Hydrogen Desorption Properties of Bulk and Nanoconfined LiBH4-NaAlH4

Nanoconfinement of 2LiBH(4)-NaAlH4 into a mesoporous carbon aerogel scaffold with a pore size, BET surface area and total pore volume of D-max = 30 nm, S-BET = 689 m(2)/g and V-tot = 1.21 mL/g, respectively is investigated. Nanoconfinement of 2LiBH(4)-NaAlH4 facilitates a reduction in the temperature of the hydrogen release by 132 degrees C, compared to that of bulk 2LiBH(4)-NaAlH4 and the onset of hydrogen release is below 100 degrees C. The reversible hydrogen storage capacity is also significantly improved for the nanoconfined sample, maintaining 83% of the initial hydrogen content after three cycles compared to 47% for that of the bulk sample. During nanoconfinement, LiBH4 and NaAlH4 reacts to form LiAlH4 and NaBH4 and the final dehydrogenation products, obtained at 481 degrees C are LiH, LiAl, AlB2 and Al. After rehydrogenation of the nanoconfined sample at T = 400 degrees C and p(H-2) = 126 bar, amorphous NaBH4 is recovered along with unreacted LiH, AlB2 and Al and suggests that NaBH4 is the main compound that can reversibly release and uptake hydrogen.