Synthesis of MXene-supported layered MoS2 with enhanced electrochemical performance for Mg batteries

In this paper, the petal-like MoS₂/MXene composite has been successfully synthesized by one-step hydrothermal method. With the combination of few-layer MoS₂ nanosheets and the high conductive MXene substrate, the composite exhibits enhanced capacities and rate performance as cathode material of Mg batteries.     

Fluorine‐Free Synthesis of High‐Purity Ti3C2Tx (T=OH,O) via Alkali Treatment

MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy‐related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium‐ion battery and supercapacitor performance. Here an alkali‐assisted hydrothermal method is used to prepare a MXene Ti₃C₂T_x (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti₃C₂T_x with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti₃C₂T_x film electrode (ca. 52 μm in thickness, ca. 1.63 g cm⁻³ in density) is 314 F g⁻¹ via gravimetric capacitance at 2 mV s⁻¹ in 1 m H₂SO₄. This surpasses (by ca. 214 %) that of the multilayer Ti₃C₂T_x prepared via HF treatments. This fluorine‐free method also provides an alkali‐etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.     

Recent advances of MXene as promising catalysts for electrochemical nitrogen reduction reaction

Electrochemical reduction of N_2,as an eco-friendly alternative,not only allows the use of protons in water as a source of hydrogen under mild conditions but also can be driven by renewable electric energy.The major challenge is to identify high-efficiency electrocatalysts.MXene is a new class of 2D transition metal carbides,nitrides,and carbonitrides that have received significant attention in electrocatalysis.The investigations on MXene in electrocatalytic nitrogen fixation are rapidly proceeding,and some breakthroughs have emerged ve ry recently due to MXenes' satisfacto ry catalytic activity.Here,the recent progress concerning the MXene-based catalysts for electrochemical N_2 reduction reaction(NRR) is highlighted.In regards to giving guidelines for exploring more efficient MXene-based catalysts for the NRR,the fabrication and surface modification of MXene are discussed.Besides,the shortcomings and challenges of current research are summarized and the future research directions are prospected.     

新型Ti3C2 MXene的化学制备及基于MXene忆阻器特性与机理

阻变器件是一种微电子器件,具有阻值可在两个甚至两个以上的阻态之间重复变化的特点。忆阻器作为新型的阻变器件,具有可连续变化的丰富阻态。近年来因其具备简单的二端结构、高集成度以及低工作电压等特性,在新型非易失性存储以及构建神经形态系统等方面被广泛研究。但其在实现应用的过程中仍存在着稳定性较差等问题。近期一些工作证明了二维材料如氧化石墨烯在优化忆阻器性能方面具备良好的应用潜力。MXene是一种具备类似石墨烯结构的新型二维过渡金属碳/氮化物,因其具备二维层状结构显现出特殊的力学以及电学特性,有望应用于忆阻器中以提高器件的电学性能。在本文中,我们通过化学湿法刻蚀制备了Ti₃C₂粉末,通过旋涂工艺在忆阻器结构中引入Ti₃C₂薄膜。Ti₃C₂ MXene与SiO₂同时作为忆阻器阻变层,制备了Cu/Ti₃C₂/SiO₂/W结构的忆阻器,并且对其相关电学特性进行了探究。在该器件上,通过实验测得忆阻器典型的开关特性曲线并在双向直流电压下针对高、低阻态的可重复性、稳定性进行了实验。结果表明该器件能够在100个扫描循环过程中保持稳定的高、低阻态达到10⁴ s以上。同时,该器件状态能够受脉冲电压调节,实现突触间典型的双脉冲易化行为。实验结果表明基于Ti₃C₂ MXene的忆阻器将有望应用于构建新兴存储设备以及人工神经形态系统。     

High-performance artificial neurons based on Ag/MXene/GST/Pt threshold switching memristors

Threshold switching (TS) memristors can be used as artificial neurons in neuromorphic systems due to their continuous conductance modulation, scalable and energy-efficient properties. In this paper, we propose a low power artificial neuron based on the Ag/MXene/GST/Pt device with excellent TS characteristics, including a low set voltage (0.38 V) and current (200 nA), an extremely steep slope (< 0.1 mV/dec), and a relatively large off/on ratio (> 10³). Besides, the characteristics of integrate and fire neurons that are indispensable for spiking neural networks have been experimentally demonstrated. Finally, its memristive mechanism is interpreted through the first-principles calculation depending on the electrochemical metallization effect.     

Recent Advances in the Synthesis of MXene Quantum Dots

Quantum dots (QDs) with ultrahigh surface-to-volume ratio, abundant edge active sites, forceful quantum confinement and other remarkable physio-chemical properties, have garnered considerable research interest. MXene QDs, as an emerging member of them, have also attracted wide attention in the last six years, and shown great achievements in many fields. This critical review systematically summarizes the various methods for synthesizing MXene QDs. The characteristics and corresponding applications of various MXene QDs are also presented. The advantages and disadvantages of various synthetic methods, and the limitations of corresponding MXene QDs are compared and highlighted. Finally, the challenges and perspectives of synthesizing MXene QDs are proposed. We hope this review will enlighten researchers to the fabrication of more advancing and promising MXene-based QDs with proprietary properties in diverse applications.     

二维M_2XO_(2-2x)(OH)_(2x)(M=Ti,V;X=C,N)析氢催化活性的第一性原理研究

MXene是一种新型的二维析氢催化材料,其表面容易被亲水基团O和OH混合覆盖。我们基于第一性原理计算的方法,研究了M_2XO_(2-2x)(OH)_(2x)(M=Ti,V;X=C,N)的析氢催化活性。计算结果显示,M_2XO_(2-2x)(OH)_(2x)的析氢催化活性与其表面OH覆盖率(X)密切相关。对Ti_2CO_(2-2x)(OH)_(2x)来说,OH覆盖率不超过1/3时,具有优异的析氢催化活性。对Ti_2NO_(2-2x)(OH)_(2x)、V_2CO_(2-2x)(OH)_(2x)和V_2NO_(2-2x)(OH)_(2x)来说,OH覆盖率分别达到4/9、1/3和5/9时,才具有最佳的析氢催化活性。接着,电荷分析显示OH覆盖率会显著影响M_2XO_(2-2x)(OH)_(2x)活性位点O基团的电荷量。最后,我们从态密度的角度揭示了析氢催化活性变化的原因,即活性位点O基团的氧化性随OH覆盖率的增大而被削弱。因此,本文提出了调节表面OH覆盖率来获取M_2XO_(2-2x)(OH)_(2x)最佳析氢催化活性状态的方法,这在工业制氢生产过程中具有重要的应用价值。     

金属修饰Ti_2N MXene吸附分解H_2S的第一性原理计算

通过第一性原理计算研究了Ti_2NO_2 MXene对H_2S的吸附、分解行为. Ti_2NO_2对H_2S气体分子的吸附结果表明,两者之间为弱的物理吸附, Ti_2NO_2无法有效吸附H_2S气体.采用过渡金属(Sc、 V)修饰Ti_2NO_2的研究结果表明,Sc和V可以在Ti_2NO_2表面上稳定存在,不易发生团聚,其最稳定吸附位为N原子上方.进一步研究了Sc、 V修饰的Ti_2NO_2对H_2S气体分子的吸附行为,结果表明金属修饰后其吸附H_2S的能力明显提高.此外还发现, H_2S分子可以在Sc/Ti_2NO_2和V/Ti_2NO_2表面直接解离为HS*和H*,而后HS*中的H原子再与H*进一步结合形成H_2, S原子则与过渡金属成键. HS*在V/Ti_2NO_2表面解离的势垒为1.69 eV,低于在Sc/Ti_2NO_2表面的2.08 eV,表明V/Ti_2NO_2有望成为吸附、分解H_2S气体的理想候选材料.     

Fast self-assembled microfibrillated cellulose@MXene film with high-performance energy storage and superior mechanical strength

The trade-off between the electrochemical performance and mechanical strength is still a challenge for Ti₃C₂T_x free-standing electrode. Herein, a facile approach was proposed to fabricate a Microfibrillated cellulose@Ti₃C₂T_x (MFC@Ti₃C₂T_x) self-assembled microgel film by means of hydrogen bonding linkage. Benefiting from the rich hydroxyl groups on the MFC, the Ti₃C₂T_x nanosheets coated on the MFC in a time scale of minutes (within 1 min) instead of hours. The ultralong 1D frame of MFC effectively mitigated the re-aggregation of Ti₃C₂T_x nanosheet. The fluffy MFC@Ti₃C₂T_x film structure and the constructed 1D/2D conducting Ti₃C₂T_x pathways in horizontal and vertical directions endowed the fast ion transport of the electrolytes and the improved accessibility to the Ti₃C₂T_x surface. As a result, the freestanding MFC@Ti₃C₂T_x microgel film delivered a high specific capacitance of 451F/g. And the rate performance was increased to 71% from the 64% of that of pristine Ti₃C₂T_x film. Furthermore, the tensile strength of MFC@Ti₃C₂T_x film was also promoted to 46.3 MPa, 3 folds of that of the pristine Ti₃C₂T_x film, due to the high strength of MFC and the hydrogen bonding effect.