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Metal hollow nanostructures have a wide range of potential applications in energy storage and conversion, owing to their low density, high surface to volume ratio, and high contact surface area.

MXene inks are promising candidates for fabricating conductive circuits and flexible devices. Here, MXene inks prepared from solvent mixtures demonstrate long-term stability and can be employed in commercial rollerball pens to write electronic circuits on flexible substrates. Such circuits exhibit a fast and accurate capacitive response for touch-boards and water level measurement, indicating the excellent potential of these MXene inks in electrical device fabrication.

The addition of CNCs into MXene dispersions enables LC-MXene phases at lower critical transition concentrations, allowing wet spinning of fibers using previously unspinnable concentrations of MXene.

High aspect ratio two-dimensional Ti3C2Tx MXene flakes with extraordinary mechanical, electrical, and thermal properties are ideal candidates for assembling elastic and conductive aerogels. However, the scalable fabrication of large MXene-based aerogels remains a challenge because the traditional preparation method relies on supercritical drying techniques such as freeze drying, resulting in poor scalability and high cost. Herein, the use of porous melamine foam as a robust template for MXene/reduced graphene oxide aerogel circumvents the volume shrinkage during its natural drying process. Through this approach, we were able to produce large size (up to 600 cm3) MXene-based aerogel with controllable shape. In addition, the aerogels possess an interconnected cellular structure and display resilience up to 70% of compressive strain. Some key features also include high solvent absorption capacity (∼50-90 g g-1), good photothermal conversion ability (an average evaporation rate of 1.48 kg m-2 h-1 for steam generation), and an excellent electrothermal conversion rate (1.8 kg m-2 h-1 at 1 V). More importantly, this passive drying process provides a scalable, convenient, and cost-effective approach to produce high-performance MXene-based aerogels, demonstrating the feasibility of commercial production of MXene-based aerogels toward practical applications.

The increasing interest toward wearable and portable electronic devices calls for multifunctional materials and fibers/yarns capable of seamless integration with everyday textiles. To date, one particular gap inhibiting the development of such devices is the production of robust functional fibers with improved electronic conductivity and electrochemical energy storage capability. Recent efforts have been made to produce functional fibers with 2D carbides known as MXenes to address these demands. Ti3C2Tx MXene, in particular, is known for its metallic conductivity and high volumetric capacitance, and has shown promise for fibers and textile-based devices when used either as an additive, coating or the main fiber component. In this spotlight article, we highlight the recent exciting developments in our diverse efforts to fabricate MXene functionalized fibers, along with a critical evaluation of the challenges in processing, which directly affect macroscale material properties and the performance of the subsequent prototype devices. We also provide our assessment of observed and foreseen challenges of the current manufacturing methods and the opportunities arising from recent advances in the development of MXene fibers and paving future avenues for textile design and practical use in advanced applications.

In this work, MgCo2O4@NiMn layered double hydroxide (LDH) core-shell structured nanocomposites on Ni foam (NF) are synthesized by facile hydrothermal and calcination methods. MgCo2O4/NF is synthesized first via a hydrothermal reaction and annealing treatment, and then utilized to prepare MgCo2O4@NiMn-LDH/NF core-shell structured nanocomposites via the second hydrothermal process. It is found that the MgCo2O4@NiMn-LDH/NF nanocomposite prepared from 6 h hydrothermal reaction (MC@NM-LDH-2) exhibits an excellent specific capacitance of 3757.2 F g−1 (at 1 A g−1). Moreover, a high capacitance retention (86.9% after 6000 cycles) and a low internal resistance (Rs) (0.565 Ω) can be achieved. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) is assembled using MgCo2O4@NiMn-LDH/NF-2 as positive electrode and activated carbon (AC) as negative electrode. The as-fabricated MgCo2O4@NiMn-LDH/NF-2//AC ASC shows a high energy density of 62.33 Wh kg−1 at 750 W kg−1. Meanwhile, the MgCo2O4@NiMn-LDH/NF-2//AC ASC device possesses an outstanding cycling stability of 93.7% retention of the initial capacitance after 6000 cycles and three ASC devices connected in series can light up a LED bulb for 15 min. Our results manifest that these core-shell structure MgCo2O4@NiMn-LDH nanocomposites could envision huge potential application in energy storage devices.

Reasonable design of materials with complex nanostructures and diverse chemical compositions is of great significance in the field of energy storage. Cu

Transition metal selenides (TMSe) are considered as potential anode materials for supercapacitors because of their abundant reserves and high safety.However, their poor conductivity limits their high rate performance and stability.In this paper, an N-doped porous nanocarbon-coated Co

Superelastic aerogels with excellent electrical conductivity, reversible compressibility, and high durability hold great potential for varied emerging applications, ranging from wearable electronics to multifunctional scaffolds. In the present work, superelastic MXene/reduced graphene oxide (rGO) aerogels are fabricated by mixing MXene and GO flakes, followed by a multistep reduction of GO, freeze-casting, and finally an annealing process. By optimizing both the composition and reducing conditions, the resultant aerogel shows a reversible compressive strain of 95%, surpassing all current reported values. The conducting MXene/rGO network provides fast electron transfer and stable structural integrity under compression/release cycles. When assembled into compressible supercapacitors, 97.2% of the capacitance was retained after 1000 compression/release cycles. Moreover, the high conductivity and porous structure also enabled the fabrication of a piezoresistive sensor with high sensitivity (0.28 kPa-1), wide detection range (up to 66.98 kPa), and ultralow detection limit (∼60 Pa). It is envisaged that the superelasticity of MXene/rGO aerogels offers a versatile platform for utilizing MXene-based materials in a wide array of applications including wearable electronics, electromagnetic interference shielding, and flexible energy storage devices.

Hypothesis MXenes (two-dimensional early transition metal carbides and carbonitrides) possess both excellent conductivity and surface hydrophilicity, enabling more diverse potential applications. However, in flexible strain sensors, the flexible substrates are usually composed of hydrophobic elastomers such as thermoplastic polyurethane (TPU). To enhance the interactions between MXenes and hydrophobic. substrates, it is wiser to change the composition of the flexible substrate than to modify the surface of MXenes, so as to improve the interactions between the flexible substrate and MXenes without losing the excellent conductivity of MXene. Experiments We introduce polyacrylonitrile (PAN) into TPU, and then fabricate a flexible TPU/PAN mat through electrospinning. A highly conductive and stretchable Ti3C2 MXene/TPU/PAN mat was then prepared by a simple dip-coating process. The interaction mechanism between Ti3C2 MXene nanosheets and TPU/PAN mat was investigated by XPS and FT-IR. Finally, we build the MXene/TPU/PAN mat into a flexible strain sensor with excellent properties. Findings By introducing PAN into flexible substrate, the interaction between Ti3C2 MXene and the flexible substrate was effectively improved without compromising Ti3C2 MXene's excellent conductivity. The MXene/TPU/PAN strain sensor possesses a wide sensing range (0–80%), a fast response ( 1750 cycles). All of these properties are demanded in wearable electronics.

Pump it up Carbon nanotube yarns can be used as electrochemical actuators because infiltration with ions causes a contraction in length and an expansion in diameter. Either positive or negative ions can cause this effect. Chu et al. constructed an all-solid-state muscle that eliminated the need for an electrolyte bath, which may expand the potential for its use in applications. By infiltrating the yarns with charged polymers, the fibers start partially swollen, so the length can increase through the loss of ions. It is thus possible to increase the overall stroke of the muscle. Further, these composite materials show a surprising increase in stroke with scan rate. Science , this issue p. 494

Tremendous efforts have been dedicated towards high-performance energy storage devices though material innovation, nanoscale structural design and hybrid fabrication approaches. A crucial technique to tune the properties of nanomaterials, such as MXene, is through introducing defects or heteroatom dopants. To improve the level of nitrogen dopant, a two-step pre-intercalation–annealing strategy is developed herein, using ammonium citrate (AC) as an all-in-one intercalant, antioxidant and nitrogen source, followed by annealing in an ammonia atmosphere. It is shown that the doping efficiency of nitrogen-doped Ti3C2Tx MXene (N-MXene) increased from 3.5% to 6.3%, compared with MXene annealed in ammonia without pre-intercalation. This high doping level induces significantly enhanced electrochemical capacitance (475 F g−1 at 5 mV s−1) compared with pristine MXene (321 F g−1), and greatly improved performance at high current density (248 F g−1 at 1 V s−1). Modelling was performed to elucidate the N-doping process of MXene and to understand the mechanism enhancing the electrochemical capacitance, which indicates that the pre-intercalation strategy promotes N-doping as surface functionalization, as well as in the MXene lattice. The pre-intercalation strategy demonstrates a new and facile pathway for functionalizing Ti3C2Tx MXene which will facilitate use in applications such as in high performance supercapacitors.

The exciting combination of high electrical conductivity, high specific capacitance and colloidal stability of two-dimensional Ti3C2Tx MXene (referred to as MXene) has shown great potential in a wide range of applications including wearable electronics, energy storage, sensors, and electromagnetic interference shielding. To realize its full potential, recent literature has reported a variety of solution-based processing methodologies to develop MXenes into multifunctional architectures, such as fibres, films and aerogels. In response to these recent critical advances, this review provides a comprehensive analysis of the diverse solution-based processing methodologies currently being used for MXene-architecture fabrication. A critical evaluation of the processing challenges directly affecting macroscale material properties and ultimately, the performance of the resulting prototype devices is also provided. Opportunities arising from the observed and foreseen challenges regarding their use are discussed to provide avenues for new designs and realise practical use in high performance applications.

Layered double hydroxides (LDHs) are widely used as cathode materials for supercapacitors (SCs), thanks to their many advantages. However, the single metal species with limited active sites limit the further improvement of the electrochemical performance of LDH materials. We successfully in situ embedded cobalt sulfide quantum dots (Co9S8-QDs) between the layers of ternary metal LDHs derived from metal–organic-frameworks (MOFs) by selective vulcanization of Co. The prepared Ni3Mn1Co@Co9S8-QDs/NF nanocomposites retain the advantages of LDH materials, such as lower charge transfer resistance. At the same time, the selectively generated ultra-small sized Co9S8-QDs reveal more active sites, which complies with the size minimization strategy, leading to the largely enhanced electrochemical properties. Due to the cooperative effect of LDHs and Co9S8-QDs, the prepared electrode has an excellent capacity (492.1 mA h g−1 at 1 A g−1), remarkable equivalent series resistance (0.499 Ω) and superior capacity retention (90.4% after 10 000 charge–discharge cycles). In addition, the carbon coated Fe2O3 nanoarray is prepared on carbon cloth (CC) as the cathode electrode (Fe2O3@C/CC), and the prepared Ni3Mn1Co@Co9S8-QDs/NF//Fe2O3@C/CC all solid-state asymmetric supercapacitor (ASC) shows an outstanding energy density (71.48 W h kg−1) when the power density is 750 W kg−1 and excellent capacity retention (93.7% after 10 000 charge–discharge cycles). As a result, the construction of composite electrodes with polymetallic LDHs and in situ embedded quantum dots should envision broad prospects.

Ti

In this study, a novel extraction method has been employed to obtain highly efficient cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) from waste hemp fibers with maximum potential. By...

Niobium nitrides possess superconductivity and stable chemical stability, which render them desirable candidates for energy storage. Therefore, they deserve exploration for potential energy storage applications. Here we report on the synthesis of 2D Nb4 N5 nanosheets by ammonization of NbS2 nanosheets as templates at 700 °C. The obtained 2D Nb4 N5 nanosheets retain their hexagon shape and display a porous structure with a pore size of 3.716 nm. These 2D Nb4 N5 nanosheets exhibit capacitor behavior as electrode materials for energy storage. This study opens a new avenue in synthesizing 2D materials based on 2D templates.

Textile-based energy storage devices offer an exciting replacement for bulky and uncomfortable batteries in commercial smart garments. Fiber and yarn-based supercapacitors, currently dominating research in this field, have demonstrated excellent performance below ∼4 cm in length, but suffer at longer lengths due to increased resistance. Herein, a new architecture of wearable energy storage devices, 3D knitted supercapacitors, is designed and prototyped with the intention of exploiting the architecture of a knit textile to improve the performance of long yarn electrodes. While Computer-Aided Design (CAD) knitting is a ubiquitous technology for producing textiles, knitted energy storage devices have been largely unexplored due to the need for meters of highly conductive yarn electrodes that meet the strenuous strength and flexibility requirements for CAD knitting. MXenes, a family of solution processable and conductive two-dimensional (2D) materials, have been realized as inks, slurries, pastes, and now dyes for the development of on-paper, on-plastic, and on-textile microsupercapacitor electrodes. In this work, Ti3C2Tx MXene was adopted as an active material for coating meters of commercial natural and synthetic yarns, enabling the production of knitted planar microsupercapacitors. The impact on electrochemical performance of knit structure and geometry was systematically studied in an attempt to produce energy storing textiles with power and energy densities that can be used for practical applications. The resulting energy storing textiles demonstrate high capacitance, up to 707 mF cm−2 and 519 mF cm−2 at 2 mV s−1 in 1 M H3PO4 and PVA-H3PO4 gel electrolyte, respectively, and excellent cycling stability over 10,000 cycles. This work represents an important step towards the mass production of MXene-based conductive yarns and 3D knitted energy storage devices and demonstrates how knit structure plays a significant role on device performance.

Recently, two-dimensional (2D) transition metal carbides and carbonitrides (MXenes), have shown great potential in micro-supercapacitors (MSCs). However, the maximum voltage output of symmetric MXene MSCs is limited to 0.6 V due to the oxidation effects at high anodic potentials. Herein, we developed asymmetric micro-supercapacitors (AMSCs) based on titanium carbide MXene (Ti3C2Tx) and MXene-MoO2 electrodes with an enlarged voltage window of 1.2 V, which is twice wider than that of symmetric MXene MSCs. The 2D-0D MXene-MoO2 microelectrode is fabricated by homogenous dispersing zero-dimensional (0D) MoO2 nanoparticles into MXene layers to impede layers stacking and MoO2 nanoparticles aggregation. Notably, the AMSCs delivered good electrochemical performances of areal capacitance of ∼19 mF cm−2 and volumetric capacitance of 63 F cm−3 at a scan rate of 2 mV s−1, and high energy density of 9.7 mW h cm−3 at a power density of 0.198 W cm−3. The AMSCs also presented exceptionally mechanical flexibility under different bending states and excellent cyclic stability, with 88% capacitance retention after 10000 cycles at a discharge current density of 0.5 mA cm−2. For practical application, the serially connected AMSCs are fully affordable to power electronics, which is beneficial for soft and wearable power devices. Keywords: 2D-0D structure, Flexible material, MXene, Molybdenum dioxide, Asymmetric micro-supercapacitors, Energy storage

The discovery of liquid crystalline (LC) phases in dispersions of two-dimensional (2D) materials has enabled the development of macroscopically aligned three-dimensional (3D) macrostructures. Here, we report the first experimental observation of self-assembled LC phases in aqueous Ti3C2Tx MXene inks without using LC additives, binders, or stabilizing agents. We show that the transition concentration from the isotropic to nematic phase is influenced by the aspect ratio of MXene flakes. The formation of the nematic LC phase makes it possible to produce fibers from MXenes using a wet-spinning method. By changing the Ti3C2Tx flake size in the ink formulation, coagulation bath, and spinning parameters, we control the morphology of the MXene fibers. The wet-spun Ti3C2Tx fibers show a high electrical conductivity of ∼7750 S cm–1, surpassing existing nanomaterial-based fibers. A high volumetric capacitance of ∼1265 F cm–3 makes Ti3C2Tx fibers promising for fiber-shaped supercapacitor devices. We also show that Ti3C2Tx fibers can be used as heaters. Notably, the nematic LC phase can be achieved in other MXenes (Mo2Ti2C3Tx and Ti2CTx) and in various organic solvents, suggesting the widespread LC behavior of MXene inks., Liquid crystalline behavior of aqueous additive-free and binder-free Ti3C2 dispersions and pure, wet-spun Ti3C2 fibers with different microstructure.

Summary Osmotic energy represents a widespread and reliable source of renewable energy with minimal daily variability. The key technological bottleneck for osmotic electricity is that membranes must combine highly efficient ion rectification and high ionic flux with long-term robustness in seawater. Here, we show that nanocomposite membranes with structural organization inspired by soft biological tissues with high mechanical and transport characteristics can address these problems. The layered membranes engineered with molecular-scale precision from aramid nanofibers and BN nanosheets simultaneously display high stiffness and tensile strength even when exposed to repeated pressure drops and salinity gradients. The total generated power density over large areas exceeded 0.6 W m−2 and was retained for as long as 20 cycles (200 h), demonstrating exceptional robustness. Furthermore, the membranes showed high performance in osmotic energy harvesting in unprecedentedly wide ranges of temperature (0°C–95°C) and pH (2.8–10.8) essential for the economic viability of osmotic energy generators.