Séminaire LMGP - 09/02/2016 - Michel BARSOUM

Abstract

By now it is well-established that the layered, hexagonal carbides and nitrides with the general formula, M_n+1AX_n, (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. They are excellent conductors of heat and electricity, damage and thermal shock tolerant and fracture toughness values as high as 15 MPa√m. Some are lightweight, stiff and have good creep and outstanding oxidation resistance. More recently we have shown that by simply immersing MAX phase powders, at room temperature, in HF the A-layers 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 > 900 F/cm³ were obtained. The potential of using MXenes in energy storage, as transparent conductive electrodes, among many other applications will be highlighted.