De-/re-hydrogenation features of NaAlH4 confined exclusively in nanopores

In the present work, a nanoconfinement system with NaAlH4 exclusively embedded in ordered mesoporous carbon (MC) was synthesized by a three-step procedure, i.e., thermal melting impregnation plus de-/re-hydrogenation. It is demonstrated that the NaAlH4 inside MC shows faster kinetics for dehydrogenation than the kinetics of pristine NaAlH4 with a reduction in activation energy by ∼70 kJ mol−1. An enhanced cycling stability is also achieved by the high-capacity retention of >80% after 15 de-/re-hydrogenation cycles. These remarkable improvements are attributed to the synergistic effects of both nanoconfinement and chemical catalysis caused by the MC, where nanoconfinement plays a dominant role. Furthermore, kinetic modeling studies suggest that the hydrogen release from the confined NaAlH4 system is governed by two processes: the initial process can be expressed by one-dimensional nucleation and growth, and the second process is jointly controlled by three-dimensional diffusion and phase boundary migration.