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Lithium (Li) metal is considered as a promising anode material for high‐energy batteries; yet, its practical application is hindered by uncontrolled Li dendrite growth, especially at a high rate. Herein, a dual conductive gradient V2CTx/MoO3 (DG‐V2CTx/MoO3) host that integrates electronic/ionic conductive gradients and lithiophilicity is prepared by layer‐by‐layer assembly for dendrite‐free Li anodes. Gradient LiF deriving from different amount of V2CTx endows a good ionic conductive gradient; while, MoO3 is regarded as a spacer to avoid the restacking of V2CTx, increasing space for Li deposition. The dual conductive gradients effectively optimize the current density and Li+ flux distribution at the bottom, achieving fast reduction of Li+ and a "bottom–up" Li deposition mode. Meanwhile, the lithiophilic V2CTx and MoO3 guide the homogeneous Li growth. As a result, the symmetrical half‐cells based on DG‐V2CTx/MoO3@Li anodes conduct 700 h at 5 mAh cm−2 and 20 mA cm−2. The DG‐V2CTx/MoO3@Li||LiFePO4 full‐cells maintain a capacity retention of 85.4% after 1350 cycles at 2 C. Remarkably, the DG‐V2CTx/MoO3@Li||LiNi0.6Co0.2Mn0.2O2 full‐cells can run 150 cycles with 80.6% capacity retention even at harsh conditions. The well‐adjusted materials and structures with both dual conductive gradients and lithiophilic properties will bring inspiration for novel material design of other metal batteries. [ABSTRACT FROM AUTHOR]

The development of MXenes using Lewis acidic salts for etching (MS-MXenes) in molten salts presents a novel, fluorine-free method attracting considerable interest. However, the behavior of various MS-MXenes and their derivatives in aqueous environments remains largely unexplored. Particularly, vanadium-based MXenes demonstrate intriguing properties in Zn ion aqueous electrolytes. Herein, a fluorine-free V2CTx MXene@VOx is synthesized by molten salt etching under an argon atmosphere. The electrochemical properties of V2CTx@VOx are tested in various aqueous electrolytes, including Zn(TFSI)2, ZnSO4, ZnBr2, ZnAc2, and ZnCl2 solutions. The V2CTx@VOx shows high redox capacities in all these Zn ion electrolytes, with the peak performance observed in 1 M ZnBr2, achieving a maximum capacity of 172 mAh g−1 at 1 mV s−1. This performance rivals that of V2CTx MXene prepared through wet-chemical methods. These results underscore the potential of MS-MXenes materials in aqueous energy storage applications.

Bacterial infections and the emergence of drug-resistant bacteria threaten human health. Photothermal sterilization has the advantages of temporal and spatial control, no drug resistance, and high efficiency and speed. Photothermal therapy (PTT) causes cell death by means of heat generation. In this work, V2CTx nanosheets are successfully prepared by an improved etching method and the biocompatibility is verified by cytotoxicity. The experiments show that the photothermal properties of V2CTx materials have a significant positive correlation with laser power and material concentration. Only 20 μg/mL of V2CTx can be heated above 70 °C in just 5 min. Photothermal conversion efficiency of V2CTx reaches 45.15% and has good photothermal stability. Taking the typical Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) as experimental bacteria. The results prove that V2CTx itself is a good antibacterial agent, but antibacterial need more than 4 h of culture time. Instead, the photothermal sterilization method shows only 0.125% and 12.72% survival rates for S. aureus and E. coli within 8 min, respectively. Therefore, the prepare V2CTx in this paper only needs 20 μg/mL to achieve efficient photothermal sterilization, which provides a good prospect for clinical treatment of diseases caused by multidrug-resistant bacteria. [ABSTRACT FROM AUTHOR]

With the progression of society and the rise in human activities, the detrimental effects of atmospheric ammonia on humans and the environment have grown more severe. Given that ammonia is widely utilized in numerous industrial sectors as a gas and is also a highly toxic and corrosive substance posing threats to human health and the environment, there is an immediate requirement for highly sensitive, selective, and precise sensing techniques to enable effective detection of ammonia. In this study, a V 2 CT x @PANI composite was prepared and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and EDS mapping to confirm the successful combination of the two materials. The composite's sensing performance for ammonia gas at different concentrations (5–100 ppm) and room temperature was also evaluated. The results demonstrated that the V 2 CT x @PANI composite sensors exhibited significantly improved response to ammonia gas and faster response/recovery times compared to both the pristine V 2 CT x -based and pure PANI sensors. Additionally, the composite displayed good long-term stability and selectivity in sensing ammonia. The study also provides a systematic discussion of the sensing mechanism, attributing the enhanced performance to the formation of heterojunctions and an abundance of active sites. Furthermore, first-principles calculations of adsorption energy and density of states were used to demonstrate the high selectivity of V 2 CT x @PANI for ammonia. • V 2 CT x @PANI composite material synthesized by ultrasonic mixing method. • The sensor can be used for rapid detection of ammonia at room temperature. • The sensor has good reproducibility, stability and selectivity. • Heterojunction formation improves the ammonia response of the sensor. • High selectivity of the sensor for ammonia verified by DFT calculation. [ABSTRACT FROM AUTHOR]

Aqueous Zn batteries exhibit significant research potential owing to their environmental friendliness and high energy density. Nevertheless, the formation of dendrites on the zinc anode and the sluggish diffusion kinetics of zinc ions adversely affect the cycle life of zinc ion batteries. In this study, we employ porous V 2 CT x (MVMX) as a protective layer for the zinc anode. The uniform porous structure of MVMX promotes active site exposure and facilitates the transport of zinc ions. Remarkably, the Zn@Ti half-cell demonstrated an average CE of 99.7% in 1500 cycles. Furthermore, the Zn-Zn symmetric battery exhibited stable cycling for 1600 h at current densities of 5 mA cm -2 and 1 mAh cm -2 . Additionally, the MVMX@Zn||V 2 O 5 full cell exhibited a capacity of 198 mAh g -1 and retained a capacity of 124.75 mAh g -1 after 5000 cycles at 1 A g -1 , demonstrating the potential of employing alternative MXenes for fabricating stable zinc anodes.

The K+ diffusion kinetics study and DFT calculations confirm that 1T-MoS 2 @V 2 CT x anode exhibits better K+ diffusion and storage behavior than MoS 2 @V 2 CT x and their individual components, which entrusts it with excellent rate performance and cyclic stability. [Display omitted] Two-dimensional (2D) materials used in potassium ion batteries (PIBs) have high theoretical capacitance and excellent rate characteristics. However, the origin of low diffusion of potassium ions and poor storage kinetics still remain challenge mainly due to the large size of potassium ions (0.138 nm) and narrow 2D interlayer spacing. Herein, the V 2 CT x -based hybrids including 1T-MoS 2 (1T -MoS 2 @V 2 CT x) has been successfully constructed by the magneto-hydrothermal method and proved to be an eminent anode, which can make PIBs have high reversible capacity and eminent rate performance at the same time. Moreover, the combination of 2D 1T-MoS 2 and V 2 CT x not only significantly promotes the transfer of interfacial charges as well as accelerates the transmission and diffusion of electrons and K+, but also helps to alleviate the volume changes caused by the insertion/extraction of large-sized K+ during the cycle, which makes the electrode exhibit good cycle stability. Density functional theory (DFT) indicates that the synergy effect between 1T-MoS 2 and V 2 CT x has significantly strengthened the potassium affinities and ion diffusion kinetics in the 1T-MoS 2 @V 2 CT x anode by reducing the ion diffusion energy barrier, thereby showing outstanding K+ storage performance, especially in 1T-MoS 2 @V 2 CF 2. As a result, the 1T-MoS 2 @V 2 CT x anode shows a high reversible capacity of 887.3 mA h g−1 at 0.1 A g−1, eminent rate performance of the capacity maintaining 563.6 mA h g−1 at 2.0 A g−1 and remarkable cycle stability of 601.2/374.7 mA h g−1 with 69.4/56.5% capacity retention after 2000 cycles at 1.0/2.0 A g−1. This work provides a new way for the exquisite design of 2D composite electrodes with excellent performance in PIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Successful preparation of a fluorine-free V 2 CT x @VO x via molten salt etching. • Exceptional performance of V 2 CT x @VO x in Zn ion electrolytes across broad pH range. • Achievement of a maximum specific capacity of 172 mAhg−1 in 1 M ZnBr 2 solution. • Superior performance of V 2 CT x @VO x compared to V 2 CT x MXene prepared by HF solution. The development of MXenes using Lewis acidic salts for etching (MS-MXenes) in molten salts presents a novel, fluorine-free method attracting considerable interest. However, the behavior of various MS-MXenes and their derivatives in aqueous environments remains largely unexplored. Particularly, vanadium-based MXenes demonstrate intriguing properties in Zn ion aqueous electrolytes. Herein, a fluorine-free V 2 CT x MXene@VO x is synthesized by molten salt etching under an argon atmosphere. The electrochemical properties of V 2 CT x @VO x are tested in various aqueous electrolytes, including Zn(TFSI) 2 , ZnSO 4 , ZnBr 2 , ZnAc 2 , and ZnCl 2 solutions. The V 2 CT x @VO x shows high redox capacities in all these Zn ion electrolytes, with the peak performance observed in 1 M ZnBr 2 , achieving a maximum capacity of 172 mAh g−1 at 1 mV s−1. This performance rivals that of V 2 CT x MXene prepared through wet-chemical methods. These results underscore the potential of MS-MXenes materials in aqueous energy storage applications. [ABSTRACT FROM AUTHOR]

• The self-charging ZIMSC based on free-standing V 2 CT x /CNT electrode was reported. • 1D CNT was introduced into 2D V 2 CT x to shorten ion transport path and increase conductivity. • The V/C-ZIMSC exhibits high specific capacitance of 246.88 mF cm−2 at 0.5 mA cm−2. • The V/C-ZIMSC exhibits excellent self-charging capabilities. • The self-powering wearable body monitoring system with high stability was designed. The flexible self-charging zinc ion micro-supercapacitors (ZIMSC) that can be effectively charged by harvesting ubiquitous energy from the air, not only achieve power supply anytime and anywhere but also improve the integrated degree without external charging plug or cable, enabling it a promising candidate for the wearable electronic device in various environmental scenarios. Herein, we reported a chemically self-charging ZIMSC based on a free-standing V 2 CT x /CNT electrode. Introducing 1D CNT into 2D V 2 CT x fundamentally overcomes the self-stacking problem of the nanosheets while providing additional ion transport paths and improving the conductivity of active electrodes. The area-specific capacity of V 2 CT x /CNT-based ZIMSC achieves 117.2 mF cm−2 after 8.0 h self-charging. The excellent self-charging performance is attributed to the oxidation of vanadium in the V 2 CT x -based cathode stimulated by ambient oxygen, accompanied by the Zn2+ deintercalation process. The flexible ZIMSC exhibited an optimal area capacitance of 246.88 mF cm−2 at a current density of 0.5 mA cm−2. Additionally, the self-charging ZIMSC is integrated with the V 2 CT x -based pressure sensors for a self-powering wearable system that exhibits excellent stability over 50,000 loading/unloading cycles. This work provides a rational design for constructing highly efficient self-charging energy storage devices and broadens the horizons of flexible wearable devices. [ABSTRACT FROM AUTHOR]

MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. However, beyond the extensively studied Ti 3 C 2 T x , other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V 2 CT x) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V 2 CT x -coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10−6 mm3 N−1 m−1). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V 2 CT x nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V 2 CT x , which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V 2 CT x (M 2 XT x) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M 4 X 3 T x (V 4 C 3 T x). [Display omitted] [ABSTRACT FROM AUTHOR]

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MXene as a novel two-dimensional (2D) material exhibits a lot of advantages in nonlinear optics. However, the common MXene, Ti3C2Tx and Ti2CTx nanosheets, easily suffer from degradation under ambient conditions, greatly limiting their practical applications. Here, we demonstrated one of MXene compounds, V2CTx, which has a strong modulation depth (nearly 50%), can serve as an excellent saturable absorber (SA) in passively mode-locked (PML) fiber lasers. More importantly, 206th harmonic order has been successfully generated in Er-doped mode-locked fiber laser, exhibiting maximum repetition rate of 1.01 GHz and pulse duration of 940 fs, which to the best of our knowledge, is the highest harmonic mode-locked fiber laser from the MXene SA so far. In addition, the high harmonic order mode-locked operation can maintain at least 24 h without any noticeable change, suggesting MXene V2CTx nanosheets have excellent stability in this mode-locked fiber laser. It is anticipated that the present work can pave the way to new design for MXene-based heterostructures for high-performance harmonic mode-locked lasers.

MXene is a promising two-dimensional (2D) material that is widely used in electro-photonic devices due to its unique properties. In this contribution, V2CTx, a novel MXene, was employed as a saturable absorber (SA) for hybrid passively mode-locked fiber lasers. An ultra-stable and self-starting mode-locked laser system with low threshold can be achieved using V2CTx nanosheets and nonlinear polarization evolution (NPE). Signal to noise ratio increased 13 dB compared with using only NPE SA. A 72 fs pulse duration is easily achieved from this hybrid mode-locked fiber laser system. To the best of our knowledge, this is the shortest pulse duration generated from the Yb-doped mode-locked fiber lasers using a hybrid or 2D SAs. This study proves that MXene V2CTx nanosheets can be developed as suitable SAs and served as potential advanced ultrafast photonic devices in the future.

MXene materials have attracted extensive attention in the field of energy storage because of their unique two-dimensional structure. The V2CTx two-dimensional nano materials can be prepared by selective etching of the Al layer atoms in the V2AlC ceramic powders. They have a high theoretical specific capacity as anode materials for lithiumion batteries. However, their etching process is difficult and the functional groups on the surface of the etching products significantly affect their electrochemical performance. Here V2CTx two-dimensional materials were prepared by using HF and HCl/NaF etchants. The crystal phase, morphology and electrochemical properties of V2CTx were used by means of XRD, SEM, EDS and electrochemical workstation. The results show that the V2CTx obtained by using HF as etcher has better cycling performance under large current density. It circulates 100 times at the current density of 0. 1 A g- 1,and the specific discharge capacity is 248 mAh g- 1 respectively. The reversible specific capacity is 94 mAh g - 1 respectively under the current density of 1 A g - 1 for 1 000 cycles. [ABSTRACT FROM AUTHOR]

MXene as a novel two-dimensional (2D) material exhibits a lot of advantages in nonlinear optics. However, the common MXene, Ti3C2Tx and Ti2CTx nanosheets, easily suffer from degradation under ambient conditions, greatly limiting their practical applications. Here, we demonstrated one of MXene compounds, V2CTx, which has a strong modulation depth (nearly 50%), can serve as an excellent saturable absorber (SA) in passively mode-locked (PML) fiber lasers. More importantly, 206th harmonic order has been successfully generated in Er-doped mode-locked fiber laser, exhibiting maximum repetition rate of 1.01 GHz and pulse duration of 940 fs, which to the best of our knowledge, is the highest harmonic mode-locked fiber laser from the MXene SA so far. In addition, the high harmonic order mode-locked operation can maintain at least 24 h without any noticeable change, suggesting MXene V2CTx nanosheets have excellent stability in this mode-locked fiber laser. It is anticipated that the present work can pave the way to new design for MXene-based heterostructures for high-performance harmonic mode-locked lasers. [ABSTRACT FROM AUTHOR]

The long-term use of antibiotics leads to drug resistance, it is insufficient to combat stubborn pathogens. Therefore, it urgently needs a material that can quickly and effectively eradicate bacteria, especially for resistant bacteria and their biofilm structures that are difficult to eliminate with conventional antibiotics. This article adopts a new 2D layered V 2 CT x MXene material, which utilizes in-situ coating method to stimulate dopamine self polymerization and fix nano silver onto V 2 CT x nanosheets. V 2 CT x @PDA@Ag showed very significant antibacterial effect under 808 nm laser illumination for 30 min. After analyzing the sterilization mechanism, the photothermal synergistic sterilization of composite mainly relies on physical contact, the generation of reactive oxygen species, and the photothermal synergistic effect. It is worth mentioning that after V 2 CT x is coated with PDA, the photothermal efficiency is improved, V 2 CT x and nano silver are also effectively connected. It proved that the composite has stable and efficient antibacterial properties. [Display omitted] • Sandwich-structured V 2 CT x @PDA@Ag nanosheet composites were successfully synthesized. • The mechanism of near-infrared photothermocatalytic sterilization was revealed. • Superior photothermocatalytic sterilization performance have been obtained. • The sterilization mainly depends on the generation of reactive oxygen species. [ABSTRACT FROM AUTHOR]

[Display omitted] • A theory-led discovery that the introduction of oxygen (O)-defects and strain to tailor the local electrons on the V 2 CT x surface for hydrogen evolution reaction (HER) is proposed. • O-defects and strain can precisely modulate the p z orbitals of O to be half-occupied, achieving an optimal hydrogen adsorption-free energy (ΔG H*) • Defective and strained exfoliated V 2 CT x sheets are constructed by in situ heating and capillary forces. • 60/Strained-V 2 CT x exhibits an overpotential of 134 mV at 10 mA cm−2 and Tafel slope of 48.4 mV dec−1, exceeding other reported MXene phase catalysts without any performance-enhancing additives. The electron density of electrocatalysts plays a vital role in governing the activity, but modifying the surface electronic structure to improve catalytic activity remains largely an empirical process, and rational designs are still extremely rare. Herein, we report a theory-led discovery that the introduction of oxygen (O)-defects and strain to tailor the local electrons on the V 2 CT x surface for hydrogen evolution reaction (HER). Our theoretical analysis shows that O-defects and strain can perturb the local electrons on the V 2 CT x surface and precisely modulate the p z orbitals of O to be half-occupied, achieving an optimal hydrogen adsorption-free energy (ΔG H*). To validate our theoretical predictions, defective and strained exfoliated V 2 CT x sheets are constructed by in situ heating and capillary forces, which exhibit an overpotential of 134 mV at 10 mA cm−2 and Tafel slope of 48.4 mV dec−1, exceeding other reported MXene phase catalysts without any performance-enhancing additives. Both theoretical and experimental data exhibit the same volcanic trend of overpotentials and unveil that the proper combinations of O-defects and strain can achieve highly efficient HER performance. This reliable strategy to tailor the local electrons of V 2 CT x will open a window for improving the catalytic performance of its structural analog. [ABSTRACT FROM AUTHOR]

To further improve the electrochemical performance for the wearable and microelectronic devices, we reported an all-MXenes zinc ion hybrid micro-supercapacitor (ZIHMSC) with a wide voltage window (1.60 V) based on V 2 CT x as the cathode and Ti 3 C 2 T x as the anode. The flexible V 2 CT x and Ti 3 C 2 T x electrodes are fabricated by the electrophoretic deposition method, which is simple and conducive to the realization of positive and negative electrodes matching. Benefiting from the synergistic effect of the two MXenes and the unique configuration, our ZIHMSCs also achieve fast ion and electron transfer kinetics, showing better rate capability than the MXene/Zn system. And the ZIHMSCs achieve excellent electrochemical performance, with high area capacitance of 200.1 mF cm−2, well stability over 5,000 charge/discharge cycles, and high energy density of 71.6 μWh cm−2 at 400.7 μW cm−2. The reason for the wide voltage window of the ZIHMSC was well revealed by the large work function difference between the two electrode materials of V 2 CT x and Ti 3 C 2 T x and the redox potential of the electrolyte. And the electrochemical energy storage mechanisms are well investigated by ex-situ XPS and XRD. In addition, the ZIHMSC displays well flexibility and mechanical property, suffering from 15,000 bending cycles under 90°. The ZIHMSCs can successfully drive digital tubes and meters and enable digital meters to operate for more than 600 s, proving their practical application potential. [Display omitted] • The flexible zinc ion hybrid capacitor (ZIHSC) with all-MXenes is designed and fabricated for wearable devices. • The ZIHSC possess 1.60 V voltage window due to the large workfunction differenceof V2CTx and Ti3C2Tx electrodes. • The ZIHSC exhibit a high energy density of 71.6 μWh cm-2 and excellent rate performance. • The diffusion coefficients and capacitive contributions ratio are used to evaluate the kinetic behavior. • The ZIHSC demonstrates stable electrochemical performance under 15,000 bending cycles. [ABSTRACT FROM AUTHOR]

• 3D carbon-coated MXene nanofiber free-standing structures were constructed, including C@V 2 CT x , C@Nb 2 CT x , C@VTiCT x , and C@Ti 2 CT x. • C@MXene nanofiber free-standing electrode exhibits excellent electrochemical performance in lithium-ion storage. • C@V 2 CT x exhibited capacities of over 600 and 400 mAh g − 1 at 0.10 and 2.0 a g − 1, respectively, as well as excellent rate performance and cycle stability. Because of the excellent conductivity, tunability of elements and surface groups, MXenes are seen as promising electrode materials for lithium-ion storage devices. However, Van der Waals force causes MXene nanosheets to aggregate and re-stack, limiting their applications. Here, we design a carbon-coated MXene nanofiber (C@MXene) free-standing electrode with a 3D conductive network and excellent flexibility to overcome the intrinsic stacking and agglomeration in MXene. Furthermore, the 3D conductive network provides fast lanes for electron transfer, improves the electrochemical activity. And the free-standing electrode structure, which is a straightforward approach for constructing the working electrode and a basis for the following large-scale manufacturing, does not require the auxiliary material and conductive agent to manufacture the electrode material. In particular, the C@V 2 CT x exhibits outstanding electrochemical performance. At 0.1 A g − 1, over 600 mAh g − 1 was exhibited after 175 cycles, and over 400 mAh g − 1 after 1000 cycles at 2.0 A g − 1, cycle retention is close to 100%. Besides, the electrochemical properties of other C@MXene (Nb 2 CT x , Ti 2 CT x and VTiCT x) are also optimized to varying degrees. The construction of 3D C@MXene free-standing electrode structure provides a new idea for enhancing the electrochemical performance of MXene. [Display omitted] [ABSTRACT FROM AUTHOR]

• V 2 CT x with controllable layers was obtained by etching and intercalation technique. • The flexible V 2 CT x electrodes were prepared by the electrophoretic approach. • The F-ZIHC exhibits outstanding areal capacity and cycling stability. • The F-ZIHC exhibits excellent anti-self-discharge resistance of 6.4 mV h−1. • This work can broaden the applications in wearable fields and integrated systems. Ti 3 C 2 T x MXene with unique physical and chemical properties are recently sparked tremendous interest in the energy storage field. Compared to Ti 3 C 2 T x , V 2 CT x MXene is a more promising candidate for energy storage due to a low number of atomic layers in the V 2 CT x structure and varied valence states of vanadium. Herein, we report a flexible V 2 CT x electrode with different layers (named accordion-like V 2 CT x , multi-layer V 2 CT x , and few-layer V 2 CT x, respectively) fabricated by using electrophoretic deposition, then assembled a flexible zinc ion hybrid capacitor (ZIHC) by virtue of zinc anode and gel electrolyte. The areal capacitance of few-layer V 2 CT x based ZIHC is 54.12 mF cm−2 at 0.1 mA cm−2, which is greater than those of accordion-like V 2 CT x and multi-layer V 2 CT x based ZIHC. The outstanding electrochemical performance of few-layer V 2 CT x based ZIHC is attributed to its richer active sites and shorter ion transport routes. Additionally, the few-layer V 2 CT x based ZIHC also owns well cycling stability, with 81.48 % capacity retention after 8000 cycles, and a low self-discharge rate of 6.4 mV h−1, making it suitable for wearable devices. So, the V 2 CT x based ZIHC is integrated with a Ti 3 C 2 T x based pressure sensor to monitor diverse human activities, demonstrating its steady and long-term power supply capacity as the energy storage device. [ABSTRACT FROM AUTHOR]

MXenes show promising potential in supercapacitors due to their unique two-dimensional (2D) structure and abundant surface functional groups. However, most studies about MXenes have focused on tailoring surface structures by alternating synthesis methods or post-etch treatments, and little is known about the inherent relationship between surface groups and M elements. Herein, we propose a simple and novel strategy to adjust the surface structure of few-layered MXene flakes by adding a small amount of Nb element. Because of the strong affinity between Nb and O elements, the as-received V 1.8 Nb 0.2 CT x and Ti 2.7 Nb 0.3 C 2 T x MXenes have much fewer -F functional groups and a higher O content than V 2 CT x and Ti 3 C 2 T x MXenes, respectively. Thus, both V 1.8 Nb 0.2 CT x and Ti 2.7 Nb 0.3 C 2 T x MXenes show enhanced pseudocapacitance performance. Especially, V 1.8 Nb 0.2 CT x delivers an ultrahigh volumetric capacitance of 1698 F/cm 3 at a scan rate of 2 mV/s. Moreover, benefiting from the high activity of MAX precursors obtained through a fast self-propagating high-temperature synthesis, the etching time to produce V-based MXenes is much shorter than that in previous reports. Therefore, the results presented here are applicable to the surface engineering and rational design of 2D MXene materials and develop them into promising, cost-effective electrode materials for supercapacitors or other energy-storage equipment.

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V 2 CT x through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V 2 CT x through a substitution reaction during the dissolution of Li 2 S in LiCl-KCl molten salts. Then, surface V 2 O 5 was obtained through the in situ electrochemical charging/discharging of the S-doped V 2 CT x (MS-S-V 2 CT x ) cathode. The assembled Zn/MS-S-V 2 CT x battery showed a high reversible discharge capacity of 411.3 mAh g -1 at a current density of 0.5 A g -1 , an 80% capacitance retention after long cycle stability tests at 10 A g -1 for 3000 cycles, and a high energy density of 375.5 Wh kg -1 in 2M ZnSO 4 . Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn 2+ ions and improved the stability of V 2 O 5 . This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.