are utilized to manipulate the LiPSs conversion kinetics. The first-principles calculations prove that β-MoTe₂ could lower the Gibbs free-energy barrier for Li₂S₂ transformation to Li₂S. The wavefunction analysis demonstrates that the p-p orbital interaction between Te p and S p orbitals accounts for the strong electronic interaction between the β-MoTe₂ surface and Li₂S₂/Li₂S, making bonding and electron transfer more efficient. As a result, a β-MoTe₂/CNT@S-based LSB cell can deliver an excellent cycling performance with a low capacity fade rate of 0.11% per cycle over 300 cycles at 1C. Our work might not only provide a universal route to prepare high-quality single-crystalline transition-metal dichalcogenides (TMDs) nanosheets for use as electrocatalysts in LSBs, but also suggest a different viewpoint for the rational design of LiPSs conversion electrocatalysts.

Ultrathin Fe-ReS2 Nanosheets as Electrocatalysts for Accelerating Sulfur Reduction in Li-S Batteries

Lithium-sulfur batteries are promising next-generation energy storage systems with high theoretical specific capacity. Despite extensive research efforts, it is still challenging to rationally design electrocatalysts with fast kinetics and effective adsorption of polysulfides. Herein, Fe-doped ReS₂ (Fe-ReS₂) ultrathin nanosheets are prepared as an electrocatalyst to trap the intermediates and accelerate the sulfur reduction reaction kinetics. Density functional theory calculations combined with activation energies in the multistep sulfur reduction reaction reveal that the Fe-ReS₂ considerably reduces the activation energy and optimizes the optimum adsorption strength of polysulfides and catalytic activity. The Fe-ReS₂/S exhibits a highly reversible discharge capacity of 882.3 mA h g^-1 at 1 C. For 500 cycles, the capacity fade rate is 0.013% per cycle. Moreover, in situ Raman spectroscopy measurements further confirmed that both sulfur reduction and oxidation processes were significantly enhanced by Fe-ReS₂.

Dual Self-Built Gating Boosts the Hydrogen Evolution Reaction

Optimizing the intrinsic activity of active sites is an appealing strategy for accelerating the kinetics of the catalytic process. Here, a design principle, namely "dual self-built gating", is proposed to tailor the electronic structures of catalysts. Catalytic improvement is confirmed in a model catalyst with a ReS₂ -WS₂ /WS₂ hybridized heterostructure. As demonstrated in experimental and theoretical results, the dual gating can bidirectionally guide electron transfer and redistribute at the interface, endowing the model catalyst with an electron-rich region. The tailored electronic structures balance the adsorption of intermediates and the desorption of hydrogen synergistically to enhance the reaction kinetics for the hydrogen evolution reaction. Interestingly, the effect of dual gating can be easily amplified by the electric field. The overpotential and Tafel slope (49 mV, 35 mV dec^-1 ) obtained under the electric field for ReS₂ -WS₂ /WS₂ catalyst with the dual self-built gating effect are far below than those (210 mV, 116 mV dec^-1 ) of the pure WS₂ catalyst, which exhibits nearly four times improvement. The concept of dual gating can be applied to more systems, offering a new guideline for designing advanced electrocatalysts.

Unveiling the Electrocatalytic Activity of 1T'-MoSe2 on Lithium-Polysulfide Conversion Reactions

The dissolution of intermediate lithium polysulfides (LiPS) into an electrolyte and their shuttling between the electrodes have been the primary bottlenecks for the commercialization of high-energy density lithium-sulfur (Li-S) batteries. While several two-dimensional (2D) materials have been deployed in recent years to mitigate these issues, their activity is strictly restricted to their edge-plane-based active sites. Herein, for the first time, we have explored a phase transformation phenomenon in a 2D material to enhance the number of active sites and electrocatalytic activity toward LiPS redox reactions. Detailed theoretical calculations demonstrate that phase transformation from the 2H to 1T' phase in a MoSe₂ material activates the basal planes that allow for LiPS adsorption. The corresponding transformation mechanism and LiPS adsorption capabilities of the as-formed 1T'-MoSe₂ were elucidated experimentally using microscopic and spectroscopic techniques. Further, the electrochemical evaluation of phase-transformed MoSe₂ revealed its strong electrocatalytic activity toward LiPS reduction and their oxidation reactions. The 1T'-MoSe₂-based cathode hosts for sulfur later provide a superior cycling performance of over 250 cycles with a capacity loss of only 0.15% per cycle along with an excellent Coulombic efficiency of 99.6%.

Screening of transition metal single-atom catalysts supported by a WS2 monolayer for electrocatalytic nitrogen reduction reaction: insights from activity trend and descriptor

The electrocatalytic nitrogen reduction reaction (NRR), as an alternative green technology to the Haber-Bosch process, can efficiently synthesize ammonia under ambient conditions and has a reduced carbon footprint. Here we systematically investigate the NRR activity and selectivity of transition metal (TM) single-atom catalyst (SAC) anchored WS₂ monolayers (TM@WS₂) by means of first-principles calculations and microkinetic modeling. The construction of the reaction activity trend and the identification of an activity descriptor, namely *N₂H adsorption energy, facilitate the efficient screening and rational design of SACs with high activity. Manipulating the adsorption strength of the pivotal *N₂H intermediate is a potential strategy for enhancing NRR activity. Utilizing the limiting potential difference of NRR and the hydrogen evolution reaction (HER) as a selectivity descriptor, we screen three SACs with excellent activity and selectivity toward NRR, i.e., Re@WS₂, Os@WS₂ and Ir@WS₂ with favorable limiting potentials of -0.44 V, -0.38 V and -0.69 V. By using the explicit H₉O₄⁺ model, the kinetic barriers of the rate-determining steps (0.47 eV-1.15 eV) of the solvated proton transfer on the screened SACs are found to be moderate, indicative of a kinetically feasible process. Microkinetic modeling shows that the turnover frequencies of N₂ reduction to NH₃ on Re@WS₂, Os@WS₂ and Ir@WS₂ are 1.52 × 10⁵, 8.21 × 10² and 4.17 × 10^-4 per s per site at 400 K, achieving fast reaction rates. The coexistence of empty and occupied 5d orbitals of candidate SACs is beneficial for σ donation and π* backdonation, endowing them with extraordinary N₂ adsorption and activation. Moreover, the screened SACs possess good dispersity and thermodynamic stability. Our work provides a promising solution for the efficient screening and rational design of high-performance electrocatalysts toward the NRR.

Remote Plasma-Induced Synthesis of Self-Assembled MoS2/Carbon Nanowall Nanocomposites and Their Application as High-Performance Active Materials for Supercapacitors

The objective of this study is to investigate the synthesis and influence of MoS2 on carbon nanowalls (CNWs) as supercapacitor electrodes. The synthesis of MoS2 on CNW was achieved by the introduction of hydrogen remote plasma from ammonium tetrathiomolybdate (ATTM) without deterioration of the CNWs. The topographical surface structures and electrochemical characteristics of the MoS2–CNW composite electrodes were explored using two ATTM-dispersed organic solvents—acetonitrile and dimethylformamide (DMF). In this study, CNW and MoS2 were synthesized using an electron cyclotron resonance plasma. However, hydrogen radicals, which transform ATTM into MoS2, were provided in the form of a remote plasma source. The electrochemical performances of MoS2–CNW hybrid electrodes with various morphologies—depending on the solvent and ATTM concentration—were evaluated using a three-electrode system. The results revealed that the morphology of the synthesized MoS2 was influenced by the organic solvent used and affected both the electrochemical performance and topographical characteristics. Notably, considerable enhancement of the specific capacitance was observed for the MoS2 with open top edges synthesized from DMF. These encouraging results may motivate additional research on hybrid supercapacitor electrodes and the rapid synthesis of MoS2 and other transition metal dichalcogenides.

Recent Developments of Cathode Materials for Thermal Batteries

Big progress has been made in batteries based on an intercalation mechanism in the last 20 years, but limited capacity in batteries hinders their further increase in energy density. The demand for more energy intensity makes research communities turn to conversion-type batteries. Thermal batteries are a special kind of conversion-type battery, which are thermally activated primary batteries composed mainly of cathode, anode, separator (electrolyte), and heating mass. Such kinds of battery employ an internal pyrotechnic source to make the battery stack reach its operating temperature. Thermal batteries have a long history of research and usage in military fields because of their high specific capacity, high specific energy, high thermal stability, long shelf life, and fast activation. These experiences and knowledge are of vital importance for the development of conversion-type batteries. This review provides a comprehensive account of recent studies on cathode materials. The paper covers the preparation, characterization of various cathode materials, and the performance test of thermal batteries. These advances have significant implications for the development of high-performance, low-cost, and mass production conversion-type batteries in the near future.

Concerted effect of Ni-in and S-out on ReS2 nanostructures towards high-efficiency oxygen evolution reaction

Herein, a one-step hydrothermal reaction is developed to synthesize Ni-doped ReS2 nanostructure with the sulphur defect. The material exhibited excellent OER activity with a current density of 10 mAcm-2 at...

The effect of morphology on electrochemical hydrogen evolution reaction of ReSe2 nano-structures

Transition metal dichalcogenides (TMDs), such as rhenium diselenide, have currently attracted a lot of attention as one of the novel candidates of the TMD family.

A Rhenium Single-Atom Catalyst for the Electrocatalytic Oxygen Reduction Reaction

Single atom catalysts (SACs) have received a great deal of attention due to their extremely high active site utilization and superior activities. The exploration of metal SACs has been carried out by screening the elemental periodic table from first-row to second-row, and even third-row transition metals. However, Re SACs have not been reported, even if Re metal sites also play essential roles in catalyzing many important reactions. The construction of Re SACs may maximize Re catalytic sites and provide new Re active sites for higher activity. Herein, we used 1,10-phenanthroline to complex Re cations on carbon black, followed by heat treatment to obtain Re SAC. The Re SAC exhibited an oxygen reduction reaction (ORR) half-wave potential of 0.72 V versus reversible hydrogen electrode (RHE) in 0.1 M KOH, superior to Re nanoparticles catalyst (0.67 V vs. RHE). Re SAC exhibited better stability at 0.5 V vs. RHE than Pt/C, showing potential as a new electrocatalyst for ORR.

Two-dimensional square metal organic framework as promising cathode material for lithium-sulfur battery with high theoretical energy density

Lithium-sulfur (Li-S) batteries are considered as new generation of energy storage which offer cost-effectiveness and high energy density. However, their commercialization is restricted due to a host of challenges associated with the cathode material which usually contains sulfur with several drawbacks, including a low electronic conductivity of sulfur, the 'shuttle effect', and a large volume expansion during discharge. Herein, a novel two-dimensional porphyrin-like square metal organic framework (MOF) was explored as a promising cathode material using first principles density function theory (DFT) assisted by genetic global search. The DFT results show that, among 7 kinds of transition-metal organic framework (TM-MOF), only V-MOF and Ru-MOF is found to possess considerable chemical interactions with S₈ and lithium polysulfides (LiPSs) in both vacuum and in electrolytic solvents, demonstrating distinguishable anchoring performance. The genetic global search and further DFT calculations indicate that the lithiation process on V-MOF exhibited a nearly constant open-circuit voltage of about 1.92 V to 1.95 V, and the theoretical energy density could reach up to 1469 Wh kg^-1 when lithiation of S₈ is considered on both sides of the substrate. The volume expansion of V-MOF during discharge is found to be about 34%, much smaller than 80% for solid sulfur. The band structure and density of states of V-MOF suggest metallic properties or a small band gap for bare surface or during the lithiation process. These results indicate that two-dimensional (2D) V-MOFs can serve as high-performance cathode material with distinguished anchoring performance to block polysulfide dissolution and thereby reduce the 'shuttle effect', and help attain ultra-high energy density. Our work points the way for designing and providing experimental realization of 2D layered materials applied in cathode with high energy density and stability.

Electrochemical Capacitor Performance of Nanotextured Carbon/Transition Metal Dichalcogenides Composites

Transition metal dichalcogenides (TMDs) are emerging low-dimensional materials with potential applications for electrochemical capacitors (EC). Here, physicochemical and electrochemical characterizations of carbon composites with two sulfides ReS₂ and FeS₂ are reported. To enhance conductivity, multiwalled carbon nanotubes (NTs) serve as a support for ReS₂ while 3D graphene-like network (3DG) is utilized for FeS₂ deposition. Unique structure of carbon/TMDs composites allows a faradaic contribution of sulfides to be exploited. Capacitance values, charge/discharge efficiency, capacitance retention, charge propagation, cyclabilty, and voltage limits of EC with carbon/sulfide composites in aqueous neutral solutions (Li₂ SO₄ , Na₂ SO₄ ) are analyzed. Special attention is devoted to energetic efficiency of capacitive charge/discharge processes. Structure-to-capacitance correlation for the composites with various TMDs loading is thoroughly emphasized. The more defected structure of layered NTs/ReS₂ composite is responsible for the lower capacitor voltage (0.8 V) owing to quicker electrolyte decomposition. Additionally, the catalytic effect of Re for hydrogen evolution reaction plays a crucial role in EC voltage restriction. Contrary, the operating voltage of capacitor based on 3DG/FeS₂ is able to be extended until 1.5 V in sodium sulfate electrolytic solution.

Recent developments in 2D transition metal dichalcogenides: phase transition and applications of the (quasi-)metallic phases

The advent of two-dimensional transition metal dichalcogenides (2D-TMDs) has led to an extensive amount of interest amongst scientists and engineers alike and an intensive amount of research has brought about major breakthroughs in the electronic and optical properties of 2D materials. This in turn has generated considerable interest in novel device applications. With the polymorphic structural features of 2D-TMDs, this class of materials can exhibit both semiconducting and metallic (quasi-metallic) properties in their respective phases. This polymorphic property further increases the interest in 2D-TMDs both in fundamental research and for their potential utilization in novel high-performance device applications. In this review, we highlight the unique structural properties of few-layer and monolayer TMDs in the metallic 1T- and quasi-metallic 1T'-phases, and how these phases dictate their electronic and optical properties. An overview of the semiconducting-to-(quasi)-metallic phase transition of 2D-TMD systems will be covered along with a discussion on the phase transition mechanisms. The current development in the applications of (quasi)-metallic 2D-TMDs will be presented ranging from high-performance electronic and optoelectronic devices to energy storage, catalysis, piezoelectric and thermoelectric devices, and topological insulator and neuromorphic computing applications. We conclude our review by highlighting the challenges confronting the utilization of TMD-based systems and projecting the future developmental trends with an outlook of the progress needed to propel this exciting field forward.

Significantly Raised Visible-Light Photocatalytic H2 Evolution on a 2D/2D ReS2 /In2 ZnS4 van der Waals Heterostructure

Owing to dwindling fossil fuels reserves, the development of alternative renewable energy sources is globally important. Photocatalytic hydrogen (H₂ ) evolution represents a practical and affordable alternative to convert sunlight into carbon-free H₂ fuel. Recently, 2D/2D van der Waals heterostructures (vdWHs) have attracted significant research attention for photocatalysis. Here, for the first time a ReS₂ /In₂ ZnS₄ 2D/2D vdWH synthesized via a facile physical mixing is reported. It exhibits a highly promoted photocatalytic H₂ -evolution rate of 2515 µmol h^-1 g^-1 . Importantly, this exceeds that for pristine In₂ ZnS₄ by about 22.66 times. This, therefore, makes ReS₂ /In₂ ZnS₄ one of the most efficient In₂ ZnS₄ -based photocatalysts without noble-metal cocatalysts. Advanced characterizations and theoretical computations results show that interlayer electronic interaction within ReS₂ /In₂ ZnS₄ vdWH and atomic-level S active centers along the edges of ReS₂ NSs work collaboratively to result in the boosted light-induced H₂ evolution. Results will be of immediate benefit in the rational design and preparation of vdWHs for applications in catalysis/(opto)electronics.

Recent Advances in 2D Group VB Transition Metal Chalcogenides

2D materials have received considerable research interest owing to their abundant material systems and remarkable properties. Among them, 2D group VB transition metal chalcogenides (GVTMCs) stand out as emerging 2D metallic materials and significantly broaden the research scope of 2D materials. 2D GVTMCs have great advantages in electrical transport, 2D magnetism, charge density wave, sensing, catalysis, and charge storage, making them attractive in the fields of functional devices and energy chemistry. In this review, the recent progress of 2D GVTMCs is summarized systematically from fundamental properties, growth methodologies to potential applications. The challenges and prospects are also discussed for future research in this field.

Contact Engineering of Vertically Grown ReS2 with Schottky Barrier Modulation

Forming metal contact with low contact resistance is essential for the development of electronics based on layered van der Waals materials. ReS₂ is a semiconducting transition metal dichalcogenide (TMD) with an MX₂ structure similar to that of MoS₂. While most TMDs grow parallel to the substrate when synthesized using chemical vapor deposition (CVD), ReS₂ tends to orient itself vertically during growth. Such a feature drastically increases the surface area and exposes chemically active edges, making ReS₂ an attractive layered material for energy and sensor applications. However, the contact resistances of vertically grown materials are known to be relatively high, compared to those of common 2H-phase TMDs, such as MoS₂. Most reported methods for lowering the contact resistance have been focused on exfoliated 2H-phase materials with only a few devices tested, and few works on distorted T-phase materials exist. Moreover, nearly all reported studies have been conducted on only a few devices with mechanically exfoliated fl Most reported methods for lowering the contact resistance have been ₂ contacts was modulated by conformally coating a thin tunneling interlayer between the metal and the dendritic ReS₂ film. Over a hundred devices were tested, and contact resistances were extracted for large-scale statistical analysis. Importantly, we compared various known materials and techniques for lowering contact resistance and found an optimized method. Finally, the reductions in barrier height were directly correlated with exponential reductions in contact resistance and increases in drive-current by almost 2 orders of magnitude.

High-performance ammonia fixation electrocatalyzed by ReS2 nanosheet array

The industrial-scale NH₃ production still heavily depends on the Haber–Bosch process, which not only demands high energy consumption but also emits a large amount of CO₂.

Kinetic Enhancement of Sulfur Cathodes by N-Doped Porous Graphitic Carbon with Bound VN Nanocrystals

The reaction kinetics of sulfur cathodes generally control the performance of lithium-sulfur (Li-S) batteries. Here, N-doped porous graphitic carbon with bound VN nanocrystals (3D VN@N-PGC), which is synthesized in one pot by heating a mixture of glucose as C source, urea as N source, and NH₄ VO₃ as V source, is reported to be an superior electrocatalytic cathode host for Li-S batteries. Notably, the VN nanocrystals, strongly bound to the N-PGC network, form via in situ reactions among the thermolytic products of starting materials. The dopant N atoms and bound VN nanocrystals exhibit synergistic electrocatalytic effects to promote the cathode reactions of the Li-S cells. The observed enhancements are supported by density functional theory simulations and by the observation of electrocatalytic N- and V-intermediate species, via X-ray absorption near-edge structure spectroscopy. Li-S cells assembled using 3D VN@N-PGC as cathode host exhibit superior performance in terms of specific capacity (1442 mA h g^-1 at 0.1 C), rate capability (641 mA h g^-1 at 4 C), and cycle life (466 mA h g^-1 after 1700 cycles at 2 C, corresponding to a capacity decay of 0.020% per cycle). The one-pot methodology is facile and scalable and offers a new approach for synthesis of various metal nitride-containing materials for other electrocatalytic applications.

2D Re-Based Transition Metal Chalcogenides: Progress, Challenges, and Opportunities

The rise of 2D transition-metal dichalcogenides (TMDs) materials has enormous implications for the scientific community and beyond. Among TMDs, ReX2 (X = S, Se) has attracted significant interest regarding its unusual 1T' structure and extraordinary properties in various fields during the past 7 years. For instance, ReX2 possesses large bandgaps (ReSe2: 1.3 eV, ReS2: 1.6 eV), distinctive interlayer decoupling, and strong anisotropic properties, which endow more degree of freedom for constructing novel optoelectronic, logic circuit, and sensor devices. Moreover, facile ion intercalation, abundant active sites, together with stable 1T' structure enable them great perspective to fabricate high-performance catalysts and advanced energy storage devices. In this review, the structural features, fundamental physicochemical properties, as well as all existing applications of Re-based TMDs materials are comprehensively introduced. Especially, the emerging synthesis strategies are critically analyzed and pay particular attention is paid to its growth mechanism with probing the assembly process of domain architectures. Finally, current challenges and future opportunities regarding the controlled preparation methods, property, and application exploration of Re-based TMDs are discussed.

Construction of reduced graphene oxide wrapped yolk-shell vanadium dioxide sphere hybrid host for high-performance lithium-sulfur batteries

Owing to the considerable theoretical energy density, lithium-sulfur batteries have been deemed as a competitive candidate for the next-generation energy storage devices. However, its commercialization still depends on the moderation of the shuttle effect and the conductivity improvement of the sulfur cathode. Herein, a novel reduced graphene oxide (rGO) wrapped yolk-shell vanadium dioxide (VO2) sphere hybrid host (rGO/VO2) is reported to simultaneously tackle these barriers. In particular, the polar VO2 sphere can chemically anchor and catalyze the conversion of polysulfides effectively both on the yolk and the shell surfaces. Meanwhile, the highly conductive 3D porous rGO network not only allows sufficient penetration of electrolyte and provides efficient transport pathways for lithium ions and electrons, but also buffers the volume variation during the lithiation process. Besides, the dissolution of the polysulfides can also be alleviated by physical confinement via the interconnected carbon network. Benefiting from these synergistic features, such designed rGO/VO2/S cathode delivers outstanding cycle stability (718.6 mA h g-1 initially, and 516.1 mA h g-1 over 400 cycles at 1C) with a fading rate of 0.07% per cycle. Even at 3C, a capacity of 639.7 mA h g-1 is reached. This proposed unique structure could provide novel insights into high-energy batteries.

Phase Evolution of Re1-xMoxSe2 Alloy Nanosheets and Their Enhanced Catalytic Activity toward Hydrogen Evolution Reaction

Two-dimensional ReSe₂ has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re_1-xMo_xSe₂ alloy nanosheets with the whole range of x (0-100%) using a hydrothermal reaction. The phase evolved in the order of 1T″ (triclinic) → 1T' (monoclinic) → 2H (hexagonal) upon increasing x. In the nanosheets with x = 10%, the substitutional Mo atoms tended to aggregate in the 1T″ ReSe₂ phase with Se vacancies. The incorporation of the 1T' phase makes the alloy nanosheets more metallic than the end compositions. The 10% Mo substitution significantly enhanced the electrocatalytic performance toward HER (in 0.5 M H₂SO₄), with a current of 10 mA cm^-2 at an overpotential of 77 mV (vs RHE) and a Tafel slope of 42 mV dec^-1. First-principles calculations of the three phases (1T″, 2H, and 1T') predicted a phase transition of 1T″-2H at x ≈ 65% as well as the production of a 1T' phase along the composition tuning, which are consistent with the experiments. At x = 12.5%, two Mo atoms prefer to form a pair along the Re₄ chains. Gibbs free energy along the reaction path indicates that the best HER performance of nanosheets with 10% Mo originates from the Mo atoms that form Mo-H when there are adjacent Se vacancies.

Adatom Doping of Transition Metals in ReSe2 Nanosheets for Enhanced Electrocatalytic Hydrogen Evolution Reaction

Two-dimensional Re dichalcogenide nanostructures are promising electrocatalysts for the hydrogen evolution reaction (HER). Herein, we report the adatom doping of various transition metals (TM = Mn, Fe, Co, Ni, and Cu) in ReSe₂ nanosheets synthesized using a solvothermal reaction. As the atomic number of TM increases from Mn to Cu, the adatoms on Re sites become more favored over the substitution. In the case of Ni, the fraction of adatoms reaches 90%. Ni doping resulted in the most effective enhancement in the HER catalytic performance, which was characterized by overpotentials of 82 and 109 mV at 10 mA cm^-2 in 0.5 M H₂SO₄ and 1 M KOH, respectively, and the Tafel slopes of 54 and 81 mV dec^-1. First-principles calculations predicted that the adatom doping structures (TMs on Re sites) have higher catalytic activity compared with the substitution ones. The adsorbed H atoms formed a midgap hybridized state via direct bonding with the orbitals of TM adatom. The present work provides a deeper understanding into how TM doping can provide the catalytically active sites in these ReSe₂ nanosheets.

A perfectly oriented, free-standing and transparent titania nanosheet film with the band gap of a monolayer

A perfectly oriented, free-standing and transparent titania nanosheet film was prepared using the spin-coating technique. The free-standing film (thickness: ∼210 nm) showed a wide band gap that corresponded to that of the monolayer nanosheet despite the stacking of hundreds of layers.

Nanoscale engineering and Mo-doping of 2D ultrathin ReS2 nanosheets for remarkable electrocatalytic hydrogen generation

Two-dimensional (2D) lamellar ReS2 nanosheets are considered a promising electrocatalyst for the hydrogen evolution reaction (HER) but suffer from poor intrinsic conductivity and catalytically inert basal planes. In this work, sub 50 nm hierarchical Mo-doped ReS2 nanospheres consisting of numerous few-layered and defect-rich nanosheets are designed and synthesized as robust and efficient HER catalysts. On the one hand, the small size of the hierarchical structure, the disordered basal planes and the expanded interlayer endow the nanosheets with plentiful defects, thereby resulting in abundant exposed active sites. On the other hand, Mo-doping offers the nanosheets with some electronic benefits of unsaturated electrons, improved intrinsic conductivity, and optimized hydrogen adsorption free energy (ΔGH) of the basal planes. Owing to the synergistic effects, the 10%Mo-ReS2 catalyst exhibits an optimized catalytic activity with striking kinetic metrics of a small Tafel slope of 62 mV dec-1, a low overpotential of 81 mV at 10 mA cm-2, and a long operation stability of 50 h, and its performance is among the best of ReS2-based catalysts. This work provides a new approach for gaining the structural and electronic benefits of ReS2 catalysts by combinational nanoscale engineering and heteroatom doping.

Hydrogen-Etched Bifunctional Sulfur-Defect-Rich ReS2 /CC Electrocatalyst for Highly Efficient HER and OER

The design on synthesizing a sturdy, low-cost, clean, and sustainable electrocatalyst, as well as achieving high performance with low overpotential and good durability toward water splitting, is fairly vital in environmental and energy-related subject. Herein, for the first time the growth of sulfur (S) defect engineered self-supporting array electrode composed of metallic Re and ReS₂ nanosheets on carbon cloth (referred as Re/ReS₂ /CC) via a facile hydrothermal method and the following thermal treatment with H₂ /N₂ flow is reported. It is expected that, for example, the as-prepared Re/ReS₂ -7H/CC for the electrocatalytic hydrogen evolution reaction (HER) under acidic medium affords a quite low overpotential of 42 mV to achieve a current density of 10 mA cm^-2 and a very small Tafel slope of 36 mV decade^-1 , which are comparable to some of the promising HER catalysts. Furthermore, in the two-electrode system, a small cell voltage of 1.30 V is recorded under alkaline condition. Characterizations and density functional theory results expound that the introduced S defects in Re/ReS₂ -7H/CC can offer abundant active sites to advantageously capture electron, enhance the electron transport capacity, and weaken the adsorption free energy of H* at the active sites, being responsible for its superior electrocatalytic performance.

Surface-Induced 2D/1D Heterostructured Growth of ReS2/CoS2 for High-Performance Electrocatalysts

Two-dimensional/one-dimensional (2D/1D) heterostructures have received much attention from researchers for their abundant catalytically active sites and low contact resistance due to formation of chemical bonds at the interface. The investigation of such heterostructures, however, is confined to lattice-matched materials, which severely limits the material candidates. Herein, we demonstrate a lattice-mismatched 2D/1D heterostructured electrocatalyst consisting of 2D ReS₂ nanosheets and 1D CoS₂ nanowires. We propose that the higher surface energy of the CoS₂ nanowire and the lattice mismatch between 1D and 2D units are crucial for the growth process of ReS₂ nanosheets. More importantly, the terminal S^2- exposed on the surface of CoS₂ nanowires serves not only as the nucleus of ReS₂ nanosheets but also as a bridge to enhance electron transport efficiency. Thus, the ReS₂/CoS₂ heterostructures show outstanding hydrogen evolution reaction performance. This work is of general interest for the design of complex multidimensional nano-heterostructures with outstanding functionalities.

Construction of nanocage-structured heterogeneous binary metal sulfides via step-by-step confined growth for boosted lithium storage properties

Nanocage-structured materials - heterogeneous binary metal sulfides (MoS₂ and Co₉S₈) in carbon nanocages (Co₉S₈/MoS₂@CNCs) - obtained via step-by-step confined growth display superior Li-storage performance, profiting from the synergistic effect of the bimetallic sulfides, high filling rate of active materials and free interspace in the nanocage structure for volume expansion.

Layered transition metal dichalcogenide/carbon nanocomposites for electrochemical energy storage and conversion applications

Layered transition metal dichalcogenide (LTMD)/carbon nanocomposites obtained by incorporating conductive carbons such as graphene, carbon nanotubes (CNT), carbon nanofibers (CF), hybrid carbons, hollow carbons, and porous carbons exhibit superior electrochemical properties for energy storage and conversion. Due to the incorporation of carbon into composites, the LTMD/carbon nanocomposites have the following advantages: (1) highly efficient ion/electron transport properties that promote electrochemical performance; (2) suppressed agglomeration and restacking of active materials that improve the cycling performance and electrocatalytic stability; and (3) unique structures such as network, hollow, porous, and vertically aligned nanocomposites that facilitate the shortening of the ion and electrolyte diffusion pathway. In this context, this review introduces and summarizes the recent advances in LTMD/carbon nanocomposites for electrochemical energy-related applications. First, we briefly summarize the reported synthesis strategies for the preparation of LTMD/carbon nanocomposites with various carbon materials. Following this, previous studies using rationally synthesized nanocomposites are discussed based on a variety of applications related to electrochemical energy storage and conversion including Li/Na-ion batteries (LIBs/SIBs), Li-S batteries, supercapacitors, and the hydrogen evolution reaction (HER). In particular, the sections on LIBs and the HER as representative applications of LTMD/carbon nanocomposites are described in detail by classifying them with different carbon materials containing graphene, carbon nanotubes, carbon nanofibers, hybrid carbons, hollow carbons, and porous carbons. In addition, we suggest a new material design of LTMD/carbon nanocomposites based on theoretical calculations. At the end of this review, we provide an outlook on the challenges and future developments in LTMD/carbon nanocomposite research.

Nucleation promoted synthesis of large-area ReS2 film for high-speed photodetectors

Rhenium disulfide (ReS₂) is a transition metal dichalcogenide with a layer-independent direct bandgap. Notably, the weak interlayer coupling owing to its T-phase structure enables multi-layer ReS₂ to behave similarly to decoupled monolayers. This inherent characteristic makes continuous multilayer ReS₂ film a unique platform for large-area electronic applications. To date, the bulk of work on ReS₂ has been conducted using mechanically exfoliated samples or small size flakes (<1 mm²) with no potential for large-scale electronics. A chemical vapor deposition (CVD) synthesis of a large area, continuous ReS₂ film directly on a SiO₂ substrate is also known to be more challenging compared with that of other 2D materials, such as MoS₂ and WS₂. This is partly due to its tendency to grow into discrete dendritic structures. In this study, a large-area (>1 cm²), continuous multilayer ReS₂ film is directly synthesized on a SiO₂ substrate without any transfer process. The polycrystalline ReS₂ film synthesized by this method exhibits one of the fastest photoresponse speeds (0.03 s rise time and 0.025 s decay time) among the reported CVD films. The photoresponsivity R _λ was also the highest among large-area CVD films. The synthesis method for a continuous multilayer ReS₂ film is amenable to large-scale integration and will pave the way for practical optoelectronic applications based on 2D layered materials.

Efficient and Stable Solar Hydrogen Generation of Hydrophilic Rhenium-Disulfide-Based Photocatalysts via Chemically Controlled Charge Transfer Paths

Effective charge separation and rapid transport of photogenerated charge carriers without self-oxidation in transition metal dichalcogenide photocatalysts are required for highly efficient and stable hydrogen generation. Here, we report that a molecular junction as an electron transfer path toward two-dimensional rhenium disulfide (2D ReS₂) nanosheets from zero-dimensional titanium dioxide (0D TiO₂) nanoparticles induces high efficiency and stability of solar hydrogen generation by balanced charge transport of photogenerated charge carriers. The molecular junctions are created through the chemical bonds between the functionalized ReS₂ nanosheets (e.g., -COOH groups) and -OH groups of two-phase TiO₂ (i.e., ReS₂-C₆H₅C(═O)-O-TiO₂ denoted by ReS₂-BzO-TiO₂). This enhances the chemical energy at the conduction band minimum of ReS₂ in ReS₂-BzO-TiO₂, leading to efficiently improved hydrogen reduction. Through the molecular junction (a Z-scheme charge transfer path) in ReS₂-BzO-TiO₂, recombination of photogenerated charges and self-oxidation of the photocatalyst are restrained, resulting in a high photocatalytic activity (9.5 mmol h^-1 per gram of ReS₂ nanosheets, a 4750-fold enhancement compared to bulk ReS₂) toward solar hydrogen generation with high cycling stability of more than 20 h. Our results provide an effective charge transfer path of photocatalytic TMDs by preventing self-oxidation, leading to increases in photocatalytic durability and a transport rate of the photogenerated charge carriers.

Large Area Vertically Oriented Few-Layer MoS2 for Efficient Thermal Conduction and Optoelectronic Applications

Large area growth of MoS₂ can show great advances in optoelectronic devices due to its unique optical and electronic properties. Here, we directly grow vertically oriented and interconnected few-layer MoS₂ over 1 × 1 cm² of p-type Si substrate using CVD technique. We report for the first time the thermal conductivity of vertically oriented few-layer (VFL) MoS₂ using the optothermal Raman technique. The reduced phonon-defect scattering due to minimal defects and strains in VFL MoS₂ results in excellent thermal conductivity of 100 ± 14 W m^-1 K^-1 at room temperature. The photoluminescence and DFT study confirm the semiconducting behavior of VFL-MoS₂. The VFL-MoS₂/Si photodiode shows high photoresponsivity of 7.37 A W^-1 at -2.0 V bias under 0.15 mW cm^-2 intensity of 532 nm laser. The enhanced light trapping and highly exposed edges of VFL MoS₂ due to vertical orientation, formation of efficient p-n junction at the MoS₂/Si interface and effective charge separation leads to the excellent performance of grown VFL-MoS₂ for optoelectronic applications.

Direct fabrication of two-dimensional ReS2 on SiO2/Si substrate by a wide-temperature-range atomic layer deposition

The building of high-quality, especially thickness-controllable ReS₂, is the crux of researching it and developing its wider application. In this work, ultrathin (1-5 layers) ReS₂ with controllable thickness and improved quality is obtained on SiO₂/Si substrates, using wide-temperature-range (WTR) atomic layer deposition (ALD). First, a WTR ALD system for building thin films and in situ annealing is constructed. ReS₂ of precise thicknesses can be achieved by regulating the number of ALD cycles, controlling the reaction temperature and plasma treatment. In particular, a method of in situ H₂S annealing is used to reduce S defects, which improves the quality of ReS₂. After annealing, the atomic ratio of S/Re in ReS₂ increases from 1.74 to 1.92, considering the presence of Re-O bond at the SiO₂-ReS₂ interface, which indicates that the S defects in ReS₂ films are completely eliminated at annealing temperature of 850 °C and 900 °C. In particular, at an annealing temperature of 900 °C, ReS₂ recrystallizes to form about 120 nm triangular grains, and its frictional force is reduced by 27.5% compared with the as-grown ReS₂.

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage

The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.