Microwave-assisted synthesis of CuSe nano-particles as a high -performance cathode for rechargeable magnesium batteries

Toward high-performance rechargeable magnesium batteries with a Cu2Se-CTAB nanoparticle cathode and Mg[B(HFIP)4]2/DME electrolyte

Developing advanced cathode materials effectively enhances the electrochemical performance of rechargeable magnesium batteries (RMBs). Herein, we designed a CTAB-assisted hydrothermal method to construct Cu2Se nanoparticles as the cathode and Mg[B(HFIP)4]2/DME as the electrolyte shows high specific capacity and great cycling performance in RMBs.

Nanosynthesis and Characterization of Cu1.8Se0.6S0.4 as a Potential Cathode for Magnesium Battery Applications

Copper selenide (Cu-Se) and copper sulfide (Cu-S) are promising cathodes for magnesium-ion batteries. However, the low electronic conductivity of Cu-Se system results in a poor rate capability and unsatisfactory cycling performance. Mg-ion batteries based on the Cu-S cathode exhibited large kinetic barriers during the recharging process owing to the presence of polysulfide species. This work attempts to circumvent this dilemma by doping Cu1.8Se by sulfur, which replaces the selenium in the CuSe lattice to form Cu1.8Se0.6S0.4 nanocrystalline powder. The presence of sulfur will increase the electronic conductivity, and the presence of selenium will mitigate the effect of polysulfide species that hinder the kinetics of Mg2+. Herein, a Cu1.8Se0.6S0.4 nanocrystalline powder was synthesized by the solid-state reaction, yielding a highly pure and stoichiometric powder. The crystallographic structure of the nanopowder and the conversion-type storage mechanism have been attested via ex situ X-ray diffraction and energy-dispersive X-ray analysis. The nanocrystalline feature of Cu1.8Se0.6S0.4 was demonstrated by high-resolution transmission electron microscopy. An apparent surface morphology change during the charging/discharging process has been visualized by a field emission scanning electron microscope. Diffuse reflectance spectroscopy has discussed the variation of the band gap during charging and discharging. The full Mg/Cu1.8Se0.6S0.4 cells presented an initial discharge capacity of 387.99 mAh g-1 at a current density of 0.02 mA cm-2; moreover, they show moderate diffusion kinetics with D Mg 2 + ≈ 10-15 cm-2 s-1.

Revolutionizing fuel production through biologically synthesized zero-dimensional nanoparticles

The sustainable management of wastewater and the production of clean fuel with a reduced carbon footprint require innovative methods, including photocatalytic degradation of pollutants and hydrogen generation. To achieve this, biosynthesized photocatalysts are necessary, with carbon quantum dots (CQDs) being a promising candidate for achieving this goal. In this study, CQDs were prepared from water caltrop peels and a composite of greenly synthesized CQDs with copper selenide (CuSe) was used for the photocatalytic degradation of pollutants and production of fuel. Thymol blue (TB) and Congo red (CR) were chosen as model dyes for degradation studies, with optimized reaction conditions being determined by varying the dose, pH, intensity, and concentration of dyes. The composite (CuSe@CQDs) showed a degradation rate of 99.4% and 97.8% for TB and CR, respectively, within 60 minutes, with a corresponding hydrogen production rate of 2360 and 1875 μmol g-1 h-1. The yield of hydrogen production using the composite was 35.7 and 29 times greater than that of CuSe alone for TB and CR, respectively. Spectroscopic techniques such as XRD, UV-Vis, FESEM, HRTEM, XPS, FTIR, BET, and TGA were used to characterize the composite, and the results revealed that the composite had superior degradation rates compared to CuSe alone, with the degradation rate being enhanced by about three times. GCMS analysis was used to investigate the intermediate and possible degradation pathways. Overall, this study highlights the potential of biosynthesized CQDs as effective photocatalysts for the sustainable management of wastewater and production of fuel.

Anion-Incorporated Mg-Ion Solvation Modulation Enables Fast Magnesium Storage Kinetics of Conversion-Type Cathode Materials

Rechargeable magnesium batteries (RMB) have emerged as one of the most promising alternatives to lithium-ion batteries due to the prominent advantages of magnesium metal anodes. Nevertheless, their application is hindered by sluggish Mg-ion storage kinetics in cathodes, although various structural modifications of cathode materials have been performed. Herein, an electrolyte design using an anion-incorporated Mg-ion solvation structure is developed to promote the Mg-ion storage reactions of conversion-type cathode materials. The addition of the trifluoromethanesulfonate anion (OTf^- ) in the ether-based Mg-ion electrolyte modulates the solvation structure of Mg²⁺ from [Mg(DME)₃ ]²⁺ to [Mg(DME)_2.5 OTf]⁺ (DME = dimethoxy ethane), which facilitates Mg-ion desolvation and thus significantly expedites the charge transfer of the cathode material. As a result, the as-prepared CuSe cathode material on copper current collector exhibits a considerable increase in magnesium storage capacity from 61% (228 mAh g^-1 ) to 95% (357 mAh g^-1 ) of the theoretical capacity at 0.1 A g^-1 and a more than twofold capacity increase at a high current density of 1.0 A g^-1 . This work provides an efficient strategy via electrolyte modulation to achieve high-rate conversion-type cathode materials for RMBs. The incorporation of the trifluoromethanesulfonate anion in the Mg-ion solvation structure of the borate-based Mg-ion electrolyte enables the fast magnesium storage kinetics of the conversion-type cathode materials. The as-prepared copper selenide cathode achieved a more than twofold capacity increase at a high rate and the highest reversible capacities compared to those of the previously reported metal selenide cathodes.

Easy, Fast, Selective, and Simultaneous Separation of Hg(II) and Oil via Loofah-Sponge-Inspired Hierarchically Porous Membranes

In this work, Cu2Se/Cu membranes (CSMs) of hierarchical pores were fabricated via chemical dissolution of Cu and Se followed by redeposition of cuprous selenide (Cu2Se) on copper membranes (CMs), and applied for adsorption/removal/separation of Hg(II) among a variety of interfering metal ions. The CSM demonstrates the best comprehensive performance among previous Hg(II) adsorption membranes, having high selectivity (KHg/M = 2.9 × 104-3.0 × 105), high efficiency (>99%, 5 s to 3 min), high adsorption capacity (505 mg/g), and high flux (2.0 × 106 L m-2 h-1). Meanwhile, effects of Hg(II) concentration, flow rate, and the number of membrane layers and adsorption cycles were also investigated on the removal of Hg(II). Moreover, a Cu2Se/Cu membrane-plasma (CSM-p) with superhydrophilicity/underwater superoleophobicity was prepared on the basis of CSM, and simultaneous removal of Hg(II) and oil was realized by using CSM and CSM-p in combination. This work not only provides a new reference for design of highly selective, efficient metal ion adsorption/enrichment/separation materials but also presents a novel approach to the removal/enrichment/separation of multiple complex contaminants by the combination of different functional membranes.

Revealing the reaction and fading mechanism of FeSe2 cathode for rechargeable magnesium batteries

Rechargeable Mg batteries (RMBs) are advantageous large-scale energy-storage devices because of the high abundance and high safety, but exploring high-performance cathodes remains the largest difficulty for the development. Compared with oxides and sulfides, selenides show better Mg-storage performance because the weaker interaction with the Mg2+ cation favors fast kinetics. Herein, nanorods-like FeSe2 was synthesized and investigated as cathodes for RMBs. Compared with microspheres and microparticles, nanorods exhibits higher capacity and better rate capability with the smaller particle size. The FeSe2 nanorods show a high capacity of 191 mAh g-1 at 50 mA g-1 and a good rate performance of 39 mAh g-1 at 1000 mA g-1. Ex-situ characterizations demonstrate the Mg2+ intercalation mechanism for FeSe2, and slight conversion reaction occurs on the surface of the particles. The capacity fading is mainly because of the dissolution of Fe2+, which is caused by the reaction between Fe2+ and Cl- of the electrolyte during the charge process on the surface of the particles. The surface of FeSe2 is mainly selenium after long cycling, which may also dissolve in the electrolyte during cycling. The present work develops a new type of Mg2+ intercalation cathode for RMBs. More importantly, the fading mechanism revealed herein has considered the specificity of Mg battery electrolyte and would assist a better understanding of selenide cathodes for RMBs.

Anionic Te-Substitution Boosting the Reversible Redox in CuS Nanosheet Cathodes for Magnesium Storage

The conversion-type copper chalcogenide cathode materials hold great promise for realizing the competitive advantages of rechargeable magnesium batteries among next-generation energy storage technologies; yet, they suffer from sluggish kinetics and low redox reversibility due to large Coulombic resistance and ionic polarization of Mg²⁺ ions. Here we present an anionic Te-substitution strategy to promote the reversible Cu⁰/Cu⁺ redox reaction in Te-substituted CuS_1-xTe_x nanosheet cathodes. X-ray absorption fine structure analysis demonstrates that Te dopants occupy the anionic sites of sulfur atoms and result in an improved oxidation state of the Cu species. The kinetically favored CuS_1-xTe_x (x = 0.04) nanosheets deliver a specific capacity of 446 mAh g^-1 under a 20 mA g^-1 current density and a good long-life cycling stability upon 1500 repeated cycles with a capacity decay rate of 0.0345% per cycle at 1 A g^-1. Furthermore, the CuS_1-xTe_x (x = 0.04) nanosheets can also exhibit an enhanced rate capability with a reversible specific capacity of 100 mAh g^-1 even under a high current density of 1 A g^-1. All the obtained electrochemical characteristics of CuS_1-xTe_x nanosheets significantly exceed those of pristine CuS nanosheets, which can contribute to the improved redox reversibility and favorable kinetics of CuS_1-xTe_x nanosheets. Therefore, anionic Te-substitution demonstrates a route for purposeful cathode chemistry regulation in rechargeable magnesium batteries.

A review of the microwave-assisted synthesis of carbon nanomaterials, metal oxides/hydroxides and their composites for energy storage applications

Currently, nanomaterials are considered to be the backbone of modern civilization. Especially in the energy sector, nanomaterials (mainly, carbon- and metal oxide/hydroxide-based nanomaterials) have contributed significantly. Among the various green approaches for the synthesis of these nanomaterials, the microwave-assisted approach has attracted significant research interest worldwide. In this context, it is noteworthy to mention that because of their enhanced surface area, high conducting nature, and excellent electrical and electrochemical properties, carbon nanomaterials are being extensively utilized as efficient electrode materials for both supercapacitors and secondary batteries. In this review article, we briefly demonstrate the characteristics of microwave-synthesized nanomaterials for next-generation energy storage devices. Starting with the basics of microwave heating, herein, we illustrate the past and present status of microwave chemistry for energy-related applications, and finally present a brief outlook and concluding remarks. We hope that this review article will positively convey new insights for the microwave synthesis of nanomaterials for energy storage applications.

Designing Nanostructured Metal Chalcogenides as Cathode Materials for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) are regarded as promising candidates for beyond-lithium-ion batteries owing to their high energy density. Moreover, as Mg metal is earth-abundant and has low propensity for dendritic growth, RMBs have the advantages of being more affordable and safer than the currently used lithium-ion batteries. However, the commercial viability of RMBs has been negatively impacted by slow diffusion kinetics in most cathode materials due to the high charge density and strongly polarizing nature of the Mg²⁺ ion. Nanostructuring of potential cathode materials such as metal chalcogenides offers an effective means of addressing these challenges by providing larger surface area and shorter migration routes. In this article, a review of recent research on the design of metal chalcogenide nanostructures for RMBs' cathode materials is provided. The different types and structures of metal chalcogenide cathodes are discussed, and the synthetic strategies through which nanostructuring of these materials can be achieved are described. An organized summary of their electrochemical performance is also presented, along with an analysis of the current challenges and future directions. Although particular focus is placed on RMBs, many of the nanostructuring concepts that are discussed here can be carried forward to other next-generation energy storage systems.

Ultralong-Lifespan Magnesium Batteries Enabled by the Synergetic Manipulation of Oxygen Vacancies and Electronic Conduction

As a potential next-generation energy storage system, rechargeable magnesium batteries (RMBs) have been receiving increasing attention due to their excellent safety performance and high energy density. However, the sluggish kinetics of Mg²⁺ in the cathode has become one of the main bottlenecks restricting the development of RMBs. Here, we introduce oxygen vacancies to spherical NaV₆O₁₅ cross-linked with carbon nanotubes (CNTs) (denoted as SNVO_X-CNT) as a cathode material to achieve an impressive long-term cycle life of RMBs. The introduction of oxygen vacancies can improve the electrochemical performance of the NaV₆O_15-X cathode material. Besides, owing to the introduction of CNTs, excellent internal/external electronic conduction paths can be built inside the whole electrode, which further achieves excellent electrochemical performance. Moreover, such a unique structure can efficiently improve the diffusion kinetics of Mg²⁺ (ranging from 1.28 × 10^-12 to 7.21 × 10^-12 cm²·s^-1). Simulation calculations further prove that oxygen vacancies can cause Mg²⁺ to be inserted in NaV₆O_15-X. Our work proposes a strategy for the synergistic effect of oxygen vacancies and CNTs to improve the diffusion coefficient of Mg²⁺ in NaV₆O₁₅ and enhance the electrochemical performance of RMBs.

An overview of the current status and prospects of cathode materials based on transition metal sulfides for magnesium-ion batteries

TMSs as cathode materials used in MIBs.

Cuprous Self-Doping Regulated Mesoporous CuS Nanotube Cathode Materials for Rechargeable Magnesium Batteries

Copper sulfides are broadly explored as the possible cathode materials for rechargeable magnesium batteries on account of their high theoretical capacity of 560 mAh g^-1. However, the CuS cathodes usually suffer from serious capacity decay caused by structure collapse during the repeated magnesiation/demagnesiation process. Herein, we present a cuprous self-doping strategy to synthesize mesoporous CuS nanotubes with robust structural stability for rechargeable magnesium batteries and regulate their electrochemical magnesium storage behavior. Electrochemical results show that the mesoporous CuS nanotubes can exhibit high specific capacity, remarkable cycling performance, and good rate capability. The observed discharge capacity of the mesoporous CuS nanotubes could reach about 281.2 mAh g^-1 at 20 mA g^-1 and 168.9 mAh g^-1 at 500 mA g^-1. Furthermore, a remarkable ultralong-term cyclic stability with a reversible capacity of 72.5 mAh g^-1 at 1 A g^-1 is obtained after 550 cycles. These results demonstrate that the mesoporous nanotube structure and the simple cuprous self-doping effect could promote the practical application of copper sulfide cathode materials for rechargeable magnesium batteries.

Monolayer Mo2C as anodes for magnesium-ion batteries

The adsorption and diffusion behaviors of magnesium (Mg) on monolayer Mo₂C have been investigated by the first principles method based on density functional theory (DFT). The structural stability and theoretical capacity of monolayer Mo₂C as anodes for magnesium-ion batteries (MIBs) have also been investigated. The results show that Mg prefer to occupy the H and T_C sites with the adsorption energies of - 1.439 and - 1.430, respectively, followed by B and T_Mo sites on Mo₂C monolayer. The Mg prefers to diffuse along the H-T_C-H path, furthermore, the other two possible paths (along H-B-H and H-T_Mo-H) also possess quite low energy barrier with the value of about 0.039 eV. The present results demonstrate that the adsorption energy per Mg atom and the volume expansion change mildly. The volume expansions change slightly from 0.7 to 7.08% with the variety of x, ranging from 0.167 to 2.0. The theoretical gravimetric capacity reaches to 469.791 mAhg^-1 with relatively small deformation and expansion as x = 2.0. The results mentioned above suggest that Mo₂C monolayer is one of the promising candidates for anode material of MIBs.

Layered H0.68Ti1.83O4/reduced graphene oxide nanosheets as a novel cathode for rechargeable magnesium batteries

Rechargeable magnesium batteries (RMBs) are promising devices for energy storage owing to their high volumetric energy density and high safety, but they still suffer from the lack of suitable cathodes.