We demonstrate that NaAlH
4 confined within the nano
pores of a titanium-functionalized metal鈥搊rganic framework (MOF) tem
plate MOF-74(Mg) can reversibly store hydrogen with minimal loss of ca
pacity. Hydride-infiltrated sam
ples were synthesized by melt infiltration, achieving loadings u
p to 21 wt %. MOF-74(Mg)
possesses one-dimensional, 12 脜 channels lined with Mg atoms having o
pen coordination sites, which can serve as sites for Ti catalyst stabilization. MOF-74(Mg) is stable under re
peated hydrogen desor
ption and hydride regeneration cycles, allowing it to serve as a 鈥渘an
oreactor鈥? Confining NaAlH
4 within these
pores alters the decom
position
pathway by eliminating the stable intermediate Na
3AlH
6 phase observed during bulk decom
position and
proceeding directly to NaH, Al, and H
2, in agreement with theory. The onset of hydrogen desor
ption for both Ti-do
ped and undo
ped nano-NaAlH
4@MOF-74(Mg) is 50 掳C, nearly 100 掳C lower than bulk NaAlH
4. However, the
presence of titanium is not necessary for this increase in desor
ption kinetics but enables rehydriding to be almost fully reversible. Isothermal kinetic studies indicate that the activation energy for H
2 desor
ption is reduced from 79.5 kJ mol
p>鈥?p> in bulk Ti-do
ped NaAlH
4 to 57.4 kJ mol
p>鈥?p> for nanoconfined NaAlH
4. The structural
pro
perties of nano-NaAlH
4@MOF-74(Mg) were
probed using
p>23p>Na and
p>27p>Al solid-state MAS NMR, which indicates that the hydride is not decom
posed during infiltration and that Al is
present as tetrahedral AlH
4p>炉p> anions
prior to desor
ption and as Al metal after desor
ption. Because of the highly ordered MOF structure and monodis
perse
pore dimensions, our results allow key tem
plate features to be identified to ensure reversible, low-tem
perature hydrogen storage.
Keywords:
p://pubs.acs.org/action/doSearch?action=search&searchText=metal%E2%88%92organic+frameworks&qsSearchArea=searchText">metal鈭抩rganic frameworks; p://pubs.acs.org/action/doSearch?action=search&searchText=nanoreactors&qsSearchArea=searchText">nanoreactors; p://pubs.acs.org/action/doSearch?action=search&searchText=metal+hydrides&qsSearchArea=searchText">metal hydrides; p://pubs.acs.org/action/doSearch?action=search&searchText=hydrogen+storage&qsSearchArea=searchText">hydrogen storage; p://pubs.acs.org/action/doSearch?action=search&searchText=reversibility&qsSearchArea=searchText">reversibility; p://pubs.acs.org/action/doSearch?action=search&searchText=nanoconfinement&qsSearchArea=searchText">nanoconfinement