Mixed Metal Amide-Hydride Solid Solutions for Potential Energy Storage Applications

Mixed solid solutions have played an important role in improving the kinetics and performance of hydrogen storage materials, as reported for the Li-Mg-N-H, K-Mg-N-H, and Rb-Mg-N-H systems. Besides, the formation of a homogeneous solid solution, mostly due to partial ionic substitution, is known to be an effective approach to improve the ionic conductivity of a material, which is an important property in electrochemical applications. We have reported a series of solid solutions based on mixed amide-hydride materials of the Group 1 elements, e.g., K(NH₂)H_1-, Rb(NH₂)H_1-, and Cs(NH₂)H_1-, via the exchange of NH₂^-/H^- anions with the change of the lattice cell of the solid solution. Extending the research in this direction, we study the M-N-H solid solution in the MNH₂-MH systems (M = K, Rb, Cs, and their combinations), i.e., KNH₂-RbH, RbNH₂-KH, RbNH₂-CsH, and CsNH₂-RbH via ex situ/in situ XRD, IR, and ¹H 2D solid-state NMR. The results obtained confirm the formation of mixed metal amide-hydride solid solutions associated with an exchange between both anionic (NH₂^- and H^-) and cationic species (K⁺, Rb⁺, and Cs⁺). With this study, we aim to create an accessible library of M-N-H solid solutions for further studies as additives for hydrogen storage materials or ionic conductors.