Tuning the Electrochemical Performance of Titanium Carbide MXene by Controllable In Situ Anodic Oxidation

MXenes are a class of two‐dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high‐rate pseudocapacitive energy storage. However, the effects that irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. Here we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti₃C₂T_x, T_x refers to ‐F, =O, ‐Cl and ‐OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV s^?1 (with respect to the lowest scan rate of 5 mV s^?1) increases gradually from 38 % to 66 % by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti₃C₂T_x is evident at high anodic potentials after oxidation. Several analysis methods are employed to reveal changes in the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti₃C₂T_x. This study demonstrates improvement of the electrochemical performance of MXene electrodes by performing a controlled anodic oxidation.     

制备条件对MXene形貌、 结构与电化学性能的影响

以Ti₃AlC₂为原料, 采用LiF+HCl一步刻蚀-插层制备Ti₃C₂T_x, 进一步通过超声处理得到单层或少层的MXene. 利用X射线衍射(XRD)、 X射线光电子能谱(XPS)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和电化学测试对样品的结构、 形貌和电化学性能进行了研究. 通过改变刻蚀剂的比例及超声剥离时间, 研究了不同刻蚀条件和剥离条件对二维晶体Ti₃C₂T_x的形貌、 结构和电化学性能的影响. 结果表明, 制备条件对MXene的片层结构和性能具有较大的影响. 当HCl浓度为6 mol/L, LiF与Ti₃AlC₂的摩尔比为7.5, 超声时间为1 h时, 所得MXene具有较小的晶格常数和较大的片层尺寸, 片层尺寸可达1 μm, 具有较多的表面含氧官能团, 电化学性能最佳, 在0.5 A/g的电流密度下, 质量比容量达到342 F/g, 当电流密度提高至20 A/g时, 质量比容量仍可保持244 F/g, 在1 A/g电流密度下循环10000周后, 容量仍能保留87%左右, 表现出较好的倍率性能与循环稳定性.     

2D MXenes as Perspective Immobilization Platforms for Design of Electrochemical Nanobiosensors

MXenes are a new group of 2D nanomaterials with fascinating properties including high electrical conductivity, hydrophilic nature, easily tunable structure and high surface area. This is why MXene modified interfaces are extremely promising for the preparation of sensitive electrochemical biosensors. While there are numerous reports on MXene‐based enzymatic biosensors for detection of a wide range of analytes, application of MXene for construction of affinity biosensors is in its infancy. The review article summarizes current state‐of the‐art in the field with a focus on MXene modifications needed for construction of robust and high performance MXene electrochemical biosensors.     

MXene–AuNP-Based Electrochemical Aptasensor for Ultra-Sensitive Detection of Chloramphenicol in Honey

A simple and label-free electrochemical aptasensor was developed for ultra-sensitive determination of chloramphenicol (CAP) based on a 2D transition of metal carbides (MXene) loaded with gold nanoparticles (AuNPs). The embedded AuNPs not only inhibit the aggregation of MXene sheets, but also improve the quantity of active sites and electronic conductivity. The aptamers (Apts) were able to immobilize on the MXene–AuNP modified electrode surface through Au–S interaction. Upon specifically binding with CAP with high affinity, the CAP–Apt complexes produced low conductivity on the aptasensor surface, leading to a decreased electrochemical signal. The resulting current change was quantitatively correlated with CAP concentration. Under optimized experimental conditions, the constructed aptasensor exhibited a good linear relationship within a wide range of 0.0001–10 nM and with a low detection limit of 0.03 pM for CAP. Moreover, the developed aptasensor has been applied to the determination of CAP concentration in honey samples with satisfactory results.     

汞在Ti2NO2 MXene表面吸附氧化的第一性原理计算

汞是一种有毒的重金属,在生产生活中以各种形式排放的汞对生态及人类健康都存在一定程度的威胁.因此,寻找高效的汞吸附剂具有十分重要的意义.本文基于密度泛函理论的第一性原理计算方法,研究了汞在Ti₂NO₂(MXene)和具有一个氧空位缺陷的Ti₂NO₂(Ov-Ti₂NO₂)上的吸附和氧化机理.计算结果表明Hg⁰在Ti₂NO₂表面的吸附为物理吸附,在Ov-Ti₂NO₂表面为化学吸附. Ti₂NO₂表面氧空位的存在可以改善HgO与Ov-Ti₂NO₂之间的相互作用,从而使吸附能提高116 kJ/mol. Hg⁰在Ov-Ti₂NO₂表面氧化为HgO的反应能垒为92.55 kJ/mol,小于其在Ti_2<...     

MAX相陶瓷的结构、制备及物理性能研究

MAX相陶瓷因具有独特的MX片层与A片层交替堆叠的晶体结构,使其兼具金属和陶瓷的优良特性,如良好的导热导电性、可加工性,同时具有良好的抗氧化性、耐腐蚀性以及耐摩擦磨损等性能,具有非常广泛的应用前景。本文首先介绍了MAX相陶瓷材料的种类与晶体结构,并简述了近几年新发现的MAX相陶瓷材料以及制备手段的发展动态。之后从MAX相物理性能的角度出发,重点综述了几种典型MAX相陶瓷材料的弹性性能、电学性能、热学性能、磁性能以及抗辐照性能的研究进展。此外,进一步介绍了MAX相的二维衍生物MXene的衍生过程、超导性以及其在电化学储能、催化领域的研究进展。最后,本文从探索MAX相材料新结构的多样性、MAX相物理性能及相关理论计算、MXene二维材料以及相应的制备、表征和应用等方面,展望了MAX相陶瓷材料的潜在研究方向及应用前景,为MAX相和MXene材料的深入研究提供了新的思路。     

Bimetallic Sulfide/Sulfur Doped T3C2Tx MXene Nanocomposites as High-performance Anode Materials for Sodium-ion Batteries

The application of transition metal dichalcogenides(TMDs) as anode materials in sodium-ion batteries (SIBs) has been hindered by low conductivity and poor cyclability. Herein, we report the synthesis of Co_xFe_1-xS₂ bimetallic sulfide/sulfur-doped Ti₃C₂ MXene nanocomposites(Co_xFe_1-xS₂@S-Ti₃C₂) by a facile co-precipitation process and thermal-sulfurization reaction. The interconnected 3D frameworks consisting of MXene nanosheets can effectively buffer the volume change and enhance the charge transfer. In particular, sulfur-doped MXene nanosheets provide rich active sites for sodium storage and restrain sulfur loss during charging/discharging processes, leading the increase of specific capacity and cycling the stability of anode materials. As a result, Co_xFe_1-xS₂@S-Ti₃C₂ anodes exhibited high capacity, high rate capability and long cycle life(399 mA·h/g at 5 A/g with an 94% capacity retention after 600 cycles).     

The potential of MXene materials as a component in the catalyst layer for the Oxygen Evolution Reaction

MXenes are a class of 2D/layered materials which are highly conductive, hydrophilic, have a large electrochemical surface area and are easily processible into electrodes for energy applications. Since the discovery of MXenes over ten years ago, these materials have been mainly used in the preparation of electrodes for batteries and supercapacitors. However, due to their aforementioned properties, MXenes could potentially be utilised as a component in the catalyst layer for the Oxygen Evolution Reaction (OER). This opinion piece will discuss some of the recent literature in the area of hybrid catalysts consisting of various Transition Metal Oxides (TMOs) and MXenes for the OER. We will also discuss current drawbacks and future outlook in this new area of research.     

Titanium Carbide (Ti3C2Tx) MXene Ornamented with Palladium Nanoparticles for Electrochemical CO Oxidation

Titanium carbide (Ti₃C₂T_x) MXene possesses various unique physicochemical and catalytic properties. However, the electrochemical CO oxidation performance is not yet addressed experimentally. Herein, Ti₃C₂T_x (T_X=OH, O, and F) ordered and exfoliated two-dimensional nanosheets ornamented with semi-spherical palladium nanoparticles (2.5 Wt. %) with an average diameter of (10±1 nm) (denoted as Pd/Ti₃C₂T_x) is rationally designed for the electrochemical CO oxidation. The fabrication process is based on the selective chemical etching of Ti₃AlC₂ and delamination under sonication to form Ti₃C₂Tx nanosheets that are used as a substrate and reducing agent for supporting in situ growth of Pd nanoparticles via impregnation with Pd salt. Interestingly, Pd-free Ti₃C₂T_x displayed inferior CO oxidation activity, while Pd/Ti₃C₂T_x enhanced the CO oxidation activity substantially. This is attributed to the combination of outstanding physicochemical properties of Ti₃C₂T_x and the catalytic merits of Pd nanoparticles.     

Bi3TaO7/MXene纳米片异质结的制备及光催化降解磺胺嘧啶钠

分别以五水合硝酸铋（Bi （NO₃）₃·5H₂O）和五氯化钽（TaCl₅）作为Bi源和Ta源,采用静电吸附和溶剂热法在2D Ti₃C₂的表面原位生长0D Bi₃TaO₇纳米颗粒制备Bi₃TaO₇/Ti₃C₂复合光催化材料。通过各种物理化学表征研究了2D Ti₃C₂纳米片对Bi₃TaO₇/Ti₃C₂复合光催化材料微结构的影响。通过可见光下降解磺胺嘧啶钠（SD-Na）溶液来评价所制备样品的光催化性能。实验结果表明,Bi₃TaO₇/Ti₃C₂复合材料的光催化性能明显增强。在最优条件下（Ti₃C₂与Bi₃TaO₇的质量比为0.02）制备的BT2展现出最高的光催化活性,其降解SD-Na溶液的表观速率常数是纯Bi₃TaO₇的2.8倍。Bi₃TaO₇/Ti₃C₂复合光催化材料性能的显著提高归因于Ti₃C₂/Bi₃TaO₇异质结的形成有利于光生载流子的快速转移和分离。