2D Ti3C2Tz MXene Synthesized By Water-Free Etching of Ti3AlC2 in Polar Organic Solvents

Abstract

MXene is a recently discovered family of two-dimensional transition metal carbides, nitrides and carbonitrides that have shown a lot of promise in the field of energy storage with applications ranging from high capacity anodes for lithium, sodium, potassium and aluminum ion batteries, supercapacitors and catalysts for hydrogen evolution, among several others. The first MXene ,Ti3C2Tz, discovered in 2011, was synthesized by etching out the ‘Al’ atomic layers from the parent MAX phase, Ti3AlC2, in a solution of concentrated hydrofluoric acid. Several new ways of synthesizing MXenes at near ambient temperatures, incorporating chemical etching using hydrochloric acid and lithium fluoride and electrochemical etching in varying electrolytes have been developed since 2011. The majority of these etching methods, however, use water as their main solvent limiting direct use of MXenes in water sensitive applications such as Li and Na-ion batteries that use organic electrolytes. In this work, we demonstrate etching and delamination of MXenes in complete absence of water, by using organic polar solvents in the presence of ammonium dihydrogen fluoride. As importantly, we show that that electrodes made from Ti3C2Tz etched in propylene carbonate, resulted in Na-ion battery anodes with twice the capacity to those etched in water. The absence of water during etching also minimized the O and OH terminations relative to F.