Synthesis and Characterization of Ternary Layered Transition Metal Borides and Chalcogenides for Energy Applications
Layered materials have been studied for several decades but only after the discovery of graphene, the vast potential of these materials have been widely explored. These materials such as graphite, hexagonal boron nitride, van der Waals chalcogenides, MAX / MAB phases etc. have been investigated for their anisotropic properties and potentials to be tailored in to nano and two-dimensional structures. The research presented in this dissertation, focuses on the synthesis and characterization of two of these layered compounds, investigates their possible exfoliation toward 2D and nano sheets and finally introduces them as potential materials for energy applications such as Li-ion batteries and hydrogen evolution. In the first part of this dissertation, Ni(n+1)ZnBn (n=1, 2) nano laminated MAB phases, were synthesized through a two-step melt solidification technique leading to the formation of pure, preferred oriented bulk MAB sheets. Studying these MAB phases for possible chemical exfoliation, led to the formation of high surface area MAB particles which led to the discovery of the first MAB phases as active Li-ion battery anodes. Subsequently, different electrodes of the synthesized Ni(n+1)ZnBn Phases were studied for their hydrogen evolution properties. It was observed that forming densified pellet of Ni(n+1)ZnBn phases provide the lowest overpotential among all the other reported MAB phases. Studying the exposed surface of the disk electrodes through microscopy and spectroscopy techniques suggested the potential basal plane activity of the synthesized MAB phases which our DFT calculations supported. While studying the synthesized layered Ni(n+1)ZnBn phases, it was observed that they tend to delaminate and break along their basal plane hinting the possibility of forming quasi-2D sheets through more severe forces such as liquid phase exfoliation. Finally, we studied the layered vdW Fe3GeTe2 (FGT) compound for its hydrogen evolution reaction (HER) activity. Liquid phase exfoliation followed by densification led to the discovery of active basal plane and edge sites in FGT, suggesting it as an active bulk hexagonal layered vdW compound, thus paving the way for future studies of iron based layered materials for HER. This dissertation contributes to the layered materials field, demonstrating the high potential of these materials for energy applications.