Chevrel Phase Research Articles

Overcoming Ion Trapping in Chevrel Phase Compounds via Tailored Anion Substitution: An Integrated Study of Theory, Synthesis, and In Operando Techniques for Reversible Aqueous Zn-Ion Batteries.

Sustainable batteries are key for powering electronic devices of the future, with aqueous zinc-ion batteries (AZIBs) standing out for their use of abundant, readily available elements, and safer production processes. Among the various electrode materials studied for AZIBs, the Chevrel Phase, Mo6S8 has shown promise due to its open framework, but issues with zinc ion trapping have limited its practical application. In this work, we employed computational methods to investigate the insertion-deinsertion mechanism in a series of isostructural Mo6S8-xSex (x = 0-8) solid solutions as materials that could balance the gravimetric capacity and reversible cycling for AZIBs. Density functional theory (DFT) calculations revealed that increasing the Se content would reduce the binding energy of Zn within the structures, enabling Zn deinsertion compared to the Mo6S8 structure. Experiments confirmed the formation of Mo6S8-xSex (x = 0-8) solid solutions, and electrochemical testing showed improved reversibility of Zn insertion/deinsertion as the amount of Se increased, consistent with the computational predictions. Furthermore, combined in operando X-ray diffraction and electrochemical studies revealed a continuous, gradual Zn-insertion process into Mo6S4Se4, in stark contrast to the abrupt phase changes observed upon Zn insertion in Mo6S8 and Mo6Se8. DFT calculations attributed the stabilization of Zn0.5Mo6S4Se4 as a prime reason for preventing phase separation, making Se-substituted compounds promising materials for high-performance AZIBs. Overall, this interdisciplinary approach, integrating computational modeling, materials synthesis, and advanced characterization techniques, offers a pathway for fine-tuning anion chemistry that can help create high-performance electrode materials for sustainable energy storage technologies.

Electrochemical studies and diffusion kinetics in the Chevrel phase (Mo6S8) for rechargeable Mg batteries

Electrochemical studies and diffusion kinetics in the Chevrel phase (Mo6S8) for rechargeable Mg batteries

SHS of copper Chevrel phase compounds

Chevrel phase (CP) compounds are a highly multifunctional class of materials but are underused due to the high energy processing required for their synthesis. Self-propagation high-temperature synthesis (SHS) is a low energy and quick alternative for synthesizing this material system. In this investigation, copper-based CPs were synthesized via SHS using either elemental or binary precursor powders. The elemental precursors produced non-stoichiometric Cu2.76Mo6S8, and consisted mainly of grown MoS2 platelets. The binary precursor, on the other hand, produced stoichiometric Cu2Mo6S8. The influences of mixing and precursor concentration are discussed as well as the reaction mechanisms operating for the elemental system and the binary system, separately. The investigation into this synthesis process aims to provide a better understanding of the Chevrel SHS mechanism to accurately control the product.

Photocatalytic Desulfurization of Thiophene with Chevrel Phase Ni2Mo6S8 Synthesized by SHS.

The Chevrel phase compounds Cu4Mo6S8, Ni2Mo6S8, and Fe2Mo6S8, synthesized by self-propagating high temperature synthesis, were evaluated as photocatalysts for visible light photocatalytic desulfurization. Investigations began with reflectance measurements from which absorbance spectra were calculated using the Kubelka-Munk transformation. The absorbance data was then used to create Tauc plots to find the direct and indirect bandgaps of the Chevrel phase compounds. Bandgaps were found to be no more than the 1.74 eV for Ni2Mo6S8, so it was selected for further study because this bandgap suggests it will use the sun's emission spectrum better than the other materials studied here. Photocatalytic desulfurization experiments studied the concentration of thiophene mixed into n-octane with and without exposure to Ni2Mo6S8 with and without light exposure because of the relative difficulty of removing thiophenes from liquid fossil fuels by the industry standard hydrodesulfurization process. Ultraviolet-visible spectroscopy was used to analyze chemical changes in the thiophene-octane solution. Spectroscopic results demonstrate that the thiophene was effectively removed by exposure to Ni2Mo6S8 and visible light together but not by exposure to Ni2Mo6S8 or visible light alone. Multiple tests with the same Ni2Mo6S8 sample demonstrate that the material is reusable as a catalyst for photocatalytic desulfurization. The proposed mechanism results in the release of SO x species, which may be controlled and captured if separated from fossil fuels in bulk during industrial processing in contrast to their uncontrolled release as vehicle fuel exhaust. Controlled generation and collection of these species can allow for further processing into elemental sulfur in the same way that H2S released by standard hydrodesulfurization is processed into elemental S.

Intercalation based synthesis of Chevrel phase superconductors

This work focuses on the superconducting and magnetic properties of Chevrel phase (CP) compounds (Cu2Mo6S8 and Ni2Mo6S8) processed via a novel self-propagating high-temperature synthesis (SHS) method involving ternary cation intercalation in MoS2 high-temperature polymorphs. Green pellets of the precursor materials sealed under vacuum and exposed to 1050 °C or 1200 °C rapidly transformed from a powder mixture into submicron CPs within minutes. X-ray diffraction analysis confirmed the presence of Cu2Mo6S8 CP (67%), and Ni2Mo6S8 (93%). This group has illustrated the first time CP were formed at low energy cost and full stoichiometry. Magnetization versus temperature data obtained for the samples under different field conditions confirmed the superconducting behavior of the Cu–CP at a critical temperature of 8.3 K. The Ni–CP behaved as a superparamagnetic at low temperature (4.2 K). The results of this work suggest that the novel SHS process offers a viable scalable synthesis route for the Chevrel family of compounds and that it is worth exploring the functional applications of the new compounds of this material system.

Establishing the NiMo6Se8 Chevrel Phase as a Promising Material Using DFT

AbstractIn this study, the NiMo6Se8 Chevrel phase is analyzed using Density Functional Theory (DFT) and the Vienna Ab‐initio Simulation Package (VASP). The analysis focuses on the phase's structural, electrical, and mechanical characteristics to fill gaps in the current literature. The presence of a rhombohedral crystal structure confirms its thermodynamic stability, as indicated by a negative formation enthalpy, which suggests that it can be synthesized under favorable conditions. The electronic properties of the phase are analyzed, indicating that it exhibits semiconductor characteristics with a bandgap of 1.07 eV. This makes it appropriate for various technological applications. The estimated elastic constants provide an indication of mechanical strength and flexibility, with a noticeable presence of anisotropic elasticity. The confirmation of dynamical stability is achieved by analyzing the phonon dispersion curve, which reveals the absence of any negative frequencies. Furthermore, the material has a low thermal conductivity, increasing its suitability for thermoelectric applications. The analysis emphasizes the versatile capabilities of the NiMo6Se8 Chevrel phase, especially in thermoelectric and energy storage applications, showcasing its promising potential for future technological implementation.

Cheverl phase Mo6Te8 nanoparticles as new anode materials for lithium-ion batteries

Lithium-ion batteries have become increasingly indispensable as a kind of energy conversion and storage device. Cheverl phase materials show potential advantages over transition metal chalcogenides in lithium-ion batteries, owing to their high three-dimensional open frameworks and good tolerance to a large current. Herein, Chevrel phase Mo6Te8 has been synthesized by high-temperature solid-phase reaction and modified with dopamine, resulting in Carbon and Nitrogen atoms anchored on the Mo6Te8 surface. During the C/N doping process, due to lattice gap and vacancy defects, C/N itself is adsorbed in the vacancy or lattice gap, resulting in lattice expansion, which makes the process of lithium ion deintercalation smoother. Compared with the original Mo6Te8, the specific capacity and conductivity of the composite Mo6Te8@C/N have significantly improved. With a maximum specific capacity close to 812 mAh g−1 at a current density of 0.1 A g−1 and a maximum capacity close to 436 mAh g−1 at a high current density of 1 A g−1, the excellent conductivity of Mo6Te8@C/N contributes to the diffusion of Li+, and the increased active site improves the efficiency of electron transfer. The direct comparison between MoTe2 and Mo6Te8@C/N clearly supports the advantages of Chevrel phase materials in batteries.

Nanosized Chevrel phases for dendrite-free zinc-ion based energy storage: unraveling the phase transformations.

The nanoscale form of the Chevrel phase, Mo6S8, is demonstrated to be a highly efficient zinc-free anode in aqueous zinc ion hybrid supercapacitors (ZIHSCs). The unique morphological characteristics of the material when its dimensions approach the nanoscale result in fast zinc intercalation kinetics that surpass the ion transport rate reported for some of the most promising materials, such as TiS2 and TiSe2. In situ Raman spectroscopy, post-mortem X-ray diffraction, Hard X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations were combined to understand the overall mechanism of the zinc ion (de)intercalation process. The previously unknown formation of the sulfur-deficient Zn2.9Mo15S19 (Zn1.6Mo6S7.6) phase is identified, leading to a re-evaluation of the mechanism of the (de)intercalation process. A full cell comprised of an activated carbon (YEC-8A) positive electrode delivers a cell capacity of 38 mA h g-1 and an energy density of 43.8 W h kg-1 at a specific current density of 0.2 A g-1. The excellent cycling stability of the device is demonstrated for up to 8000 cycles at 3 A g-1 with a coulombic efficiency close to 100%. Post-mortem microscopic studies reveal the absence of dendrite formation at the nanosized Mo6S8 anode, in stark contrast to the state-of-the-art zinc electrode.

Electrochemical control over stoichiometry via cation intercalation into Chevrel-phase sulphides (CuxMo6S8, x = 1–3)

This work presents a systematic investigation of the electrochemical intercalation of aqueous copper cations into the Chevrel phase (CP) Mo6S8 and its effect on the host's electronic and structural characteristics as a function of stoichiometry.

Revisiting the quasi-aromaticity in polynuclear metal chalcogenide clusters and their derivative "cluster-assembly" crystalline structures.

The concept of aromaticity is primarily invented to account for the high stability of conjugated organic compounds that possess a specific structural and chemical stability with (4n + 2) π electrons. In 1988, quasi-aromaticity was theoretically proposed for the Mo3S44+ core in the Mo3(μ3-S)(μ-S)3(χ-dtp)3(μ-dtp) L compound (χ: chelating ligand; dtp: (EtO)2PS2-) illustrated by canonical molecular orbitals. However, the origin of the quasi-aromaticity and chemical bonding remains ambiguous, lacking a thorough analysis in terms of stability and quantitative measurement of the aromatic character. Thus, in this work, we systematically reported the electronic structure and aromaticity of a series of polynuclear metal chalcogenide clusters [M3X4(H2O)9]4+ (M = Cr, Mo, W, and Sg; X = O, S, Se, and Te) to explore an efficient tool of NICS index values at specific points to measure the quasi-aromaticity and to figure out the (d-p-d) π three-center bonding as the predominant origin from the arrangement of three Mo atoms and three bridged X atoms. Interestingly, derived from the Mo3⋯S3 quasi-plane, the extended sandwich cluster model of a S3⋯Mo3⋯S3 (Mo3S6) structure can be seen as the seed unit of the popular MoS2 nanomaterials, with the resemblance between both molecular and periodic systems regarding geometries, electronic structures, and chemical bonding. Additionally, the highly symmetric Mo3S4 core in [Mo3X4(H2O)9]4+ can be arranged in a staggered and stacked manner to create the Mo6S82- building block, corresponding to the crystalline structures in BaMo6S8 Chevrel phases, albeit with slight deformations. But the neutral Mo6S8 cluster can be seen as the seed structure for the Mo3S4 periodic materials for the high resemblance in terms of geometry, electronic structures and chemical bonding. Drawing upon the observed similarities between cluster models and materials, we propose a new concept termed "cluster-assembly" materials. This concept involves the expansion from a high-symmetry and/or aromatic stable cluster seed unit to form the corresponding derivative materials, presenting an alternative paradigm for investigating crystals and enriching our comprehension of the stabilities exhibited by both gas-phase clusters and solid-state materials. The concept of "cluster-assembly" materials not only contributes to the formulation of design strategies for novel materials or stable clusters but also provides valuable insights into the extension of periodic aromaticity.

A doping strategy to regulate the adsorption energy of Li2S4 and Li2S to promote sulfur reduction on Chevrel phase Mo6Se8 in lithium-sulfur batteries.

Atomic doping in catalysts is an effective strategy for adjusting their catalytic activity, which has recently been applied to promote sulfur reduction reactions (SRRs) on the cathode of lithium-sulfur (Li-S) batteries. Herein, the electrocatalytic SRR mechanism of eight metal atom (Ca, Ti, V, Cr, Mn, Fe, Co or Ni) doped Chevrel phase Mo6Se8 were investigated using density functional theory (DFT) calculations. The results reveal that the interaction between polysulfides and the catalyst mainly originates from the coupling of dz2 and dxz orbitals of doped metals and the 3p orbitals of S. The Ti-doped Mo6Se8 system significantly reduces the overpotential of the SRR to only 0.21 V. After analyzing SRR processes over doped and undoped Mo6Se8, no scalar relationship was found between the adsorption energies (Ead) of various polysulfides. Instead, a linear relationship is established between 4Ead-Li2S* - Ead-Li2S4* and overpotential. Finally, a linear relationship between overpotential and descriptors was established based on a machine learning (ML) method, which can accurately predict the overpotential of the SRR over the Mo6Se8 catalyst. This work provides new theoretical insights into the SRR mechanism over metal-selenides and the rational design of a catalyst for Li-S batteries.

Critical Roles of Chalcogenide Anion on Strengthening Stability of Ni2Mo6Te8 for Almost Exclusive Electrocatalysts Nitrate to Ammonia Conversion

AbstractElectrochemical hydrogenation of nitrate to ammonia using renewable electricity is a promising route for sustainability but lacks catalysts that can deliver balanced selectivity, activity, and durability. Here, a new family of noble metal‐free and high‐performing Chevrel phase Ni2Mo6T8 (T = S, Se, and Te) catalysts that have similar structural and textural properties and differ presumably only in chalcogenide anion is systematically studied. The side‐by‐side comparisons allow the uncovering of the critical roles of chalcogenide anions in impacting kinetic activities and long‐term durability. The incorporation of anions with larger size and smaller electronegativity from sulfide to selenide and telluride invokes stronger inhibition of the otherwise competing hydrogen evolution reaction (HER) and steers the hydrogenation toward the selective formation of ammonia, thus improving both Faradic selectivity and the turnover frequency to high levels of 99.4% and 21.5 s−1, respectively, on the Ni2Mo6Te8 catalyst. More significantly, the bulkier anion in the Ni2Mo6T8 catalyst kinetically inhibited the intercalation of electrolyte cations, a major degradation mechanism in the catalyst family examined here and delivered several times improved durability. Therefore, this study introduces novel active motifs for selective nitrate reduction and provides insights into the catalyst degradation mechanism and practical ways to improve durability.

Rationally Designed Spherical V2O5 Encapsulated by 2d-VS2 as High Capacity Insertion Cathode for Mg-Ion Battery

Owing to high energy density and economic viability, rechargeable Mg-ion batteries (MIB) are considered as alternative to lithium-ion batteries. However, beside chevrel phase, none of conventional inorganic cathode materials demonstrate reversible intercalation/deintercalation of Mg+2 ions in anhydrous electrolyte system. The lack of high voltage and high-capacity cathode frustrates the realization of MIB. Previous studies indicated that vanadium pentoxide (V2O5) has potential to reversibly insert\\extract Mg ions. However, many attempts to utilize V2O5 demonstrated limited electrochemical response, due to hindered Mg ion mobility in solid. Herein, we demonstrated a tailored approach to synthesize uniformly dispersed spherical V2O5 homogeneously coated with 2D VS2 through a facile in-situ chemical method and study the electrochemical activity in 0.2 M Mg(TFSI)2 + MgCl2 in DME electrolyte system and Mg metal anode. The V2O5@VS2 cathode exhibit the highest reported 1st discharge capacity of ~ 260 mA.h.g-1, excellent stability, retention and restricted capacity fading after 100 cycles which witness the prominence of VS2 coating in rationally designed V2O5 as a cathode material in non-aqueous electrolyte system for next generation high capacity MIB. Most interestingly, exact phase and morphology is completely retained even after repeated Mg+2 ion intercalation/deintercalation at different current rates, demonstrating pronounced electrochemical activity in anhydrous magnesium electrolyte and realization of a practical MIB.

Insights into Corrosion of Current Collectors for Magnesium Batteries

To enable the shift towards renewable energy, the use of low-cost energy storage systems is necessary. Magnesium (Mg) is an abundant and safer raw material than lithium for electrochemical energy storage systems such as batteries, due to its reduced sensitivity to air. Promising intercalation materials for cathodes include Chevrel phase Mo6S8 and Prussian green FeFe(CN)6. Although magnesium perchlorate-based electrolytes are practical for early-stage cathode research, they are not compatible with Mg metal due to corrosion. The organo-metallic all phenyl complex (APC) based electrolyte is a potential candidate for magnesium full cells, but both systems contain reactive chloride species that cause severe corrosion of the current collector.This study utilizes linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy to identify suitable materials for current collectors, including carbon-coated Al and Ni. The selected materials must withstand a polarization potential of 2 V vs. Mg/Mg2+. A Graphite-based current collector is shown to be the most promising candidate due to its low areal density, which can increase the energy density of practical Mg batteries.

Monitoring of Energy Storage Mechanism of Zn/Meso-MnO2 Battery System Using X-Ray Absorption Fine Structure

As energy storage systems, LIBs, which are most frequently used, have excellent capacity, power, and long lifespan performance [1]. However, as the reserves of the raw minerals used—lithium and cobalt—are exhausted, prices are escalating. A further issue with LIB is that it heats up to a high temperature during charging, which leads to a string of fire or explosion catastrophes. To solve these safety or cost challenges, various next-generation batteries are being developed, and we are exploring about aqueous zinc ion battery (AZIB), which attracting attention as the next-generation battery due to outstanding safety and cost competitive advantage. Generally, zinc metal acting as an anode, has a high theoretical capacity of 820mAh/g as it is gives two electrons (2e-). Also, because of its sparse reactivity with water and ability to employ water-based electrolytes with strong ion conductivity and low ignition risk, it is particularly advantageous in terms of safety. There have been a variety of cathode materials utilized, such as manganese oxide, vanadium oxide, Prussian blue analogues (PBAs), polyanion compounds, and Chevrel phase compounds [2-4]. Especially, manganese dioxide (MnO2) has been addressed by prior studies that Zn2+ can be inserted into crystal structure because it exhibits several crystal structures (α, β, γ, δ, and λ) with tunnel-type or layer-type structure. Mn4+ ions occupying octahedral holes formed by hexagonal close-packed (hcp) oxide ions compose the fundamental unit of the crystal structure of MnO2 polymorphs. To construct a [MnO6] octahedral unit, each Mn4+ ion is precisely surrounded by six oxygen neighbors, and these units are connected by the edges and/or corners [5]. Understanding the energy storage mechanisms is essential for the one-step evolution of cathode materials for AZIB. However, these polymorphs significantly affect the electrochemical reaction, thus involving complex reaction mechanisms [5-7]. Additionally, it is extremely challenging to research the mechanisms of AZIB since protons (H+) are known to participate in the reaction by acting as charge transfer as well as Zn2+ ions. Therefore, while several efforts are being conducted to unveil the exact reaction mechanism, a mesoporous nanostructured material with a large specific surface area is adopted, which can more precisely grasp the electrochemical reaction studies of electrode/electrolyte surface [8,9]. X-ray absorption fine structure (XAFS) is a powerful technique used for the analysis of nanostructured materials, widely used in the field of battery research [10]. It involves the measurement of the absorption of X-ray by the material, which can provide information about oxidation state, chemical bonding of the materials and the local geometry structure during charge/discharge process. This analysis method gives great insight into the complex energy storage pathway of MnO2 materials with various polymorphs. Based on this knowledge, we synthesized ordered mesoporous β-MnO2 through nano-casting method by using KIT-6 as hard-template and used it as the cathode active material. As depicted in Figure 1, we performed ex-situ XAFS analysis at the states of charge during 2nd cycle to monitor energy storage mechanisms. The oxidation state changes could be quantitatively estimated by edge energy analysis by comparing the reference MnO2 and Mn2O3 samples. It was also possible to unveil further about the reaction mechanism at each voltage by examining the structural change in the local geometry of [MnO6] unit through a careful analysis of pre-edge region and EXAFS spectra. During discharge process, insertion mechanism, which causes relatively larger distortion in the local geometry compared to conversion mechanism, results in a increment of pre-edge intensity, which opposes the decline in pre-edge intensity due to the reduction of the oxidation state. This fact demonstrates that although H+ conversion could not have a significant effect on pre-edge intensity in the early discharge stage, Zn2+ insertion was the phenomenon responsible for the rise in pre-edge intensity during late discharge stage. In addition, through EXAFS spectra analysis, the irreversible change in corner sharing Mn-Mn bond distance during charge/discharge process could be seen that an irreversible phase transition of MnO2 occurred due to Zn2+ insertion, indicating clue to identify the cause of capacity fading. These findings contribute to further understanding of the reaction mechanisms and capacity fading phenomenon and suggest practical strategies for next-generation zinc-ion batteries.

A material perspective on advanced magnesium-ion batteries for electric vehicles

PurposeThis paper aims at analyzing the potential of new materials in magnesium-ion batteries (MIBs) with a particular focus on options for electrodes and electrolyte solutions while also carefully considering the barriers to their entry in this application for MIBs, with a particular focus on the material options for electrodes and electrolyte solutions.Design/methodology/approachPotential materials for MIBs were examined for sustainability, safety and efficiency to develop the sustainable and well-working MIBs.FindingsFor anode materials, the use of Mg-bismuth alloys has shown promise, whereas Chevrel phases or layered molybdenum disulfide have potential as cathode materials. Potential electrolytes range from traditional materials to the development of tailored solid-state and liquid-based options.Originality/valueThis study considers the growing need for Mg-based ion batteries, as well as the need for suitable electrode and electrolyte materials and analyzes suitable options.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0081/

The Effect of Chlorides on the Performance of DME/Mg[B(HFIP)4]2 Solutions for Rechargeable Mg Batteries

One of the major issues in developing electrolyte solutions for rechargeable magnesium batteries is understanding the positive effect of chloride anions on Mg deposition-dissolution processes on the anode side, as well as intercalation-deintercalation of Mg2+ ions on the cathode side. Our previous results suggested that Cl− ions are adsorbed on the surface of Mg anodes and Chevrel phase MgxMo6S8 cathodes. This creates a surface add-layer that reduces the activation energy for the interfacial Mg ions transportation and related charge transfer, as well as promotes the transport of Mg2+ from the solution phase to the Mg anode surface and into the cathodes’ host materials. Here, this work further examines the effect of adding chlorides to the state-of-the-art Mg[B(HFIP)4]2/DME electrolyte solution, specifically focusing on reversible magnesium deposition, as well as the performance of Mg cells with benchmark Chevrel phase cathodes. It was observed that the presence of chlorides in these solutions facilitates both Mg deposition, and Mg2+ ions intercalation, whereby this effect is more pronounced as the purity level of the solution is lowered.

Reversible Electrochemical Anionic Redox in Rechargeable Multivalent-Ion Batteries.

Rechargeable multivalent-ion batteries are of significant interest due to the high specific capacities and earth abundance of their metal anodes, though few cathode materials permit multivalent ions to electrochemically intercalate within them. The crystalline chevrel phases are among the few cathode materials known to reversibly intercalate multivalent cations. However, to date, no multivalent-ion intercalation electrodes can match their reversibility and stability, in part due to the lack of design rules that guide how ion intercalation and electron charge transfer are coupled up from the atomic scale. Here, we elucidate the electronic charge storage mechanism that occurs in chevrel phase (Mo6Se8, Mo6S8) electrodes upon the electrochemical intercalation of multivalent cations (Al3+, Zn2+), using solid-state nuclear magnetic resonance spectroscopy, synchrotron X-ray absorption near edge structure measurements, operando synchrotron diffraction, and density functional theory calculations. Upon cation intercalation, electrons are transferred selectively to the anionic chalcogen framework, while the transition metal octahedra are redox inactive. This reversible electrochemical anionic redox, which occurs without breaking or forming chemical bonds, is a fundamentally different charge storage mechanism than that occurring in most transition metal-containing intercalation electrodes using anionic redox to enhance energy density. The results suggest material design principles aimed at realizing new intercalation electrodes that enable the facile electrochemical intercalation of multivalent cations.

Highly Reversible Chevrel Phase Mo6Se8 Cathode with Low Voltage Hysteresis for Rechargeable Aluminum Batteries.

Rechargeable aluminum (Al) batteries have attracted considerable interest as potential large-scale energy storage technologies due to the abundance, high theoretical capacity, and high safety of Al. We report here a highly reversible Al-Mo6Se8 prototype cell with low discharge-charge hysteresis (approximately 50 mV under 30 mA g-1 at 50 °C), ultra-flat discharge plateau, and exceptional cycle stability: the reversible capacity retaining at a steady 77 mA h g-1 after more than 1800 cycles. The Al intercalation-extraction mechanism is probed with ex situ and operando XRD techniques, revealing the reversible intercalation reaction from Mo6Se8 to Al4/3Mo6Se8. The stable electrochemical performance and unambiguous intercalation mechanism of the Al-Mo6Se8 system provide an alternative for beyond-lithium battery technologies.

Investigation of Tungsten‐Based Seleno‐Chevrel Compounds with Different Compositions for Efficient Water Splitting

AbstractThis study investigates the photocatalytic water splitting performance for Chevrel phases with the chemical formula MxMo6Ch8, where M is a metal and Ch is a chalcogen, with x being 0, 1, 2, 3, or 4. Density Functional Theory (DFT) is used to study the Chevrel phases, which includes earth‐abundant elements for this specific study as an essential consideration for photocatalytic water splitting. The electronic properties are calculated for the NiW6Se8 and Ni2W6Se8 compounds with thermodynamical, mechanical, and dynamic stabilities. For photocatalytic water splitting, the band gaps below 1.23 eV are excluded, and the conduction and valence band levels are determined to examine the reduction and oxidation potentials for efficient photocatalytic water‐splitting materials. An examination of the selected band gaps, along with the conduction and valence band levels, reveals that NiW6Se8 is suitable for both reduction and oxidation reactions; whereas, Ni2W6Se8 is a convenient material only for the reduction reaction. This is the first attempt, as far as the literature reveals, to study Chevrel phases in detail and to identify a suitable compound for photocatalytic water splitting.