Surface-Functionalized Nanoporous Carbons for Kinetically Stabilized Complex Hydrides through Lewis Acid–Lewis Base Chemistry

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, LiBH 4 may be melt-infiltrated into a nanoporous carbon (LiBH 4 @NPC), where electron-withdrawing boron concomitantly incorporates into the substrate, facilitating the wetting of the pores with molten LiBH 4 . 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 LiBH 4 may produce electron-accepting BH 3 defects at the surface of the hydride forming a stabilizing capping layer. Isothermal hydrogen desorption measurements indicate an activation energy increase of greater than 30 kJ/mol for LiBH 4 confined in N-doped versus undoped substrates. Further, temperature-programmed desorption (TPD) measurements show a temperature increase of over 25 °C in the diborane (B 2 H 6 ) signature, marking the beginning of the dehydriding reaction. Stabilizing metal hydrides kinetically through the formation of a capping layer induced by substrate functionalities may allow the use of a wide class of unstable complex metal hydrides with enthalpies below 15 kJ/mol H 2, such as AlH 3, in hydrogen storage systems.