Hydrogen sorption and reaction mechanisms of nanoconfined 2LiBH4–NaAlH4

• Published in: Journal of alloys and compounds 2015-06, Vol.633, p.484-493
• Main Authors: Thiangviriya, Sophida, Plerdsranoy, Praphatsorn, Wiset, Nuntida, Javadian, Payam, Jensen, Torben R., Utke, Rapee
• Format: Article
• Language: English
• Subjects: Composite hydrides; Hydrogen storage; LiBH4; Metal hydrides; NaAlH4; Nanoconfinement
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.02.030

•Nanoconfinement of 2LiBH4–NaAlH4 is first time reported.•Suitable conditions for nanoconfinement are determined.•High H2 released and reproduced up to 89% and 74%, respectively, are obtained.•Effective reversibility and fast kinetics are achieved after nanoconfinement. Nanoconfinement of 2LiBH4–NaAlH4 in carbon aerogel scaffold (CAS) via direct melt infiltration is proposed for reversible hydrogen storage. Weight ratios of CAS:2LiBH4–NaAlH4 (2:1, 2:1.5, and 1:1) and melt infiltration temperatures at 185 and 310°C are varied to obtain the most suitable condition for nanoconfinement. It is found that the sample melt infiltrated at 310°C under CAS:2LiBH4–NaAlH4 weight ratio of 2:1, denoted as s1@310 offers the best results based on effective nanoconfinement, high hydrogen content released, and fast dehydrogenation kinetics. Further studies on reversibility shows that up to 89% and 74% H2 with respect to theoretical storage capacity release from s1@310 during the 1st and 2nd dehydrogenations (T=400°C under vacuum), respectively, while those of milled 2LiBH4–NaAlH4 are only 57% and 32%, respectively. The reaction between LiBH4 and NaAlH4 during nanoconfinement produces LiAlH4 and NaBH4. During dehydrogenation, an intermediate phase (LiNa2AlH6) is formed and it decomposes in the temperature range of 203–350°C. Moreover, significant reduction in decomposition temperature of NaBH4 of s1@310 with respect to those of milled 2LiBH4–NaAlH4 and pristine NaBH4 (ΔT=137 and 197°C, respectively) is accomplished. Reversibility of NaBH4, LiAlH4, and LiBH4 are achieved together with unreacted LiH and metallic Al (T=400°C, p(H2)=80bar for 12h). Although irreversibility of metallic Al leads to deficient content of hydrogen desorbed in the 2nd cycle, greater amount of hydrogen reproduced of s1@310 with respect to milled sample is obtained. This is due to the recovery of NaBH4 after rehydrogenation of s1@310, whereas that of milled 2LiBH4–NaAlH4 was not possible due to the evaporation of metallic Na during dehydrogenation.