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Rechargeable magnesium batteries (RMBs) are promising next‐generation low‐cost and high‐energy devices. Among all RMBs, anode‐free magnesium metal batteries that use in situ magnesium‐plated current collectors as negative electrodes can afford optimal energy densities. However, anode‐free magnesium metal batteries have remained elusive so far, as their practical application is plagued by low Mg plating/stripping efficiency due to nonuniform Mg deposition on conventional anode current collectors. Herein, for the first time, an anode‐free Mg‐metal battery is developed by employing a 3D MXene (Ti3C2Tx) film with horizontal Mg electrodeposition. The magnesiophilic oxygen and reactive fluorine terminations in MXene enable an enriched local magnesium‐ion concentration and a durable magnesium fluoride‐rich solid electrolyte interphase on the Ti3C2Tx film surface. Meanwhile, Ti3C2Tx MXene exhibits a high lattice geometrical fit with Mg (≈96%) to guide the horizontal electrodeposition of Mg. Consequently, the developed Ti3C2Tx film achieves reversible Mg plating/stripping with high Coulombic efficiencies (>99.4%) at high‐current‐density (5.0 mA cm−2) and high‐Mg‐utilization (50%) conditions. When this Ti3C2Tx film is coupled with a pre‐magnesized Mo6S8 cathode, the anode‐free Mg‐metal full‐cell prototype exhibits a volumetric energy density five times higher than its standard Mg‐metal counterpart. This work provides insights into the rational design of anode current collectors to guide horizontal Mg electrodeposition for anode‐free Mg metal batteries. [ABSTRACT FROM AUTHOR]

Magnesium metal batteries are promising candidates for next‐generation high‐energy‐density and low‐cost energy storage systems. Their application, however, is precluded by infinite relative volume changes and inevitable side reactions of Mg metal anodes. These issues become more pronounced at large areal capacities that are required for practical batteries. Herein, for the first time, double‐transition‐metal MXene films are developed to promote deeply rechargeable magnesium metal batteries using Mo2Ti2C3 as a representative example. The freestanding Mo2Ti2C3 films, which are prepared using a simple vacuum filtration method, possess good electronic conductivity, unique surface chemistry, and high mechanical modulus. These superior electro‐chemo‐mechanical merits of Mo2Ti2C3 films help to accelerate electrons/ions transfer, suppress electrolyte decomposition and dead Mg formation, as well as maintain electrode structural integrity during long‐term and large‐capacity operation. As a result, the as‐developed Mo2Ti2C3 films exhibit reversible Mg plating/stripping with high Coulombic efficiency of 99.3% at a record‐high capacity of 15 mAh cm−2. This work not only sheds innovative insights into current collector design for deeply cyclable Mg metal anodes, but also paves the way for the application of double‐transition‐metal MXene materials in other alkali and alkaline earth metal batteries. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials like conventional graphene, hexagonal boron nitride (h-BN, monolayer), and transition metal dichalcogenides (2D TMDCs) have gotten a lot of attention lately because of their unparalleled possibilities for a variety of applications. MBenes, a family of two-dimensional (2D) transition metal borides, have recently attracted significant attention. Their elemental compositions, surface terminations, geometrical forms, and properties (chemical and physical) are unique and fascinating. These two-dimensional compounds hold promising potential for environmental applications because of their exceptional electrical conductivity, high hydrophilicity, rich surface chemistry, and outstanding stability. The newly discovered MBenes are incredibly stable, with isotropic and ultrahigh Young's modulus. Furthermore, MBenes have superior catalytic activity, optical and thermal properties. Given many potential MBenes, theoretical and experimental applications are expected soon. This review presents the synthetic approaches, properties (optical, thermal, mechanical, and electrochemical), and diverse applications of MBenes-based heterostructures. The numerous strategies for further investigation MBenes for applications in the energy sector (storage and conversion) are highlighted. [ABSTRACT FROM AUTHOR]

In this work, we report green synthesis of Cu-doped carbon quantum dots (CQDs), abbreviated as Cu@CQDs, using CQDs derived from Citrus limetta waste pulp, as a reducing and capping agent. Synthesis parameters are optimized in terms of synthesis temperature and thus optimized Cu@CQDs are characterized for their structural and optical properties. They exhibit a surface plasmon peak at ~575 nm and are of size ~6 nm. The as prepared Cu@CQDs are studied for colorimetric and absorbance based sensing of histidine and arsenate (As (V)), respectively. The imidazole side chain of histidine act as a coordinating ligand, and the results into aggregation of Cu@CQDs, leading to their color change from colorless to blue. With this approach, Cu@CQDs is found to detect histidine with high selectivity and in a wide concentration range of 10 to 100 mM. The detection limit is further found to be 17.82 mM, Moreover, the rich surface functionalities of Cu@CQDs are also utilized for absorbance based detection of As (V) detection. The Cu@CQDs were found to detect As (V) in 10–1000 ppb concentration range with a detection limit of ~18 ppb (standard deviation ~0.03). [ABSTRACT FROM AUTHOR]