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Two-dimensional (2D) materials are used in energy storage and conversion due to their unique electronic structure and large specific area. In this work, 2D vanadium carbide (V 2 CT x MXene) is fabricated and studied as an efficient and earth-abundant electrocatalyst for electrocatalytic N 2 reduction reaction (NRR). When tested in 0.1 M Na 2 SO 4 , such electrocatalyst achieves a large NH 3 yield rate of 12.6 μg h –1  mg –1 cat. and a Faradaic efficiency of 4% at –0.7 V vs. reversible hydrogen electrode. Theoretical calculations show a low reaction barrier of 0.88 eV in the distal route for this catalyst. Graphic Abstract

Vanadium carbide (V2CTx) MXene is a 2D nanomaterial widely investigated for energy storage applications due to its superior electrochemical properties. However, V2CTx quickly degrades in water, which limits its performance and longevity. Furthermore, the relationship between V2CTx MXene synthesis parameters and their corresponding aqueous stability is underexplored. In this study, delaminated V2CTx MXene films synthesized with four tetraalkylammonium hydroxide intercalants were characterized for their structural and aqueous stability differences. Delaminated V2CTx MXene d‐spacing, flake edge lengths, and surface morphology were generally dependent on the intercalant radius. Specifically, the intercalant radius exhibited a positive correlation with d‐spacing and a negative correlation with flake edge lengths. These structural differences have direct impacts on the aqueous stability of V2CTx. For example, Raman spectra of each thin film indicated that amorphous carbon formation upon water exposure positively corresponded with flake edge lengths. 3D printed film holders were fashioned to mimic electrochemical cell configurations to evaluate vanadium dissolution from each film when exposed to water. Vanadium dissolution from each film was statistically similar (i.e., no correlation with intercalant radius) and substantial (i.e., ppm concentration range). These findings will benefit aqueous applications of V2CTx MXenes, where material degradation and vanadium release may impact MXene performance. Vanadium carbide (V2CTx) MXene dispersions and films were synthesized using four commonly used tetraalkylammonium hydroxide intercalating agents of varying alkyl chain length. The corresponding effects of MXene structure d‐spacing, flake size and morphology, and vanadium dissolution from MXene thin films were systematically investigated to better understand the relationship between the V2CTx MXene synthesis conditions and its physicochemical properties. The findings from this work provide new information regarding V2CTx structure and aqueous stability which can drive V2CTx performance in current and emerging MXene applications.

This research work demonstrates the in-situ carbonization technique to fabricate the symmetric supercapacitors using a two-dimensional vanadium carbide-based MAX phase derived from agricultural waste biomass \"coconut shell\" without using any stabilizer or binary-solvent systems. The electrochemical characterization of the MAX phase using three electrode setups along with insights from tools, such as XRD and SEM analysis. This unique structure contributed to a high specific capacity of 289 C g −1 at a scan rate of 10 mVs −1 , accompanied by an impressive capacity retention of approximately 92% even after 2000 cycles, indicating exceptional volumetric stability. Furthermore, well-defined diffusion channels facilitated rapid charging and discharging processes, positioning V 2 AlC MAX as a promising contender among pseudocapacitive materials.

In this study, four kinds of heat treatments were performed to obtain a certain amount of retained austenite, which can result in good toughness and low brittleness accompanied with wear resistance of an in situ VC particle reinforced iron-based composite (VCFC). Microstructure, mechanical properties and wear resistance of the samples under heat treatment of QP, QPT, MQP and MQPT were compared. The experimental results indicated that there is a huge difference in microstructure between MQPT and the other heat treatments. High-proportion retained austenite and white net-like precipitates of M7C3 carbide existed in the MQPT-treated sample, but thick M7C3 carbide with brittleness was discovered in the other sample. Thereby, high-proportion retained austenite contributed to its low hardness of 634 HV and high tensile strength of 267 MPa, while a maximum hardness of 705.5 HV and a minimum tensile strength of 205 MPa were exhibited in the QPT-treated sample with a V-rich carbide of high hardness, a Cr-rich carbide of brittleness and a high-proportion martensite. Meanwhile, a phase transformation from retained austenite to martensite could increase the hardness and enhance wear resistance based on the transformation-induced plasticity (TRIP) effect; its wear rate was only 1.83 × 10−6 mm−3/(N·m). However, the wear rates of the samples under QP, QPT and MQP heat treatments increased by 16.4%, 44.3% and 41.0%, respectively. The wear mechanism was a synergistic effect of the adhesive wear mechanism and the abrasive wear mechanism. The adhesive wear mechanism was mainly considered in the MQPT-treated sample to reduce the wear rate attributed to high-proportion retained austenite and the existence of wear debris with a W element on the surface of the wear track. However, the abrasive wear mechanism could exist in the other samples because of a lot of thick, brittle M7C3, thereby resulting in a higher wear rate due to immediate contact between the designed material and the counterpart.

Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr 2 C 3 , MoC, and W 2 C) and covalent carbides (B 4 C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo 2 C and metastable α-MoC 1-x and η-MoC 1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>10 4  K s −1 ). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo 2 C showing the best performance. Nanoscale carbides provide access to ultra-strong ceramics and show activity as high-performance catalysts. Here, the authors report a flash Joule heating process for the ultrafast, general synthesis of various transition metal carbides nanocrystals with phase controllability.

Reactive oxygen species (ROS) are generated and consumed in living organism for normal metabolism. Paradoxically, the overproduction and/or mismanagement of ROS have been involved in pathogenesis and progression of various human diseases. Here, we reported a two-dimensional (2D) vanadium carbide (V 2 C) MXene nanoenzyme (MXenzyme) that can mimic up to six naturally-occurring enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione peroxidase (GPx), thiol peroxidase (TPx) and haloperoxidase (HPO). Based on these enzyme-mimicking properties, the constructed 2D V 2 C MXenzyme not only possesses high biocompatibility but also exhibits robust in vitro cytoprotection against oxidative stress. Importantly, 2D V 2 C MXenzyme rebuilds the redox homeostasis without perturbing the endogenous antioxidant status and relieves ROS-induced damage with benign in vivo therapeutic effects, as demonstrated in both inflammation and neurodegeneration animal models. These findings open an avenue to enable the use of MXenzyme as a remedial nanoplatform to treat ROS-mediated inflammatory and neurodegenerative diseases. Materials with enzymatic-like activities are of interest for a wide range of applications. Here, the authors report on 2D vanadium carbide MXene nanozymes capable of mimicking multiple enzymes and demonstrate application to treat reactive oxygen species-mediated inflammatory and neurodegenerative diseases.

The article provides results of testing excess introduction of vanadium into a molten aluminum cell through baked anodes. This stage of special technology is preliminary and required before the boriding heavy metal impurities in molten aluminum. The requirement of a preliminary stage is dictated by the presence of an insulating aluminum carbide layer on the surface of the carbon hearth that reduces the efficiency of aluminum boriding technology. The specific properties of vanadium and its compounds make it possible to organize chemical cleaning of the cathode from an Al4C3 layer, replacing it with a VC substrate. It is shown that with constant introduction of vanadium into melt dynamic equilibrium is established between vanadium and its compounds entering the cell and removed from it. Stabilization of a VC-coating requires organization of boriding technology for molten electrolyte and aluminum, creating a viscous low-mobility layer of a metal-boride Me–B suspension wetted with aluminum on the hearth.

The production of duplex stainless steel powders with the addition of carbides by high-energy mechanical milling is a novel method for recycling chips. With the increase in the consumption of raw material and energy and of the generation of residues, recycling is necessary due to environmental and industrial reasons. In this study, the effect of the addition of vanadium carbide on the morphology, particle size, and magnetic properties of the powders was investigated. The milling was realized using a planetary ball mill for 50 h at a milling speed of 350 rpm. The ball-to-powder weight ratio used was 20:1 and the 0, 1, and 3% wt. vanadium carbide addition. Produced duplex stainless steel powders from recycling chips were characterized by a scanning electron microscope (SEM), a laser particle size analyzer, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and magnetic characterization. The milling process led to the formation of martensite induced by deformation phase. It was verified that the addition of 3% carbide was the most effective in reduction of the particle size when compared to milling without carbide. The particle size of fabricated powders after 50 h of milling with 3% vanadium carbide addition was about 174 times lower than that of initial chips.

A VC coating was prepared on the surface of mold steel Cr12MoV using the TD composite treatment process. The differences in microstructure and properties between the two composite treatment processes and the VC coating obtained from the ordinary TD vanadium infiltration process were compared using a microhardness tester, scratch tester, X-ray diffraction, etc. The results show that both composite processes can improve the unevenness of matrix carbides; The hardness of the VC coating obtained by the two composite processes is slightly higher than that of the ordinary TD; The TD+vacuum quenching process has to some extent improved the adhesion between the coating and the substrate; The valence state of the VC coating obtained by the secondary TD process has undergone significant changes.