Two-dimensional graphene-HfS2 van der Waals heterostructure as electrode material for alkali-ion batteries

WS2-Graphene van der Waals Heterostructure as Promising Anode Material for Lithium-Ion Batteries: A First-Principles Approach

In this work, we report the results of density functional theory (DFT) calculations on a van der Waals (VdW) heterostructure formed by vertically stacking single-layers of tungsten disulfide and graphene (WS2/graphene) for use as an anode material in lithium-ion batteries (LIBs). The electronic properties of the heterostructure reveal that the graphene layer improves the electronic conductivity of this hybrid system. Phonon calculations demonstrate that the WS2/graphene heterostructure is dynamically stable. Charge transfer from Li to the WS2/graphene heterostructure further enhances its metallic character. Moreover, the Li binding energy in this heterostructure is higher than that of the Li metal's cohesive energy, significantly reducing the possibility of Li-dendrite formation in this WS2/graphene electrode. Ab initio molecular dynamics (AIMD) simulations of the lithiated WS2/graphene heterostructure show the system's thermal stability. Additionally, we explore the effect of heteroatom doping (boron (B) and nitrogen (N)) on the graphene layer of the heterostructure and its impact on Li-adsorption ability. The results suggest that B-doping strengthens the Li-adsorption energy. Notably, the calculated open-circuit voltage (OCV) and Li-diffusion energy barrier further support the potential of this heterostructure as a promising anode material for LIBs.

Properties of Layered TMDC Superlattices for Electrodes in Li-Ion and Mg-Ion Batteries

In this work, we present a first-principles investigation of the properties of superlattices made from transition metal dichalcogenides for use as electrodes in lithium-ion and magnesium-ion batteries. From a study of 50 pairings, we show that, in general, the volumetric expansion, intercalation voltages, and thermodynamic stability of vdW superlattice structures can be well approximated with the average value of the equivalent property for the component layers. We also found that the band gap can be reduced, improving the conductivity. Thus, we conclude that superlattice construction can be used to improve material properties through the tuning of intercalation voltages toward specific values and by increasing the stability of conversion-susceptible materials. For example, we demonstrate how pairing SnS2 with systems such as MoS2 can change it from a conversion to an intercalation material, thus opening it up for use in intercalation electrodes.

Interfacial effects on lithium-ion diffusion in two-dimensional lateral black phosphorus-graphene heterostructures

Lateral heterostructures constructed from different two-dimensional (2D) materials can be potentially used in lithium-ion batteries (LIBs). The interface between two different components strongly affects LIB charge and discharge processes. Herein, the atomic structures, electronic properties, and Li-ion diffusion characteristics of lateral black phosphorus-graphene (BP-G) heterostructures are studied via first-principles calculations. The obtained results reveal that BP-G heterostructures with either zigzag (ZZ) or misoriented interfaces constructed according to Clar's rule possess a small number of interfacial states and are electronically stable. Furthermore, compared with the perfect ZZ interface of BP-G, Clar's interfaces provide a larger number of diffusion paths with much lower energy barriers. The findings of this study suggest that lateral BP-G heterostructures can provide insights for rapid charge and discharge processes in LIBs.

Temperature-Dependent Absorption of Ternary HfS2-xSex 2D Layered Semiconductors

In this study, we present the investigation of optical properties on a series of HfS_2-xSe_x crystals with different Se compositions x changing from 0 to 2. We used the chemical-vapor transport method to grow these layered ternary compound semiconductors in bulk form. Their lattice constants and crystal properties were characterized by X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. We have performed absorption spectroscopies to determine their optical band-gap energies, which started from 2.012 eV with x = 0, and gradually shifts to 1.219 eV for x = 2. Furthermore, we measured the absorption spectroscopies at different temperatures in the range of 20-300 K to identify the temperature dependence of band-gap energies. The band-gap energies of HfS_2-xSe_x were determined from the linear extrapolation method. We have noticed that the band-gap energy may be continuously tuned to the required energy by manipulating the ratio of S and Se. The parameters that describe the temperature influence on the band-gap energy are evaluated and discussed.

First principles study on structural, electronic and optical properties of HfS2(1-x)Se2x and ZrS2(1-x)Se2x ternary alloys

Alloying 2D transition metal dichalcogenides (TMDs) with dopants to achieve ternary alloys is as an efficient and scalable solution for tuning the electronic and optical properties of two-dimensional materials. This study provides a comprehensive study on the electronic and optical properties of ternary HfS_2(1−x)Se_2(x) and ZrS_2(1−x)Se_2(x) [0 ≤ x ≤ 1] alloys, by employing density functional theory calculations along with random phase approximation. Phonon dispersions were also obtained by using density functional perturbation theory. The results indicate that both of the studied ternary families are stable and the increase of Selenium concentration in HfS_2(1−x)Se_2(x) and ZrS_2(1−x)Se_2(x) alloys results in a linear decrease of the electronic bandgap from 2.15 (ev) to 1.40 (ev) for HfS_2(1−x)Se_2(x) and 1.94 (ev) to 1.23 (ev) for ZrS_2(1−x)Se_2(x) based on the HSE06 functional. Increasing the Se concentration in the ternary alloys results in a red shift of the optical absorption spectra such that the main absorption peaks of HfS_2(1−x)Se_2(x) and ZrS_2(1−x)Se_2(x) cover a broad visible range from 3.153 to 2.607 eV and 2.405 to 1.908 eV, respectively. The studied materials appear to be excellent base materials for tunable electronic and optoelectronic devices in the visible range.

Adding Selenium to HfS₂ and ZrS₂ two-dimensional materials allows tuning the optical properties in a wide visible spectrum that can be used in various electronic and optical applications, including solar cells.

Opportunities and challenges for 2D heterostructures in battery applications: a computational perspective

With an increasing demand for large-scale energy storage systems, there is a need for novel electrode materials to store energy in batteries efficiently. 2D materials are promising as electrode materials for battery applications. Despite their excellent properties, none of the available single-phase 2D materials offers a combination of properties required for maximizing energy density, power density, and cycle life. This article discusses how stacking distinct 2D materials into a 2D heterostructure may open up new possibilities for battery electrodes, combining favourable characteristics and overcoming the drawbacks of constituent 2D layers. Computational studies are crucial to advancing this field rapidly with first-principles simulations of various 2D heterostructures forming the basis for such investigations that offer insights into processes that are hard to determine otherwise. We present a perspective on the current methodology, along with a review of the known 2D heterostructures as anodes and their potential for Li and Na-ion battery applications. 2D heterostructures showcase excellent tunability with different compositions. However, each of them has distinct properties, with its own set of challenges and opportunities for application in batteries. We highlight the current status and prospects to stimulate research into designing new 2D heterostructures for battery applications.

Effect of the sulfur termination on the properties of Hf2CO2 MXene

A computational study was carried out to investigate the effect of surface termination on Janus Hf₂COS MXene by substituting partly the O-terminated layer with S atoms. Our predictions confirm that this chemical strategy allows one to tailor the band gap of MXenes. Indeed, the semiconducting character of Hf₂CO₂ MXene decreases by the exchange of O by S atoms. From a structural point of view, dynamical, mechanical, and thermal analysis confirm the thermodynamic stability of the Janus Hf₂COS MXene, which shows metallic character. Furthermore, topological chemical analysis indicates an ionic nature of Hf₂CO₂ MXene that tends to be reduced by increasing the concentration of S atoms, promoting a covalent character. Shortly, the present study illustrates how the properties of MXenes can be tailored by functionalizing them with different chemical terminations.

Janus monolayer HfSO with improved optical properties as a novel material for photovoltaic and photocatalyst applications

First principles calculations were performed to investigate the photocatalytic behavior of 2D Janus monolayer HfSO at equilibrium and under the influence of strains and external electric fields.

HfS2 thin films deposited at room temperature by an emerging technique, solution atomic layer deposition

As a member of the two-dimensional metal dichalcogenide family, HfS2 has emerged as a promising material for various optoelectronic applications. Atomic layer deposition is widely used in microelectronics manufacturing with unique properties in terms of accurate thickness control and high conformality. In this work, a simple and versatile method based on the atomic layer deposition principles is presented to generate hafnium disulfide from the solution phase ('solution ALD' or sALD). For ease of comparison with the traditional gaseous atomic layer deposition (gALD) method, the same precursors are used, namely tetrakis-(dimethylamido) hafnium(IV) and H2S. The deposit is characterized on several different oxide substrates by spectroscopic ellipsometry, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the saturated regime, the growth rate depends on the substrate nature and is between 0.4 and 0.6 Å per sALD cycle. This growth rate determined at room temperature is lower than with the gALD process reported at 100 °C recently. At those low deposition temperatures, the films remain in an amorphous state. This success in sALD expands the range of material classes available by the new method, adding transition metal dichalcogenides to the list containing oxides, cubic sulfides, hydrides, and organics so far. It promises to overcome the precursor constraints associated with the traditional gALD method, in particular the volatility requirement.

Van der Waals Heterostructures-Recent Progress in Electrode Materials for Clean Energy Applications

The unique layered morphology of van der Waals (vdW) heterostructures give rise to a blended set of electrochemical properties from the 2D sheet components. Herein an overview of their potential in energy storage systems in place of precious metals is conducted. The most recent progress on vdW electrocatalysis covering the last three years of research is evaluated, with an emphasis on their catalytic activity towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). This analysis is conducted in pair with the most active Pt-based commercial catalyst currently utilized in energy systems that rely on the above-listed electrochemistry (metal-air battery, fuel cells, and water electrolyzers). Based on current progress in HER catalysis that employs vdW materials, several recommendations can be stated. First, stacking of the two types vdW materials, with one being graphene or its doped derivatives, results in significantly improved HER activity. The second important recommendation is to take advantage of an electronic coupling when stacking 2D materials with the metallic surface. This significantly reduces the face-to-face contact resistance and thus improves the electron transfer from the metallic surface to the vdW catalytic plane. A dual advantage can be achieved from combining the vdW heterostructure with metals containing an excess of d electrons (e.g., gold). Despite these recent and promising discoveries, more studies are needed to solve the complexity of the mechanism of HER reaction, in particular with respect to the electron coupling effects (metal/vdW combinations). In addition, more affordable synthetic pathways allowing for a well-controlled confined HER catalysis are emerging areas.