25th anniversary article: MXenes: a new family of two-dimensional materials.

Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2 AlC, Ti3 AlC2 , and Ta4 AlC3 . MXenes -combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as "conductive clays". This article reviews progress-both -experimental and theoretical-on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.

Naguib M ，Mochalin VN ，Barsoum MW ，Gogotsi Y ... -  《-》

Selective Etching of Silicon from Ti(3) SiC(2) (MAX) To Obtain 2D Titanium Carbide (MXene).

Until now, MXenes could only be produced from MAX phases containing aluminum, such as Ti3 AlC2 . Here, we report on the synthesis of Ti3 C2 (MXene) through selective etching of silicon from titanium silicon carbide-the most common MAX phase. Liters of colloidal solutions of delaminated Ti3 SiC2 -derived MXene (0.5-1.3 mg mL-1 ) were produced and processed into flexible and electrically conductive films, which show higher oxidation resistance than MXene synthesized from Ti3 AlC2 . This new synthesis method greatly widens the range of precursors for MXene synthesis.

Alhabeb M ，Maleski K ，Mathis TS ，Sarycheva A ，Hatter CB ，Uzun S ，Levitt A ，Gogotsi Y ... -  《-》

Vanadium MXenes materials for next-generation energy storage devices.

Batteries and supercapacitors have emerged as promising candidates for next-generation energy storage technologies. The rapid development of new two-dimensional (2D) electrode materials indicates a new era in energy storage devices. MXenes are a new type of layered 2D transition metal carbides, nitrides, or carbonitrides that have drawn much attention because of their excellent electrical conductivity, electrochemical and hydrophilic properties, large surface area, and attractive topological structure. This review focuses on various synthesis methods to prepare vanadium carbide MXenes with and without etchants like hydrofluoric acid, lithium fluoride, and hydrochloric acid to remove the 'A' layers of the MAX phase. The goal is to demonstrate the utilization of a less toxic etching method to achieve MXenes of comparable properties to those prepared by traditional methods. The influence of intercalation on the effect of high interlayer spacing between the MXene layers and the performance of MXenes as supercapacitor and battery electrodes is also addressed in this review. Lastly, the gaps in the current knowledge for vanadium carbide MXenes in synthesis, scalability, and utilization in more energy storage devices were discussed.

Sijuade AA ，Eze VO ，Arnett NY ，Okoli OI ... -  《-》

MXenes and Their Applications in Wearable Sensors.

MXenes, a kind of two-dimensional material of early transition metal carbides and carbonitrides, have emerged as a unique class of layered-structured metallic materials with attractive features, as good conductivity comparable to metals, enhanced ionic conductivity, hydrophilic property derived from their hydroxyl or oxygen-terminated surfaces, and mechanical flexibility. With tunable etching methods, the morphology of MXenes can be effectively controlled to form nanoparticles, single layer, or multi-layer nanosheets, which exhibit large specific surface areas and is favorable for enhancing the sensing performance of MXenes based sensors. Moreover, MXenes are available to form composites with other materials facilely. With structure design, MXenes or its composite show enhanced mechanical flexibility and stretchability, which enabled its wide application in the fields of wearable sensors, energy storage, and electromagnetic shielding. In this review, recent progress in MXenes is summarized, focusing on its application in wearable sensors including pressure/strain sensing, biochemical sensing, temperature, and gas sensing. Furthermore, the main challenges and future research are also discussed.

Xin M ，Li J ，Ma Z ，Pan L ，Shi Y ... -  《-》

M(5)X(4): A Family of MXenes.

Downes M ，Shuck CE ，Lord RW ，Anayee M ，Shekhirev M ，Wang RJ ，Hryhorchuk T ，Dahlqvist M ，Rosen J ，Gogotsi Y ... -  《-》