Tetra-n-butylammonium borohydride semiclathrate: A hybrid material for hydrogen storage

In this study, we demonstrate that tetra-n-butylammonium borohydride [n-C ₄H ₉) ₄NBH ₄] can be used to form a hybrid hydrogen storage material. Powder X-ray diffraction measurements verify the formation of tetran-butylammonium borohydride semiclathrate, while Raman spectroscopic and direct gas release measurements confirm the storage of molecular hydrogen within the vacant cavities. Subsequent to clathrate decomposition and the release of physically bound H ₂, additional hydrogen was produced from the hybrid system via a hydrolysis reaction between the water host molecules and the incorporated BH ₄- anions. The additional hydrogen produced from the hydrolysis reaction resulted in a 170% increase in the gravimetric hydrogen storage capacity, or 27% greater storage than fully occupied THF + H ₂ hydrate. The decomposition temperature of tetra-n-butylammonium borohydride semiclathrate was measured at 5.7 °C, which is higher than that for pure THF hydrate (4.4 °C). The present results reveal that the BH ₄- anion is capable of stabilizing tetraalkylammonium hydrates.