MXenes, a recently discovered class of 2D nanomaterials derived from MAX phase precursors, have demonstrated utility in a wide variety of applications including energy storage, catalysis, and sensing. Due to the chemical and structural diversity of parent MAX phases available, there are countless possible MXene compositions with different possible metal atoms “M”, number of atomic layers, and carbon or nitrogen “X” constituents. By varying the MXene composition, it is possible to tailor the properties of the MXene to specifics applications. However, the bulk of MXene research to date focuses on Ti₃C₂T_z, the first MXene discovered. Recently, layer-by-layer (LbL) assembly has shown promise for making polymer/MXene multilayer thin films and coatings. While this method shows promise for using novel MXene types for thin film assembly, it is not clear how different MXene types will influence the assembly and properties of the resulting multilayer. Herein, we report on the first use of MXenes other than Ti₃C₂T_z for LbL assembly of polycation/MXene multilayers. Specifically, we use Ti₂CT_z and Nb₂CT_z in conjunction with poly(diallyldimethylammonium) (PDADMA) which enables us to evaluate how changing M (Ti vs. Nb) and n (Ti₃C₂T_z vs. Ti₂CT_z) affects film growth and the properties of the multilayer. In detail, we compare the oxidative stability, optoelectronic properties, and radio frequency response of each multilayer. We observe that MXene-based multilayers with higher n are more electrically conductive and oxidatively stable and that Nb₂CT_z-based multilayers have lower optical band gaps and refractive indices at the cost of lower electrical conductivities as compared to Ti₂CT_z-based multilayers. Our work demonstrates that the properties of MXene-based multilayers are highly dependent on the MXene used for assembly and that the MXene type can be altered to suit specific applications.

Ju-Hyun Oh

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