Michel W. Barsoum

Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104

By now it is well-established that the layered, hexagonal carbides and nitrides with the general formula, Mn+1AXn, (MAX) where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element and X is either C and/or N – sometimes referred to as polycrystalline nanolaminates because every basal plane is a potential deformation or delamination plane - combine some of the best attributes of metals and ceramics. More recently we showed that by simply immersing MAX phase powders, at room temperature, in HF or HCl and LiF solutions, the A-layers – mostly Al - are selectively etched to produce 2D materials that we labeled MXenes to emphasize the loss of the A-group element and their similarities to graphene. Unlike hydrophobic graphene, MXenes are hydrophilic and behave as “conductive clays”, a hitherto unknown combination. MXenes such as Ti₂C, V₂C, Nb₂C and Ti₃C₂ can be used as electrode materials in lithium-ion batteries (LIBs) and supercapacitors (SC) as well as transparent conductive electrodes, with performances that are quite impressive. In all cases, when used as anodes in LIB, MXenes showed an excellent capability to handle high cycling rates. Flexible, additives-free electrodes of delaminated Ti₃C₂ showed reversible capacities of > 400 mAhg^-1 at 1 C and 110 mAhg^-1 at 36 °C, the latter for > 700 cycles. SC's with volumetric capacitances of > 1100 F/cm³ have been obtained. The potential of using MXenes – possibly the largest family of 2D materials known with > 20 members and with new ones being discovered almost monthly - as transparent conductive electrodes, electromagnetic shielding, water remediation, among many other applications will be highlighted.