Abstract
Light metal borohydrides have been extensively investigated as potential hydrogen storage candidates due to their high gravimetric capacities, but they are irreversible. However, a nanosizing approach may provide unprecedented opportunities to change this. This thesis aims to establish a nanosizing strategy for LiBH4 and NaBH4 so that practical reversible hydrogen capacities may be reached under moderate conditions.
Previous nanosizing methods have relied on the use of bulky supports, which severely limit the gravimetric capacity, as confirmed in the present work. In order to overcome this, a range of techniques for the preparation of isolated borohydride nanoparticles were investigated. These resulted in some improvements in hydrogen storage properties over the bulk materials, but despite extensive optimisation the resulting nanoparticles were not sufficiently stabilised.
To improve the stabilisation, a core-shell strategy was developed, where a NaBH4 nanoparticle core was contained within a Ni shell (NaBH4@Ni). This novel strategy led to exceptional hydrogen storage properties. NaBH4 became fully reversible for the first time with 5 mass % hydrogen desorption/absorption occurring at only 4 MPa hydrogen pressure and 350 °C with fast kinetics.
The technique was further extended to other systems, using a variety of shell metals and different core materials. LiBH4@Fe in particular has the potential to reach even higher reversible capacities than NaBH4@Ni under even milder conditions. This unique approach challenges the way hydrogen is conventionally stored, and provides a highly promising avenue for practical developments in energy in the future.