A solvothermal approach to nano-designing M-N-H systems: unveiling new pathways to dimensional control in the lithium nitride hydride ammonia synthesis catalyst

Abstract

The Li–N–H system spans a rich network of reactive phases that encompass Li₃N – Li₄NH – Li₂NH – LiNH₂ – LiH, interconnected through a number of solid solutions and mediated via NH₃, H₂, and/or N₂ exchange. Realizing the full potential of these Li–N–H systems in ammonia catalysis and hydrogen storage applications has been hindered by the inability to ‘nano-design’ them beyond conventional bulk synthesis. Here, we present a novel solvothermal route for the synthesis and nanostructurisation of Li–N–H and Li–Na–N–H materials, providing a solution-phase route to these air-sensitive and reactive materials. The method enables enhanced morphological and dimensional control compared to solid-state routes, yielding nanostructures such as wires, rods, and particles with characteristic sizes from 300 to 900 nm. We systematically explore the structural and microstructural evolution of these phases, and demonstrate the influence of mineralisers on the sample morphology. We report evidence of enhanced nitrogen activation, air-stability and ammonia synthesis activity for these samples, balanced against their propensity for carbon contamination. This work opens the possibility of a significantly expanded synthesis approaches to Li–N–H materials, and M-N-H materials more broadly.