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Confining NaAlH4 in nanoporous carbon scaffolds is known to alter the sorption kinetics and/or pathways of the characteristic bulk hydride reactions through interaction with the framework at the interface, increased specific surface area of the resulting nanoparticles, decreased hydrogen diffusion distances, and prevention of phase segregation. Although the nanosize effects have been well studied, the influence of the carbon scaffold surface chemistry remains unclear. Here we compare the hydrogen sorption characteristics of NaAlH4 confined by melt infiltration in nitrogen-doped/undoped ordered nanoporous carbon of two different geometries. 23Na and 27Al MAS NMR, N2 sorption, and PXRD verify NaAlH4 was successfully confined and remains intact in the carbon nanopores after infiltration. Both the N-doped/undoped nanoconfined systems demonstrate improved reversibility in relation to the bulk hydride during hydrogen desorption/absorption cycling. Isothermal kinetic measurements indicate a lowering of the activ...

Complex metal hydrides are an attractive hydrogen storage option due to their high gravimetric hydrogen capacities, but the re/dehydriding reactions generally possess unfavorable thermodynamics and kinetics. Recent studies have attempted to alter these properties through confinement of complex hydrides in nanoporous substrates. For example, LiBH4 may be melt-infiltrated into a nanoporous carbon (LiBH4@NPC), where electron-withdrawing boron concomitantly incorporates into the substrate, facilitating the wetting of the pores with molten LiBH4. We present results of the surface functionality displayed by incorporation of electron-donating nitrogen into a nanoporous carbon. The presence of pyridinic nitrogen in the substrate, confirmed by XPS analysis, acts as a Lewis base. Our results indicate partial decomposition on melt-infiltration of LiBH4 may produce electron-accepting BH3 defects at the surface of the hydride forming a stabilizing capping layer. Isothermal hydrogen desorption measurements indicate an ...