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

Abstract

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 Ti2AlC, Ti3AlC2, and Ta4AlC3. 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. MXenes are a new family of two-dimensional early transition metal carbides and carbonitrides produced by etching a metal layer from ternary layered carbides called MAX phases. This review describes the progress - both theoretical and experimental - in the synthesis, understanding of structure, measuring of properties, and development of applications of MXenes. In addition, future research directions and challenging open questions are discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.