Facile Synthesis of Large Area Two-Dimensional Layers of Transition-Metal Nitride and Their Use as Insertion Electrodes

A new versatile technique of synthesizing large area, vertically oriented two-dimensional (2D) layers of molybdenum nitride (MoN) is reported that involves synthesis of 2D nanosheets of MoO3 through a hot-filament chemical vapor deposition process and subsequent phase transformation to δ-MoN. This simple two-step approach of phase transforming 2D oxide layers potentially enables easy synthesis of a wide variety of MXenes of nitrides, sulfides, and carbides of tunable composition. When used as electrodes in Li-ion batteries, the 2D layers of MoN show an unusual Li+ storage mechanism. Using combined differential capacitance, X-ray diffraction, and X-ray photoemission spectroscopy, it is shown that unlike their bulk form, which behaves as conversion electrodes, 2D layers of MoN behave as insertion electrodes that do not involve chemical transformation. As a result, the electrode shows stable capacity of 320 mAh/g for more than 200 cycles without any structural and electrochemical degradation.