Ternary LiBH4–MgH2–NaAlH4 hydride confined into nanoporous carbon host for reversible hydrogen storage

Abstract

Ternary hydride of LiBH4–MgH2–NaAlH4 confined into carbo n aerogel scaffold (CAS) via melt infiltration for reversible hydrogen storage is proposed. Nanoconfinement of hydrides into CAS is obtained together with surface occupation of some phases, such as Al and/or LiH. Regarding nanoconfinement, not only multiple-step decomposition of LiBH4–MgH2–NaAlH4 hydride reduces to about single step, but also reduction of dehydrogenation temperature is significantly observed, for example, ∆T up to 70°C regarding last dehydrogenation step. Moreover, decomposition of NaBH4 in nanoconfined sample can be done at 360°C (dehydrogenation temperature in this study), which is 115 and 180°C lower than that of NaBH4 in milled LiBH4–MgH2–NaAlH4 and bulk NaBH4, respectively. The reaction of LiBH4+NaAlH4→LiAlH4+NaBH4 takes place during nanoconfinement and the decomposition of LiAlH4 is observed, resulting deficient hydrogen content liberated. However, hydrogen content released (1st cycle) and reproduced (2nd–4th cycles) from this ternary hydride enhances up to 11% and 22% of full hydrogen storage capacity due to nanoconfinement. After rehydrogenation (T=360°C and P(H2)=50bar H2 for 12h), NaBH4, MgH2, and Li3AlH6 are reversible, whereas Li3AlH6 and NaBH4 in milled sample cannot be recovered due to deficient hydrogen pressure (T=360°C and P(H2)=80bar) and probably evaporation of molten sodium during dehydrogenation, respectively. The latter results in inferior hydrogen content reproduced from milled sample to nanoconfined sample.