2D molybdenum and vanadium nitrides synthesized by ammoniation of 2D transition metal carbides (MXenes)

Abstract

MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti₄N₃ and Ti₂N are the only nitride MXenes reported so far. Here by ammoniation of Mo₂CT_x and V₂CT_x MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures of the resulting Mo₂N and V₂N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo₂N retains the MXene structure and V₂C transforms to a mixed layered structure of trigonal V₂N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo₂N and V₂N are three and one order of magnitude larger than those of the Mo₂CT_x and V₂CT_x precursors, respectively. This study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis.