Abstract :
Hydrogen-rich complex metal hydrides, particularly ammine metal borohydrides (AMB), are promising candidates for solid-state hydrogen storage but suffer from difficult off-board regeneration
once dehydrogenated. This thesis addresses the regeneration challenge for Li–Al based AMB by combining electrochemical and chemical steps to restore key hydride species under milder, more energy-efficient conditions. First, the electrochemical dehydrogenation–rehydrogenation behaviour of Li–Al and Li–B systems in non-aqueous media under hydrogen pressure is investigated using voltammetry, chronoamperometry and ex-situ NMR/XRD, identifying LiH, AlH3 and BHx intermediates and quantifying BH4− reformation under optimised conditions. Second, an ionic-liquid-mediated digestion route is developed for B–N–H residues derived from ammonia borane and Li–Al AMB, showing that a chloroaluminate ionic liquid combined with dimethyl sulfide can cleave B–N bonds at low temperature and stabilise reactive boron and aluminium hydrides as molecular adducts instead of inactive salts. Finally, metal separation via electrodeposition from mixed Li–Al non-aqueous electrolytes is demonstrated and evaluated in terms of deposition efficiency, enabling recovery of Li and Al suitable for reintegration into the AMB synthesis cycle. Overall, the thesis proposes a realistic regeneration scheme that couples electrochemical hydrogenation, ionic-liquid digestion and metal recovery, and provides thermodynamic and mechanistic insights to support the development of more circular and scalable hydrogen storage materials.