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To design and prepare novel composites with strong electrode structure and superior electrochemical performances via a facile and convenient synthesis method is a significant challenge to develop the high-performance materials for energy storage and conversion devices. Herein, we fabricated a novel hybridization of two dimensional (2D) Ti3C2-MXenes nanosheets and one dimensional (1D) nickel-cobalt sulfide (NiCo2S4) hollow nanotubes though the favorable electrostatic interaction between the negatively charged Ti3C2 and positively charged NiCo2S4 nanotubes. The electrode combined the good metallic conductivity of Ti3C2-MXenes and high pseudo-capacitance of NiCo2S4 demonstrated the outstanding electrochemical performance for supercapacitors. Herein, 2D Ti3C2-MXenes/1D NiCo2S4 hybrid electrode achieved an excellent specific capacitance of 1927 F g-1 at 2 mV s-1, long cycling stability for 4000 cycles and charming rate performances, which is mainly ascribed to the synergistic effect and interfacial interaction between two components. Particularly, the novel hybrid material with 1D and 2D hierarchical structures can provide additional electrochemical reaction sites, supply shorter paths for ions diffusion and electron transport, and effectively raise the charge transfer kinetics during the electrochemical process, which explores a new strategy aimed to develop 2D Ti3C2-MXenes energy storage devices with high electrochemical performance, and is possible potential for expansion into other application fields.

A novel Ti 3 C 2 @PDA/NiCo 2 S 4 composites as high performance supercapacitor electrodes were synthesized by the hydrothermal treatment process. The chemical modification and uniformly coating of Ti 3 C 2 surface by polydopamine (PDA) can prevent the structural collapse and over-oxidation of Ti 3 C 2 during the hydrothermal synthesis of NiCo 2 S 4 . Furthermore, the confined-synthesis of smaller NiCo 2 S 4 particles between the Ti 3 C 2 layers, not only prevent the restacking of Ti 3 C 2 that between the adjacent monolayers during cycling, but also afford high surface areas accessible to charge transfer and ion diffusion. Thereby, enhance the electrochemical cycling stability of the Ti 3 C 2 @PDA/NiCo 2 S 4 composite. It is significant to explore how NiCo 2 S 4 alters the microstructure, morphology as well as supercapacitors performance of Ti 3 C 2 to tune the microstructure and performance of Ti 3 C 2 by appropriate hydrothermal synthesis strategy. The experimental results exhibit a prominent improvement in the supercapacitor performance, the gravimetric capacitance of Ti 3 C 2 @PDA/NiCo 2 S 4 composites achieve as high as 495 F g -1 at 2 mV s -1 , which increase the 10 times as compared to the pristine Ti 3 C 2 . Furthermore, the cycling stability of the Ti 3 C 2 @PDA/NiCo 2 S 4 composites electrode was enhanced significantly by the hierarchical architecture, and showed exceptional capacitance retention (81.16%) even after 3000 cycles. The dramatic improvement in the supercapacitors performance of Ti 3 C 2 @PDA/NiCo 2 S 4 electrodes is attributed to impressive conductive matrix Ti 3 C 2 , the effective modification of small size Ni 2 Co 2 S 4 , and the strong interfacial interaction between Ti 3 C 2 @PDA and NiCo 2 S 4 . This study demonstrating its attractive application prospect of Ti 3 C 2 Mxenes modified with bimetallic sulfide as electrode materials for high-performance supercapacitors.

A novel organ-like Ti3C2/PPy nanocomposite has been synthesized via in-situ polymerization of pyrrole monomers to form well-defined and uniformly dispersed polypyrrole nanoparticles on the organ-like Ti3C2 nanosheets under a low temperature. The microstructures and electrochemical properties of Ti3C2/PPy composites with the different mass ration of PPy and Ti3C2 were studied by means of measurement. The analyses reveal that organ-like Ti3C2/PPy nanocomposite exhibits the highest specific capacitance of 184.36 F g−1 at 2 mV s−1 and keeps excellent cycling stability almost 83.33% capacitance retention after 4000 charging-discharging cycles at 1 A g−1. Notably, the high specific capacitance and excellent cycling stability are mainly attributed to the combination of organ-like Ti3C2 nanosheets with electric double-layer capacitor (EDLCs) mechanism and PPy nanoparticles with pseudocapacitance behavior, which take advantages of the synergistic effect between different electrode materials and different energy storage mechanisms to improve the electrochemical performance. The organ-like Ti3C2 as framework limits the growth of PPy, prevents the stacking of PPy, and promotes structural stability of Ti3C2/PPy nanocomposite. Additionally, the intercalation of homogeneous PPy nanoparticles expands the interlayer spacing of Ti3C2, and the highly aligned polymer chains can afford more pathways for electrolyte ions diffusion and charge transfer, therefore increasing the specific capacitance and decreasing the charge transfer resistance. And most of all it has shown a low-cost and convenient way to fabricate large-scale Ti3C2/PPy nanocomposites which has great potential and promising prospect as electrode materials for supercapacitors.

Fluorescent modified Graphene oxide/Polyaniline (Xn-GO/PANI, or Xn-GP) composites with ordered PANI nanowhiskers were successfully fabricated through a facile in situ chemical oxidation polymerization doping the fluorescent agents, Fluorescein (F), Rhodamine B (R) and Coumarin (C), respectively. The ordered PANI nanowhiskers (∼25 nm) were uniformly grown onto the surface and edge of GO sheets. TEM and SEM images demonstrated a quasi-two-dimensional (2D) architecture of Xn-GP nanocomposites. FT–IR, UV–vis, and Fluorescence emission analysis further verified the Xn-GP composites. As electrode materials for supercapacitors, the electrochemical results confirmed that the Fn-GP, Rn-GP and Cn-GP nanocomposites possessed the high electrochemical specific capacitance (555.6 F/g, 473.5 F/g and 459.5 F/g, respectively) at 0.5 A/g, the low charge transfer resistance, and excellent electrochemical stability by CV, GCD, EIS and cycle stability. The superior electrochemical performance of the Xn-GP ternary composites are principally ascribed to the fine synergistic effects of Xn, GO and PANI, which offered a quasi-2D conductive matrix for effective electron transfer, suitable channels for ion diffusion, good π–π interactions, and valid buffer for volume expansion of the PANI nanowhiskers during charge/discharge process. Especially, the novel Xn-GP composites with fluorescence property have the promising applications as smart electrode materials for supercapacitors.

An integrated system of heterostructure composites which can protect and optimize the structure and performance of single composition shows the positive signal of being interested in energy storage and conversion field. Recently, MXenes with versatile physicochemical properties are intriguing candidate materials for energy storage. Herein, by in situ nucleation and ion-exchange reaction, open NiCo2S4 nanosheets were intimately anchored onto the surfaces of ultrathin nitrogen-doped Ti3C2-MXene nanosheets (N-Ti3C2) to form the novel hierarchical N-Ti3C2/NiCo2S4 nanosheets. Furthermore, ultrathin N-Ti3C2 serves as a favorable conductive substrate not only to maintain structural stability, but also to afford the electrophilicity of electroactive centers and harmonize the electrochemical properties in multi-composition systems. On the other hand, NiCo2S4 nanosheets supply the effective channel for charge transport resulting in improved reaction kinetics and offer higher pseudocapacitance. Owing to the unique heterostructure and friendly interfacial interaction, the N-Ti3C2/NiCo2S4 electrode exhibits outstanding electrochemical performances with specific capacitance of 1849 F g−1 at 2 mV s−1, low internal resistance, excellent rate performance, and stable cycle life, which is much better than that of Ti3C2-MXene electrode. The results demonstrate that the heterostructure N-Ti3C2/NiCo2S4 was an advanced electrode, and this strategy provide the useful method to design MXenes-based electrode with superior electrochemical performance for supercapacitors.

The global existence of weak solutions for the three-dimensional axisymmetric Euler-$\alpha$ (also known as Lagrangian-averaged Euler-$\alpha$) equations, without swirl, is established, whenever the initial unfiltered velocity $v_0$ satisfies $\frac{\nabla \times v_0}{r}$ is a finite Randon measure with compact support. Furthermore, the global existence and uniqueness, is also established in this case provided $\frac{\nabla \times v_0}{r} \in L^p_c(\mathbb{R}^3)$ with $p>{3/2}$. It is worth mention that no such results are known to be available, so far, for the three-dimensional Euler equations of ideal incompressible flows.

The bulk Ti3(Al1−x,Gax)C2 (x including 0, 0.1, 0.2, 0.3, and 0.4) materials have been successfully synthesized by hot pressed sintering method using Ti, Al, TiC, and Ga as raw materials. The crystalline phases and microcosmic morphology were characterized by X-ray diffractometry and scanning electron microscope, etc. The analysis and simulation for the XRD patterns of Ti3(Al1−x,Gax)C2 are used to quantitatively study the effect of solid-solution on lattice parameters, and the results show that the reduced c-lattice parameter (especially the c/a ratio) of Ti3(Al,Ga)C2 solid solutions could improve the coordination and symmetry of the intergranular deformation, indicating improved mechanical properties of the solid solutions. The Vickers hardness, flexural strength, and fracture toughness of Ti3(Al0.7,Ga0.3)C2 are 7.87 GPa, 403.17 MPa, and 7.03 MPa·m1/2, respectively. The hardening and strengthening mechanism are investigated in detail. The damage modes of the fracture surfaces and energy-consuming mechanisms in these materials are also discussed.

We demonstrated a novel and convenient synthesis of amino-Ti3C2/polyaniline (N-Ti3C2/PANI) composites as high-performance supercapacitors electrode by chemical bonding between organ-like N-Ti3C2 and PANI chains, which were successfully deposited on FTO-glass substrates by a facile two-steps electrochemical reactions. Owing to effective chemical bonds between PANI chains and N-Ti3C2 layers, and well-defined Ti3C2 layers profiting from organ-like structures, it could afford the rapid pathways for charge/ion transfer and prevent the restacking of Ti3C2 layers. Herein, the effects of the electrochemical time of aniline, morphology, structure and electrochemical properties of organ-like N-Ti3C2/PANI composites were explored. Experimental results show that N-Ti3C2 can act as active sites to combine with the amine nitrogens of PANI chains and promote the growth of aniline monomers on the interlamination and surface of Ti3C2 layers. PANI possesses the good pseudocapacitance behavior which can enhance surface area and interlaminar spacing of the Ti3C2 Mxenes. The N-Ti3C2/PANI composites achieve the maximum area capacitance as high as 228 mF cm−2 at a scan rate of 5 mV s−1, and almost 85% capacitance retention is obtained after 1000 charging/discharging cycles. Moreover, the facile synthesis of organ-like N-Ti3C2/PANI composite can provide a convenient and green strategy to prepare promising electrode materials for supercapacitors.